open delta connection PT

[pichu1970]

hi
if i have open delta connection that connect to relay to detect earth fault u0.
the pt is 0.1/3 kv.
in normal condition each phase is 33.3v and the sum is 0
if i have a ground fault in one phase what im going to measure each fhase?

 

[dpc]

Do you have three PTs or two? In the US, if you have three PTs, it's referred to as a broken delta. If two PT, it's called an open delta. Outside of the US, this is not the case, apparently.

Assuming you have three PTs and a broken delta - for a single line-to-ground fault, there will be 3Vo across the opening. This works out to 3 times the normal Line to neutral voltage.

Homework problem?

 

[waross]

I don't often disagree with you, David but this time.....
Assuming three PTs, when one phase is grounded, the voltage to ground on the ungrounded phases rises to 1.73 of the line to neutral voltage.
The two ungrounded PTs will be developing 58 Volts.
These voltages are displaced by 120 electrical degrees so the resultant voltage across the open or break will be 58 Volts.
The voltage across the grounded phase PT will drop to zero.
Each PT may be monitored separately to determine which phase is grounded.
80, 90, 100 years ago, it was common to connect lamps across the PT secondaries.
In the event of a grounded phase, the lamp for that phase goes out and the other two lamps become brighter.
Often transformer type pilot lamps were used.
The units would be selected for line to line voltage.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[davidbeach]

One could always just bring all three phases into a decent relay and have it both calculate a 3V0 value as well as tell what's going on on each phase.

I’ll see your silver lining and raise you two black clouds. - Protection Operations