What is relay co-ordination ?

-Relayco-ordinationplaysanimportantroleintheprotectionofpower system.Forproperprotection,properco-ordinationofrelays with appropriate relay settings is to be done. Relay settings are done in such a way that proper co-ordination is achieved along various series network. However the review of Co-ordination is always essential since various additions / deletion of feeders and equipments will occur after the initial commissioning of plants. As power can be received from generators of captive power plant, the analysis becomes complex.

-Relay co-ordination can be done by selecting proper plug setting and time multiplication setting of the relay, considering maximum fault current at the relay location. After selecting the plug setting and time multiplier setting, the co-ordination can be checked graphically.

-When plotting co-ordination curves, certain time intervals must be maintained between the curves of various protective devices in order to ensure the correct sequential operation of the devices when co-coordinating inverse time over current relays.

-For a given fault current, the operating time of IDMT relay is jointly determined by its plug and time multiplier settings. Thus this type of relay is most suitable for proper co­ordination. Operating characteristics of this relay are usually given in the form of a curve with operating current of plug setting multiplier along the X axis and operating time along Y axis.