Functions
2.11 Thermal Overload Protection (ANSI 49)
SIPROTEC, 7UM62, Manual
C53000-G1176-C149-7, Release date 03.2010
88
If the temperature input is used, the trip times change if the coolant temperature deviates from the internal ref-
erence temperature of 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 TEMP. RISE I)
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
Θ
NMach
= 93 °C
τ
th
= 600 s (thermal time constant of the machine)
Current transformer: 500 A/1 A
With a supposed load current of I = 1.5 · I
N, Device
and a preload I
Pre
= 0, the following trip times result for different
ambient temperatures Θ
K
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