ABB RELION SMU615 Technical Manual page 175

1MRS758407 C
Accumulation of I y t
Accumulation of I
known as the current exponent. The factor y depends on the type of the circuit
breaker. For oil circuit breakers, the factor y is normally 2. In case of a high-voltage
system, the factor y can be 1.4...1.5.
Remaining life of the breaker
Every time the breaker operates, the life of the circuit breaker reduces due to
wearing. The wearing in the breaker depends on the tripping current, and the
remaining life of the breaker is estimated from the circuit breaker trip curve
provided by the manufacturer.
Example for estimating the remaining life of a circuit breaker
Figure 119: Trip Curves for a typical 12 kV, 630 A, 16 kA vacuum interrupter
Nr
Ia
Calculation of Directional Coef
The directional coefficient is calculated according to the formula:
Directional Coef
SMU615
Technical Manual
y
t calculates the accumulated energy ΣI
the number of closing-opening operations allowed for the circuit breaker
the current at the time of tripping of the circuit breaker
 
B
log  
 
A
= = −
. 2 2609
 
I
f
 
log
I
 
r
Condition monitoring functions
y
t, where the factor y is
(Equation 7)
175