Protection System Requirements and a few primary terminologies used 
• The essential necessities for a safety device are as follows: 
Reliability: 
It is the cappotential of the safety device to function correctly. The reliability function has  primary elements, which might be dependability and security. The dependability function needs the knowledge of a accurate operation of the designed device, on prevalence of any fault. Similarly, the safety function may be described because the cappotential of the designed device to keep away from wrong operation all through faults. A complete statistical 
technique primarily based totally reliability examine is needed earlier than the safety device can be commissioned. The elements which have an effect on this selection of any safety device relies upon on a number of the subsequent few elements. 
· 
Quality of Component used 
· 
Maintenance time table 
· 
The deliver and availability of spare components and shares 
· 
The layout precept 
· 
Electrical and mechanical pressure to which the blanketed a part of the device is subjected to. 
Speed: 
Minimum working time to clean a fault with a view to keep away from harm to equipment. The velocity of the safety device is composed usually of  time periods of interest. 
The Relay Time : 
This is the time among the on the spotaneous of prevalence of the fault to the on the spotaneous at which the relay contacts open. 
The Breaker Time: 
This is the time among the on the spotaneous of final of relay contacts to the on the spotaneous of very last arc extinction within the medium and elimination of the fault. 
Selectivity: 
This function targets at preserving the continuity of deliver device with the aid of using disconnecting the minimal phase of the community essential to isolate the fault. The belongings of selective tripping is likewise recognized as “discrimination”. This is the purpose for which the whole device is split into numerous shielding zones in order that minimal protion of community is remoted with accuracy. Two examples of usage of this selection in a relaying scheme are as follows 
a) Time graded structures 
b) Unit structures 

 Adequacy: 
It is economically unviable to have a 100% safety of the whole gadget in concern. Therefore, the price of the designed safety gadget varies with the criticality and significance of the included zone. The safety gadget for greater crucial quantities 
is typically costly, as all of the functions of an excellent safety gadget is maximized here. But a small motor may be included with the aid of using a easy thermally operated relay, which is easy and cheap. Therefore, the price of the safety gadget must be ok in its price. 1.4.7 Some simple terminologies utilized in safety gadget Some simple terminologies usually used withinside the safety gadget are enlisted below. i) Measuring Relay ii) Fault Clearing Time iii) Auxilliary relay iv) Relay Time v) Pick up price vi) Reset Value vii) Drop out viii) Reach ( beneathneath and over reaches) ix) Relay Burden x) Unit/ Non unit safety xi) All or Nothing relay.