Overcurrent Protection 50, 51, 50N, 51N; General - Siemens SIPROTEC 4 Manual

Functions

2.2 Overcurrent Protection 50, 51, 50N, 51N

2.2 Overcurrent Protection 50, 51, 50N, 51N
The overcurrent protection is provided with a total of four elements each for the phase currents and the
ground current. All elements are independent from each other and can be combined as desired.
If it is desired in isolated or resonant-grounded systems that three-phase devices should work together with
two-phase protection equipment, the overcurrent protection can be configured in such a way that it allows
twophase operation besides the three-phase mode (see Section
The high-set elements 50-2, 50-3, 50N-2, 50N-3 as well as the overcurrent elements 50-1 and 50N-1 always
operate with a definite tripping time (51), the elements 51 and 51N always with an inverse tripping time (50).
Applications
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The non-directional overcurrent protection is applicable for networks that are radial and supplied from a
single source or open looped networks, for backup protection of differential protective schemes of all
types of lines, transformers, generators and busbars.

General

2.2.1
The overcurrent protection for the ground current can either operate with measured values Ι
quantities 3Ι0 calculated from the three phase currents. Which values are used depends on the setting of
parameter 613 Gnd O/Cprot. w. and the selected type of connection of the current transformers. Informa-
tion on this can be found in Chapter
Examples. Devices featuring a sensitive ground current input, however, generally use the calculated quantity
3Ι0.
All overcurrent elements enabled in the device may be blocked via the automatic reclosing function
(depending on the cycle) or via an external signal to the binary inputs of the device. Removal of blocking
during pickup will restart time delays. The Manual Close signal is an exception in this case. If a circuit breaker
is manually closed onto a fault, it can be re-opened immediately. For overcurrent elements or high-set
elements the delay may be bypassed via a Manual Close pulse, thus resulting in high speed tripping. This pulse
is extended up to at least 300 ms.
The automatic reclosure function 79 may also initiate immediate tripping for the overcurrent and high-set
elements depending on the cycle.
Pickup of the definite-time elements can be stabilized by setting the dropout times. This protection is used in
systems where intermittent faults occur. Combined with electromechanical relays, it allows different dropout
responses to be adjusted and a time grading of digital and electromechanical relays to be implemented.
Pickup and delay settings may be quickly adapted to system requirements via dynamic setting changeover
(see Section 2.4 Dynamic Cold Load
Tripping by the 50-1 and 51 elements (in phases), 50N-1 and 51N elements (in ground path) may be blocked
for inrush conditions by utilizing the inrush restraint feature.
The following table gives an overview of the interconnections to other functions of the devices 7SJ80.
Table 2-2
Overcurrent
Protection
Elements
50-1
50-2
50-3
51
50N-1
50N-2
50N-3
56
2.1.3.2 Setting
Pickup).
Interconnection to other functions
Connection to
Automatic
Reclosing
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2.1.3.2 Setting
Notes, connection examples in Appendix
Manual Dynamic Cold Load
CLOSE Pickup
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Notes).
or with the
N
C Connection
Inrush Restraint
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SIPROTEC 4, 7SJ80, Manual
E50417-G1140-C343-A8, Edition 12.2017
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