Short Circuit Current Carryin capacity in multi run Cables
Short Circuit Current Carryin capacity in multi run Cables
(OP)
I have to size the 11 kV cables for a very high fault level system. My requirement is 110 kA(rms) for 1 Second. I intent to put multi runs singel phase cables. I have the short time current ratings of 1 core cables. can we directly multiply with no of runs to get the fault level of mult run cables. Rated current carrying will not be the issue in deciding the cable size.
Need your opinion on this.
Thanks
Need your opinion on this.
Thanks
Akhilesh Solanki
VA Tech Hydro (I) Ltd






RE: Short Circuit Current Carryin capacity in multi run Cables
My understanding is since the short circuit rating of a cable depends on the type of insulation it is possible to multiply by the no. of runs. (Reasonable assumption: Short circuit current is equally divided among the number of runs)
Kiribanda
RE: Short Circuit Current Carryin capacity in multi run Cables
a- Conductor area (Size).
b- Conductor material (Cu, Al,)
c- Impedance (Z = R+jX)
d- Protective device operating time (fuse, circuit breaker, etc).
For single conductor cable, the following formula applies:
I = A.[(k/t) .log(T2-234)/(T1-234)]1/2
Were:
A = Conductor size in circular mills
k= 0.0297 for copper
T1- = Operating temperature
T2- = Insulation SC rated temperature
t = protective device time to open the circuit.).
For multiple conductors in parallel, the impedance Z is:
Resistance: The total resistance is the resistance of one conductor divided by the number of parallel conductors. (Rn=R1 conductor/n
Reactance: Is a function of the cable size, number of cable, distances among cable (physical configuration
RE: Short Circuit Current Carryin capacity in multi run Cables
RE: Short Circuit Current Carryin capacity in multi run Cables
RE: Short Circuit Current Carryin capacity in multi run Cables
You may consider consulting a cable manufacturer who has experience in this type of application.
RE: Short Circuit Current Carryin capacity in multi run Cables
In such an event, I would have preferred bus duct (may be isolated type - presuming the generator is fairly large going by the fault level).
Are there any constraints!!!
If Cables are a must, then it would help if pilot wire differential protection or circulating current differential protection (high impedance, fast acting type) is also included.