Transformer calculation
Answer Posted / faiyaz
We know that, Transformer always rated in kVA. Below are two simple formulas to find the rating of Single phase and Three phase Transformers.
Rating of Single Phase Transformer:
P = V x I.
Rating of a single phase transformer in kVA
kVA= (V x I) / 1000
Rating of a Three Phase Transformer:
P = √3. V x I
Rating of a Three phase transformer in kVA
kVA = (√3. V x I) /1000
but lets me try to explain.
Here is the rating of Transformer is 100kVA.
But Primary Voltages or High Voltages (H.V) is 11000 V = 11kV.
And Primary Current on High Voltage side is 5.25 Amperes.
Also Secondary voltages or Low Voltages (L.V) is 415 Volts
And Secondary Current (Current on Low voltages side) is 139.1 Amperes.
In simple words,
Transformer rating in kVA = 100 kVA
Primary Voltages = 11000 = 11kV
Primary Current = 5.25 A
Secondary Voltages = 415V
Secondary Current = 139.1 Amperes.
Now calculate for the rating of transformer according to
P=V x I (Primary voltage x primary current)
P = 11000V x 5.25A = 57,750 VA = 57.75kVA
Or P = V x I (Secondary voltages x Secondary Current)
P= 415V x 139.1A = 57,726 VA = 57.72kVA
Once again we noticed that the rating of Transformer (on Nameplate) is 100kVA but according to calculation…it comes about 57kVA…
The difference comes due to ignorance of that we used single phase formula instead of three phase formula.
Now try with this formula
P = √3 x V x I
P=√3 Vx I (Primary voltage x primary current)
P =√3 x 11000V x 5.25A = 1.732 x 11000V x 5.25A = 100,025 VA = 100kVA
Or P = √3 x V x I (Secondary voltages x Secondary Current)
P= √3 x 415V x 139.1A = 1.732 x 415V x 139.1A= 99,985 VA = 99.98kVA
Consider the (next) following example.
Voltage (Line to line) = 208 V.
Current (Line Current) = 139 A
Now rating of the three phase transformer
P = √3 x V x I
P = √3 x 208 x 139A = 1.732 x 208 x 139
P = 50077 VA = 50kVA
Is This Answer Correct ? | 4 Yes | 0 No |
Post New Answer View All Answers
what is meant by class 1 E in electrical power supply?
What is the instrument to check the rotating diode fuse of alternator in running conditions?
how many electricity poles are there and what are the names and their sizes.
What are the raitings of Mcb,mccb and Acb in detail ??
What is the disadventage of gland earthing(power cable) if any. ?
What is Electrical Grade Aluminum for Tubular BusBars. i am confused between 6063 and T6 or T5 and what is BS 2898 and BS 159?
EXPLIAN THE IMPORTANCE OF POLY PHASE CIRCUIT.
The transmission does not have options: a)Partition noise b) Flicker noise c) resistance d) Short noise and reason
gas turbine genrator reactances
Draw a circuit diagram in which if button is open we can use socket and bulb as a series test circit and if button is close than simple we can use socket as any load purpose.
how to calculate the change over time for star delta starter for different KW motor?
what is the formula to calculate voltage drop/loss on 66KV Transmission Line?
what is the excess air in furnace
This is urgent!! What is a Thyristor-based 3-ways selector switch with Zero crossing control? how does it operate and where is it mostly found in a system?
What are the operation carried out in thermal power station?