DESCRIPTION : 

The 7SG17 Rho 3 is a multi-function numerical Motor Protection relay suitable for all types of a.c. induction motors up to the highest ratings available.
Whilst medium voltage 3-phase motors are very reliable and robust, modern designs operate much closer to the limits of thermal margins and to give adequate protection, sophisticated protection relays are required. In addition, increased industrial use of power electronics leads to corruption of power systems and unless specific equipment is installed to eliminate the corruption it can cause considerable rotor overheating. The relay has been designed to protect the motor against these phenomena as well as known abuses such as mechanical overload, stalling, single phasing, terminal box and cabling failures, and too frequent starts.
The relay can be set to accurately mimic both the heating and cooling characteristics of the protected motor and consequently ensure that the thermal withstand of the machine is not exceeded, at the same time allowing full use of the motors thermal capability.

FUNCTION OVERVIEW :

• Advanced motor protection - for medium voltage motors
• Easily programmable settings and user interface
• Thermal overload and restart inhibit protection
• Stall and locked rotor protection
• Short circuit and earth fault protection
• Phase unbalance protection
• Undercurrent detection
• Limitation of number of starts
• Optional thermistor or resistance temperature detector (RTD) inputs
• Circuit breaker fail
• Trip circuit supervision
• CT supervision
• Earth fault trip inhibit for contactor control application
• Status inputs with programmable independent pickup and drop off timers.