DCDB EARTH FAULT 1

[Raji2410]

HELLO SIR/MADAM,
IN OUR POWER PLANT IF ANY DC-SUPPLY IS EARTHED DUE ANY TO REASONS IN ONE PANEL, DUE TO THAT IT IS SHORTED +VE TO EARTH OR -VE TO EARTH VOLTAGE WILL GET REDUCED. SO DUE TO THIS WE HAVE TO CHECK ALL THE DCDB BOARD PANELS WERE FAULT HAPPEN AND IT IS TIME TAKING PROCESS.
I REQUEST YOU TOO ANY ADVANCE METHOD TO CHECK EARTH FAULT TO IDENTIFY EASILY IN PARTICULAR SECTION BECAUSE IN OUR PLANT USING EARTH FAULT KIT BUT WE HAVE CHECK EACH PANEL AND IT IS TIME CONSUMMING PROCESS.

KINDLY REPLY FOR ABOVE MENTIONED PROBLEM.

 

[RRaghunath]

DC system is critical for the safety of the plant and for that reason, the DC system is earthed through a high resistance and any earth fault is alarmed. The high resistance earthing allows continuity of power supply even when there is an earth fault. Any second fault if it happens on the other pole of the DC supply will be a positive-to-negative short and will cause one or more services to lose this critical power supply. This could be serious as it can cause production loss or even safety issues.
It is not possible to indicate the faulty feeder in this system and one is supposed to systematically switch off one by one feeder to locate the faulty feeder.
Easy is to pay attention to the panels where DC supply is wired to make sure there are maintained clean, doors are properly closed, wires are properly lugged and terminated (no wire strands are allowed to hang out) etc. Such steps will make the faults rare and save the trouble of locating the fault.
There are instruments available (such as 'Grouser') which can be used to locate the DC fault. You can browse them online and try.

R Raghunath

 

[Kiribanda]

Your DC system seems to be an "ISOLATED FROM GROUND" which is acceptable.
As a result of this ISOLATED configuration, during an earth fault ANYWHERE on the system,
you get +ve to earth and -ve to earth various voltages but finally you will find that
the addition of those are equal to your DC nominal voltage (125V or 250DC).
Therefore, in this isolated ground system, when there is an earth fault anywhere on the system,
you have no choice other than isolating the feeders on the DC panel board one by one to locate the faulty feeder.

The alternate method is to convert your system to a -ve earth or +ve earth system. In that case you have to have a properly
time/ current coordinated DC protection system so that ONLY THE FAULTY FEEDER or BRANCH CIRCUIT is isolated
during an earth fault which is not easy to implement.

But in the isolated DC system, only when there is a +ve to -ve direct short circuit only the protection will operate.

 

[sushilksk]

DC earth fault locator kits (based on low frequency injection) are avaiable, which does not require isolation to some extent. But it needs expert person to identify exact location.