Real Transformer Flashcards
The real voltage ratio is almost the same as the ideal voltage ratio (at no load) and diverges due to voltage drops, increases in resistance, or decreases in current?
Voltage drops
The real current ratio is almost the same as the ideal current ratio (at no load) and diverges as the load decreases due to voltage drops, increase in resistance, or exciting current becoming more signnificant?
Exciting current becomes more significant.
Exciting current is located in ONLY the primary, ONLY the secondary, or BOTH windings?
Only the primary
Exciting current will be present and will not change (remain stable) because the system is energized and the system voltage is unstable. True or false?
False. As long as the system is energized and the system voltage is stable the exciting current will be present.
Exciting current is dependent of the load (True/False)
It is independent of the load.
What are the 4 things that can be done to reduce the exciting current?
- Increase permeability
- Reduce the air gaps
- Insulation on the lamination
- A lower flux density
With regards to reducing exciting current, increasing permeability results in what?
Higher quality core steel
With regards to reducing exciting current, reducing air gaps can be done in 2 ways. What are they?
- Better quality of construction
- Interleaving
Insulation on the lamination reduces eddy current or voltage in the core?
Eddy current
A lower flux density results in a higher exciting current. True/False?
False. It results in a lower exciting current.
Small transformers below 2000VA may have an Iex in the range of 25%, 5%, or 10%
10%
Small transformers between 2000VA and 100kVA may have an Iex in the range of 15%, 10%, or 5%?
5%
Larger transformers at 1000kVA, the Iex% is 1%, 100%, 50%, or 35%?
1%
For very large transformers that are oil filled what is the percentage Iex?
0.1%
A transformer with a 1:1 ratio is rated at 120V and 15A. What would the %Iex be?
S = V * I = 120 * 15 = 1800VA, therefore %IEX ≈ 10% (from above)
IEX = ( %IEX * IRated ) / 100 = 10 * 15 / 100 = 1.5A
What would the real current ratio be?
A transformer with a 1:1 ratio is rated at 120V with a 15A resistive load. What would the % exciting
current be, approximately?
S = V * I = 120 * 15 = 1800VA, therefore %IEX ≈ 10%
IEX = ( %IEX * IRated ) / 100 = 10 * 15 / 100 = 1.5A
IPRI = I1 + IEX = √(152 + 1.52 ) = 15.075A
ISEC = 15.00A
Real ratio: a = ISEC / IPRI = 15.00 / 15.075 = 0.995
Ideal ratio: a = I2 / I1 = 15.0 / 15.0 = 1.000
For system losses, there are losses in the generator. What are these 3 losses?
Magnetic
Electrical
Frictional
Transmission line losses from the generator to the transformer are known as ________ losses
Electrical
Transformer losses are made up of _____ and ______
- Core loss
- Winding loss
Winding loss is also known as _______
Load losses
Core loss is also known as _____
No load losses
Line losses from the transformer to the load are electrical, magnetic, or mechanical?
Electrical
Is it possible for the load to have losses?
Yes. There may be losses due to lighting, heat, motors, etc.
If we have 120V rated primary with 22 Turns, what is the secondary voltage if there are 5 turns?
a = N1 / N2 = 22 / 5 = 4.4
V2 = V1 / a = 120 / 4.4 = 27.27V
Why must HV and LV turns must be correct?
The correct voltage will not appear at the terminals
The CSA standards for voltage is 10%, 0.6%, 0.2% or 0.5%?
