How to protect against frequent breakdown of soft starters at a water pumping station?

[SA07]

Hi
We have a pumping station with the following pumps supplied by soft starters. We noticed frequent breakdown of soft starters. The station is supplied by the utility grid 22 kV through a 22kV/400 V transformer. There are frequent faults on this 22 kV and we have no control on it. It seems sometimes we have 1 phase missing due to fuse blown off.
What protection equipment can we install to protect our soft starters?

pump borehole 110 kW : soft starter
pump 110 kW : soft starter
pump borehole 45 kW: star delta
pump 75 kW : star delta

 

[LionelHutz]

Give details on the soft-starter failures?

FYI, any good soft-starter will protect against a phase loss or phase unbalance without extra external equipment.

 

[TugboatEng]

Who buys soft staters anymore? A VFD can do everything a soft stater can and so much more. It eliminates the need for bypass relays which is the most likely failure in your soft stater from the conditions you have described. The VFD puts less stress on your grid and may reduce grid failures. And if you size it correctly, you can keep your motor running even when single phased. The demand for soft staters is dwindling to the point that they actually cost more than a VFD in many cases.

 

[waross]

Who buys soft staters anymore?

People on a budget when the plant was originally built.

For an existing plant, try adding phase loss relays.
The back EMF the motor is pushing back to the open phase may be disturbing the SS..

 

[TugboatEng]

From what I have seen, a conventional soft stater with a bypass relay requires an additional contactor for tripping in the event of a fault because the bypass relay can be damaged if opened while passing currents less than the motor nameplate rating.

As for price, I understand that soft staters used to be less expensive. So were magnetic contactors and autotransformers. That's changed.

But let's also look for improvement. If there is a regular failure it's time to stop doing what you always so and make an evaluation. If OP gets single phased regularly, a VFD will allow the OP to continue operations during the single phase event. There will be some creativity required on the control circuit side, maybe.

 

[SA07]

We installed a new borehole pump + new VSD last year. Both broke down after only a few months of operation. It seems VSD does not work well with borehole pump which must be started < 3 s. We have switched to soft starter.
Star -delta also creates shock in water pipe.

 

[waross]

VSD does not work well with borehole pump

This configuration is very common in SAGD sites.
However either a sign wave filter or an isolating transformer must be used.
The transformer is on the output of the VFD.
I have seen sites where both methods are used for different wells.
The distance to the pump in a SAGD well may be many times the typical distance in a water well.
A SAGD well will turn horizontal at hard bottom and may then continue for several kilometers.