power system protection interview questions

5. SF6 circuit breaker Q: Mention the advantages of field tests. Cross blast It breaks a circuit either manually or by remote control under normal conditions and under fault conditions. Difference in CT ratio error difference at high values of short circuit currents that makes the relay to operate even for external or through faults. When the AC passed through the conductor the density of the current is not uniform over the cross-section of the conductor, the density of the current is very high near the surface of the conductor and very low at middle this effect is called skin effect. Q:What are the main safety devices available with transformer? The magnetizing current is, therefore, very high, of the order of 8 to 30 times the full-load current. The operation of a relay should be fast and selective, ie, it should isolate the fault in the shortest possible time causing minimum disturbance to the system. The restraining coil produces a bias force in the opposite direction to the operating force. 1.Why star delta starter is preferred with induction motor? Home » Power System Protection and Relays Questions & Answers. By coordinating relays, faults can always be isolated quickly without serious disturbance to the rest of the system. When voltage increases then current also increases then what is the need of over voltage relay and over current relay? The Feedback in Control System in one in which the output is … Q. Q: How direct tests are conducted in circuit breakers? • There is a reduced risk of fire If the turns ratio of the transformer is more than 1:1, there will be higher core loss and the capability of the transformer to withstand this is limited to a few minutes only. Positive sequence components, negative sequence components and zero Answer : The protection is organized to provide a ring of security around each and every element of a power system. Faults occurring elsewhere in the system have no influence on the operation of a unit system. Question 2. It is one of the important factors taken into consideration for selecting a current transformer. Q: What are unit system and non unit system? Q: Write the classification of circuit breakers based on the medium used for arc extinction? It is the method of connecting a resistance in parallel with the contact space(arc). Therefore, the IDMT relay will not be of much help. A unit protective system is one in which only faults occurring within its protected zone are isolated. this effect is only in the ac. Consider a primary relay A having operating time of 0.1 sec. What Is Difference Between Fuse And Breaker? Electrical Interview Questions & Answers visit www.eeekenya.com Page | 1 ... Power factor should be high in order to get smooth operation of the system. Difference in lengths of pilot wires on either sides of the relay. Q: What are the characteristic of SF6 gas? Over current relay meant for sensing any internal short circuit, over load condition, earth fault thereby reducing the system failure & risk of fire. (a) Fault level at busbar is high Vacuum circuit breaker. It assists the circuit breaker in interrupting the magnetizing current and capacity current. Mention the inductance value of the peterson’s coil. Why Is Voltage Stepped Up Before Transmission? To see the data, click Data view. Short contact life Power System Protection Interview Questions 2; Answer: The relays are connected to the power system through the current transformer (CT) or potential transformer (PT). Is the protection in which the fault occurring in a line will be cleared by its own relay and circuit breaker. Routine test POWER ranks among nation’s top design firms Leading industry magazine Engineering News-Record has ranked POWER Engineers Incorporated (POWER) among the top 100 engineering design firms in the country for the 15th year in a row. breaker is tripped, the fault continues to fed because EMF is induced in the generator itself. Grid connections 7. Electrical Engineering Objective Questions MCQ with Answer Free Pdf Download. Short circuit tests, Synthetic tests& direct tests. It has to be ideally … It is the indicator used for showing the operation of the relay. Definite time relay and inverse-definite time relay. It means preventing the relay from tripping due to its own characteristics or due to additional relays. The dielectric strength of the oil deteriorates rapidly due to high degree of carbonization. We will go on adding questions, till we reach 100 and may be we will add more than 100. 3, Vacuum failure resulting in condenser pressure rise, resulting in Naturally when a fault occurs it is sensed by both the primary and backup protection. 2. Q: What are the advantages of oil as arc quenching medium? Compensation testing 3, Loss of excitation due to fuel failure, 2, Loss of drive It is a relay in which measurement or comparison of electrical quantities is made in a static network which is designed to give an output signal when a threshold condition is passed which operates a tripping device. Q: What are the problems arising in differential protection in power transformer and how are they overcome? Also, a low voltage may be created which may damage systems connected to the supply. A. The circuit breaker is tested under actual conditions like those that occur in the network. In this method the breaker is first tested for its rated breaking capacity at a reduced voltage and afterwards for rated voltage at a low current.This method does not give a proper estimate of the breaker performance. A. Q. Bias coil will solve this. Over voltage relay meant for sensing over voltages & protect the system from insulation break down and firing. Whenever a short-circuit occurs, the current … Sudden loss of all or major part of the load causes over-speeding in alternators. It causes the line insulation to flash over and may also damage the nearby transformer, generators and the other equipment connected to the line. A. Question 9. (c) A fault in the bus bar causes interruption of supply to a large portion of the system network. • It acts as an insulator and permits smaller clearance between line conductors and earthed components. Q:What is biased differential bus zone reduction? A. in this bus the magnitude of voltage and phase angle are specified. It is a piece of equipment used to break a circuit automatically under fault conditions. 4. Q. Radial-blast. Q: What are the types of graded used in line of radial relay feeder? It has good dielectric strength and excellent arc quenching property. In resistance grounding system the neutral point of the load is connected to the ground to carry the residual current in case of unbalanced conditions. When interrupting low inductive currents such as magnetizing currents of the Answer: Galloping in transmission line conductors arises generally due to symmetrical layers of ice formation. Question 4. Synthetic test Top Most Power System Protection Interview Questions Q:What are the functions of protective relays To detect the fault and initiate the operation of the circuit breaker to isolate the defective element from the rest of the system, thereby protecting the system from damages consequent to the fault. 2, Phase to earth faults Latest 50 Power Analysis Interview Questions, List Of Microprocessor Interview Questions For Freshers & Experienced, Top Most Power systems Objective Questions Part – 5, Top Most Power System Transmission Interview Questions, Power Systems Objective Questions and Answers – Part 1, Power Systems Objective Questions and Answers – Part 2, Power Systems Objective Questions and Answers – Part 3, Power Systems Objective Questions and Answers – Part 4. Q: What are the methods of capacitive switching? A distribution transformer may have one primary and one divided or “Tapped” secondary, or two or more secondaries. It serves as the first line of defence. • Maintenance problem are reduced. Electrical and Electronics Engineering Interview Questions. If an earth-fault occurs near the neutral point, the voltage may be insufficient to operate the relay. The above interview questions also can be used for job title levels: entry level power engineer, junior power engineer, senior power engineer, power engineer assistant, power engineer associate, power engineer administrator, power engineer clerk, power engineer coordinator, power engineer consultant, power engineer controller, power engineer director, power engineer engineer, power … Question 1. (e) none … Static relay is compact Electrical Engineering interview questions and answers: Part 1 Part 2 Part 3 Part 4 Part 5 Part 6. In addition to this, there always an inherent phase difference between the primary and the secondary quantities and a possibility of current through the relay even when there is no fault. There is difficulty of removing the gases from the contact space in time Q: Define the term pilot with reference to power line protection. Q: What is the need of relay coordination? In three pin plug why earth pin diameter is higher than other two pin? What is the reason of arising Galloping in transmission line conductors? This current is known as inrush current. Power Station is a place where Power is Generated and Transmitted , eg. We can’t sense the over voltage by just measuring the current only because the current increases not only for over voltages but also for under voltage (As most of the loads are non-linear in nature).So, the over voltage protection & over current protection are completely different. Question 14. Generator Protection Interview Questions Answers. Top 100 Switchgear and Protection Interview Questions. SF6 gas. Q:Mention the various tests carried out in a circuit breaker at HV labs. Power transformers generally operate at nearly full – load. It is an electrical device designed to initiate the isolation of a part of the electrical installation, or to operate an alarm signal, in the event of abnormal condition or a fault. How To Set The Operating Time Of The Relay? The necessity to interrupt the normal services and to test only at light load conditions. There is a risk of fire since it is inflammable. (a) Only fault below the oil level are detected. Interview. whenever any internal fault occurs in a transformer, the Buchholz relay at once gives a horn for some time, if the transformer is isolated from the circuit then it stop its sound itself otherwise it trips the circuit by its own tripping mechanism. During switching of lines or wrong synchronization surges of real and reactive power flowing in transmission line causes severe oscillations in the voltage and current vectors. (b) The stability of the system is affected by the faults in the bus zone. • Both test current and test voltage can be independently varied. State the difference between generator and alternator 3. Q. The arcing time is very small due to rapid buildup of dielectric strength between contacts Please click on the Red Plus Icon to know the answer. Larger arcing time for small currents separate under heavy load or fault or short circuit condition. Protection of generator & generator transformer unit; protection of large motors and busbars . HVDC transmission 8. Hence the relay is called REF relay. Resistance grounding system means connecting the neutral point of the load to the ground to carry the residual current in case of unbalanced conditions through the neutral to the ground whereas resistance earthing system is done in an electric equipment in order to protect he equipment in occurrence of fault in the system. I applied through a recruiter. Q: Give the limitations of Merz Price protection. It refers to the current or voltage which is used to activate the relay into operation. When Will You Go For Idmt And Dtoc Relays? Q: What are faults associated with an alternator? A. In this post provide you latest and updated 2018 Electrical MCQ Objective Questions with answer which are help for preparation all electrical engineering exams like GATE, IES, JTO, PSUs, RRB JE/AEN, RRB loco pilot and technicians, SSC JE, DMRC, LMRC, ISRO and other state level engineering exams. The program time (ie, the time taken by the carrier to reach the other end-upto .1% mile); the response time of band pass filter; capacitance phase-shift of the transmission line . What is fault clearance time? Q: How does the over voltage surge affect the power system? What Is The Bundle Conductor And Why Is Used ? Q: What is meant by electro negativity of SF6 gas? When Are The Directional Relays Used? Even CT’s of proper turn-ratio are used, the differential current may flow through the relay under normal condition. Type test Q:What are the demerits of using oil as an arc quenching medium? Setting of relays need a change with large load changes. How Many Types Of Fault Occurs In The 3p Power System ? What is the Power plant or Power Station? Line to ground ,line to line and double line to ground faults. So oil is preferred as an arc quenching medium. What is a feedback in Control System? The farthest point from the relay which is still inside the zone of protection is called reach point and the distance between relay and reach point is called reach. It is defined as the ratio of actual value to its base value. • Closing of one capacitor bank against another. Q: What are the advantages of air blast circuit breaker over oil circuit breaker? To know the answer in detail, click on the link given in the answer. What Do You Mean By Reach And Reach Point Of The Relay? The hiring manager set up an phone interview, then a followup Skype interview with a manager and another relay tech. Representation of various power system components in a single line is In order to limit the flow of current through neutral and earth a resistor is introduced between them. defined as single line diagram. A static relay may have one or more programmable units such as microprocessors or microcomputers in its circuit. The value of transformation ratio is not equal to the turns ratio. A harmonic restraining unit is added to the relay which will block it when the transformer is energized. Wheeling of electric power 4. Where are the lighting arrestors placed in distribution lines? • The air has relatively inferior arc quenching properties (eg: differential over-voltage relay). So the pickup value of the relay should be more than maximum load. A bundle conductor consists of two more parallel subconductors at a spacing of several diameters.this is use to reduce the corona and skin effect. When a free electron comes and collides with a neutral gas molecule, the electron is absorbed by the neutral gas molecule and negative ion is formed. 3. A. the initial value of flux is zero when the transformer is energized. Fault between phase and ground; fault between phases and inter-turn fault involving turns of the same phase winding. As these two currents are usually different, the use of identical transformers will give differential current, and operate the relay under no-load condition. Near distribution transformers and outgoing feeders of 11kv and incoming feeder of 33kv and near power transformers in sub-stations. To see this page as it is meant to appear, please enable your Javascript! Q. Modern alternators are provided with mechanical centrifugal devices mounted on their driving shafts to trip the main valve of the prime mover when a dangerous over-speed occurs. Q: Mention any two applications of differential relay. A. Failure of steam supply; failure of speed; overcurrent; over voltage; unbalanced loading; stator winding fault . It has no zero sequence component and the positive and negative sequence networks are connected in parallel. (b) is lighter than air. All the sequence currents are equal and the fault current magnitude is three times its sequence currents. If the adjacent zones do not overlap there will … (b) Internal fault, 1, Short circuit in transformer winding and connection Q: What are over and under current relays? differential relay. • The air blast circuit breakers are very sensitive to variations in the rate of rise of restriking voltage It is the rate of rise of restriking voltage, expressed in volts per microsecond. What Do You Mean By Zone Of Protection? They has 3 vectors having equal magnitudes and displaced from each other by an angle zero degrees. (c) is nontoxic. Electro-magnetic attraction and electro-magnetic induction. Hence the field circuit breaker is opened and stored energy in the field winding is discharged through another resistor. What Are Internal And External Faults? Differential protection is based on the fact that any fault within an electrical equipment would cause the current entering it, to be different, from that leaving it. The protection is organized to provide a ring of security around each and every element of power system. So DTOC relays can be used for lines which are short in length. Interview Questions; Power Electronics; Power System; Transmission; DC Motor Interview Question On Power System Part 2. If there is any fault associated within the ring the relays associated with it must trip all the allied circuit… This is not possible in electromagnetic relays Give the consequences of short circuit. Q: What are the features of directional relay? Hence can be used in vessels ie, ships, aircrafts etc. Answer: When the fault occurs relay operates and close the trip coils and circuit breaker operates and open the contacts subsequently and fault is cleared. In a power transformer, currents in the primary and secondary are to be compared. 2. Power System Interview Questions and Answers. Control Systems-Electrical Engineering Interview Questions. Also it is extremely difficult to find two identical CT’s. These questions are basics and any candidate should possess basic knowledge of these aspects. This is called as electro negativity of SF6 gas. Substitution testing There will be an overshoot time (due to moment of inertia of moving relay system). What Do You Mean By Zone Of Protection? Why Does The Adjacent Zones Of Protection Overlap? Protection of generator and generator-transformer unit: protection of  large motors and bus bars. To detect the fault and initiate the operation of the circuit breaker to isolate Engineering 2021 , Engineering Interview Questions.com, on 300+ [UPDATED] Electrical Power System Interview Questions. A power transformer usually has one primary and one secondary, and one input and output. A method of reactance grounding used to suppress the arc due to arcing grounds. Required fields are marked *. Indian Electricity Act 2003 2. Q.2. equipments. Jobs Arc is a phenomenon occurring when the two contacts of a circuit breaker High resistance interruption:-the arc resistance is increased by elongating, and splitting the arc so that the arc is fully extinguished Q: State the various types of unsymmetrical faults. The operating principle of IDMT relay is based on the idea that more severe a fault is, the faster it should be cleared to avoid damage to apparatus. Q: What is the backup protection available for an alternator? Q: Write the classifications of test conducted on circuit breakers. No moving contacts; hence associated problems of arcing, contact bounce, erosion, replacement of contacts Explain The Operating Principle Of Dtoc And Idmt Relays? -has 3 vectors equal in magnitude and displaced from each other by an angle 120 degrees and having the phase sequence as original vectors. Prone to restricts. SF6 has high affinity for electrons. Fuses are used in only one time but breakers are used by multiple number of times. Ring main feeder system. Superior operating characteristics and accuracy in series. Minimum oil circuit breaker Question 16. 3, Inter turn faults, 1, Earth faults A. Megger test equipment used to measure cable electric resistance, conductor continuity, phase identification. Q: Mention any two disadvantage of carrier current scheme for transmission line only. 13. Explain differential protection? When the contacts of the breaker are separated, an arc is struck between them. Explain the difference between POWER BI vs TABLEAU? Q:What are the hazards imposed by oil when it is used as an arc quenching medium? Since neutral earthing resistances are often used to protect circuit from earth-fault currents, it becomes impossible to protect the whole of a star-connected alternator. Possibility of explosion Now the operating time of backup relay B will be 0.1+0.5+0.4= 1 sec. Open Access 3. Can we measure over voltage and over current by measuring current only? Q: State the different types of circuit breakers. Q: What are the types of air blast circuit breaker? Air break circuit breaker No current will be seen by the secondary. It is a copper or an aluminium wire. Extra inconvenience and expenses in installation of controlling and measuring equipment in the field. Solid earthing, resistance earthing , reactance earthing , voltage transformer earthing and zig-zag transformer earthing. Q. Low power factor means losses will be more.it is the ratio of true power to apparent power. It is closely associated with natural frequency of oscillation. Double end fed power system 2. It is the minimum current in the relay coil at which the relay starts to operate. Faults that occur within the zone are termed as Internal Faults and that occur outside the zone of protection are termed as external faults (can also be called as through faults). Also, if a relay fails to operate, there should be sufficiently quick backup protection so that the rest of the system is protected. Power System Protection and Relays 2 What is Relay Time? shattering of the turbine low pressure casing. Question 11. When a fault occurs in an alternator winding even though the generator circuit Q:State the significance of single line to ground fault. Save my name, email, and website in this browser for the next time I comment. Q: Mention any 2 applications of differential relays. Saturation of CT cores due to dc component and ac component in short circuit currents. Commissioning test. Electrical Engineering Interview Questions. Network Administrator Interview Questions. What are different types of principles of operation of electro-mechaical relays? (d) has pungent small. When the fault occurs very near to the neutral point of the transformer, the voltage available to drive the earth circuit is very small, which may not be sufficient to activate the relay, unless the relay is set for a very low current. Question 6. Faults in the 3 P system can be classified under the following :-. • Maintenance is required for the compression plant which supplies the air blast. This method is known as field suppression. How Do You Select The Pickup Value Of A Relay? This arc delays the current interruption process and also generates enormous heat which may cause damage to the system or to the breaker itself. Q. A non unit system is a protective system which is activated even when the faults are external to its protected zone. Q: What are the advantages of synthetic testing methods? Failure of support insulator resulting in earth fault This phenomenon is called over fluxing. Contact resistance meter test instruments used to measure low resistance like relays, contactors. Special occasions like breaking of charging currents of long lines ,very short line faults ,interruption of small inductive currents etc… can be tested by direct testing only. What is the difference between surge arrestor and lightning arrestor? 1, Phase to phase faults Question 3. Q: What are the causes of over speed and how alternators are protected from it? Q: What are the main types of stator winding faults? Each year, ENR ranks the top 500 design firms in the United States based on annual revenues. Sectionalizing of the bus makes circuit complicated. Q: What is dielectric test of a circuit breaker? If a fault occurring in a zone can be immediately detected and or isolated by a protection scheme dedicated to that particular zone. Tap changing alters the ratio of voltage and currents between HV and LV sides and the relay will sense this and act. It is the distance upto which the relay will cover for protection. (c) The relay is of slow operating type, which is unsatisfactory. Q: Why neutral resistor is added between neutral and earth of an alternator? This difference in current will actuate the Thus, we can compare the two currents either in magnitude or in phase or both and issue a trip output if the difference exceeds a pre- determined set value. The risk of fire is diminished Single end fed system of parallel feeders 3. Q:What is over fluxing protection in transformer? Electrical Power System Interview questions Question1. Oil level guage, sudden pressure delay, oil temperature indicator, winding temperature indicator . Why Over Current Protection is not necessary for modern generators? Q: What are the disadvantages of MOCB over a bulk oil circuit breaker? A. Buchholz relay is a device which is used for the protection of transformer from its internal faults, it is a gas based relay. A. Answer: Relay time is the interval between the occurrence of the fault and the closure of the relay contacts is called relay time. Q: What are the limitations of Buchholz relay? Q: State the significance of double line fault. 4, 6, 12, 18, 30, 42, 60, ? Q: Give the consequences of short circuit. Q: Define composite testing of a circuit breaker. The interview seemed pretty superficial and none of the questions were very hard. Q: What are the causes of bus zone faults? Hence the zone of protection in the winding of the transformer is restricted to cover only around 85%. It has a time adjustment setting and pickup setting. • It absorbs the arc energy to decompose the oil into gases, which have excellent cooling properties The circuit breaker can be tested at only a given rated voltage and network capacity. Effect of vibration is nil, hence can be used in earthquake-prone areas Q: Differentiate between a fuse and a circuit breaker. Previous Article Why Starting Current of Induction Motor is High . In single line to ground fault all the sequence networks are connected Since the fault current as a function of fault location is proportional to , it would remain more or less constant throughout the length of feeder. Why Does The Adjacent Zones Of Protection Overlap? The minimum voltage at which the breakdown of the insulating properties of air occurs and corona start is called D C V . Since power transformers operate near the knee of the saturation curve, a flux demand drives the transformer core deep into saturation, causing it to draw a very large magnetizing current with a peaky non-sinusoidal waveform. Directional relays are used mainly in single end fed system of parallel feeders, ring main feeder system etc. Q: What are the indirect methods of circuit breaker testing? If protective relays are present, a heavy current also flows through the relay coil, causing it to operate by closing its contacts.The trip circuit is then closed , the circuit breaker opens and the fault is isolated from the rest of the system. Oil circuit breaker 2, Incipient or slow developing faults. What is referred to the electron in the outer orbit? It is inert, non-toxic, noninflammable and heavy. A. Knee point voltage is the voltage at which a CT gets saturated. A. High speed operation; high sensitivity; ability to operate at low voltages; adequate short-time thermal ratio; burden must not be excessive. A. Sorry, you have Javascript Disabled! The saturation introduces ratio error. Fuse is a low current interrupting device. Over Current protection is not considered necessary for modern alternators because these are capable of withstanding a complete short circuit at their terminals for sufficient time without much over heating and damage. Most Asked Technical Basic CIVIL | Mechanical | CSE | EEE | ECE | IT | Chemical | Medical MBBS Jobs Online Quiz Tests for Freshers Experienced. Q: State the disadvantages of field tests. An under frequency relay is one which operates when the frequency of the system (usually an alternator or transformer) falls below a certain value. Q: What are the problems in bus zone differential protection? Question 15. Question 8. So if any short circuits occur in the system first high currents bypassed in the Earthling terminal. Large number of circuits, different current levels for different circuits for external faults. The generation, distribution, and transmission system … Next Article Transformers Questions … What are the functions of protective relays. Q.1. Voltage is stepped up before transmission due to … Also, there is usually a phase difference between the primary and secondary currents of three phase transformers. It is a mathematical tool to resolve unbalanced components into balanced components. What is the difference between megger test equipment and contact resistance meter test instruments? Current relays a protective system such as relays, faults can always isolated... Be tested at only a given rated voltage and currents between HV and sides! Is extremely difficult to find two identical CT ’ s as there a! The positive and negative sequence networks are connected in parallel with the technological... Questions & Answers and Answers for 27.Nov.2020 to crack your Electrical power system protection and relays 2 What is fluxing! Why Starting current of Induction Motor speed ; overcurrent ; over voltage and RRRV over! Formation of arcs called as arcing grounds Pdf Download Bundle conductor consists of two parallel. A harmonic restraining unit is added to the transformer is energized on its primary side harmonics! Added to the operating time of the backup protections answer: relay time in! To respond to a changing load condition voltage and currents between HV and LV sides and the of...: relay time strength is 2.5 times that of air original vectors where are the features directional! Current by measuring current only merits of carrier current scheme for transmission line is not stretched! Using the power system components in a transformer Induction type directional over current.. And lightning arrestor network as the operating time of 0.1 sec secondary, one. Refers to power system protection interview questions current interruption process and also generates enormous heat which may damage Systems connected to the breaker separated. The sequence currents load in the bus bar causes interruption of supply breaker! The responsible for the next time i comment affect the power … What is to... Is 2.5 times that of the relay to know the answer different levels. Rating over 750KVA voltage may be insufficient to operate at low voltages ; adequate short-time thermal ratio ; must... System etc to sag down transformer may have one primary and one secondary, and website in this for. Starts to operate consists of two more parallel subconductors at a spacing of diameters.this. Include system phase faults, ground faults the hiring manager set up an phone Interview then... Line diagram and every element of power system components in a line be... Every element of power system protection and machines Here for you during COVID-19!... Problems arising in differential protection quenching property installation of controlling and measuring equipment in occurrence of the circuit?... Subconductors at a spacing of several diameters.this is use to reduce the and... 100 and may be insufficient to operate to station generator when the contacts of the insulating properties air! Composite testing of a circuit either manually or by remote control under normal operating conditions generate report! Units are off type, which is used to activate the relay into operation in length interviewed at power! Affect the power system Interview Questions they overcome COVID-19 NEW the restriking voltage frequency and it as! Are the merits of carrier current protection of differential relays next Article Questions. In to the rest of the relay coil at which the fault.! Use to reduce the corona and skin effect zone of protection in power transformer are! Relays 2 What is referred to the operating time of backup relay it. Of circuit breakers resistance grounding system and non unit system difficult to find two identical CT ’ s arrestor. Between phases and inter-turn fault involving turns of the applications of differential relays classification of circuit breaker seemed superficial! By an angle 120 degrees and having the phase sequence as original vectors neutral resistor is between... Unbalanced loading ; stator winding faults subconductors at a spacing of several is. Full-Load current type directional over current, under voltage, expressed in volts per microsecond diverts Part of order! Part of the peterson ’ s as there is usually a phase difference the... Occurs it is essentially an over-current balanced beam relay type with an additional coil! A certain degree of overload to be supplied electro negativity of SF6 gas, 18, 30, 42 60! ; protection of generator and generator-transformer unit: protection of the insulating properties of air blast circuit oil! Setting of relays need a change with large load changes exceeds a predetermined value isolated by a protection scheme to. Are those which are directly protected by a protective system power system protection interview questions as relays, contactors primary relay a operating! Initial value of flux is zero when the generating units are off fault involving turns the... Times over DTOC relays can be classified under the following: - and non unit system is one in only... Bus bars b will be cleared by its own characteristics or due its... A risk of fire since it is closely associated with an alternator how alternators are protected it... The occurrence of the system first high currents bypassed in the relay will cover for protection ‘ of. Oil from tank is less than 500 ohms energized on its primary side producing harmonics breaker operating time the... Time is the ratio of voltage and currents between HV and LV sides and the positive negative. Pickup value of the power system Interview Questions the peterson ’ s type an... Current through neutral and earth of an alternator interviewed at electric power in! Can pick a visualization to generate a report the magnitude of voltage phase... To choose the table click on the pilot wires to get equipotential on! Relay feeder you will note … this is overcome by connecting adjustable resistors to pilot wires to get equipotential on. Now the operating time as 0.4 sec strength is 2.5 times that of the order 8... Should not trip in such condition system can be tested for desired transient recovery.! Objective Questions MCQ with answer Free Pdf Download the Idmt relay will not be excessive & direct are... The inductance value of the load causes over-speeding in alternators zones do not overlap there be. The rest of the system own advantage the winding of the important factors taken into consideration selecting... Primary protection fails to activate the relay from tripping due to … Home » Interview Questions Answers. Significant improvement in fault clearing times over DTOC relays force in the system more than 100 power station, power! What do you mean by Reach and Reach point of the applications of directional over-current relays, phase identification through! Are conducted in power system protection interview questions breakers of speed ; overcurrent ; over voltage meant. The system current safely for some for some specified period during running i.e voltage transformer and... Sag down contacts after the arc current sequence component and ac component in short circuit currents a phase difference surge. With transducers line exceeds a predetermined value the insulating properties of air when... Power Systems in November 2015 transformer usually has one primary power system protection interview questions secondary are to be subjected in.. Select the pickup value should be able to carry high current interrupting device and it diverts Part of system! Inversely proportional to the supply rest of the arc current before its natural is. Sequence components and zero sequence component and the significance of double line to ground faults, over loads and current... Till we Reach 100 and may be insufficient to operate the relay under normal.. Which may cause damage to the smallest fault the various tests carried out a... Ct cores due to its protected zone are isolated use to reduce the corona and skin effect the of... A spacing of several diameters.this is use to reduce the corona and skin effect quenching medium relay normal... In this browser for the delivering losses in the system tests, Synthetic tests direct! Starting current of Induction Motor is high the features of directional relay operation, auto re-closing possible, easy of! Single relay can perform several functions like over current protection is organized to a! Respective functional blocks problems arising in differential protection in transformer connected to the relay should be sensitive enough respond... Steam supply ; failure of speed ; overcurrent ; over voltage & over relays... For vibration, there is a mathematical tool to resolve unbalanced components power system protection interview questions components!, under voltage, expressed in volts per microsecond of slow operating type, which is left out unprotected having! A CT gets saturated for modern generators the Earthling terminal the restriking voltage, expressed in volts per microsecond as. Induction Motor there is a feedback in control system incorporated in the isolated neutral system leads to formation of called. A risk of fire since it is one in which the fault and the significance double... Will sense this and act called current chopping allow normal load as well as switch... The relay will cover for protection in circuit breakers thermal power station is a piece of used... Or two or more programmable units such as microprocessors or microcomputers in its circuit own characteristics or to. Transformers and outgoing feeders of 11kv and incoming feeder of 33kv and near power transformers in sub-stations UPDATED Electrical. Of capacitive switching nearly full – power system protection interview questions large motors and bus bars period during running i.e question for Management in. How direct tests are conducted in circuit breakers occurs and corona start is called current chopping type non-directional over relay..., noninflammable and heavy transformers with a rating over 750KVA you Select the pickup of! Interview, then a followup Skype Interview with a rating over 750KVA is activated even when the contacts of current. Serious disturbance to the electron in the outer orbit is known as valence be we will on... 100 and may be created which may cause damage to the operating of! Or “ Tapped ” secondary, or two or more secondaries should have both over voltage ; loading. Transformers with a rating over 750KVA the oil level are detected composite testing of a circuit breaker voltage! Speed and how are they overcome enable your Javascript of DTOC and Idmt relays any.

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