2000 KVA Transformer - Body Leakage of 24 A

I agree with PW.

To answer the OP question (again). NO! It is not at all normal! Get working to fix it right now! Follow PW's guidance, as it is good.

certainly it is more current. make independent neutral earthing with 50X6 mm GI flat, at the same time with Body also. transformer earthing should not connect with grid earthing, check tap operations, may be relay triping on instantaneous current. check settings, commonly megger values, you may found something if you open inspection top cover...like opened winding, etc, carbonised oil.

24A earth leakage current is very dangerous. Indicates some insulation deterioration. Pl. investigate & rectify immediately.

Are you saying that the grounding conductor that connects the metal tank/case of this transformer to your earth pit sees a current flow of 24 amps? If so, have you tried to measure the voltage across the circuit between the tank and the earth pit?

What happens to this current flow when you unload the transformer? Open its downstream breaker and see what the current flow is.

Does the transformer have powered cooling fans mounted on it? If so... check them very carefully.

From transformer body to where...to neutral, to earth, phase (heaven forbid)?

What is the reference?

1. PWSLACK has given some guidance on the 24A leakage current. However if the current persists when the LV side is disconnected, you may have a HV fault and this needs to be resolved quickly. With the transformer isolated from supply (HV and LV) check insulation resistance HV to Tank, LV to Tank and HV to LV. Check the arrangement of the HV system neutral earthing.

2. The tripping on energising is possibly due to inrush current. ((I>> is usually instantaneous and thus will operate if the inrush is greater than the setting) This can be up to 6 times full load current, and may not be balanced. Review the protection settings to ensure that instantaneous (I>>) settings take account of inrush current.

Is it from the transformer or from your MV cables, (earth leakage and cirrcualting earth faults)? Did you disconnect the cables and measure the amps?

Also, it is time people defined their voltage ratrher than telling us HT. 11, 22, 33, 66kV, is NOT HT. If you place the correct information here, people can assist you better. i.e voltage, cable type, etc. Cheers.

I am surprised! What are you talking? If 11, 22, 33, 66kV are NOT HT, then what are they? Are they LT?

Reference is drawn to IEC 60038, wherein it is mentioned that LV is less than 1kV, HV Range 'A' is above 1kV but less than or equal to 245kV and HV Range 'B' is above 245kV.

And, just in case you don't know, LV is Low Voltage & HV is High Voltage.

Pl. do not post incorrect statements.

He never claimed he was High IQ. Just IQ.

As in real estate,location is everything.In power transmission, above 35Kv is considered High Voltage.

The IEC defines High Voltage as above 1000Volts for AC and above 1500 volts for DC.

The NEC defines it as any voltage above 600 volts AC,and British Standard has it's variance from these definitions also.

Rather than show ignorance here, IEC 60038 is for Standard Voltages. It does not state what is MV, HV or EHV. So dipstick, for your education it works as such.

1kv to 132kV Distribution voltage. which covers MV and HV. 11kV is MV, 132kV - 400kV is HV, 500kV and above is EHV and super EHV. 1MV is operational in China. Know you voltages.

Electronic Protection Relay installed on the upstream of transformer (HT Panel) As quoted, HT panel? Rather state a voltage then folks know and can help.

God help you on a transmission line or sub station. But to answer the lads concern, it could be coming from the Tfx or more likely the cable and if this was oil filled cables, there is an earth issue on a cable. If this is XLPE cable it can be the termination, the cable screen, the cable core holed and the semi con leaking into the screen. It could even be a joint breaking down, if there is a joint in the cable. The far side earth protection should have tripped, if the cable is faulted to that side. If it is closer to the near side breaker the fault will not be seen by the relays. And this depends on earthing of the cables. So in your jest, you should perhaps keep quite as there are people who don't waste time with 17th edition as it has no value in 132kV systems. Wipe the shit from your eyes and learn for a change. And I guarantee this is a MV cable fault and very close the to the termination. It just makes it easier when one knows a voltage, rather than assumed terminology. But then if this is NOT your field, then tolerating fools and horses is hard work for us F'wits.

Read Note 3, page 10, IEC 60038 Ed 6.2, 2002-07.

Voltage levels have been defined and classified by various National and International Standards as also by certain electric power utility companies. The following are the definitions given in various Indian & International Standards for AC Voltages.

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India: As per the Indian Electricity Rules, 1956, vide Rule 2(av), the following are the limits:

Low Voltage: Not exceeding 250V

Medium Voltage: Not exceeding 650V

High Voltage: Not exceeding 33000V

Extra High Voltage: Exceeding 33000V

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But, in IS 13234 - 1992, which is the "Guide for short-circuit current calculation in Three-phase A.C. Systems" - it is mentioned vide Table I that:

Low Voltage: 100V to 1000V

Medium Voltage: > 1kV to 35kV

High Voltage: > 35kV to 230kV

As can be seen from the above, there is no harmony between the IS and the IE Rules in this issue.

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France: Vide a publication dated 14^th November 1998, the French Regulations define three voltage levels as below:

Low Voltage: < 1kV

High Voltage A (HTA): > 1kV but </= 50kV

High Voltage B (HTB): > 50kV

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CENELEC (The European Electrotechnical Standardisation Committee): Vide a publication dated 27^th July 1992, the CENELEC recognises the following voltage levels:

Low Voltage: < 1kV

Medium Voltage: > 1kV but </= 35kV

High Voltage: > 35kV

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IEC (International Electrotechnical Commission): In IEC 60071, the following ranges are defined:

Low Voltage: < 1kV

High Voltage Range I: > 1kV but </= 245kV

High Voltage Range II: > 245kV

The acronyms EHV (Extra High Voltage) and UHV (Ultra High Voltage), though are being used elaborately in India, have never been officially defined in any of the above three standards.

USA:

i) Vide IEEE Std. 241-1990 (IEEE Recommended Practice for Electric Power Systems in Commercial Buildings), Clause 3.1.1.2,

Low Voltage: A class of nominal system voltages 1000V or less

Medium Voltage: A class of nominal system voltages greater than 1000V and less than 100000V

High Voltage: A class of nominal system voltages equal to or greater than 100000V or less than 230000V

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ii) Vide ANSI C84.1-1989 (Voltage ratings for electric power systems and equipment),

Low Voltage: 120V to 600V

Medium Voltage: 2400V to 69000V

High Voltage: 115000V to 230000V

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iii) Vide ANSI C92.2-1987 (Power Systems - Alternating Current Electrical Systems and Equipment Operating at Voltages above 230kV Nominal - Preferred Voltage Ratings)

Extra High Voltage: 345000V to 785000V

Ultra High Voltage: 1100000V

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Note: IEEE - Institution of Electrical and Electronic Engineers

ANSI - American National Standards Institute

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As can be seen from the above, there is no clear cut demarcation for classification of various voltage levels in AC Electric Power Transmission and Distribution. Also, there is no single standard across the globe, with various countries defining various limits for these voltages. And, as in the case of India and USA, even within one country, two standards do not match, when it comes to these limitations. It is wished that the electrical community across the globe meets and takes a decision soon to bring harmony across the countries of the world in standardizing the limits for various voltage classifications.

Thanks everyone for your suggestions and sarcasm!!

First of all Trandformer incoming voltage is 11 KV we conducted all the test of transformer like HV to LV Meggar, HV Meggar, LV Meggar, Cable Meggar, TTR, horn conditions and everything is fine.

We observed that the leakage is from our downstream network and is being observed at transfromer body as both LT and Transofrmer share a common earth.

We removed entire plant load and then tried to reset the VCB but it tripped again!!

Transformer vendor has suggested that our protection CTs "5P20" might be entering into saturation region and since we have set 0.0 sec delay on IE>> fault, VCB is being tripped instantly...

Interestingly after performing all transformer tests when we reset the VCB it did not tripped and since yesterday it is working fine!!!

Regards,

Farhan Javed

Did the 24A leak go away at the same time, though?

Ok Farhan, everyone here has express their best opinion but far away from site, now take your notebook and choice the better of each one because you are touching the problem.

Reference to the voltage designation, please check standard ANSI-84 1 -2006 despite voltage designation now is not your top priority.

Good luck

Bye

I find this thread an exercise in human obtuseness.

There is a 24Amps leak somewhere, supposedly.

There is no measurement presented, but somebody's say so.

Well, I do not believe so.

An approximately 5kWatts leakage is loud, cannot be hidden.

I asked for some measurements with independent instrumentation, like oscilloscope. The fellow comes back with Meggering parts. By the way, it is Megger, not meggar. Who cares?

A relay trips for a reason, that is for sure. That is not sure at all, what the reason is. The relay not tripping for a day for unknown reasons is not an achievement in my book.

Actual measurements, anyone. As in verifying, if the 24Amps is real in the first place, and its nature, if it exist at all?!?

Hi,

Leveles thank you for pointing out the tests. I have taken over maintenance of this particular transformer after my predeccesor Farhan. I conducted the tests. Below are the results;

1) Unloaded LT, leakage current on earth : 16A

2) Unloaded LT, voltage on transformer body to earth busbar : 0V

3) Unloaded LT, voltage on neutral to earth : 0V

4) Unloaded LT, leakage current frequency : 150 Hz

5) Unloaded LT, leakage current THD : 250%

6) Unloaded LT, power quadrant 1, net power 0W, PF 1.00, tan 0.00

With LT on load the above values remain same except the frequency changes to 50Hz (our system freq).

We do not have an oscilloscope on site, the THD values were noted from a power analyser we use (PEL 100). An interesting observation here is that while the transformer neutral is earthed seperately, the transformer body earth is common with the plant distribution ( body earth connection made to a bus bar where multiple equipment and feeders have been earthed including a generator neutral connection). I do not believe that the leakage is resulting from damage to transformer or some neutral to phase cross over. I do not believe the current is ohmic (though the 1.0 PF seemed disturbing). What are your thoughts?

A few questions need answering to satisfy my curiosity,and eliminate some variables that may be obvious to some, but ambiguous to other:

Re: The generator you mentioned:Is it running while conducting the tests you mentioned?

Do you have a lot of Switch-mode power supplies in the plant;computers,UPS's etc?

The fact that the current is a 3rd harmonic indicates such devices on premises that are supplied by another source.

Even though the individual currents may be small, due to the nature of 3rd harmonics,the currents are additive.

I suspect this may be the source of the current.

HiTek the answers to your queries are given below;

1) Is the generator running while test was conducted : Yes, Transformer primary was also available, LT was unloaded. Load was on generator.

2) Yes there are significant SMPs installed at our plant. UPSes, computers and DC power supplies.

3) Why would you say that the current is 3rd harmonic dominanat. Beacuse of the frequency of 150Hz?

Yes,the 150hz frequency is the reason,presuming your system is 50hz.

Instead of going into possible remedies here, I can direct you to a good source to help resolve your issues.

Link:http://www.hammondpowersolutions.com/files/HPS_article_Harmonics_PhaseShifting.pdf