Mho circles and quadrilateral characteristic are essentially the most popular characteristics used all across the world since they are inherently directional and provide well defined reach A. impedance relay . Its characteristic on R-X diagram is a circle whose circumference passes through the origin as illustrated in figure showing that the relay is inherently directional and it only operates for faults in the forward direction. Although a mho element is inherently directional, it is customary to supplement the mho distance calculation with a directional element. digital relay are mho and quadrilateral. Fig. A. Need and Types of Rectifier, Mho relay is voltage controlled directional relay. 4.28. Putting K1 = 0, K2 = -1 and K4 = 0 we get the Torque in MHO Relay … mho relay incoparates features of reactance relay with an addition that it is inherently directional. it needs directional element. Directional feature 4. What is Mho Relay- How it Works, and its Applications. B. MHO relay. Percentage differential relay. Draw a neat labeled diagram to show protective system for AC traction and give the function of each relay used in it. All the Relays react to voltage or current with the end goal that they open or close the contacts or circuits. It is also noted that, by using This relay is suitable for short length lines. The Mho relay combines the properties of impedance and directional relays. The effect of power swing on reactance relays is maximum. As a result, you obtain a directional mho operating characteristic. IDMT relays are mostly non directional and since transmission lines are networks interconnecting multiple nodes fault current can flow in either direction. By making the τ equal to, or little less lagging than Θ, the circle is made to fit around the faulty area so that the relay is insensitive to power swings and therefore particularly applicable to the protection of long or heavily loaded lines. Working, Types, Applications, Air Circuit Breaker- Working Principle, Construction, Types, Advantages, Applications, What is Buchholz Relay? D. Always a separate directional relay is required. CHECK ANSWER. Different Types of HVDC Links- Monopolar HVDC System,Bipolar HVDC System, Homopolar HVDC System. The relay which is most sensitive to power swings (maloperation) is (a) Mho relay (b) reactance relay (c) Impedance relay (d) all are equally affected.  7. In this relay operating torque is obtained by the volt-ampere element and the restraining torque is developed due to the voltage element. The operation can be better understood when plotted on an impedance plane. The transmission line distance protection relay having the property of being inherently directional is For protection of rotating machines against lightning surges _______ is used. Another option is to use a modified impedance relay (mho relay) which is obtained by offsetting the impedance circle and placing it in the origin. Over Current Relay- Working Principle, Types, Drawbacks, What is SF6 Circuit Breaker? Thus, a directional relay is commonly used together with the impedance relay, and a mho relay is used as a starting unit for the reactance relay. It cleverly combines the discriminating qualities of both reach control and directional control, thereby eliminating the ‘contact race’ problems that may be encountered with separate reach and directional control elements. The relay is called Mho relay because its characteristic is a straight line, when plotted on an admittance diagram. Mho Relay The mho impedance element is generally known as such because its characteristic is a straight line on an admittance diagram. The mho has been renamed the Sieman (S) by ISO. It is also sometimes called an angle impedance relay. Mho relay is a high speed relay and is also known as admittance relay. Reactance relay is an overcurrent relay with directional limitation. So, with the reverse Its characteristic is inherently directional and the relay only operates for faults in front of the relay location. Next. 1 … … Fig. The transmission line distance protection relay having the property of being inherently directional is For protection of rotating machines against lightning surges _______ is used. • Mho relay characteristic is a circle whose circumference passes through the origin. The relay is inherently non-directional. There is one type of relay which functions depending upon the distance of fault in the line. A mho relay using the induction cup structure is shown in the figure below. 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