Overcurrent Protection (50, 50N, 51, 51N); Description Of Instantaneous Overcurrent Protection; Definite Time, Instantaneous Overcurrent Protection (50, 50N) - Siemens SIPROTEC 7SJ62 Instruction Manual

Functions
6.2

Overcurrent Protection (50, 50N, 51, 51N)

General
6.2.1

Description of Instantaneous Overcurrent Protection

6.2.1.1

Definite Time, Instantaneous Overcurrent Protection (50, 50N)

6-18
Time-overcurrent protection is the main protective function of the 7SJ62 relay. It may
be enabled or disabled for phase or ground faults, and may be configured with various
time-overcurrent characteristic curves.
There are four definite time (Instantaneous elements with optional timers) and two in-
verse time-overcurrent elements in the device. The definite time elements include two
phase elements and two ground elements. The definite time (Instantaneous) phase el-
ements are designated 50-2 and 50-1, whereas the definite time (Instantaneous)
ground elements are designated 50N-2 and 50N-1. The inverse time elements include
a phase element designated as 51 and a ground element designated as 51N.
All overcurrent elements, inverse and definite time, enabled in the device may be
blocked via an external signal to the binary inputs of the device. Removal of the exter-
nal signal to the binary input will re-enable these elements. Also, a feature described
as Manual Close Mode can be configured to improve fault clearing times associated
with Switch-on-to-Fault Conditions. Under this situation, the time delay may be by-
passed for one of the three time-overcurrent phase elements and one of the three
time-overcurrent ground elements via an impulse from the external control switch,
thus resulting in high speed tripping. This impuls is prolonged by a period of 300 ms.
The phase and ground elements utilized for high speed tripping in this situation are
selected at addresses  and  respectively.
Pickup and delay settings may be quickly adjusted to system requirements via Cold
Load Pickup function (see Section 6.4).
Tripping by the 50-1, 51, 50N-1, and 51N elements may be blocked for inrush condi-
tions by utilizing the inrush restraint feature (see Section 6.5).
The 50-2 and 50N-2 overcurrent elements, phase and ground currents are compared
separately with the pickup values of the 50-2 and 50N-2 relay elements. Currents
above the pickup values are detected and recorded within the protective relay. After
the user-configured time delay has elapsed, a trip signal is issued.
Figure 6-11 shows the logic diagram for the 50-2 and 50N-2 protection.
The 50-1 and 50N-1 overcurrent elements, phase and ground currents are compared
separately with the pickup values of the 50-1 and 50N-1 relay elements. Currents
above the pickup values are detected and recorded within the protective relay. After
the user-configured time delay has elapsed, a trip signal is issued.
If the inrush restraint feature is enabled (see Section 6.5), and an inrush condition ex-
ist, no tripping takes place, but a message is recorded and displayed indicating when
the overcurrent element time delay elapses.
Different messages are recorded and displayed appear depending on whether tripping
takes place or the time delay expires without tripping.
7SJ62 Manual
C53000-G1140-C121-1