Siemens 7SR11 Argus Manual page 5

50/51 Phase Fault
50 INST/DTL and 51 IDMTL/DTL elements provide overcurrent
protection, each with independent settings for pickup
current, time-multiplier (51) and time-delays. User can select
IEC or ANSI time current characteristics. The IDMT stage has
a user programmable reset characteristic, either DTL or
shaped current ~ time reset characteristic, to improve
grading with electromechanical protection.
50G/51G/50N/51N Earth Fault/Sensitive Earth Fault
Two earth fault measurement modes are available. One
mode directly measures the earth current from an
independent CT, or the residual connection of the 3 line CTs.
This input can be ordered as either earth fault or sensitive
earth fault (50G/51G).
The second mode derives the earth current internally from
the 3 phase CT inputs to give earth fault (50N/51N). 50
INST/DTL and 51 IDMTL/DTL elements provide overcurrent
protection, each with independent settings for pickup
current, time-multiplier (51) and time-delays. User can select
IEC or ANSI time current characteristics. The IDMT stage has
a user programmable reset characteristic either DTL or
shaped current ~ time reset characteristic to improve grading
with electromechanical protection.
1000
100
Time
(sec)
10
1
0.1
2 3 4 5
1
Current (multiples of setting)
Fig 5. IEC Overcurrent Curves
Siemens Protection Devices Limited
Long Time Inverse
Normal Inverse
Very Inverse
Extremely Inverse
6 8 20 30 40 50 60
10
1000
100
Time
(sec)
10
1
0.1
2
1
Fig 6. ANSI Overcurrent Curves
51V Voltage Controlled Overcurrent
Each phase shaped overcurrent element can be
independently controlled by the level of measured input
voltage. For applied voltages above setting the 51-n
element operates in accordance with its current setting but
for voltages below the setting a multiplier is applied to
reduce the 51-n pick up current setting.
59N Neutral Overvoltage
Neutral overvoltage can be used to detect earth faults in
high impedance earthed or isolated systems.
Operates if the neutral voltage exceeds setting for duration
of delay.
60CTS CT Supervision
The relay has two methods of CT supervision depending
upon the relay model. The 7SR11 monitors each phase
current input and operates if any one or two inputs fall
below the setting. The 7SR12 considers the presence of
negative phase sequence current, without an equivalent
level of negative phase sequence voltage, for a user set time
as a CT failure.
80
100
Both element types have user operate and delay settings.
60VTS VT Supervision
The VT supervision uses a combination of negative phase
sequence voltage and negative phase sequence current to
detect a VT fuse failure. This condition may be alarmed or
used to inhibit voltage dependent functions. Element has
user operate and delay settings.
Moderately Inverse
Extremely Inverse
3 4 5 6 8 20 30
10
Current (multiples of setting)
Very Inverse
40 50 60 80
100
5