Siemens 7SA511 manual Feature

7SA511 Line Protection Relay Chapter 2

Feature

Ground fault detection

Tripping characteristics and distance zones

Directional measurement

Trip delays

Phase-selective tripping

Automatic blocking of the distance protection function

Fault location and clearance

Description

Ground faults are detected by ground current ( IE )or displacement voltage (VE ).

Either the impedance of the three phase-to-phase loops or three phase-to-ground loops are calculated depending on the ground fault detection. The effect of apparent impedance in unfaulted phases during ground faults is eliminated by a compensation method.

The relay has polygonal tripping characteristics with separate settings for reactance and resistance. Separate settings are provided for the resistance for multi-phase and phase-to-ground

￿faults.

Five distance zones are provided, and they may be independently set in the forward direction, reverse direction, or nondirectional. Two of the zones may also be used for zone extension schemes.

Directional measurement using sound phase voltages or voltage memory

Seven independent trip delays are provided

Phase-selective tripping is available for use with single-pole or single and three-pole automatic reclosing schemes

To prevent incorrect distance measurement, automatic blocking of the distance protection function is provided following loss of measured voltages

Fault location (distance-to-fault) is provided through calculation of the fault impedance. The distance-to-fault may be output in distance units (miles or kilometers), or percentage of line length. An optional parallel line compensation function is available.

When a fault is detected, the relay initiates the following procedures for selective clearance of the fault:

1.Starts the delay times

2.Selects the measured values

3.Releases the impedance calculation and directional identification

4.Releases the trip command

5.Initiates other auxiliary functions

6.Indicates the faulty conductor(s)

July 27, 1995 2-9