Meggering a xfmr that has sat idle
- Thread starter 1808921
- Start date
- Status
- Location
- Lockport, IL
- Occupation
- Retired Electrical Engineer
You are going to have to complete your sentence. I do not know if you are asking how to do it, or whether to do it, or when to do it, or what results you should be getting when you do it, or how to tell that it?s time to do it, or whether any of us have done it.
brian john
Senior Member
- Location
- Leesburg, VA
Single phase, 3 phase, delta/wye?
What are the primary to secondary voltages?
Short simple answer is, primary to ground, primary to secondary, with the secondary ground to neutral bond lifted secondary to ground.
What are the primary to secondary voltages?
Short simple answer is, primary to ground, primary to secondary, with the secondary ground to neutral bond lifted secondary to ground.
micromind
Senior Member
- Location
- Fernley, NV. (near Reno)
Since it's a 167, it's likely single phase. 3 of these makes a 500KVA bank.
What kind of a megger do you have? Some of the less expensive digital units may not be able to 'fill up the core' on a xfmr this size. A hand-crank one will though.
Has this xfmr ever been energized? If so, and it is oil filled, you'll likely be ok. If it's a dry-pack, you might need to burn the moisture out of it to get it to pass. In northern Nevada you wouldn't, humidity runs in the single digits frequently). If it's never been energized, there are other tests that would be useful. A 167 can make a pretty big bang.
What kind of a megger do you have? Some of the less expensive digital units may not be able to 'fill up the core' on a xfmr this size. A hand-crank one will though.
Has this xfmr ever been energized? If so, and it is oil filled, you'll likely be ok. If it's a dry-pack, you might need to burn the moisture out of it to get it to pass. In northern Nevada you wouldn't, humidity runs in the single digits frequently). If it's never been energized, there are other tests that would be useful. A 167 can make a pretty big bang.
mdshunk
Senior Member
- Location
- Right here.
The procedure is...
:grin:
(I can't tell you how many people will check a transformer secondary to secondary, or primary to primary and think they've got a major issue on their hands. That's a useless measurement. You're meggerring the same piece of wire when you do that!)
brian john said:
:grin:
(I can't tell you how many people will check a transformer secondary to secondary, or primary to primary and think they've got a major issue on their hands. That's a useless measurement. You're meggerring the same piece of wire when you do that!)
brian john
Senior Member
- Location
- Leesburg, VA
One contractor I know replaced 3 panels and associated transformers because of this.
mdshunk
Senior Member
- Location
- Right here.
Ouch. I hope that wasn't education at the customer's expense.brian john said:
zog
Senior Member
- Location
- Charlotte, NC
"I can't tell you how many people will check a transformer secondary to secondary, or primary to primary and think they've got a major issue on their hands. That's a useless measurement. You're meggerring the same piece of wire when you do that"
Right, but you do want to do a winding resistance test.
Right, but you do want to do a winding resistance test.
mdshunk
Senior Member
- Location
- Right here.
Which is not accomplished with a megger.zog said:
brian john
Senior Member
- Location
- Leesburg, VA
Marc government job and they footed the bill material and overtime
masterelect1
Senior Member
- Location
- Baltimore
1808921 said:
Attach one of the 2 megger leads to ground and check resistance of each connection (primary and secondary with the other lead) for resistance- should be infinity.
Now use the megger or VOM on the ohms scale from point to point on each side (primary and secondary) and the result should be balanced on each side, i.e. primary reading should be the same and the secondary reading should be the same but will be not alike from primary to secondary
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