ANSI C2 and clearance in a 230 kV system

[tolin]

I am a littel bit confused regarding all the tables listed in ANSI C2. In table 235-6 the clearance in any direction from line conductor to support arm is listed to 1240 mm. This value conflicts with the requirement to electrical clearance, 2150 mm (IEC 2100 mm) according to table 232-4. Can anyone tell me what the 1240 mm shall be used for, and inform me if i am right or wrong in specifying the minimum requirement to clerance to support structur as 2150 mm.

In addition, is it correct of me to use table 233-1 (2800 mm + evt. sagging) when specifying the vertical clearance to another 230 kV circuit which we are crossing.

In advance, thank you.

 

[jghrist]

Rule 232, and Table 232-4 apply to clearance above ground, roadway, rail or water surfaces, not to the surfaces of supports. Rule 235E is what you should be using for clearance to supports. Note that the clearances in Table 235-6 must be reduced if suspension insulators are used and are unrestrained from movement, see 235E.2. Also, clearances can be reduced if you know the switching surge factor, see 235E.3.

The voltage adder for Rule 233C governing crossings is based on phase to ground voltage of effectively grounded circuits and circuits where ground faults are promptly de-energized. The 2800 mm was calculated with phase to phase voltages. You need to consider the upper circuit at its maximum sag and the lower circuit at its minimum sag for the same ambient temperature. The worst case might be at a high ambient with the upper circuit loaded to the max and the lower circuit unloaded. It also might be at 0 deg C with ice on the upper circuit and no ice on the lower circuit. You may also be able to reduce clearances per 233C.3 if you know the switching surge factor.

 

[stevenal]

I think Jim mean't to say clearances must be increased in the case of unrestrained suspension insulators.

 

[jghrist]

stevenal is right.