EddyWirbelstrom
Electrical
- Feb 17, 2002
- 215
The attached spreadsheet SKM-PTW and IEC 60909-0 Manual Calc.xlsx includes data for a ABB VD4 1212-40 circuit-breaker.
The calculations on Tab ABB VD4 of attached spreadsheet confirms that the breaker has following IEC 62271.100 short-circuit withstand ratings:
Rated short-circuit breaking current ( Ics ) = 40 kA at contact parting time => 72.4 msec
Rated d.c. component of 20% ie. 0.20 * ( sqrt(2)*40 ) = 11.31 kA See Note 1.
Rated peak withstand current (Ip ) or Make current (Im) = 2.5 * 40 = 100 kA
Note 1. IEC 62271.100 Figure 8 demonstrates the a.c. current wave offset due to the apparent presence of d.c. current.
The ratio between breaker Isc and d.c. component ensure sufficent time between a.c. current zeros for the breaker to deionize the arc between breaker contacts.
The calculations on Tab ABB VD4 of attached spreadsheet confirms that the breaker has following IEC 62271.100 short-circuit withstand ratings:
Rated short-circuit breaking current ( Ics ) = 40 kA at contact parting time => 72.4 msec
Rated d.c. component of 20% ie. 0.20 * ( sqrt(2)*40 ) = 11.31 kA See Note 1.
Rated peak withstand current (Ip ) or Make current (Im) = 2.5 * 40 = 100 kA
Note 1. IEC 62271.100 Figure 8 demonstrates the a.c. current wave offset due to the apparent presence of d.c. current.
The ratio between breaker Isc and d.c. component ensure sufficent time between a.c. current zeros for the breaker to deionize the arc between breaker contacts.