Overcurrent Protection 50, 51, 50N, 51N; General; Definite Time, High-Set Elements 50-3, 50-2, 50N-3, 50N-2 - Siemens 7SC80 Manual

2.2

Overcurrent Protection 50, 51, 50N, 51N

The overcurrent protection is the main protection function of the 7SC80 relay. Each phase current and ground
current is provided with three definite time and several inverse time 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
twophase protection equipment, the overcurrent protection can be configured in such a way that it allows
twophase operation besides three-phase mode (see Section
The high-current elements 50-3 and 50-2 as well as the overcurrent element 50-1 always operate with a defi-
nite 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.

General

2.2.1
Depending on the parameter 613Gnd O/Cprot. w., the overcurrent protection for the ground current can
either operate with measured values Ι
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 thresholds, delay times, and the characteristic type can be adapted to the system conditions tempora-
rily in interaction with the dynamic cold load pickup function (see Section
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.
2.2.2

Definite Time, High-set Elements 50-3, 50-2, 50N-3, 50N-2

For each element, an individual pickup value 50-3 PICKUP, 50-2 PICKUP or 50N-3 PICKUP, 50N-2
PICKUP is set. For 50-3 PICKUP and 50N-3 PICKUP, it is possible to measure the Instantaneous in
addition to Fundamental and True RMS. If set to Instantaneous, the element picks up at 2 · √2 · setting
value (rms). Each phase current and the ground current is compared separately per element with the common
pickup values element 50-3 PICKUP, 50-2 PICKUP or 50N-3 PICKUP, 50N-2 PICKUP. If the respective
pickup value is exceeded, this is signaled. If the inrush restraint feature is used, either the normal pickup indi-
cations or the corresponding inrush indications are issued, depending on the inrush detection. After expiry of
the associated delay times 50-3 DELAY, 50-2 DELAY or 50N-3 DELAY, 50N-2 DELAY, the trip commands
are output if no inrush current is present or inrush current detection is not active. If an inrush current condi-
tion is detected while the inrush current detection is active, no trip is initiated, but a message is generated
indicating that the timer has elapsed. Tripping signals and signals on the expiration of time delay are available
separately for each element. The dropout value is roughly equal to 95 % of the pickup value for currents > 0.3
. If measurement of the instantaneous values is parameterized for the 50-3 or 50N-3 element, the dropout
Ι
Nom
ratio is 90 %.
SIPROTEC Compact, 7SC80, Manual
E50417-G1140-C486-A8, Edition 07.2017
2.1.3.2 Setting
or with the quantities 3Ι0 calculated from the three phase currents.
N
2.2 Overcurrent Protection 50, 51, 50N, 51N
Notes).
2.4 Dynamic Cold Load
Functions
Pickup).
71