A Flashcards
Current rating formula
VA ÷ V
KVA (apparent power) formula
V X A ÷ 1000
Watts in a transformer formula
VA X PF
Volts per turn of wire formula
V/turn = V ÷N
Actual primary voltage % tap formula
Actual primary voltage - rated primary voltage ÷ rated primary voltage
KVA (apparent power) formula
KVA = V X A ÷ 1000
Watts formula
VA X pf
Taps - actual prime voltage formula
Actual prime voltage - rate prime voltage ÷ rated prime voltage
Number of turns formula
V ÷ V / per turn
Each winding lead that is marked with an even number
Should have the same polarity
The relative direction of the transformer prime voltage compared to the direction of its induced secondary voltage
Transformer polarity
If a transformer is constructed so terminal X1 is diaganal from terminal H1
Additive polarity transformer
Transformer constructed so X1 is directly opposite H1
Subtractive polarity transformer
Ways taps can be changed
- manually changing the leads
- moving connecting bars
- installing a mechanical device
5% Full capacity below normal (FCBN)
Used when primary supply voltage is 5% lower than rated voltage
5% Full capacity above normal (FCAN)
Supply voltage is 5% higher than rated voltage
Taps
2.5% reduced capacity below normal RCBN
Supply voltage is 2.5% lower than rated voltage
Additive or subtractive.
Same polarity =
Subtractive
Different polarities
Are they additive or subtractive?
Additive
Explain secondary winding taps
Transformers have taps arranged in the primary (high voltage) winding so that the proper secondary voltage is obtained
The process where an EMF is produced in a conductor from the interaction of the conductor and magnetic field is called
Induction
The property of a coil that apposes a change in current is called
Inductance
When a change of current in one curcuit causes a voltage to be induced into another circuit it is called?
Mutual induction. Also called transformer action
A basic mutual induction transformer has at least how many coils
2
The opposition offered to the establishment of magnetic flux in a circuit is called
Reluctance.
Air has high reluctance
Iron has low
Eddie currents are produced by
Heat
Two types of core losses are
Eddie current and hysteresis
What do transformer name plates list
Primary voltage
Secondary voltage
KVA rating
Name a transformers 3 functions
Step up voltage
Step down voltage
Isolate one curcuit from another
What isolates the conductors on the output side from the ground
Isolation transformer
What test is performed to get impedence
Short circuit test
Opposition to a change of current in a coil is?
Inductance
A change in current in one curcuit causes a voltage to be induced in another is called?
Mutual induction
A change in current in a circuit induces a voltage into itself
Self induction
Name 3 construction types of transformers
Core type
Shell type
H type
They have 95% - 98% efficiency
Copper losses are measured with what test?
Short circuit test
