DC voltage dip

[HighPotter]

We have a bank of lead acid batteries providing substation dc power.

Recently, during an event, we had a dip in our station power, which of course caused a dip on the input voltage to the charger.

At the exact same time the station power dipped, our DC voltage dipped from 134v to 78v, but for only 10 cycles, then recovered to full voltage.


Comments?

HP

 

[davidbeach]

No storage capacity left in the batteries, running only on the charger?

 

[itsmoked]

I would agree. Batteries toast?

 

[waross]

It sounds like batteries. Take a deep breath and turn the charger off for a few seconds. Be careful, we just had a discussion about batteries exploding when they're in bad shape and running on the charger.
yours

 

[ScottyUK]

Knackered batteries and a charger trying to recover its output voltage during the dip?

Was the dip longer than 10 cycles? What kind of charger is it: switchmode or thyristor? The switchmode types are usually more forgiving of input disturbances because they can react very quickly and typically have very broad input voltage ranges.

Invest in a load discharge test for your battery. A fault in a substation whose breakers have no tripping power could turn ugly very easily. If people argue over cost of the test and probably a new battery too, enquire whether their budget stretches to a new substation.


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I don't suffer from insanity. I enjoy it...

 

[HighPotter]

The AC dip was for slightly more then 50 cycles. The DC dip was only for 10 cycles.

The bank was just recently tested and all was good. It was not however discharge tested or load tested.

Have any of you heard of the term " Coup De Fouet "


HP

 

[itsmoked]

How can the bank have been tested if it wasn't at least load tested?

 

[waross]

Hi itsmoked.
Probably the insurance carrier told management that the batteries must be tested but did not specify the test procedure on the same page. Management issued a directive,
"Check the batteries but don't take too much time and don't take anything out of service."
I believe it's called "Checking the boxes."
I often don't know if I'm a cynic or a realist.
yours

 

[HighPotter]

When the batteries are only 3 years old, and its your ONLY bank, then strap and spG reading are the extent of testing.

HP

 

[waross]

Hello HighPotter
I apologise. I understand your restraints. Is it possible to turn off the battery charger and monitor the voltage for long enough to see if the voltage drop is excessive?
yours

 

[stevenal]

Number of banks should not affect the testing schedule. Criticality of the load should. I would suggest cell and interconnection resistance or impedance testing, and IR scans. 20 year rated VRLA batteries have been known to die in three years, although your spg comment suggests you have flooded cells. See IEEE standards for recommended maintenance and intervals. My French is long gone, please explain the term.

 

[itsmoked]

Certainly you should be able to turn off the charger and watch the results.. Otherwise disaster WILL occur. And if you can do this, then you should be able to hang some sort of load out there to really test the capacity. Otherwise you're really flying blind.