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4.5 R1/2 49 Resistor Thermal Overload
Thermal overload element applied to each phase of each resistor independently.
Accuracy
Pickup
Reset
Repeatability
Operate Time
Frequency Range
Operating Time
Characteristic
THERMAL
IEC 60255-8
τ Factor
4.6 50 Resistor Open Circuit
An instantaneous/delayed overcurrent element measures the difference in currents on each resistor on a phase-by-
phase basis.
Accuracy
Pickup
Reset
Repeatability
Operate Time
Operating Time
Current Applied
2 x setting
4 x setting
4.7 49 Reactor Thermal Overload
Thermal overload element applied to each phase of the reactor independently.
Accuracy
Pickup
Reset
Repeatability
Operate Time
Frequency Range
Operating Time
Characteristic
THERMAL
IEC 60255-8
τ Factor
4.8 50 Backup Overcurrent
Three phase definite time overcurrent element.
©2011 Siemens Protection Devices Limited
MSCDN – MP2A Performance Specification
100% of setting ± 5% or ± 0.02 I
≥ 95% of I
s
± 2%
± 5% or ± 0.1s
st
nd
th
1
, 2
...15
Harmonic
Ranges
Operate times are calculated from:
⎧
−
2
2
I
I
=
τ
×
⎨
P
t
ln
(
)
−
×
2
2
⎩
I
k
I
B
τ = thermal time constant
I = measured current
I
= prior current
P
I
= basic current
B
k = constant
1 to 10000 Δ 0.5 seconds
100% of setting ± 5% or ± 0.02 I
≥ 95% of I
s
± 2%
± 1% or ± 10ms
Typical
2 cycles
1.5 cycle
100% of setting ± 5% or ± 0.02 I
≥ 95% of I
s
± 2%
± 5%
st
nd
th
1
, 2
...15
Harmonic
Ranges
Operate times are calculated from:
⎧
−
2
2
I
I
=
τ
×
⎨
P
t
ln
(
)
−
×
2
2
⎩
I
k
I
B
τ = thermal time constant
I = measured current
I
= prior current
P
I
= basic current
B
k = constant
1 to 1000 Δ 0.5 minutes
n
⎫
⎬
⎭
n
n
⎫
⎬
⎭
Chapter 2 Page 9 of 13
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