I2T - 31,5kA/1s x 31,5kA/3s
I2T - 31,5kA/1s x 31,5kA/3s
(OP)
Hi there.
I got a disconnector switch with short current rated to 31,5KA/1s, I need to demonstrate that his contact are able to support 31,5kA/3s. Based on type tests recorded earlier, the only information I have are the contact resistance and contact area, can anybody give me a tip if it is possible to "SIMULATE" this extra thermal stress? I really don´t think that i²T is saying anything about this extra contact thermal efforts.
Best regards;
Manoel.
I got a disconnector switch with short current rated to 31,5KA/1s, I need to demonstrate that his contact are able to support 31,5kA/3s. Based on type tests recorded earlier, the only information I have are the contact resistance and contact area, can anybody give me a tip if it is possible to "SIMULATE" this extra thermal stress? I really don´t think that i²T is saying anything about this extra contact thermal efforts.
Best regards;
Manoel.






RE: I2T - 31,5kA/1s x 31,5kA/3s
Beware that HV disconnect switches are not rated for interrupt current. The main function of HV disconnect switches are for isolation and should be operated after the circuit breaker is opened.
RE: I2T - 31,5kA/1s x 31,5kA/3s
145KV is the sytem voltage, the 31,5KA is the short circuit withstand current, of course the DS will not OPEN with this current.
RE: I2T - 31,5kA/1s x 31,5kA/3s
If the limit is given for one second, it is probably a thermal limit. So you shall look at temperature after three seconds instead of one second.
That alone says that the disconnet can not carry 31.5 kA for three seconds. Temperature rise (T) is proportional to power times time T=I^2*R*t (actually, R is not constant - but increases with T) so you needn't do any complex calculations using contact resistance or contact area and resistivity.
In my view, it can't be done.
Gunnar Englund
www.gke.org
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Half full - Half empty? I don't mind. It's what in it that counts.
RE: I2T - 31,5kA/1s x 31,5kA/3s
Thanks.
RE: I2T - 31,5kA/1s x 31,5kA/3s
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: I2T - 31,5kA/1s x 31,5kA/3s
Regards
Marmite
RE: I2T - 31,5kA/1s x 31,5kA/3s
I trying to figure out how I can evaluate with the data I have to give some degree of thrust that our DS will hold 31,5ka/3s.
RE: I2T - 31,5kA/1s x 31,5kA/3s
Rafiq Bulsara
http://www.srengineersct.com
RE: I2T - 31,5kA/1s x 31,5kA/3s
Do you understand what we are saying? There's no way you can do that!
Why do you so desperately need to 'prove' something that cannot be proved?
Beware. There is legislation. You will be sorry if you carry on with this.
Gunnar Englund
www.gke.org
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Half full - Half empty? I don't mind. It's what in it that counts.
RE: I2T - 31,5kA/1s x 31,5kA/3s
I am not so desperately to prove anything.... and for sure, if we will export to US, be sure that TOSHIBA will provide the needed equipment according with your requirements ok?. No issues about that.
The problem is that, for some disconnector switches, rated to 31,5KA/1s, we made recently the tests for 40kA/3s, and the DS had passed gratefully on this much more severe condition. I remember that the model was different from this one in case. The first, we discuss a central brake, the second was a vertical opening.
What I trying to do is a mathematical approaching to this one central opening DS, just to check if I need to improve something in the contacts sets, in other to guarantee that the disconnector switch will, for sure, passes the short circuit test with 31,5/3s.
The two types of disconnector switches are totally different, but the contacts area, contact type and others things are really very similar, that's why I trying to do this approach.
This shows that, the equipment is fairly away from the thermal limits, and this is exactly what I trying to discover, what is the thermal limit of our equipments, without expensive tests, like short circuit type tests ok?
Regards;
Manoel.
RE: I2T - 31,5kA/1s x 31,5kA/3s
What does the manufacturer say? He has done all the testing.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: I2T - 31,5kA/1s x 31,5kA/3s
I work at TOSHIBA.
See, I think I could not make myself clearly, sorry for that.
I remember that I trying to receive some help, not to fight or been "warning" for some reason.
Please let it go,
Thanks for all.
Regards.
RE: I2T - 31,5kA/1s x 31,5kA/3s
I realize that a switch with a higher rating may be more expensive, but the people who make and test switches know this better than I do. If it was possible for a valid test to show a higher rating for this switch, the manufacturer may list the switch for the higher rating and sell it for a lot more money.
Bill
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"Why not the best?"
Jimmy Carter
RE: I2T - 31,5kA/1s x 31,5kA/3s
The annex of C37.32-2002 provides some equations for calculating temperature rise of switch components. However it does require knowing the conductivity, cross section and maximum allowable temperature of all components of the switch. As others have stated this wouldn't let you exceed the nameplate ratings. You could use it as sanity check to see if the manufacturer might do more testing for you.
RE: I2T - 31,5kA/1s x 31,5kA/3s
RE: I2T - 31,5kA/1s x 31,5kA/3s
RE: I2T - 31,5kA/1s x 31,5kA/3s
Calculation of the thermal short-circuit resistance of a disconnecting switch is complicated.
For rated current only the contact temperature depends on a lot of factors as the material resistivity, force applied
on contact, material compressive strength, thermal conductivity and other[ all these depend on temperature].
In short-circuit case a repulsing force will diminish the force applied on contact and an elevated temperature could conduit to welding of contacts. If for short time [one second or less] one may consider adiabatic heating for 3 second some heat could be evacuated outside.
ANSI Standard C37.20.2-1999 specified rated short-circuit for 2 second, MOM [momentary short-circuit] for 10 cycles and peak short-circuit rating.
Rated momentary withstand current: This is the maximum rms total (asymmetrical) current that the switchgear bus must withstand, and is measured at the major peak of the maximum cycle of the maximum offset phase. The test to verify this rating requires a test duration of at least ten cycles of power frequency. During this test, the peak current at the major peak in the maximum cycle must be at least 260% of the rated short-time current of the switchgear.
Peak withstand current: This is not strictly a rating, but it is the peak current value (260%) that must be attained during the momentary withstand current test described above.
Short-time withstand current rating: This is the average symmetrical current that the switchgear must be able to withstand for a period of two seconds.
So if you know the peak withstand current you may divide by 2.6 and this is the short-time withstand current for 2 sec.
From some manufacturer's catalog the short-time withstand is stated for 3 sec. and is the same as calculated for 2 sec. according to ANSI. But no mention of 1 sec. withstand.
RE: I2T - 31,5kA/1s x 31,5kA/3s
Regards
Marmite