If the above trf tested for OC ..... connecting primary to Com and 415V ....what would be the effect .....Note the rating of trf is 300VA
Seems the winding for 415 V was blown - between the 415 V and the 400 V terminals. The resistances for 380 and 400 V are reasonable - indicating some 5 % more windings for 400 V. The 1150 kOhms look like some residual resistance. Regarding the 25+ Ohms of windings resistance: these would account for significant ohmic losses. Are you absolutely sure about the 300 VA rating?
Thank you for your inputs prof. Dreher, the transformer is 300VA rating only, wanted to b understand in this situation if the primary voltage is connected will this cause higher thermal temperature and burn....
Hello, the rating 300 VA is about power - telling nothing about operating voltage. It is quite unusual for the primary winding to blow. But your answer seems to indicate that you - maybe - hooked the transformer to a significantly higher voltage. Under these circumstances it might happen.
Thanks Prof. Dreher! Sharing the details measured on defective transformer again to understand under what possibilities it can burn due to excess thermal temperature
Primary Resistance readings measured are, C= Common terminal
C to 380V -26.5Ω, C to 400V- 28Ω
C to 415V- 168KΩ and C to PE- 1.115KΩ
Secondary Resistance readings measured are, OS = Secondary tapping
OS to 69V =1.8Ω
OS to 20V =0.7Ω
OS to 55V=1.7Ω
OS to 110V= 2.5Ω
OS to 23V = 0.5Ω
OS to 23V= 0.5Ω
Regards,
Anand R
Your first measurement of Common to 415 was 1150 k, now 168 k ?
Looks like it blew, leaving some charring which might conduct - and change conductance considering the potential influence of varying humidity levels. The other resistance values look fine. Thus the transformer should be still operational when operated from the 380 V or 400 V terminals - given the proper voltage is applied. I'd also suggest to install a fuse on the primary side: if no indication is given on the transformer, a 1 A "slow blow" fuse should do fine.
Prof Dreher:
There is fuse 3A in the primary which blew, trying to understand what would have caused the primary to blew (C-415V)
The primary resistance Com to 415V is 168K,
Regards
Missed the followup somehow ...
The usual culprits for a blown fuse in line with a transformer:
Really looks like some secondary overload. You have to understand that a transformer is not intrinsically safe in any way regarding overload.
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