Back Synchronization

[mkhamsi]

Dears,
i am having a project with back synchronization with utility.
when utility returns we should get sensing from PTs before and after utility incoming breaker (6.6 KV) synchronize the genset with the sensed utility voltage then send the breaker (6.6 KV) closing comand.

now my problem is that the utility incoming cell in the Switch gear doesnot include the PTs for sensing before the 6.6 KV breaker! only after it.
so cutomer want us to get the sensing from the primary of the utility transformer (33/6.6) where there are PTs there, the power transformer is Dny11.

my question: is there is any device that can compensate the phase shift between the transformer primary and secondry voltage so that we can synchronize based on that sensing.

Marwa

M.Khamis

 

[ScottyUK]

Yes, you can use an interposing transformer to provide equivalent phase shift and match up the voltages. It should be possible to provide very reasonable matching because the power transformer is unloaded (breaker open) and won't contribute any phase shift or volt-drop due to its own impedance. You will probably need tappings on the interposing VT to get the voltages matched - you could do this with the LV breaker closed and then adjust taps for best matching.


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If we learn from our mistakes I'm getting a great education!

 

[GTstartup]

Yes, the device is the synchronizer itself, no need for any auxiliary equipment.

You can compensate for any phase angle or voltage differences in most synchronizers these days.

 

[davidbeach]

Yes, as GTstartup mentions, any decent synchronizer (as well as any decent synch check relay) can compensate for any phase shift, or at least any multiple of 30 degrees of phase shift, between the two voltage sources.

 

[mkhamsi]

Dears,
thanks a lot for your replies

Scotty: iam checking for teh interposing transformer solution , would that to be additional to the sensing PT(i.e in series to it)?


M.Khamis

 

[ScottyUK]

Yes, it would.

But don't disregard the comments from the other guys - most modern relays can internally correct the vector shift.


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If we learn from our mistakes I'm getting a great education!

 

[mkhamsi]

Dears,

as an update on the above
the module that i am using for synch is Deepsea 7560 and by contacting the vendor i had found that it doesnot include vector compensation function , so i will be upgrading to a newer version DSE8660

by comminucating with othe rvendors , i had also found that woodward easygen3400/3500 have the vector compensation function while easygen3200 doesnot

Also dief AGC 3 do have the vector compensation function

i believe that will solve the transformers phase shift issue, thanks a lot for your help

but still not sure how to solve the tap changing issue
the utility transformer is 33/6.93KV – 20MVA – Tap Transformer – DYN11.
with Automatic tapchanger
do you think you can help

Marwa


M.Khamis

 

[GTstartup]

Quote

"but still not sure how to solve the tap changing issue the utility transformer is 33/6.93KV – 20MVA – Tap Transformer – DYN11.with Automatic tapchangerdo you think you can help"

How about helping us out and telling us what you perceive the issue to be.

 

[mkhamsi]

sorry GT didnot got what you mean

M.Khamis

 

[ScottyUK]

GTstartup,

If sensing on the HV side of the breaker and synchronising on the LV side then the voltage matching will only be correct for one tapchanger position, probably at the neutral position. The further away from the neutral position the tapchanger is then the worse the synchronising conditions will be across the breaker. Depending on how unstable the grid voltage is, it may not be possible to put the OLTC to the neutral position and match up the machine terminal voltage.


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If we learn from our mistakes I'm getting a great education!

 

[GTstartup]

Thanks Scotty,

I guess the question is, is the range of the tapchanger outside the range of the generator voltage.

So mkhamsi what is the range of the tap changer vs the upper and lower limits on the AVR?