Substation DC Power

[MD88]

Hello,

I had a question about substation power... I have a pretty simple 69kV-4160V substation (69kV breaker, 12MVA transformer, 4160V switchgear lineup w/ about 10 breakers). The relays and breakers will run on 125VDC... I was wondering how I can figure out what kind of battery/charger set up I need. I imagine you guys will need some more info... please ask, it'll help me know which issues I need to consider.

Thanks!

 

[djohns6]

You will need to determine how many devices you are operating . Trip/close coils , Lockout relays , Auxillary relays , Indicating lamps , annunciators , Motor operated switches , breaker spring rewind motor , etc. , etc.
In other words , ANY possible instantaneous load . AND constant current load . That's a start .

 

[djohns6]

Lead acid batteries or NiCad ?

 

[MD88]

Hmm... Come to think of it, I don't even know what these batteries are for! Is it just for operation of the breakers if there's an outage?

 

[richxtlc]

What are you presently using? You need to know the maximum number of breakers that can operate at one time, e.g., bus trip, the total current required to meet that demand. Also, how long do you need to rely on battery power in the event of loss of all ac to your substation. This will determine the ampere-hours for the battery. The charger will need to be able to maintain the charge, (trickle charge), charge the battery in accordance with the battery's manufacturer's spec, and supply current for normal operation of alarms, indications, and operation of single breakers or other equipment connected to the dc bus.

 

[dicklaxt]

In my experience this has always been the responcibilty of the Substation vendor be it a containerized sub or individual components,this is purchased with the gear .

dick

 

[Hameedulla-Ekhlas]

Hello,

I had a question ---

Thanks!

DC low voltage supplies are required to provide power for the operating mechanisms of circuit breakers, for operating alarm, protection and control systems, and for emergency back up lighting. Typical DC voltage levels used at substations are 48, 110, 220 volts. The battery and the associated charger capacities are determined from the average load in association with the peak demand. Duplicate DC systems are sometimes installed at the larger substations to ensure high reliability.

Smoking!

 

[zog]

Hmm... Come to think of it, I don't even know what these batteries are for! Is it just for operation of the breakers if there's an outage?

Not for just an outage, for all operations of the breaker, the battery system is your control power and without it your breakers and relays are worthless, they won't do squat.

 

[brian john]

Not for just an outage, for all operations of the breaker, the battery system is your control power and without it your breakers and relays are worthless, they won't do squat.

This item is overlooked in substation maintenance and the price for that is high.

 

[zog]

This item is overlooked in substation maintenance and the price for that is high.

Yep, the most important part of a power system, nothing works without them, and like you said, often neglected.

 

[djohns6]

Good old ALCAD batteries . NiCad , with chrome plated straps . I spent many miserable hours cleaning those things .

 

[jdsmith]

Not for just an outage, for all operations of the breaker, the battery system is your control power and without it your breakers and relays are worthless, they won't do squat.

Batteries are required even when the battery charger is online because batteries can handle the high inrush current required by trip coils and close coils. Standard duty station battery chargers are only trickle chargers and can not source enough current to operate coils. If you want to be able to take the battery bank offline for repairs and maintain full control power, make sure you specify a "battery eliminator" type charger which is capable of sourcing the current spikes required for trip and close coil operation.

You will need to determine how many devices you are operating . Trip/close coils , Lockout relays , Auxillary relays , Indicating lamps , annunciators , Motor operated switches , breaker spring rewind motor , etc. , etc.
In other words , ANY possible instantaneous load . AND constant current load . That's a start .

We found the best source of information to learn about battery system sizing is from the battery vendors themselves. Their application engineers can size a string if you provide them the total current demand for your continuous users (microprocessor relays, indicating lights, annunciators, etc) and the inrush current rating on your trips coils, along with the worst case number of trip coils that would be activated at the same time, typically for a bus differential trip. Some design standard ( I don't remember what) says that the battery bank should be able to supply the continuous users for 8 hours and still be able to perform the worst-case trip after 8 hours of supplying continuous load. You may think that relays and lights don't take much power, but it does add up and caused us to go from a 200 amp-hour string to a 300 amp-hour string in a recent project.

 

[WastefulMiser]

Some design standard ( I don't remember what) says that the battery bank should be able to supply the continuous users for 8 hours and still be able to perform the worst-case trip after 8 hours of supplying continuous load. You may think that relays and lights don't take much power, but it does add up and caused us to go from a 200 amp-hour string to a 300 amp-hour string in a recent project.

IEEE 485 is what you are thinking of.