air circuit breaker
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ACBTRANSCRIPT
Air Circuit Breaker, Current Injection Testing12/24/2013 5:19 AM
I want to know what is the correct procedure for current injection testing an Air CIRCUIT BREAKER (ACB) of rated current 1600 Ampere .
I have confusion in first of all to determine :-
a) What value of current , I should inject ? and when I have injected and noted down the time it takes to trip ..How to compare it with the current Time curve of the same breaker .
b) there are terms like Short time , Long time and instantaneous Time .
c) on the trip unit there are various adjustable knobs - how to use those settings and what effect do they produce ? ( Magnetic Delay and current multiple setting)
Re: Air Circuit Breaker, Current Injection Testing
01/25/2014 7:57 AM
Long time pick up - normal over current - Settings between 0.1 to 1 ( 10% to 100%)
Short time - for starting current of motor etc. this can be set as per your load charecterstics, for example 1.5 times, 2 times etc.
Instantaneous trip - for the short circuit current - can be set to 2 to 10 times to the rated current
Someone should have already done a protection study on this breaker. It will give you the settings so that cables and equipment are correctly protected. Usually these settings are put into the relay by a competant person who is both familiar with the relay and through experience would also see if a figure was horibly wrong through a typing error. With these values in your hand you could think about testing. I think you should also wonder whether you are suitable skilled to undertake the task and give consideration to the lives you could be putting at risk. Fiddling with these knobs and buttons could be that serious.
12 October 2006 05:00 AM
geeli
Posts: 61Joined: 21 April 2005
having post the same topic on the Wiring & Regulation Thread and received no reply hence decide to put it at this Thread (Power Sector)
1) how do one conduct a PI and SI test?
2) is the any good website showing pictures of how such a test is to be conducted and the cabling that is to be connected to the terminal.
3) would appreciate if there is a step by step procedure on such a test.
12 October 2006 10:04 AM
duncan_gould
Posts: 114Joined: 19 April 2002
Geeli,
Primary and secondary current injection tests are normally conducted to check the operation of breaker and their protective relays/devices.
The protective devices installed vary from circuit to circuit depending on the protection needs and philosphy but typical relays/devices include overload, over current, reverse power, earth fault, differential protection, etc., etc.
Primary injection testing normally involves injecting the actual current required to operate a protective device power through the CIRCUIT BREAKER .
Primary injection testing normally requires specialist injection sets/test rigs and measurement equipment (particularly for high power and MV and above) and can be extremely arduous where the CIRCUIT BREAKER interrupts large currents, shortening its life or requiring repair after. In many cases, primary injection testing is only conducted by specialists and in some cases primary injection testing may not be required through life. Testing and research of this form is certainly carried out by CIRCUIT BREAKER manufacturers. Primary injection testing may be the only means of testing some LV circuits.
Secondary injection testing is normally different to primary injection testing because it is normally conducted when the CIRCUIT BREAKER is closed but is not carrying any current throught its main poles.
Secondary injection testing normally involves disconnection of the protective device from it's normal VT/CT and connection to a specialist test set that can inject and measure/record the required operating signal directly into the protective device relay to cause it to operate the circuit breaker.
The advantage of secondary injection testing is that the circuit breaker does not have interrupt large current and only low voltage signals are injected to operate the device.
A perceived disadvantage of secondary injection testing is that the actual operation of the 'whole' system is not tested but this may be compensated by the fact that the circuit breaker has operated without having to interrupt a large current and the circuit breaker type has tested and rated by its manufacturer.
However, specialist equipment and knowledge is still required, including significant knowledge of the actual protection scheme and philosophy. Furthermore, disconnecting of VT/CT can also lead to potential danger. For this reason, secondary injection testing is also often conducted by specialists.
In other words, it is not something that is jumped into without significant experience and knowledge.
The book Protection of Industrial POWER SYSTEMS by T. Davies may be of interest, or try an internet search for the GE Art & Science of Protective Relaying.
I hope that's helpful.
Duncan
-------------------------Duncan
Edited: 12 October 2006 at 10:07 AM by duncan_gould
12 October 2006 10:21 AM
cheewah
Posts: 11Joined: 17 May 2006
a. PI & SI are normally referring to the CT's Primary & Secondary Injection current depending on the purposes i.e. setting of protection, instrumentation, etc and depending on CT's of ?/5A or ?/1A. b. Due to the danger and risk involved, we normally apply SI: However, we still apply PI if neccessary. c. I am a Commissioning & Servicing Engineer up to 33 KV. You can write to me directly by my e-mail to [email protected] & my W/S is Link removed/cmeelectrical d. Good luck!
Cheewah
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12 October 2006 10:32 AM
cheewah
Posts: 11Joined: 17 May 2006
Mr Duncan, a. SI rather tha PI is normally employed as you have already explained. b. For recalibration & maintenace, we normally encourge to carry out the tests on CT's including the ratio test. Best rdgs cheewah
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12 October 2006 10:48 AM
duncan_gould
Posts: 114Joined: 19 April 2002
Cheewah,
a. agreed.
b. agreed, this would be the norm.
Given your position, would you agree it is important to highlight the need for competence and experience in praticing in this area in addition to helpful tools such as step-by-step procedures for every installation?
BR,
Duncan
-------------------------Duncan
Edited: 12 October 2006 at 11:21 AM by duncan_gould
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12 October 2006 12:29 PM
geeli
Posts: 61Joined: 21 April 2005
To Mr Duncan thank you for the explanation and the great website you have given. it is indeed a good site. i am still in the process of downloading the PDF for my leisure read.
To Mr Cheewah thanks for your contribution too. however at the present moment i am unable to engage your service :-)
My understanding of the injection tests is as follow
Primary Injection Test 1) to ensure wiring connection of protection system is correct 2)to check CT ratios and polarities 3) to check Overcurrent relays and Earth Fault relays (both DTL type) are set to correct setting 4) to check Direct Acting Tripping element of the main MCCB.
Secondary Injection Test 1)If the protection relays (overcurrent and/or earth fault relays) are IDMTL type then Secondary Injection Test is required.
As such having read the replies. i am a bit puzzled why PI is less used and SI is more commonly being used.
Are not all Main Switchboard protection relays need to be tested and sealed before energisation?
I am referring to all Low Voltage 3 phase 400V switchboards with current ranging from 200A to 1000A.
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12 October 2006 12:51 PM
duncan_gould
Posts: 114Joined: 19 April 2002
Geeli
As such having read the replies. i am a bit puzzled why PI is less used and SI is more commonly being used.
Primary injection testing normally requires specialist injection sets/test rigs and measurement equipment (particularly for high power and MV and above) and can be extremely arduous where the circuit breaker interrupts large currents, shortening its life or requiring repair after.
The advantage of secondary injection testing is that the circuit breaker does not have interrupt large current and only low voltage signals are injected to operate the device.
it is important to highlight the need for competence and experience in praticing in this area in addition to helpful tools such as step-by-step procedures for every installation
I hope that helps,
Duncan
-------------------------Duncan
Edited: 12 October 2006 at 12:53 PM by duncan_gould
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14 October 2006 02:37 AM
cheewah
Posts: 11Joined: 17 May 2006
Mr Duncan, a. Fully agreed with you. b. Tester must be qualified and examined particularly for his practical skill before they are allowed to go for site testing. Proper authorisation from the the right 'authority' is highly recommended! c. Furthermore, he must be well disciplined and sincerely in carry out these trust-worthy tasks as it involves the 'real time protection' of human lives, equipments and the buildings as well. d. I am a Malaysian and work in Malaysia. Therefore I must follow Malaysia's guidelines and standards. e. Mr Duncan, thanks for your contribution, guidance and idea-sharing. Best regards Cheewah
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18 October 2006 11:54 AM
geeli
Posts: 61Joined: 21 April 2005
Primary Injection Test (PI Test) 1) to ensure wiring connection of protection system is correct 2)to check CT ratios and polarities 3) to check Overcurrent relays and Earth Fault relays (both DTL type) are set to correct setting 4) to check Direct Acting Tripping element of the main MCCB.
Secondary Injection Test (SI Test) 1)If the protection relays (overcurrent and/or earth fault relays) are IDMTL type then Secondary Injection Test is required.
I would like to confirm and reassure myself that my understanding of the above two tests serve different purposes and its purposes are as stated above.
Am i correct?
Would appreciate replies.
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27 October 2006 01:25 AM
deleted_Colhind
Posts: 6Joined: 06 September
2006
G'day, Primary injection (sometimes referred to as a trip test) is generally carried out as a test to determine the integrity of the whole secondary protection circuit including CTs, CT leads and control CUBICLE wiring. In other words it proves that the CB trips in response to an overcurrent. The test is performed after secondary injection tests and CT ratio tests and when all the secondary test links are closed and ready for service. Hence it is often the last test perfomed in the commissioning process.
The PI test is usually performed by injecting a current at low volatage (say 5 -10 V) from a purpose built transformer with high current capable secondary winding. The current is passed through the breaker or busbar section as appropriate. The magnitude of current injected is generally not considered important so long as it is above the minimum operating current determined by the protection relay settings. Sometimes the current and time to trip is measured but owing to the inability to provide currents as large as the prospective HV fault currents no attempt is made to perform full Time-Current Characteristic tests of the protection scheme.
Secondary injection tests are performed by injecting currents into the relay terminals to determine that the relay is operating correctly and in accordance with its settings. Such tests are usually carried out in the control room at test links provided for the pupose. These tests include injecting currents of various magnitudes from MinOp all the way up to 10 or 20 times MinOP and measuring the relay operating time if your TEST EQUIPMENT
is up to the task. Anything less than 10 times MinOp and you will need to carefully the
risk of the relay being off characteristic at the higher currents and what affect that might have on co-ordination with other schemes.
CT ratio tests are performed to determine that the relationship between primary current and secondary current seen by the relay is correct.
CT saturation tests are also performed as proof that the CT is up to the job of providing accurate output at the prospective fault levels.
Having performed these tests you have done all that is reasonable to prove the correct operation of the protection scheme.
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30 October 2006 11:52 AM
geeli
Posts: 61Joined: 21 April 2005
thanks Colhind for your reply.
however i am cofused at the moment between your elaboration on the primary injection (sometimes referred as trip test) and the PI test.
aren't PI test is termed as primary injection test?
i am fully aware that there are lots of electrical professionals in the forum however am upset that the replies to this thread is wanting.
it might be that there are people that can perform those tests but are not sure where to term those tests.. just my thought.
i am sharing with Colhind on this as you are the last person to share your view after a number of days lapse...
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02 November 2006 09:58 PM
deleted_1_rbcatlow
Drop me a line at [email protected] if you need more information
My team do primary and secondary injection tests every week from 11kV to 132kV on a weekly basis
Posts: 15Joined: 15 September
2001
Richard
-------------------------rbcatlow
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23 November 2011 07:45 AM
NickCarter23
Posts: 1Joined: 16 March 2009
Does anyone know where I can buy a decent secondary injection tester?
Looking to secondary injection test a MiCOM Electronic Protection Relay?
Cheers
Nick
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23 November 2011 08:35 AM
ArthurHall
Posts: 736
If you are just doing a few relays I would hire a test set. If you are in the UK there are a few companies that hire them. You could try Cuthbertson & Laird as one example. A basic test set will cost at least £1500 going up to about £30000. Dont be tempted to make do with a transformer and VARIAC as distorted waveforms could give you false results.
Joined: 25 July 2008
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23 November 2011 12:15 PM
AdrianWint
Posts: 262Joined: 25 May 2006
Slightly OT..... AREVA/ALSTOM documentation seems to suggest that SI testing is no longer considered necessary with digital protection relays.
What is the general feeling on this?
Adrian
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23 November 2011 03:42 PM
ArthurHall
Posts: 736Joined: 25 July 2008
The relays may be OK but what about the wiring and trip relays?
IMHO Primarys are done once on commissioning after that it is only required to carry out an insulation resistance check at 1000 or 500 Volts.
Secondary injection tests are carried out at regular intervals and should include a trip through to the breaker.
Communications channels usually need testing more frequently that secondary injection tests.
Trip tests should be carried out at least annually
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23 November 2011 07:01 PM
Peddler
Posts: 36Joined: 28 May 2008
I'll throw my tuppence in,
got to aggree with Arthur usually after commissioning, primary Injection is not periodically required. If the CT was commissioned and is wasn't upside down at commissioning and start up stage then its not likely to be after it. Same goes with the ratio, and how many people here have had many problems with saturation after being commissioned by a specialist?. In my experience it's the actual relay that causes the most problems, perhaps the response curves need adjusted if inrush is a problem etc etc. This is normal "BATH TUB curve" theory once your handing over a project or signing a handover certificate anyway. I remember years ago we carried around cumbersome and heavy injection sets, Injected lots of overload relays for motor protection etc and I must confess I sure we caused some of them to have smoke belching out of them . probably weakened perfectly good thermal overload relays. My advice is not to do this type of testing unless you know exactly what your doing, go on a protection course , there's one up at ASET in Aberdeen. Good Course. Also the injection testing is the easy bit , its the designing of the protection system that's the real skill. You got to admire those protection Engineers , its art work.
P
-------------------------You can Learn from an Apprentice
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23 November 2011 08:20 PM
JonathanHill
Posts: 225Joined: 09 September
2002
I'm highly suspicious of claims that SI of electronic/ microprocessor/ numerical relays is not necessary. Recent, bad, experience of a project where limited relay testing was carried out convinces me that this is required.
The complete trip circuit needs verification from CTs to trip action in any event so I'm with Arthur (and others) and would insist on Primary & Secondary Injection on 1st commissioning (including trip tests), followed by periodic reruns of SI at intervals <5yrs. During these periodic maintenance, the battery condition should also be reviewed. Personally, for VRLA (sealed lead-acid) type batteries, which should be specified as 10-yr design life as per Part 4 of BS ????, I'm in favour of replacing these at 5 or 6-yearly intervals.
-------------------------Jonno
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23 November 2011 10:14 PM
alancapon
Posts: 5779Joined: 27 December
2005
I would agree with the comments above. Primary Injection on initial commissioning and if the CTs are replaced, otherwise Secondary Injection into the relay. Either way, I like to see the CIRCUIT BREAKER trip at least once as a result of the injection. There is a bit of a controversial view held by an employee of a company that makes test sets, but even he suggests that it is important to Secondary Inject to prove the relays are reading the correct currents / voltages, and also prove all the output contacts are still working.
I believe that the important thing with a modern electronic relay on commissioning, is not only to prove that it will do all the things you want it to do, but also prove that it won't do all
the things you think you have turned off in the software!
Regards,
Alan.
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31 August 2012 07:10 AM
squelch
Posts: 2Joined: 31 August 2012
Good read.. BM