MSCDN – MP2A Commissioning
accelerate testing of the thermal elements it is possible to reset the thermal state between tests via a setting
via the FASCIA LCD only:
R1 49 Reset Therm State
Control that allows thermal state to be manually reset
NO, YES
and
R2 49 Reset Therm State
Control that allows thermal state to be manually reset
NO, YES
Selecting YES will reset the thermal state for either R1 or R2.
Alternatively it is possible to program a status input to reset the thermal state, which may be conveniently
operated from a spare thermal trip contact if a full characteristic is required. Applying rated current to each
resistor should result in the thermal state of the element settling to the following level:
%
100
2
2
×
=
θ
θ
I
I
F
I = applied thermal current
I
θ
= thermal overload current setting (or k.I
B
)
The thermal pickup level can be checked by decreasing the thermal time constant to 1s and adjusting the
currents so that about 100% thermal capacity is shown on the Instruments. The operate time can be checked
by first calculating the expected value and injecting current at a multiple of pickup to cause a thermal trip. It is
worth using the thermal time constant to be used during this test but inject current at a high multiple of setting
to speed up the test.
Resistor 1
A B C
Current Applied
Amps
Final thermal state
%
PU Test
A
A
A
Th. Capacity=100%
Timing Test; Tau TC =
Calculated Time= _ _ _._ _s
Current Injected _ _._ x PU
(s)
Repeat for R2.
Resistor 2
A B C
Current Applied
Amps
Final thermal state
%
PU Test
A
A
A
Th. Capacity=100%
Timing Test; Tau TC =
Calculated Time= _ _ _._ _s
Current Injected _ _._ x PU
(s)
Check that the Nominal Currents on the Instruments display value are at an expected value.
8.3 Checking the open circuit protection
Apply the same current (nominal or below) to all phases.
Enable the resistor open circuit elements.
G
n
50 OC
Selects whether the DTL Resistor
Open Circuit Overcurrent element is
enabled
Disabled, Enabled
Enabled
The element should NOT operate at this time. If operation occurs please check the instruments display and
ensure that R1 and R2 nominal current meters all display the same current (within defined tolerances).
©2010 Siemens Protection Devices Limited
Chapter 7 Page 7 of 9
