EE301 – Three Phase Power, Schemes and Mind Maps of Electrical and Electronics Engineering

Download EE301 – Three Phase Power and more Schemes and Mind Maps Electrical and Electronics Engineering in PDF only on Docsity! EE301 – Three Phase Power 1 11/16/2016 cos cos sin sin P VI S Q VI S         (W) (VAR) 2 2cos RV P V I I R R        = = phase power 3T an bn cnP P P P P    3LV V 2 2sin XV Q V I I X Q X           (VAR) = 3 sinT L LQ V I  (VAR) Learning Objectives a. Compute the real, reactive and apparent power in three phase systems b. Calculate currents and voltages in more challenging three phase circuit arrangements c. Apply the principles of Power Factor Correction to a three phase load Recall that the power triangle graphically shows the relationship between real (P), reactive (Q) and apparent power (S). We will first examine three-phase power in the context of a wye-load; then we’ll examine a delta load. Power to the Wye-Load Active (Real) Power. Suppose that each phase has impedance . Then the active (real) power per phase (P) is given Because we are considering a balanced system, the power per phase (P) is identical in all three phases, and thus the total active power (PT) is simply PT = 3 P. Using line voltage ( ) and line current (IL=I), we have Reactive Power The reactive power per phase (Q) is given by The total reactive power can be calculated similar to the total active power: Apparent Power The apparent power per phase (S) is given The power factor (FP) is given cosT P T PP F S S       3 3 cos 3 cos 3 cos 3 L T L L L V P P V I I V I               (W) 2 2 3T L L V S V I I Z Z S V I            (VA) (VA) Z R X j      Z EE301 – Three Phase Power 2 11/16/2016 3T ab bc caP P P P P    3LI I 3 3 cos 3 cos 3 cos 3 L T L L L I P P V I V V I               (W) Power to the Delta () Load Active (Real) Power. Total active power (PT) is simply PT = 3 P Using line voltage (VL=I) and line current ( ): Which was the EXACT same equation as for Y loads Reactive and Apparent Power The equations for calculating total reactive and apparent power are also identical to the Wye load versions: The applicable portion of the equation sheet: 3 sinT L LQ V I  (VAR) 3T L LS V I (VA) EE301 – Three Phase Power 5 11/16/2016 Example: In the circuit shown, EAB = 2080 V a. Determine the line currents b. Determine total real power delivered by the generator c. Total real power dissipated by the load d. Determine the load phase voltage Van Solution: 3 EE301 – Three Phase Power 6 11/16/2016 Example: In the circuit shown, EAB = 2080 V a. Find the load phase voltage Vab b. Find ST, QT, and PT delivered by the generator c. Find ST, QT, and PT of the load Solution: 4 EE301 – Three Phase Power 7 11/16/2016 Power Factor Correction Recall: In order to cancel the reactive component of power, we must add reactance of the opposite type. This is called power factor correction. In a three phase circuit, capacitors are connected in parallel with each load phase (presuming the actual load is inductive, which is usually the case) Solution steps: 1. Calculate the reactive power (Q) of ONE PHASE of the load 2. Insert a component in parallel of the load that will cancel out that reactive power e.g. If the load has QΦ=512 VAR, insert a capacitor with QΦ= -512 VAR 3. Calculate the reactance (X) that will give this value of Q Normally the Q=V2/X formula will work 4. Calculate the component value (F or H) required to provide that reactance