# GE L60 Instruction Manual Page 388

Line phase comparison system, ur series.

5.6 CONTROL ELEMENTS
The thermal overload protection element corresponds to the IEC 255-8 standard and is used to detect thermal overload
conditions in protected power system elements. Choosing an appropriate time constant element can be used to protect dif-
ferent elements of the power system. The cold curve characteristic is applied when the previous averaged load current over
the last 5 cycles is less than 10% of the base current. If this current is greater or equal than 10% than the base current, then
the hot curve characteristic is applied.
The IEC255-8 cold curve is defined as follows:
The IEC255-8 hot curve is defined as follows:
In the above equations,
t
= time to operate.
op
τ
= thermal protection trip time constant.
op
I = measured overload RMS current.
I
p
k= IEC 255-8 k-factor applied to I
I
= protected element base (nominal) current.
B
5
To ensure element accuracy for high overcurrent conditions, the maximum value of I/(k x I
istically it is exceeding this value.
The reset time of the thermal overload protection element is also time delayed using following formula:
In the above equation,
τ
= thermal protection trip time constant.
rst
T
is a minimum reset time setting
min
5-250
2
I
τ
×
------------------------- -
t
ln
=
op
op
2
(
)
I
kI
B
2
2
I
I
p
τ
×
------------------------- -
t
ln
=
op
op
2
(
)
I
kI
B
, defining maximum permissible current above nominal current.
B
2
(
)
kI
B
τ
×
---------------------------- -
t
ln
=
rst
rst
2
2
I
(
kI
)
B
L60 Line Phase Comparison System
2
2
) is limited to 8, even when real-
B
T
+
min
5 SETTINGS
(EQ 5.27)
(EQ 5.28)
(EQ 5.29)
GE Multilin  