Working Principle of Distance or Impedance Relay
The working rule of distance relay or resistivity relay is extremely easy. there’s one voltage component from potential transformer and a current component fed from current transformer of the system. The deflecting torque is created by secondary current of CT and restoring torque is created by voltage of potential transformer.
In normal operational condition, restoring torsion is quite deflecting torque. therefore relay won’t operate. however in faulty condition, this becomes quite giant whereas voltage becomes less. Consequently, deflecting torque becomes quite restoring torque and dynamic parts of the relay starts moving that ultimately shut the No contact of relay.
Hence clearly operation or working principle of distance relay depends upon the ratio of system voltage and current. because the ratio of voltage to current is nothing however impedance therefore a distance relay is additionally referred to as resistivity relay. The operation of such relay depends upon the preset worth of voltage to current ratio. This ratio is nothing however resistivity. The relay can solely operate once this voltage to current ratio becomes but its preset worth. Hence, it are often same that the relay can only operate once the resistivity of the road becomes but preset resistivity (voltage/current). because the resistivity of a transmission line is directly proportional to its length, it will simply be all over that a distance relay will only operate if fault is occurred among a preset distance or length of line.
Types of Distance or Impedance Relay
There are mainly two types of distance relay–
- Definite distance relay.
- Time distance relay.
Let us discuss one by one.
Definite Distance Relay
This is simply a spread of balance beam relay. Here one beam is placed horizontally and supported by depend upon the center. One finish of the beam is force downward by the magnetic force of voltage coil, fed from potential electrical device hooked up to the road. alternative finish of the beam is force downward by the magnetic attraction of current coil fed from current electrical device connected asynchronous with line. due to torque created by these 2 downward forces, the beam stays at an equilibrium position. The torsion thanks to voltage coil, is restraining torsion and torque due to current coil, is deflecting torque.
Under traditional in operation condition restraining torque is bigger than deflecting torsion. thence contacts of this distance relay stay open. once any fault happens within the feeder, under protected zone, voltage of feeder decreases and at identical time currentt will increase. The ratio of voltage to current i.e. impedance falls below the pre-determined price. during this scenario, current coil pulls the beam additional powerfully than voltage coil, thence beam tilts to shut the relay contacts and consequently the circuit breaker related to this impedance relay can trip.
Time Distance Impedance Relay
This delay automatically adjusts its operational time in step with the gap of the relay from the fault purpose. The time distance resistance relay won’t only be operated relying upon voltage to current ratio, its operational time additionally depends upon the worth of this ratio. That means,
Construction of Time Distance Impedance Relay
The relay mainly consists of a current driven component like double winding sort induction over current relay. The spindle carrying the disc of this component is connected by means that of a spring coupling to a second spindle that carries the bridging piece of the relay contacts. The bridge is generally control within the open position by an coil control against the pole face of an magnet excited by the voltage of the circuit to be protected.
Operating Principle of Time Distance Impedance Relay
During normal operational condition the attraction force of coil fed from pt is over force generated by induction component, thus relay contacts stay in open position once a brief circuit fault happens within the line, this within the induction component will increase. Then the induction within the induction component will increase. Then the induction component starts rotating. The speed of rotation of induction parts depends upon the amount of fault i.e. amount of current within the induction component. because the rotation of the disc take, the spring coupling is wound up until the tension of the spring is ample to pull the armature away from the pole face of the voltage excited magnet.
The angle through that the disc travels the disc travel before relay operate depends upon the pull of the voltage excited magnet. The bigger the pull, the bigger are going to be the travel of the disc. The pull of this magnet depends upon the road voltage. The bigger the road voltage the bigger the pull thus longer are going to be the travel of the disc i.e. operational time is proportional to V. Again, speed of rotation of induction component more or less proportional to current during this component. Hence, time of operation is reciprocally proportional to current. Hence , operating time proportional to 1 ratio I . Therefore time of operation of relay, T proportional to V ratio I or T proportional to Z.