Directional Polarity; Definite Time Overcurrent (50N); Inverse Time Overcurrent (51N) - Siemens 7SR21 Manual

2.6.1

Directional Polarity

See section Directional Earth Fault Polarity Check above for testing details.
MTA
Lag (point C)
Pick-up
MTA-85
.............
...........
Derived EF
2.6.2 Definite Time Overcurrent
If DTL setting is small, gradually increase current until element operates.
If DTL is large apply 0.9x setting, check for no operation, apply 1.1x setting, and check operation
Apply 2x setting current if possible and record operating time
Check correct indication, trip output, alarm contacts, waveform record.
Note that these elements can be set to directional.
Is
Phase Dir.
(Amps)
E
If VTS action is set to BLOCK, this option should be tested. Apply balanced voltage and current. Reduce a-phase
voltage to cause a VTS condition. Increase 3P current and check that the element does not operate.
If VTS action is set to Non-Directional, this option should be tested.. Apply balanced voltage and current. Reduce
a-phase voltage to cause a VTS condition. Increase a-phase current and check that the element operates at its
normal setting. Reverse the voltage phase direction whilst checking that the element does not reset.
2.6.3

Inverse Time Overcurrent (51N)

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
P.U.
D.O. Ph. Dir
&
TIMING
E
TESTS
©2010 Siemens Protection Devices Limited
Forward
Lead (point A)
Drop-off Pick-up
MTA+85
............
(50N)
DTL P.U. Current
(sec) Amps
Char.
Is
(NI EI VI LTI, TM
(A)
DTL)
7SR21 & 7SR22 Argus Commissioning and Maintenance
Lead(point B)
Drop-off Pick-up Drop-off
MTA-85
............
Operate Time
2 x Is
Operate Current
P.U. D.O.
Tol
(Amps) (Amps)
Reverse
Lag (point D)
Pick-up Drop-off
MTA-85
............
NOTES
Operate Time
2 x Is 5 x Is
Tol
(sec) (sec)
Chapter 6 Page 26 of 69