[paulmac_ie]

The company I work for provides Demand Response to the Irish grid operator.

In cases like this, our systems would detect the frequency deviation, and shut off loads within 100 milliseonds to reduce the demand on the grid. This helps in cases where demand is greater than supply.

The entire system is automated - the required time frames are so quick that you don't have time for humans to be involved. By the time we're aware that an event has occurred, we've already reduced demand on the grid.

Handling high frequency events where supply is greater than demand is tricker. Sites that have long running generation can be instructed to shut down their generation, but large-scale batteries are probably the best solution in these cases. They can be switched quickly to start charging (if they have spare capacity).

As you've identified, one potential issue is that you can end up over-responding to the event and move from a low frequency event to a high frequency event.

The way we do in in Ireland is that our response is proportional to the frequency nadir. Not everything is tripped off at the same time.

As other posters have noted, the actual frequency deviations that occurred are not that big. 49.7 Hz is not that low compared to normal grid frequency. In fact, some of our systems wouldn't even activate at this level. They would see it, but wouldn't trip off any loads.

[xoob]

I’m curious about this. What kinds of load is your company is running? How do you take them offline and online so quickly without affecting production or leading to long restart cycles?

[paulmac_ie]

We control a mixture of loads, but for Fast Frequency Response (FFR), it's mainly compressor/ motors, with the occassional mains breaker thrown in. Large cement factories, refrigeration companies etc.

As for how we control them so quickly, it's usually via a direct connection to a breaker of some description, or where there's a SCADA system that can trip out the loads in the required time frames. Before the site can participate in these services, we perform extensive testing to ensure they meet the required time constraints.

Our system monitors the grid voltage and current at 8 kHz, and we down sample that to 50 Hz (average grid frequency). We can detect a frequency event across 3 phases within 60 milliseconds. (We check all three phases for multiple cycles to reduce any false positives.)

When we trip out the loads, production stops. We'll notify the client why their loads have been turned off, but the SMS message will usually arrive a few seconds after the trip.

The clients that participate in these services get paid quite well to make their loads available and they're aware of the process. They agree to turn off demand without notice when there's a frequency event.

It's not suitable for every site. We work quite a lot with pharma companies for "regular" demand response, but very few can do FFR. Shutting down a pharma plant with no notice can cost a lot of money in wasted product and down time as they clear the wasted product off the production lines.