There is an inherent safety problem in earth resistance testing that requires care and planning by the user of the test set. Megger clamp on ground testing guide pdf instrumart. Hi friends, in this article, i am going to describe the earth tester working principle and method of earth resistance measurement by it. In megger, the combined action of both the voltage coils v 1 and v 2 are considered. The det3tc will perform the traditional 3pole measurements like other earth testers. The megger insulation tester is a small, portable instrument that gives you a direct reading of insulation resistance in ohms or megohms. A practical guide to earth resistance testing pdf free download. Megger leads are connected to lv bushing studs and transformer tank earth point to measure insulation resistance ir value in between the lv windings and earth. Electrical test equipment power station to plug megger. Voltage source ammeter 17 basic test methods for earth resistance megger instruments for earthresistance tests in clude.
Getting down to earth 3 table of figures safety fig. A practical guide to earth resistance testing the word megger is a registered trademark. The resistance of the earth can be measured with the help of megger earth tester or earth megger. Det3td digital ground tester det3td digital ground tester. The simplest and somewhat misleading idea of a good ground for an electrical system is a section of iron pipe driven into the earth with a wire conductor connected from the pipe to the electrical circuit figure 1. Page there is an inherent safety problem in earth resistance. Please refer to meggers booklet getting down to earth for further information. D e t 3 2 digital earth tester description the megger det32 digital earth tester is a compact instrument designed to measure earth electrode resistance and soil resistivity. Getting down to earth is available, covering many other test techniques. Instruction manual for transformer ohmmeter dc winding.
Understanding insulation resistance testing pdf 0206 rev. The megger det14c and det24c ground resistance clamp testers represent a new generation of earth ground clampon resistance testers. Benefits simple to use, one touch operation auto switch off to save battery power rugged, weatherproof case large, clear lcd indicators show if reading may be. This guide makes these processes easier to understand for both large and small ground systems, with detailed studies of various relevant testing methods. Ensuring an effective earth system is essential in a telecommunications system, and megger is expert in earth testing having been there right from the start. All of the new megger earth testers can perform this test and unlike some instruments, no external linking on the instrument is required. In this method, four smallsized electrodes are driven into the earth at the same depth and equal distance apart in a straight line and a measurement is taken. If the resistance of the insulation is high, the pointer of the moving coil deflects towards the infinity, and if it is low, then the pointer indicates zero resistance. Getting down to earth 9 8 getting down to earth equipment can also be damaged similarly by overvoltages caused by highresistance ground systems. Timeresistance testing method this method is fairly independent of temperature and often. We would be pleased to have a representative call on you to discuss your application. The complete guide to electrical insulation testing. Megger det23 digital ground resistance tester manual pdf.
It is stiff near the zero end of the coil and becomes very weak near the infinity end of the spring. The device is being used since 1889, popularity raised during 1920s since the long back device is same in its uses and purpose of testing, few real improvements appeared in recent years with its design and quality of tester. The det23 automatic earth test instrument is designed to measure earth electrode resistance and soil resistivity, with highly accurate results. The megger is the instrument uses for measuring the resistance of the insulation. The det23 can be used on large or more complex earth systems. The det23 can be used on large or more complex earth systems, which include communications earth systems and difficult test environments. Function up scroll down enter ir port on off 00k 0 0m g v 0g t 00g t k m 00m m 000v 500v 2500v to ground 5 k, 5 w resistor insulation step voltage test figure 37. Bureau of standards now nist developed the theory behind this test in 1915 see reference pg. These days, megger offers topend systems for design and soil surveys as well as tough, easytouse testers for field engineers. Fourterminal earthground resistance and soil resistivity. The return lead senses the current that is being carried by the device under test and compares it to the voltage being applied to calculate a resistance.
The empirical relation as below gives the recommended minimum value for ir, its unit being mega ohm m. Earth tester working principle your electrical guide. But the advantage of the earth that is, the planet itself, or the immediate portion of it is simply that there is so much of it. Two nos of wire leads for connecting megger with electrical external system to be tested. Please refer to meggers booklet getting down to earth for further information on fall of potential tests and soil resistivity tests. This technique is done with an earth resistance tester, often called a megger. It was dr george tagg who pioneered earth testing at megger, and since megger has been at the forefront of innovative development and design. Suitable applications where there is doubt about a particular application, reference should be made to the advice and guidance contained in the publication, getting down to earth which is available from megger, part number 21500 072. Megger makes electrical test equipment to help you install, improve efficiency and extend the life of assets and cable networks at high, medium and low voltage. If you are unclear as to the meaning of sphere of influence, more information can be found in the megger publication getting down to earth, part number 21500 072. Fault current from a grounded electrical system can be dissipated effectively once it has cleared the immediate hurdle of transferring from the electrode into the surrounding soil and to infinite earth. Troubleshooting with insulation resistance test instruments. It is capable of performing 2, 3 and 4 point testing with variable frequency, attached rod technique via optional clamp sold separately, stakeless testing again via optional clamp, leakage current and ground noise voltage measurements. For a three phase motor, insulation resistance is usually measured between each motor winding or phase and between each motor phase and motor frame earth using an insulation tester or megger.
It is powered by an internal rechargeable battery which has a long usage period. A practical guide to earth resistance testing megger on photo. Meggers det4tc2 is a portable, lightweight instrument used for easy measurements of earthing. The megger det14c and det24c ground resistance clamp testers represent a new generation of earthground clampon resistance testers. Convert the 4 ft to centimeters to obtain a in the formula.
These instruments induce a test current into earth systems and measure ground resistance in multi ground installations without needing to disconnect the ground. This method is the most commonly used for measuring soil resistivity, which is important for designing electrical grounding systems. Getting down to earth a megger guide to earth testing 21500072 ordering information electrical specifications ingress protection. Insulation resistance failure of an electric motor is one of the first signs that the motor is about to fail. The megger det3td ground tester features a large selector switch makes selection of 2 pole or 3 pole test easy with gloved hands. Guide to clampon ground testing 3 clampon testing versus fall of potential testing fall of potential testing as mentioned, clampon, or stakeless, ground testing is a relatively. Factors influencing requirements for a good grounding system in an industrial plant or other facility that requires a grounding system, one or more of the following must be carefully considered see fig. How to test three phase ac motors learning electrical. The det range of instruments can be used in agricultural locations as per iec 615575. Getting down to earth manual avtm25ta det62d threeterminal ground resistance tester ordering information test equipment depot 800. Buy megger det3td earth ground resistance tester ireland. The instrument is suitable for the testing of earth electrodes and measuring earth resistivity. The earth megger is essentially a direct reading ohmmeter and it has a hand driven generator which supplies the testing current.
Stakeless earth ground testing new det14c and det24c clamps getting around any challenge introduction megger has been designing, manufacturing and selling earth ground testers for well over 50 years. A practical guide to earth resistance testing getting down to earth. The spring compresses the low resistance portion and opens the high resistance of the spring, which is the. When the test switch is closed to the left, the current passing through the electrode under test from the testing generator and the voltage drop between the electrode under test and the potential spike are used as inputs to the log ratio computer. The megger insulation tester is essentially a highrange resistance meter ohmmeter with a builtin directcurrent generator. A megger should be used the same way that a hipot or a power factor set would be used with the red positive lead being the hot and the black negative lead being the return. The instrument uses the fourterminal method of measurement, in which the resistance of the current circuit does not affect the reading. Megger has published a book titled getting down to earth, a practical guide to earth resistance testing. Getting down to earth a practical guide to earth resistance testing earth testing and resistivity measuring requires sensitive equipment and sophisticated calculations. Earth testing kits including suitable test spikes and leads and a book describing several testing techniques entitled getting down to earth are also available. The megger det family of test instruments offers a unique solution to the measurement of earth or ground electrode rod resistance and soil resistivity.
Megger working principle types history uses of megger. In other words, if the distance a between the electrodes is 4 ft, you obtain the average earth resistivity to a depth of 4 ft as follows. D e t 3 2 digital earth tester test equipment depot. Digital ground testers det4td2 and det4tr2 digital ground. Switches use to select electrical parameters ranges. The resistance of the earth can be measured with the help of megger earth tester or earth megger earth tester working principle. From years of experience in supplying instruments for the tests involved, megger can provide advice to help you make specific tests. Det62d threeterminal ground resistance tester det62d. Fourterminal earth ground resistance and soil resistivity.
Thank you for purchasing the megger earth ground tester. Fourterminal earthground resistance and soil resistivity tester. The megger det3td ground tester is used to test for inherant dangers and potential cost implications of disconection of the earth spike. The simplest and somewhat misleading idea of a good ground for an electrical system is a section of iron pipe driven into the earth with a wire conductor connected from the pipe to the electrical circuit figure 1 a practical guide to earth resistance testing megger on photo. The megger det3td design makes the fitting of shorting links to perform 2 pole tests a thing of the past. The det3ta provides 2 and 3wire measurements and offers an analogue display.
The result will cause either be the clamp low symbol appearing or an unexpectedly high reading. The family has seven variants supporting 2, 3 and 4wire measurements. For good insulation, the resistance usually reads in the megohm range. A digital display to show ir value in digital form. These days, megger offers topend systems for design and soil surveys as well as tough, easy to use testers for field engineers.
It can be used to test in accordance with bs 7430 earthing, bsen62305. Earth testing det14c and det24c technical getting down to earth a practical guide to earth resistance testing. An insulation step voltage test is a test that creates electrical stress on internal insulation cracks to reveal aging or damage not found during other motor insulation tests. Getting to know the mto product overview 300330 the megger transformer ohmmeter is a lineoperated, fieldportable instrument designed specifically to measure the dc resistance of all types of magnetic windings safely and accurately. Getting down to earth 11 added salt percent by weight of moisture resistivity, ohmcm 0. Alternatively visit the megger earth testing website.
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