We have emergency 440 V DG set for black start of 11 kV GTG. The DG set neutral is floating (unearthed). We have to sychronise this DG set momentarily with the 11/.44 kV Dyn11 (with solid grounded neutral) transfomer during the black start.
Is it acceptable to synchronise the DG set (with floating neutral) with GTG through Dyn11 (solid grounding) transformer? Will there be any problem? Any idea?

Let me ask - if the 440V generator is basically ungrounded, you can sync frequency & rotation, but how can you match voltages? You have 2 sources that will float relative to one another?

Dumb suggestion maybe, but is there a way you could temporarily ground the generator for syncing purposes, then let it float later?

A better question is this - do these sources stay paralelled during normal ops of just for load transfer? I'm presuming you parallel for load transfer, then disconnect.

Radar

Oh wait - now I see the word "momentary". Guess I oughtta learn to read, heh?

[This message has been edited by Radar (edited 01-18-2006).]