PT broken delta winding should be earthing?
PT broken delta winding should be earthing?
(OP)
Some PT's broken delta secondary winding is earthing,but some is not. Why ?Which one is right? The earthing is for safety,why not earthing? And how to earthing?
Please help me.
http://f iles.engin eering.com /getfile.a spx?folder =2263f742- 4bd2-48a4- a26d-19551 edcec6d&am p;file=IMG _20110610_ 171301.jpg
http://f iles.engin eering.com /getfile.a spx?folder =b1b11b54- c262-4b02- aa2f-733ae 2a58be6&am p;file=IMG _20110610_ 172058.jpg
Please help me.
http://f
http://f






RE: PT broken delta winding should be earthing?
In the ungrounded circuit, the primary voltage may be low enough that the hazard is minimal and/or the ungrounded winding may be shielded by the grounded windings on the same core. Then again there may be a capacitively coupled common mode voltage present on the ungrounded delta.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: PT broken delta winding should be earthing?
RE: PT broken delta winding should be earthing?
RE: PT broken delta winding should be earthing?
But why it should always have reference to ground?
I think earthing is for safety as what waross said, not for reference.
PT can work well without secondary winding reference to groud if there's no capacitive coupling voltage from primary winding.
I am confused.
RE: PT broken delta winding should be earthing?
RE: PT broken delta winding should be earthing?
There are small transformers made for isolation that are used in patient care areas and operating theaters that have a grounded metallic screen between the primary and secondary windings. In the event of a transformer burnout, the screen prevents the primary winding from shorting to the secondary winding. In normal operation the primary winding is capacitively coupled to ground and the secondary winding is capacitively connected to ground. There is no transfer of energy between the primary winding and the secondary winding by capacitive coupling.
But as David says, you cannot avoid capacitive effects when conductors are separated by an insulator.
As far as I know the special screening feature is not available in potential transformers.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: PT broken delta winding should be earthing?
Ground "reference" is needed to prevent the secondary winding(s) from floating up to a higher potential due to capacitive coupling between the primary and secondary. Also, grounding/ground reference provides safety in the event of a transient.
As an example, for a VT without ground reference on the secondary, the voltage between the secondary terminals (e.g. X1-X2) would be per the nameplate ratio (e.g. 120V), but the entire winding could float up to 5 kV due to capacitive coupling from the primary winding.