GE UR Series L90, Инструкция по эксплуатации

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GE Multilin L90 Line Current Differential System 5-295
5 SETTINGS 5.7 CONTROL ELEMENTS
5
The reset time of the thermal overload protection element is also time delayed using following formula:
(EQ 5.36)
In the above equation,
•
τ
rst
= thermal protection trip time constant.
• T
min
is a minimum reset time setting
Figure 5–159: IEC 255-8 SAMPLE OPERATE AND RESET CURVES
The thermal overload protection element estimates accumulated thermal energy E using the following equations calculated
each power cycle. When current is greater than the pickup level, I
n
> k × I
B
, element starts increasing the thermal energy:
(EQ 5.37)
When current is less than the dropout level, I
n
> 0.97 × k × I
B
, the element starts decreasing the thermal energy:
t
rst

rst
kI
B
 
2
I
2
kI
B
 
2
–
-----------------------------
 
 
 
ln

T
min
+ =
,,SNS
WPLQ
ƌUVW
ƌRS
7PLQ
$&'5
E
n
E
n 1
–
t

t
op In
 
---------------
+ =