GE 850 User Manual

6–52 850 FEEDER PROTECTION SYSTEM – INSTRUCTION MANUAL
CURRENT ELEMENTS CHAPTER 6: PROTECTION SETPOINTS
Restricted Ground Fault (87G)
The 850 relay is equipped with the Restricted Ground Fault (RGF) element, sometimes
referred to as the Restricted Earth Fault (REF) element.
The Restricted Ground Fault (RGF) protection provides ground fault detection for low-
magnitude ground fault currents primarily for ground faults close to the neutral point of
the wye connected winding. An internal ground fault on an impedance grounded wye
winding produces a low magnitude ground fault current depending on the position of the
fault with respect to the winding neutral point.
The diagram below shows the dependence of the fault current on the fault distance from
the neutral point.
Figure 6-19: Fault current with respect to distance from neutral
The resultant primary current can be negligible for ground winding faults within 35% of the
distance from the neutral point since the fault voltage is not the system voltage, but rather
the result of the transformation ratio between the primary windings and the percentage of
shorted turns.
Application of Restricted Ground Fault protection extends the fault coverage towards the
neutral point for low-impedance grounded winding.
Figure 6-20: Restricted Ground Fault zone of protection

GE 850 Specifications

General

Brand	GE
Model	850
Category	Protection Device
Language	English

Summary

850 Feeder Protection System

Front Control Panel Interface

Common Setpoints

Provides a general description of common setpoints and their operational characteristics.

Device

Covers device configuration modes (Simplified/Regular) and custom configuration options.

Current Elements

Details various current-based protection elements like TOC, IOC, and directional overcurrent.

Trip and Close Circuit Monitoring

Local Control Mode (breakers and switches)

Details local control operations for breakers and switches via front panel or contact inputs.

FlexLogic

Explains the arrangement of internal digital logic and user-programmed parameters for flexible control.

Specifications

Provides detailed technical specifications for the device, including protection, input/output, and communication parameters.

Software Interface

Voltage Elements

Introduces undervoltage, overvoltage, and frequency protection elements.

Breaker Health

Breaker Failure (50BF)

Details the Breaker Failure scheme for detecting and responding to breaker failures.

Testing

Fault Reports

Cautions and Warnings

Outlines safety indicators, general precautions, and specific warnings for installation and operation.

Working with Setpoints & Setpoints Files

Security

Explains Basic Security and CyberSentry features, including roles, password complexity, and AAA server authentication.

Autoreclose

Covers the Autoreclose scheme for automatic reclosing after faults.

Transient Ground Fault Detection