Deck 11: Transformer Cooling

Question 1

A control transformer is a transformer that supplies voltage to energize industrial motor starters. Many large control transformers are shell-type transformers.

Answer 1

False

Question 2

If ____ is not removed from a transformer, it will build up to an extremely high temperature and eventually destroy the insulation in the transformer.

A) water
B) excess oil
C) PCB
D) heat

Answer 2

D

Question 3

A(n) ____ is used to remove dust and dirt from a deenergized transformer.

A) air blower
B) industrial dust cloth
C) vacuum cleaner
D) industrial sponge

Answer 3

C

Question 4

Transformers mounted on poles and used to supply power to residential and small commercial locations are filled with special oil. This oil provides insulation between the metal parts of the transformer and the energized windings.

Question 5

Some large transformers, especially those enclosed in vaults where air circulation is not practical, may have their cooling oil circulated by pumps through ____-cooled heat exchangers.

A) Askarel
B) air
C) water
D) freon

Question 6

Some larger pole-mounted transformers have ____ welded to the outside of the tank to allow more surface area for the transfer of heat to the surrounding air.

A) flaps
B) fingers
C) wings
D) fins

Question 7

While most dry-type air-cooled transformers are cooled by natural convection, it is sometimes necessary to design a transformer with ____ for additional cooling in order to reach maximum load rating.

A) forced-air fans
B) an attached radiator
C) an attached air conditioner
D) extra ventilation

Question 8

Large industrial dry-type transformers are used in unit substations to reduce distribution voltages, typically ____ volts, to voltages used in the industrial unit.

A) 8,300
B) 13,800
C) 15,600
D) 18,300

Question 9

Sizes from 1 MVA through 8 MVA are typical for large industrial dry-type transformers.

Question 10

The design of shell-type transformers places some of the core material outside the windings, which allows heat to ____.

A) remain within the transformer
B) be radiated away from the transformer
C) surround the windings, increasing transformer efficiency
D) none of the above

Question 11

A typical 500 VA single-phase control transformer with 95% efficiency would produce only about 75 VA (watts) of heat at maximum rated load.

Question 12

The maximum power ratings of large transformers equipped with radiators, fans, or other heat-removing equipment is partially based on the proper functioning of the heat-removing devices.

Question 13

Transformers are very efficient machines with 90% to 99% efficiency. The 1% to 10% losses are mostly from I2R loss, eddy current loss, and hysteresis loss.

Question 14

Some larger transformers include ____ controlled fans that circulate air through the radiators to further assist in heat removal.

A) thermostatically
B) remote-
C) electrically
D) alarm-

Question 15

If water is allowed to enter a large transformer that has a water-cooled heat exchanger, it could destroy the dielectric strength of the insulating liquid and cause a disastrous short circuit between energized parts.

Question 16

Pad-mounted oil-cooled power transformers range in size from a few hundred kVAs to several hundred MVAs.

Question 17

Some transformers require increased cooling provided by a material that will absorb heat from the windings and core material. One common oil used for this purpose is known as Askarel. A special type of Askarel oil, called polychlorinated biphenyl (PCB), is a highly toxic substance now banned in the United States except for use with transformers.

Question 18

Small industrial and commercial ____-type transformers are used to provide power for lighting and convenience outlets and other small loads.

A) airy
B) wet
C) storage
D) dry

Question 19

Larger control transformers are usually placed inside the ____ cubicle and have no external case.

A) Transformer Control Center
B) Central Control Station
C) Motor Control Center
D) Energy Control Station

Question 20

One hazard with dry-type transformers is that because they are usually installed in utility rooms, they often have material stored on or around them, blocking the ventilation.