IEEE C37.32 Table 5 Phase-to-phase spacing

[rs1756]

I have few questions regarding IEEE standard C37.32-1996 Table 5. For a 69kV system the table gives centerline-to-centerline phase spacing for Rigid Busses as 60 inches, but for rigid conductors it requires the phase spacing metal-to-metal as 31 inches. If I have surge arrestors, or PTs, or CCVTs, or just plain strain (non-rigid) conductors, which clearance do I go by, 31 inches metal-to-metal or 60 inches centerline-to-centerline? Is rigid bus is the same thing as rigid conductor or is it different? If I am adjusting the phase-to-phase clearance for using strain (non-rigid) conductors instead of rigid conductors do I apply that adjustment to phase spacing for rigid buses as well?

 

[bacon4life]

The 2002 version actually lists different centerline clearances based on whether you are using vertical break, horn gap or side break switches. Depending on the situation, we may use the same centerline clearance or a somewhat larger clearance for flexible connections. I thought we had a requirement flexible connections to be at least 1.5 times the minimum metal to metal clearance, but I can't find it listed anywhere.

Rigid bus and rigid conductor is the same as far as I can tell.

 

[Viceng]

"The minimum metal-to-metal clearances should be maintained at all times with the switches in the open position, closed position, or anywhere between the open and closed positions." - the metal-to-metal clearance seems to apply to the scenario of disconnect switch positions which would make sense as C37.32 - deals with High voltage switches. I would imagine this distance (31 inches) would be required to avoid arcing to unwanted metal as a switch moves.

I believe the centerline-to-centerline spacing is between phases and would not apply between the same phase while the other distance does.

 

[Kiribanda]

rs1756,

1)Column 3 (31 inches) is ONLY for rigid buses like IPS Aluminum pipes. So if your line side or load side is connected to set of rigid buses you have to use Column 3.

Note:Also if you use very short ACSR conductors either on the line side or load side still you can use Column 3 because the possibility of conductor sway/ swing is very minimum.In that case a very short run (2-3 m max for me)of ACSR conductor can be reasonbly approximated to a rigid bus!!

2)Column 6 (60 inches) is exclusively the minimum distance to be maintained if you are using ACSR conductor spans. Sometimes you may have to increase the given centre line spacing if you expect a possible conductor sway during short circuit conditions at the location.

Trust the above helps

 

[stevenal]

The centerline to centerline phase spacings are for conductors run geometrically in parallel. The minimum metal to metal distances are for other situations, such as a transverse oriented bus or for bus to other live parts of another phase.

Example: High bus at 7.5kV runs east west using 18" phase spacing. Low bus at the same voltage and spacing runs north south and taps the high bus in the center with a short vertical run. The vertical run must be at least 7" to achieve the metal to metal requirement of high bus phase A to low bus phase B.

In my experience, strain bus uses the same spacings. If long spans are needed, extra space might be advisable, though.