61. Value of insulation resistance test or IR value test, i.e. It is the total resistance in respect of two parallel paths, one through the body and other over the surface of the body. Recommended Home Insulation R–Values. For determining minimum insulation resistance use the following formula. Equal to 1. c. Less than 1. d. A negative value. (B) just at cut-off. … Testing wiring and cable installations I don't agree. What about installations with multiple levels of distribution? For example, even the simple case of Main three-phase switchboard fee... … If the insulation strength is high, value of R will be low and if the insulation is weak the IR will be low with high current. At the same time, the electric energy becomes heat energy, which prepares the conditions for thermal breakdown and increases the possibility of thermal breakdown. The insulating material used for cables should have all of the following except. (A) Earthing of Plate (B) Rod earthing (C) strip earthing (D) Both (A) and (C) Answer - (C) 7. The insulation resistance is checked by megger or insulation tester. Megger Multiple Choice Questions and Answers. View Answer. PART 3: MCQ from Number 101 – 150 Answer key: PART 3. Megger is used to measure. 60—100 metres. C. 500,00 ohms. A resistance of value 10Ω approximately is to be measured by ammeter-voltmeter method with resistance of ammeter is 0.02Ω and that of voltmeter is 5000Ω. A. Minimum motor insulation resistance of the winding to the ground is measured with 500 V DC. Insulation resistance needs to be maintained at safe levels to not only shield against loss of production but also to protect against electric shocks to humans. Reason (R): The breaking capacity of a CB is expressed as √3 * VI * 10-6 MVA. With a little record-keeping and common sense, however, you can get a good picture of the insulation condition from values that are only relative. After driving the instrument the value of insulation resistance is indicated on the analog or digital dial of the instrument directly. The ohmmic value of the insulation resistance is expressed in megohms (MΩ). (A) 1 Ω (B) 0.5 Ω (C) 2 Ω (D) 5 Ω Answer (B) 6. If any value other than 0 displays, reconnect the test leads to ground and retest until a 0 reading is obtained. Testing the integrity of insulation requires measuring its resistance to current flow across it. A high level of resistance means that very little current is escaping through the insulation. Conversely, a low level of resistance indicates a significant amount of current may be leaking through and along the insulation. So 1100m of 1mm2 cable would be around 19.8 Ω .Divide that by the CSA; e.g. 78 Ampere. Insulation Resistance or IR Test is carried out by maintenance engineers to ensure the healthiness of the overall insulation system of electrical equipment.. high resistance. During the charge phase, the voltage is ramped from zero to the selected voltage, which provides stabilization time and limits the inrush current to the DUT. RMS value of the sine wave; average value of the sine wave; form factor of the sine wave; peak- peak value of the sine wave (Ans.) Earth resistance. … Ques 5. MCQs on Transformer. Ground wires. IR Value for Panel Bus: IR Value for Panel = 2 x KV rating of the panel. 13. a. 33. Insulation resistance values that are consistent over time indicate that the equipment’s insulation properties are good. Care must always be taken not to measure the insulation resistance if the temperature is lower than 5. Consider system A at uniform temperature t and system B at another uniform temperature T (t > T). Polarity of solenoid can be determined by. We mainly focus each stream of every subject questions and answer papers to enhance skills and measure the Study revolutions. In addition to reading the questions and answers on my site, I would suggest you to check the following, on amazon, as well: ... An ammeter has a resistance of G ohms and range of I amperes. We normally take the reading of the measurement at a certain time after application of test voltage. Insulation Resistance Acceptance Test Values for Motor Windings (1 Minute @ 40°C) a Rated line-to-line voltage for three-phase ac machines, line-to-ground voltage for single-phase machines, and rated direct voltage for dc machines or field windings. low reluctance. The winding temperature must be 25°C +/- 15°C. Ans: b. A. Insulation level are specified by R-Value. The purpose of this booklet, therefore, is to: n Acquaint the reader with making diagnostic insulation resistance tests. Bonding element in a strain gauge must have _____ a) zero insulation resistance b) low insulation resistance c) high insulation resistance d) infinite insulation resistance Answer: c Explanation: In a strain gauge, the bonding element must have a high value of insulation resistance. 250,000 ohms. 0.234 * 10 9 Ω b. Metallic supply pipework can be used for an earth electrode if a) It is water utility pipework b) It is other than water utility pipework c) It is an unused gas pipe that is less than 10 years old Insulation Resistance: It may be defined as the resistance between two conductors (or systems of conductors) usually separated by insulating materials. In modern Megger as shown in figure above these range can be selected. Answer: c. Explanation: There are three modes of heat transfer i.e. Fourier’s law of heat conduction is valid for 32. The measurement of insulation resistance is a common routine test performed on all types of electrical wires and cables. For three phase units kVA3Ø = v3 x kVA1Ø. temperature halves the insulation resistance, while a 10 °C reduction doubles the insulation resistance value. 200 – 300 meters. In a series circuit with unequal resistances. radiation, convection and conduction. high reluctance. Electrical resistivity is inversely proportional to the depth of grounding / earthing rod into the ground. Switchgear and Protection MCQ Objective Questions and Answers Page - 7. D. None of the above. 1,000,000 ohms. 1. There is no documented justification for the 1 megohm minimum value of insulation resistance, but it has survived the test of time and in practice has proved to be a useful starting point when determining the condition of the insulation of cables and electrical equipment. 35. 78. R = … What is the size of copper strips used for strip earthing? The minimum value of insulation resistance for 230v domestic installation is a) 0.5Ù b) 1mÙ c) 2MÙ d) 1MÙ (Table61) 2. PART 1: MCQ from Number 1 – 50 Answer key: PART 1. B. The resistance should be measured. (d) 330 kV. The ohmmic value of the insulation resistance is expressed in megohms (MΩ). this guide covers inductors multiple choice questions (mcqs) with answers and explanation. (a) the highest resistance has the most of the current through it. In this case, the metallic water supply line can be assumed as the auxiliary ground rod whose resistance value is approximately 1 Ω or less. The value of the quantity that can be made out by observation is. Two wires “A” & “B” of same materials and length L and 2L have radius r and 2r respectively. For the continuity, a rough rule of thumb for copper is 18 milli Ω per metre for 1mm2 (it varies with temperature). The protection against direct lightning strokes and high voltage steep waves is provided by. Insulation resistance test is conducted in most of the substation equipment is high and medium voltage substations. The general rule of thumb that is used for acceptable values for safe energization is 1 MΩ per 1000 V of applied test voltage plus 1 MΩ. Mesaurement of inslation resistance is quite important. Measure the insulation resistance to ground (IRG). Multiple Choice Questions / Quiz (3) Rectifier and Regulated Power Supply (8) Resistance and Resistive circuits (13) Semiconductor (6) Sinusoidal state of RLC circuit (13) Synthesis of passive network (2) Tech (7) Thermoelectricity (4) Three Phase Circuits (3) … (c) 100 kV. The minimum value of insulation resistance should be 1 megohm. Typical recommendations for exterior walls are R-13 to R-23, while R-30, R-38 and R-49 are common for ceilings and attic spaces. No other way of measuring ground resistance is more accurate. (b) equal to the charge of an electron. The increase in length of the insulation. If the value is less than 0.2 megohms , replace the motor. Should be made of material having a low resistance temperature co-efficient with the value of swamping resistance equal to meter resistance; Should be made of materials having low resistance temperature co-efficient and should have a value of about 20 to 30 times that of meter resistance. With a little record-keeping and common sense, however, you can get a good picture of the insulation condition from values that are only relative. We define insulation resistance as the ratio of applied direct voltage across an insulation to the corresponding current through it. a) Air blast circuit breaker. Lightning arresters. Limitation of insulation Resistance (IR) Test The insulation resistance change with temperature and humidity. (C) nearly twice cut-off. IR value will be usually high (several hundred Megaohms) for a dry insulation system. insulation (resistance decreases in temperature or moisture). Home >> Category >> Electrical Engineering (MCQ) questions and answers >> Testing and inspection of installation. The higher the R-value, the better. Divide the voltage by the current that escapes through the insulation and returns to the meter. 1. This value should be 0 MΩ. Conductive leakage current (I L) Conductive current is a small (micro-amp) amount of current that normally flows through insulation, between conductors or from a conductor to ground. gkenyon: AJJewsbury: Therefore each circuit can pass an insulation test, but the whole board can fail, so what do you do next? But there is no BS 7... For example, a unit has 2 gig-ohm resistance, but a low PI of 1.05, we could make the determination that the unit was suitable for service due to the excellent IR values and attribute the low PI to humidity. Asbestos cloth is used for---A. sleeves of heating devices B. for equipment working at high temperature C. in panels for switchgear and arcing D. insulation for traction motors … 500 V is used to measure the Insulation resistance of control cable for Insulator which can withstand up to 1.1 kV voltage. (c) equal to the charge of the number of electrons in an atom (#) zero. Ceramics Properties of Ceramics Types of Ceramics Another Classification of Ceramic ii). boo. poles are. I cannot answer that, but I can pour water on troubled oil by adding another observation. The 1 meg limit is for a DC test and as such ignores any... Question. If the specific resistance of insulation is 5.5 * 10 14 Ω -cm, what will be the insulation resistance for a length of 3 km? 1) What will be the maximum leakage current, if a domestic installation uses 20 points of 40 watt lamps and 5 fans of 100 watts each? Divide the voltage by the current that escapes through the insulation and returns to the meter. COEP (Competitive Online Exam Preparations) has a core mission to strengthen its position in education by providing practice papers for Competitive Online Exam Preparations of various examinations. R - One minute 500 volt dc minimum insulation resistance in megohms C - Constant for 20 °C (68 °F) measurements (see below) E - Winding voltage rating. C. Lightning arresters and ground wires. R-value is a measure of a material's ability to slow down heat flow. 1. Depending on where you live and the part of your home you’re insulating (walls, crawlspace, attic, etc. (A) at midpoint of load line. d) Both r.m.s. 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. So, these are the types of ohmmeter. For instance, when we would like to calculate the value of resistance below 10Ω. By pressurizing a conductor with a given voltage, it's possible to use Ohm's Law (R=V÷I) to apply a numerical value to resistance measurements. Then the resistance whose value to be known should be in parallel connection to the meter. Example, for a 5 KV panel, the … Let the two systems be brought into contact and be thermally insulated from …

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