Utility sources sync. criteria

[tctctraining]

Our customer is going to use a switchgear to perform a paralleling function of two separate sources. these are utility sources and there is no gen. involved.
They intend to use voltage sensors with 3% mag. tolerance and 1 deg. phase angle error.
There are no info on slip frequency data.
What are industry standards to use base line criteria of paralleling two sources?

 

[cranky108]

Most sync-check relays have a default setting of 20 degrees.

 

[davidbeach]

Permission from the utility is the first criteria. Once you have that, they can tell you everything else you need to know.

 

[cranky108]

These are based on studies, or experence. In some systems there will be specific values based on studies, or experence. In other systems where there usually aren't many issues, you may not get an answer. So the default is a good starting point, but it is worth asking the utility.

Another issue is the limits on closing of the breakers.

 

[tctctraining]

cranky108, what study would determine these criteria?
would that be a transient switching study?
I agree that relay manufacturers default values would be the first step, (in this case SEL 751) however I appreciate your experince on this subject?
Thanks

 

[stevenal]

In most cases two utility sources will either parallel or not. Why do you expect the two sources to slip?

 

[tctctraining]

That's a true statement Stevenal
However, we are checking for "Not" sync situation for any reason.

 

[waross]

Your sync check for utility sources is to prevent a connection if phases have been swapped or rolled.
Measure the voltage difference and the phase angle error. Use judgement and experience to decide if it is safe or desirable to parallel. If yes, close the switch. You may increase your experience at this point. Now you have the information to set the sync check relay.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[tctctraining]

Waross, I was expecting more of calculation based approach than gaining experince by try to see if it works.
I'll start with relay default values as a start point.
Thanks afor all replies

 

[pwrtran]

We do not allow paralleling two sources that have more than 15 degrees phase angle difference and 20% voltage magnitude difference.

 

[Jebb]

Be aware of circulating currents when the 2 sources are tied together!!!! The utility probably wants to know what you’re doing. I would contact them before spending too much time…

 

[stevenal]

Your sync check for utility sources is to prevent a connection if phases have been swapped or rolled

. If this is the case, the slip frequency will not be an issue. The relays I've familiar with sync based on a single phase. Feeling lucky?

 

[PHovnanian]

Are you going to be operating with paralleled sources or is this just part of a no break transfer scheme?

As others have said, contact the utility first. If you tie two of their systems together, you are going to mess with their system protection coordination and personnel safety.

Aside from switching transients, your utility will inform you of the regulation schemes of each source and what kinds of circulating currents your system might experience should a tap changer on one circuit step up or down.