Inverse Time Overcurrent (51C); Figure 2-5 Cold Load Logic Diagram - Siemens 7SR21 Manual

Pick-up Time
CB Open
Drop-off Time
CB Closed
Reduced
Reduced
Current Level
Current
c
Enabled
Disabled
<
IL1
<
IL2
<
IL3
Ensure that the Cold load active is not raised. This can be reset by CB closed for more than the Cold Load Drop-
off Time or current less than the Reduced Current Level for greater than the Reduced Current Time. Check the
Cold Load Pick-up Delay by applying or simulating CB Open. Measure the time delay before Cold Load Active is
raised. Apply current above the Reduced Current Level if this functionality is Enabled before applying CB Closed.
Measure the time for Cold Load Active to reset.
2.4.1

Inverse Time Overcurrent (51C)

It will be advantageous to map the function being tested to temporarily drive the relevant Pickup output in the
Pickup Config sub-menu in the Output Config menu as this will allow the Pick-up led to operate for the function.
Gradually increase current until Pickup LED operates.
Apply 2x setting current and record operating time.
Apply 5x setting current and record operating time.
Compare to calculated values for operating times
Ph. Dir
P.U.
D.O.
&
I (I )
L1 A
TIMING
I (I )
TESTS
L2 B
I (I )
L3 C
©2010 Siemens Protection Devices Limited
Cold Load
Enabled
Disabled
Reduced Current DTL
&

Figure 2-5 Cold Load Logic diagram

Char.
(NI EI VI Is
TM
(A)
LTI,
DTL)
7SR21 & 7SR22 Argus Commissioning and Maintenance
&
S
Q
1
R 51c-n Setting
51c-n Charact
51c-n Time Mult
51c-n Delay (DTL)
51c-n Min. Operate Time
51c-n Follower DTL
51c-n Reset
c
start
L1 Dir En c
start
c
L2 Dir En
start
c
L3 Dir En
Operate Current
P.U. D.O.
(Amps) (Amps)
51c
See Delayed
Overcurrent
(51-n)
1
General Starter
trip
1
trip
51-n
trip
Operate Time
2 x Is 5 x Is
Tol
(sec) (sec)
Chapter 6 Page 22 of 69
Tol