grounding 13.8kV delta system
grounding 13.8kV delta system
(OP)
We intend to ground a 13.8kV delta system with isolated cables, by zigzag transformer used for signal only, not for trip. Question is:
1- What current is convenient for alarm?
2- How many time of alarm? (5 minutes , One hour..)
3-What are recomendation for insulation level of cables and voltage.
4- is there any reference or guide for this application?
1- What current is convenient for alarm?
2- How many time of alarm? (5 minutes , One hour..)
3-What are recomendation for insulation level of cables and voltage.
4- is there any reference or guide for this application?






RE: grounding 13.8kV delta system
RE: grounding 13.8kV delta system
I would say 15kA , if zig-zag neutral were solidly grounded.
But my intention is to install a high resistance in the neutral of zigzag.
RE: grounding 13.8kV delta system
RE: grounding 13.8kV delta system
My intention is to choose a ground fault current that can be supported 1 hour (for instance) after alarm. This time, is enough to remove the area of fault point by switching system ,keeping others parts of system in operation.
RE: grounding 13.8kV delta system
What current would you like? A hint - it should be higher than the capacitive charging current, but beyond that your choice.
Continuous duty resistor and it can be in alarm forever with no damage to the resistor. But that's a lot of heat. 5A is probably a minimum and you would need to dissipate around 40kW.
Everything on the system needs to be rated for full line-line voltage as the two unfaulted phase will be at line-line voltage to ground. This increases the risk of a second ground fault on a different phase. You really don't want that to happen.
RE: grounding 13.8kV delta system
BOOK:industrial power system - shoaib khan
Extract page 72 -4.3.3
4.3.3-example of a high resistance grounding calculation
The objective is to design a HR grounding for 4.16kV system. The system is connected to a 10 MVA transformer ...
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The faulted circuit should be removed quickly on a line-to-ground fault, and the tripping can be delayed to permit the operator to take corrective action. The following criteria must be met:
* the ground-fault current Ir + 3Ico <= 8.0 A
* the phase-to-ground insulation level for motors, switching equipment, and cables needs to be rated for phase-to-phase voltageif the faulted circuit is mainteained indefinitely, or 133% if the faulted circuit is removed within one hour.
.....
RE: grounding 13.8kV delta system
RE: grounding 13.8kV delta system
If that implies unshielded cables, I would have to ask if such cables are available in the 25 kV class.
If it implies shielded cables grounded at the zig-zag, and isolated at the load (or vice versa) I would worry that any remote fault could create a large voltage difference between the shield(s) and the local ground potential. That could seem to eliminate the dead front rating of any equipment, and to risk shield-to-local-ground flashovers and personnel hazard.
RE: grounding 13.8kV delta system
page 26- 1.4.3 - resistance grounding
... In general the use of high-resistance grounding on systems where the line-to-ground fault current exceeds 10A should be avoided because of the damage potential of an arcing current larger than 10A in a confined space.
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I would like to understand the meaning of CONFINED SPACE. In my project 13.8kV system with high-resistance grounding is a mesh of isolated cables inside ducts and cable-trays running 2 km of a hydro-powerplant complex.
This is a major river (madeira) in the Amazonian jungle climate with high humidity and high temperature.
Is this a confined space?
RE: grounding 13.8kV delta system
David Castor
www.cvoes.com
RE: grounding 13.8kV delta system
What does it mean 133%