P-1 Flashcards
What is Mutual Induction?
The action by which a change in current in one conductor induces a voltage in a neighbouring conductor.
Whenever the current through a conductor increases, the magnetic flux around the conductor ______
Increases
Transformers have efficiencies in the range of _________
96-99%
Ideally, the material used in the core of a power transformer should have the properties of _______, __________, and _______.
Low retentivity, high permeability, and high resistance
Are instrument Transformers normally additive or subtractive polarity?
Subtractive
On a transformer, how can the high-voltage bushings be distinguished from the low-voltage bushings?
The high voltage bushings are longer than the low voltage bushings
Is it important to observe the relative polarity of winding leads when making multi winding transformer connections?
Yes if not there will be large short circuit currents between the transformers
List three conditions that must be met before transformers may be paralleled?
- Same Primary Secondary Ratings
- Polarity must be observed when connecting
- Must have the same percent impedance
What causes the terminal voltage of a transformer to change as the load changes?
The terminal voltage drops as the transformer is loaded, IZ increases as I increases
If transformers of unequal percent impedances are paralleled, which one will carry more than its share of load?
The transformer with the lowest percent impedance will carry more than its share of the load
When a voltmeter closure test is performed on the secondary of two transformers being paralleled, the meter should read ______ volts.
Zero Volts
Name two copper losses in a transformer
High Voltage and Low voltage winding Isquare x R
The IsXs voltage drop:
Leads the secondary load current by 90degrees
Difference between no load and on load tap changer
No load to be used only when circuit is de-energized.
On load is used when energized without interfering the flow of power to the load
Which of the two types tap changer never open the circuit?
Onload
What is the purpose of the reactor in an on load tap changer?
Prevents short circuiting of the tap connecting during the switch
Why does the reactor in the on-load tap changer offer negligible resistance to the primary circuit current once switching is complete?
The reactor is centre tapped, both flux each other out therefore no inductive reactance
In a step down auto transformer, the secondary winding is apart of the primary winding? T or F
True
Auto transformer, what is the relationship between the primary VA and the Secondary VA?
Equal
Two most common types of instrument transformers?
Potential Transformers and Current Transformers
How is the primary winding of a CT connected to the Primary circuit?
Series
How is the Potential transformer connected?
Parallel
Type of transformer often used for starting large motors?
Auto Transformer
Pole mounted transformer in a residential area is called?
Distribution Transformer
A 50kva transformers at a hydro-electric site is referred to as?
A power transformer
A small transformer used to power residential inter-com systems is an example of?
A Signal Transformer
Does core loss change significantly as load is added to the transformer?
No
Do copper loss change significantly as load is added to the transformer?
Yes
Could a leading power factor load cause a rise in line bus voltage on the secondary of a transformer?
Yes
