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Synchronization checks using different type of PTs

05/27/2022 3:52 AM

We need support regarding connection of New MV switchgear PT with existing PT (on another busbar which will remain there until AC busbar replacement is done) for synchronization circuit.

Kindly confirm if that there is no phase change i.e. vector groups are identical for following PTs:

New MS1B Switchgear PT Terminals D11 and D12(Common Terminal)

Existing Switchgears PT Terminal M2/4 & M2/5(Common Terminal)

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#1

Re: Synchronization checks using different type of PTs

05/27/2022 2:33 PM

..." synchronizing transformers to an existing power system is as simple as matching the number and order of phases, the distribution voltage and frequency and phase angle. However, most of those parameters are determined by the voltage source, and cannot be altered at the transformer. This can be problematic when matching phase angle, but if a circuit breaker is used, and this is a known synchronization point, there should be a synch-scope to at least monitor the phase angle and connect the circuits at the moment of synchronization, even if there is no way to adjust the phase angle."...

https://www.quora.com/How-do-I-synchronize-two-to-three-power-transformers

https://www.linquip.com/blog/what-is-synchroscope/

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#2

Re: Synchronization checks using different type of PTs

05/27/2022 10:47 PM

You need a phase shifting transformer to check synchronism. The new switchgear has line to neutral PTs, the old has line to line PTs. A phase shifting transformer is not uncommon to handle problems like this, and should be readily available.

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#3

Re: Synchronization checks using different type of PTs

05/28/2022 4:14 AM

The <...support...> comes from the vendors of the <...New MV switchgear PT...> as that organisation will have both indemnity insurance cover and the ability to read and review the drawing from which the above image was obtained. One presumes that the vendor's telephone number is available and that a relationship is in place with a technical specialist who can provide that support.

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#4
In reply to #3

Re: Synchronization checks using different type of PTs

05/28/2022 6:52 AM

All correspondence should be in written form to avoid misinterpretation,and to provide reference if future action needs to occur.

Multiple hard copies should be stored in off site locations.

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#5

Re: Synchronization checks using different type of PTs

05/29/2022 11:21 AM

A very simple method,is to put a clear 20 watt bulb across 2 of the same phases,and when the light is totally dark,they are synchronized.If it glows even a little bit,they are out of sync.This was used in older generator systems to synchronize the connection to the grid phases.

For example Phase A on utility,to phase A on generator.

Same should work on PT's

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#6
In reply to #5

Re: Synchronization checks using different type of PTs

05/29/2022 9:12 PM

If the PT connection is incorrect, then the synchroscope will tell you you are synchronized when in fact you are 30 degrees out of phase. Not a problem, the protective measures will trip the generator off, hopefully before mechanical damage occurs. When in doubt, we use full voltage phasing sticks on the breaker connections, to confirm your instrumentation.

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#7
In reply to #6

Re: Synchronization checks using different type of PTs

05/29/2022 10:38 PM

Kindly elaborate full voltage phasing sticks on the breaker connections

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#8
In reply to #7

Re: Synchronization checks using different type of PTs

05/30/2022 1:24 AM

These are voltage measuring devices on insulated sticks you directly measure the phase difference. The breaker is typically removed from the circuit, the shutters are opened and with high voltage gloves you measure the voltage between the input and output of the breaker, per pole.

This is more difficult if checking to a generator, as someone needs to keep adjusting the speed of the machine.

You need phase shifting transformer. it is 120V to 120V typically, so the phase angle of wye is corrected to delta, your switchgear people should know what you need, and know how to connect it to the correct polarity, to match the open delta of your old switchgear. The full voltage check would not normally be necessary unless poor engineering skills are employed.

When working with systems requiring synth check, I always made sure I had open delta PTs on both sides of all breakers, and if I needed ground relay polarization, that was always a second set of potential transformers connected in wye.

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#9
In reply to #8

Re: Synchronization checks using different type of PTs

05/30/2022 2:00 AM

Sir thank you for very comprehensive guidance

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#10

Re: Synchronization checks using different type of PTs

05/30/2022 5:35 AM

As there is no phase shift between star / star PT... Is there any phase shift between PRIMARY AND SECONDARY of open delta PT ?

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#11
In reply to #10

Re: Synchronization checks using different type of PTs

05/30/2022 7:48 AM

Well, there ought not to be, though the actual installation cannot be seen from here.

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#12
In reply to #10

Re: Synchronization checks using different type of PTs

05/30/2022 10:19 AM

If your secondary voltage on your wye PTs is 69 volts, can’t be seen from here, then you can use the 120V between phase 1 and 2 to synchronize. There is no phase shift delta delta or wye wye as PWSlack notes. You may need an isolating transformer because phase 2 is grounded on one set, not on other.

The synchroscope may expect a grounded phase 2 connection, you need to check on that also.

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#13
In reply to #12

Re: Synchronization checks using different type of PTs

05/30/2022 10:56 PM

Thank you for very comprehensive clarification sir

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