Siemens SIPROTEC 4 7SJ61 User Manual

Ground Fault Protection 64, 67N(s), 50N(s), 51N(s)
Depending on the variant, the fourth current input of the multi-functional protection relays Depending on the
variant, the fourth current input of the multi-functional protection relays 7SJ62/64 is equipped either with a
sensitive input transformer or a standard transformer for 1/5 A. is equipped either with a sensitive input trans-
former or a standard transformer for 1/5 A.
In the first case, the protective function is designed for ground fault detection in isolated or compensated
systems due to its high sensitivity. It is not really suited for ground fault detection with large ground currents
since the linear range is transcended at about 1.6 A at the sensitive ground fault detection relay terminals.
Applications
•
Sensitive ground fault detection may be used in isolated or compensated systems to detect ground faults,
to determine phases affected by ground faults, and to specify the direction of ground faults.
•
In solidly or low-resistance grounded systems, sensitive ground fault detection is used to detect high
impedance ground faults.
•
This function can also be used as supplementary ground fault protection.
Current Elements 50Ns, 51Ns
The current elements for ground faults operate with the magnitudes of the ground current. They only make
sense where the magnitude of the ground current can be used to specify the ground fault. This may be the
case on grounded systems (solid or low-resistance) or on electrical machines which are directly connected to
the busbar of an isolated power system, when in case of a network ground fault the machine supplies only a
negligible ground fault current across the measurement location, which must be situated between the
machine terminals and the network, whereas in case of a machine ground fault the higher ground fault
current produced by the total network is available. Ground current protection is mostly used as backup protec-
tion for high resistance ground faults in solid or low resistance grounded systems when main fault protection
does not pickup.
For ground current detection, a two-element current/time characteristic can be set. Analog to the overcurrent
protection, the high-set current element is designated as 50Ns-2 PICKUP and 50Ns-2 DELAY and is
provided with a definite time characteristic. The overcurrent element 50Ns-1 PICKUP works with a definite
time delay (50Ns-1 PICKUP and 50Ns-1 DELAY). The 51Ns PICKUP element can be operated with either
a userdefined characteristic (51Ns PICKUP and 51NsTIME DIAL) or an inverse time characteristic according
to IEC or ANSI standards. Additionally, a current element with logarithmic inverse characteristic or logarithmic
inverse characteristic with knee point is implemented. The characteristics of these current elements can be
parameterized.
Settable Dropout Times
The pickup can be stabilized for ground fault protection with definite time curve by a settable dropout time.
This facility is used in power systems with intermittent faults. Used together with electromechanical relays, it
allows different dropout responses to be adjusted and time grading of digital and electromechanical relays to
be implemented.
Logic
The following figure illustrates a state logic of the sensitive ground fault protection. The ground fault detec-
tion can be turned ON or OFF (address 3101). When ground fault protection is ON, tripping is possible. The
entire function may be blocked via binary input. Switching off or blocking means the measurement logic
shown in Figure 2-52 is deactivated. Therefore, time delays and pickup messages are reset.
All elements can be blocked individually via binary inputs. In this case, pickups are still reported but tripping is
prevented because the time stages are blocked.
2.9
2.9.1
2.9.2
Functions
2.9 Ground Fault Protection 64, 67N(s), 50N(s), 51N(s)
132 SIPROTEC 4, 7SJ61, Manual
C53000-G1140-C210-6, Edition 05.2016

Siemens SIPROTEC 4 7SJ61 Specifications

General

Brand	Siemens
Model	SIPROTEC 4 7SJ61
Category	Relays
Language	English