Question 1

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

Accepted Answer

Pole-mounted distribution transformers are indeed often oil-filled, but they are designed to be low-maintenance, requiring checks and potential maintenance at longer intervals compared to other types of equipment.

Question 2

A high-voltage tester, generally referred to as a "HiPot," develops a high voltage and measures any current leakage caused by weak or defective ____.
A) insulation
B) windings
C) connections
D) switches

Accepted Answer

The purpose of a HiPot test is to check the integrity of insulation by subjecting it to a higher than normal voltage. If there is any current leakage, it is an indication that the insulation is weak or defective. The other options (windings, connections, switches) are not directly related to insulation testing.

Question 3

In many larger installations, ____ are placed on each side of the transformer after it is deenergized to protect workers.
A) insulating materials
B) wooden walkways
C) grounds
D) plastic walkways

Accepted Answer

Grounds are placed on each side of the transformer after it is deenergized to protect workers. This ensures that any residual electric charge is safely discharged to the ground, preventing electric shock. Insulating materials or plastic walkways may provide some protection but do not fully discharge the electric charge, while wooden walkways can be a fire hazard.

Question 4

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

Accepted Answer

Cleaning the outside of the transformer with an approved solvent or cleaner is necessary to remove rust and corrosion.

Question 5

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.

Accepted Answer

The frequency of maintenance for a large industrial dry-type transformer is determined by its operational environment, load conditions, and manufacturer's recommendations, not solely by initial weekly inspections. Initial inspections can help identify immediate issues but don't dictate long-term maintenance schedules.

Question 6

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.
A) 10
B) 20
C) 60
D) 75

Accepted Answer

The normal concentration of oxygen in the air is approximately 21%. If the concentration of oxygen drops below 19.5%, it is considered to be oxygen-deficient and can pose a health threat to workers, making option B (20%) the correct choice.

Question 7

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.
A) removed and calibrated
B) replaced
C) cleaned
D) tested

Accepted Answer

The answer of If a pad-mounted oil-cooled transformer is equipped...

Question 8

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

Accepted Answer

The megger voltage rating should be at least twice the rated voltage of the winding being tested. In this case, a 480-volt rated winding would require a megger with a voltage rating of at least 960 volts. The closest option is 500 volts, making it the best choice.

Question 9

____ permit power to be supplied from another source in the event of equipment failure.
A) Double-connected transformers
B) Generators
C) Remote substations
D) Double-ended substations

Accepted Answer

Double-ended substations have two separate sources of power supply, allowing for power to be supplied from the alternate source in case of equipment failure. Double-connected transformers only provide redundancy in case of transformer failure, generators are a source of power themselves and remote substations do not necessarily have redundancy built in.

Question 10

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.
A) monthly
B) quarterly
C) semi-annually
D) annually

Accepted Answer

Large control transformers supplying a motor control center should be tested annually with a megger to determine the condition of the insulation. This is a standard maintenance practice to ensure the reliability and safety of the electrical system.

Question 11

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.

Accepted Answer

It is necessary to test for the presence of combustible and/or toxic gases before entering a transformer tank for maintenance purposes.

Question 12

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.

Accepted Answer

It is important to be aware of potential dangers and to take proper safety precautions when maintaining industrial dry-type transformers, as there may still be dangerous voltages present even when the transformer is deenergized.

Question 13

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

Accepted Answer

The answer of It would not be uncommon for a...

Question 14

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.

Accepted Answer

Transformers, despite having no moving parts, still degrade over time due to thermal, electrical, and environmental stresses. Regular maintenance is crucial to ensure their reliability and longevity.

Question 15

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

Accepted Answer

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

Question 16

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.

Accepted Answer

Transformers with a gas blanket do have pressure switches to trigger an alarm if the gas pressure drops too low.

Question 17

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.
A) dirt
B) bits of insulation
C) water
D) liquid acetylene

Accepted Answer

During the sampling process, water can accumulate in the oil, and it can cause corrosion, wear, and damage to the lubricated machinery. Therefore, after the sampling process, the oil samples should be allowed to stand for a while to allow for any free water to settle to the bottom of the sample.

Question 18

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.
A) visual
B) infrared
C) infrared thermographic
D) quick

Accepted Answer

An infrared thermographic inspection is the best choice for inspecting a large industrial dry-type transformer. This type of inspection uses thermal imaging to detect any abnormal temperature patterns, which can indicate potential issues such as loose connections or faulty wiring. It should be done under normal load conditions to accurately assess the transformer's performance. Visual inspections may not reveal all problems, and quick inspections may miss important details.

Question 19

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.

Accepted Answer

Whenever working with high-voltage equipment, it is important to have a detailed switching procedure outlining each step of the process to ensure safety and prevent accidents. This is especially important for larger transformers with high-voltage connections where the margin for error is small and the potential consequences could be severe.

Question 20

The type of maintenance procedures and intervals between procedures are governed by the ____ of the transformer.
A) manufacturer
B) cooling system
C) type of ventilation
D) type, size, location, and application

Accepted Answer

The type, size, location, and application of the transformer determine the maintenance procedures and intervals necessary for optimum performance and longevity. Different types of transformers may have unique cooling or ventilation systems, but these factors are secondary to the overall characteristics of the transformer. Manufacturers may provide guidelines for maintenance, but ultimately it is the operating conditions of the specific transformer that determine the appropriate maintenance schedule.

Quiz 12: Transformer Maintenance

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

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

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

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

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.

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.

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.

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

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

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.