Mis-connection and cable faults of batteries in parallel

[bernardgreen]

Old BT health and safety video regarding sealed lead acid batteries.

Five racks, each providing 54 Volt from series connected lead acid batteries,

 

[ericmark]

The same problems with nickel iron batteries used with milk tankers and buses, the current available is so much higher with nickel iron to lead acid.

I had to work in a battery room with lead acid batteries, and I put the gas detector on the top of a set of steps to get it high up, my boss walked in and saw it and said that should be on the ground, I said no looking for hydrogen which is lighter than air, he said hydrogen isn't a problem is it, my reply which I knew was wrong was have you not heard of a hydrogen bomb, oh yes he said, I did not point out not splitting atoms.

But the gases given off is a real problem with lead acid. Including hydrogen sulphide.

 

[SUNRAY]

Old BT health and safety video regarding sealed lead acid batteries.

Five racks, each providing 54 Volt from series connected lead acid batteries,

I reckon those guys only made the film as an excuse for having a great time.

I've been in an exchange when 2 bussbar shorts occurred:
1, Guy checking routiner pulse generator (motor driving a block of different shaped cams and contact springs) lifted cover off with screwdriver in one hand and tuning fork in the other. screwdriver pierced busbar insulation and tuning fork touched something above. Screwdriver, metal cover & tuning fork were welded together (but not to the busbar or earted metalwork) which fortunately blew the 125A suite fuse. The only real complaint was the suite included level 9 group selectors and there were 2x 999 calls in progress.

2, Contractor laid a piece of hardboard on the cable grid to kneel kneel on, using a small galvanised metal bucket full of mixed vermiculite, placed it beside him and when he moved the bucket slipped off the hardboard and landed between the main bussbars, damaging the insulation. The bucket vapourised depositing the wet vermiculite on test equipment below.

Both went with a big bang but only the second had the firework display.

 

[SUNRAY]

So I've had a silly PM asking why the bucket didn't blow a fuse, complete with a statement of poor circuit design? Even I won't admit w ho.

To explain the power installation in older exchanges and that one in particular:

There was a 50V open topped lead acid battery, each cell being appoximately 4x4x2.5ft HxWxL the full battery being ~60ft long that size battery will be circa 5000AH and at the 50V end will be a fuse of maybe 1000A (usually something up to ¼ of the AH capacity)
There was a second similar battery.
There was a suite of 'rectifiers' usually rated at 1000A with a matching fuse on the output and in a quantity to give at least 150% of peak current at the busy period and they automatically switch in as required.
In normal use both batteries and sufficient rectifiers would be connected directly to the bussbars which meander around the exchange.
That exchange had 4 rectifiers and at that time of day would have likely had 2 rectifiers running, one supplying the full 1000A and the other supplying close to a second 1000A.
Tha bussbars leading away from the battery/rectifier combination being a lamination of 6 12"x1" copper (45000mm²)

More usually each battery is arranged in 2 halves side by side but this example shows the pair in a straight line each side of the battery room, all dependant on the space available. I've known them to be distributed between different rooms and even floors.

So feeding the short circuit created by a bucket touching the bussbars are 2x1000A rectifiers and 2 batteries capable of maybe 200,000A, albeit limited by a pair of 1000A BS88 fuses. The touch of the poor bucket didn't stand a chance, it would have instantly blown a hole and as the bucket dropped down each new contact being another flash.

The installation I've tried to describe no longer exists in standard UK exchanges.