EGSA Voltage Regulation and Excitation 4

Question 1

A voltage sensing circuit in an AVR fails to read one phase. What effect will this typically have on excitation output?

Accepted Answer

The AVR will sense low voltage and over-excite, raising terminal voltage

Answer

Excitation will drop to minimum to protect the generator

Answer

The AVR will switch to manual control automatically

Answer

Excitation will remain at the last known setpoint indefinitely

Question 2

What is meant by the 'field forcing' capability of an excitation system?

Accepted Answer

The ability to momentarily drive field current well above rated value to improve transient voltage recovery

Answer

The ability to maintain rated voltage at rated load continuously

Answer

Forcing the field current to zero during de-excitation

Answer

Setting the AVR to manual mode to force a fixed field current

Question 3

The V/Hz limiter in an excitation system is designed to protect against:

Accepted Answer

Magnetic core saturation caused by high volts-per-hertz ratio at low frequency

Answer

Overvoltage at rated frequency

Answer

Reverse power flow to the exciter

Answer

Stator insulation breakdown from high current

Question 4

During parallel operation, if an AVR's reactive droop is set too high on one generator, the result will be:

Accepted Answer

That generator will carry most of the reactive load, possibly exceeding reactive capability

Answer

Improved voltage regulation at the load bus

Answer

Increased real power output from that generator

Answer

System frequency will increase

Question 5

What type of feedback signal does a current transformer (CT) provide to a compound excitation system?

Accepted Answer

A current signal proportional to stator output current for compounding

Answer

A voltage signal proportional to terminal voltage

Answer

A frequency signal for speed regulation

Answer

A power factor signal for reactive load sharing

Question 6

A generator's open-circuit characteristic (OCC) becomes nonlinear at high field currents primarily due to:

Accepted Answer

Magnetic saturation of the stator and rotor iron core

Answer

Increased copper losses in the field winding

Answer

Frequency deviation from rated speed

Answer

Brush contact resistance increasing with temperature

Question 7

What is the purpose of an excitation system stabilizer (ESS) or PSS (Power System Stabilizer)?

Accepted Answer

To add damping to generator rotor oscillations by modulating excitation

Answer

To maintain constant terminal voltage during steady-state operation

Answer

To prevent overexcitation by limiting field current

Answer

To synchronize the generator to the bus during paralleling