Running MV/HV Cables in Flat Formation vs. Trefoil
Running MV/HV Cables in Flat Formation vs. Trefoil
(OP)
Running cables inside substations in trefoil formation ensures balanced voltages; however, due to ampacity requirements, flat formation proves to be more economical.
What is the criterion to select running cables in flat vs. trefoil other than ampacity?
Regarding voltage unbalances in flat formation,it appears very similar to running a 220 kV bus with flat tubular bus, I have never seen anyone cares about unbalance voltages at the level.
However, with MV cables on 11 kV (13.8 kV), A power transformer may be connected to switchgear with flat cables, usually with multiple runs per phase, I doubt the unbalance may be reasonable.
Any similar experiences or calculations references?
What is the criterion to select running cables in flat vs. trefoil other than ampacity?
Regarding voltage unbalances in flat formation,it appears very similar to running a 220 kV bus with flat tubular bus, I have never seen anyone cares about unbalance voltages at the level.
However, with MV cables on 11 kV (13.8 kV), A power transformer may be connected to switchgear with flat cables, usually with multiple runs per phase, I doubt the unbalance may be reasonable.
Any similar experiences or calculations references?






RE: Running MV/HV Cables in Flat Formation vs. Trefoil
For underground cable the shielding method are usually more relevant than the phase voltage difference.
RE: Running MV/HV Cables in Flat Formation vs. Trefoil
To get the rating benefit of the increased cable spacing with flat formation, you would probably need to use single point bonding. If you bonded the screens solidly at both ends, the increased circulating current in the screens would act to cancel out the benefit of flat formation.
Regards
Marmite
RE: Running MV/HV Cables in Flat Formation vs. Trefoil
RE: Running MV/HV Cables in Flat Formation vs. Trefoil
Power0020, there are fundamentally 3 types of HV power cable shielding method: One end-grounded,both ends-grounded and cross bonding. Sometime variation with surge arrester (shield voltage limiters) are used. Below is an excerpt from various sources captured in a table and a generic plot with additional info of cable performance for flat and trifoil configuration.
Hope this help.
RE: Running MV/HV Cables in Flat Formation vs. Trefoil
May you please upload the photo in a file form, the text is unreadable.
RE: Running MV/HV Cables in Flat Formation vs. Trefoil
I assume that it can go less than the single point bonding in case of unbalance in minor section lengths raising some circulating amps?
RE: Running MV/HV Cables in Flat Formation vs. Trefoil
Per your request, a readable pdf file is uploaded.
RE: Running MV/HV Cables in Flat Formation vs. Trefoil