Power Systems Protection Lab Manual in PTUK, Lab Reports of Electrical Engineering

Download Power Systems Protection Lab Manual in PTUK and more Lab Reports Electrical Engineering in PDF only on Docsity! Faculty of Engineering and Technology Department of Electrical Engineering Electrical Power Systems Protection Lab Manual (12120204) First Edition Student Manual Prepared by: Eng. TareQ FoQha 2021 Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha II | Page Electrical Power Systems Lab Abstract The power systems protection laboratory is designed to directly apply theory learned in lectures to devices that will be studied in the laboratory. Power system protection is concerned with protecting electrical power systems from faults within the network by isolating the faulted components so as to leave as much of the remaining the electrical network operational as possible. Moreover, by properly protecting the system components from overloading, the probability of fires and other catastrophic and expensive system failures can be minimized. In understanding power protection, it is necessary to understand what is actually being protected. Providing superior protection is essential in mitigating the effects of disruptions on system stability. As such, it is essential for power engineers to understand the concepts and practices underlying power protection. The creation of a Power System Protection Lab at Palestine Technical University gives students the opportunity to gain some real world experience in protection. Moreover, a laboratory of this type facilitates educational opportunities. It also provides numerous additional benefits such as research. Objectives The laboratory course is intended to provide practical understanding of power system protection. The main goal is to enable students to apply and test theoretical knowledge they mastered in previous years of studies. The laboratory course enables them to develop practical skills in various fields of power engineering in a controlled environment. The Laboratory covers all phases for the Protection devices specific of this field. All protection and control devices of the electrical machines are exactly equal to those installed in the industrial units. So, the sequences of control maneuvers in the control stations are exactly equal to those necessary in the industrial units. Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 1 | Page Electrical PS Protection Lab Chapter 1 Introduction Contents Experiment (1) General Considerations on Protection Devices 02-05 Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 2 | Page Electrical PS Protection Lab Introduction: This part of the manual describes the main protection devices employed on electrical lines or central stations. The purpose is to obtain a set of easily consultable news referring to the bibliography for the known notions. For the relays we will generally provide the following information: 1) Function identification number (ANSI / IEEE C37.2), 2) News on the purpose and possible applications, 3) Characteristic equations and functional diagrams, 4) Base insertion diagrams and relays block diagram, 5) Service controls and installation modes. The standard CEI 94-4 (Italian), CEI EN 61810-1 (European) "Non-specified time ON/OFF electromechanical relays" (Standard processed on the base of international publications IEC 61810-1); we suggest a set of definitions for the protection relays, protection systems, etc. There are three kinds of electrical protections: 1) Electromechanical, 2) Static and 3) Microprocessor. The electromechanical protections exploit the electrodynamic forces (electromagnetic and induction relays) and the thermal power (thermal, bimetallic relays) to cause the intervention of the cut-off devices. In the static protections (electronic) the electromagnetic and thermal functions are performed by the electronic circuits without parts in motion (static) except for the output relays contacts. These protections enable finer and more accurate calibrations than those that can be obtained from the electromagnetic relays, besides more functions can be grouped into a single envelope. The microprocessor protections are more evolved and complete and can also be programmed and transmitted at a distance from the detected data. The microprocessor protections enable not only finer and more continuous calibrations than the last protections but also the modification of the intervention curve to be matched to the different needs. These protections, interfaced to personal computer can provide a large quantity of data for the statistic analysis. They are obviously provided with output relay contacts to act on external opening and/or signaling circuits. Experiment (1) General Considerations on Protection Devices Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 3 | Page Electrical PS Protection Lab For the static equipments, the term relay can be used when it carries out a specific elementary logic function while the term relay device is applied to equipment including a total logic function corresponding to the combination of more elementary logic functions. Protection Device or Automatic Relay Device: Relay device performing a specific protection or automatism function as it results from the qualification of the same device. Relay Protection System: These are among plant engineering systems designed for a specific purpose, in which a determinant part is played by the electrical relays which are sets with the purpose of protection. A protection system includes the measurement transformers, the transmission channels, the cables or conductors, the release circuits, etc. necessary to achieve the purpose. The designer qualifies the protection system specifying the job it must perform and describing in details the characteristics of the elements composing the same system. Electrical Relay: Equipment to be used to cause predetermined changes of state in its output electrical circuits when particular power supply conditions occur across its input electrical circuits. Relay Device: Set of relays connected between them so that they fulfill the purpose the device is supposed to perform and with which the manufacturer qualifies the same device. The terms relay and relay device are usually applied equipments of electromechanical kind, while for those of static kind it is sometimes difficult to find the border between the relay and relay device. Characteristic Variable of a Measurement Relay: Electrical variable which passage across a specified value, which is associated to a given accuracy, determines the relay operation; the characteristic variable characterizes the name of the relay. In the relays with one input power supply variable the names of the characteristic variable and the input power supply ones usually coincide; however there are exceptions: e.g. those relays in which the characteristic variable is the frequency, that are generally powered with a voltage. Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 6 | Page Electrical PS Protection Lab Chapter 2 Protection Relays For High And Low Voltage Networks Contents Experiment (1) Overcurrent Relay (SR1) 07-11 Experiment (2) Max/Min three-phase voltage Relay (SR3) 12-16 Experiment (3) Directional Relay (SR10) 17-24 Experiment (4) Differential Relay (SR14) 25-38 Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 7 | Page Electrical PS Protection Lab Objectives: 1. Connection and study of a fixed time maximum current relay and of a 3- phase line short-circuit one with different currents. 2. To measure the tripping time of maximum-current (over load and short-circuit) in a three-phase network with different current values; Theory and concepts: Code CEI: 50 Instantaneous intervention relays 51 Delayed intervention relays 50N-51N max homopolar current relays. These are the most famous protection relays. Main purpose is the detection of the phase to phase or phase to ground faults. In particular the relay 50N or 51N can be used also with networks with insulated neutral under particular conditions.  The three-phase amperometric relay set to maximum current (overload) protection function enables to fix the limit of the current provided by an alternator (its nominal power) or the current that a power line can usually stand.  The values of the currents are adjustable and so is the intervention time delay.  The three-phase amperometric relay set to protection function against short-circuit intervenes instantly when the controlled current overcomes the set value. The current values are adjustable, but the time delay is not so as it is instantaneous. Usually the relay acts on the main switch to set the controlled object out of service (alternator or line).  The current value (overload, short-circuit) as well as the delay time, must be adjusted and checked during the test phase and next in the periodical testing to be sure the protection device operates. For the fixed time relay: (figure 1) Iint = K I1 /In for the overload Iint = K I2 /In for the short-circuit Experiment (1) Overcurrent Relay (SR1) Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 8 | Page Electrical PS Protection Lab Figure (1) SR1 Max current three-phase relay description: Three-phase maximum-current (overload and short-circuit) relay at definite time and three-phase short-circuit. Overcurrent Relay settings/Current and time settings (overload and short circuit): The technical characteristics of the device are shown in appendix A. SI1 first level regulation range (overload). SI2 second level regulation range (short-circuit) Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 11 | Page Electrical PS Protection Lab Questions: 1. Suppose you have to protect a three–phase induction motor from an overload condition, the nameplate of the motor is shown in figure 1. (A) Sketch the connection needed to connect three-phase induction motor with: (1) 3-phase supply (2) Contactor (3) SR1: Overcurrent relay (B) Explain how to put the settings of the relay? (C) Explain how to reset the relay after removing the cause of overload? (D) Explain the operation of the relay in this case? Hints: 1) Motors with a service factor (SF) of 1.15 or more, the settings of the overload relay should be 125% of the full load current. 2) Motors with a service factor (SF) less than 1.15, the settings of the overload relay should be 115% of the full load current. Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 12 | Page Electrical PS Protection Lab Objectives: 1. Connection and study of a maximum and minimum voltage relay in a 3-phase network. 2. To measure the tripping time of maximum/minimum in a three-phase network with different voltage values; Theory and concepts: Code CEI: 59 Maximum voltage relay 27 Minimum voltage relay The purpose of the maximum and/or minimum voltage relays is to detect anomalous voltage rising or dropping near the production or usage centers so to prevent damages of machines or OFF parallel situations. The three-phase voltage relay detects the limits of the triad of voltage generated in ordinary service of the alternator or distributed by the transmission line. Usually, the relay acts on the main switch to set the controlled object out of service (alternator or user connected to the line) when a rise or drop of voltage can cause malfunctions or damages. The characteristic equation is: V = KV1 / VN Experiment (2) Max/Min 3-phase voltage Relay (SR3) Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 13 | Page Electrical PS Protection Lab Operation diagram of the relay Figure (1) The technical characteristics of the device are presented in appendix A. Necessary Material: 1. AMT-3/EV: Variable three-phase power supply mod. 2. SR-3/EV: Max/min three phase voltage relay. 3. IL-2/EV: Variable inductive load mod. 4. Contactor with on-off control. 5. AZ-VIP: Digital instrument. Experimental Procedures: 1. Connect the circuit as shown in figure 1. Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 16 | Page Electrical PS Protection Lab Questions: 1. Suppose you have to protect a three–phase induction motor from an undervoltage condition, the nameplate of the motor is shown in figure 1. (A) Sketch the connection needed to connect three-phase induction motor with: (1) 3-phase power supply; (2) Contactor; (3) SR3: Max/Min voltage relay. (B) Explain how to put the settings of the relay to protect the motor from undervoltage condition; the voltage applied to the motor should be at least 95% of the nominal voltage? (C) Explain how to reset the relay after removing the cause of undervoltage? (D) Explain the operation of the relay in this case? Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 17 | Page Electrical PS Protection Lab Objectives: 1. Connection and study of a maximum current directional relay for maximum current. 2. To measure the tripping time with inverse current flow. Theory and concepts: Code CEI: 67 Directional relay 32 Directional or power inversion relay It is a much extended family of equipment sharing the capacity to operate a control on the power direction. The concept of direction in the alternated currents is not proper; we should rather talk of angular relation between the voltages and the phase currents. However, by convention, we have fixed to consider as positive a vector direction resulting from the composition of a reference vector with another set within ± 90° from the first; as negative the one resulting from the composition with a superior angle. The diagram of figure 1 shows straight line “L” called inversion or limit or threshold. One of the pros of directional relays is just the one to operate, near the inversion straight line, without operation uncertainties. To fulfill their purpose, the directional relays carry out the measurement comparing two variables in module and in phase: the voltage and the current. Generally they are defined on the plane V–I and can be reproduced by the equation: Figure (1) Experiment (3) Directional Relay (SR10) Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 18 | Page Electrical PS Protection Lab Generally, with the help of watt-meters, ammeters and voltmeters, the positive or negative power directions are checked associating the open or closed state of the output relay. The control of the power provided by the production central station or absorbed by the user is a need appeared since the first electrical power distribution. This is due by the fact that the power market is made of more producers and also by the control of the contractual conditions (active, reactive power, absorbed power excess, etc.). It is more obvious that the simple current control, actuated with the maximum or minimum current protections, in case of more or less shifted loads does not show the actual degree of work or the involved power. As function of the needs of the different users and producers, it is advisable to carry out protections sensible to the power expressed in one of the three relations: Apparent power: S = V I Active power: P = V I cos φ Reactive power: Q = V I sin φ In fact, while the generators keep equally employed for the production of the components in quadrature, the dissipation by Joule effect considers only the resistive component, so, in different power factor conditions, there are different dissipations to equal active power, too. The power relays must measure the two variables, V and I, so that it is possible to compare the phase (analogously to the watt-meters). The adjustment of the intervention threshold of the power directional relays is expressed by the following equation: F = K Iiv cos φ where the constant K is a factor of proportionality depending on the relay constructional characteristics. In the protection relays against inverse power it is necessary for the polar operating quadrants, block and threshold, to be clearly defined to prevent operation uncertainties near the inversion zone when the generator is used to produce reactive instead of active power. A characteristic situation is represented in figure 2 where a small alternator is set in parallel on a considerable network. Figure (2) Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 21 | Page Electrical PS Protection Lab Necessary Material: 1. AMT-3/EV: Variable three-phase power supply mod. 2. SR-10/EV: Maximum current directional relay. 3. RL-2/EV: Variable resistive load mod. 4. IL-2/EV: Variable inductive load mod. 5. AZ-VIP: Digital instrument. SR10 Maximum current directional relay description: Maximum current directional relay The installed device is a directional relay (In = 5 A) which, with the current or power direction following the input one (input in the higher terminals) does not enter alarm state; with current a little over the threshold set in Is and with the current or power in the reverse direction, it alarms after the time Ts. Intervention Current Is = Inominal (5 A) x [Weight of the dip-switches (0-8.5) + 1] x K (0.02) Intervention time Ts = [Weight of the dip-switches (0-16.5) + 0.1] The technical characteristics of the device are shown in appendix A. Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 22 | Page Electrical PS Protection Lab Experimental Procedures: 1. Connect the circuit as shown in figure 1. Figure (1) 2. Connect the terminals (Power Supply) to the 230-Vac auxiliary power supply line, but do not connect the voltage. Connect the terminal PE to the protection conductor, too. 3. Connect the terminals (Voltage Input) respectively to L1 and L2 of the variable three- phase power supply source. Connect a voltmeter to measure the relay input alternated voltage (line voltage). 4. From the same three-phase power supply source mentioned above, by-pass the three- phase load consisting in the RC rheostat (Y-connection load), the current I1 (also called R1) must reach the terminals (Current Input). Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 23 | Page Electrical PS Protection Lab 5. Connect an ammeter to measure the relay input alternated current (load current). In practice, it is sufficient to insert the load only on the conductor L1 – Neutral. 6. Suppose and adjust the device with the following design data: - Dip-switch angle α = 30°; - Delayed intervention dip-switch = ON; - Inverse current threshold (Is) = 0,7 A (dip-switch a 2 + 4 ON); - Intervention time (Ts) = 5 s (dip-switch t 0.1 + 0.8 + 4). 7. Some important considerations: - SR-10/EV senses only one phase current (the L1 phase). - If the load is balanced, the three currents L1-L2-L3 are equal, so sensing one of them is enough. - If the load is not balanced, the relay will trip ONLY if the L1 current is over the limit. 8. As set, it is a directional relay that, with the current direction (In = 5A) to the input (input in the higher terminal) 9. Check the correspondence of the output relay contacts (powered device not in alarm state). 10. The relay reset is manual; it can be done only after the current goes back under the threshold, with the pushbutton on the front panel or with the insertion of a jumper into the RESET terminals. Test (1): Resistive Load Only. 1. Increase the current over 0.7-A, simulating a reverse current over the accepted limit. (Full line in the last design in figure 1). Measured With AZ-VIP/EV Calculated Comments I1RL (A) PF I1R = I1RL * PF (A) 2. To simulate the direct current invert the SR-10 current input terminals, Modify the load to increase the current over 0.7 A, and up to 2 A. (Dotted lines in the last design in figure 1). Measured With AZ-VIP/EV Calculated Comments I1RL (A) PF I1R = I1RL * PF (A) Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 26 | Page Electrical PS Protection Lab The heart of the device is a toroidal magnetic core that has 3 coils: - Two coils are run by the two currents of the single-phase current. Both coils are exactly equal, and due to the currents, both produce the same magnetic flux, but opposite direction. - The third coil, the differential coil, generates a voltage only when there is a resultant magnetic flux in the toroid. This voltage, processed by the internal circuits of the ELCB, provokes the opening of the breaker. The ELCB equations are (all equations are vectorial type, not algebraic): when there is no fault: |Ф1 + Ф2 | = 0 when there is a fault: |Ф1 + Ф2 | = ФR as one of the currents is predominant, and therefore, one of the two fluxes is higher than the other. ELCBs are sensitive to different currents differences |I1 + I2 | = Idn, according to the protected device. Then we have: - Low sensitivity, Idn ≥ 1 A - Medium sensitivity: 100 ≤ Idn ≤ 500 mA - High sensitivity: Idn ≤ 30 mA Principle of operation of the Differential Protection The Differential Protection is based in the comparison of two currents, one at the input, one at the output of the protected device. The comparison is of vectorial type, including module and phase of the currents. Fig. 2 shows the basic connection of the differential protection, Fig. 3 shows the same circuit with an external fault, and Figs. 4 the same circuit with an internal fault. Figure (2) Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 27 | Page Electrical PS Protection Lab Figure (3) Figure (4) Differential protection of devices with two or more wounds Fig. 5 shows the currents in case of an internal fault. Observe the use of CTs. The analysis is done on the currents through the differential protection: a fault over i3, produces an imbalance in the relay that will cause it to trip. A similar situation (imbalance) could occur even when there is no fault; it is the case when there is a load imbalance or when a breaker is open for any reason. The differential protection will “see” these cases, as only one of the sides of the differential protection is affected. Figure (5) Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 28 | Page Electrical PS Protection Lab Percentage Differential Relays The disadvantage of the current differential protection is that the CTs must be identical, otherwise there will be current flowing through the CTs for faults outside of the protected zone or even under normal conditions. Briefly, it is a problem on the CTs sensitivity and their errors; the protection device could trip even with no fault. The technique named percentage differential relays reduces the CTs’ sensitivity so to avoid the above mentioned problem. Fig. 6 shows the circuit, where the difference with the previous ones are the restraint coils, in series with the secondary currents of the CTs. The purpose of the restraint coil is to prevent undesired relay operation due to CTs errors. The operating relay current |i1 - i2| required for tripping is a percentage of the average current through the restraint coils, given by: | i1 - i2 | ≥ k | i1 + i2 | / 2 K is the proportion of the operating coil current to the restraint coil current. The restraint coils collect the currents relative to the machines, increasing the currents through the operating coil. By so doing, the error sensitivity of the CTs is lowered. Figure (6) Differential Protection of Three Phase Power Transformers Differential protection of 3- phase transformers should take into account the change in magnitude and phase angle between primary and secondary currents. Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 31 | Page Electrical PS Protection Lab Experimental Procedures: Part I: SR-14 in a single phase line. Simulation of a fault: current imbalance between wires. 1. Connect the circuit as shown in figure 1 and 2. Figure (1) 2. Put the settings of the relay as follows: With NO power applied to the relay, set the following parameters: Time adjustment 0.1 Second constant multiplier: tx10 Fault Current adjustment 0.25 A constant multiplier: IΔnx1 AUTO – MAN Reset The Reset is carried out with the Reset pushbutton. N – FS FS = relay positive safety activated. 3. Give power to the relay (230 VAC). With the DMM (ohmmeter), check the continuity. Check also the other set of output contacts. Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 32 | Page Electrical PS Protection Lab Figure (2) 4. Normal Condition: Apply balance load (switch A) to the circuit with the switches of RL-2A/EV (1); Condition Relay operation Normal IΔ Tripping Time Notes 5. Set RL-2A/EV (2) as indicated in Test 1 with various value of resistance, and connect as the dotted line. This connection simulates a “controlled imbalance load” (the imbalance current is controlled by RL-2A/EV (2)). Test R-load Relay operation IΔ Tripping Time Notes Test (1) A Test (2) B Test (3) A||B Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 33 | Page Electrical PS Protection Lab Part II: SR-14 in a Three phase line without neutral wire. Simulation of a fault: current imbalance between wires. 1. Connect the circuit as shown in figure 3 and 4. Figure (3) 2. Put the settings of the relay as follows: With NO power applied to the relay, set the following parameters: Time adjustment 0.2 Second constant multiplier: tx10 Fault Current adjustment 0.5 A constant multiplier: IΔnx1 AUTO – MAN Reset The Reset is carried out with the Reset pushbutton. N – FS FS = relay positive safety activated. 3. Give power to the relay (230 VAC). With the DMM (ohmmeter), check the continuity. Check also the other set of output contacts. 4. Normal Condition: Apply a balance load (switch A) to the circuit with the switches of RL-2A/EV (1); Condition Relay operation Normal IΔ Tripping Time Notes Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 36 | Page Electrical PS Protection Lab Figure (6) 5. Set RL-2A/EV (2) as indicated in Test 1 with various value of resistance, and connect as the dotted line. This connection simulates a “controlled imbalance load” (the imbalance current is controlled by RL-2A/EV (2)). Test R-load Relay operation IΔ Tripping Time Notes Test (1) A Test (2) B Test (3) A||B Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 37 | Page Electrical PS Protection Lab Part IV: SR-14 in a Three phase line with neutral wire. Simulation of a fault: current imbalance between wires. 1. Connect the circuit as shown in figure 7 and 8. Figure (7) 2. Put the settings of the relay as follows: With NO power applied to the relay, set the following parameters: Time adjustment 0.2 Second constant multiplier: tx10 Fault Current adjustment 0.25 A constant multiplier: IΔnx1 AUTO – MAN Reset The Reset is carried out with the Reset pushbutton. N – FS FS = relay positive safety activated. 3. Give power to the relay (230 VAC). With the DMM (ohmmeter), check the continuity. Check also the other set of output contacts. 4. Normal Condition: Apply a balance load (switch A) to the circuit with the switches of RL-2A/EV (1); Condition Relay operation Normal IΔ Tripping Time Notes Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 38 | Page Electrical PS Protection Lab Figure (8) 5. Set RL-2A/EV (2) as indicated in Test 1 with various value of resistance, and connect as the dotted line. This connection simulates a “controlled phase to ground fault” (the imbalance current is controlled by RL-2A/EV (2)). Test R-load Relay operation IΔ Tripping Time Notes Test (1) A Test (2) B Test (3) A||B Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 41 | Page Electrical PS Protection Lab The electrical and the operation diagram of this relay are shown in the following figures: 2. Relay for Max/min three-phase voltage. It detects the limit of the voltage triad produced in normal operation by the synchronous generator, or distributed to the transmission line. Usually, the relay, acts on the main switch to set the controlled object out of service (synchronous generator or user connected with the line) when a voltage rise or drop can cause malfunctions or damages. Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 42 | Page Electrical PS Protection Lab 3. Relay for Max/min frequency of a power production plant. The relay enables the max/min frequency control of the alternating power output by the synchronous generator in normal operation. As protection device, it acts on the main switch of the synchronous generator. It is used to protect the synchronous generator in case of over or under speed of the prime mover. The electrical and the operation diagram of this relay are shown in the following figures: SR5 Max/min frequency Relay description: Max/min frequency Relay settings: - Adjustment of the intervention threshold for maximum frequency with rotary switch from 0.5 to 10 Hz. - Adjustment of the intervention time for maximum frequency with potentiometer Delay max from 0.1 to 30 s. - Adjustment of the intervention threshold for minimum frequency with rotary switch from 0.5 to 10 Hz. - Adjustment of the intervention time for minimum frequency with potentiometer Delay min from 0.1 to 30 s. Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 43 | Page Electrical PS Protection Lab Dip Switches: 4. Relay for Maximum current (overcurrent) to a three-phase line The three-phase ammetric relay operating as maximum current (overload) protection enables to fix the limit of current output by a synchronous generator (its rated power) or the current a power line can usually bear. Usually the relay acts on the main switch to set the controlled object (synchronous generator or line) out of service. The overload settings (current and delay time) are shown in the following table: Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 46 | Page Electrical PS Protection Lab Test 1: Max voltage relay. Increase the voltage supplied by the synchronous generator by increasing the excitation current and record the time between the “overvoltage” moment and the same output relay tripping one. Reduce the voltage again to its rated value (400 V) and check the alarm suppression (the maximum voltage output relays is reset). Consider that the relay has a hysteresis of 3% with respect to the set point. Determine at which value of voltage will the relay reset? Maximum voltage threshold % Line voltage (V) Maximum voltage intervention delay Measured delay (Sec) Reset Value (V) 105% 5 sec 110% 5 sec Test 2: Min voltage relay. Way 1: Decrease the voltage supplied by the synchronous generator by decreasing the excitation current and record the time between the “undervoltage” moment and the same output relay tripping one. Increase the voltage again to its rated value (400 V) and check the alarm suppression (the minimum voltage output relays is reset). Consider that the relay has a hysteresis of 3% with respect to the set point. Determine at which value of voltage will the relay reset? Minimum voltage threshold % Line voltage (V) Minimum voltage intervention delay Measured delay (Sec) Reset Value (V) 95% 5 sec 90% 5 sec Way 2: Complete the wiring including the step resistive load mod. RL-2/EV. Be sure that all step switches of each phase are in position of load excluded (OFF). Set the synchronous generator under load with the insertion of the resistive load (with different values of the resistive load) and measure the following: Resistive Load in Ω Minimum voltage threshold % Line voltage (V) Minimum voltage intervention delay Measured delay (Sec) Reset Value (V) A 95% 5 sec A||B 90% 5 sec Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 47 | Page Electrical PS Protection Lab Part III: Max/min frequency Relay. 1. Remove jumpers of the max/min voltage relay and Insert two jumpers into the terminals set to power the max/min frequency relay as indicated in Figure 3. 2. Connect an ohmmeter to check the state of the output relay contact and complete the wiring of the GCB-3/EV panel as shown in Figure 3. Figure (3) Test 1: Max frequency relay. Increase the test frequency using RPM potentiometer and record the time between the overfrequency and the same output relay tripping one. Maximum frequency threshold Frequency (Hz) Maximum frequency intervention delay Measured delay (Sec) 50.2 Hz (+10%) 3 sec 50.4 Hz (+20%) 3 sec Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 48 | Page Electrical PS Protection Lab Test 2: Min frequency relay. Decrease the test frequency using RPM potentiometer and record the time between the under frequency and the same output relay tripping one. Minimum frequency threshold Frequency (Hz) Maximum frequency intervention delay Measured delay (Sec) 49.8 Hz (-10%) 3 sec 49.6 Hz (-20%) 3 sec Part IV: Overcurrent and Short circuit Relay. 1. Remove jumpers of the max/min frequency relay and connect the 3-Phase Overload and the Short-Circuit relay with the proper terminals via six jumpers as indicated in Figure 4. 2. Connect an ohmmeter to check the state of the output relay contact and complete the wiring of the GCB-3/EV panel and complete the wiring including the step resistive load mod. RL-2/EV to obtain the current regulation in the ammetric relay as shown in Figure 4. Figure (4) Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 51 | Page Electrical PS Protection Lab 3. Based on the relay for phase sequence, phase failure and voltage asymmetry experiment answer the following questions: (a) Sketch the connection needed to connect synchrouns generator with: 1. Relay; 2. 4-pole contactor (on-off) (to switch off the load when phase sequence or phase failure or voltage asymmetry occur); 3. Variable three-phase resistive load. (b) If the load attached on the synchronous generator is (C,A,A) and the settings of the relay are: - Asymmetry = 10%; - Delay = 10 Second; - Reset delay = 0.1 Sec. The measurements from the power analyzer are: Line voltages (V) Va Vb Vc 312 347 345 1. Explain how to put the settings of the relay? 2. Explain the operation of the relay in this case? Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 52 | Page Electrical PS Protection Lab Chapter 4 Transmission Line Protection Contents Experiment (1) Protection of Transmission lines using Electromechanical Relays. 53-56 Experiment (2) Protection of Transmission lines using Digital Relays. 57-69 Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 53 | Page Electrical PS Protection Lab Objectives: 1. Protection against overcurrent in a power transmission line using overcurrent relay SR1/EV. 2. Protection against Single line to ground fault in a power transmission line with insulated neutral conductor using differential relay SR14/EV. Theory and concepts: Sometimes the current crossing the conductors of a power transmission line may be higher than the rated current. These situations occur when the line is overloaded, because too many users are connected with the line or some users require greater power at the same time, and when there are short circuits due to breaks in the supports of bare conductors or to insulation losses between active conductors. An overload occurs when the line is crossed by a current exceeding the rated current (generally it is approximately 10 times as high); this provokes the overheating of conductors and devices, and it can be borne for a certain time. The current/time relation may be fixed: when a certain current value is exceeded, after a certain time of tolerance the protection relay will control the power device (switch) to put the line out of commission. But this protection ratio may also be of inverse time/current type where a shorter intervention time corresponds to a higher current. Short circuits generate a very strong current with thermal and mechanical phenomena and destructive electric arcs, therefore the reaction time of the protection relay must be instantaneous. Necessary Material: 1. SEL-1/EV: Simulator of electric lines mod. 2. P14A/EV: Three-phase transformer mod. 3. Contactor with On-Off control 4. AMT-3/EV: Variable three-phase power supply mod. 5. SR-1/EV: Overcurrent relay. 6. SR-14/EV: Differential relay. 7. IL-2/EV: Variable Inductive load mod. 8. RL-2K/EV: Variable Resistive load mod. Experiment (1) Protection of Transmission lines using Electromechanical Relays Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 56 | Page Electrical PS Protection Lab 3. With no power supply adjust the relay settings as required 4. Enable and adjust the voltage of the power supply at 380 V. 5. Turn the breaking-control switches at the origin and at the end of the LINE 2 to ON. 6. At normal condition with balanced resistive load (A) measure the fault current and tripping time for this case. 7. Perform a single line to ground fault at the receiving end point by connecting between the phase 1 and ground then measure the fault current and tripping time. Load Condition Settings of the differential relay Fault current (mA) Tripping time (sec) R-(Ω) IΔn T (sec) IΔn T (A,A,A) Normal 0.025 2 (A,A,A) SLG (L1-G) 0.025 2 Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 57 | Page Electrical PS Protection Lab Objectives: To configure the protection device SR16/EV with the use of the DIGSI software as: 1. Instantaneous [50] and delayed [51] maximum current relay to protect a no-load power transmission line against phase-phase faults. 2. Instantaneous [50N] and delayed [51N] maximum homopolar current relay to protect a no-load power transmission line against phase-ground faults. 3. Max ground directional current relay [67N], to protect a no-load power transmission line against phase-ground faults. 4. Distance relay [21], protection against phase-ground and phase-phase fault in a no-load power transmission line. Theory and concepts: The Impedance Relay (IR) is one of the most important protection relays against short circuits. It is mainly used when the current overload relays do not provide adequate protection; these relays can work even when the short circuit current is low and the overload relays could not operate safely. Additionally, the speed operation of the IR is independent from the short circuit current value. Basically, it is a relay that senses the current and voltage of the protected device. With these values, the IR calculates the impedance Z of the device. The IR compares the real impedance Z of the protected device against Z0; if Z is equal or less tan Z0, it means that a failure has occurred (could be a solid or not short-circuit). When the measured impedance of the protected device Zmed is greater or equal to Z0, it is the normal condition. In the opposite case, the protected device is in abnormal condition, and the IR will trip. Necessary Material: 1. SEL-1/EV: Simulator of electric lines mod. 2. PC with DIGSI software installed. 3. SR16/EV: Distance relay mod. 4. SR20/EV: Power transmission line simulator mod. 5. SR21/EV: Isolation transformer mod. 6. UAT/EV: Fixed Power supply mod. 7. RC3-PT/EV: Rheostat mod. Experiment (2) Protection of Transmission lines using Digital Relays Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 58 | Page Electrical PS Protection Lab Experimental Procedures: Part I: Configuration of SR16 as maximum current relay [50], [51], [50N] and [51N] Protections [50N] and [51N] are fed by the amperometric transformer I4 (inside SIPROTEC 7SA610 device). The transformer reproduces the short-circuit current to the secondary in case of a phase-ground fault. During normal operation, the currents vectorial sum in the three phases is 0; the magnetic flux produced by the currents is consequently 0. During a ground fault, the vectorial sum of the three phase currents is different from 0. This means that the resultant magnetic flux concatenates with the secondary coil of the current transformer, resulting in a non-zero current. The protection senses the generated homopolar current and intervenes. 1. Perform the electrical connections following the electrical diagram of figures 1 and 2. Figure (1) Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 61 | Page Electrical PS Protection Lab 3. Turn ON the power supply mod. UAT/EV 4. Push the NO button 1I on panel mod. SR16/EV. Part I-1: Phase – Phase Fault 1. Connect the T.M.C.B. between 2 phases, as shown in figure 3. 2. Turn ON the switch to perform a phase-phase fault, respectively at 25, 50, 75 and 100 km. 3. Measure the fault current with SIGRA program. Figure (3) 4. Insert the data obtained with the measurements in the following table: Phase – Phase Fault PH-PH fault Line (km) T start (ms) T trip (ms) Fault Current (A) Protection intervetion L1 – L2 100 L2 – L3 75 L3 – L1 50 L1 – L2 25 Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 62 | Page Electrical PS Protection Lab Part I-2: Phase – Ground Fault 1. Connect the T.M.C.B. between the phase and ground, as shown in figure 4. 2. Turn ON the switch to perform a phase-ground fault, respectively at 25, 50, 75 and 100 km. 3. Measure the fault current with SIGRA program. Figure (4) 4. Insert the data obtained with the measurements in the following table: Phase – Ground Fault PH-E fault Line (km) T start (ms) T trip (ms) Fault Current (A) Protection intervetion L1 – E 100 L2 – E 75 L3 – E 50 L1 – E 25 Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 63 | Page Electrical PS Protection Lab Part II: Configuration of SR16 as maximum ground directional current relay [67N] This protection also has the I4 homopolar amperometric transformer (inside the SIPROTEC 7SA610 device). The protection [67N], besides measuring the homopolar residual current in a ground fault, measures the homopolar voltage V0. That’s why we use three voltmetric transformers (n=1000/100) without open Delta connection of the secondaries, because calculation of the homopolar voltage V0 is internally calculated. During a normal operation the vectorial sum of the three voltages over the secondaries of the VT is zero. In case of a phase- ground fault, the sum of the three voltages is different from zero. Once the homopolar current vector I0, the homopolar voltage vector V0 and their phase shift φ are measured, the protection will be able to estimate the real power, that is equal to P0= V0*I0*cos φ. The power sign (positive or negative) allows the relay [67N] to determine the fault current direction, and then to establish if the fault is upstream or downstream. Due to this property the protection [67N] is called ground directional relay. Since the protections are selective, the directional relay [67N] controls the breaker opening only in case of a downstream ground fault. 1. Perform the electrical connections following the electrical diagram of figures 1 and 5. Figure (5) Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 66 | Page Electrical PS Protection Lab Part III: Configuration of SR16 as distance relay [21] The distance relay Siemens 7SA610 mounted on panel mod. SR16/EV presents a polygonal intervention characteristic. This characteristic is defined by a parallelogram that intersects the R and X axes. There are 6 intervention zones in total (the sixth is not shown in the figure). For each zone it is possible to set up the intervention direction (it depends on the network type that is considered, unidirectional as in our case, where the power flow has only one sense). Distributed “smart grids” where the power flow can be bidirectional, can be Forward, Reverse or Non –Directional. Figure 7 shows for example an intervention zone Z1 of Forward type, while zone 3 is of Reverse type, and zone 5 of Non – Directional type. Figure (7) 1. Perform the electrical connections following the electrical diagram of figures 1 and 8. 2. Set the Parameters of the protection device SR16/EV and power system data using DIGSI software as follows: (A) Setting Group A – distance protection – General settings: 1. Distance protection [No. 1201] = ON 2. Phase current threshold for dist. Meas. [No. 1202]= 0.1 A 3. Angle of inclination, distance characteristic [No. 1211]= 52o Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 67 | Page Electrical PS Protection Lab (B) Setting Group A – distance zones (quadrilateral)-: 1. Zone Z1: (a) Operating mode Z1[No. 1301] = Forward (b) R(Z1), Resistance for PH-PH faults [No. 1302] = 42.000 ohm (c) X(Z1), Reactance [No. 1303] = 49.000 ohm (d) RE(Z1), Resistance for PH-E faults [No. 1304] = 42.000 ohm (C) Configuration matrix (Masking I/O): 1. Dis. General (a) Dis.Gen. Trip [No. 03801]  Led (3) : L (latched) 3. Turn ON the power supply mod. UAT/EV 4. Push the NO button 1I on panel mod. SR16/EV. Part III-1: Phase – Phase Fault 1. Connect a 20 Ω resistor in series to the T.M.C.B between two phases as shown in Figure. 8. 2. Turn ON the switch to perform a phase-phase fault, respectively at 25, 50, 75 and 100 km. 3. Measure the fault current with SIGRA program. Figure (8) Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 68 | Page Electrical PS Protection Lab 4. Insert the data obtained with the measurements in the following table: Phase – Phase Fault PH-PH fault Line (km) Measured line distance (km) T start (ms) T trip (ms) Fault Current (A) Protection intervetion L1 – L2 100 L2 – L3 75 L1 – L3 50 L1 – L2 25 Part III-2: Phase – Ground Fault 1. Connect a 20 Ω resistor in series to the T.M.C.B between the phase and ground as shown in Figure 9. 2. Turn ON the switch to perform a phase-phase fault, respectively at 25, 50, 75 and 100 km. 3. Measure the fault current with SIGRA program. Figure (9) Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 71 | Page Electrical PS Protection Lab Objectives: 1. Checking the operation of a differential switch with operating differential rated current Idn = 30 mA - type A (Q11). 2. Checking the operation of a differential switch with operating differential rated current Idn = 30 mA - type AC (Q12). 3. Checking the operation of a differential selective switch [S] with operating differential rated current Idn = 0.3 A - type A (Q2). 4. Checking the operation of a delayed differential switch with adjustable operating differential rated current Idn and time t, type A. Theory and concepts: Checking the operation of a differential switch By reducing the value of the variable resistance Rp will provoke an increase of the current. Then the voltage is measured between the exposed-conductive-parts (UT touch voltage) and an independent auxiliary earth electrode (voltage probe). Also the operating current Id of the differential device is measured: this current must never be higher than the rated current Idn of the switch under test. The following condition: UT > UL * (Id / Idn); where UL is the conventional limit of touch voltage, must be complied with. This method uses an auxiliary earth electrode. Experiment (1) Checking the Operation of the Protection Devices with Differential Current Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 72 | Page Electrical PS Protection Lab Necessary Material: 1. PDG-R/EV: Neutral Point Connection panel mod. 2. Multimeter for a.c. voltages. 3. Ammeter tongs for alternating currents. Experimental Procedures: Part I: Checking the operation of a differential switch with operating differential rated current Idn = 30 mA - type A (Q11). 1. Connect the circuit as shown in Figure 1. Figure (1) Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 73 | Page Electrical PS Protection Lab 2. Assemble a system in configuration of TT distribution system as indicated in the fig. 1 where the output of the measuring instrument is connected with the differential protection under test (switch Q11), according to the method explained previously. 3. Insert the jumpers RE1 of 1 Ω, RE2 of 20 Ω. 4. Power the system (panel) and turn all the protection switches involved in this experiment to ON. 5. Turn the selector EQUIPMENT to the position ~, the warning light on indicates that the power-absorbing equipment is powered correctly. 6. Use the “combination” of two earth faults to obtain various current values and to check the operation of the differential protections. 7. Change the combination of the two earth faults as shown in table (1) and measure the fault current with describing the operation of the differential switch Q11. Differential switch with operating differential rated current Idn = 30 mA - type A (Q11). Combination of two faults Current (mA) Comments Fault (1) Left (Ω) Fault (2) Right (Ω) 50k 50k 15k 50k 15k 15k 5k 0 5k 5k 8. Then turn the selector EQUIPMENT to the position =, the earth fault current crossing the power-absorbing equipment will be of unidirectional pulsating type. 9. Repeat the test changing the value of the earth fault and make sure that the differential protection of class A is immediately enabled, like in the case of the sinusoidal fault (EQUIPMENT in the position ∼), then tabulate your results in table (2). Differential switch with operating differential rated current Idn = 30 mA - type A (Q11). Combination of two faults Current (mA) Comments Fault (1) Left (Ω) Fault (2) Right (Ω) 50k 50k 15k 50k 15k 15k 5k 0 5k 5k Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 76 | Page Electrical PS Protection Lab Part III: Checking the operation of a differential selective switch [S] with operating differential rated current Idn = 0.3 A - type A (Q2). 1. Connect the circuit as shown in Figure 3. Figure (3) 2. Assemble a system in configuration of TT distribution system as indicated in the fig. 1 where the output of the measuring instrument is connected with the differential protection under test (switch Q2), according to the method explained previously. 3. Insert the jumpers RE1 of 1 Ω, RE2 of 2 Ω. 4. Power the system (panel) and turn all the protection switches involved in this experiment to ON. 5. Turn the selector EQUIPMENT to the position ~, the warning light on indicates that the power-absorbing equipment is powered correctly. 6. Use the “combination” of two earth faults to obtain various current values and to check the operation of the differential protections. Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 77 | Page Electrical PS Protection Lab 7. Change the combination of the two earth faults as shown in table (5) and measure the fault current with describing the operation of the differential selective switch Q2. Differential selective switch with operating Idn = 0.3 A - type A (Q2). Combination of two faults Current (mA) Comments Fault (1) Left (Ω) Fault (2) Right (Ω) 15k 15k 5k 5k 1.5k 1.5k 0.5k 0 0.5k 0.5k Table (5) 8. Then turn the selector EQUIPMENT to the position =, the earth fault current crossing the power-absorbing equipment will be of unidirectional pulsating type. 9. Repeat the test changing the value of the earth fault and check how the differential protection behaves with a unidirectional fault, then tabulate your results in the following table. Differential selective switch with operating Idn = 0.3 A - type A (Q2). Combination of two faults Current (mA) Comments Fault (1) Left (Ω) Fault (2) Right (Ω) 15k 15k 5k 5k 1.5k 1.5k 0.5k 0 0.5k 0.5k Table (6) Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 78 | Page Electrical PS Protection Lab Part IV: Checking the operation of a delayed differential switch with adjustable operating differential rated current Idn and time t, type A (RCCB coupled with the switch Q1 via the CRC coil). 1. Connect the circuit as shown in Figure 4. Figure (4) 2. Assemble a system in configuration of TT distribution system as indicated in the fig. 1 where the output of the measuring instrument is connected the differential protection under test (output of RCCB device), according to the method explained previously. 3. Insert the jumpers RE1 of 1 Ω, RE2 of 2 Ω. 4. Set a current Idn = 0.3A and a time t = 500 ms in the adjustable differential RCCB. 5. Power the system (panel) and turn all the protection switches involved in this experiment to ON. 6. Turn the selector EQUIPMENT to the position ~, the warning light on indicates that the power-absorbing equipment is powered correctly. Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 81 | Page Electrical PS Protection Lab Objectives: 1. Verification of selectivity among devices against overcurrents 2. Verification of selectivity between differential devices connected in parallel (horizontal selectivity) 3. Verification of selectivity among differential devices connected in series (vertical, amperometric and time selectivity) Theory and concepts: Standard CEI 64-8536.1 Selectivity among protection devices against overcurrents When more protection devices are connected in series and service needs require this solution, the operating characteristics of these devices must be chosen so that only the part of the system suffering the fault can be disconnected from the power supply. The operational situation requiring selectivity must be defined by the principal and designer of the system. Standard CEI 64-8536.3 Selectivity among differential devices A selectivity among differential devices connected in series can be ordered for operational reasons, in particular when safety is involved, so that the parts of the system not touched by the possible fault are anyway powered. This selectivity can be obtained with the choice and installation of differential devices: in fact, although ensuring the necessary protection to the various parts of the system, these devices disconnect the supply voltage only from the parts of the system positioned after the device installed before, and near the point of the fault. The selectivity of the two differential devices connected in series is ensured when these devices simultaneously comply with the following conditions: 1) The time-vs-current curve of non-operation of the upstream device must be positioned above the time-vs-current disconnection curve of the downstream device; 2) The rated differential current of the upstream device must be properly higher than that of the downstream device. Experiment (2) Selectivity among Protection Devices Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 82 | Page Electrical PS Protection Lab Selectivity among Devices against Overcurrent A distribution system (indifferently TN, TT or IT) becomes selective with respect to overcurrents if the protection devices installed upstream have higher rated currents (or currents adjusted with higher values) than those of the devices installed downstream. The comparison (superposition) of the curves of their I 2 t leads to state whether the two devices are completely selective (case where the curve of the downstream device, with lower current, is completely below the curve of that with higher current installed upstream), or they are partially selective (crossing point of the two curves). A protection device B installed downstream in a distribution system is selective with respect to another one (A) installed upstream if a fault on the power-absorbing equipment connected with B provokes the intervention only of B and not of A. As regards the electric diagram, the selectivity occurs when the circuits C and D go on working regularly after a fault affecting B. An assessment of the selective behavior among automatic magnetothermal switches will require to consider the thermal and magnetic interventions separately. The operate times of the thermal release, suitable for the protection against overloads, are inverse with respect to current, and selectivity is sure if the operating zone of A is completely above that of B; consider that the width of the operating zone between the rated currents must not be lower than 2 InB, as shown in the fig. 1. Figure (1) A magnetic release, suitable for the protection against short circuits, offers two options: 1) The short-circuit current has a value of intensity that exceeds the releasing threshold of B, but not that of A; 2) The current pulse allowed by B has not shape nor quantity suitable to provoke the release of A, for instance, when the downstream switch is much faster than that upstream. Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 83 | Page Electrical PS Protection Lab The limiting power and operate times between the switches having to become selective, must be compared to their respective curves I²t. As shown in the fig. 1, selectivity is enabled up to the intersection point between the horizontal tangent to the minimum value concerning the switch A and the curve of the upper limit of the switch B (value Is). A distribution system very often includes various protection devices against overcurrents and against indirect contacts: these are not always of the same type; automatic magnetothermal switches and fuses can coexist. The selectivity among various protections of a circuit is the property that enables the protections to operate only in the section of circuit where this is necessary, avoiding to disconnect the other parts not suffering any trouble. The fig. 2 compares the curves of a fuse (upstream) and of a magnetothermal switch (downstream). There is selectivity when the prearc value I²t of the fuse is higher than the total value I²t of the automatic magnetothermal switch, or during the whole interval when the two operating curves do not meet. Figure (2) The fig. 3 compares the curves of a magnetothermal switch (upstream) and of a fuse (downstream). There is complete selectivity (apart from the value of short-circuit current) when the two operating curves do not intersect. Figure (3) Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 86 | Page Electrical PS Protection Lab - Differential relay with separate toroidal transformer: differential rated current Idn adjustable from = 0,03 A to 5 A by five steps, class A, operate time adjustable from 20 ms to 5 s by five steps. This differential relay has an output contact without potential that changes its state in alarm conditions, and it can be used to control the release coil of an automatic magnetothermal switch; - Quadripolar automatic differential switch, with rated current In = 25 A; differential rated current Idn = 0.3 A; class A (suitable for sinewave and unidirectional fault currents with d.c. offsets), selective “S” operation; - Fuse holder of three fuses with breakable neutral conductor and fuses type of 1 and 2 A; - Two-pole automatic magnetothermal differential switch, with rated current In =1 A, curve C, differential rated current Idn = 0.03 A, class AC (suitable for sine-wave fault currents), type of general “G” operation; - Two-pole automatic magnetothermal differential switch, with rated current In =1 A, curve C, differential rated current Idn = 0.03 A, class A, type of general “G” operation. Necessary Material: 1. PDG-R/EV: Neutral Point Connection panel mod. 2. Multimeter for a.c. voltages. 3. Ammeter tongs for alternating currents. Experimental Procedures: Part I: Verification of selectivity among devices against overcurrents 1. Connect the circuit as shown in Figures 1 and 2. Figure (1) Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 87 | Page Electrical PS Protection Lab 2. Assemble a system in configuration of TT distribution system as indicated in the electric diagram of the fig. 1 and in the lay-out of the fig. 2. Figure (2) 3. Insert the jumpers RE1 of 1 Ω, RE2 of 2 Ω. 4. Power the system (panel) and turn all the protection switches involved in this experiment to ON. 5. Turn the selector EQUIPMENT to the position ~, the warning light on indicates that the power-absorbing equipment is powered correctly. The two power-absorbing apparatuses available on the right and on the left of the panel, are protected separately by the two automatic magnetothermal switches Q11 and Q12 and they are powered, downstream, by the automatic magnetothermal switch Q1. These circuits are selective in horizontal way (Q11 with respect to Q12) and in vertical way (Q1 with respect to Q11 and Q12). Selectivity is the characteristic shown by an electric system (conduits and protection devices) where a fault provokes the disconnection only of that part of circuit affected by the fault. This fault could be an overcurrent (overload or short circuit) or an earth fault. Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 88 | Page Electrical PS Protection Lab 6. Put the proper settings of the Q1,Q11 and Q12 switches. Protection devices settings Comments Q1 Q11 Q12 Current Time Current Time Current Time 7. Simulate a short circuit across the output terminals of Q11 and Q12, on the panel, to obtain an overcurrent and to study its effects on the protection devices. 8. Measure the short-circuit current with the ammeter tongs and tabulate your results in the following table. Condition Short circuit current Protection devices stauts Comments Q1 Q11 Q12 Short circuit Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 91 | Page Electrical PS Protection Lab Part III: Verification of selectivity among differential devices connected in series (vertical, amperometric and time selectivity) 1. Connect the circuit as shown in Figures 5 and 6. Figure (5) 2. Assemble a system in configuration of TT distribution system as indicated in the electric diagram of the fig. 3 and in the lay-out of the fig. 4. 3. Insert the jumpers RE1 of 1 Ω, RE2 of 2 Ω. 4. Power the system (panel) and turn all the protection switches involved in this experiment to ON. 5. Turn the selector EQUIPMENT to the position ~, the warning light on indicates that the power-absorbing equipment is powered correctly. Suppose that the power-absorbing equipment available at the left of the panel is powered by a line shunted by a zone distribution board; in its turn, this board is shunted by a main control board which is powered by the substation switchboard. This sequence of protection devices must be coordinated to ensure selectivity. This concept of selectivity is called vertical selectivity. The fault of the terminal circuit is “seen”, for obvious “logistical” reasons, not only by the downstream protection Q12, but also by the upstream protection device Q2 and by the unit Q1-RCCB. Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 92 | Page Electrical PS Protection Lab Figure (6) 6. Put the proper settings of the Q1,Q2 and Q12 switches. Protection devices settings Comments Q1 Q2 Q12 Current Time Current Time Current Time 7. Simulate earth faults on the panel to obtain a current equal to or higher than the Idn of the differential switch under examination. 8. Measure the fault current with the ammeter tongs then tabulate your results in the following table: Condition Fault current Protection devices stauts Comments Q1 Q2 Q12 Earth fault Palestine Technical University-Kadoorie Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha 93 | Page Electrical PS Protection Lab 9. If the optimum coordination can be reached if an Idn of 1A and a time of 1-sec are set in the differential RCCB, After checking that the system described is selective and coordinated, try to change only the time from 1-sec to fast in the differential RCCB, What happens if the clear earth fault is simulated in Q12 output?