Voltage Monitoring Relays - what delay?

I suppose it wouldn't be against the letter of G98/99 to disconnect ordinary loads in a shorter times, especially for larger over-voltages (if leaving any embedded generation connected to the grid) - so I could still use a faster disconnection time to provide some protection to more sensitive loads,

Maybe not in the spirit of keeping the grid stable, but larger over-voltages I suspect are more likely due to a local LV faults rather than a wider grid situation - something approaching 400V L-N as a result of a broken PEN in LV distribution system seems much more likely than 400V appearing due to the HV network running at 170% normal voltage (where there are no distributed Ns to break or star connected loads, that might have produced similar a condition to a LV broken N). And disconnection due to a local LV fault is hardly going to affect wider grid stability.

   - Andy.

AJJewsbury said:

I suppose it wouldn't be against the letter of G98/99 to disconnect ordinary loads in a shorter times,

No, but it will affect grid stability if this approach is adopted en-masse.

EMC testing does include testing to cover voltage spikes, transitions, interruptions and flicker, to cover "short time" events, so I would be concerned whether products that need such disconnection actually conform to the essential requirements of legislation.

Worth also looking at BS EN 50160 which looks at the quality of public electricity supplies.

The EMC limits are a lot closer to the surge arrester case - certainly no big upset condition that is sustained for a time scale of whole seconds.

In terms of spikes,  not all kit with a CE mark needs to be tested anyway, but even if it was the longest single surge test in  IEC 61000-4-5 is the 700 microsecond one, and often mains inputs are only tested to the class 1 easy one of 500V for 50 microseconds.. Hold that voltage for ten times this duration and a lot of electronics will be dead.

The EFT (fast transients) test calls up bursts of 75 pulses of 50 nanosecond duration, spaced 100usec apart  with burst repeating 3 times a second, may also be tested at 500V or higher, but that is also a lot less energy than a sustained overvoltage long duration event.

Flicker 61000-3-3 is generally stepped voltage changes of less than 10%, and the test levels of the fluctuations are a lot less if if repeated  more than a few times per minute.


Y axis, "d" is the voltage droop or uptick, 10%, 1% or whatever, and the frequency in events per minute is the X axis.



Dips however are allowed to be quite severe, to 70% of mains voltage for up to 25 cycles at a time on a 50Hz system, 


In summary, nothing in an EMC test that includes all the possibly applicable IEC 61000 tests, verifies or assures any protection against significantly out of spec over-voltages (say 300v plus) on the mains that persist for more than,  at best, just under a millisecond, and for most domestic gear, probably more like 50 microseconds..
I'd not want to rely on the CE / UKCA mark alone to protect me ;-)
Mike.`

The EMC limits are a lot closer to the surge arrester case - certainly no big upset condition that is sustained for a time scale of whole seconds.

In terms of spikes,  not all kit with a CE mark needs to be tested anyway, but even if it was the longest single surge test in  IEC 61000-4-5 is the 700 microsecond one, and often mains inputs are only tested to the class 1 easy one of 500V for 50 microseconds.. Hold that voltage for ten times this duration and a lot of electronics will be dead.

The EFT (fast transients) test calls up bursts of 75 pulses of 50 nanosecond duration, spaced 100usec apart  with burst repeating 3 times a second, may also be tested at 500V or higher, but that is also a lot less energy than a sustained overvoltage long duration event.

Flicker 61000-3-3 is generally stepped voltage changes of less than 10%, and the test levels of the fluctuations are a lot less if if repeated  more than a few times per minute.


Y axis, "d" is the voltage droop or uptick, 10%, 1% or whatever, and the frequency in events per minute is the X axis.



Dips however are allowed to be quite severe, to 70% of mains voltage for up to 25 cycles at a time on a 50Hz system, 


In summary, nothing in an EMC test that includes all the possibly applicable IEC 61000 tests, verifies or assures any protection against significantly out of spec over-voltages (say 300v plus) on the mains that persist for more than,  at best, just under a millisecond, and for most domestic gear, probably more like 50 microseconds..
I'd not want to rely on the CE / UKCA mark alone to protect me ;-)
Mike.`