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Start by
Naveed Shahzad
12-11-2013 10:13 PM

Buchholz Relay Alarm in Winter

It has been observed that transformer buchholz relay produce an alarm in winter. Can any one suggest why exactly this is happening in winter.

Transformer all parameters are normal, oil level is also normal, no gas accumulation is seen yet in winter alarm pops up.

- Can any one suggest to check what precautions can be taken to avoid having this alarm?
- What could be the reason of this alarm?
- What further actions to be taken to investigate the actual root cause of this alarm?
12-12-2013 01:05 AM
Top #2
Chris Tigwell
12-12-2013 01:05 AM
No indication of the size of the transformer, but if the heat loss is insufficient to maintain the oil temperature above ambient (or at normal daytime/summer temperatures), then the oil in bucholtz float chamber will drop, and mimic the presence of gas. In the northern UK, we used to set the oil level about 2in (3cm) above the 15degC calibration mark. This allowed for a "normal" combination of low temperature and low loss. Nevertheless, as a standby engineer, I received occasional calls at 4am in deep winter suggesting Buckholtz operation from a 7.5MVA transformer. Action to take - go back to sleep! (investigate oil level in normal hours)
12-12-2013 03:32 AM
Top #3
Romulus Badea
12-12-2013 03:32 AM
the information is too general. Normally are not technical reasons for that to alarm. I recommend to check if the relay is calibrated if isolation ball valve between the relay and the oil conservator is open. Which is the average temperature in the summer, and which is the temperature which trigger in winter? How many steps has the relay (one for alarm and transformer disconnection or two, each one separately)?
12-12-2013 06:06 AM
Top #4
Eduardo Castilla Pascual
12-12-2013 06:06 AM
You had controled the real oil level. One time we have the indicator fixed at a current value, and the real level were less than the correct.
12-12-2013 08:27 AM
Top #5
Glenn Stephens
12-12-2013 08:27 AM
Generally these relay are prone to false positive due to the orfice becoming clogged. In thirty years, I had not seen these relays operate for an actual fault until last year. It operated and the differential did not operate. The relay saved damaged to the transformer and potenial major failure of the unit.
12-12-2013 11:20 AM
Top #6
Constantin Moldoveanu
12-12-2013 11:20 AM
There is no other reason for false alarm/trip than low oil level.
Oil level indicator may be fault. You have to double check the oil level - observing the oil level indicator is not good enough.
12-12-2013 01:50 PM
Top #7
Calum Jardine
12-12-2013 01:50 PM
Try looking in the terminal box of the bucholz, if the gasket or seal isn't particularly good the box can sometimes suffer from moisture ingress (or even fill with water) which shorts out the contacts appearing as an alarm.
12-12-2013 04:13 PM
Top #8
Eric Stark
12-12-2013 04:13 PM
Unfortunately, you didn’t provide any data to go on by.

Still, from my substation trafo experience, I can say that there are 3 main reasons for Buchholz Relay Alarms:
1. Low oil level or wrong calibration. Very cold weather (like we have, sometimes, in Canada) may lead to contraction of the oil, falsely indicating GAS in the system
2. Faulty relay
3. Real fault
So, if your relay is known to be 'good', check oil levels, if ‘good’, consult the thermal contraction table for the oil in the known temperatures at stack (INCLUDING wind-chill charts), to see how much will the oil go down.

Kind regards,

Eric Stark 
12-12-2013 06:39 PM
Top #9
Philippe Mertens
12-12-2013 06:39 PM
A false Buchholz signal is probably cause by:
- a high DC voltage over the NO alarm (or trip) contact; 110V DC or 220V DC
- moisture ingress in the buchholz terminal box
The moisture ingress is can be caused by temperature variations inside the Buchholz terminal box for instance during winter, when the transformer is loaded, the Buchholz is warm and when the load drops during night time, the air inside the buchholz terminal box shrinks and aspires cold humid air from outside, it may form water droplets on the cold metal parts of the Buchholz microswitch and the DC voltage creeps towards the opposite loaded microswitch contact.
My advise: Dry the Buchholz terminal compartment (f.i. with a hair dryer), clean the ventilation openings in the Buchholz terminal box (see Glenn's comment). If these are not clogged, you may spray the blanc metal parts of the microswitch and terminals with a kind of varnish to minimise the condensation on the connection parts (of course the connections should be tight so everything should work perfectly with the thin varnish coat).
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