I don't understand how we get a surge. You'd think the power would sag.

But anyway, power surges after supply is reinstated seem to be a thing. So what sort of devices can get damaged? 

As I understand it, everything on my backed up circuits will be protected because the inverter doesn't reconnect immediately, but what about a pool pump? A washing machine that is plugged in but not in use?

2 hours ago, Bobster. said:

I don't understand how we get a surge. You'd think the power would sag.

But anyway, power surges after supply is reinstated seem to be a thing. So what sort of devices can get damaged? 

As I understand it, everything on my backed up circuits will be protected because the inverter doesn't reconnect immediately, but what about a pool pump? A washing machine that is plugged in but not in use?

It is known that gadgets with a digital display that is always on like a microwave as well as the modern fridges are at risk. When the grid comes on my induction plates give a sound. So does my convection oven. The TV and other hifi items that are on standby and not off. For low power gadgets up to 1kW which is my imposed limit one can have a Sonoff which is set to remain off when power returns and one has to switch them on when power returns. I just switched on my outside lights via Sonoff as they remained off after my LS that ended 18h20. They are now on a small inverter for LS during the night. 

3 hours ago, Bobster. said:

I don't understand how we get a surge. You'd think the power would sag

Hang on! The VOLTAGE drops. So to get the same power, devices will try to pull more current.

Is that it? 

That sound you can hear may be a penny dropping. 

Transformers have tappings that can be adjusted to compensate for losses as well as overloading. So in a perfect world it would be set for 230v because there is no overloading etc. But in our world all transformers are overloaded and the startup voltages would be above 230v to compensate for this - so as the transformers start up the volts are above 230v untill the demand stabilises.

Watch the sparks on online videos to see how hazardous switching on transfromers is - well designed systems use remote switching.

I trip my db main breaker when the power goes off - but I’m retired and at home most of the time.

1 hour ago, Johandup said:

Transformers have tappings that can be adjusted to compensate for losses as well as overloading. So in a perfect world it would be set for 230v because there is no overloading etc. But in our world all transformers are overloaded and the startup voltages would be above 230v to compensate for this - so as the transformers start up the volts are above 230v untill the demand stabilises.

Watch the sparks on online videos to see how hazardous switching on transfromers is - well designed systems use remote switching.

I trip my db main breaker when the power goes off - but I’m retired and at home most of the time.

I do see it differently. During LS the load is lower and voltage will rise. TRFRs can be tapped lower to keep voltage at 230. After LS the voltage would be lower and not higher until they are tapped back. 

Further even if TRFRs are on the wrong tap would not be the sole reason to give surges that damage equipment. There are other main reasons for the surges causing damage. These are specific to the local network feeding consumers. 

1 minute ago, Scorp007 said:

until they are tapped back. 

This is a manual process that involves a lot of work and safety procedures.

13 minutes ago, Scorp007 said:

I do see it differently. During LS the load is lower and voltage will rise. TRFRs can be tapped lower to keep voltage at 230. After LS the voltage would be lower and not higher until they are tapped back. 

Further even if TRFRs are on the wrong tap would not be the sole reason to give surges that damage equipment. There are other main reasons for the surges causing damage. These are specific to the local network feeding consumers. 

You are right but the problem is that in our towns the distribution transformers in our minisubs don't have automatic tap changers, commonly known as  on load tap changers, they are all manual taps, so there is no way that the output voltage can be controlled, only in the big substation usually the ones receiving power from EISHKOM have transformers with on load tap changers.

Edited December 8, 20223 yr by Antonio de Sa

It is cheap to install surge protection inside a db. The value of home contents justify this protection.

11 minutes ago, Antonio de Sa said:

our towns the distribution transformers

In my town I suspect most of the earthing copper wire in the minisubs (which are never locked anymore) is stolen so the earth leakage system is suspect of you depend on this.
Santam has just notified us that they are no longer covering “surge damage due to loadshedding” because of high claims.

10 minutes ago, Johandup said:

It is cheap to install surge protection inside a db. The value of home contents justify this protection.

In my town I suspect most of the earthing copper wire in the minisubs (which are never locked anymore) is stolen so the earth leakage system is suspect of you depend on this.
Santam has just notified us that they are no longer covering “surge damage due to loadshedding” because of high claims.

Remember that the earth leakage is in your DB, there is no earth leakage on the minisubs however, as you say the best is to install a surge protection device in your on DB.

On the minisub transformers are usually a type DYN, the D side is the primary winding usually 11 KV and the Y windind the LV side is 420 V the neutral of the Y winding is connected to earth.

Edited December 8, 20223 yr by Antonio de Sa

39 minutes ago, Johandup said:

This is a manual process that involves a lot of work and safety procedures.

you are 100% right, to change the transformer tapping in our minisubs one would have to switch the 11 KV incomer off, they cannot be changed on load.