Curious about Automatic Transfer Switch operation

[silvarblade]

Hi

I wanted to install a Grid Tied solar system in my place. However, I curious as to how the ATS works from a technical point of view. The inverter I am looking at takes input from solar panels and the grid with a connection to a battery as well. It shifts from solar power etc when there is not enough power being generated.

Since I don't plan to add the maximum solar capacity to the system at the moment, I was curious as to how does it determine whether the power is 'enough'. Because as far as my understanding goes (and I might be wrong here), the solar charger would maintain a battery charging voltage as long as the solar panels output a voltage within its input range and regulate the current as the voltage increases/decreases thus changing the available power.

Does the transfer mechanism (typically speaking) just look at the voltage (and thus leaving the responsibility of taking care that the load doesnt exceed the power generated to me as the user) or does it actively perform power measurement and performs the switch?

 

[Nigel Goodwin]

Assuming you are selling your surplus to the grid, there's no switching involved - your panels simply feed the grid.

If you're not feeding the grid, and it switches, presumably it will be syncronised to the grid, and do so at the zero crossing point.

 

[silvarblade]

Ah ok. It does sell to the grid so I guess it the first case you pointed. I always thought the switching took place.

Thanks for the clarification Nigel!

 

[KeepItSimpleStupid]

I think how it works is basically the same way master/slave DC supplies work with a twist.

The grid-tie inverter first tracks the voltage and it inserts the inverter output as a current. In order to do that the voltage limit has to be slightly higher than the grid voltage.

When the grid goes away, there is no reference.

An ATC first starts with a mechanically interlocked relay. The safety starts there. It's not physically possible for generator and grid to be connected at the same time.


Let's look at restart first. You need a power OK signal. So you;ll be looking at frequency, value and stability (How long has it been OK). Once it transfers back to the utility, the generator enters a cool down phase and then powers down.

For transfer to generator, you need a power not OK signal, so you do almost the same, but with a warm-up period.

You have to implement testing with or without transfer on some schedule.

Alarms: Oil level, gas level, battery, oil and water temperature, start sequence failed. You have to look at the generator electrically too.

 

[shortbus=]

Let's look at restart first. You need a power OK signal. So you;ll be looking at frequency, value and stability (How long has it been OK). Once it transfers back to the utility, the generator enters a cool down phase and then powers down.

For transfer to generator, you need a power not OK signal, so you do almost the same, but with a warm-up period.

You have to implement testing with or without transfer on some schedule.

Alarms: Oil level, gas level, battery, oil and water temperature, start sequence failed. You have to look at the generator electrically too.

For a solar system?

 

[KeepItSimpleStupid]

For a solar system?

Got me there. Never saw the word solar.

 

[EmmaSim]

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