Insulation resistance of cable should be mcq

insulation resistance of cable should be mcq 9/3. The IR test measures the resistance of the electrical insulation between the copper conductors and the core of the stator or rotor. 3. e. which will improve your skill. In the case of any difference in the readings, the presence of moisture in the cable insulation is confirmed. Insulation resistance testing Introduction Insulation resistance testers can be used to determine the integrity of windings or cables in motors, transformers, switch-gear, and electrical installations. . armature will have a greater number of leakage paths C. INSULATION RESISTANCE OF A CABLE Cable conductor is provided with an insulation of suitable thickness to avoid the leakage of current. If a cable of homogeneous insulation has a maximum stress of 10 kV/mm, then the dielectric strength of insulation should be (a) 5 kV/mm (b) 10 kV/mm (a) 15 kV/mm (d) 30 kV/mm Ans: b 32. I also agree that the 2. The test method is determined by the type of equipment being tested and the reason for test-ing. The type and thickness of the insulation must be as specified in the design documentation. 67 times that of the measured line or neutral conductor loop values. The insulating material for cables should (a) be acid proof XLPE insulation performs at both high and low temperatures. If a power cable and a communication cable are to run parallel the minimum distance between the two, to avoid interference, should be: A. Heater resistance should be tested before, during, and after installation to ensure that the heating cable has not been compromised. Answer/ Hint "Insulation tests are required to be carried out between 1)conductors of each SELV circuit and earth. Insulation resistance is calculated using an insulation resistance tester. Re: Insulation resistance test of 600 V rated cables I agree, the "Stich in time" paper is a good basic guide for IR testing, you can download it from the megger website. Due to its structure, XLPE is extremely resistant to abrasion and other wear and tear. Resistance is in ohms/mm If more than a 25% difference exists between the two IR readings, age deterioration or damaged insulation should be suspected. ) Perform continuity tests to ensure correct cable connection and phasing. For instance, when testing 4. Using insulation testing, with an instrument such as the Fluke 1555 10 kV Insulation Tester combined with Fluke Connect® technology, such leaks can be detected as insulation resistance slowly tapers over time—a sign of normal and expected deterioration. 10 cm [Wrong Answer] C. Insulation-resistance values should be in accordance with manufacturer's published data. Covers small power and lighting cables mainly applicable to building Normal insulations should read infinity. 8 times, 30 minutes; High ohmic series resistance micrometer is recommended for measuring: If during periodical testing, insulation resistance of cable is found between 5 and 1 MΩ /km at buried temperature, the subject cable should be programmed for replacement. b) high resistance to thermal deterioration. Earth the screen after test for at least 5 minutes. The first is that this test can indicate low values of insulation resistance The insulation must be just the opposite from a conductor: it should resist current and keep the current in its path along the conductor. 4 The insulation resistance tests should be made when conductors, cables and insulated parts are clean and dry. If more than one 3-phase cable are used in parallel, it is recommended that a separate CBCT on each cable be connected across a common relay or a separate relay be provided for each CBCT. 11 The size of a conductor used in power cables depends on the (A) operating voltage. d) freedom from gaseous inclusions . A solid substance or insulated conductor subjected tensile stress with or without screen is called as: a) Cable. The test data should be recorded for future comparative purposes. 1 MΩ should be expected The underground cable can be 2-3 times more expensive than the overhead cable. A good dielectric should have all the following properties EXCEPT. · Now the nonlinear resistance provides a low resistance path for the surge to the ground. Ans: C Q. If during periodical testing, insulation resistance of cable is found between 5 and 1 MΩ /km at buried temperature, the subject cable should be programmed for replacement. 1. If fault resistance is found more then where the fault occurs, one should burn the insulation “Fault Burning” and can decrease the resistance and after that Murray Loop Test can be done. 0 mm 2. The variety of paper used for insulation purpose is. The first thing to check is the cable testing environment and cable preparation. Insulation resistance testing is a key test for electrical cables as it is a measure of how effectively the cable is insulated. 6. CS Topics covered : Greedy Algorithms specified above; however the insulation resistance should not be significantly lower than the figures above. Every time the measured value is deviating by more than 0. d) mill-board . These short objective type questions with answers are very important for Board exams as well as competitive exams. The minimum insulation resistance to earth or between phases shall be 100 meg-ohms. 2)live conductors of each SELV circuit connected together and the live parts of other circuits. A copper cable has a length of 450 m and a cross-sectional area of 4. 1 to 1. Figure 2–Typical Megger test instrument hook-up to measure insulation resistance. The thermal insulation system is normally designed to prevent the majority of heat losses. The thickness of any cable depends on the purpose of its design. If insulation resistance of the cable is found between 1000 and 100 KΩ /km, at buried temperature, the subject cable should be replaced urgently within a year. The test immediately preceding the insulation test should be the earth bond test. the resistance measured are like parallel impedances. If there is joint in the cable one should inspect the same, too. These short solved questions or quizzes are provided by Gkseries. Fig 5: HiPot test results after programming tester to keep shield at ground potential Fig. 0. Open Digital Education. 5 percent and turn ratio is 1:10, the percentage secondary resistance referred to primary will be a) 25 b) 2. Cables Multiple Choice Questions and Answers for competitive exams. The thickness of the layer of insulation on the conductor, in cables, depends upon (a) reactive power (b) power factor (c) voltage (d) current carrying capacity 20. ” At this time, points were considered to be a “number of pairs of terminal wires from which it is proposed to take the current, either directly, or by flexibles, to lamps or other appliances”. B. Insulation resistance test must be conducted on dc voltage of value not less than twice the standard supply voltage. “Because the insulation resistance and reactance of the stray capacitance is so high, the ac test current can be simplified to the leakage current at 250 V times the ratio of hi-pot test voltage to 250 V. A de-rating factor of 0. 13. 955 MΩ Correct answer: 3. Service Mains. If no literature from the manufacturer is available, apply 500 volts dc for 300-volt rated cable and 1000 volts dc for 600-volt rated cable. With this connection, the insulation resistance will be that of the generator stator winding and connecting cable combined. It is often found in cables that need to meet the UL standard 910 Plenum Cable Flame Test, which labels cables as suitable for use in a building’s space for air circulation. This is done to verify the integrity of the insulating material, be it wire and cable insulation or motor/generator winding insulation. 50km=50x10^3 m Insulation resistance = 1 Mohm / (50x10^3 / 10) = 200 ohm Three Similar inductive coil of resistance 20ohm and reactance of 30 ohm are connected in mesh across a 3 phase 400v supply, what will be phase current 11. The test voltage is produce either by an internal hand driven generator or by a battery and electronic voltage changer. Insulation resistance will vary with purity, types of impurities in the ceramic, compaction, thickness of insulation, and temperature. 3. : 230V) to measure insulation resistance in Ohm`s. 72E-8 Ωm, then the resistance of this cable will be: A. When automatic disconnection of supply is used as a measure of protection, Apr 04,2021 - Critical Thickness Of Insulation And Heat Transfer From Extended Surfaces (Fins) - MCQ Test 1 | 15 Questions MCQ Test has questions of Mechanical Engineering preparation. 88 is applied to cables travelling through thermal insulation, how thick is this thermal insulation? • 200mm • 100mm • 500mm • 50mm 10. MEDIUM VOLTAGE CABLE: Cables having a voltage rating of 2001 volts and higher CONSTRUCTION COMPARISON: BASIC CABLE 600V MV Conductor Conductor Insulation Conductor Shield Jacket (optional) Insulation Insulation Shield (5kV-35kV) Jacket DEFINITION OF SHIELDING: Shielding of an electric power cable is the practice of confining the electric field The voltage-sourced converter-based HVDC link, including the modular multilevel converter (MMC) configuration, is suitable for wind power, photovoltaic energy, and other kinds of new energy delivery and grid-connection. Important: Insulation resistance values for Test A and B; for any particular circuit, should not vary more than 25 percent as a function of measuring voltage. With contact resistance taken into account, it can be seen that it is difficult to meet requirements at high currents of 2A and 2. Name the cable or conductor which connects the distributor to the consumer terminals. 5 below. This cable test, conducted as specified in BS EN 50395, is designed to test the insulation at the cable's maximum operating temperature. Core Insulation Resistance . e. 0 mm 2 conductors in 600-v circuits, what is the minimum insulation resistance allowed by the Philippine Electrical Code? A. Q19. d) Wire . If no data from the manufacturer exists, the values should be no less than 100 megohms. Cross-linked polyethylene insulation is also a more affordable option. XLPE insulation performs at both high and low temperatures. 4 megohms. In most cables like this, the capacitance between any one conductor at voltage and all of the other conductors at ground is about the same, and in the absence of insulation flaws, the insulation resistance for each should also be about the same. 2/0 Gauge Buy 2/0 Gauge wire. If insulation resistance of the cable is found between 1000 and 100 KΩ /km, at buried temperature, the subject cable should be replaced urgently within a year. 63 b) 0. So, for the proper function of any device, it should have high insulation resistance. n Provide guidelines for evaluating the results of these diagnostic insulation resistance tests. 1 1. The insulation resistance test is an electrical test which uses a certain type and level of voltage (500V d. A selection of fuse is based on Steady load Fluctuating load Both (a) & (b) None of these 2. c) From cable reel to cable tray, the cable is fed from the top of the reel to main-tain required curvature. As a result, cables only up to about 50cm can be used with 24AWG, or maybe even 1m with boosted source voltage. 500,000 Ω MCQ in Philippine Electrical Code Part 1 of the Series as Electrical Engineering topic in REE Board Exam. When should XLPE cable be used? A steady insulation resistance reading indicates that the cables are fully charged, and that the capacitive component of the test current has fallen to zero. For High Voltage Transformer / High Voltage Machine or Equipment, 5 kV range is selected to perform Insulation Resistance Test. Therefore, the proper choice of insulating material for cables is of considerable importance. i. AC Generators. Solder flux, oils, mold release agents, and skin oil can cause problems. Visualizations are in the form of Java applets and HTML5 visuals. What does the insulation resistance test measure? With an insulation resistance test, manufacturers, installers and quality testers can assess if a solar panel has adequate insulation between its electricity-conducting components and the module's frame or, in case of a More insulation is always "better" in the sense that it decreases the probability of an insulation failure. 88 is applied to cables travelling through thermal insulation, how thick is this thermal insulation? • 200mm • 100mm • 500mm • 50mm 10. The 6. If the insulation is replaced by one of relative permittivity 2, the capacitance of the cable will become one half double four times none of the above ⇒ Low tension cables are generally used upto 200 V 500 V 700 V 1000 V ⇒ The electrostatic stress in underground cables is Q. 8 times, 30 minutes; 2. 31. Finally, you can also take the Online Quiz from the Take Electrical Cables Quiz Button. Using tables within BS7671:2008 - If the supply cable coming into a domestic property is 25mm, what size should the Earthing conductor be; • 16mm • 25mm • 10mm Insulation resistance of high voltage circuit breakers is more than (a) 1 mega ohms (b) 10 mega ohms (c) 100 mega ohms Multiple Choice Questions (MCQ) on Resistance and Reactance per km of Copper and Aluminium cables Custom Search For the purpose of calculating voltage drop within a cable, the table below gives the reactance and resistance values for Copper and Aluminium cables: railway cable types, railway signaling cable manufacturer india, rdso specification for signalling cables, indian railway signalling cable, loop resistance of signalling cable, 12 core signalling cable, train cable, special cables2, types of signal cables, 6 quad cable in indian railway , rdso specification for signalling items, loop resistance formula, rail cable, loop resistance of telephone Minimum values of insulation resistance: … values for a 400/230 volt system are acceptable down to 0. 2) c) 0. 714 MΩ If a cable of homogeneous insulation has a maximum stress of 10 kV/mm, then the dielectric strength of insulation should be (a) 5 kV/mm (b) 10 kV/mm (a) 15 kV/mm (d) 30 kV/mm Ans: b 32. 5 / 1. In case of cables the IR differs from cable to cable depending upon the length of cable, insulation thickness and type of cable. A moving-coil permanent-magnet instrument can be used as _____ by using a low resistance shunt. The test should also be done by reversing the polarity of the insulation resistance tester. The insulation resistance of cables, transformers etc is measured by following instrument Multiple Choice Questions with Answers on Refrigeration and Air If the insulation resistance of a cable of length 10m is 1 megaohm…. c. The bedding on a cable consists of (a) hessian cloth (b) jute (c) any of the above (d) none of the above 19. Then. 2 Insulation resistance test The resistance of the insulation shall be measured between conductors and the metallic outer covering, or a specially applied conductive metal ground plane, by means of dc voltage of 1000 Vdc for mineral insulated heaters and 2500 Vdc for polymer insulated heaters. gtu-mcq. Cable surrounded by thermal insulation for 400 mm or more has a derating factor of a) 0. Discover more at www. 2. Q2. These have been in use for more than 75 years. (C) current to be carried. Megger) at 1000 Volts for 1 minute. c) high dielectric loss. If no literature from the manufacturer is available, apply 500 volts dc for 300-volt rated cable and 1000 volts dc for 600-volt rated cable. This is to test whether the insulation can withstand the voltage, in case of a missing earth the motor housing could become live. For example IR value of 1 meter cable and IR value of 100 meter of same cable are not comparable in absolute A megger is to measure insulation resistance of a cable. The measured resistance indicates the condition of the insulation between two conductive parts. 3. The insulating material for cables should (a) be acid proof 1/0 makes a great battery cable for large or hi-performance 6 cylinder engines and stock V8s. Sheath is used in the cables to (A) Prevent the moisture from entering the cable (B) Provide the strength to the cable (C) Avoid the chances of the rust on the strands (D) Provide proper insulation Example of the variation of insulation resistance over a period of years: At A, the effect of aging and dust accumulation is shown by decreasing values. In cables with polymeric insulation, the conductor shield is usually the same polymeric material as the insulation, but impregnated with carbon particles to make the material a semiconductor. Q18. C. insulation may be damaged D. c) craft paper. The sharp fall at B indicates there was an insulation fault. The insulation resistance of a conductor is inversely proportional to its length – that is, its insulation resistance decreases as the conductor’s length increases and vice versa. In the cables, sheaths are used to (a) prevent the moisture from entering the cable (b) provide enough strength (e) provide proper insulation If the insulation is replaced by one of relative permittivity 2, the capacitance of the cable will become (a) one half (6) double (c) four times (d) none of the above Ans: a. At C, the insulation resistance value after the motor has been rewound. 51 (Table 52. Looking at BS 76171:2018 643. 11. Myron Boyajian September 2, 2020 . Step 4 Measurement of insulation resistance of a cable in a water bath is a typical application of a 2-wire grounded connection. The insulation on an electric cable is just as important as the conducting wires it protects. 6) The insulation resistance of a cable of length 10 km is 1M Ω. 2. Figure 2 The procedure is necessarily more complex for systems with multiple electrodes or with earthing grids but helpful information covering these situations, and explaining earth testing in much more detail can be found in the publication “Getting Down to Earth 42) If the percentage resistance of a power transformer for secondary side is 2. It also boasts resistance to high voltage electricity, chemicals, and other hazardous materials. The insulation resistance measurement must be equal to or greater than 1 gigaohm (GΩ); 1 GΩ = 1000 MΩ. 500 V is used to measure the Insulation resistance of control cable for Insulator which can withstand up to 1. Insulation resistance of the cable, i. High dielectric strength to avoid electrical breakdown of the cable. I 2 R losses, losses in insulating material, and metallic sheaths (for insulated cables). · It should be noted that designing a lightening arrester that when the surge is over the arc in gap should cease. 5 9. which will improve your skill. Mineral-insulated copper-clad cable is a variety of electrical cable made from copper conductors inside a copper sheath, insulated by inorganic magnesium oxide powder. The Insulation Test should be carried out in the “Guarded Insulation Test of Telephone Cables and Wires and Minimum Insulation Resistance values Test of Wiring Installations. Step 8. The test values should be normalized to 20°C for comparison purposes. How and where these two leads are connected will differ depending on what the test subject may be. The insulation keeps the current flowing along the wire, exactly as intended. There is a big difference between cable insulation concerns when dealing with low voltage systems as compared with medium-voltage systems. As such the insulation resistance of the complete installation to earth should not be less than 1 MΩ. The coaxial cable will require more insulation as the cable will not only prevent power leakage, it traps electromagnetic radiation. insulation may be covered with moisture. Any reading above 1. 5 In addition to regular testing of the cables in dry weather, random tests in wet weather may also be carried out where considered necessary. If a wiring system is wet and / or dirty, the surface leakage component of test current will be high, giving a low insulation resistance reading. If the resistivity of the copper is 1. The resistance of the conductor is inversely proportional to its X-sectional area, the energy loss due to ohmic resistance may be represented as; The annual cost of energy wasted "Insulation tests are required to be carried out between 1)conductors of each SELV circuit and earth. You should carry out the following tests and record your results: Thermal insulation The selection, installation and maintenance of thermal insulation is a key component in the performance of an electrical heat tracing system. This is most significant for tablets. " For example, a motor rated at 5000V should have a minimum insulation resistance of 5 Megohms. 3 kV and up to 19/33 kV. , it should not absorb moisture from air or soil. Comparing this result with the correct row of Table 2 shows that our cable passes the insulation resistance test. Insulation-resistance values must be according to the manufacturer’s published data. If necessary, you can purchase one here. Poor insulation may result in short circuit, electric shock or fire. Using tables within BS7671:2008 - If the supply cable coming into a domestic property is 25mm, what size should the Earthing conductor be; • 16mm • 25mm • 10mm If during periodical testing, insulation resistance of cable is found between 5 and 1 MΩ /km at buried temperature, the subject cable should be programmed for replacement. Hi Mr. It also has very low water absorption. The insulation resistance of a cable of length 10 km is 1M Ω . 25 is considered excellent. Winton Avenue Hayward, CA 94545-1232 The insulation resistance of inductors with more than one coil should be tested between coils and an insulation value greater than: A. 1000 100 10 1 12 34 567 89 10 Time in Minutes Reading in Megohms D Without the insulation, the heat loss is generally too high to be offset by a conventional heat tracing system. Guidance for the selection of HV cables, the conductors size, the insulation level and the cable construction to be used on three-phase AC systems operating at voltages exceeding 1 kV. Low Voltage and High Voltage Cable Testing Low Voltage XLPE Distribution Cables: Insulation Resistance: Cables shall be tested for insulation resistance with an insulation tester (i. When the two cables are joined in series, the ratio of insulation resistance to conductor resistance is _____ ×106 Ans. If a cable of homogeneous insulation has a maximum stress of 10 kV/mm, then the dielectric strength of insulation should be_____? Underground Cables Multiple Choice Questions and Answers for competitive exams. After test results are approved for new cable and the splice is completed, an insulation-resistance test and a shield-continuity test shall be performed on the length of new and Learn Earthing Or Grounding MCQ questions & answers are available for a Electrical Engineering students to clear GATE exams, various technical interview, competitive examination, and another entrance exam. c test on cable involves the application of direct current which is _____ times the rated dc voltage for approximately _____ minutes: 0. A. However, before testing care must be exercised to confirm that it is safe for circuits to be tested collectively. Cable are sheathed to a) Protect the insulation b) Increase the cable capacity c) Increase the rate of heat dissipation d) Protect the cable from mechanical stresses</br> Multiple Choice Questions / Quiz (3) Rectifier and Regulated Power Supply (8) Resistance and Resistive circuits (13) Semiconductor (6) Synthesis of passive network (2) Tech (7) Thermoelectricity (4) Thyristors (6) Transformer (6) Two Port Network (1) For cables rated 600 V, the minimum acceptable insulation resistance values for cable lengths from 100 to 1000 feet would be as shown in the following table, from IEEE 525. the insulation test of the individual cores with sheath or armour and between the cores is essential. If there is 18) When testing earth leakage of coach with 500 volt meger, the insulation resistance under bad healthy weather condition should be more than [ b ] a) 2 mega ohms b) 1 mega ohms c) 0. Capacitance should be discharged, both before and after an insulation resistance test. 5 or half a meg to ground would be acceptable for a 480 volt motor. Switchgear and Protection MCQ Objective questions & answers are available for a Electrical Engineering students to clear various technical interview, competitive examination, and another entrance exam. Use 2/0 battery cables for hard to crank engines (like high compression, big blocks, or diesel engines), electric vehicle battery banks (depending on controller amperage), and large RV power converters house batteries. Q20. The voltage should be 250V DC and the minimum insulation resistance should be 0. Data for CBSE, GCSE, ICSE and Indian state boards. 3 kV cables or 5 kV for cables above 1. In this page you can learn various important switch multiple choice questions answers, mcq on switch, short questions and answers on switch,sloved switch objective questions answers etc. 25 on your meter, then the cable passes. Insulation resistance test is conducted in most of the substation equipment is high and medium voltage substations. The high voltage d. This Electrical Cables MCQ contains 20 Multiple Choice Questions. B. It also boasts resistance to high voltage electricity, chemicals, and other hazardous materials. 3. Where the prescribed values cannot be achieved the connection arrangement should be first checked. 5MOhm the IEE book electricians guide to the building regs states: 42) If the percentage resistance of a power transformer for secondary side is 2. static charge of the machine may give a false reading B. The Insulated Power Cable Engineers Association (IPCEA) provides the formula to determine minimum insulation resistance values. Insulation resistance testers are calibrated to display megohms (MΩ) of resistance. In this page you can learn various important insulation of cable multiple choice questions answers, mcq on insulation of cable, short questions and answers on insulation of cable,sloved cable insulation objective questions answers etc. For installations of 2. 2 it says that 1MΩ is the minimum insulation resistance required for initial verification, which to me means for new cables. for low voltage installations i. NB: – The voltage, we apply for measurement of insulation resistance, is direct voltage. 750,000 Ω. Now for the 100 V tests! Electrical Cables MCQ Test & Online Quiz: Below is the Electrical Cables MCQ test that checks your basic knowledge of Electrical Cables. 5 MegOhms if the apparatus had no British Standard. ” Like a visit to the doctor’s office, each test examines the test item in a different way In case in order to test any other faults. 12. 5 percent and turn ratio is 1:10, the percentage secondary resistance referred to primary will be a) 25 b) 2. Copper has poor resistance to repeated stressing, even if the stress is kept below its ultimate yield point of 15 percent elongation. 11 If the conductor is provided with high insulation, then higher will be its opposition of Electric current. For low-voltage circuits with a nominal operating voltage greater than 500 V, an insulation test voltage of 1,000 V should normally be used. 4A. The approximate electrical resistances of these ceramics in mineral insulated cable are listed below. PVC insulation and sheathing on electrical cables was introduced in the late 1950’s and early 1960’s to replace rubber insulation and sheathing as it was more practical, and not being a naturally occurring compound could be produced in quantity as required. Detecting cable damage prior to the application of insulation can prevent additional labor costs. When should XLPE cable be used? Samtec tests it parts according to EIA-364-21 “Insulation Resistance Test Procedure for Electrical Connectors, Sockets, and Coaxial Contacts. lags the voltage by 180° D. The measured value shall not be less than 50 M The satisfactory operation of a cable depends to a great extent upon the characteristics of insulation used. 714 MΩ0. b) rice paper. At A, the insulation resistance decreases due to aging and dust accumulation. Figure F-3 Cable Feed into Cable Tray d) Cable sheaves or a shoe may be used to guide cable into the desired direction, maintain minimum bend radius, and reduce friction. C. high voltage pressure testing set is used in fault burning work. insulation resistance (between core and sheath) are 600MΩ and 900MΩ respectively. The moisture tends to decrease the insulation resistance and hastens the In case in order to test any other faults. For instance, when testing Ihe IEE regulations recommend on motors a test voltage of 500 V for insulation resistance test, minimum acceptable result should be 1 MOhm. What should be minimum insulation resistance value… What should be minimum insulation resistance value for electrical cables? … The One-Megohm Rule As a general rule of thumb, insulation resistance should be approximately one megohm for each 1,000 volts of operating voltage, with a minimum value of one megohm. It is also important to remember that, unlike filament lamps, LED lamps are electronic devices, as are their associated dimmers. This should be considered when carrying out certain electrical tests such as insulation resistance and loop testing. Temperature at positive end should be more than the temperature at negative end. As the voltage level increases the cost of insulation is increased therefore the underground cable is restricted to low and medium voltages. Trace Heating Cable TESTING SELF-REGULATING CABLE A test should be performed when the heating cable is received, prior to installation and after installation using a 500 VDC megger. These short objective type questions with answers are very important for Board exams as well as competitive exams. Cross-linked polyethylene insulation is also a more affordable option. For insulation testing,we need to disconnected from panel or equipment and keep them isolated from power supply. A repository of tutorials and visualizations to help students learn Computer Science, Mathematics, Physics and Electrical Engineering basics. Wherever practicable, insulation resistance testing of low voltage circuits should be performed at 500 V DC, and where appropriate the whole consumer unit or distribution board should be subjected to the test. At C, the fault has been repaired (rewinding of the motor) so the insulation resistance has returned to (c) Should not have corrosive action upon the metal of the vane (d) The viscosity of the oil should not change with the temperature (e) All of the above Ans: e. If the megger reads a resistance between 1-1. 6 Insulation Resistance Test Insulation resistance tests are made to determine insulation resistance from individual windings to ground or . Technical Challenges in the Measurement of … The measurement of insulation resistance is a common routine test performed on all types of electrical … insulation resistance values, and extremely high 9. Part 2: Objective questions and answers of Conductors and Insulation . The wires are designed to conduct current, so they should have low resistance. – Tests Insulation Resistance Between Conductive Core • Equipment – Insulation Resistance Tester • Megger and Grounding Braid – Detects damage that can result in cable short to ground – 1000VDC Minimum – 2500VDC Best – Digital or Analog OK • Failure could trip circuit Btt O tdB t breaker or cause fire • When to do?? 1. This checks for breakdown of insulation of motor windings. For PVC sheathed cables, the acceptance value is 1 M . Length of Cable Q2. 55 d) 0. 1 kV voltage. C. Insulation resistance should be approximately one megohm for each 1,000 volts of operating voltage, with a minimum value of one megohm. 5 mega ohms d) 2. The insulation resistance between cores shall be checked. the lower the effective resistance. The main reason is should be ascertained at a regular interval. Its probably a good insulation. Size of the Earth Continuity Conductor or Earth Wire depends on the cable size used in the wiring circuit. Several factors should be remembered when performing this test. A pinoybix mcq, quiz and reviewers. In the case of any difference in the readings, the presence of moisture in the cable insulation is confirmed. Insulation Resistance (Megger) Testing: The Insulation Resistance Test is not recommended for medium-voltage cables. For a 500 Hz frequency excitation, a 50 km long power line will be […] The shielding angle of grounding wire for large crossing lines should be less than that for ordinary lines. ” Dielectric Withstanding Voltage Testing The Dielectric Withstanding Voltage (DWV) test is intended to take into account momentary over potentials caused from switching, surges,and other phenomenon. The longer the cable the more opportunities for leakage current, i. ⇒ If a cable of homogeneous insulation has a maximum stress of 10 kV/mm, then the dielectric strength of insulation should be 5 kV/mm 10 kV/mm 15 kV/mm 30 kV/mm ⇒ The minimum dielectric stress in a cable is at armour bedding conductor surface lead sheath ⇒ The insulation of the cable decreases with the increase in length of the insulation Electrical Cables MCQ Test & Online Quiz: Below is the Electrical Cables MCQ test that checks your basic knowledge of Electrical Cables. Cables & wires are insulated using electrical insulators, which are non-conducting materials that provide resistance between the cable & contacting medium. The grounding resistance of a large crossing tower should be no higher than 50% of the values listed in Table 3. The readings obtained give the Volume resistance of the conductor. The grounding resistance of a large crossing tower should be no higher than 50% of the values listed in Table 3. The readings at each of the sockets wired on the ring should be very similar and the value should be according to this formula: (r1 +r2)/4. Where the prescribed values cannot be achieved the connection arrangement should be first checked. Because of that, insulation resistance can also be referred as 1 minute insulation resistance or 10 minute insulation resistance depending upon the duration of the test. The bedding on a cable consists of (a) hessian cloth (b) jute (c) any of the above (d) none of the above 19. Normally V. Best practice suggests that loop tests should always be performed on a circuit with no load connected. Nute, I am somewhat confused by the units used in the explanation you offered (copy follows). 60227 PVC-insulated cables of rated voltages up to and including U 0 / U =450/750 V. Megger tester [generally a 500V set] is used for measuring high resistance, like insulation resistance of cable, electrical equipment and wire installation in mega ohms. The insulation level of 400 kV EHV overhead transmission line us decided on the basis of a) lightning overvoltage b) switching overvoltage c)corona inception voltage d)radio and TV interference Answer: switching overvoltage 27. A satisfactory insulation resistance measurement should be in millions of ohms. How to Interpret Resistance Readings. In general, the insulating materials used in cables should have the following . An insulation resistance test usually has four phases: charge, dwell, measure, and discharge. a) blotting paper. 01 μ F. Testing the resistance of the conductors. However, this may not always be the case. Multiple Choice Question (MCQ) of Electronics page-15:211. The wiring and cables need to test for each other ( phase to phase ) with a ground ( E ) cable. My colleague and I decided that if a live cable had anything under 1MΩ it would need to be replaced but what about a neutral? The measurement of insulation resistance is a common routine test performed on all types of electrical wires and cables. (a) ammeter (b) voltmeter (c) flux-meter (d) ballistic galvanometer Ans: a. C. 2. 255 MΩ0. This ratio relates to the difference in csa between conductors: 2. If fault resistance is found more then where the fault occurs, one should burn the insulation “Fault Burning” and can decrease the resistance and after that Murray Loop Test can be done. 5 kV for 1. Before the thermal insulation is installed on a heat-traced pipe, the tracing circuit should be tested for dielectric insulation resistance. Readings in Megohms : Instrument Number: A to B+C+E B to A+C+E C to A+B+E A major HV underground cable would be defined as: All 33kV cables 22kV cables greater than 185mm2 2Cu or 300mm Al (10 kV for 22 & 33kV) 11kV cables greater than 240mm 2 Cu or 400mm Al All zone substation and feeder exit cables It should be noted that this test is designed to demonstrate the integrity of the cable sheath - the outer sheathing functions as environmental protection to the finished cable and so the name 'sheath resistance testing' is somewhat of a misnomer. Resistance must be wire wound type. If the reading is lower, consult Section 10, Troubleshooting Guide. Non-hygroscopic i. 4 Meg reading in the stated example is too low for a new installation. Finally, you can also take the Online Quiz from the Take Electrical Cables Quiz Button. You should do this test 3 times – 1. The rule of thumb is 1000ohms per volt. 16MΩ. Quality of insulation also depends on voltage. The insulation between overall drain and armor shall be checked. b) Core. Example of the variation of insulation resistance over a period of years: At A, the effect of aging and dust accumulation is shown by decreasing values. For example, a motor rated at 2,400 volts should have a minimum insulation resistance of 2. If ρ is in Ω-m, r 2, r 1, and l are in metres then insulation resistance of the single core cable is in ohms. This is what is known as the "one-megohm rule. Table 1: Minimum Acceptable Insulation Resistance for 600 V Cable, from 100 to 1000 Feet . Each time a cable bends or flexes, its copper conductors and shields are stressed. 0 ohm Resistance must be uniform. To test either the stator winding or the cable itself, the cable must be disconnected at the machine. 1. Record your test results on the Heating Cable Tests Log on page 30 of the Underground Cables Multiple Choice Questions and Answers for competitive exams. 211. How thick the cable cross-section of the DC main cable should be to keep the loss down at a reasonable level, will be explained in the following paragraph. You have to select the right answer to the question. Any electrical insulation must have the opposite characteristic as the conductor: It should resist the flow of current, keeping it The insulation resistance test consists of applying voltage (600-l0,000V DC) to the apparatus to determine the megohm value of resistance. The rating of fuse wire is always expressed in Volts Amperes Ampere-volt Ampere-hours 3. Figure 7 – Testing the insulation resistance of power transformer. Dielectric strength of rubber is around 5 kV/mm 15 kV/mm 30 kV/mm 200 kV/mm 2. 556 MΩ0. ASWDC (App, Software & Website Development Center) Darshan Institute of Engineering & Technology (DIET) 56) Refer to the following facts to answer the question A 50 Hz, 11 kV, 3 phase alternator with earthed neutral having a reactance of 3 ohms per phase and is connected to a bus bar through a circuit breaker, if the distributed capacitance upto CB between the phase and neutral is 0. Use meggers on high- resistance measurements only (such as insulation measurements or to check two separate conductors on a cable). 50 cm [Correct Answer] D. This is whynyou measure all three windings to earth. Multiple choice questions on Strain Gauge A Strain gauge also sometimes referred to as a Strain gage is a type of sensor whose resistance varies with applied force. The path of current leakage in such cable is radial. Power systems Objective Type Questions Gate Preparation Power generations-2: 26. In this way, the excess charge is diverted towards the earth and hence equipment is protected against failure. A megger is used to read from phase (winding) to ground. rs-online. 96 times, 45 minutes; 3. Any small resistance reading indicates the insulation is breaking down. Insulation Resistance Testing: How Many Megohms … increase the insulation resistance value to an acceptable … the minimum insulation resistance value, … Insulation Resistance – TalkTalk Minimum values of insulation resistance: … values for a 400/230 volt system are acceptable down to 0. This MCQ test is related to Mechanical Engineering syllabus, prepared by How to Insulation Resistance Test a Cable November 21, 2020 November 21, 2020 admin 0 Comments Insulation resistance test is one of the most important checks Electrical Engineers should perform before energizing the circuit. These values are averaged from many sources and should be used for comparison only. Due to its structure, XLPE is extremely resistant to abrasion and other wear and tear. All insulation resistance values should be greater than 1000 megohms. If there is Insulation resistance testing Introduction Insulation resistance testers can be used to determine the integrity of windings or cables in motors, transformers, switch-gear, and electrical installations. e. The graph below shows an example of the insulation resistance readings on an electric motor. If the Cable Does Not Pass If a cable does not pass the test the cable still may be good but additional cable evaluation should be per-formed. Subject: Conductors and Insulation 2. The thickness of the layer of insulation on the conductor, in cables, depends upon (a) reactive power (b) power factor (c) voltage (d) current carrying capacity 20. Each cable has an ohmic resistance. If we use AC to conduct the insulation test, we will be measuring impedance instead of the resistance as the insulation has a substantial capacitive reactan A temperature rise test of a transformer is an important test which should be included in any type test of an oil transformer. You have to select the right answer to the question. This test does not indicate the quality of primary insulation. 3 shows a typical scale, which reads increasing resistance values from left up to infinity, or a resistance too high to be measured. 5M/ohms, … extreme problems should be resolved between the cable manufacturer, the shipment company, and the customer, as replacement material may be required. The limitation for this test is in its interpretation of the test measurements. SIDEBAR: Basic Theory. 1. This will ensure that the cable has not been damaged while exposed on the uninsulated pipe. 1810 W. Insulation resistance tests can be performed with insulation multi- meters (IMMs) or megohmmeters. 1. An equivalent circuit for electrical insulation is shown in Fig. PVDF is a relatively low-cost insulation option, so it is used in a wide range of industries and applications. View An Insulation Resistance Test of the Primary Insulation should be carried out with an Insulation Resistance Tester, with a minimum DC voltage of 2. 5 = 1. The insulation resistance test ensures that the insulation that surrounds an appliances’ live parts has a sufficiently high resistance level. lags the voltage by 90° B. This test is Rated positive by 91% students preparing for Mechanical Engineering. The standard duration of voltage application are 1 minute or 10 minutes. 21. If the insulation resistance of cable of length 10 km is 1 MΩ its insulation resistance for 70 km will be: 0. The top terminal might be the center conductor of a power cable, and the bottom terminal, its shield. 5 It is account of energy lost in a conductor due to its ohmic resistance. Cables flex in one or more of the four basic motions illustrated in Figure 1. Note: Do not use a megger in excess of 2500 VCD. Q1. 2)live conductors of each SELV circuit connected together and the live parts of other circuits. One of the neutral cables we have is getting a reading of 0. 67. Current studies are focused on the MMC principles and controls and few studies have been done on the overvoltage of transmission line for the MMC-HVDC link. . 1. The insulation resistance of the cable is given by, The purpose of the IR test is to check for damaged insulation, this can be mechanical damage or damage by heat, (overloaded cables), readings less than 2 Mohm indicate damaged insulation, readings of 2-50 Mohm are indicative of long circuit lengths, moisture and contamination and do not indicate the insulation quality, therefore readings of 2 www. 1000 100 10 1 12 3 4 56 7 89 10 Time in Minutes Reading in Megohms High insulation resistance to avoid leakage current. 300 Question 5 Electrical Machine (MCQ) The resistance value in this region is the resistance of the earth electrode. Sheaves, or a shoe, may be used to guide the cable into the tray. One designs the DC main cable so that its loss is smaller than 1% of the PV generator peak output. TM-11-6625-298-14 Ohmmeter ZM-21/U ( NSN 5950-00-645-2191 ) Ohmmeter ZM-21A/U ( N S N 6625-00-643-1030) and Ohmmeter ZM-21B/U ( NSN 6625-00-581-2466) Manual 3. 600 V cable is also used on 600 V systems, for that matter. 10 The surge resistance of cable is A 5 then the dielectric strength of insulation should be In this page you can learn various important cable multiple choice questions answers, mcq on cable and connector, short questions and answers on cable,sloved cable objective questions answers etc. If no data from the manufacturer exists, the values should be no less than 100 megohms. 8. The test method is determined by the type of equipment being tested and the reason for test-ing. In fact in the 14th edition wiring regs. (B) power factor. If insulation resistance of the cable is found between 1000 and 100 KΩ /km, at buried temperature, the subject cable should be replaced urgently within a year. which will improve your skill. e. Insulation resistance testing is carried out by applying a constant voltage to the equipment under test while measuring the flowing current. The cable should be connected to (a) Battery (b) DC supply (c) AC supply (d) No supply Diagnostic insulation testing at voltages above 1 kV is an area that is less familiar to many electrical maintenance personnel. the insulation test of the individual cores with sheath or armour and between the cores is essential. leads the voltage by 90° C. com 4 Guide to Wire and Cable Insulation and Coverings pressure environments For maximum accuracy extension cables should be used and terminals and connectors should be of thermocouple materials to maintain continu ity. 9/3. Insulation resistance is used to verify the integrity of the insulation material, whether cable insulation or motor/generator winding insulation. The name is often abbreviated to MICC or MI cable, and colloquially known as pyro (because the original manufacturer and vendor for this product in the UK was a company called Pyrotenax). Earthing Or Grounding MCQ question is the important chapter for a Electrical Engineering and GATE students. Therefore Polyethylene is widely used for insulation on telephone signal and control cables, high frequency electronic cables, high and low voltage power cables, line wire, neutral supported secondary and service drop cable. The Insulation Resistance test is typically done on every cable tested and usually done at 300 to 500 Vdc with 100 to 500 MegaOhms resistance. Similarly, if the insulation resistance provided is weak, then there is more chance of flowing of heavy currents that damage the equipment. When the soil resistivity is larger than 2000 Ω·m, the grounding resistance should be no greater than 20 Ω. In modern Megger as shown in figure above these range can be selected. For a length of 100 km of the same cable, what will be the insulation resistance? Test Set - 7 - Power System - Transmission & Distribution - The test carries questions on topics such as Under Ground Cables-II, Insulation & Insulating materials, Cable types, Insulation Resistance and Capacitance, Dielectric Stress in a Single Core Cable, Grading of Cables & Capacitance of Three core cables etc. The insulation resistance between conductor to screen and to armor shall be checked. As previously mentioned, insulation resistance readings should be considered relative. Before testing insulation with a megohmmeter, the windings of large machines should be grounded for about 15 minutes just prior to the test, because the . The materials whose electrical conductivity is usually less than 1 × 10 6 mho/m are a) Semiconductors b) Conductors c) Insulators. 5MOhm the IEE book electricians guide to the building regs states: The shielding angle of grounding wire for large crossing lines should be less than that for ordinary lines. To test your heating system you will need a digital multimeter with a 200 ohm setting. Get to us…. 22 times, 57 Correct answer: 2. Earth the screen after test for at least 5 minutes. If the megger reads a resistance under 1 (1,000 ohms) on your meter after the initial 60-second interval, the cable has failed and the cable should be removed. However, they need not to exceed 500 V for medium voltage circuits. fixed wiring was to have an insulation resistance of at least 1 Meg Ohm, but disconnected apparatus could have a minimum insulation resistance of 0. 400 cm [Wrong Answer] Features of insulated cable It is noted that the cable insulation resistance is determined by the purpose of its design, there are some factors that the engineer should consider before designing the cable. testing 600 v cable T here are a variety of technologies and methods used to test the insulation of wire and cable, in-cluding high-potting, very low frequency (VLF), power factor, partial discharge, time-domain reflectom-etry (TDR), and “thumping. 3. 2 cm [Wrong Answer] B. Insulation Resistance (IR) and Polarization Index (PI) are two universally accepted diagnostic tests for insulation tests. In the cables, sheaths are used to (a) prevent the moisture from entering the cable (b) provide enough strength (e) provide proper insulation One of the most fundamental of electrical installation and maintenance tasks is taking insulation resistance (JR) readings. 250,000 Ω. If a cable of homogeneous insulation has a maximum stress of 10 kV/mm, then the dielectric strength of insulation should be (a) 5 kV/mm (b) 10 kV/mm (a) 15 kV/mm (d Regulation no. 2. The insulation resistance of cables, transformers etc is measured by following instrument Multiple Choice Questions with Answers on Refrigeration and Air The cable should be immersed for at least 24 hours in slightly alkaline water at a room temperature (approx. Otherwise if the arc does DC alone is used because we need to measure only the resistance of the winding insulation. This test should be conducted before and after repair or when maintenance is performed. e. Where this is the case, the end-to-end resistance values measured for each conductor loop should result in the cpc having a resistance approximately 1. e. Graphical Educational content for Mathematics, Science, Computer Science. 5 Ω, 1 Ω and 2 Ω at 1% tolerance 1 W - for typical loads - 10 Ω, 15 Ω, 20 Ω and 50 Ω at 1% tolerance 1 W - for insulation resistance - 10 kΩ, 1 MΩ and 10 MΩ at 1% tolerance 1 W temporary test bridges - short lengths, say 300 mm, of flexible cable fitted An insulator should have high insulation resistance, typically many megohms. high voltage pressure testing set is used in fault burning work. ⇒ A certain cable has an insulation of relative permittivity 4. High mechanical strength to withstand the mechanical handling of cables. This Electrical Cables MCQ contains 20 Multiple Choice Questions. . The purpose of this booklet, therefore, is to: n Acquaint the reader with making diagnostic insulation resistance tests. (D) type of insulation used. Answer: leads the voltage by 90° 19 If a cable of homogeneous insulation has a maximum stress of 10 kV/mm, then the dielectric strength of insulation should be A 5 kV/mm B 10 kV/mm Questions Electrician and Wireman: Conductors and Insulation 2. 1. 8 times, 15; 1. Go back to Equipment To Test ↑ 8. Normally V. 12 Out of the following methods of heating the one which is independent of supply frequency is (A) electric arc heating (B) induction heating If there is joint in the cable one should inspect the same, too. 20˚) which will provide return path for the current as in Figure 2. In single core cables armouring is not done to avoid excessive sheath losses make it flexible either of the above none of the above 3. However, the insulation is designed to do the exact opposite, which is to block the current and keep it confined to the wires, so it has to have a high resistance to current The insulation resistance test is an electrical safety test and shows whether a solar module offers adequate insulation. 5M/ohms, … Minimum Insulation Resistance in M/ohms . Its objective is to measure the ohmmic value of the insulation under a direct voltage of great stability, generally 50, 100, 250, 500, or 1000 VDC. There are 2 tests to perform – Conductor Resistance and Insulation Resistance. 21. leads the voltage by 180° If a cable of homogeneous insulation has a maximum stress of 10 kV/mm, then the dielectric strength of insulation should be_____? resistance values: - for earth resistance testing - 0. At C, the insulation resistance value after the motor has been rewound. 13. 1. In simple words, resistance of earth wire should be less than 1Ω. These short solved questions or quizzes are provided by Gkseries. At B, the sharp drop indicates an insulation failure. a) high mechanical strength. 5 mega ohms 19) The size of the AL cable used for alternators 3 phase wires are PVC unsheathed is [ a ] 9. Measurement Procedure. Generally, two leads are connected into a circuit in order to carry out the test. d) Alloys Read more Multiple Choice Question (MCQ) of Electronics page-14:196. The resistivity of the semicon is required by standards to be below 100 Ohm-meters, but modern semicons have lower resistivity, generally below 10 Ohmmeters. c) Conductor. 1 M (mega-ohm) resistance for a 1000V supply gives a leakage of 1 milliampere which acceptable in most systems. Use a multi meter (on the relevant Ohms or kOhms setting) to measure the resistance between the two centre cores, live (brown) and neutral (blue). 5 The choice of ratio should therefore be left to the manufacturer to obtain the best possible results. Low Density Polyethylene (LDPE) LDPE exhibits good fluid resistance at room temperature. 1,000,000 Ω. If no data from the manufacturer exists, the values should be no less than 100 megohms. Perform continuity test to ensure proper cable According to IEEE rules, resistance between consumer earth terminal and earth Continuity conductor (at the end) should not be increased than 1Ω. Properties (i) High insulation resistance to avoid leakage current. Insulation-resistance values should be in accordance with manufacturer's published data. The ohmmic value of the insulation resistance is expressed in megohms (MΩ). It is definitely poor insulation when the supply voltage is 11 KV or more. C Power D Insulation resistance Answer D Marks 2 Unit 1 Topic: Topic: Classification of measuring instrument and range extension Question The resistance of a shunt for a precision grade ammeter can be best measured by A De Sauty bridge B Schering bridge C Maxwell bridge D Kelvin double bridge Answer D Question The resistance from 0. D. When the soil resistivity is larger than 2000 Ω·m, the grounding resistance should be no greater than 20 Ω. A de-rating factor of 0. Insulation resistance is the most commonly measured parameter to check the health of Electrical Insulation. D. In this test, we check whether the temperature rising limit of the transformer winding and transformer oil is as specified by the manufacturer. The highest reading is the (R1+R2) for the circuit. Ques 3. Note, however, that no insulation is perfect so some electricity does flow through the insulation to ground. Current should be proportional to size of resistance. 78 stated that “the insulation resistance to earth must not be less in megohms than 30 divided by the number of points under test. If the appliance does not pass the earth bond test do not proceed to the insulation test. Multiple choice questions on Strain Gauge with brief explanatory answers and explanations. com is an online portal for the preparation of the MCQ test of Degree and Diploma Engineering Students of the Gujarat Technological University Exam. 5 ohms, the connection at the accessory terminals should be investigated. The Hioki IR4053 Insulation Resistance Meter provides a solution by taking into consideration that very energy into the calculation of resistance to deliver the correct insulation resistance value of PV panels, ensuring safety both during measurement and handling of the PV panels upon proper testing. In other specified above; however the insulation resistance should not be significantly lower than the figures above. The test is very sensitive to contamination in the assembly process. Conductors with damaged insulation must be replaced. The test should also be done by reversing the polarity of the insulation resistance tester. A. However, tests between the SELV and PELV conductors themselves, as well as tests between PELV conductors and PELV protective conductors, should be performed at 250 V. The voltage should be 250V DC and the minimum insulation resistance should be 0. At B, the sharp drop indicates an insulation failure. the insulation resistance of the cable varies inversely as the length of the cable (R INS α 1/l). For PVC sheathed cables, the acceptance value is 1 M . When new cables are spliced into existing cables, the acceptance test shall be performed on the new cable prior to splicing in accordance with Section 7. insulation resistance of cable should be mcq