Where did Phase Clearance above grade come from?
Where did Phase Clearance above grade come from?
(OP)
I am trying to find any research papers or articles on the topic of minimum phase-phase, phase to ground and particularly clearance above grade.
I know that for 138kV you need 13ft clearance above grade and for 345kV 18ft etc, but I don't know how these numbers are derived.
Any help or direction will be much appreciated.
I know that for 138kV you need 13ft clearance above grade and for 345kV 18ft etc, but I don't know how these numbers are derived.
Any help or direction will be much appreciated.






RE: Where did Phase Clearance above grade come from?
Your clearances seem low. Reduced values are allowed for pedestrian only areas, but anywhere a four wheel drive can possibly get to must be considered to have vehicle access.
Don't know about any research, though.
RE: Where did Phase Clearance above grade come from?
Alan
RE: Where did Phase Clearance above grade come from?
Also see 1427-2005 IEEE Guide for Recommended Electrical Clearances and Insulation Levels in Air Insulated Electrical Power Substations
"This guide, covering three-phase ac systems from 1 kV to 800 kV, provides recommended electrical operating and safety clearances and insulation levels in air-insulated electric supply substations; addresses insulation coordination procedures; provides design procedures for the selection and coordination of the insulation levels within the station as they relate to substation clearances; and addresses how reduced clearances in high-voltage ac substations will allow for compact bus arrangements and substation voltage uprating applications."
IEEE Std 1427 includes a discussion of the historical background of clearances as well as the technical requirements, but does not cover the electrical safety clearances of the NESC or ANSI C37.32 in detail.
RE: Where did Phase Clearance above grade come from?
RE: Where did Phase Clearance above grade come from?
I also noticed that 1427 has a clause suggesting that there my be conflicts between it and NESC and in case of conflicts local laws and regulations prevail.
The reason for me asking this question is because I am working on a project where people are experiencing shocks while opening breaker cabinets or around the fence, and one possible scenario that has been suggested is that the 345kV bus height is at its minimum clearance of 18ft and might be causing some induced voltage. I am trying to find a way to verify that statement.
RE: Where did Phase Clearance above grade come from?
SG6 has been rescinded. All these rules are for safety. The static like shocks you describe are not considered to be dangerous.
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RE: Where did Phase Clearance above grade come from?
RE: Where did Phase Clearance above grade come from?
I especially liked the "run for your life" comment.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Where did Phase Clearance above grade come from?
Induced voltage can happen when the object is insulated from the ground.
RE: Where did Phase Clearance above grade come from?
I would assume that this induced voltage would be something equal to
E = Io x (Zap+Zbp+Zcp) + I1 x (Zap+ a^2 x Zbp +a x Zcp)+ I2 x (Zap+ a x Zbp + a^2 x Zcp)
RE: Where did Phase Clearance above grade come from?
RE: Where did Phase Clearance above grade come from?
RE: Where did Phase Clearance above grade come from?
jghrist,
I agree with you that the voltage would be like a capacitive divider, but I am trying to come up with an equation that would describe this voltage drop as one moves away from the phase conductors.
RE: Where did Phase Clearance above grade come from?
Induced voltages on fence wires and pipelines by AC power transmission lines
Abdel-Salam, M. Al-Shehri, A.
Dept. of Electr. Eng., King Fahd Univ. of Pet. & Miner., Dhahran, Saudi Arabia;
This paper appears in: Industry Applications, IEEE Transactions on
Publication Date: March-April 1994
Volume: 30 , Issue: 2
On page(s): 341 - 349
ISSN: 0093-9994
CODEN: ITIACR
INSPEC Accession Number:4708413
Digital Object Identifier: 10.1109/28.287525
Current Version Published: 2002-08-06
Abstract
A method is developed for calculating the induced voltages on fence wires/pipelines underneath AC power transmission lines. The method is based on the charge simulation technique and takes into account the disturbances of the electric field and potential due to the presence of the fence wire/pipeline underneath the line. The calculated values of the induced voltage on fence wires are compared with those measured before. Induced voltages on pipelines underneath 230- and 380-kV lines are measured, correlated to the calculated values and discussed in the light of electric field induction on objects adjacent to AC power transmission lines
RE: Where did Phase Clearance above grade come from?
The process described by Abdel-Salam is very complicated and he just assume some numbers for several vriables without describing why. As such I am back to square one. I noticed that the topic has been discussed in the past and veritas suggested that he had a spreadsheet that does the calculation for him. I wonder if he could shed some light on the topic. The spreadsheet I have created only accounts for induced voltage due to phase imbalance and I am looking for one that would predict induced voltage even during normal operation.
RE: Where did Phase Clearance above grade come from?
RE: Where did Phase Clearance above grade come from?
where
w= 2*pi()*f
D = eo x E
A = surface area
however I am having difficulty correlating the two and trying to find out what the actual induced voltage would be.
Any suggestions?