Measurement Modes - ABB 615 series Technical Manual

1MAC059074-MB A
5.7.4.6
5.7.5
615 series ANSI
Technical Manual

Measurement modes

The full operation of 21FL requires that all three phase-to-ground voltages are measured.
The voltages can be measured with conventional voltage transformers or voltage dividers
connected between the phase and ground (VT connection is set to "Wye"). Another
alternative is to measure phase-to-phase voltages (VT connection is set to "Delta") and
residual voltage (V0). Both alternatives are covered by setting the configuration
parameter Phase voltage Meas to "Accurate".
When the Phase voltage Meas setting is set to "Ph-to-ph without Uo" and only phase-to-
phase voltages are available (but not V0), only short-circuit measuring loops (fault loops
"AB Fault", "BC Fault" or "CA Fault" or "ABC Fault") can be measured accurately. In
this case, the ground-fault loops (fault loops either "AG Fault", "BG Fault" or "CG Fault")
cannot provide correct fault distance estimates and the triggering of the function in case
of ground fault is automatically disabled.
Application
The main objective of the feeder terminals is a fast, selective and reliable operation in
faults inside the protected feeder. In addition, information on the distance to the fault point
is very important for those involved in operation and maintenance. Reliable information
on the fault location greatly decreases the downtime of the protected feeders and increases
the total availability of a power system.
21FL provides impedance-based fault location. It is designed for radially operated
distribution systems and is applicable for locating short circuits in all kinds of distribution
networks. Ground faults can be located in effectively grounded and low resistance/low-
reactance grounded networks. Under certain limitations, 21FL can also be applied for
ground-fault location in ungrounded distribution networks.
Configuration example
A typical configuration example for 21FL triggering is illustrated in
external triggering is applied, that is, Calculation Trg mode is set to "External". The TRIP
signal from non-directional overcurrent function 51P is used to provide an indication of
a short circuit fault. The TRIP signal from the directional ground-fault function 67/51N
is used to provide an indication of a ground fault at the protected feeder.
21FL with the autoreclosing function
When 21FL is used with the autoreclosing sequence, the distance estimate from the first
trip is typically the most accurate one. The fault distance estimates from successive trips
are possible but accuracy can be decreased due to inaccurate load compensation. During
the dead time of an autoreclosing sequence, the load condition of the feeder is uncertain.
Protection related functions
Figure 418
Section 5
where
825