EGSA Voltage Regulation and Excitation 3

Question 1

The per-unit voltage regulation formula is (V_NL - V_FL) / V_FL. If no-load voltage is 480V and full-load voltage is 460V, what is the voltage regulation?

Accepted Answer

4.35%

Answer

VR = (480 - 460) / 460 = 20/460 = 0.0435 = 4.35%.

Question 2

What is the function of a power factor controller (PFC) used with some AVRs?

Accepted Answer

To maintain the generator at a fixed power factor setpoint

Answer

A PFC mode AVR regulates excitation to hold a target power factor rather than a target voltage, commonly used when a generator operates in parallel with an infinite bus (utility).

Question 3

What does the term 'synchronous reactance' (Xs) represent in a generator?

Accepted Answer

The AC reactance that limits armature current under steady-state fault conditions

Answer

Synchronous reactance is the effective AC impedance of the stator that governs steady-state current flow and is a key parameter in calculating voltage regulation.

Question 4

A generator's AVR is set to maintain 480V at the generator terminals. A remote sensing option instead measures voltage at:

Accepted Answer

A point further in the distribution system, such as main bus or load center

Answer

Remote sensing allows the AVR to regulate voltage at a point downstream from the generator terminals, compensating for feeder voltage drops under load.

Question 5

Which condition can cause an AVR to ceiling excitation (drive field current to maximum)?

Accepted Answer

A three-phase fault near the generator terminals causing voltage collapse

Answer

During a terminal fault, generator voltage collapses to near zero, causing the AVR to detect a large error and drive excitation to its ceiling to try to restore voltage.

(EGSA) Electrical Generating Systems Association Certified Practice Test

(EGSA) Electrical Generating Systems Association Certified Practice Test

EGSA Voltage Regulation and Excitation 3