Alternator meggering and AVR Card

[DmanD]

Hi,
I am new to alternators and AVR cards. I would like to know the reasons(and consequences) of isolating the AVR card before meggering the alternator.

 

[power2020]

We have an experience on 5000kVA 11kV alternator- While meggering (2.5kV) the stator, its AVR card damaged. However AVR power supply is coming from auxiliary winding (additional winding on stator) of the alternator. High step voltage (while MEGGERING ) might induce in aux. winding and damaged the AVR card.
After isolating AVR card during meggering, no more damages recorded .

 

[stardelta]

The high-voltage DC generated by the Megger can and often does damage semi-conductors. This includes AVR cards, exciter-doides, brake-rectifiers and VFD`s. Take any components that include semi-conductors fully out of circuit before conducting any Megger tests.

 

[aolalde]

Tthe reason to disconnect the AVR while megger testing is that the operating voltage design for the AVR is low as compared to the generator.
The consequences will be destruction of delicate elements like chips and integrated circuits.

 

[DmanD]

Hi,
Thanks for the input. In fact the practice of isolation is followed by the engineers here. But in a case under emergency they somehow missed the step isolating the AVR card. BUT no damage occured to the AVR card.

D'man

 

[waross]

If your power supply is grounded, then meggering with the AVR connected may subject the sense circuit of the AVR to the megger voltage as a common mode voltage to ground. The power circuit may be held at ground potential by the power source.
I use the word may because of the many varied connections of both the power circuits and the sense circuits of AVRs that are in common use.
I'm glad to hear that no damage was done, but most of us don't take a chance. we disconnect the AVR before meggering.
respectfully

 

[DmanD]

Dear Warros,
Sorry for the inevitable delay. Your input is commendable. I actually proposed to disconnect the stator feedback to AVR card and do the meggering again (with stator disconnected from the outgoing ckt). Now, with your input I am rethinking it.

Thanks and Regards
D'man