Wastewater Treatment Plant

In order to confirm our proposal, two connection situations were tested. The test results show that, the SFCs removing the grounding leads are intact, but the SFCs keeping grounding lead connected are failed.

 

 

Solution and Alternatives

 

 

It was recommended to remove the SFC grounding lead, or connect this grounding port to remote grounding （an independent grounding system）to avoid the voltage surge impact from grounding point.

 

 

Decision and Recommendation

 

 

The plant accepted the proposal of disconnect the SFC grounding lead and did not create any operation problem.

 

 

Results

 

 

After removing the SFC’s grounding lead, the failure caused by voltage surge didn’t happen.

 

 

Room for Improvement

 

 

In order to keep the neutral voltage of delta connected motors, SFC’s grounding port can connect to a remote grounding.

To avoid SFC’s damage during voltage dip, the following items worth mentioning:

• When breaker opens because of voltage dip, the restoration sequence should be: close the high voltage side breaker first, after system stable, then close SFC’s breaker.
• This plant is underground distribution system, the surge voltage frequency will be very high, SFCs should have the capability to withstand this voltage.