Overcurrent Protection 50, 51, 50N, 51N; General - Siemens SIPROTEC 7SC80 Series Manual

Functions

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

2.2 Overcurrent Protection 50, 51, 50N, 51N
Overcurrent protection is the main protection function of the 7SC80 relay. Each phase current and the ground
current is provided with four elements. All elements are independent from each other and can be combined as
desired.
If it is desired in grounded or compensated 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 two-
phase operation besides three-phase mode (see Section 2.1.3.2).
The high-current elements 50-3 and 50-2 as well as the overcurrent element 50-1 always operate with a definite
tripping time.
Applications
• Non-directional overcurrent protection is suitable for networks that are radial and supplied from a single
source, or open looped networks, and for backup protection of differential protective schemes of all kinds.
2.2.1

General

Depending on the parameter 613 Gnd O/Cprot. w., the overcurrent protection for the ground current can
either operate with measured values I
The timer for each Element can be blocked via binary input, thus suppressing the trip command. If the blocking
is canceled during pickup, the timer will be restarted. The Manual Close signal is an exception. If a circuit
breaker is manually closed onto a fault, it can be re-opened immediately. For overcurrent elements or high-
current elements, the delay may be bypassed via a Manual Close pulse, thus resulting in instantaneous tripping
after pickup. This pulse is extended up to at least 300 ms.
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 re-
sponses to be adjusted and a time grading of digital and electromechanical relays to be implemented.
Utilizing the inrush restraint feature, tripping by the 50-1 elements in the phases and ground path may be
blocked when inrush current is detected.
The following table gives an overview of the interconnections to other functions of 7SC80.
Table 2-2 Interconnection to Other Functions
Overcurrent protection elements
50-1
50-2
50-3
50N-1
50N-2
50N-3
54
or with the quantities 3I0 calculated from the three phase currents.
N
Manual Inrush current restraint
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E50417-G1140-C486-A1, Release date 12.2011
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SIPROTEC, 7SC80, Manual