Busbar joint resistance value?

[lz5pl]

We have to test contact resistance of busbar joints of newly installed 400 kV switchyard. My problem is that I have no idea what value will be considered as a good. Probably some standard exists (here is IEC world), but I haven't it. Colleagues told me that there is some "rule of thumb" that contact resistance have to be less that resistance of one meter of connected busbars, but I suppose it is just some practical rule.
Any suggestions also from ANSI-world will be wellcomed - the law of Ohm is the same there too


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It may be like this in theory and practice, but in real life it is completely different.
The favourite sentence of my army sergeant

 

[Zogzog]

No real standard, ANSI says that phases should be compared and should be within 50% of the lowest reading. But really you are looking for a few microhms.

 

[NCTHAI]

When I used to do this maintenance checks . we were getting readings in micro ohms ranging from 2-3 micro ohms to 7-8 micro ohms. The lesser the better.

Few practical tips - measure the resistance and ambient temperature / humidity also. Temperature Correction factors needs to be applied for future comparisons.

Good guidelines should be erections time results' documentation. They should provide base line values.

Hope this helps.

Regards,

NCTHAI

 

[lz5pl]

Thank you for your input, guys.
Actually we are on erection stage, so our measurements will be the basis for future maintenance tests. I expect values in the same range, busbars are 400 sq.mm, compression type joints. Well, we will see...
My microohmmeter has option for internal thermal correction, but we will include ambient temperature in the test records for future reference.

------------------------
It may be like this in theory and practice, but in real life it is completely different.
The favourite sentence of my army sergeant

 

[desertfox]

Hi iz5pi

Look at this site it might help:-

http://www.copperinfo.co.uk/busbars/pub22-copper-for-busbars/sec7.htm#Joint

Resistance

desertfox

 

[lz5pl]

Thank you desertfox, very interesting material. On the same website I found also interesting material for grounding grid.
Finally I found some national norm (not that it was too much hidden, but up to now we work mostly with relay protections and were asked for a first time to measure contact resistance)for this value - resistance of busbar joint must be less that 2 times resistance of a busbar with the same length as the joint. We found that typically resistances tested are slightly over the resistance of plain busbar, so it seems that installation contractor's work is OK.

------------------------
It may be like this in theory and practice, but in real life it is completely different.
The favourite sentence of my army sergeant

 

[desertfox]

Hi iz5pi

Your welcome