Continuous monitoring of stator insulation when the machine is offline

[NickParker]

Online monitoring refers to tests conducted while the motor or generator is in operation.
Offline monitoring is performed when the machine is not operating.
I came across a spec "Continuous monitoring of stator field winding insulation during the generator is offline shall be provided".

You just conduct offline tests. Why is continuous monitoring of stator field winding insulation required when the generator is not in operation?

 

[waross]

Given a choice between off-line insulation monitoring and anti-condensation heaters (24/7) I would go with the heaters.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[oldfieldguy]

Why not both?

I'm 'burnt' over space heaters to maintain winding insulation integrity due to my service area being adjacent to the Gulf Of Mexico. High humidities are a constant, and the 'normal' space heaters often are not sufficient to keep windings dry. Talking our engineers into specifying extra heat hasn't been successful.

Having equipment out of service for extended periods, 'trusting' the space heaters to keep things dry, is often prescription for disaster, and continuous offline monitoring might give warning that things are approaching a dangerous level. It's far better to remediate a slightly damp winding than to dry out one that's had a chance to get really bad.

old field guy

 

[waross]

We had heater failure alarms on our anti condensation heaters.
These were on diesel generators about 400 feet from the gulf of Mexico.
We used 240Volt rated heaters fed 120 Volts and they were very dependable.
When an alarm did go off, I got a phone call and I was on the next flight out to the island.
Actually, the heater was good, but corrosion had done in a connection at a terminal strip.
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[NickParker]

Does any one have experience with the Bender module for medium voltage?

 

[edison123]

Never seen off-line 24x7 IR monitoring of windings. Properly sized space heaters keep the IR values up and you check in periodically. Don't see the point of continuous monitoring.

Muthu

http://www.edison.co.in

 

[crshears]

The word should be "while" or "whilst," not "during."

I'm with Bill, provided this is an air-cooled machine; better to prevent condensation on insulation while shut down than monitor insulation integrity 24/7. Besides, although there may be ways of doing this, I cannot once in my forty-plus-year career recall ever seeing a system in place for it, let alone in use.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[JG2828]

I've seen this a few times. It injects a sub-harmonic signal through the generator and reads it to see if anything is grounded. I know ABB used to make one version, not sure if they still do. I think Beckwith Electric also makes one.
Here is a paper on the topic:

https://truc.org/wp-content/uploads...by-low-frequency-injection-for-generators.pdf

 

[wcaseyharman]

SEL makes one as well, I thinks it’s the 2660S. As you probably know these are really to achieve 100% stator protection on high resistance grounded generators - the 59G voltage element can only be set to cover 95% of the winding, without a 3rd harmonic element or a injection system you can’t protect for the last 5%. We typically use the 3rd harmonic element because it comes with the SEL generator relays, but one model machine in particular doesn’t generate enough 3rd harmonic voltage, so we have looked at the 100% protection for future installs.

I’ve used a 480V Bender IR relay, but that was only for an ungrounded bus. Does your generator have a high resistance neutral connection?

 

[panter]

Does any one have experience with the Bender module for medium voltage?

We have them on 5,1 MW , 1200 V , DC motors and they have proven to be very reliable. Recommendation .