If equipment is rated at 50/60Hz, which frequency should be selected for heating test

[Roland chung]

Hi all,

As you can see from the caption, I am confused how to select the rated frequency for heating test when equipment is rated at 50/60 Hz. Do both frequencies need to be chose?

For high capacity equipment, there is no a voltage/frequency regulator, only one rated frequency (in my country, MAINS is 50Hz) is available. Is equipment tested at 50Hz only accepted?

Thanks,
Roland

 

[Mikishots]

Re: If equipment is rated at 50/60Hz, which frequency should be selected for heating

Hi all,

As you can see from the caption, I am confused how to select the rated frequency for heating test when equipment is rated at 50/60 Hz. Do both frequencies need to be chose?

For high capacity equipment, there is no a voltage/frequency regulator, only one rated frequency (in my country, MAINS is 50Hz) is available. Is equipment tested at 50Hz only accepted?

Thanks,
Roland

It would be dependent on where that product would end up.

 

[Marc]

Re: If equipment is rated at 50/60Hz, which frequency should be selected for heating

As you can see from the caption, I am confused how to select the rated frequency for heating test when equipment is rated at 50/60 Hz. Do both frequencies need to be chose?

For high capacity equipment, there is no a voltage/frequency regulator, only one rated frequency (in my country, MAINS is 50Hz) is available. Is equipment tested at 50Hz only accepted?

Could you let us know what heating test you are referring to? Is this from a specific standard or requirement?

 

[Peter Selvey]

Re: If equipment is rated at 50/60Hz, which frequency should be selected for heating

It is possible to select the test frequency based on the worst case.

For equipment with mains transformers, motors or other windings connected directly across the mains, the worst case is the lowest frequency. Transformers operate more efficiently at higher frequencies (lower magnetizing currents). So, temperature tests at 50Hz should be enough.

Usually, this is confirmed by power input current measurements at both frequencies, showing that 60Hz input is lower than 50Hz. Also, leakage current worst case is the higher frequency. This means that you may still be stuck doing some tests at 60Hz. However, for very high power equipment it may be possible to avoid 60Hz by using special arguments.

 

[Roland chung]

Re: If equipment is rated at 50/60Hz, which frequency should be selected for heating

Thank you for all.

Could you let us know what heating test you are referring to? Is this from a specific standard or requirement?

The heating test is another word for temperature test.

Usually, this is confirmed by power input current measurements at both frequencies, showing that 60Hz input is lower than 50Hz. Also, leakage current worst case is the higher frequency. This means that you may still be stuck doing some tests at 60Hz. However, for very high power equipment it may be possible to avoid 60Hz by using special arguments.

Yes, the 60Hz should be used for leakage current test. In my case, the equipment is permanently installed and protectively earthed. So the leakage current is actually not that critical. I think this is reasonable argument.

 

[Roland chung]

Re: If equipment is rated at 50/60Hz, which frequency should be selected for heating

Based on this topic, I would like to ask another question in regard to temperature test.

Either IEC 60601-1:1988/A2 or IEC 60601-1:2005, the standards states that during the temperature test, thermal cut-outs shall not operate.

Here the standard does use the term "thermal cut-outs" instead of "protective device". If other type protective device operates, does it constitute a failure?

Thanks,
Roland

 

[Peter Selvey]

Re: If equipment is rated at 50/60Hz, which frequency should be selected for heating

Technically, it's should not be a failure for IEC 60601-1, although it might be understandable concern for a test lab if the protective device is necessary for basic safety. For example, a fuse which opens in normal condition is not good design.

For other protective devices it really is a case by case decision as to what the function or purpose of the protective device, the severity of harm if the protective device were to fail when needed, and the overall probability of harm, including:

a) probability of the event which causes the protective device to operate
b) probability of the protective device failing
c) any other factors which might reduce the probability of harm (e.g. operator can detect the situation and take action)

In other words, classic risk management.

 

[Marcelo]

Re: If equipment is rated at 50/60Hz, which frequency should be selected for heating

Is equipment tested at 50Hz only accepted?

You might also have problems depending on where you are using the tests. For example, for Brazil, where 60 Hz is used, you won't manage to get accepted tests only in 50 Hz (even if engineering sound).

 

[MIREGMGR]

Re: If equipment is rated at 50/60Hz, which frequency should be selected for heating

For equipment with mains transformers, motors or other windings connected directly across the mains, the worst case is the lowest frequency. Transformers operate more efficiently at higher frequencies (lower magnetizing currents). So, temperature tests at 50Hz should be enough.

I would agree with this for plain inductive components operating at line frequency, but I don't think this is a sufficient approach when ferroresonance is part of the voltage change design approach, or when the device is a switching-type design with its primary inductive component operating at the switched high frequency and with different line frequencies resulting in different harmonic mixes, or for some three phase designs. In those cases, testing at both 50Hz and 60Hz is appropriate, I think.