2.9 Thermal Overload Protection (ANSI 49)
67
7UM61 Manual
C53000-G1176-C127-3
If the temperature input is used, the trip times change if the coolant temperature devi-
ates from the internal reference temperature of 104.00 °F or 40 °C. The following
formula can be used to calculate the trip time:
with
τ TIME CONSTANT (address 1603)
k K-FACTOR (address 1602)
I
N
Nominal Device Current
I Actually Flowing Secondary Current
I
Pre
Previous Load Current
Θ
N
Temperature with Nominal Current I
N
(Address 1605)
Θ
K
Coolant Temperature Input (Scaling with Address 1608 or 1609)
Example:
Machine:
I
NMach
= 483 A
I
maxMach
= 1.15 I
N
at Θ
K
= 40 °C
τ
th
= 600 s (thermal time constant of the machine)
Current transformer: 500 A/1 A
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