Automatic Source transfer

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mbrooke

mbrooke

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Does anyone know of a good relay that will pull off automatic source transfer, with sync check built in? Here is the simplified single line:
 
mbrooke

mbrooke

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SG-1 said:
I do not see the bus differential in the one line.

Bus differential should not respond to overcurrent. The same current entering the bus differential zone is leaving the bus differential zone.
Click to expand...


But lets say I had a bush differential zone between source 1 and 2 and the transformer breaker. Would those not take care of 50/51?
 
SG-1

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mbrooke said:
But lets say I had a bush differential zone between source 1 and 2 and the transformer breaker. Would those not take care of 50/51?
Click to expand...

87s are generally not concerned with the magnitude of current, just if it sums, current into the zone = current out of the zone, 50 A or 50,000 A. A good bus differential circuit is immune to a through fault. Over current relays would respond to the over current in their zone.

If your bus differential relay also has overcurrent functions like the SEL 587Z, you might be in business, if you spring for the extra CTs.
 
mbrooke

mbrooke

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SG-1 said:
87s are generally not concerned with the magnitude of current, just if it sums, current into the zone = current out of the zone, 50 A or 50,000 A. A good bus differential circuit is immune to a through fault. Over current relays would respond to the over current in their zone.
Click to expand...

Of course, 87 is not supposed to care about current coming in and out of its sums. Thats the whole point of differential. Do not trip on anything outside of the zone of protection regardless of 1 amp or 63,000 amps.



If your bus differential relay also has overcurrent functions like the SEL 587Z, you might be in business, if you spring for the extra CTs.
Click to expand...


You don't need over current to protect a bus bar. Thats why I am asking why I need 50/51 for the two source supply breakers.
 
R

rian0201

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Automatic Source transfer

87B is expensive in this case with only three terminals and from the info, only one source works at the time.

but 87B could take care of that. even 50/51 with syn check or auto synch could do it.

the line side relays in my opinion is for switching, but it comes already with a standard OC relays, so three relays.

or, just use voltage relays..


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mbrooke

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rian0201 said:
87B is expensive in this case with only three terminals and from the info, only one source works at the time.

but 87B could take care of that. even 50/51 with syn check or auto synch could do it.

the line side relays in my opinion is for switching, but it comes already with a standard OC relays, so three relays.

or, just use voltage relays..


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Click to expand...


But it has to do it automatically- in a controllable timing sequence. I need a relay that senses a loss of potential, trips the NC breaker, verifies the breaker is in the open position, and then closes the other NO breaker.


The reason why I want to use 87B instead of 51/51G is because I would need to coordinate the source breakers with the transformer 51 which will only make things more complicated- and that a bus fault will take longer to clear- meaning more damage and arc flash. And yes people will argue using a 50 instantaneous pickup which will trip as fast as 87B, however I am concerned about transformer inrush and hot load inrush tripping it.
 
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R

rian0201

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huh? you could still do it in the things i have mentioned. for example lets say sel351a LOP is already a standard feature.

87b is really expensive... for me..

by the way, what voltage are we talking about? in low voltage, there are devices available for this scheme, it could even start a standby generator..


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mbrooke

mbrooke

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rian0201 said:
huh? you could still do it in the things i have mentioned. for example lets say sel351a LOP is already a standard feature.

87b is really expensive... for me..

by the way, what voltage are we talking about? in low voltage, there are devices available for this scheme, it could even start a standby generator..


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Click to expand...


34.5kv primary 12.47kv secondary. No generator, just two sub-transmission lines. 20/22.5MVA LTC transformer with a second one in the future.
 
SG-1

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mbrooke said:
Of course, 87 is not supposed to care about current coming in and out of its sums. Thats the whole point of differential. Do not trip on anything outside of the zone of protection regardless of 1 amp or 63,000 amps.






You don't need over current to protect a bus bar. Thats why I am asking why I need 50/51 for the two source supply breakers.
Click to expand...

I am not arguing that you need overcurrent protection, I do not have the details, only that the automatic transfer could be done with SEL 751s, or similar relays.

I have always thought that a high impedance bus differential relay was faster than a 50.
 
mbrooke

mbrooke

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SG-1 said:
I am not arguing that you need overcurrent protection, I do not have the details, only that the automatic transfer could be done with SEL 751s, or similar relays.

I have always thought that a high impedance bus differential relay was faster than a 50.
Click to expand...

Ok, I think we can agree here then :)
 
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