VCB vd4

[hasanhadi]

hi
We have in AIS ABB substation breaker 33kv (VD4) VCB made in ABB china
But when breaker in service position and open and incomer is live( I mean 33kv is found)
Problem the bus is reading vn=400v or VL-L=700v why? Must be reading zero because breaker off
Now if breaker is drawing to test position reading voltage in bus become zero
Where reason ?

 

[DTR2011]

capacitance across the open poles of vacuum interrupter

 

[hasanhadi]

Mr. smallgreek
what you mean
please i need more information
you mean distance between fixed contact and verable contact is not enough to reducing capacitive
how solution this problem

 

[DTR2011]

No solution - you have to understand what you are doing and the tools you are using. You are reading with high impedance voltmeter, yes? Use a low impedance (analog) meter and voltage will be zero. If this is a permanent concern, use some kind of loading resistor in the meter circuit.

 

[hasanhadi]

thank you master


look when breaker in service position and open and incomer is live( I mean 33kv is found)
Problem the bus is reading vn=400v or VL-L=700v
i mean founding VT capacity 100VA but when loading by big transformer the voltage will zero
now VCB test by car test but the car no reading any current
i mean connect line from car to breaker anther terminal connect to ground (breaker off) no current record in the car

Mr. now ask why crossing small voltage to busbar the VCB is not good
when change breaker with new breaker but same Specifications the same problem
can you calculated capacitance or how can be testing for checking only please help me and thanks sir

 

[DTR2011]

hasanhadi-

I'm not sure if you are using some kind of translation program to translate into English, but it is not working. I did not understand much of what you are saying.

What exists, exists - the capacitance of the open contacts is there and your meter is reading that - in primary values. 33kV/700V is 47 volts secondary - not a big deal and obviously not a rel value. Read the measurement with a low impedance meter (or connect a 15 watt light bulb in parallel) and your reading will be zero. If you are reading with a Fluke or similar meter you are reading the effects of the capacitance.

The VCB is just fine. I had a similar situation 15 years ago when I was new to the job. I did not take the time to understand what I was doing and failed to see what the problem really was. Understand your tools, understand that the voltage inputs on the relays are high impedance. Understand you can place a resistor in parallel with the input on the relay and see the voltage drop to zero.

 

[hasanhadi]

sir
iam sorry but cannot connect resistance why? because the device relay is reading 400v voltage to neutral and 700 volt phase-to-phase
this voltage is real in busbar now can be obtain zero voltage by drawing breaker in test position
but only i need know reason for why voltage 700 in basbar must be zero
this switch gear is AIS made in ABB

 

[DTR2011]

Read the voltage with a low impedance meter - it will be zero volts.
If you choose to to take my advise, please don't ask further.

 

[hasanhadi]

Mr.smallgreek
today measuring voltage by using anloge meter but reading not change
after that connect light no change in reading i mean Vn=400 v
VL-L=710v and connect resistance also no change in reading
Mr will drawing state in the file attachment

 

[DTR2011]

Did you test the vacuum bottles on the circuit breaker? Did they test good? I am referring to AC HyPot test, or similar to verify that the vacuum bottles are indeed acceptable. If the answer is yes the vacuum bottles are good and they pass the test - then what else could it be?

You state when the breaker is in test position or racked out then voltage is zero. Research capacitive coupling in basic electricity books.

I have not seen you drawings, but many times in the secondary circuit of VT, there are indicating lights (voltage on or off), but more important, these dampen the capacitance you may read into high impedance metering. Suggest 20 Watts or so. The lights are in parallel with other meters, etc (L-N Connection).

Try using light in parallel with your analog meter. Talk to ABB or whoever designed your switchgear about your concerns.

Most important, please be careful. It sounds like you need some more experienced help on site from this question and others you ask with so much desperation.

 

[hasanhadi]

thank you.