When a fault occurs in any portion of the power system network, the primary relay must act first. But to be on the safer side a Back-Up relay to the Primary relay is also provided with a proper discrimination time in their operation. Discrimination time is provided so as to allow the primary relay to act first. In case if it fails, then the back-up relay acts. This is done so as to isolate the healthy portion the faulty portion.



Time of operation is basically determined by the following relay settings:

1. Plug Setting Multiplier (PSM), and,

2. Time Dial Setting (TDS)

So for a given fault current we have a desired -When a fault occurs in any portion of the power system network, the primary relay must act first. But to be on the safer side a　Back-Up　relay to the　Primary　relay is also provided with a proper discrimination time in their operation. Discrimination time is provided so as to allow the primary relay to act first. In case if it fails, then the back-up relay acts. This is done so as to isolate the healthy portion　the faulty portion.



Time of operation is basically determined by the following relay settings:

1. Plug Setting Multiplier (PSM), and,

2. Time Dial Setting (TDS)

So for a given fault current we have a desired