Because electrical insulation will exhibit dynamic behavior during the course of your test. The insulation resistance tester, generally known by its trade name megger, is capable of providing critical information regarding the condition of motor insulation. 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. Find here insulation testing and continuity, power protection, power transformer testing, power cable infrastructure, cable fault location, general electrical test. To test a cable with a megger, you connect one probe to the outside of the. Wide range of megger technical guides, application notes, academic papers and product support material. The megger insulation tester is a small, portable instrument that gives you a direct reading of insulation resistance in ohms or megohms. When performing insulation resistance testing, you must maintain consistency. A megger insulation resistance tester is especially useful when you have carried out electrical work on your home and want to make sure you didnt damage insulation or make a wiring mistake. How to use a megger to measure and test motor insulation. Insulation resistance testing introduction insulation resistance testers can be used to determine the integrity of windings or cables in motors, transformers, switchgear, and electrical installations. Insulation testing technical guides megger insulation.
The procedure of the insulation resistance test are given below first, disconnect all the line and neutral terminals of the transformer. This is certainly not a new test, and has been in use for a number of years. The circuit under test must be switched off, deenergised, isolated and checked to be safe before insulation test connections are made. The megger insulation tester is essentially a highrange resistance meter ohmmeter with a builtin directcurrent generator. A megger is an ohmmeter that measures resistance in the megohm scale. For good insulation, the resistance usually reads in the megohm. After a benchmark is established, periodic measurements should be taken and recorded along with notation of temperature, humidity and duration of the megger.
Insulation resistance testing of low voltage cables in the. Insulation resistance of all the significant electrical appliances should be measured at regular intervals and recorded for comparison purposes as it is a useful guide for. Principle of insulation testing and influencing factors insulation resistance measurement is based on ohms law. The procedure of insulation resistance test or megger test are given below. Insulation resistance test or megger test procedures with circuit diagram in this article we will go through megger test first of all i want to say both insulating resistance tests and megger test are. Setting up a megger mft for continuity and insulation. A guide to diagnostic insulation testing above 1 kv. For good insulation, the resistance usually reads in the megohm range. Readings should be within the specifications provided by the manufacturer. Regular testing of the insulation on an installation or machine is therefore a useful way of monitoring this type of deterioration so you can act before total failure occurs. Most can be classified as spot reading shorttime tests, timeresistance tests, or step voltage tests.
Well learn how to identify windings, check windings resistance and insulation. A common rule of thumb is insulation resistance changes by a factor of two for each 10 degrc change. The following is a summary of insulation resistance ir testing commonly referred to as megger testing of low voltage cables rated less than 5 kv, recognized by nexans. Increases safety by reducing ladder time minimizes the risk of measurement errors due to incorrect connections. Megger has offered a 10 kv insulation resistance tester since 2001. The test icon will appear in the bottom right corner until the test is complete. It is commonly used in the industry for acceptance testing prior to energizing the cable and for maintenance testing programs.
Learn how insulation resistance test is done developed early in the 20th century, the insulation resistance ir test is the oldest and most widely used test for assessing the quality of insulation. Figure 2 typical megger test instrument hookup to measure insulation resistance. Understanding insulation resistance testing pdf 0206 rev. Insulation resistance testing is a nondestructive test procedure. Standard for acceptance testing specifications for. View and download megger det14c user manual online. The insulation resistance test is of value for future comparison and also for determining if the transformer is to be subjected to the applied voltage. Make sure the circuit is not reenergised whilst the instrument is. The complete guide to electrical insulation testing. Time resistance testing method this method is fairly independent of temperature and often. The megger company registered the name megger in may 1903 and today offers a wide variety of ir testers. Meggering insulation resistance testing of drytype. In march 2000, the ieeesa standards board approved a revision to ieee std 431974.
Insulation resistance testing megger testing southwire. Offering cat iv, the mit1025 is compact, light 10 kv insulation resistance tester for the diagnostic testing and maintenance of high voltage electrical equipment. Push the test button of the megger to generate the voltage. Insulation testing as directed by bs7671, when performing an insulation test on a 415 v circuit, you should select the 500 v range on your insulation tester. To perform the tests needed, you will need an insulation resistance tester or a multifunctional tester such as the megger 1553. Find here insulation testing and continuity, power protection, power. Threephase dualvoltage motor insulation resistance testing. A 1954 camera is ideal for all applications in the building, electrical maintenance and mechanical maintenance. Student training aid for how to set up a megger mft for testing continuity and insulation resistance. The test measures the insulation resistance between the phases andor between phase and ground. The goal is to determine if the insulation of a wire has been compromised. If the resistance is higher than the maximum display range, the megger will display the symbol on the left side of the screen.
One of the reasons that it is still such a popular option. Similarly, if the insulation resistance provided is weak, then there is more chance of flowing of heavy currents that damage the equipment. Timeresistance tests on large rotating electrical machinery especially with high operating voltage require high insulation resistance ranges and a very constant test voltage. Megger leads are connected to lv and hv bushing studs. Power factor testing of surge lighting arresters megger. Insulation resistance test or megger test procedures with. In this video you will find out how to test 3phase induction motor. The generator can be handcranked or lineoperated to develop a high dc voltage which causes a small current through. Understanding insulation resistance testing jm test systems. The leads used for connecting megger testing with the circuit should be fault free and the two connecting. The following sections of the ansineta standard for acceptance testing specifications for.
When temperature increases, insulation resistance decreases, and vice versa. A catalogue, for quick reference, of the range of megger test instruments for the maintenance of electrical power systems. Section 7 of the ansineta standard for acceptance testing specifications for electrical power equipment and systems may be reproduced and used on a cut and paste basis for the particular type of equipment to be tested. In response, megger expanded our line of insulation testers to offer the mit10202, a 10 kv model dedicated to the provisions of the revised standard. First we will disconnect all the line and neutral terminals of the transformer.