Technical description
2 Protection functions
2.4 Distance protection Z<
VM259.EN007
VAMP 24h support phone +358 (0)20 753 3264
59
X-, R- and Load resistance settings are secondary impedances.
Primary values of settings are displayed in VAMPSET
and display.
Teleprotection signals
Signalling between two distance protection relays
(teleprotection) can be implemented using the normal DI and
DO signals of the relay. An external signal transfer system is
needed to transfer signals from one relay to another. The
signal transfer system has to have an internal signal
supervision and fault indication.
The DO output signals can be activated by protection zone‘s
start or trip signals or by the programmable logic functions.
The DI input can be used to block protection zone(s) or it can be
used as input into the programmable logic of the device.
Different type of permissive tripping conditions such as,
permissive under reach (PUTT), permissive over reach (POTT),
acceleration or blocking conditions can thus be implemented.
The relay‘s object control can be used to trip the breaker via the
―DI for remote open ctr‖ or ―DI for local open ctr‖ input of the
object. Outputs of the relay programmable logic can be
connected to ―DI for remote open crt‖ or ―DI for local open ctr‖
inputs via the internal ―Virtual output‖ signals.
2.4.3.
Double earth fault
Vamp 259 -line manager is equipped with DEF (Cross country
fault) functionality which operates together with distance
protection (21). DEF is planned to operate in compensated and
isolated meshed network. The single phase to earth -fault in
this case does not correspond to a short-circuit cause only a
small capacitive or compensated earth-current flows. In
mentioned network types system can be operated with the fixed
earth-fault for several hours, until the earth fault is located
and removed by the isolation of the faulted feeder. The distance
protection must not operate during such single-phase earth
fault. This can be ensured by using DEF –algorithm.
When small impedance earth fault occur the voltage of the
faulty phase will drop and the voltage of the two other phases
will increase almost to the amplitude of line to line voltage.
Due the raise of phase-earth voltage, on the healthy phases in
the entire system, double earth faults may result. The result is
similar to two phase short-circuit, however, the short circuit is
here from one earth fault location to the other via earth. The
second fault may be at any other position in the galvanic
connected system, depending on where the weakest point in the
insulation is.