2 thoughts:-

1. you have a really poor transformer (very poor quality)

2. you only told us a very small portion of the story

Dear Rogerqqbr,

Yesterday ABB service came to our plant.

They checked transfromers turn ratio and they did isolation tests, dc resistance test.

Everything is OK.

But when we gave energy to the transfromer via incoming cell CB was tripped by relay

cause of unbalance.

And then we change the relay settings that we change the delay from 300 ms to 1s

and we changed the treshold from %20 to %30..

But it didn't work. So we cancelled the unbalance protection.

Then ABB Service needs to come back, to witness, and examine the cause of, the thing tripping.

It is still under warranty, isn't it?

Dear PWSlack,

Yes İt's the tarnsformer and MV switchgear cells are unser warranty..

So today Schneider Electric is coming here..

Quote "A month ago while we give energy firstly to the MV system the circuit breaker that is in transformer protection cubicle was tripped cause of inrush current ( unbalance fault ). It was normally."

Inrush current usually refers to the current that flows when the transformer is unloaded when it is energized. You comment (unbalanced fault) leads me to believe other wise.

Quote "But this circuit breaker was tripped again and again.."

This does not do the breaker any good.

Quote "Two days ago when we start 200 kW fan motor this circuit breaker was tripped after that we give start for 5 times at last electrical arc was occurred between the secondary windings of transformer."

This sounds as if you did energize the transformer with out a problem and tripped the breaker with the starting of the 200 hp fan. Was that start across the line or with a starter?

The "engineering" answer: the transformer (finally) failed due to the repeated abuse that it received as a result of the multiple reclosures into a fault of undetermined origin.

The "management" answer: it failed because no-one took the time or effort required to investigate why the "...breaker was tripped again and again...". The only plausible "reason" for this was a lack of properly trained and/or qualified personnel at the job-site.

Another case of "...no time/money to do it right, but plenty of time/money to do it over..."

Give more information like:type of OC relay,its settings,value inrush current,motor starting current,type of starter,when motor was started what was the load current already in transformer,commissioning test results etc

Dear Pnaban,

MV switchgear cells are Schneider SM6-36.. and transformer is ABB drye-type.

MV relays is Sepam T-20.

Setting value is 32 A.

We are starting the motor Y/delta method.

Check the disturbance recorder, what caused the trip.

A 200kW fan load at 400V is a fair load. You don't mention how you are starting this. Are we looking at VSDs, soft or DOL.

Likewise you don't mention whether the transformer is already electrically loaded before you try and start the fan.

Suggest you stand well back on your tests cos it sounds as though safety is taking a day off!

Dear Silverfox,

We are starting 200 kW fan motor Y/Delta method. And while we are starting this motor the other system was running. At this time transformer gives unbalance fault.

We are still controolling/checking the MV/LV system...

When you energise any inductive piece of kit - motor or transformer etc only one of the phases will see the high inrush current. (think of your 3 phase sine wave - 1 of the phases will going high whilst the other 2 will have passed). This might show up on your protection as an inbalance fault.

You need to determine whether the transformer trips when being energised or only trips when you are trying to start the motor. Work out where the fault is - is it at the motor or is it the transformer.

Gut feel is something is breaking down under load and causing these trips.

Check your protection - it is there for a reason.

Dear Silverfox,

I'll check the current both on MV system ( R,S,T ) via sepam relay and via LV system ( R,S,T, N ) via ammeter.

Why don't you use a data logger/power analyser,measure harmonics too.

Dear M.UCAN,

From your reports, it is revealed that, the trafo was run healthy for one month and after that the fault has been developed. You/ ABB Servive men carried out Turn Ratio test,Isolation test and D.C.Resistance test and found normal. The unbalance element of the relay actuates only by I2(negative sequence) current. Therefore, you should investigate the cause of generation of negative sequence current while starting 200kW fan motor. The negative sequence may be generated while starting induction motor due to various reasons; major reason is unbalance voltage. So please check line to line voltage, condition of cable terminations at Trafo as well as motor/controlgears, contact condition of Trafo tapchanger etc. Also there must be in-built arrangement for blocking 2nd harmonic component in the relay during inrush current while switching ON of trafo.

Manindra

you still need to determine the location of the fault.

Is the MV supply to the transformer tripping due to a fault on the primary of the transformer or is being inter-tripped by a fault on the LV side.

I agree with others you do not want to be tripping MCCBs on a regular basis.

while energising unloaded t/f from hv,you need to have a second harmonic restrain relay