Voltage Regulation ECE 441 1 Voltage Regulation continued

Voltage Regulation ECE 441 1

Voltage Regulation (continued) • Enl = no-load output voltage – Measure with a voltmeter when no load is connected to the transformer • Vrated = 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! ECE 441 2

Voltage Regulation (continued) • Measurements are not always easy to make, so use the equivalent circuit. ECE 441 3

When the breaker is open, no current flows in Req, LS , j. Xeq, LS , or ZLOAD, LS , therefore Vout = VLS = E’LS = Enl ECE 441 4

With rated load on the secondary, E’LS = ILSZeq, LS + VLS ILS = rated low-side current at a specified power factor VLS = rated low-side voltage Zeq, LS = equivalent impedance of the transformer referred to the low-side ECE 441 E’LS = no-load low-side voltage 5

Example 2. 7 • The equivalent low-side parameters of a 250 k. VA, 4160 – 480 V, 60 Hz transformer are. Req, LS = 0. 00920 Ω and Xeq, 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 ECE 441 6

– the no-load voltage – The actual input voltage on the high-side – The high-side current – The input impedance – 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. ECE 441 7

ECE 441 8

Low-Side Output ECE 441 9

ECE 441 10

ECE 441 11

The high-side current The input impedance ECE 441 12

The voltage regulation ECE 441 13

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. ECE 441 14

The “tip-to-tail” phasor diagram for the 0. 840 power factor lagging load. ECE 441 15

Component Phasors ECE 441 16

Tip-to-Tail Addition ECE 441 17