under voltage and over current trip

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sivagurunathan
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under voltage and over current trip

Postby sivagurunathan » Fri Jan 24, 2014 10:25 am

how to check the generator under voltage trip and over current trip onboard?

rodrigger
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Re: under voltage and over current trip

Postby rodrigger » Fri Jan 24, 2014 2:38 pm

undervoltage prevents closer of the circuit breaker under dead bus condition, its calibrated by voltage injection. Overcurrent trip is usually only done in drydock by current injection by firm who are specialized to work on circuit breakers

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Big Pete
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Re: under voltage and over current trip

Postby Big Pete » Sat Jan 25, 2014 1:49 am

If the undervoltage trip prevented closure of the breaker on a "Dead" switchboard, it would be impossible to recover from a Blackout!
Must have been a typo or senior moment!
The Under Voltage trip stops you putting a generator that is not generating full voltage onto the board.

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JK
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Re: under voltage and over current trip

Postby JK » Sat Jan 25, 2014 3:28 am

Primary and secondary injection by a qualified company. We've done them alongside with the ship on shore power.
TP127 clearly lays out the requirements for regulatory electrical requirements in Canada with the intervals.

http://www.tc.gc.ca/eng/marinesafety/tp-tp127-menu-263.htm


http://www.hqs.sbt.siemens.com/gip/general/dlc/data/assets/us/SIILV/SIE_IS_WL_PrimaryInjectTesting.pdf
http://www.switchserve.co.uk/secondary-injection-testing/
http://www.dymaxservice.com/UserFiles/File/PDF/Dymax%20Lead%20Gen/NETA-Acceptance-7-6-1-2.pdf
Google is your friend, my friend.

What level ticket are you going for?

sivagurunathan
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Re: under voltage and over current trip

Postby sivagurunathan » Sat Jan 25, 2014 7:34 am

To mr. JK......sir thank u for ur reply. iam giving my class 2 examinations from chennai, india.

sivagurunathan
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Re: under voltage and over current trip

Postby sivagurunathan » Sat Jan 25, 2014 8:07 am

some more doubts in primary and secondary current injection.....while injecting the current what should be the position of acb...should it be in test mode or disconnected mode( fully pulled out of main switch board). i read some where in the manual during test mode the control supply is still connected. and in both disconnected and test mode could we able to close the acb breaker(considering UV trip) during all these process should the generator in question be running idle (off loaded) or it should be stopped.

correct me if iam wrong...kindly share ur experience. thanx in advance

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Re: under voltage and over current trip

Postby rodrigger » Sat Jan 25, 2014 10:45 am

thanks for correcting my typo....senior moment....not quite there yet. It should have been dead "generator" condition. if you try to close the cb of a dead generator if there was no uv protection, then the dead generator would be equivalent to a short circuit on the busbar and cause a blackout

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Big Pete
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Re: under voltage and over current trip

Postby Big Pete » Sun Jan 26, 2014 7:16 am

I would always check the makers Instruction Manual for the specific breaker before trying to do anything.

As other people have said this is a procedure that is usually carried out for the Classification Society Special Survey of Electrical Equipment, and will usually be carried out by a specialist electrical contractor, often the licensed service agent for the Breaker Manufacturer. It would usually be carried out as part of the 5 yearly Special Survey during a drydock when the vessel would be on shore power.

No testing would normally be carried out with the Alternator running yet alone on load. The Breaker would have to be electrically isolated from the Generators and the Main Bus Bars to test it. So it would usually be "Racked out" of the Board.

Old Breakers have simple electo mechanical trips for overload and undervoltage, and can only be tested by current injection. This involves connected the low voltage, high current windings of a transformer across the breaker, the output current, delivered at only a few Volts, is adjusted until the breaker trips.

More Modern breakers have sophisticated Electronic devices to trip the breaker in addition to the electro mechanical system and sometimes these can be tested by adjusting the set points for undervoltage and over current to the actual operating conditions and thus causing the breaker to trip. However, these devices are often not accepted by Class or Statutory Surveyors who require the Electro Mechanical system to be working.
Testing the trips by changing the set points is only acceptable if you can prove that the calibration of the sensors is correct at the normal trip point.

Hope this helps.

BP
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sivagurunathan
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Re: under voltage and over current trip

Postby sivagurunathan » Sun Jan 26, 2014 8:31 pm

thank u mr. Big pete......u r answer helps me in understanding better. one more doubt.... u have mentioned " This involves connected the low voltage, high current windings of a transformer across the breaker, the output current, delivered at only a few Volts, is adjusted until the breaker trips."

when the acb is racked out the under voltage trip is de energized and it should prevent the breakers from closing .and we are injecting only low volt hi current across breaker (so i consider the volt is less than the trip volt).

is there any mechanism/ system to take care of the under voltage trip (to keep it energised so that the breaker can be closed) while testing the over current trip when the acb is racked out.

correct me if iam wrong...thanx in advance

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Big Pete
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Re: under voltage and over current trip

Postby Big Pete » Mon Jan 27, 2014 12:53 am

I if I remember correctly the service Engineers connect voltage from a "step up transformer" across the undervoltage coil to keep that in, and test the UV coil by reducing that voltage.

BP
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sivagurunathan
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Re: under voltage and over current trip

Postby sivagurunathan » Mon Jan 27, 2014 5:36 am

thank u mr. Big pete...

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Re: under voltage and over current trip

Postby Vegman » Sun Feb 23, 2014 5:09 pm

Google may be your friend , but unfortunately it does not always match conditions in the real world.

UV trip is relatively easy to test on most generators while the machine is running.- if the machine has voltage trim or has the breaker easily adjustable settings.

The overcurrent trips are more complicated and would usually be carried out at the special survey by shore contractors.

I notice that some of the links given specify "primary injection testing" - That is injecting the full fault current though the main terminals of the breaker- We are potentially talking large currents here and would be quite a specialised operation to do safely. I. would imagine that this would only be done once- when the breaker is new at the manufacturers workshop.
For later tests, it would be more practical to do the secondary injection testing.
In the ACB , usually a current transformer converts the main current into a lower signal current to operate the trip mechanism. I have seen this done once in a dry dock in Nagasaki. With the breaker racked out, but the control supply connected, the shore electricians connected up a special power supply to the trip unit and tested the various trips, i.e short time , long time. Unfortunately as is usual in a dry dock I was extremely busy and didn't get time to see and understand as much of the process as I would have liked, plus the electricians couldn't speak a word of english so they couldnt tell me much anyhow.

Later, I was class surveyor for a while. In my area there were no big drydocks so the only special surveys I did was on small tugs and work boats.
The class rules specified testing of the breakers but didnt go into details- instead referencing an IEE publication, which you cant get for free and my office wouldnt pay for ( one of the reasons I am no longer a class surveyor- but thats a long story).
On one survey on a tug, the local electricians said they knew how to do it and they mucked around all day with a home made current injector made out of a welder, but in the end - they couldnt do it.
The breakers ended up being removed and sent to a specialist work shop ashore . The owner complained much about the cost- apperently no other surveyor had ever asked him to do this before.

So to cut a long story short, in my opinion, it is only something you would do at the five year special survey, hopefully when you are in a dry dock, and you would contract the job to specialist electrical contractors, but you would still need to oversee them to ensure that they know what they are doing. As in all things , when all else fails read the instructions!, i.e in this case manufacturers manual and or recommendations.

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JK
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Re: under voltage and over current trip

Postby JK » Tue Feb 25, 2014 4:21 am

you are correct, primary injection requires the breakers being removed ashore and being tested with full voltage to test the contacts and structure.
The secondary is done on the ship and tests the protective relays and alarms.
It is amusing how owners bitch about costs of doing tests, but the implications of a failure are much more destructive. I guess they look at it as insurance costs and who cares about the human element.
We have the same battle here to get standards and documents and (gasp) have to pay for them.


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