Monitoring Transformer NGR for integrity

[rockman7892]

Is anyone familiar with any monitoring systems for an application of monitoring integrity of Neutral Grounding Resistor (Low Resistance) in utility or industrial MV applications?

We have a customer that has experienced these NGR's burning up in the past and are looking to monitor for part of failure detection an preventative maintenance.

Are there monitoring devices intended to monitor temperature at NGR?

In some past applications I did with HRG systems there was a relay dedicated to monitoring integrity of NGR by injecting a small amount of current through NGR and monitoring return path to verify integrity.

 

[Kiribanda]

NGR monitoring systems are currently available (e.g. LITTLE FUSE) and used in the industry.
Have you investigated why the NGRs are burning at the first place?
In a HRG system if the NGR is properly sized to the charging current of the system, then unless the capacitance current
is increased due to system expansion, I am curious to know why they are burning.

 

[waross]

Monitor the current through the resistor.

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

 

[RRaghunath]

We used to have Instantaneous element set for 150% of NER rating so that the transformer is isolated instantaneously in case of NER flashover or NER support insulator failure.
This is in addition to the time overcurrent protection in the transformer incomer that is set to coordinate with the earth fault protection in outgoing feeders from the switchgear.
This presumes that the NER failure generally happens during earth faults due to the dynamic forces experienced by the NER.

 

[rockman7892]

Yes I'm aware of primary means of monitoring and protection is with current monitoring set to trip system breaker before NGR tolerance is reached.

Was also interested in any additional monitoring including temperature, and voltage to provide additional monitoring.