Power Frequency Variations

[nightfox1925]

An electrical governing body in our location is recommending to increase the normal operating system frequency limit from +/- 0.3 Hz to +/- 0.5 Hz. This means that the generators will need to operate normally between 59.5 to 60.5 Hz and the System Operator will not intervene if the system frequency is within these limits.

If the recommendation is approved, it will be implemented as a grid frequency variation limits requirement.

In this regard, i would like to solicit your comments regarding the impact on the existing machines. As I understand, NEMA motors may run within +/-5% at rated voltage.

Furthermore, are there supposed to be a steady state frequency and transient state frequency limits?

Any technical links that would be of reference will be appreciated.

GO PLACIDLY, AMIDST THE NOISE AND HASTE-Desiderata

 

[Zogzog]

Its not the machines that care its the electronics, anything that uses a clock circuit. Where is the location you mentioned? I believe in the US the limit is +/- 0.1 Hz.

 

[gepman]

I don't think that it will affect your driven machines as much as any generators that you have. All of our generators tied to the grid would have tripped if we were off frequency by that much for any period of time. You may have to adjust all of 81 functions.

 

[itsmoked]

What's the motivation for this increase?

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[dpc]

Wind turbines, maybe? They are horrible when it comes to frequency control.

I agree with gepman, at plus/minus 0.5 Hz, the biggest concern would be under/over frequency relays and maybe governor settings, if you have anything running isochronous.

I suppose any highly speed-sensitive machines running from synchronous motors could be a concern as well.

 

[jraef]

And by the way, NEMA motor design secs allow +- 10% on voltage. +-5% is better of course.

 

[byrdj]

A 0.5 Hz swing would cause a 17% governor swing assuming 5% regulation (the normal for Steam Turbines in US)

 

[waross]

I have a lot of experience with diesel standby sets. They typically use a droop governor with a 3% speed variation. 61.8 Hz unloaded, pulled down to 60 Hz at full load. The only problems I have encountered have been with the odd UPS that wants to see exactly 60 Hz and beeps constantly. Most UPS's are quite happy with the diesel power. The sets are sized for A/C starting and normally run at 61 Hz or more.
The clocks will all be flashing to indicate a power failure and will be reset when the normal power returns.
In conclusion I don't see a potential problem with connected equipment with an increase to +/- 0.5 Hz variation in frequency.
As for clocks, the present 0.3 Hz variation would result in a clock error of over 7 minutes a day, so I imagine that whatever system is presently used to balance over frequency against under frequency will continue to function with the new standard.
In the old days, of flyball governors, the word would be,
"We are quite a few cycles behind today. We are running "Balls to the walls" until we catch up."

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[gepman]

So that is where that saying came from!

 

[Compositepro]

You have to define a measurement period along with the freaquency tolerance. Power grids will put out the correct number of cycles per day to keep the clocks accurate.

 

[tajin23]

Is still in use making zero freq error at the end of the day?.
Seems like you are widened the band for frequency contribution, which will allow poor regulation machines to contribute to the system, in some cases the problem is also time response not just wide the freq band, as you said wind power plants could be the reason, it would required as already said review the adjustments for under/over frequency relays.

 

[nightfox1925]

Thanks for all the comments...I finally got a tip that this may be because of the emergence of several wind turbine generators interconnected to the grid on temporary basis during specific time of the day.

GO PLACIDLY, AMIDST THE NOISE AND HASTE-Desiderata

 

[dpc]

Wind turbines are "temporary" almost by definition.