International Journal of Advanced Culture Technology Vol. No. 144-148 (2015)

Total loss = Noload loss + load loss 
= 120w + 284.832w 

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146
International Journal of Advanced Culture Technology Vol.3 No.2 144-148 (2015)
 
This section presents an example of total loss calculation of a 30 kVA single phase distribution 
transformers. No load loss equal 120 Watt and full load loss equal 430 Watt are estimated from Table I. 
A load factor is calculated from equation (3) and full load loss of transformer is selected from Table 1 and 
then substitution of LF and full load loss in equation (2) is shown as: 

Average
Install

kVA
LF =
kVA
24
=
30
kVA
kVA
= 0.8

where 
Average

kVA
is from a total of measured load currents to a full load rated current multiplied by 
transformer capacity sizing. 
2
Load Loss = FullLoad Loss? 0.86*LF + 0.14*LF)
 



= 430Watt? 0.86 0.64+ 0.14 0.8)

= 284.832Watt
 
Therefore, the total loss of 30 kVA single phase distribution transformer is calculated as following: 
 
 

Total Loss = No Load Loss + Load Loss 


= 120Watt 284.832Watt
 
? 404.832Watt
 
3.2 Calculation by the transformer loss calculation program provided 
This section presents the program for transformer loss calculation which is provided for PEA Suphanburi 
office by RMUTSB students. The program are created by Visual Basic 6.0 and Access 2007.
Figure 2. A diagram of the transformer loss calculation program. 

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Losses in Power Distribution Transformers