Rx Diagram Of Mho Relay
S electrical relay | Admission or Angle Admittance Relay
Mho Relay Construction and precept of Operation
A simple form of Mho relay | Admittance or angle admittance relay shown in the figure below:
The torque equivalence is given by T = K1 Sextet (Φ – α) – K2V2 – K3
The top and lower poles are energized by a voltage V to produce a polarizing flux. The capacitor adjacent nonparallel provides memory sue. The left is energized away a current is the in operation quantity. The left pole due to current I interacts with the polarized flux due to V produce the operating torsion K1VI Cos (Φ – α).
The angle α can be varied by adjusting the resistance in the phase shifting circuit provided happening the far left pole. The right hand broadside pole is energized by the potential difference and the flux produced aside it interacts with the polarizing flux for producing the restraining torque, K2V2.
A Mho relay measures a component of entree |Y|∠ θ . But its characteristic when plotted on the impedance diagram (i.e., R-X diagram ) is a circle passing thro' the origin shown in the fig. It is inherently a social control electrical relay as it detects the geological fault only in the forward direction. The relay is called Mho relay because its characteristic is a straight rail line, when plotted on an admittance diagram (G-B axes i.e., conductance – susceptance axes) atomic number 3 in the figure.
- Learn: Directional Over Current Electrical relay
- Read: Solid Sate Relay or Static Electrical relay
Mho Relay Characteristic Expression
The operational torque for a Mho electrical relay is by V-I factor and restraining torque is by voltage element.
Hence, a Mho relay buttocks be called as a voltage restrained directional relay.
T = K1 Sise Cos (Φ – α) –K2V2, neglecting the effect of the spring.
K2V2 < K1VI Cos (Φ – α)
K2V < K1I Cos (Φ – α)
(V/I Cos (Φ – α)) < K1/K2 or (V/I) < (K1/K2) Romaine (Φ – α) or Z < (K1/K2)Cos (Φ – α)
At balance conditions, the operating torque is up to restraining torsion.
i.e., K1VICos (Φ – α) = K2V2
(I/V)Cos (Φ – α) = (K2K1) = K
(1/Z) = (K / Cos (Φ – α)) = Y
Y = K / Cos (Φ – α) = admittance in mho.
There units of S relays are used for the protection of a section of the line. I unit is a high speed unit to protect 80% to 90% of the line section. The II unit protects the rest of the line section and its reach extends up to 50% of the abutting line part. The III building block is meant for backup protection of the nigh line section. The II and III units operate with a preset time delay, normally 0.2 s to 0.5 sec and 0.4 Securities and Exchange Commission to 1sec respectively. The sentence distance characteristic is a stepped one as shown in chassis.
Operation of Impedance and Mho Relay during powerfulness Swing
Comparison of Mho device characteristic and Electrical resistance Characteristic subordinate power swing conditions BA is the line to be preserved. Impedance characteristic relay will trip even out for the fault points behind emplacemen A which is nothing but a 'pain tripping'.
Whereas, the S characteristics relay requiring a comparatively small area of circle for the line AB, does not mother wit the faults buns A. Hence many points splashy by the electrical resistance characteristic are in the negative torque part of Mho distinguishing.
Locus of the power swing, occurring along the long transmission lines during wicked synchronization etc. beingness a temporary phenomenon is a curve which enters into the operating zone of an impedance relay earlier than that of Mho relay is a curve in the diagram. This is not a desirable uncomparable because before allowing the tycoo swing to die down, the transmitting line itself is tripped under the take hold of of protection by the electric resistance relay. However, in the event of severe and fast occurrence of power swing, the locus whitethorn enter the zone of military operation of Mho electrical relay which will act as and break up the line which is also unsuitable. Thu, ready to avoid this sort of billet, offset Mho relay is victimized Eastern Samoa indicated under.
During the power swing music, the locus of the impedance measured by relay moves along the curve. As soon as IT comes within the positive torsion area of the offset Mho characteristic (point P), the offset Mho relay Acts and blocks the measuring relay for bank line B.C.. Therefore the S relay does not operate during power swing.
Comparison Table
| S. No | Type of Relay | Operating Torque Element | Restraining Torque Element | Used for Protection |
| 1 | Impedance Relay (Z) | Current (I) | Voltage (V) | Form faults in medium length lines |
| 2 | Reactance Relay (X) | Current (I2) | Voltage – Current SinΦ ( V – I sin Φ) | Reason faults in clipped lines |
| 3 | Admittance Relay (Y) | VI Cos (Φ – α) | V | Phase faults in long Lines |
Source: http://www.mytech-info.com/2016/08/mho-angle-admittance-relay.html
Posted by: songetson.blogspot.com