Ground Fault Protection 64, 67N(S), 50N(S), 51N(S); Ground Fault Detection For Cos-Φ-/Sin-Φ Measurement (Standard Method) - Siemens 7SC80 Manual

Functions

2.13 Ground Fault Protection 64, 67N(s), 50N(s), 51N(s)

2.13 Ground Fault Protection 64, 67N(s), 50N(s), 51N(s)
Depending on the variant, the 4th current input of the 7SC80 multifunctional protection device is equipped
either with a sensitive input transformer or a standard transformer for 1/5 A.
In the first case, the protection function is designed for ground fault detection in isolated or grounded systems
due to its high sensitivity. It is less well suited for ground fault detection with large ground currents, since the
linear range is left at about 1.6 A at the device terminals for sensitive ground current connection.
If the device is equipped with a standard transformer for 1/5 A currents, large currents can also be detected
correctly.
The input range of the 4th current transformer can be configured.
This function can operate in two modes. The standard procedure, the "cos-φ– / sin-φ – measurement", evalu-
ates the part of the ground current perpendicular to the settable directional characteristic.
The second procedure, the "U0/I0-φ –measurement", calculates the angle between ground current and
displacement voltage. For this procedure, two different directional characteristics can be set.
For capacitive voltage measurement, the function uses an increased tolerance range.
In the order variant position 7 = 1, no voltage transformer is available. Ground-fault detection then works
without ground-voltage detection and without direction detection. In the order variant position 7 = 3, ground
fault detection is fully available.
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.
Ground Fault Detection for cos-φ–/sin-φ Measurement (Standard Method)
2.13.1
Voltage Element
The voltage element relies on a pickup initiated by the displacement voltage V
faulty phase is determined. The displacement voltage V
tion voltage 3 · V
Parameter 213 VT Connect. 3ph in Section
the calculation of the summation voltage 3 · V
voltage inputs must therefore be connected to the voltage transformers in a grounded-wye configuration.
When setting Vab, Vbc, VGnd, the three phase-to-ground voltages of both connected phase-to-phase
voltages and the connected displacement voltage are calculated. If the device is only provided with phase-to-
phase voltages, it is not possible to calculate a displacement voltage from them. In this case, the direction
cannot be determined.
If the displacement voltage is calculated, then:
3 · V = V + V + V
0 A B
If the displacement voltage is directly applied to the device, then V
not affected by parameter Vph/Vdelta (address 206).
The displacement voltage is used both to detect a ground fault and to determine direction. When the voltage
element picks up, a preset time delay must elapse before detection of the displacement voltage is reported to
be able to record stable measurement quantities. The time delay can be configured (T-DELAY Pickup) and
its factory setting is 1 s.
Pickup performed by the displacement voltage can be delayed (64-1 DELAY) for tripping.
It is important to note that the total tripping time then consists of the displacement voltage measurement
time (about 50 ms) plus the pickup time delay T-DELAY Pickup plus the tripping delay 64-1 DELAY.
248
can be calculated according to the connection type of the voltage transformer (see also
0
C
can be directly applied to the device, or the summa-
0
2.1.3 Power System Data 1). When setting Van, Vbn, Vcn,
is based on the three phase-to–ground voltages. The three
0
is the voltage at the device terminals. It is
0
or 3 · V . Additionally, the
0 0
SIPROTEC Compact, 7SC80, Manual
E50417-G1140-C486-A8, Edition 07.2017