DEFINITION:- 
Its operation is generated thru the ratio of done V to I is the protected cht. 
PRINCIPLE:- 
Here, the torque produced thru a I element is adversarial thru the torque produced thru a V element 
These relays characteristic even as the ratio of v/i is a lot much less than a pre- determined value. 
CONSTRUCTION:- 
Voltage excited thru pt from line to be protected I element excited thru pt is series with the street 
AB - Protected zone. 
WORKING:- 
Under normal condition - impledance of protected zone is Zl 
Relay is designed such that it close to contacts even as the impedance of protected zone is a lot much less than Zl. 
Under fault condition - impedance z=v/i is issue F1 
So relay operates 
If fault l occurs - relay does now not operates , because it faults beyond the protected zone AB. 
Advantages:- 
Simple and fast operation, 
High line loading permissible, 
Re adjustments of seltings is possible 
APPLICATION:- 
A.C transmission and distribution line protection, 
Protection in competition to 3 segment faults, 
Phase - segment faults, 
Phase - earth faults. 
Eg., ohmmeter 
Types:- 
Impedance relay -actual distance relays 
- 
time diatance relays 
Reactance relay, 
Admiltance relay (mho) 
(a) DEFINITE DISTANCE TYPE IMPEDANCE RELAY:- 
DEFINITON:- 
It is a relay which operates instantaneosly for fault upto a pre determined distance from relay. 
CONSTRUCTION:- 
It consists of a pivoted beem `F` and a couple of eletromagnets energised thru I and V redesign is the protected cht. 
Armature of the 2 electromagnets are automatically coupled to the beam on the opposite sides. 
Beam is provided with a bridging piece for the adventure constacts. 
Relay is so designed 
that the torque produced thru the 2 eletromagnets are in opposite direction.

OPERATION:-

UNDER NORMAL CONDITIONS - Pull due to V element is > than I element 

So relay constact remains open.

UNDER FAULTY CONDITIONS - I element > V element 

Ratio of v/i faults below a pre determed value.

Pull of I element.

So beam is a direction to close the trip contacts.

(B) TIME DIATANCE IMPEDANCE RELAY:-

DEFINITION:-

It is a relay is which the time of operation is to distance of fault from the relay point. A fault nearer to the relay will operate it earlier than a fault for ther away from the relay.

Construction:-

It is a typical induction type- time distance impedance relay.

It has  a I driven induction element.

Spindle carrying the disc of this elements is connected by a spiral spring coupling to a second spindle which carrier the bridging piece of the relay trip contacts.