GE Multilin L60, Instruction Manual

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GE Multilin L60 Line Phase Comparison System 5-283
5 SETTINGS 5.6 CONTROL ELEMENTS
5
Figure 5–141: 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 5.30)
When current is less than the dropout level, I
n
> 0.97 × k × I
B
, the element starts decreasing the thermal energy:
(EQ 5.31)
In the above equations,
• Δ t is the power cycle duration
• n is the power cycle index
• t
op ( In )
is the trip time calculated at index n as per the IEC255-8 cold curve or hot curve equations
• t
rst ( In )
is the reset time calculated at index n as per the reset time equation
• I
n
is the measured overload RMS current at index n
0.1 1 10 100
I / Ipkp
t (min)
0.01
0.1
1
10
100
τ = 30
rst
τ = 30
op
T = 10
min
827724A1.CDR
E
n
E
n 1
–
t

t
op In
 
---------------
+ =
E
n
E
n 1
–
t

t
rst In
 
---------------
– =