Toshiba GRD110 Manual page 7

GRD110
Thermal Curves (Cold Curve -
1000
100
10
1
0.1
0.01
1
Overload Current (Multiple of k.I
IEC60255-8 'Cold' Curve
t = time to trip for constant overload current I (seconds)
I = overload current (largest phase current) (pu)
I = previous load current (pu)
P
k.I (or I ) = thermal overload current setting (pu)
FLC
= thermal time constant (seconds)
Ln = natural logarithm
IEC60255-8 Thermal Characteristics
no prior load)
=100
=50
=20
=10
10
FLC
I 2
t . Ln
2
I 2 k . I
FLC
Figure 2 - IEC60255-8 Thermal Characteristics
Thermal Curves (Hot Curve -
90% prior load)
1000
100
10
1
0.1
=5
0.01
=2
=1
0.001
1
) Overload Current (Multiple of k.I
; t . Ln
IEC60255-8 'Hot' Curve
7
=100
=50
=20
=10
=5
=2
=1
10
)
FLC
I 2 I 2
P
2
I 2 k . I
FLC