EGSA Voltage Regulation and Excitation 5

Question 1

Which exciter type produces excitation voltage proportional to residual magnetism without any external power supply?

Accepted Answer

Self-excited shunt wound DC exciter using residual flux to bootstrap

Answer

Static exciter with thyristor bridge

Answer

Brushless AC exciter with PMG pilot exciter

Answer

Battery-backed static excitation system

Question 2

What effect does increasing generator excitation have on a generator operating in parallel with an infinite bus (grid)?

Accepted Answer

Increases reactive power output (lagging vars injected into grid)

Answer

Increases real power output

Answer

Raises system frequency

Answer

Reduces stator current automatically

Question 3

The short-circuit ratio (SCR) of a synchronous generator is defined as:

Accepted Answer

Ratio of field current for rated open-circuit voltage to field current for rated short-circuit current

Answer

Ratio of full-load armature current to short-circuit current

Answer

Ratio of synchronous reactance to subtransient reactance

Answer

Ratio of rated kVA to short-circuit kVA

Question 4

An overexcitation relay (OEL or 59F) on a generator excitation system will activate when:

Accepted Answer

Field current exceeds a set threshold for a defined time period

Answer

Field current falls below minimum for a set time

Answer

Terminal voltage exceeds rated voltage by more than 110%

Answer

The AVR transfers to manual mode unexpectedly

Question 5

What happens to a generator's terminal voltage waveform if one rotating rectifier diode in a brushless excitation system fails open?

Accepted Answer

Terminal voltage develops ripple at twice the exciter frequency due to half-wave rectification

Answer

Terminal voltage drops smoothly to zero

Answer

Terminal voltage remains normal because redundant diodes carry full load

Answer

Terminal voltage increases due to reduced field losses

Question 6

In AVR tuning, increasing the proportional gain (Kp) without adjusting other terms will typically cause:

Accepted Answer

Faster response but increased tendency for voltage oscillation or hunting

Answer

Slower voltage response with better steady-state accuracy

Answer

No change in transient response, only steady-state improvement

Answer

Reduced exciter ceiling voltage

Question 7

What is the significance of the generator's 'ceiling voltage' specification in excitation system design?

Accepted Answer

The maximum exciter output voltage available during transient forcing conditions

Answer

The maximum steady-state voltage the AVR will regulate to

Answer

The maximum voltage the stator insulation is rated for

Answer

The setpoint at which the V/Hz limiter activates