How to make sourc transfer work for swgr with Utility Source Y-G and Emergency source DELTA

[power2engineer]

The Main switchboard is 13.KV S&C Fusible disconnect switch with Source Transfer controller for Manual OR Automatic Transfer scheme
I have 13.8 KV Grounded - WYE Utility incoming Power on main distribution switchgear.
On site Generator is 480V/277V WYE Stepped up to 13.8KV using 480/277V WYE-13.8KV Delta Transformer.
The S & C SOURCE TRANSFER CONTROLLER is supplied 3 Phase control voltage from voltage sensing VTs on Source sides of Utility & Em.Generator disconnect switches.
The STC essential looks for loss of Source 1 (Utility) and corresponding Switch Open condition to allow closing of Source 2 (Em.Gen.) Switch Manually or Automatically.
THE PROBLEM Em.Generator source coming from Delta winding of 480/277-13.8KV Step up transformer there is no reference ground for Em.Generator votage and the S & C STC does not work
because it is looking for voltage similar to Utility transformer.
How to provide the same ground reference to Em Generator 3 phase power(voltagees) as Utility 3 Phase Power ?

 

[waross]

Take your reference from the 480/277 system.
If you are using Primary voltage to 120 Volt PTs it will work fine and the STC will never know yhe difference.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[power2engineer]

Thank you waross for your response, but the Generator is quite far from the switchgear, voltage drop will be an issue.

 

[waross]

Or, if you have existing PTs with 120 Volt secondaries, connect them in wye and ground the wye point.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[power2engineer]

Gen Transformer voltage is 13.8KV Delta so are you suggesting use 13.8KV /120V PTs connect them Y/Y-G? or Delta/Y-G?

 

[waross]

Delta:Y-G
The PT Secondaries are a seperstely derived source and may be grounded without affecting the Delta primary.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!