Help, I have zero battery experience and limited switchgear experience. I have a lineup of 5kV switchgear, I need to design a battery system to switch the coils in the switchgear when the utility is down. I haven't had any luck tracking down the load of the coils. Does anyone have an idea of how much load is in a section of switchgear? Is there a method to determine how long I need these batteries to support the load?
Battery Sizing
- Thread starter 81025
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ron
Senior Member
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- New York, 40.7514,-73.9925
What do you mean when you say switch the coils.
Battery run time is a design decision and I do not believe is covered by the NEC.
Battery run time is a design decision and I do not believe is covered by the NEC.
petersonra
Senior Member
- Location
- Northern illinois
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- engineer
Re: Battery Sizing
if the power goes off, why do you need to keep the coils energized?
81025 said:
if the power goes off, why do you need to keep the coils energized?
jtester
Senior Member
- Location
- Las Cruces N.M.
I worked for electric utilities for years, and we had batteries to switch substation breakers during an outage. They were large banks, often dozens of lead acid cells the size of a box of cereal.
I don't know much about designing that system, but I'd look in the substation field for reference.
Jim T
I don't know much about designing that system, but I'd look in the substation field for reference.
Jim T
rcwilson
Senior Member
- Location
- Redmond, WA
Most switchgear suppliers can come up with the amps needed for a breaker close coil, trip coil, indicating lights, spring charging motors and other devices. Add any continuous loads such as indicating lights, protective relay and metering power supplies, PLC communications devices or control relays. This will give you a list of current draw per device.
The engineer, owner or designer has to decide how long the DC system is supposed to supply power when AC is down and what is supposed to happen at the beginning, during and at the end of the outage.
A typical scenario is: Trip all breakers at start of outage, maintain 300 watts of continuous load for 24 hours and still have enough battery power to close, trip and close "x" breakers to return power. (Make sure protection and tripping power is available when AC returns. The breaker(s) might have to trip right away if there is a problem.) Remember, when most breakers trip or close, their spring charging motors run to recharge the operating spring. Include those amps.
Combine the list of amps per device and the operating scenario to come up with a time profile for the battery. Consider all of the trips and breaker recharge last one minute even though it may only be 1-2 seconds. (IEEE battery sizing standard). The end of interval loads are also counted as one minute minimum.
Send the load profile to a battery supplier and they can size the battery.
Decide whether to use Ni-Cad, Lead Acid, or other battery types.
As to why DC power? Many utility and industrial switchgear systems use DC control to make sure that tripping power is available in a fault. The high voltage switchgear breakers do not have integral trip units like molded case CB?s. They need a signal from a protective relay to trip.
The engineer, owner or designer has to decide how long the DC system is supposed to supply power when AC is down and what is supposed to happen at the beginning, during and at the end of the outage.
A typical scenario is: Trip all breakers at start of outage, maintain 300 watts of continuous load for 24 hours and still have enough battery power to close, trip and close "x" breakers to return power. (Make sure protection and tripping power is available when AC returns. The breaker(s) might have to trip right away if there is a problem.) Remember, when most breakers trip or close, their spring charging motors run to recharge the operating spring. Include those amps.
Combine the list of amps per device and the operating scenario to come up with a time profile for the battery. Consider all of the trips and breaker recharge last one minute even though it may only be 1-2 seconds. (IEEE battery sizing standard). The end of interval loads are also counted as one minute minimum.
Send the load profile to a battery supplier and they can size the battery.
Decide whether to use Ni-Cad, Lead Acid, or other battery types.
As to why DC power? Many utility and industrial switchgear systems use DC control to make sure that tripping power is available in a fault. The high voltage switchgear breakers do not have integral trip units like molded case CB?s. They need a signal from a protective relay to trip.
DGrant041
Senior Member
- Location
- Peoria, Illinois
Welcome to the forum!
rcwilson has the right idea. You are going to need some information from your switchgear provider. In my line of work, switchgear is built to the customers specification--which I would have thought came from you. But in any case, you have a few different options for vacuum breakers that you'll need all the info. before you try to size your batteries.
For switchgear control power, we use 24 VDC from the generator set batteries. This is a common voltage for a lot of devices and "should" always be there. This is protected by a 10 Amp fuse and should use very little of that.
Vacuum breaker tripping power is usually 24 VDC but I'm sure you have options. Closing power could be 120 VAC, 130 VDC or some else I haven't thought of.
When you find out this info along with the VA/current draw, you should be able to size-up the batteries. IMO you should also leave yourself some extra room for expansion. You'll only need it if you don't have it. :wink:
Best of luck!
rcwilson has the right idea. You are going to need some information from your switchgear provider. In my line of work, switchgear is built to the customers specification--which I would have thought came from you. But in any case, you have a few different options for vacuum breakers that you'll need all the info. before you try to size your batteries.
For switchgear control power, we use 24 VDC from the generator set batteries. This is a common voltage for a lot of devices and "should" always be there. This is protected by a 10 Amp fuse and should use very little of that.
Vacuum breaker tripping power is usually 24 VDC but I'm sure you have options. Closing power could be 120 VAC, 130 VDC or some else I haven't thought of.
When you find out this info along with the VA/current draw, you should be able to size-up the batteries. IMO you should also leave yourself some extra room for expansion. You'll only need it if you don't have it. :wink:
Best of luck!
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