2-4-12 Overload Capabilities of Electrical Equipment (A)

A transformer's capability is decreased by ? for an increase of each degree above 30°C.

1.5%

A substation transformer's kVA rating can be increased by as much as ? by adding fans.

10%

A transformer can routinely be loaded to ? of its rated capacity if there are periods where its oil can cool.

125%

The kVA rating of a transformer is based on it being at ? .

30 deg C

When starting a motor, a 25-kVA transformer can supply as much as 50 kVA for ? without suffering damage.

30 sec

The resistance of the copper in the windings increases with a temperature increase in a transformer; therefore, the I2R loss is decreased.

False

Transformers are the only pieces of electrical equipment that have problems with dispelling heat.

False

In a mid-northern climate, a substation transformer can carry more load in the month of ? than at any other time of the year.

January

Transformer insulation usually breaks down because of heat or ? .

a voltage surge

When a transformer is operating under full load, heat is produced by the ? and ? losses.

copper / core

A piece of electrical equipment can carry more load in the summer than in the winter because the air temperature is closer to the heat of the oil inside the equipment.

false

The nameplate rating of a piece of equipment is all the amperage it can tolerate before it burns out.

false

The number one enemy of electrical equipment is the ? .

heat

Heat is produced in electrical equipment by the ? .

movement of molecules

Instrument transformers are cooled by ? .

natural air circulation

The continual circulation of transformer oil through the cooling tubes on the outside of the transformer is known as ? .

the thermo-siphon principle

A transformer can be overloaded if the load varies.

true

Devices used on transformers to help dissipate heat are radiators.

true

It would not be economical for a utility or customer to use oversized equipment that can tolerate the load and not overheat.

true

The capacity of a transformer is determined by the amount of heat it can dissipate.

true

There is a limit to the size of radiators that may be installed on substation power transformers.

true

When transferring load from one transformer to another, heating of the receiving transformer is a major factor.

true