1. ECE 4411 Voltage Regulation

2. ECE 4412 Voltage Regulation (continued) E nl = no-load output voltage –Measure with a voltmeter when no load is connected to the transformer V rated = voltmeter reading at the output terminals when the transformer is supplying the rated apparent power These voltages are all either High-side or Low-side voltages!

3. ECE 4413 Voltage Regulation (continued) Measurements are not always easy to make, so use the equivalent circuit.

4. ECE 4414 When the breaker is open, no current flows in R eq,LS, jX eq,LS, or Z LOAD,LS, therefore V out = V LS = E’ LS = E nl

5. ECE 4415 With rated load on the secondary, E’ LS = I LS Z eq,LS + V LS I LS = rated low-side current at a specified power factor V LS = rated low-side voltage Z eq,LS = equivalent impedance of the transformer referred to the low-side E’ LS = no-load low-side voltage

6. ECE 4416 Example 2.7 The equivalent low-side parameters of a 250kVA, 4160 – 480V, 60 Hz transformer areR eq,LS = 0.00920 Ω and X eq,LS = 0.0433 Ω. The transformer is operated in the step-down mode and is delivering rated current at rated voltage to a 0.840 power- factor lagging load. Determine

7. ECE 4417 –the no-load voltage –The actual input voltage on the high- side –The high-side current –The input impedance –The voltage regulation –The voltage regulation if the power factor of the load is 0.840 leading –Sketch the tip-to-tail phasor diagram of the secondary circuit for the 0.840 power factor lagging load. Show all voltage drops.

8. ECE 4418

9. 9 Low-Side Output

10. ECE 44110

11. ECE 44111

12. ECE 44112 The high-side current The input impedance

13. ECE 44113 The voltage regulation

14. ECE 44114 Voltage Regulation if the power factor is 0.840 leading Regulation is negative because of a voltage rise in the transformer due to resonant effects.

15. ECE 44115 The “tip-to-tail” phasor diagram for the 0.840 power factor lagging load.

16. ECE 44116 Component Phasors

17. ECE 44117 Tip-to-Tail Addition