Bushing Seperation vs. Bus seperation
Bushing Seperation vs. Bus seperation
(OP)
I've had a question posed by one of my construction crews regarding a 115kV to 69kV station we are converting to all 115kV. All the bus work is designed to meet 115kV standards already, but the low side switch currently on site is a 115kV switch spaced at the 69kV separation of 6'. We are in the process of moving these switches to allow a separation of 7'6" based on ANSI C37.32-2002 (7' minimum spacing between conductors). We are also increasing the separation of the PT's and station service.
However, we have noticed that the arrester and bushing phase separation of the high side of the existing 115kV to 69kV auto transformer is approx. 59". So the question has been asked, why can the transformer bushings and arresters on the transformer be spaced less than the open air bus they feed? I've been scouring the ANSI resources we have on hand but cannot find the section that governs phase separation on equipment.
Can you all point me int he right direction?
Thanks,
Tom
However, we have noticed that the arrester and bushing phase separation of the high side of the existing 115kV to 69kV auto transformer is approx. 59". So the question has been asked, why can the transformer bushings and arresters on the transformer be spaced less than the open air bus they feed? I've been scouring the ANSI resources we have on hand but cannot find the section that governs phase separation on equipment.
Can you all point me int he right direction?
Thanks,
Tom






RE: Bushing Seperation vs. Bus seperation
of different phases of the same voltage
RE: Bushing Seperation vs. Bus seperation
What should be the consideration for the gap between bushing and lightning arrester of same phase? Any standard available?
RE: Bushing Seperation vs. Bus seperation
Allow me to offer a few comments:
1) The bushing clearance of electrical apparatus, including transformer and breakers is verified by laboratory testing proven for many years.
2) Air insulated substations are typically composed of assemblies of insulators, bus, and connectors not tested in a factory setting.
3) If reduced clearance is decided, the engineer should prepare an insulation coordination study considering a representative bus gap factor similar to the one published in the enclosed file.
4) For most stations layout, the disconnect switch phase-to-phase clearance is a determinant factor to drive rigid bus metal-to-metal separation.
5) Disconnect switch phase-to-phase is determined by the potential arcing that could be expected on the switch blade (vertical, center, double break, etc.)
5) If flexible cable (string bus) is used instead rigid bus, usually the phase to phase separation is larger except for short run connecting bus to breaker or transformers.
RE: Bushing Seperation vs. Bus seperation