309A Transformers and Power Distribution 3

Question 1

What is the purpose of a potential transformer (PT) in a power distribution system?

Accepted Answer

To provide a scaled-down voltage signal for metering and protection relays

Answer

To step up voltage for transmission

Answer

To correct power factor

Answer

To provide backup power

Question 2

What causes transformer humming noise during operation?

Accepted Answer

Magnetostriction — the expansion and contraction of the core laminations

Answer

Loose electrical connections

Answer

Overloaded secondary windings

Answer

Defective insulation

Question 3

What is the primary purpose of laminating a transformer core?

Accepted Answer

To reduce eddy current losses

Answer

To increase mechanical strength

Answer

To improve heat dissipation

Answer

To reduce the weight of the core

Question 4

In a three-phase transformer bank, what happens if one transformer fails in a delta-delta configuration?

Accepted Answer

It can operate as an open delta at reduced capacity (57.7%)

Answer

The entire system shuts down

Answer

It continues at full capacity

Answer

It automatically switches to wye configuration

Question 5

What is the voltage regulation of a transformer?

Accepted Answer

The percentage change in secondary voltage from no-load to full-load

Answer

The ratio of primary to secondary voltage

Answer

The efficiency of the transformer

Answer

The maximum voltage the transformer can handle

Question 6

What type of cooling system is designated ONAN for a transformer?

Accepted Answer

Oil natural, air natural (self-cooled)

Answer

Oil natural, air forced (fan-cooled)

Answer

Oil forced, air natural

Answer

Oil forced, air forced