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Anonymous Poster #1

Underfrequency Trips and Overcurrent

01/28/2021 2:34 AM

Hello Gents ,

I had an issue with my generators while we finish the comissioning in waukesha 700 kw gas genset , when we put it in parallels with existing 700 kw diesel genset we trip in under frequency on existing 700 kw diesel genset ... the issue it happen only after 1hour to 2 hours when both genset are sharing load...what could be the issue , i had change the UVR on existing genset. what could be the causes of various platform shutdown trip when both genset are online ???

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#1

Re: underfrequency trips and overcurrent

01/28/2021 2:37 AM

How did the telephone discussions with the <...genset...> manufacturers go?

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#2

Re: Underfrequency Trips and Overcurrent

01/28/2021 4:54 AM
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#3

Re: Underfrequency Trips and Overcurrent

01/28/2021 5:40 AM

One of the possibilities is that:

total load > 2x <...700 kw...>

at the moment of tripping.

However, no other CR4 subscriber was there at that instant to witness this.

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#4

Re: Underfrequency Trips and Overcurrent

01/28/2021 6:51 AM

Just a guess...

If for lack of fuel supply or other reason the engine for the new gas alternator were to cease providing power, the existing engine would have the entire load in addition to dragging the new gas alternator and engine, which would be acting like a motor with a load.

Try running the gas genset by itself for a few hours.

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#5

Re: Underfrequency Trips and Overcurrent

01/28/2021 7:32 AM
  • Perhaps the inlet air damper closed inadvertently
  • Perhaps a fuel or air filter blocked
  • etc.

The forum can only guess, because no other CR4 subscriber was there at that instant to witness it.

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#6

Re: Underfrequency Trips and Overcurrent

01/28/2021 4:47 PM

Some questions I might ask if I were there [knowing nothing about your system]...

  1. Was there a real under-frequency? Have you checked the setting of the relay that tripped?
  2. What controls the frequency? Is it OK or does it drift down?
  3. Are the sets sharing load when the trip occurs?
  4. Does the addition of a genset come with new extra loads on the system?
  5. Was some load switched-on just before the trip?
  6. What is the usual frequency and what are Under- frequency relay frequency and time delay type and settings?

67model

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#7

Re: Underfrequency Trips and Overcurrent

01/29/2021 9:17 AM

My guess is the operators are not qualified to be doing this operation. They should either hire somebody qualified (consultant?) or at the very least contact the generator manufacturers for advice and or training.

It's possible that the selected Universal Voltage Regulator (UVR) replacement is missing a critical attribute for synchronous operation. You may even have a simple loose connection, vibration can loosen many things. This forum cannot tell that from here.

Fortunately the engineering designers of both generators provided enough equipment protection circuitry to prevent permanent damage to these generators when misuse occurs. The equipment protection circuitry is doing its job.

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#8

Re: Underfrequency Trips and Overcurrent

01/29/2021 12:15 PM

One more question has yet to be asked, are the generators supplying all of the load or is your power system linked to another power system, such as a utility?

Your underfrequency relay is probably set to a much higher setting than necessary for an islanded power system, if you are operating islanded.

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#9

Re: Underfrequency Trips and Overcurrent

01/29/2021 1:17 PM

Assuming that your two generators are the only two sources of power for your loads, one generator governor is set to Isochronous mode, the other must be set to Droop, so it will share load.

My guess is both are set to Isochronous, so eventually one generator will attempt to eventually take all the load, causing both over current and low frequency.

Droop mode prevents that generator from hogging all the load.

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#10
In reply to #9

Re: Underfrequency Trips and Overcurrent

01/29/2021 1:36 PM

You also need to make sure your voltage regulators are set up so that one is either manual or or set up with droop. Otherwise one of the generators will attempt to supply all of the system reactive power.

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#11

Re: Underfrequency Trips and Overcurrent

01/30/2021 2:48 PM

On the system settings, are the alarm/freq settings set the same? If it's connected in parallel I would think that they should be the same or one would trip if it's set at a lower rating than the other....

Loss of phase.....

Shorted phase on the load side.....

Guessing really....

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