Answer / namit

it depends on the load.

Answer / madhu253

Transformer size is depends upon the load.
For example

Take one building having load of 630KW
Now we can calculate the t/f size of the building

KW=KVA*P.f
630=KVA * 0.8
KVA = 630/0.8
KVA = 787.5 KVA

So the Transformer size is 800KVA

Answer / sachin

actually at the time of transformer rating decided the
following factor to be consider
1.Connected Load
2.Power fACTOR
3.fUTURE eXPANSION

KW=KVA*P.f
630=KVA * 0.8
KVA = 630/0.8
KVA = 787.5 KVA

So the Transformer size is 800KVA

THIS CALCULATION IS EXACTLY CORRECT

BUT FOR FUTURE EXPANTION WE CONSIDER 30 % MARGINE FOR THAT

Answer / sanjay

The transformer sizing depends on (i) Continuous load +
(ii) Intermittant Load + (iii) 30% spare capacity.

With this you will get the required KVA size of the
transformer. Apart from this the consideration shall be
also on the type of load that the transformer shall feed.
In case of motor consideration shall be given to the
loading during starting of the biggesr motor along with hoe
many motors to be started at any one time.

Answer / ravi

it depends upon flux density & kva rating

Answer / tarun

Check the following
1.) Max connected load
2.) Type of load
3.) impedence drop as per IS
4.) Drop for cable used
5.) Load factor
6.) transformer efficency
7.) % loading
8.) provision for future expansion

Answer / narendra

Check the following
1.) Max connected load
2.) Max demand
3.) Load factor
4.) transformer efficency
5.) % loading
6.) provision for future expansion
Example
Total Connected Load in kW 870.00
Total Maximum Demand in kW (80% of CL) 696.00
Total kVA @ 0.8 PF 870.00
Total kVA @ 0.9 Load Factor 783.00
Transformer Capacity Chosen 2000

Answer / kamlesh rudra

Requierd ment Of Load.

Answer / satya mahesh

load factor(LF) and utilization factor(UF) will play a
major role in transformer selection.
Connected load-4810
Maximum demand in a month-1582 Amps
Average load which will be the average of running loads
came in a month-1173 Amps
LF=average load/max demand
=1173/1582
=0.74
UF=No.of hours running Equip/total hours in a month
=(30*20)/(30*24)
=600/720
=0.83
Transformer size= Connected load X LF X UF
=4810 X 0.74 X 0.83
=2954 Amps
for 2954 Amps 2500 KVA(3484 Amps) transformer was suitable
in continution to the future loads also.

Answer / sakhile benedict mbhele

(Volt X Amp X 1,732)÷1000= KVA

How will you justify IR value and Charging voltage of any motor,transformer and Cables.......???? . . . . . . . . Plz tell me any body Baljeet Singh, engineer_89@refiff.com

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