What are proper steps to start investigating Undervoltage trips?

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Kaaud

Kaaud

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We have 2 Diesel generators 1.5M each ,6.6Kv.
The problem is the Sepam relay on M.V. panel and the generator relay both and of the 2 generators sequentially trip because undervoltage . We dont know what is the reason.

Engineers here in this forum are very experienced , thx for reading my post.
 
Are they tripping from undervoltage at start up, or after running for a while?
What kind of load is on the generators, percentage wise?
Do you have the proper maintenance schedule on them?
How long have they been installed? Did this start after they have been installed for some time? If so, what changes have occured to the loads or the generator itself, if any?
 
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Many of the SEPAM relays have a wave capture capability, that will record the AC curve before and for a programed period after a trip. Download the relay and compare to other recording meters you may have elsewhere in the distribution. Compare characteristics until you find the culprit.
Is this during initial commissioning or has it been working for a while. Check that the trip settings are valid.
 
Can you clarify your description a little more? Are all of relays Sepams? How many relays are there? Are the generators and relays in island mode or are they paralleled when the trips occur? Which protective function is tripping (i.e. 27D)? What model Sepam do you have?
 
Kaaud said:
We have 2 Diesel generators 1.5M each ,6.6Kv.
The problem is the Sepam relay on M.V. panel and the generator relay both and of the 2 generators sequentially trip because undervoltage . We dont know what is the reason.
Engineers here in this forum are very experienced , thx for reading my post.
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In the absence of more information, the first thing I'd want to do is use some independent means of monitoring the voltage. Either the voltage remains within acceptable tolerance, or it doesn't. How you proceed from there depends on which.
 
The undervoltage trips occur during running operation , not at start up.
The plant is still under construction. The loads are 700 KW out of 1550 KW diesel generator. They are HVAC ,lighting , 230KW Air compressor and a resistive load bank.

The relay is Sepam 40 , I dont think it records wave forms.

The diesel engine runs in island mode.

What devices can I use to monitor the Voltage wave form??
 
Kauud,

Years back, we had an old freight elevator that would kick the bio-lab servers into Shutdown mode.

I had to sit for eight hours watching an oscilloscope,
and then finally identified the 'time of day' exactly,
and went looking for what happened at that time.

Try a recording oscope method.
 
My first thought would be the start up event of the 230 kw air compressor.

Start the Air compressor while monitoring the voltage.

If that is the cause for voltage drop go for soft starter for air compressor.

Also check whether both generators are in isochronous mode when they are in parrallel.

I have also seen cases where actually speed drops ( due to blocked diesel filter) and that causes the undervoltage relay to pickup.

cheers.
 
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