Transformer cooling

[nandrade]

we have installed a 90/120/160 MVA Power Tranformer, 65 oC rise temperature. We have two groups of radiator, each one with 8 fans.
This 16 cooling fans which start, one part (8) in the first lever of cooling and second part (6) in the second level of cooling together with 2 oil pumps (one upper tank and one down tank). 2 fans remains for a reserve in case of fan failure.

1. I have a doubt with the design of the cooling (especially) in the flow determinated for the fans (18.0003/h). Does anybody could indicate me where i find information about the fans cooling dimensions.

2. Does anybody could explain why a buccholz (for the same transformer) could operate (oil flow) caused by the start of one pump (upper tank). When both start together never trip the relay.

Thanks.

 

[electricpete]

I have heard of sudden pressure tripping on pump start, presumably due to pressure transient although it's not supposed to happen.

If there were a check valve in the system it would slam when one pump started but not two which certainly is a more abrupt transient. Check valves are very common where multiple pumps are in our plant systems but I have never seen one in a transformer.

Can someone refresh my memory on Buchholz... is that like a sudden pressure or a gas accumulation relay or something else?

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[RalphChristie]

Pete:

A Buchholz-relay is a gas operated relay fitted into the oil pipe between the transformer and the conservator tank - used on conservator type transformers (only).

The Sudden Pressure relay is a pressure operated relay common on sealed tank transformers, but it can also be used on conservator type transformers.

Nandrade:

The J&P Transformer Book have some info regarding cooling. I don't have a copy right now, but when I return to work I'll will look if they state some standards.

Regards
Ralph

 

[ko99]

Even if you don't have specs on the fans, you can estimate the performance. Do you know the fan diameter, power, or speed?

ko (

http://www.ecooling.biz)

 

[ScottyUK]

ePete,

http://www.emb-online.de/Buchh_en.htm

is fairly typical of a European Buchholz relay.

This type has two floats in a chamber and a pivoted flapper plate suspended between the inlet and outlet ports. The two floats operate reed switches via magnets mounted on the float arm. In normal conditions the relay chamber is full of oil. If a gassing fault occurs, gas collectes in the chamber, causing the float to fall as trapped gas displaces the oil. The upper float is usually configured to alarm when gas accumulates in the chamber. The gas may be removed for analysis. The lower float is usually configured as a trip, being activated by large volumes of gas or low oil level. The trip contact is also operated by the flapper which responds to oil surge in the conservator pipe by pivoting from its neutral position. Oil surge typically signifies a major problem developing within the tank.



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[prc]

To understand your problem it is necessary to know how the pump is mounted .Normally only one pump is provided in the cooling circuit .One at the bottom of cooler to suck oil from radiators and to push in to lower part of tank .Other application is at the top of the cooler to suck oil from top part of tank and to push in to oil-water shell -tube heat exchanger or to oil to air finned tube coolers . This is the first time I hear two pumps used in the same radiator bank .Please correctly find out the position of the pumps in the cooler circuit with respect to tank and cooler and ratings of pumps (lpm )

electricpete, Buchholtz relay is used with open type conservators (free breathing or with air cell ) in place of gas accumulating relay used in US with nitrogen sealed trfs.

Operation of Buccholtz with start of pump is not un common .It means an oil surge is created in the oil pipe (hope relay trip is working and not alarm )when the pump sucks or pushes the oil .Sometimes it may be due to wrong design of pipe lines (cooler and Buchholtz) By closely watching the trf when pump is switched on ,one can normally detect the cause of maloperation .Practical solution at site :slightly desensitise the relay or modify pipe line.Normally manufactuers should check and ensure that relay is not activitated by the start of pump.

Why doubt the cooling by fan ? Any indications -excessive oil temp rise ? Check whether the fan direction is correct.Normally propeller fans will be pushing air in to radiators.Of course all radiator valves must be in open condition !If you give size of raiators (length *width *no of elements ) &fan details (sweep ,1/3 phase, flow rate ) I can comment.