Creepage Distance of CT

[Ekwena1]

Hello the positive thinkers,
Pls l want to know the major way/s of calculating the Creepage distance of power equipments, mostly for current Transformer.
Secondly, How can phase to ground fault be avoided if snow covers the corrugated surface of a power equipment since snow itself is a very good conductor of electricity.
Thanks i do appreciate for your answers.

 

[waross]

Much like glass, water is not a conductor in the solid state. The problem is when the warmth of the CT melts the snow on its surface.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[7anoter4]

Creepage is the shortest path between two conductive parts (or between a conductive part and the bounding surface of the equipment) measured along the surface of the insulation. A proper and adequate creepage distance protects against tracking, a process that produces a partially conducting path of localized deterioration on the surface of an insulating material as a result of the electric discharges on or close to an insulation surface. The degree of tracking required depends on two major factors: the comparative tracking index (CTI) of the material and the degree of pollution in the environment. Used for electrical insulating materials, the CTI provides a numerical value of the voltage that will cause failure by tracking during standard testing. IEC 112 provides a fuller explanation of tracking and CTI.1 Tracking that damages the insulating material normally occurs because of one or more of the following reasons:
• Humidity in the atmosphere.
• Presence of contamination.
Corrosive chemicals.
Altitude at which equipment is to be operated.
See [for up to 1000 V insulation]:

http://www.ce-mag.com/ce-mag.com/archive/01/03/ProductSafety.html

The creepage path is divided into a number of segments half of them protected[shaded] and half of them exposed. The creepage path along an exposed part will be of less electrical resistance then those of unexposed part. But the exposed part may be washed by rain and maintained clean, so a controlled sequence of exposed and concealed segments is the best solution for a certain pollution degree.
The creepage path length to the insulator rated voltage ratio for a medium voltage overhead line may be from 1.7 to 3.5 cm/kV function of polution degree.
Regards

 

[homoly]

See also

http://www.creepage.com/

The IEC 60950 is refered there

 

[7anoter4]

The IEC Standard for Electric Power Equipment Insulators is IEC 815.
IEC 60950 is applicable to mains-powered or battery-powered information technology equipment[telecommunication],
including business equipment and associated equipment, with a rated voltage not exceeding 600V.
The standard is also applicable to such equipment designed and intended to be connected directly
to a telecommunication network and forming part of a subscriber's installation.
Regards

 

[Ekwena1]

7anotre4,
Thanks your link helped.
Thanks all