I've noticed this week that the grid frequency has been fluctuating between 49.6 and 50.26 Hz. Has anyone else observed the same in the Pretoria area?

This is just a short period of today.

Frequency is a Eskom grid feature, not just localized to Pretoria.

39 minutes ago, frivan said:

Frequency is a Eskom grid feature, not just localized to Pretoria.

Yeah it's interesting. The concern is mostly the min/max values, as it makes inverters disconnect. It does seem as though the grid is barely holding on, and the solar exporting is what is keeping it up.

Should we expect exactly 50hz? I don't track the frequency, but usually it's 50.something.

The settings on my inverter (factory, not modified) are to accept 47 to 52.

The grid frequency is 50hz and could vary up or down by 0.5hz.

1 hour ago, TaliaB said:

The grid frequency is 50hz and could vary up or down by 0.5hz.

Is this much deviation as per the graph, normal in such a short timespan? Asking out of curiosity, or do you think that people exporting to the grid is playing a role?

Good morning

This is normal

Cape Town yesterday in your timeframe

the frequency change in the graph is exacerbated by the short time span,

if we increase the timespan it is within the "normal" distribution

cheers

Edited March 5, 20251 yr by ZS1SCI
grammar slammer

Also from Pretoria for similar timeframe

Kathu Northern Cape

3 hours ago, TaliaB said:

The grid frequency is 50hz and could vary up or down by 0.5hz.

So 49.5 to 50.5 - which is what the various graphs presented here are showing. They just look scary because the Y axis is actually in small increments.

It's usually not just the frequency - same also with the grid voltage.

Which is exactly why I have a smart breaker in my system to manually disconnect from the grid when I don't need it. So that my house gets 'clean' power and does not follow the Eskom mood swings...

41 minutes ago, wolfandy said:

It's usually not just the frequency - same also with the grid voltage.

Which is exactly why I have a smart breaker in my system to manually disconnect from the grid when I don't need it. So that my house gets 'clean' power and does not follow the Eskom mood swings...

Which smart breaker do you use and is it on your main incoming Eskom / municipal feed?

46 minutes ago, wolfandy said:

It's usually not just the frequency - same also with the grid voltage.

Which is exactly why I have a smart breaker in my system to manually disconnect from the grid when I don't need it. So that my house gets 'clean' power and does not follow the Eskom mood swings...

This is particularly the reason I started looking at the frequency and voltage as well. My voltage reached 253v before inverter disconnected, blew some older equipments fuses that were rated at 253 (perhaps already degraded). After which, the inverter started complaining about grid over frequency.

Edited March 5, 20251 yr by Pho3niX90

Some insight between grid frequency and grid voltage:

A.Frequency Control (System-Wide)

Target: 50 Hz ± 0.2 Hz (normally).

Method: Eskom balances power generation with demand in real time.

How It Works:

If frequency drops (e.g., 49.5 Hz) → There’s more demand than supply → Eskom increases generation (or sheds load).

If frequency rises (e.g., 50.5 Hz) → There’s more supply than demand → Eskom reduces generation.

Control Mechanisms:

1. Primary Frequency Response (Seconds)

Power stations automatically adjust their output when frequency changes.

Example: If frequency drops, generators increase power to stabilize it.

2. Secondary Control (Minutes)

Eskom’s National Control Centre adjusts generator outputs to bring frequency back to 50 Hz.

3. Load Shedding (Last Resort)

If demand still exceeds supply, Eskom cuts power to some areas (load shedding) to prevent system collapse.

B. Voltage Control (Local & Regional)

Target: ±10% of nominal voltage (e.g., 230V ± 23V).

Method: Voltage is managed using transformers, capacitor banks, and reactive power control.

How It Works:

If voltage drops (due to high demand or long transmission lines):

Eskom boosts voltage using transformer tap changers or reactive power compensation.

Large customers may be asked to reduce reactive power (e.g., by improving power factor).

If voltage rises (due to low demand or excess generation):

Eskom lowers voltage using transformer tap changers.

Reactive power compensation (like capacitor banks) may be adjusted.

Edited March 5, 20251 yr by TaliaB

22 hours ago, wolfandy said:

It's usually not just the frequency - same also with the grid voltage.

Which is exactly why I have a smart breaker in my system to manually disconnect from the grid when I don't need it. So that my house gets 'clean' power and does not follow the Eskom mood swings...

The numbers that @TaliaB gives allow a 1% movement in frequency either way.

Voltage is nominally 230V, but on a grid where demand and supply are in a constant state of flux you will never have that nominal value at all times. There is also an allowance made for deviation from the standard. So we allow 10% either way.

Your inverter should catch any over/under voltage and disconnect..

19 hours ago, TaliaB said:

Some insight between grid frequency and grid voltage:

A.Frequency Control (System-Wide)

Target: 50 Hz ± 0.2 Hz (normally).

Method: Eskom balances power generation with demand in real time.

How It Works:

If frequency drops (e.g., 49.5 Hz) → There’s more demand than supply → Eskom increases generation (or sheds load).

If frequency rises (e.g., 50.5 Hz) → There’s more supply than demand → Eskom reduces generation.

Control Mechanisms:

1. Primary Frequency Response (Seconds)

Power stations automatically adjust their output when frequency changes.

Example: If frequency drops, generators increase power to stabilize it.

2. Secondary Control (Minutes)

Eskom’s National Control Centre adjusts generator outputs to bring frequency back to 50 Hz.

3. Load Shedding (Last Resort)

If demand still exceeds supply, Eskom cuts power to some areas (load shedding) to prevent system collapse.

B. Voltage Control (Local & Regional)

Target: ±10% of nominal voltage (e.g., 230V ± 23V).

Method: Voltage is managed using transformers, capacitor banks, and reactive power control.

How It Works:

If voltage drops (due to high demand or long transmission lines):

Eskom boosts voltage using transformer tap changers or reactive power compensation.

Large customers may be asked to reduce reactive power (e.g., by improving power factor).

If voltage rises (due to low demand or excess generation):

Eskom lowers voltage using transformer tap changers.

Reactive power compensation (like capacitor banks) may be adjusted.

That was some really good information. Sent me down a rabbit whole of looking up videos of what each does.

In short it seems pushing to the grid for me is out of the question, since it raises the voltage too much, will just have the batteries do the heavy lifting.

On 2025/03/04 at 6:27 PM, frivan said:

Frequency is a Eskom grid feature, not just localized to Pretoria.

I hope those that are unsure read this a few times. The Eskom grid runs at the same frequency as a few generators cannot pull some in a certain area lower or higher. Further for safety reasons if the frequency had to move below 49Hz by global rules the generation have to shut down and it will cause a total collapse.

No supply around 49-51Hz should cause any problems or keep you awake. As @Bobster. indicated the inverter has settings at which level is should disconnect.

Lastly the current amount of PV installed in SA also cannot move the grid frequency.

The above is my understanding and would gladly be corrected😀

"Clean" electricity has been mentioned. Also blown fuses.

Doesn't the inverter take the punch and provide your house with "clean" electricity? The grid can bounce up and down, your inverter should manage this and provide a stable connection to your house.

3 hours ago, Scorp007 said:

I hope those that are unsure read this a few times. The Eskom grid runs at the same frequency as a few generators cannot pull some in a certain area lower or higher. Further for safety reasons if the frequency had to move below 49Hz by global rules the generation have to shut down and it will cause a total collapse.

No supply around 49-51Hz should cause any problems or keep you awake. As @Bobster. indicated the inverter has settings at which level is should disconnect.

Lastly the current amount of PV installed in SA also cannot move the grid frequency.

The above is my understanding and would gladly be corrected😀

Last I read, private solar makes is around 45Mw, if 10% feeds back to eskom, wouldn't that push the frequency up? Even though it's sending at the same frequency, there is more generation than demand at this point?

27 minutes ago, Pho3niX90 said:

Last I read, private solar makes is around 45Mw, if 10% feeds back to eskom, wouldn't that push the frequency up? Even though it's sending at the same frequency, there is more generation than demand at this point?

That would be 4.5MW. I don't think that makes a lot of difference over the South African grid.

Inverters on the SANS list will all sync with the grid voltage and frequency. EG if the voltage where I live is 240V and grid frequency is 50.1 Hz, then that's what my invert puts out - even inside the house.

@McGuywer ,

No, the Inverter doesn't take the "punch", it is designed to follow the grid (i.e. keeps in sync).

Quickly plotted Grid vs Inverter Output Voltages to confirm this.

The "clean" part is also not true, if the grid is available.

Yes, the inverter's output does become "clean", as in 230V @ 50Hz, the moment there's a grid failure.

Here below an illustration of how the inverter goes to exactly 50Hz & 230V during the time of Grid outage.

You can clearly how the frequency stabilizes when Inverter is disconnected from Eskom Grid.

Should have added a Inverter Frequency plot. Just ran out of space!

1 minute ago, Bobster. said:

That would be 4.5MW. I don't think that makes a lot of difference over the South African grid.

I just checked. There are about 4000 homes in my property. Most of them have a 60A main breaker. 4.5MW is equivalenmt to 326 of those homes running flat out.

OK... those houses are unlikely to be running flat out. Let's assume 6kW per home. That's 750 homes. At 3kW it's 1500, still not even half the suburb.

I don't think that 4.5MW, dispersed across the country, is going to make a big difference.

4 minutes ago, Sidewinder said:

No, the Inverter doesn't take the "punch", it is designed to follow the grid (i.e. keeps in sync).

It does stay in sync, within limits. We have had instances of very low voltage in my neck of the woods. LIke down in the 180s. My inverter disconnects and waits for the voltage to go up again.

Well.... depending on settings. That's how it behaves with the safety code set to SA 230V. If I put in the default 230V mode it will keep on following the grid voltage, which I'm not sure is good for it.

On the SA 230V code it will also disconnect on a high voltage.

40 minutes ago, Pho3niX90 said:

Last I read, private solar makes is around 45Mw, if 10% feeds back to eskom, wouldn't that push the frequency up? Even though it's sending at the same frequency, there is more generation than demand at this point?

Correction. Had to do some searches.

Eskom generation total = 44000 Mw:
Coal-Fired Stations: approximately 37,698 MW.
Nuclear Power: 1,860 MW
Renewable and Hydroelectric: Drakensberg Pumped Storage Scheme (1,000 MW) and the Ingula Pumped Storage Scheme (1,332 MW).

Private solar (October 2024) = 8970 Mw:

I would have thought, that in instances of cloud coverage etc, the instant power fed back into the grid would increase the Hz. But my understanding of this is very limited

7 minutes ago, Bobster. said:

I just checked. There are about 4000 homes in my property. Most of them have a 60A main breaker. 4.5MW is equivalenmt to 326 of those homes running flat out.

OK... those houses are unlikely to be running flat out. Let's assume 6kW per home. That's 750 homes. At 3kW it's 1500, still not even half the suburb.

I don't think that 4.5MW, dispersed across the country, is going to make a big difference.

"There are about 4000 homes in my property"

@Bobster. How big is you property?😁