Pole-mounted transformers in a residential area are referred to as ________ transformers
Distribution
A 50 kVA transformer at a hydroelectric site is referred to as a ________ transformer
Power
A small transformer used to power a residential intercom system is an example of a ________ transformer
Signal
Transformers operate on the principle of ________
Mutual induction
Whenever the current through a conductor increases, the magnetic flux around the conductor ________
Expands
The winding of a transformer that is connected to the source is referred to as the ________
Primary
Transformers typically have efficiencies in the range of ________ %
95-99%
Ideally, the material used in the core of a power transformer should have the properties of ________ retentivity, ________ permeability, and ________ resistance
Low retentivity, high permeability, and high resistance
If the secondary coil of a transformer has more turns than the primary, the secondary voltage will be ________ than the primary voltage
Greater
In a transformer with an open secondary, the primary operates essentially the same as a(n) ________
Inductor
The voltage induced in the secondary of a transformer is a result of the CEMF of the primary and therefore is ________ with the primary voltage
180 degrees out of phase
The primary and secondary coils of a transformer are ________ coupled together
Magnetically
What are the three essential components of any transformer?
A primary coil or high-voltage winding, a secondary coil or low-voltage winding, and a core
When identifying leads of a transformer, the low voltage winding is marked with the prefix ________ and the high voltage winding is marked with the prefix ________
X, H
Increasing the secondary load on a transformer causes the CEMF of the primary winding to be ________
Reduced
Name the 5 classifications of transformers
Cooling method, number of phases, construction, voltage level, and function
________ is the small amount of current that flows into a transformer’s primary winding to create the magnetic field needed for its operation, even when no load is connected to the secondary winding
Excitation current
The ________ of a transformer is a ratio that indicates how much extra heat the transformer can withstand due to the results of non-linear circuit loading and harmonic currents
K-rating
The two basic methods to test or determine transformer polarity are the ________ and the ________
AC voltmeter test and DC inductive kick test
True or false: when performing the AC voltmeter test, if the voltmeter reads the sum of the applied voltage and the induced secondary voltage, the transformer has additive polarity
True
True or false: when performing the AC voltmeter test, if the voltmeter reads the difference between the applied test voltage and the induced secondary voltage, the transformer has additive polarity
False. The transformer has subtractive polarity
List the three conditions that must be met before transformers may be paralleled
- The transformers must have the same primary and secondary voltage ratings
- The terminal polarity of the transformers must be observed when the connections are being made
- The transformers must all have the same percent impedance
When the primary disconnect for one transformer is opened, the transformer may still be energized by the secondary bus, creating a hazard known as ________
Back-feed
The energy losses that occur in transformers are classified as either ________ or ________
Core losses, copper losses
