Its been a while since I delved into Electrical books to have a deeper understanding of the subject. A couple of weeks back I visited a reputed consultant to discuss the product offerings I sell and our discussion turned towards Transformers . As a person selling for a decade, I started on how I could help with products dimensioned to protect both sides of the Transformer from internal and external faults. However, he wasn't interested in my pitch . He instead asked me if I could help him with calculating Transformer losses . The first thing I did was google IS 1180-2014 (Latest standard for TRF) and share him a chart for 11kV Distribution Transformers .

He wasn’t impressed with the chart and said every manufacturer gives me this but my TRF operate at loads from 45% to 100% and the losses would vary too. Can I have a tool to calculate the losses at various load levels based on the above data . My mind stared working and I was on to excel in a flash . We all know that No-load losses (Iron Losses) remain constant throughout the load cycle while Load Losses (Copper Losses) vary directly to the square of load . As I had the data for total losses , I could get calculate both. I deducted a formula as below (We have all done this during our engineering days but I doubt if any of us remember it still) . Lets call No Load Loss as NLL , Total Loss at 50% as TL50 , Total loss at 100% as TL100 and Full Load Loss as FLL .

NLL = (4/3)TL50 –(1/3)TL100
FLL = TL 100 – NLL



I presented my equation to my client and he asked me to make a chart for 45% to 100% Load profile. I decided to oblige for a rating of 1000kVA with level2 Losses (His requirement for the project) and for rest all cases , I trained his assistant to feed the formula into excel to deduct the values based on the available data . I am attaching the 1000kVA Chart for your reference .

TRF Capacity
% Loading
Std Ref
No Load Losses
Copper Losses
Total Losses
1000
45%
 
1153
1326
2479
1000
50%
2790
1153
1637
2790
1000
55.00%
 
1153
1980
3134
1000
60.00%
 
1153
2357
3510
1000
65.00%
 
1153
2766
3919
1000
70.00%
 
1153
3208
4361
1000
75.00%
 
1153
3683
4836
1000
80.00%
 
1153
4190
5343
1000
85.00%
 
1153
4730
5883
1000
90.00%
 
1153
5303
6456
1000
95.00%
 
1153
5908
7062
1000
100.00%
7700
1153
6547
7700

With the chart available, it is possible to calculate TRF Losses for every loading pattern and understand the transformer efficiency at all points. This will help in system design . You can make your own chart in excel with the right data available. Feel free to ping me if you need any help .

I believe a satisfied and aware customer is the key to long term business success.

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