Answer / vijendra joglekar

First of all do you know what is the reoson for using
Circuit breaker in electrical equipment/device means it
will protect the device whenever the fault occurs it will
trip the breaker or open the contacts ( fixed /moving
contacts).And you told that there is some humming sound is
there in CB that means it will harm the equipment (may
chance to fire) just you need to check whether all the
contacts/connections in the breaker/device is tightly
connected by loose connections also you getting these type
of errors/faults even tho the current rating is samall (
you told 50A)
You need to check:
1.Tightness (mandotary)
2.Check the calibration of the equipment
2.Check the technical specification (i know you already
checked before installing)
Go ahead dont stop the work if you are still getting sound
means u just repalce the breaker unless why u r taking risk.

Answer / hussain

Thanks Vijendra Joglekar
The breaker has been serviced already and nothing wrong
found, the load is 1200 Amps, but the current fluctuation
is around 50 Amps (+&- 25Amps)when load increased, the
sound started at load above 800 Amps, while the breaker is
rated up to 2500 Amps.

Answer / k.prakashchandra

Check the hold coil, if it has any.

Answer / yusuf

Can you tell me what is the circuit Breaker settings like
overload,shortcircuit,ground fault & Instantaneous s/c
settings.Acc to your details max load that can be derived
from X'mer is 2228.56 amps & from 800 amps onwards Breaker
is creating this problem.So around from 25% load CB is
creaing problem also tell me about any release installed
(Closing,shunt,undervoltage).

Answer / hussain

This is an old breaker and has no protection devices, close
and open manually. closes by operating rod and opens by
trip button. Protection in the HV side of the transformer
incomer. I suspect the contacts got wear and tear due to
long time service and intending to change the fix and
moving contacts. Small gaps ( not seen by eyes) between
contacts could cause this sown as far as I know.

Answer / yusuf

Yes,it can be.A very small gap can't seen by naked eyes
between CB main contacts could create this problem.Exactly
from which area this sound is comming? Is is some Clicking
sound/Buzzing sound.Can u give me Breaker details like make
(Siemens/L&T/ABB/Scneider) & Type no, 3pole/4 pole any
neutral earth fault protection provide extra to the
breaker,two breaker earthing & neutral connection.I am
talking of two main transformer breaker.Please furnish some
details to rectify the problem.

we have a 2000kva step down transformer at our site. The HT side is charged from 22000V. So the primary current will be 52.48A. So why the HT breaker(SF6 ABB) is rated of 1250Amps ?

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