When a differential current exceeding the setting of the relay flows, timer T1 is reset and timer T2 … Timing Circuit. Medium voltage switchgears are used for switching medium voltage loads through associated control, measuring, protective and regulating equipment. Ans: (a), a) Generators b) In two zones Z Z R cos (ɸ – θ) ≥ 0. In a static relay, the measurement is performed by static councils. Ans: (b), a) After the transformer For example in an over-current relay it will compare the actual current supplied by … a) UJT https://emadrlc.blogspot.com/2014/04/power-system-protection-course.html After operation of the measuring unit, the output is amplified by the amplifier. The relaying quantity such as voltage/current is rectified and measured. c) Surge absorbers The moving parts are present only in the actual tripping circuit and not in the control circuit. Relay pick up current Primary side = 0.7875 * 800 = 630A The mho function uses the current and voltage measured at the relay to determine if the ... than would be obtained with a self-polarized mho function. Relay pick up current Primary side = 1.05 * 600 = 630A. 3 All mho distance functions require voltage in order to operate. Static relays …, Generator Transformer Protection : Generator Transformer Protection – Protective relays, being component parts of electrical switchgear, should be closely associated with the control section of such systems, e.g. c) Free electrons are always present in the semiconductor. Economics of Operation page-2, Objective Type Question or MCQ of B. The relay pick-up current value is set at 0.8, time multiplier setting is 7 and the fault current is 8000 A. Static Relay: The term ‘static relay’ is generally referred to a relay incorporating solid state components like transistors, diodes, resistors, capacitors, etc.In this type of relay, the functions of comparison and measurement are performed by static circuits wherein there are no moving parts. d) None of these : 4 The first protective relays were electromagnetic devices, relying on coils operating on moving parts to provide detection of abnormal operating conditions such as over-current, overvoltage, reverse power flow, over-frequency, and under-frequency. An 1000 Amp breaker protected by relay with Standard Inverse characteristic. 2. Ans: (c), a) Solid grounding It is an electromechanical switch whose input is electrical with mechanical output.It is used to disconnect the faulty part of the circuit from the faulty part such that the due to the faulty part the whole circuit is not affected.It is achieved by comparing two quantities either in amplitude or in phase . b) 50 Kms correlates to the actual tripping of a Static VAr Compensator (SVC). a) The saturation voltage VCF of silicon transistor is more than germanium transistor. c) Balanced beam type 3. These principles and design criteria determine how well the basic function is performed and how in practice it deviates from the ideal. The materials whose electrical conductivity is usually less than 1 × 106 mho/m are The output is obtained from the output devices only when the measurand has the well-defined value. d) Inner and bound electrons are always present in the semiconductor. Economics of Operation page-3, Objective Type Question or MCQ of B. †Percent of thermal unit number, element number, or relay ratingis obtained by dividing the overload current by the number stamped on the thermal unit nameplate and multiplying by 100. Delays of the order of microseconds can be obtained …, Transistor Switch Circuit : Transistor Switch Circuit – The characteristics of modern transistors are specially suited to the functional requirements mentioned above. What does the first part consist of? b) Conductors In an impedance relay, fault current is maximum if fault occurs near the, a) Relay The burden or current transformers gets considerably reduced thus smaller CT.s can be used. Time vs. PSM Curve of Relay Actual tripping of a static relay is obtained by. The moving parts are absent. Output. Reversal of current through the relay from I F1 to I F2 when C opens could then result in incorrect tripping of the healthy line if the directional unit R D operates before the impedance unit resets. When no current is flowing for a time exceeding 1/4f seconds, timer T2 is held reset and the differential relay that may be controlled by these timers is blocked. History of Relay: The static relay are next generation relays .The Solid Static relays was first introduced in 1960’s. Hence, actual operating time of the relay is 3 × 0.1 = 0.3 sec. In the above figure, the relay circuit is divided into three parts. c) Holes These principles and design criteria determine how well the basic function is performed and how in practice it deviates from the ideal. View Answer / Hide Answer c) 90 kms short circuit levels at the line ends, pre-fault conditions, i.e. d) Surge attenuators In electrical engineering, a protective relay is a relay device designed to trip a circuit breaker when a fault is detected. b) After the distributor The results are all formulated and then evaluated in order to produce a conclusion and bring forward recommendations to Eskom in order to effectively ensure the Dedisa/Grassridge power system is reliable once The actual source of the trip point of the relay must be located and replaced, if found defective. a) Majority carriers b) Minority carriers The term ‘static’ implies that the relay has no moving mechanical parts in it. The name level detector is derived from the fact that …, Overcurrent Relay : Overcurrent Relay – In a three phase system of relays, it is economical to build it on a single phase basis. Economics of Operation page-6, Objective Type Question or MCQ of B. In which of the following device the base resistors are not added in the package but added externally? b. Definition of Protective Relay. The output device is activated and gives the tripping command to the trip circuit. A relay is automatic device which senses an abnormal condition of electrical circuit and closes its contacts. Ans: (c), a) Surge reflectors 25. The function will not oper-ate for an inductive fault behind them. c) The saturation voltage VCE for silicon transistor is same as that for germanium. - from the table α = 0.02, K = 0.14 - pick-up current setting = 1000 A x 0.8 = 800 A The variables such as current, voltage, phase angle or frequency and derived values obtained by differentiation, integration or other arithmetical operations, appear always …, Types of Relay Elements : The Important Types of Relay Elements or also called Electromagnetic Types are 1.Induction Disc Relay The shaded pole type gives the most effective form of an electromagnet since it has the following: Higher torque/VA. Compared to the Electromechanical Relay, the Solid Static relay has longer life-span, decreased noise when operates and faster respond speed. Which of the following statement is true? Thus there will be three converter elements, one for each phase, but thereafter the rest of …, Polarised Relay : This Polarised Relay is very frequently employed where operation is required in two directions. Secondary of the CT and the operating coil. Ans: (a), a) 10 Kms Which of the following statement is correct? Characteristic Functions of Protection Relay : Characteristic Functions of Protection Relay elements using different operating principles. In this type of relay, the functions of comparison and measurement are performed by static circuits wherein …, Time Delay Circuit : Time Delay Circuit – Several choices are available in the selection of suitable circuits for obtaining time delay depending on the magnitude of the time delay required. in a d.c. polarized relay contact A is closed when current in the operating winding flows in one direction contact B will be …, Static Relay : The term ‘static relay’ is generally referred to a relay incorporating solid state components like transistors, diodes, resistors, capacitors, etc. b) Under ground cables Multiple Choice Question (MCQ) of Electronics page-16:226. Ans: (d), a) Persistent arcing grounds are eliminated Note ... (tripping) direction. It means a mho relay is a voltage controlled directional relay. Multiple Choice Question (MCQ) of Electronics page-17:241. The static relay only gives the response to the electrical signal. The trip circuit operates the circuit breaker which isolates the faulty section. Relay is a switch which senses fault in a system and once fault is sensed by the Relay, it issues trip command to the Circuit Breaker, CB to isolate the faulty section of the network from the healthy section. 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Case-2 for New CT: New CT Ratio- 800/5A. If fault occurs at point A on load at bus 646, primary relay R 1 will operate first. b) Resistance grounding A simplified block diagram of a single input static relay is given in the above figure. e) Holes and electrons simultaneously, Objective Type Question or MCQ of Electrical Circuits and Magnetic Fields page-20, Objective Type Question or MCQ of Electrical Circuits and Magnetic Fields page-19, Objective Type Question or MCQ of Electrical Circuits and Magnetic Fields page-18, Objective Type Question or MCQ of Electrical Circuits and Magnetic Fields page-17, Objective Type Question or MCQ of Electrical Circuits and Magnetic Fields page-16, Objective Type Question or MCQ of Electrical Circuits and Magnetic Fields page-15, Objective Type Question or MCQ of Electrical Circuits and Magnetic Fields page-14, Objective Type Question or MCQ of Electrical Circuits and Magnetic Fields page-13, Objective Type Question or MCQ of Electrical Circuits and Magnetic Fields page-12, Objective Type Question or MCQ of Electrical Circuits and Magnetic Fields page-11, Objective Type Question or MCQ of Electrical Circuits and Magnetic Fields page-10, Objective Type Question or MCQ of Electrical Circuits and Magnetic Fields page-9, Objective Type Question or MCQ of Electrical Circuits and Magnetic Fields page-8, Objective Type Question or MCQ of Electrical Circuits and Magnetic Fields page-7, Objective Type Question or MCQ of Electrical Circuits and Magnetic Fields page-6, Objective Type Question or MCQ of Electrical Circuits and Magnetic Fields page-5, Objective Type Question or MCQ of Electrical Circuits and Magnetic Fields page-4, Objective Type Question or MCQ of Electrical Circuits and Magnetic Fields page-3, Objective Type Question or MCQ of Electrical Circuits and Magnetic Fields page-2, Objective Type Question or MCQ of Electrical Circuits and Magnetic Fields page-1, Objective questions and answers or MCQ of Electrical Machines page-22, Objective questions and answers or MCQ of Electrical Machines page-21, Objective questions and answers or MCQ of Electrical Machines page-20, Objective questions and answers or MCQ of Electrical Machines page-19, Objective questions and answers or MCQ of Electrical Machines page-18, Objective questions and answers or MCQ of Electrical Machines page-17, Objective questions and answers or MCQ of Electrical Machines page-16, Objective questions and answers or MCQ of Electrical Machines page-15, Objective questions and answers or MCQ of Electrical Machines page-14, Objective questions and answers or MCQ of Electrical Machines page-13, Objective questions and answers or MCQ of Electrical Machines page-12, Objective questions and answers or MCQ of Electrical Machines page-11, Objective questions and answers or MCQ of Electrical Machines page-10, Objective questions and answers or MCQ of Electrical Machines page-9, Objective questions and answers or MCQ of Electrical Machines page-8, Objective questions and answers or MCQ of Electrical Machines page-7, Objective questions and answers or MCQ of Electrical Machines page-6, Multiple Choice Question (MCQ) of Protective Relays page-4, Multiple Choice Question (MCQ) of Protective Relays page-3, Multiple Choice Question (MCQ) of Protective Relays page-2, Multiple Choice Question (MCQ) of Protective Relays page-1, Multiple Choice Question (MCQ) of Circuit Breaker page-3, Multiple Choice Question (MCQ) of Circuit Breaker page-2, Multiple Choice Question (MCQ) of Circuit Breaker page-1, Objective Type Question or MCQ of B. d) All of these d) None of the above, Multiple Choice Question (MCQ) of Electronics page-13:181. Ans: (d), a) SCR a) SCR b) Thyristors c) UJT d) None of these Ans: (d) 34. The output device is activated and gives the tripping command to the trip circuit. d) None of these d) 110 Kms d) All of these Where, Z is the fault impedance and is equal to ratio of V and I, Z R is the replica impedance in the relay, ɸ is the phase angle between V and I and θ is the relay characteristic angle. Static relay consists of following units for operation: Auxiliary Voltage Supply:24 V D.C. supply is required for energizining the circuitry of the static relay. The stability setting applies only during external faults. Ans: (d), a) Hinged armature type The amplified output is given to the output circuit to cause trip/alarm. a) Inner electrons are always present in the semiconductor. All versions are available with an S-value of : 0.5, 0.66, 0.80 and 0.85. Ans: (d), a) Straight line characteristic b) Bound electrons are always present in the semiconductor. Ans: (b), a) In three zones In such type of relays, the output is obtained by the static components like magnetic and electronic circuit etc. (For a B19.5 thermal unit, 100% corresponds to 19.5.) A single coil which permits use …, COPYRIGHT © 2014 TO 2020 EEEGUIDE.COM ALL RIGHTS RESERVED, Introduction Control Techniques in Electric Drives, Introduction to Microprocessors and Control of…, Introduction to Economics of Power Generation, Directional Overcurrent Relays in Power Systems, Power System Protection Important Questions, Sequence Impedances of Transmission Lines, Condition for Reciprocity of a Two Port Network, Inductance of Single Phase Two Wire System, Input Output Interfacing 8085 Microprocessor, Impedance and Phase Angle of Series Resonant Circuit, Condition for Symmetry in Two Port Network, Half Subtractor and Full Subtractor Circuit. d) The saturation voltage VCE for silicon transistor is lower than germanium transistor. c) Transformer Tripping of the bus is obtained when both the SR and dR operate simulta- neously. indicating and signalling systems. Lower part: The lower part of the Buchholz relay is concerned with the detection of serious or major faults and thus completes the trip circuit to open the circuit breaker operating the transformer. b) The saturation voltage VCE for germanium transistor is more than silicon transistor. b) Non-linear characteristic Economics of Operation page-4, Objective Type Question or MCQ of B. Ans: (a). a) Semiconductors In this relay operating torque is obtained by the volt-amperes element and the controlling element is developed due to the voltage element. This obtained by converting 230V a.c. to 24V d.c. and in some cases station battery voltage of 110V to 24V d.c. Comprator:It compares the actual quantity with the pre-set quantity. Electronic Relay. The output device activates the trip coil only when the relay operates. The various advantages of static relays are: 1. c) UJT Thus the signalling and indicating systems must also be designed on a static basis. 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