Max Cable Length with Generator
Max Cable Length with Generator
(OP)
Designing a 10kV generator installation with about 300 meters between alternator and breaker. Concerns raised that cable length may be aproblem. Apart from burden on CT's which is OK are there any factors e.g. capacitances that limits cable length.
Thanks.
Thanks.






RE: Max Cable Length with Generator
RE: Max Cable Length with Generator
The only thing I can speculate is that capacitance on the cable may excite the machine and cause over-voltage or for example sustain over-voltage when the breaker is opened on load. Possible cable side VT failure?? I think any problem could only be with the breaker open.
RE: Max Cable Length with Generator
Additional capacitance on the generator terminals can
affect the LCI operation.
Otherwise, I'm not aware of any generator issues with long cables. I would be uneasy about the exposure to faults and would make sure the protection system included the cables in a differential zone.
RE: Max Cable Length with Generator
Given that surge capacitors are sometimes installed on generator terminals, I don't anticipate a capacitive problem with long feeders.
Protection may be an issue though.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Max Cable Length with Generator
waross is right:
Just measure the capacitance of the stator winding. Its a simple procedure and can be done with 120 Volts/60 Hz (or similar) by using a divider transformer (Trenntransformator in German). Connect all three phases of the stator winding (usually they are allready star-point connected). Apply voltage to one of the motor terminals and connect the other leg to the stator core (stator core to be grounded), measure voltage and current flow and determine total winding capacitance (all three phases) as follows:
C = I / 2 * 3.14 * f * U
C = capacitance
I = current
f = frequency
U = voltage
Good luck and best regards
Wolf
www.hydropower-consult.com
RE: Max Cable Length with Generator
GerH:
The proper term is "isolating transformer", not divider transformer. Sorry for that.
Regards
Wolf
www.hydropower-consult.com
RE: Max Cable Length with Generator
RE: Max Cable Length with Generator
RE: Max Cable Length with Generator
If you go to 300% ampacity with your cables, you may stretch out to 7.5 meters before the breaker.
Check your local codes.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Max Cable Length with Generator
There are two issues here,
1. one is the earthing method of generator. If the generator is a large one and high impedance earthing is proposed, then long cable is a concern. If the generator is medium resistance earthed (say 100A), then 300m cable may not be a concern.
2. Secondly, requirement for isolation close to the generator. Generally, this is a safety requirement and governed by national codes. To my knowledge, some codes stipulate that there should be an isolation facility within fifteen meters from the equipment.
RE: Max Cable Length with Generator
Under Canadian codes, the supply TO equipment must be isolated within 15 meters. (With exceptions)
Protection for conductors must be within 3 meters of the source. (With exceptions) In Canada the 3 meter rule would apply rather than the 15 meter rule.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Max Cable Length with Generator