ZCT setting in ungrounded systems
ZCT setting in ungrounded systems
(OP)
How do you set the current setting coming from the ZCT? Does ZCT produce any secondary current at all?
If it is a single feeder in a power system (against the radial) the ZCT balances the charging current 3Ic in case of single phase to ground fault and produces zero flux. On the other hand, in case of radial feeders there would be some small current from the ZCT? Has my understanding right?
If it is a single feeder in a power system (against the radial) the ZCT balances the charging current 3Ic in case of single phase to ground fault and produces zero flux. On the other hand, in case of radial feeders there would be some small current from the ZCT? Has my understanding right?






RE: ZCT setting in ungrounded systems
Ground Fault Protection for an Ungrounded System
http://www.ece.mtu.edu/faculty/bamork/EE5223/EE522...
https://cdn.selinc.com/assets/Literature/Publicati...
GROUND FAULT PROTECTION ON UNGROUNDED AND HIGH RESISTANCE GROUNDED SYSTEMS APPLICATION GUIDE
http://www.postglover.com/download/high-resistance...
RE: ZCT setting in ungrounded systems
The trick there is to wire the shielding earth wire back through the ZCT. Keep in mind that any earth wire should never pass through the ZCT. That way the summation of the currents flowing on the phase conductors in the ZCT does not include the ground currents flowing in the shielding screen.
RE: ZCT setting in ungrounded systems
My question is how to make the ZCT sense the fault current even if it is very small
RE: ZCT setting in ungrounded systems
Secondaries connected in broken delta. (Open delta in IEC land?)
The CTs will show the unbalanced current to ground.
You may use a loading resistor to convert the current output into a voltage output.
The PTs will show any event that causes the voltage to ground of any phase to drop.
Bill
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"Why not the best?"
Jimmy Carter
RE: ZCT setting in ungrounded systems
Isn't using residual connection of 3 CT's same as using ZCT?
RE: ZCT setting in ungrounded systems
It looks like the application of protection scheme is not appropriate to the system, i.e; ungrounded system.
Detection of earth fault becomes difficult using a ZCT and a non-directional relay. The capacitive current introduces some a 90° phase shift. This confuses many people. I would suggest you to go with the time tested ground fault detection and protection scheme for the ungrounded system.
At least in the IEC world, the ungrounded systems are now becoming rare and used only in some special cases.
RE: ZCT setting in ungrounded systems
RE: ZCT setting in ungrounded systems
For the small network can use the 3V0 element for detection (PTs connected in grounded wye indicated by Waross).
The phase to earth capacitive charging produces more high values of residual voltage (3V0) (opposite to big network that for the same fault type have low values of 3V0)