Transformer

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busman

busman

Senior Member
Location
Northern Virginia
Occupation
Master Electrician / Electrical Engineer
There is usually a fuse as part of the cut-out, but I couldn't tell you the size. A 10 kVA would be awfully small for a PoCo pole-mounted transformer though.

Mark
 
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templdl

Senior Member
Location
Wisconsin
It is not uncommon for pole mount transformers to include an oil emersed themal oil circuit breaker that is installed toward the top of the tank above the core and coil. This is characterized by a small lever located on the side of the transformer toward the top of the tank with a ring on the end for hook stick operation.
While as a sales engineer for Westinghouse we sold these oil breakers to RTE.They were a kind of crude looking device.
I believe those transformers are refered to by "self protecting."
 
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curt swartz

Electrical Contractor - San Jose, CA
Location
San Jose, CA
Occupation
Electrical Contractor
e57 said:
In my area - none... Most poco T's have no OCP here - no matter the size...
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Mark, I have never seen a PG&E transformer that didn't have built in overcurrent device such at Templdl described or a cutout mounted on the cross arm above the transformer.
 
mivey

mivey

Senior Member
curt swartz said:
Mark, I have never seen a PG&E transformer that didn't have built in overcurrent device such at Templdl described or a cutout mounted on the cross arm above the transformer.
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I would think so. They are required by the NESC to have something.

NESC 153: Short-circuit protection of power transformers

Power transformers shall be provided with means to disconnect automatically the source of supply of current for a high magnitude short circuit (fault) within the transformer.

The devices...either locally or remotely connected to the transformer.
Click to expand...
 
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templdl

Senior Member
Location
Wisconsin
The breaker is over current only sensing oil temp protecting the transformer from overload. I also understand that there is also a red indicating light that lights indicating that the breaker has tripped.

The cutout is for short circuit protection.
 
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hillbilly1

Senior Member
Location
North Georgia mountains
Occupation
Owner/electrical contractor
templdl said:
It is not uncommon for pole mount transformers to include an oil emersed themal oil circuit breaker that is installed toward the top of the tank above the core and coil. This is characterized by a small lever located on the side of the transformer toward the top of the tank with a ring on the end for hook stick operation.
While as a sales engineer for Westinghouse we sold these oil breakers to RTE.They were a kind of crude looking device.
I believe those transformers are refered to by "self protecting."
Click to expand...

Ahhh! so thats what that is! I thought it might have been a tap changer to allow a single transformer to be able to work on two different line voltages. When they doubled the line voltage on our system, the new transformers they installed were this type. I just figured it was an easy way to bring everybody back on quickly when they changed the voltage, instead of having to rush changing out 30-40 transformers. Learn something new everyday!
 
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shepelec

Senior Member
Location
Palmer, MA
The red light indicates the transformer has been overloaded. All of the ones I have seen are just an indicator, nothing to do with the internal breaker.

Drive around at night you will see quite a few red lights on.:)
 
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templdl

Senior Member
Location
Wisconsin
shepelec,
Cool,
I sold those little red lights also but never thought much about how they worked. I may still have one in my "hope to find it" drawer in my work shop. I don't know where they got there thermal sensing ability, that is there must be a thermal switch related to the oil temperature somewhere that I'm not aware of.
 
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