GRD110
7
Figure 2 - IEC60255-8 Thermal Characteristics
IEC60255-8 Thermal Characteristics
Thermal Curves (Cold Curve -
no prior load)
0.01
0.1
1
10
100
1000
1
10
Overload Current (Multiple of k.I
FLC
)
O
pe
ra
te
T
im
e (
m
in
ut
es
)
W
=1
W
=2
W
=5
W
=10
W
=20
W
=50
W
=100
Thermal Curves (Hot Curve -
90% prior load)
0.001
0.01
0.1
1
10
100
1000
1
10
Overload Current (Multiple of k.I
FLC
)
O
pe
ra
te
T
im
e (
m
in
ut
es
)
W
=100
W
=50
W
=20
W
=10
W
=5
W
=2
W
=1
»
¼
º
«
¬
ª
2
2
2
.
.
FLC
I
k
I
I
Ln
t
W
;
»
¼
º
«
¬
ª
2
2
2
2
.
.
FLC
P
I
k
I
I
I
Ln
t
W
IEC60255-8 ‘Cold’ Curve
IEC60255-8 ‘Hot’ Curve
t = time to trip for constant overload current I (seconds)
I = overload current (largest phase current) (pu)
I
P
= previous load current (pu)
k.I
FLC
(or I
T
) = thermal overload current setting (pu)
W
= thermal time constant (seconds)
Ln = natural logarithm
08.02.18 GRD110_CS3.indd
Summary of Contents for GRD110
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