Problem: High cable sheath current for 34.5kV distribution system
Problem: High cable sheath current for 34.5kV distribution system
(OP)
Greeting,
In 34.5kV distribution system, the cable distance between 34.5kV CB (upstream) and 34.5kV/13.8kV transformer is about 300meter. Unfortunately, each phase (single core cable) has high sheath current (AWA current = 100A for B, 80A for R&Y). Cable is single core 500mm and at terminals the AWA at CB & primary of transformer are solidly grounded. The transformer vector group is Dyn1.
This high AWA current causes frequent hot spot at CB terminals, and hence lead to repeated repair work.
The question: How to eliminate the high sheath current?
Is it a must to solidly ground both ends of cable?
Appreciate your help to minimize/reduce this sheath high current with no standard violation.
In 34.5kV distribution system, the cable distance between 34.5kV CB (upstream) and 34.5kV/13.8kV transformer is about 300meter. Unfortunately, each phase (single core cable) has high sheath current (AWA current = 100A for B, 80A for R&Y). Cable is single core 500mm and at terminals the AWA at CB & primary of transformer are solidly grounded. The transformer vector group is Dyn1.
This high AWA current causes frequent hot spot at CB terminals, and hence lead to repeated repair work.
The question: How to eliminate the high sheath current?
Is it a must to solidly ground both ends of cable?
Appreciate your help to minimize/reduce this sheath high current with no standard violation.






RE: Problem: High cable sheath current for 34.5kV distribution system
The other approach would be to interrupt the sheath at about 100 and 200 meters and cross bond the phases. That will help if the sheath currents are induced from the phase conductors, but would not be as much help if the driver is a difference in ground potential between the two ends.
RE: Problem: High cable sheath current for 34.5kV distribution system
Can you help for standard reference? This will help to convince others and expedite the corrective action.
RE: Problem: High cable sheath current for 34.5kV distribution system
RE: Problem: High cable sheath current for 34.5kV distribution system
ANSI/IEEE Std 575-1988
IEEE Guide for the Application of Sheath-Bonding Methods for
Single-Conductor Cables and the Calculation of Induced Voltages and Currents in Cable Sheaths
RE: Problem: High cable sheath current for 34.5kV distribution system
Cross bonding with cables at this distance wouldn't be economical.
RE: Problem: High cable sheath current for 34.5kV distribution system
Tyco Electronics Energy Division Cross bonding and sectionalisation for high-voltage cable systems
http://www.coronabd.com/download/Raychem%20132KV%2...
RE: Problem: High cable sheath current for 34.5kV distribution system
But the unbalance in the sheath current is really strange. The sheath current for two phases = 75A/phase, while for the third = 95A.
Is there any explanation for that?
RE: Problem: High cable sheath current for 34.5kV distribution system
RE: Problem: High cable sheath current for 34.5kV distribution system
The armor [aluminum wires] current it could be measured at the connection with the shield [copper tape] and the total current could be affected by this connection [one link is missing, for instance].
RE: Problem: High cable sheath current for 34.5kV distribution system
RE: Problem: High cable sheath current for 34.5kV distribution system
You have mentioned that the cable is having an AWA (Aluminium Wire Armour). If the armour is Aluminium then how there are induced currents due to the line current flowing in the main conductor?
Also could you please mention how many runs per phase and the cable laying configuration (whether tre-foil or flat formation)?
But I suspect due to AWA bonding at both ends, the Aluminum armour may be a good path for other ground currents (such as third harmonic currents) prevailing in that area?