DC For emergency lube oil pump in steam turbine

[sparky1976]

Hi,

I work in Power Plant that its sister company has steam turbine breakdown caused by failure of DC emergency during black out,

We've bid to replace the battery system, Since the supplier or battery manufacturer trying to sell us their product so I feel their "technical input" is somewhat bias.

We thinking of having additinal DC system as back up during black out if one of the steam turbine DC lube oil fail it will swicth over to back up DC system.

We might go to some company like Alber for consultation, but I would like to hear experince in this forum about VLA (which I think still the best choice, but we have room restriction), AGM VRLA and GEL VRLA.

Thanks
Yamin

 

[ScottyUK]

In this size of battery and for a critical application I would not consider anything but vented lead-acid. I would expect the bank to be approximately 1000AH at 120V or 500AH at 240V for a typical turbine battery, but obviously that will depend on the size of turbine. My estimate is against a fairly large machine of about 350MVA. Vented Ni-Cad is technically available but likely to be prohibitive on cost at that size. Dual battery strings are a good solution if you have the space and can convince the customer that the additional cost is justified. The best time to justify the additional cost is after a turbine wreck!

VLA maintenance is essential if you expect your battery to be available when it is needed. What caused the failure of the battery?


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Sometimes I only open my mouth to swap feet...

 

[sparky1976]

Scotty,

Thanks,

The battery that fail is 4 years old, after sending to a company that do battery autopsy it was dry out and internal corrosion problem not sulphation, the battery is VRLA GEL tubular plate. the size is 1800 Ah, 2V/cell, 60 cell.

On your reply you said "dual battery strings are good solution" you mean its better I purchase 2 banks of battery (each 60 cells), connect the 60 cell banks in paralel because the battery charger is oversize and could charge both battery.

Dis some one could tell me if theres a emergency lube oil pump for steam turbine run by residual steam from boiler during blackout ?

 

[GTstartup]

A back up battery bank for a back up pump is a bit unusual. The most common back up for this would be a diesel gen set. Which, at least could backup some other equipment as well.

I think a better approach would be to devise a scheme to periodically prove your battery. Granted, on a base loaded plant this may be difficult. However, you could devise a scheme where your pump is started while the charger is disconnected thereby proving at least you have a battery intact (up to that point)

 

[oldfieldguy]

I agree with ScottyUK--

Flooded-cell vented battery bank is the way to go.

Couple that with observation and maintenance by a knowledgeable work group, and you have the makings of a much more reliable installation.

One of my former clients changed to VRLA for several remote metalclad outdoor substations based on the idea that they require less maintenance. After a couple of spectacular events where the batteries failed to provide trip ower to clear faults, we did a quick load test of twenty banks and found about half which would not perform to a minimum expectation, much less to manufacturer ratings.

The problem for this guy was that his substations were subject to high ambient temperatures and the VRLA cell's life is cut drastically short by elevated temperatures. He went back to flooded cell banks.

old field guy

 

[GTstartup]

The question isn't what's the best type of battery(please correct me if I'm wrong). The question is whether a parallel battery bank to back up the primary bank is necessary. In other words, a backup to the backup. I've never see this designed into a plant from conception so I am inclined to believe it's overkill. Better to come up with a way to test your existing battery.

Actually what the OP described also happened to me once. A plant with 4 units inadvertently disconnected from the grid at the switchyard. With no way to resynch we had to shut the units down. The last unit coming down "in the dark" as we say. After the last unit coasted down safely on DC emergency pumps we noticed that the second to last unit came off turning gear. Lucky it wasnt the last unit or bearings goodbye. 4 to 1 shot, we got lucky. The end result was a better battery testing program for the plant.

 

[rcw retired EE]

We have a current client who demands VRLA batteries on all power plant batteries including a 450 MVA steam turbine lube oil. I could not dissuade him. His company has not had a known problem with the VRLA for over 10 years. (Good luck?). Your reports are scaring me.

I have never seen a battery back up for DC LO pump battery. Two battery banks in parallel probably won't help unless they can be isolated to prevent a common failure, then the switching system gets too complicated and increases the chances of a failure.

Several turbine designs have mechnical shaft driven pumps or run down tanks, but usaully on smaller units < 10 MW.

A diesel generator backing up the AC LO pump is a good alternative, but it may not get running in time.

One of our smaller installations had a gasoline driven, manually started lube oil pump mounted outside the control room. It was more for extended black plant turning gear operation than for emergency run down.

Most turbine control systems have a DC LO pump test feature that drains the oil from the pressure switch and auto starts the back up pumps. This could be used as GT Startup suggested to prove the system on line with the charger off.

I've only seen four turbine failures due to no DC lube oil on a plant trip. Most were from poor maintenance of battery systems- a loose battery terminal connection melting, a bad charger ignored, and poor maintenance on the auto start pressure switch. Worst one was the plant with the PLC operated controls they had retrofitted on an old turbine. The DC lube oil start was done by the PLC, which required AC power. Three bearing and shaft rebuilds later, they finally took our advice and changed to hard wired, fail safe systems where the pump started on AC power failure. I don't knwo if they ever looked at their batteries?

 

[itsmoked]

Seems to me if a plant cannot properly test and maintain one bank two is an expensive joke. In fact you will end up with even less maintenance because; "ahh if one fails there's always the other" (Spoken like that evil skipper in the James Bond Movie after the guy falls in and he sez "ahh the sharks have him, lets go..")

yamin; I think running either an oil pump or generator from steam that is capable of providing for the lube makes a great bit of sense. There must be some small robust turbines. Heck, steam locomotives all had steam powered generators they were smaller than a five gallon pail.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[ScottyUK]

Multiple battery strings are fairly common in the UPS world where either a single string simply isn't big enough, or especially with VRLA's, where a cell failure is a realistic possibility and dropping the load isn't acceptable.

We have been having some terrible problems with VLA cells from Hawker suffering casing ruptures down the corners of the cells. The cells are almost new, the maintenance has been good, and there is no sign of plate expansion. We believe it is a manufacturing defect, but the manufacturer has closed up shop and we are on our own now. 'Expensive' is one way to describe the problem!

Maintenance and testing is the key as others have said. In our case a float switch in the battery enclosure to detect acid leakage might help too!

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Sometimes I only open my mouth to swap feet...

 

[sparky1976]

guys dont get me wrong, we do Monthly maintenance on the battery banks, the failed battery was tested about 3 weeks before black out and fails. Weekly run emrg LO pump, and 2 yearly do load bank test with individual cell recorded

Seems VLA is the best choice, I will try to squeeze the electrical room and make well ventilated battery room for VLA.

Before that I might consult Alber or Midtronic expert, since its very serious decision.

Thanks for the input,

yamin