Transducer failures abound! 1

[NorEE]

Kind sirs,

Please share some of your expertise.

Our 8mos. old CoGen Power plant has been operating in island mode and around 3 mos. ago our transducers began failing.

first was the DC Voltage trans, then a Freq. Trans,then a kW Trans, and just this early morning our other freq trans gave in.

Wew! Please tell me that this is normal, hehehe.

Could anyone give me an idea as to what might have caused (or is continually causing this problems)?

Any comment is very welcomed.

Thanks in advance!

 

[rasevskii]

What about the auxiliary supply to the transducers? Is this from DC (station battery) or AC (station service)? It sounds like at first glance that the voltage is too high (beyond the spec of the transducer). It could be also that the PT voltage is too high. Normally a PT secondary voltage of about 110V is standard at normal system operating voltage.

Is your island system operating at normal voltage and frequency ratings? Is the metering working correctly. If transducers are failing then the metered values that you see (panel instruments?) may be all wrong and the station is operating at unsafe levels.

Any relay protection operations? Overvoltage? Underfrequency?

What sort of plant is this and what are the prime movers?

rasevskii

 

[rasevskii]

Another thing may be the ambient temperature is too high at the location of the transducers. Check the temperature specs of the units and compare with the ambient.

rasevskii

 

[rasevskii]

I see from another thread by yourself about SEL relay event logs that this is an industrial plant. It can be an issue on how the system is grounded and configurations of transformers. If it is (likely) a resistance grounded system, then, due to earth faults and switching operations it is possible that the transducers (and other equipment) are being subjected to short time (momentary) overvoltages on the PT inputs phase to ground or phase to phase, resulting in failures.

Not to mention harmonics...any VFDs on the system?

A system study by a professional EE may be a good investment...

rasevskii

 

[cranky108]

I've seen this after an indirect lighting stroke. Also found relays failed, and cable grounds.

I say indirect, because the radio and tower took the lighting, and it was believe it got into the DC power.

 

[NorEE]

To all who dropped by,

Thanx!


To sir rasevskii,

Our transducer aux. supplies are 110 Vac.
Plant operating voltage and freq is at 13.8kV and 60hz respectively w/ +-10% tolerance.
Also there were no relays activated at the isntant of failures.
We an an STG Power Plant using low resistance grounding.
And yes, we have VFD's sir.
Amb temp sir is 29-32degC and component dont indicate any temp requirements.

I suspect the aux supply spikes are causing the failures because there is frequent change in load demand from Production. (still to be verified)

 

[rasevskii]

For NorEE:

It might be a good idea to supply the 110VAC to the transducers over a UPS working off the station battery or to replace the transducers with ones that can use a DC supply directly. It may be a quality control issue as the ambients are normal.

DC supplied transducers are available from several suppliers. AC supply from the station service is not at all a good idea, as a blackout or loss will wipe out all the metering and the operators will have no idea what is happening. Seen this myself...

Where are you located?

rasevskii

 

[NorEE]

ok sir, i will confirm first where were getting the aux. supplies from.

im in Philippines sir.

Thanks a bunch!

 

[NorEE]

Sir resevskii

i forgot to mention some important details in my orig post.

the DC Voltage trans is supplied from 220 ac, 60Hz coming from our UPS.

The other failed trasnducers are all 110 DC supplied (batt.)..

Would you have commented differently?

thanks!

 

[rasevskii]

for NorEE

Then the failed transducers must have been affected by transients on the PT or CT inputs, or were of not the best quality. Or there is somthing wrong or unclean with the UPS supply.

Here in Europe transducers made by Camille Bauer (I think now an ABB company) are widely used and seem to be top quality.

It may be your system has some bad transients or overvoltages. The AVRs of the generators can also be adversely affected by harmonics possibly from the VFDs if the VFDs are significant parts of the loads.

We have here on the forum many VFD experts for such problems.

rasevskii

 

[rasevskii]

for NorEE:

Another thing: What is the actual battery voltage. 110VDC is the nominal voltage, but on float charged systems it can be as high as 130 or 135V. It can be the transducers are failing on high DC voltage. Measure the actual DC voltage and check against the tolerance values stated on the transducer specs.

This is a rather common situation on station battery systems.

rasevskii

 

[NorEE]

Sir rasevskii,

Thanks so much for the insights, i will look into them immediately.

more power!

NorEE