loading transformer

You have a calculator problem. 2500 kva at 415 volts = 3482 amps. So adding

200 amps to the load of 3000 amps = 3200 amps = 2297 kva 92%. Do you know the power factor of the load? You may be able to add some capacitors to reduce the load. Is this a continuous load or is it off line part of the day?

Thanks, but what i mentioned is the name plate details of that transformer. hv side 11kv,131.22amps, Lv side 433volts,3333.43amps. installed capacitor bank is 650kvar.

With 87% loading at your existing transformer, I am sure, that your transformer winding and your transformer oil temperature has increased to about 40 degree to 45 degree centigrade. Addition another 200 Amp to the existing transformer. I think your boss want the transformer to explode.

With another 200 Amp to the existing transformer, you are loading the transformer up to 92% of the total loading of the transformer. This will cause your transformer temperature to increase future and eventually, you will reduce the life of your transformer, your transformer oil will degraded, moisture of your oil will increased, total dissolved gases will increased and many other factor will cause the life of your transformer to reduce.

In my control, all the transformer is allow up to 75% to 80% only. That why our transformer still working very good even up to 45 years old.

Thanks, absolutely right. now the transformer oil temperature indicator showing 58degree celsius. i informed to my higher authority people.

Let me tell you my 'horrible'experience it was 20yrs ago when I was an engineer in a factory,I had loaded 1000kva 6600/415v transfomer to 1400A which is about 110% loaded for few years but of course the oil temp rise up to about 90deg C ,I install additional external oil cooler plus oil circular pump,I used 6 units of high flow blast fans blowing this transfomer from various direction.later when we carry major repair of the tranformer but just cost us about 15% of the transformer initial cost,we replace oil,termination gasket etc,don't worried of tranformer it never explode if loading less 100%.

Thanks for shared your experience. All the loads which is connected to that transformer is motor load (262kw motor *4nos. we using softstarter for starting these motors and remaining motors we using vfd for starting). pls tell me the starting current percentage for softstarter.

It all depend on what type of soft-starter you are using. I have some motors using ABB soft-starter. The older version of the ABB soft-starter is the current limit soft-starter where you can limit the starting current of your motors. The starting current is about 2.5 time of your full load current.

The latest version of the ABB soft-starter is very good starter. During the starting of the motor, you can see that the starting current started from 0 amp and ram up to the full load current of the motor. With this type of starting method, you don't have to worry about your starting current of the motor.

There is a lot of different type of soft-starter in the market but you have to chose the correct type for your application.

Thanks mr.simon wan, we are using ASTAT type of softstarter. i have been monitoring the starting current of all the motors for example 262kw motor its starting current 865.2amps and running current 406 amps. we kept the transformer in open place. here ambient temperature is now 42 degree celsius. in summer season it my reach upto 48 degree celsius.

That is some experience you have with the transformer. How much is the total cost that you spend to install a additional external oil cooler plus oil circular pump,6 units of high flow blast fans blowing this transformer and the repair of the transformer.

But then again, your transformer temperature alarm should be already activated and trip off your VCB since your oil temperature shot up to 90 deg C. The oil temperature is set at 65deg C for alarm and tripping at 75deg C.

I totally agree with Simon, although he did push it a bit. The transformer will not explode even if you operate this transformer @ 90% loaded for 24 - 7 it is ok.

Remember this transformer is not yet fully loaded, all you need to do is to record a DGA test yearly include water content and this will tell you what is going on with the transformer.

Regards

Granville