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Exam 12: Transformer Maintenance

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Question 1

True/False

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When maintaining a large industrial dry-type transformer used in a unit substation, weekly inspections when the transformer is first installed will indicate how often the unit will have to be taken out of service for maintenance.

A) True
B) False

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Question 2

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A ____-volt megger would be used to test the insulation on a transformer with a 480-volt rated winding.

A) 120
B) 240
C) 500
D) 1,000

E) B) and C)
F) A) and D)

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Question 3

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After an oil sample is drawn for testing, it should be allowed to stand for a while to permit any free ____ to settle to the bottom of the sample.

Excessive current draw or a large deviation from the rated voltage of a winding are good indicators of a shorted winding.

The outside of the transformer should be cleaned with an approved solvent or cleaner so that rust and corrosion are removed.

Transformers that have a gas blanket on top of the insulating oil have pressure switches that actuate an alarm system if the gas pressure on the blanket drops below a certain point.

The type of maintenance procedures and intervals between procedures are governed by the ____ of the transformer.

Transformers are usually thought of as stationary objects with no moving parts. Because of this misconception, they are often neglected and left out of routine preventive maintenance schedules.

Pole-mounted distribution transformers are usually oil-filled and require a great deal of maintenance.

In some of the maintenance procedures, it is necessary to enter a transformer tank. When this is part of the maintenance procedure, the atmosphere in the tank must be tested for the presence of sufficient oxygen, but there is no need to test for the presence of combustible and/or toxic gases.

When maintaining large industrial dry-type transformers for use in unit substations, be aware that there might be dangerous voltages present in the cubicle for control circuits or space heaters that might not be deenergized when the transformer is deenergized.

Even on larger transformers with high-voltage connections, it is generally not necessary to prepare a written switching procedure detailing each step of the process of deenergizing the equipment.

When maintaining large control transformers supplying a motor control center, these units should be tested ____ with a megger to determine the condition of the insulation.

It would not be uncommon for a transformer winding rated at 24 volts to measure 34 to 38 volts with no load connected.

In many larger installations, ____ are placed on each side of the transformer after it is deenergized to protect workers.

A high-voltage tester, generally referred to as a "HiPot," develops a high voltage and measures any current leakage caused by weak or defective ____.

If a pad-mounted oil-cooled transformer is equipped with auxiliary cooling equipment, the temperature and pressure switches and gages should be ____ yearly to ensure proper operation.

When inspecting a large industrial dry-type transformer that is used in a unit substation, a(n) ____ inspection of the transformer, connections, and busses, or wiring under normal load conditions, will indicate any trouble spots.

____ permit power to be supplied from another source in the event of equipment failure.

When a worker must enter a transformer tank, if the concentration of oxygen is less than ____%, it could be a health threat to the worker.