ANSI Circuit Breaker using on 50Hz system

[sykimk]

Hello,

Do you have any idea what if ANSI circuit breaker (60Hz) will be used on a 50Hz power system?
I guess manufacturer declared short circuit duties (ANSI, 60Hz) should be derated on a 50Hz power system. If so, do you have any reference materials on this issues? I tried to search IEEE papers related to this issues on IEEEXplore but couldn't find out.

Any concerns?

 

[rocmor]

My comments are based on my past experience in vacuum interrupter (VI) design and application. I feel fairly confident that they will apply equally to SF6 CBs. Both technologies are robust and well suited for the kind of application you seem to be targeting.

The issue of going from an ANSI to IEC environment is only minimally, if at all, related to the change in frequency. Of primary concern, if it's really a concern, is that the preferred values for key parameters like max rated voltage and short circuit current differ. IEC standards for max rated voltage have preferred values of 12, 24 and 36 kV, for medium voltage equipment, whereas ANSI values are 15, 27 and 38 kV. Corresponding BIL and power-frequency withstand voltages may differ slightly as well. But, truth be told, the only differences between VIs sold for ANSI 15 kV, 500 MVA and IEC 12kV, 25kA ratings were that the external dimensions were in SAE units for the one, metric for the other. The internal geometries were the same. Likewise for 24/27 kV and 36/38 kV applications.

As to the question of "derating" (presumably) the short circuit current values when going from 60 to 50 Hz power frequency: in the former case, the average arcing time (symmetrical short circuit interruption) is about 4 ms, for the latter, 5 ms. Significant? No. Where we would derate short circuit interruption capability was if we were proposing a VI for railroad application where power frequency might be, for example, 16 2/3 Hz. In this case, the additional arc time is significant.

This said, the CB manufacturers have spent perhaps many $100,000 to get their CBs certified at independent high-power test labs for the ratings (ANSI and/or IEC) that they list in their publications. These labs do not recognize the near equivalences that I mentioned above. So, can a manufacturer tell you that a particular CB, certified to ANSI C37.06 for 15 kV, 500 MVA will work in an IEC 12 kV 25 KA application? Yes, they could, but the conservative nature of the industry has pushed many end users (esp. utilities) to adopt a "show me" attitude where they insist on having a certificate that states that the CB has passed testing at the levels prescribed by the standard they specify. As for industrial users, if you place an ANSI rated CB in an IEC environment, it may work perfectly well, but you are accepting the risk, in case of failure, that the manufacturer will not support you as you applied their product in an application for which it is not rated or recommended.

 

[sykimk]

rocmor/

Appreciate your comments.

By the way, I need to add a bit details of my case. That is, everything (system voltage, breaker's rated SC capacity, etc.) is the same except system frequency changing from 60Hz to 50Hz. Basically, I wonder what if a ANSI CB (60Hz) will be used on 50Hz system in order to interrupt short circut current. Will the interrupting capabilities of ANSI CB (designed/tested at 60Hz) be derated at 50Hz system?

I don't really worry about the insualtion level, continuous current rating/temperature rise, etc. but I am a little afraid of short circuit capabilities of the breaker.

 

[rocmor]

As I said, my best guess, based on what you've told me, is that the CB will likely perform properly as far as interruption is concerned. Beyond that, there are other components within a CB (solenoids, charging motors, etc.) that could be adversely affected by the change in frequency. I recommend you contact the manufacturer and ask for a modified rating sheet for this style CB that states 50/60 Hz instead of 60 Hz for the rated power frequency. IMHO, even though the perceived risks of something catastrophic happening may be low, the consequences of knowingly applying a high-power safety device outside of its published ratings are far too severe. It's a risk I would not take, and recommend not doing.

 

[odlanor]

We had this problem with 230kV circuit breakers. CB type tests was to 50Hz; system was 60Hz.
After 3 months of research and decision it was discovered that there was no problem in using 50Hz-CB in a 60Hz system except:
- When applied to shunt capacitor bank, IEC standards had some parameters that, if they were required in technical specification of the circuit breaker, manufacture should assure the circuit breaker would have to be 60Hz.