EGSA Paralleling and Switchgear Controls 2

Question 1

What is the primary purpose of a dead bus close (DBC) relay in a paralleling switchgear system?

Accepted Answer

To allow closing onto a de-energized bus without synchronization checks

Answer

To prevent closing onto an energized bus

Answer

To trip a generator when bus voltage drops

Answer

To measure reactive power imbalance

Question 2

In isochronous load sharing between two paralleled generators, what controls the power output of each unit?

Accepted Answer

A load share controller that trims governor speed references

Answer

Voltage regulators proportionally split reactive load

Answer

Speed droop governors adjusted by operators

Answer

The generator with higher rated kW takes priority

Question 3

Which condition must be verified before closing a generator breaker onto a live bus using a synchroscope?

Accepted Answer

Synchroscope pointer rotates slowly clockwise and approaches 12 o'clock

Answer

Generator voltage equals exactly 1.0 per unit

Answer

Generator frequency is 5 Hz higher than bus frequency

Answer

Generator power factor equals unity

Question 4

What fault condition does a reverse power relay (32) protect against in a paralleled generator set?

Accepted Answer

Motorizing of the generator when it draws power from the bus

Answer

Over-frequency caused by load rejection

Answer

Reverse reactive power from a leading power factor load

Answer

Negative sequence voltage on the bus

Question 5

In a transfer switch application, what defines a 'closed transition' transfer?

Accepted Answer

Both sources are briefly connected simultaneously during the transfer

Answer

The load is disconnected before the alternate source is connected

Answer

The transfer occurs only when the load is at zero current

Answer

The normal source is locked out before the emergency source closes

Question 6

What role does the phase angle matching requirement play during automatic synchronizing?

Accepted Answer

It prevents the breaker from closing when voltage phase difference exceeds a set limit

Answer

It ensures generator terminal voltage magnitude matches bus voltage

Answer

It controls the reactive current sharing between generators

Answer

It measures the slip frequency between the two systems

Question 7

When a generator experiences a loss-of-excitation (40) condition while paralleled to a bus, what is the expected behavior?

Accepted Answer

The generator under-excites and absorbs reactive power from the system, risking stator overheating

Answer

The generator over-excites and exports excessive reactive power

Answer

The generator immediately loses real power output and trips on reverse power

Answer

The generator voltage rises above nominal and activates the overvoltage relay