In order to measure the insulation resistance in electrical wiring and electrical motors, electricians use the megohmmeter, also known as a megger. Megger mit1525kit mit1525 with a vf2 voltage detector, 3m. The generator has centrifugal clutch due to which the generator supplied the constant for the insulation test. Megger safety precautions when you use a megger, you could be injured or damage equipment you are working on if the following minimum safety precautions are not observed. Electrical stress insulation is designed for a particular application. Connect one lead of the megger to the conductor, and the other lead to ground, and see what reading you get with the megger. Connection schemes for testing insulation resistance of.
Diagnostic insulation testing stephan drennan,vice president of sales, megger limited a stitch in time when it comes to the maintenance of plant and equipment, the old adage a stitch in time saves nine is as true today as it ever was. If the result shows that the resistance is under 1 on the meter, after the first 60 seconds, it likely means that the cable has an issue and needs to be removed. Dec 14, 2014 before making these observations, be sure that all capacitance is discharged by short circuiting or grounding the apparatus. Electrical insulation testing first published in 1966 by the james g. Temperature correction factors powerdb lookup tables. Limited time only sign up and learn about the new mtr105 motor tester and. Megger developed a 10 kv unit to meet the new testing recommendations outlined by the ieee. Megger makes several testers that will check actual insulation resistance. This is an earlier unit which came without the meter built in. A guide to diagnostic insulation testing above 1 kv. Our products support damped ac dac, sinusoidal ac and cosinerectangular test technologies.
Before making these observations, be sure that all capacitance is discharged by short circuiting or grounding the apparatus. Megger, a stitch in time the complete guide to electrical insulation testing, a free book which is an excellent resource on ir testing. A stitch in time 7 whether you test monthly, twice a year, or once a year depends upon the type, location, and importance of the equipment. Buy products related to megger testing products and see what customers say about megger testing products on free delivery possible on eligible purchases. The megger is the instrument uses for measuring the resistance of the insulation. From the utility transformer secondary, 480y277, we pulled 600 kcmil conductors 350 ft, underground in pvc to our main distribution panel. Verified purchase angel l pantoja on dec 07, 2016 i found this helpful 0. Figure 6typical curve of insulation resistance in megohms with time for the short time orspotreading test method. Imo a stitch in time is the bible for megger testing. At this time, laboratories developed resistance elements, constructed of. They interact with each other and cause a gradual spiral of decline in insulation quality. A, b, and neutral readings were 999 mohms maxed the resolution of the megger. A disk with user guide and the e book a stitch in time an excellent resource.
This is the procedure paul gill lays out in his book. The stich in time from megger is good but it is also highly lacking in details for some situations. We used the ideal megger set at 500v and checked each conductor. How does one interpret the results of the megger test.
A guide to diagnostic insulation testing above 1 kv 5 what causes insulation to degrade. The dielectric absorption or timeresistance test is an extension of the insulation resistance test where instead of a spot test, the testing device is applied to the insulation for up to 10 minutes. A guide to diagnostic insulation testing above 1 kv 5. Your megger account allows you to register your equipment for warranty, and access a wide range of support material including software updates and technical documents. This file contains a number of industry standard temperature correction factors. This analog megohmmeter gives installers more information than the more common light up megohmmeters. This is an insulation test of motor windings, commonly referred to as megging, to megger, or to meg a motor. Understanding insulation resistance testing pdf 0206 rev. The schemes also show in principle how equipment must be disconnected from other circuits before the instrument is connected. When using a motordriven or rectifieroperated instrument, the time intervals are usually 1 minute and 10 minutes from the time the testing voltage is applied. Megger mit1525kit mit1525 with a vf2 voltage detector, 3m large leadset x3 safety. Technical library to guide electrical testers megger. The idea is that the insulation resistance should increase over time as the atoms in the insulation are. The following schemes show how to connect a megger insulation tester to various types of electrical equipment.
A timeresistance test is performed over five to 10 minutes. In this test, the testing device is applied and ir measurements are taken at 1 minute and 10 minutes. Insulating components, for example cable jackets, must be tested for their insulation strength at the time of commissioning and as part of maintenance of high voltage electrical equipment and installations. Never use the tester or any of its leads or accessories for any purpose not described in this book. The dielectric absorption or time resistance test is an extension of the insulation resistance test where instead of a spot test, the testing device is applied to the insulation for up to 10 minutes. Insulation resistance should be approximately one megohm for each volts of operating voltage with a minimum value of one megohm. Perform a time resistance testing method using a megger, and take successive readings at specific intervals. The megger company were the original manufacturers of ir test equipment over 100 years ago and have become synonymous with insulation resistance testing. For good insulation, the resistance usually reads in the megohm range. A time resistance test is performed over five to 10 minutes. The fault took a while to find as the shorted component was connected. The megger technical library provides access to a range of additional content and resources such as technical guides, application notes and more. The megger insulation tester is a small, portable instrument that gives you a direct reading of insulation resistance in ohms or megohms. It differs from an ohmmeter in that, unlike the ohmmeter, it is able to measure resistances in ohm values of more than one million.
This instructional dvd on portable appliance testing is an ideal aid for anyone involved in pat testing, whether you are a complete novice or wish to increase your knowledge of the subject. Megger testing of instrument cables electric motors. Connection schemes for testing insulation resistance of electrical. Ive never seen that windings should be shorted for dc tests, and we never do. Record the results at 60 seconds, and then in 30second intervals thereafter. How to megger a motor also known as an insulation test. This test method is described and illustrated in the megger booklets a stitch in time and a. 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. How does a megger test measure insulation resistance. Temperature correction factors powerdb lookup tables 703 lookup tables page 1 a file called lookuptables. Megger has offered a 10 kv insulation resistance tester since 2001.
Electrical test equipment power station to plug megger. Megger astitchintime the complete guide to electrical insulation testing. The complete guide to electrical insulation testing year. Weve assembled helpful technical guides on insulation testing from leading manufacturers in the field. The goal is to determine if the insulation of a wire has been compromised. The dielectric absorption or timeresistance test is an extension of the insulation resistance. Use meggers on highresistance measurements only such as insulation measurements or to check two separate conductors on a cable. Every electric wire in your plant whether its in a motor, generator, cable.
Most modern ir testers are digital, portable handheld units and some have multifunctional capabilities e. When i worked at one company, we gave that book to the electricians in a class we gave them. Jan 10, 20 this instructional dvd on portable appliance testing is an ideal aid for anyone involved in pat testing, whether you are a complete novice or wish to increase your knowledge of the subject. An instructional video on how to megger a motor and the proper use of a megohmmeter.
A variety of measuring instruments may be used to detect and diagnose malfunctions in electric motors. Megger is the expert in cable test, diagnostics and fault location, supporting you with inhouse knowledge and welltrained application engineers. A general guide to interpreting the pi test results are as follows. Aug 26, 2007 from the utility transformer secondary, 480y277, we pulled 600 kcmil conductors 350 ft, underground in pvc to our main distribution panel. Diagnostic insulation testing stephan drennan,vice president. Jan 19, 2018 its actually an insualtion resistance test. As electrical insulation breaks down, there are many hazards that can occur. Customer reported this unit had tripped the rcdgfi, i traced the fault and found it was due to a faulty pressure dual switch. Megohmmeter or insulation resistance tester is a special type of ohmmeter used to measure the electrical resistance of insulators. Dec 16, 2015 customer reported this unit had tripped the rcdgfi, i traced the fault and found it was due to a faulty pressure dual switch. 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. During my first week of use, i was tasked with testing a very oil leak prone air compressor.
For example, a small pump motor or a short control cable may be vital to a process in your plant. Timeresistance testing method this method is fairly independent of temperature and often. A senior tech once told me the megger guard terminal is the same potential as the negative terminal. Never connect a megger insulation tester to energized lines or equipment. Use meggers on highresistance measurements only such as insulation measurements. In particular, the insulation resistance tester or megohmmeter, generally known by its trade name megger, can provide critical information regarding the condition of motor insulation. You do this by using a high voltage and looking for voltage leaking through the insulation. The constant voltage is used for testing the insulation having low resistance. A stitch in time megger insights any persistent downward trend is usually fair warning of trouble ahead, even though the readings may be higher than the suggested minimum safe values.
You can find it in meggers biddle a stitch in time the complete guide to electrical insulation testing on page 9. Com 99 washington street melrose, ma 02176 phone 7816651400 toll free 18005178431 visit us at. Megger astitchintime the complete guide to electrical. The megger is capable of applying different voltages, and the level should be coordinated with the type of equipment under test and the scope of the inquiry. The complete guide to electrical insulation testing. The completeguide a stitch in time the complete guide to electrical. Shorting transformer windings for pi, why is it done. A very valuable manual with the wonderful title a stitch in time is available at no cost at. These days i have a yokogawa digital one that also will function as a voltmeter too. The curves were plotted from spot readings taken with a megger instrument over a period of months. When you broke out a biddle megger, no one and i do mean no one argued with you about the quality of your megger.
Perform a timeresistance testing method using a megger, and take successive readings at specific intervals. Diagnostic insulation testing stephan drennan,vice. Standard for acceptance testing specifications for. Im not sure if this holds true with modern test equipment, but i think this should be taken into consideration when guarding equipment that could be damaged by a high test voltage, such as a low voltage transformer winding. There are five basic causes for insulation degradation. Time resistance testing method this method is fairly independent of temperature and often. Megger megohmmeter insulation resistance testers megohmmeters, or insulation resistance ir testers, are used to measure the resistance, integrity and safety of electrical wiring insulation. Insulation resistance quality of an electrical system degrades with time, environmental conditions i.
The pin will point to the megohm reading giving you a number you can track and monitor to determine if the loop is shorting to ground. It also deteriorates due to the presence of electrical and mechanical stress. Insulation is designed to contain the current used to. The megger insulation tester is essentially a highrange resistance meter ohmmeter with a builtin directcurrent generator. The onemegohm rule, i am going to quote out of a book featuring megger insulation testing. Cativ v rated to 3000 m always ready to test dual liion batteries or ac supply ease of use rotary switches point to function and mode required convenient, safe remote control operationthe megger mit1525 is a 15 kv insulation tester with a full range of dc insulation test modes and the ability to save. A guide to low resistance testing test equipment depot. It should be discharged for a period about four times as long as test voltage was applied in a previous test. The testing voltage is usually 500, or 2500 v which is generated by the hand driven generator. The megger insulation tester is essentially a highrange resistance meter ohmmeter with a built in directcurrent generator. The insulation resistance ir test also commonly known as a. How does one interpret the results of the megger test if the result shows that the resistance is under 1 on the meter, after the first 60 seconds, it likely means that the cable has an issue and needs to be removed.
1109 668 1227 877 1114 1372 766 899 474 1157 682 865 170 1410 94 1408 558 714 815 822 88 545 1519 993 1223 28 1104 941 977 451 1019 975 215 477 1148