IEEE C37.90:1989 pdf download.IEEE Standard for Relays and Relay Systems Associated with Electric Power Apparatus.
IEEE C37.90 applies only to relays and relay systems used to protect and control power apparatus. It does not cover relays designed primarily for industrial control, for switching communication or other low-level signals. or any other equipment not intended for the control of power apparatus.
2. Purpose
The purpose of this standard is to specify standard service conditions, standard ratings, performance requirements, and requirements for testing of relays and relay systems associated with ixwer apparatus.
3. Definition of a Relay
A relay is an electric device designed to respond to input conditions in a prescribed manner and, after specified conditions are met, to cause contact operation or similar abrupt change in associated electric control circuits.
NOTES:
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 unils. each responsive to a specified input, with the combination of units providing the desired overall performance characteristic of the relay.
4. Relay Terms and Terminology and Classification by Function
Definitions of relay terms are not included in this standard. Refer to ANSI/IEEE C37.1 00-1981, Definitions for Power
Swiwhgear. for definitions of relay terms. These terms are also included in ANSI/IEEE Std 100-1988, IEEE Standard
Dictionary of Electrical and Electronics Terms.
Relay terminology covers a wide ares from the detailed relay structural principles through complex power system relay applications.
The following basic areas of power system relay applications provide a convenient method of classification by function:
Protective Monitoring Regulating Auxiliary
5. Service Conditions
5.1 Usual Service Conditions
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.
5.1.2 Relative Humidity
The average relative humidity may be up to 55% outside of enclosures or covers for temperatures up to 40 °C, with excursions up to 95% for a maximum of 96 h. without internal condensation.
5.1.3 Altitude
The usual condition ot’ altitude shall be less than 1500 m.
5.2 Unusual Service Conditions
The use of relays and relaying devices at conditions other than specified in 5.1 shall be considered as unusual
conditions.
5.2.1 Altitude Derating
5.2.1.1 Air Insulation
Air insulation is to be derated when the relay is applied or tested at altitudes in excess of 1500 m (see Table 1).IEEE C37.90 pdf download.