Power plant tripped by capacitor explosion

[SA07]

Hi
Our power plant tripped by explosion of 1 capacitor in a capacitor bank. The latter is connected to a panel supplying 4 motors 690 Vac. All four motors stopped by under voltage on simocode.
Each stages of capacitors has fuses.
1.Are fuses gG/gl appropriate?
2.Can we replace with another type of fuse which reacts faster?

It is the first time we have an explosion of a capacitor since 2017,2018 after the installation.
All our substations are air cond.
Since we are a power plant exporting to the utility grid, the capacitor banks are used to reduce max MVA demand during start up.

3 Is it appropriate to switch off all capacitor banks during normal operation and then switch them on only during start up of power plant?

4. What is the usual lifetime of such capacitors?
Please see attached pictures.

Thanks

 

[RRaghunath]

I suppose the capacitor failure is thermal related.
Whenever all motors trip suddenly, the busbar voltage rises and affects the capacitors.
As you may be aware, capacitors are sensitive to overvoltage and when subjected to overvoltage frequently, could fail prematurely.
Power plant generates VARs as well as Watts. So, there is no concern of PF penalties from distribution company. Hence, I suppose you can switch-off these capacitors when power plant is running.
When power plant is down and being started up, these capacitors may be useful even for improving the bus voltage and hence good to keep connected.

 

[LionelHutz]

You have an under-voltage so what caused the initial trip which turned off the power causing that under-voltage? Your plant should have been able to ride through that fault by letting the fuses clear.

Over-voltage is the quickest way to damage a capacitor. Are there de-tuning reactors on these capacitors? It might have been harmonics that caused a voltage ring-up which then caused the failure.

I would turn the capacitors off if you don't need them when running. No point adding wear and tear to the capacitors as well as another possible failure point if they serve no purpose once you get the plant running.

 

[SA07]

Yes there are de-tune reactors on the capacitor bank

 

[LionelHutz]

Your big question then is - What is the fault current when a capacitor fails and how long will the fuses take to clear it?

 

[SA07]

Can we replace the gG/gl fuse with aR fuse or another type which is faster?

 

[bacon4life]

Power factor requirements are highly specific to each utility, so you may have to do some digging to make sure of the impacts for turning off the capacitor banks after starting your generator. Many distributed generators have capacitor banks in order to meet the requirements for having the generator provide voltage support to the grid.