The document discusses the key characteristics and components of a relay system. It explains that a relay needs input information from the system to make decisions, and is programmed with settings to determine when its inputs have surpassed a threshold. The relay then operates a switch or provides a visual output to indicate its decision. It also discusses the importance of a relay's reliability, selectivity, sensitivity, speed, pickup and reset levels, operating and reset times, and the differences between primary and secondary relays.

1. INPUT:- A relay needs information from the system to
makedecision.
SETTING:- The userprograms setting thatallow relay to
makedecision.
PROCESS:- Once inputareconnected and setting are
program, the relaycompares there and makedecision.
OUTPUT:- The relay will operatea switch to indicate that
the input has surpassed a setting. Or the relaycan provide
notification through visual feedback such as a meteror LED.

2. Reliability:-
It must operate when it is required. Inherent reliability is a matter of design
based on experience.
Selectivity:-
it should be possible to select which part of the system is faulty and which
is not and should isolate the faulty part of the system.
Speed:-
A protective relay mustoperate at required speed.It should neither be too slow
nor too fast may result in undesired operation during transient fault.
Sensitivity:-
A relay should be sufficiently sensitive so that it operates reliablywhen
require under the actual condition in the systemwhich produce the least
tendency foroperation.

3. Pick up level of actuating signal:-The value of actuating quantity
(voltage or current) which on threshold above which the relay initiates to
be operated.
Reset level:- The value of electric current or voltage below which a relay
open itscontactsand comes in original position.
Operating time of relay:-The time which elapses between the instant
when actuating quantity exceeds the pick up value to the instant when the
relaycontactsclose.
Reset time:-The time which elapses between the instant when the
actuating quantity becomes less than the resetvalue to the instantwhen
relaycontacts return to its normal position.
Primary relay:-The relaywhich areconnected directly in thecircuit to
be protected.
Secondary relays:- The relay which are connected in the circuit
to be protected through current and potential transformer.

4. BUS
CT
RELAY
PT
OTHER
COMMUNICATIONS
STATION
BATTERY
POWER
LINE
CIRCUIT
BREAKER