Intro To Transformers Flashcards
What is induction?
When a voltage is induced through relative motion between a conductor and a magnetic field
The property of a circuit that opposes the change in current is called…..
Inductance
The process by which a voltage is produced by the interaction of a conductor and a magnetic field is called….
Induction
What is transformer action?
Mutual induction
Define mutual induction
When the change of current in one circuit induces a voltage in another circuit.
(Two coils wound around the same core)
The coil connected to the source is called the
a) series coil
b) primary coil
c) common coil
d) secondary coil
b) primary coil
What is reluctance?
The opposition to the establishment of magnetic flux in a magnetic circuit
Air has (high/low) reluctance
Air has HIGH reluctance
Iron has (high/low) reluctance
Iron has LOW reluctance
A transformer (conducts / transfers) energy from once circuit to another through ____________ induction.
A transformer TRANSFERS energy from one circuit to another through ELECTROMAGNETIC induction
List 3 basic types of transformers.
Shell
Core
H-type
The core type transformer has the most
a) core losses
b) Eddy currents
c) leakage flux
d) magnetic flux
c) Leakage flux
The H-type transformer is usually found in low voltage applications (true/false)
False.
H-type transformers are found on high-voltage distribution transformers
What is the efficiency rate of transformers?
Between 95% and 98% over a wide range of loads
What are core losses?
Power losses due to hysteresis and Eddy currents
What are hysteresis losses?
Hysteresis losses are due to molecular friction caused by the reversal of the direction of current flow. The friction causes heat, which is a power loss.
The CAPACITY of a transformer is rated in ______________
The capacity of a transformer is rated in Volt-Amperes (VA)
The VA rating on a transformer nameplate represents
a) full load input
b) no load output
c) no load input
d) full load output
d) full load output
What determines transformer impedance?
transformer impedance is determined by:
- The amount and type of core material
- winding wire size
- Number of winding turns
- The degree of magnetic coupling
What are the three transformer functions?
Step up voltage
Step down voltage
Isolate circuits
How would you calculate the rated current?
I = VA / V
How do we calculate volts per turn?
V/turn = V / Turns
How do we calculate the voltage ratio?
V ratio = Vpri / Vsec
Vpri (primary voltage)
Vsec (secondary voltage)
How do we calculate the current ratio?
Current ratio = Ipri / Isec
Ipri (primary current)
Isec (secondary current)
How do we calculate the apparent power ratio?
VA ratio=
Vpri • Ipri) / (Vsec • Isec
When the H1 and X1 terminals are diagonally opposite from each other, their polarity is said to be (additive/subtractive)
Additive
When the H1 and X1 terminals are directly across from each other, their polarity is said to be (additive/subtractive)
Subtractive
Why are voltage taps needed?
Because the applied voltage (supply) attached to the primary does not always exactly match the name plate.
How do we calculate
% Tap?
%Tap =
actual Vpri - rated Vpri) / (rated Vpri
What is FCBN?
Full Capacity Below Normal
Used when supply voltage is lower than Tx rated voltage
How are transformers cooled?
By using liquid dielectric, or Air
