Frequent fuse blowing

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Sahib

Senior Member
Location
India
One question regarding frequent blowing of the transformer primary fuse. If frequent transformer primary fuse blowing were not due to inrush current, what might be other causes? One interesting point is whenever the POCO warns that there might be dead short downstream on our side. But when the blown fuse is replaced by them, the power supply invariably resumes There is no heavy starting load on our side .............. Thanks.
 

ramsy

Roger Ruhle dba NoFixNoPay
Location
LA basin, CA
Occupation
Service Electrician 2020 NEC
Please show oscilloscope waveform of transient blowing fuse, or at least a diagram of fuse relative to POCO, and short location.
 

Sahib

Senior Member
Location
India
It is POCO fuse upstream to our 1600KVA indoor transformer in our premises that is blowing. I will also post a photo of POCO pole structure where their incoming fuse is present shortly.
 

synchro

Senior Member
Location
Chicago, IL
Occupation
EE
A malfunctioning rectifier might be creating DC current in the transformer secondary which saturates the core. If so this would cause a large AC current in the primary and blow a fuse. Do you have any large loads with rectifiers?
 

Sahib

Senior Member
Location
India
It seems the problem is settled. The POCO foreman was of the view that the metering CT should not be damaged and so he used to put thinner fuse wires: he has been transferred recently and with thicker fuse wire, no fuse blowing so far. Incidentally, the metering CT is also not damaged as the fuse wire size corresponds to 150% of our transformer rated current ( The impedance of our transformer is more than 4%).. Thanks..
 
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