Cable-charging breaking current

[jokerx]

Dear all expertise,
Please help me to explain what cable-charging breaking current is? What is different between 10A and 22A cable-charging breaking current in load break switch?
Can anyone provide a tutorial, or point me to a publication that can give me a good background on the subject?

Thank you very much.

 

[jbartos]

Suggestion: Visit

http://www.abb.com/GLOBAL/abbzh/ABB...ile/9.+SafeRing+SafePlus+-+Technical+Data.pdf

page 73 item 12 "Earth Fault Cable Charging"

http://www.abb.com/GLOBAL/ABBZH/ABB...0556E9D/$file/EDT+Compact+ENG_Ed2_May2001.pdf

http://www.cgswgear.com/products/sf72.5sfm.pdf

Transmission lines, especially high voltage ones, are charged with a capacitive charge that causes the cable charge breaking current.
There is also charging current to ground, which is a different current. It is often used for a selection of the system grounding method.
The charging current is a capacitive current that usually flows from electrical equipment to ground and flows to the system neutral.
Reference:
Electrical Transmission and Distribution Reference Book by Central Station Engineers of the Westinghouse Electric Corporation, East Pittsburgh, Pennsylvania, 1064,
Page 279 Section IV Typical Transmission Line Characteristics

 

[jokerx]

Dear jbartos,
Thank you very much for your answer. However, it doesn’t correct exactly. The question is what phenomena happen during open circuit connected with cable. And what is different between 10A and 22A breaking current?

Thank all expertise for helping again.

 

[jbartos]

Comment: The cable capacitive reactance in Ohms/mile for example, is making the cable a charged distributed capacitor. Distributed capacitance or capacitor means that the total cable capacitance consists of many small capacitances added along the cable length. If the cable has an interrupter open at its load end, then the load break switch at the source side will be "making" or closing 10A flowing into discharged distributed capacitance along the cable length. Conversely, if the cable has its distributed capacitance charged and interrupter is breaking the capacitive current flowing in the cable, it will be interrupting the 22A capacitive current of the capacitively charged cable viewed as the distributed capacitor along the cable length.
If there is any particular load break switch under consideration, then the load break switch manufacturer might be contacted for an application note for this product to have the switch parameters demonstrated via interruption of the cable charging and cable breaking capacitive reactance current that is a result of the stored capacitive energy in the cable.

 

[jokerx]

Dear jbartos,
Thank you very much for your answer. However, it doesn’t clear for me. I think that because of open question so it’s hard to answer. I shall ask again.
1. Difference in rated cable charging breaking current is up on difference in line capacitive, right?
2. What happen on contact of load break switch during breaking? …. High voltage transient or etc?


Thank all expertise for helping again^2.

 

[stevenal]

I think the difference is 12A. Cable charging current is nearly 90 degrees out of phase with the voltage. The arc of the openning switch will tend to break near the current zero crossing. At this point, maximum voltage has developed across the switch contacts, so restrike is likely. The process may then repeat. An underated switch will likely continue to restrike until the arc breaks over to ground or an adjacent phase. May be some info at the Joslyn web site.

 

[jbartos]

Suggestion: Reference:
IEEE Std 399-1997 (Brown Book) IEEE Recommended Practice for Industrial and Commercial Power System Analysis,
Chapter 11 Switching Transient Studies on page 313
Section 11.1.6 Transient Example: Capacitor Voltage
Figure 11-11 Capacitor Bank Switching
etc.