Connection of Two Distribution Systems

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eng. harb's picture
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Joined: 2014-08-12

Hello everyone,
I work in a factory where we manufature electrical panels.
I was asked recently to connect two separately fed distribution panels togother via an 2500A ACB, where this connection must not occur unless the two sources are synchronized, I searched and found about a synchro-check relay but I cant find one in KSA, and was wondering if theres any other way to do it. 

sankaran03's picture
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Joined: 2014-08-14

Hi eng.harb,
What are those two sources from which the two distribution panels are fed? Utility and Diesel Generator set? Or from the same common bus but with two separate cables?
If it is from the same bus,the closing of the ACB will result in paralleling (Bus coupling) of the Distribution panels. But before closing, the phase sequence and polarity need to be checked and matched.
If the sources are Utility and DG, then the ACB can be closed ONLY on synchronization by adjusting the voltage,frequency and phase angle.

Fazal Rahim Sheikh's picture
Joined: 2014-08-16

Apart from a Synch Check relay Ensure the Percentage Impedances of the Transformers feeding the two panels are identical and the Vector Group as well to avoid cross currents. You can get a Synch check relay from SEL or Schneider. If you need LV Synchcheck try Tyco or Basler.

eng. harb's picture
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Joined: 2014-08-12

Thanks for the information, the two sources are utility so it is a bus coupling, I dont know if checking phase sequence and polarity is enough, for it was stated to me they need to check voltage, frequency, phase shift and phase sequence. I went to Schneider, ABB and Lovato but the distributors here never heared of such a relay. Tyco and Basler do not exist in KSA but Tyco has an office in Dubai. I will contact and get back.
Thanks!

sankaran03's picture
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Joined: 2014-08-14

There is a lack of information here. You say both the distribution panels are fed from the utility. Common bus? I presume there is only one service connection from the utility to your factory. Any intervening transformers between the common bus and distribution panels? A single line diagram will have more clarity.

eng. harb's picture
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Joined: 2014-08-12

sankaran03, thanks for your reply. There is a lack of information I'm afraid regarding whether I must check sync or not, but the problem I had is how to make it if no synchro-check relay available.

sankaran03's picture
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Joined: 2014-08-14

Hi eng.harb
Unless more information is provided regarding your present set up it is difficult to say whether synchronization is required or not.However let me try.
You have stated both the panels are getting the supply from utility.
1.Directly, without any transformers in between? If so, synchronization is NOT required. Only correct phases are to be identified and connected (i.e.,U to U, V to V and W to W) through the Bus coupler CB
2.Both the panels getting the supply through two transformers? If so, closing of the Bus coupler circuit breaker will parallel the transformers. But before paralleling, we have to make sure the following conditions are satisfied.
-polarity
-voltage ratio
-% impedance
-phase rotation
-identical vector group and phase displacement.
After checking the above, conduct phasing out test procedure. Interchange the leads if required. Then, the transformers can be paralleled by closing the ACB. For paralleling of transformers, you do not require a Synchcheck relay.

Synchronization is required only when two different sources are connected via utility and generator.
Or Synchcheck is done when two lines from different substations of a grid are connected to a common bus, to ensure the parameters match.

eng. harb's picture
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Joined: 2014-08-12

sankaran03 - thanks for the information it was helpful,. I will set another meeting with their engineers and discuss it further.

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