Siemens 7SA511 manual High-Resistance Ground Fault Protection optional

7SA511 Line Protection Relay Chapter 2

2.4.6 High-Resistance Ground Fault Protection (optional)

High-resistance ground fault protection is another optional feature of the relay (models 7SA511*- **A5*-0/2**2/3) that is used for detection of ground faults in grounded systems where the fault path resistance can be extremely high (e.g., overhead lines without lightning protection conductors, or ground paths in sandy soils). In such cases, overcurrent and underimpedance elements do not always pick up, so phase selection for the distance measurement is not possible. You can select the high-resistance ground fault protection function to work in one of two ways: directional or nondirectional protection.

Directional ground fault protection (definite time, overcurrent protection) incorporates nondirectional backup and standby protection. This function can be extended by integrated directional comparison logic so a carrier channel can be used

￿for fast, selective tripping for high-resistance ground faults.

Nondirectional fault detection using inverse time overcurrent, with adjustable characteristics, can be selected. This method is used most frequently for highly interlinked ground systems with high-resistance ground faults where the ends of the faulty line section carry the largest fault current and thus produce the shortest tripping time.

When using impedance fault detection, ground fault impedances can occur which appear to lie outside the pickup characteristic of the relay. The high-resistance ground fault protection function of the 7SA511 relay also prevents this occurrence.

July 27, 1995 2-11