the existing maximum demand for my plant is 2000KW, the transformer rating is 1.5MVA voltage 415V. if i want to add a 400KW motor to the plant will the existing transformer be sufficient?

 

Responding to Anonymous' Tue, Jul 19, 6:43pm query:

Before a meaningful answer can be given specific detail is requred

Q1) Normal demand and pf? Duration of max demand? 15 minutes? 15 hrs?

Q2) Starting kVA to Hp ratio?

Q3) Is the existing transformer equipped with alternate coolng facilities? Air? Oil? Combination?

Q4) What is minimum voltage tolerated on 415V bus?

Q5) What is rated temp-rise of existing xfmr?

Q6) Age of existing xfmr?

Regards,
Phil Corso, PE {Boca Raton, FL, USA}
[[email protected]] ([email protected])

 

It depends on how frequently you are reaching your maximum demand. now itself the transformer is around 25% overloaded during your maximum demand. if the transformer is further loaded, due to its regulation its output voltage will drop and all the motors will draw more current and some of them may burn also.

But there is a way out,normally transformers can be little overloaded by providing forced air colling by usind external fans.

consult your transformer supplier.

Rajan

 

I think that it is not sufficient already.

Explanation:
You have Trafo 1.5MVA. If your load has cos phi=0.8 (asynchron motors) then available power=1.5MVA*0.8=1200kW. If your simultaneous power demand is 2000kW then you have lack of 800kW power. May be you have SUMMARY power demand 2000kW but not simultaneous power demand? If so then you have to do more accurate calculations for simultaneous pwer demand.

Brgds

 

First of all, based on your statement, your transformer is already overloaded as it is.

2 MW is greater than 1.5 MW (max real power you can get from 1.5MVA)

ANA

 

Adding 400kW of motor load to the 1500 kW that has a peak demand of 2000 kW depends on several factors:

1. What is the average continuous load on the transformer?

2. Is the 1500 kW transformer rated at 55 deg. C or 65 deg. C. Perhaps fans can be added to increase the transformer capacity.

3. The transformer and system motor starting capacity should be verified. An AC motor draws about six times its full load current when starting for an aveage of 20 seconds.

4. What type of load will the new 400kW motor operate? Some loads such as fans can be harder to start that others.

5. Transformers can typically tolerate a 10% overload for a short time typically no more than 5 minutes.

6. What is the duty cycle for the 400 kW motor - continuous or many stops and starts.

I hope this is of some assistance to you.

 

it sounds like you are already overloading the existing transformer at times.

It would appear that unless you implement some form of load shedding or load interlocks to control the maximum load, you will have problems.