Star-Broken Delta PT rating
Star-Broken Delta PT rating
(OP)
I have circuit of Primary Star secondary broken delta connection connected to 12kv system.
Each individual PT ratios are 14400/120
As in star, each PTs are sublected to phase voltage only. Can I select the PT of ratios (14400/1.732)/120 for this connection?
Keyrose
Each individual PT ratios are 14400/120
As in star, each PTs are sublected to phase voltage only. Can I select the PT of ratios (14400/1.732)/120 for this connection?
Keyrose






RE: Star-Broken Delta PT rating
Yes. If the star point it grounded, you can use single-bushing PTs. If the star point is not grounded, you need to use 2-bushing PTs.
RE: Star-Broken Delta PT rating
RE: Star-Broken Delta PT rating
RE: Star-Broken Delta PT rating
Almost 400 hits.
One of the first hits.
3V0 (broken delta) Resistor Sizing
thread238-225126: 3V0 (broken delta) Resistor Sizing
Bill
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"Why not the best?"
Jimmy Carter
RE: Star-Broken Delta PT rating
RE: Star-Broken Delta PT rating
Your comments are correct. However, depending on the protection, a 2-bushing PT with a L-G ratio (i.e. 7200:120) can be used if the protection will clear in a time that meets the over-voltage limits set-out in the standard (i.e. IEEEC57.13), i.e. 1.73 - 1 minute.
RE: Star-Broken Delta PT rating
Yes, if the protection scheme is set to clear under 1 minute on SLG faults. Some ungrounded system protection setup do not trip but just "indicate" the occurrence of a SLG fault, allowing the crew to correct the problem. It may take hours of checking and CTs can saturate.
RE: Star-Broken Delta PT rating
The rule does appear to be universal. Depends on indoor versus outdoor, group and on voltage rating. 140% is the 1 minute rating for many of them.
RE: Star-Broken Delta PT rating
Yes...the overvoltage factor varies with group no., that's why I listed "i.e.".