IEEE C37.90-1989 pdf free.IEEE Standard for Relays and Relay Systems Associated with Electric PowerApparatus.
IEEE C37.90 This standard applies only to relays and relay systems used to protect and control power apparatus. It does not coverrelays designed primarily for industrial control, for switching communication or other low-level signals, or any otherequipment not intended for the control of power apparatus.
The purpose of this standard is to specify standard service conditions, standard ratings, performance requirements, andrequirements for testing of relays and relay systems associated with power apparatus.
A relay is an electric device designed to respond to input conditions in a prescribed manner and, after specifiedconditions are met, to cause contact operation or similar abrupt change in associated electric control circuits.
1- Inputs are usually electrical but may be mechanical, thermal, or other quantities, or a combination of quantities. Limit
switches and similar simple devices are not relays.
2— A relay may consist of several relay units, each responsive to a specified input, with the combination of units providing the
desired overall performance characteristic of the relay.
Definitions of relay terms are not included in this standard.Refer to ANSIIEEE C37.100-1981,Definitions for PowerSwitchgear, for definitions of relay terms. These terms are also included in ANSIIEEE Std 100-1988,IEEE StandardDictionary of Electrical and Electronics Terms.2
Relay terminology covers a wide ares from the detailed relay structural principles through complex power systemrelay applications.
The following basic areas of power system relay applications provide a convenient method of classification byfunction:
Protective Monitoring Regulating Auxiliary
Relays and relaying devices conforming to this standard shall be suitable for operation under the following conditions:5.1.1 Ambient Temperature
This is the temperature of the air measured 30 cm from the outside surface of enclosures or covers of relay equipment.This temperature shall be within the limits of -20 C to 55 °C.
The average relative humidity may be up to 55% outside of enclosures or covers for temperatures up to 40 °C, withexcursions up to 95% for a maximum of 96 h, without internal condensation.IEEE C37.90 pdf download.