At a, the insulation resistance decreases due to aging and dust accumulation. Several different types of insulation resistance tests are performed when troubleshooting electric motors. Curve b shows same values corrected to 20c see page 22, giving a definite downward. The three tests discussed here are used primarily to test motor, generator and transformer insulation. Troubleshooting with insulation resistance test instruments. Three phase dualvoltage motor insulation resistance testing three phase dualvoltage motors are used for most daytoday operations in todays industrial plants. Therefore, the final conclusion was to plan an overhaul within the next three to six months. Motors are susceptible to the gradual failure of their insulation resistance. This is a basic explanation about insulation resistance and what it means and how to apply it to every day electrical work. Typically we megger motor just one phase of the motor to ground as the phases are all connected inside the motor.
Induction motor, no load test, blocked rotor test, vibration test, temperature test, phase sequence test, insulation resistance test. If the motor is not put into operation immediately upon arrival, it is. Insulation resistance testing test equipment depot. Introduction the induction motor is one of the most important motors used in industrial applications. This motor can be wired in either delta or wye but only one voltage. In order to measure the insulation resistance in electrical wiring and electrical motors, electricians use the megohmmeter, also known as a megger. As shown below, the indicated terminal matrix blue lines shows the way the windings of a 3 phase motor should be tested with an ohmmeter. Always use a lead set thats designed for the instrument, appropriate for the test voltage youre planning to use and suitable for the test object youre. Megger guide to electrical insulation testing pdf instrumart.
To operate correctly, the coiled wire should have a predetermined. Insulation resistance testing on a 3 phase motor youtube. This test is used to find the insulation resistance of motor for 1 min or 10 min through high voltage insulation tester. The test should also be performed after a motor is. The insulation resistance tester, generally known by its trade name megger, is capable of providing critical information regarding the condition of motor insulation. If there is a 4 pole isolator,the neutral can be i. This is an insulation test of motor windings, commonly referred to as megging, to megger, or to meg a motor.
The basic steps in ascertaining the health of a threephase ac motor are given below. Test inter phase resistance by disconnecting the leads from each terminal with a flathead screwdriver, then touch any two terminals with the two probes. Insulation resistance testing is a nondestructive test procedure. If a fraction of current flows, it can be measured by these highly sensitive meters. A 1954 camera is ideal for all applications in the building, electrical maintenance and. Insulation resistance varies very little with rating. As an electrician you may be required to use a 500 v or v.
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. What was good insulation has become a partial conductor. The test method is determined by the type of equipment being tested. Guide to low voltage motor testing test equipment depot. Understanding insulation resistance testing jm test systems. Manufacturers of insulation resistance testers go to a lot of trouble to produce test lead sets that will help make their instruments safe and convenient to use. When an electric current flows though the wire, a magnetic field is induced inside the coil of wire. During the measurement and immediately afterwards, some of the terminals. Qualifications of testing organization and personnel 3. Electric motors are made up of a multitude of components that when. Before conducting a transformer winding resistance test, it is important to observe all safety warnings and take proper precautions. Most, if not all our motors only have 3 leads coming out of the connection box.
Evaluation of medium and high voltage machines with motor. It is used to convert electrical energy into mechanical energy. The test method is determined by the type of equipment being tested and the reason for testing. The above variables should be controlled as much as possible to promote accurate insulation resistance measurement data. The test method is determined by the type of equipment being tested and the reason for test ing. The measured resistance indicates the condition of the insulation between two conductive parts. In this video you will find out how to test 3phase induction motor. An electrical induction motor contains windings, or wire wrapped around a cylindrical shaft.
The insulation resistance tester or megohmmeter, generally known by its trade name megger, can provide critical information regarding the condition of motor insulation. Electrical testing usually consists of insulation resistance meg ohm m. An insulation spot test is an insulation resistance test that can be used to verify the condition of the insulation over the life of the motor. Figure 3typical scale on the megger insulation tester. To determine whether a 3 phase motor is still good or has gone bad, a simple ohmmeter test across the windings of the motor will reveal its true state of health. Ensure that all equipment to be tested is properly grounded and treat all highvoltage power equipment as energized until proven otherwise by using the proper lockouttagout procedures. Measurement of winding resistance and insulation resistance of 3 phase 11 kv 433 v, 16kva oil cooled type transformer conference paper pdf available august 20 with 5,618 reads how we. In order to test the condition of winding insulation, a surge test has to be performed. A typical 3 phase squirrelcage motor has six connection leads in the electrical connection box for the three coils. We are testing the motors insulation, more specifically between the motor windings and the motor casing.
Threephase dualvoltage motor insulation resistance testing threephase dualvoltage motors are used for most daytoday operations in todays industrial plants. How to interpret resistance readings as previously mentioned, insulation resistance readings should be. How insulation resistance is measured you have seen that good insulation has high resistance. Motors of all hp, voltage, and phase rating have similar values of insulation resistance.
Megging a motor is a term used to test a 3 phase motor to check the resistance and. To effectively test the motor, you must disconnect the field coils where possible. How to test three phase ac motors learning electrical. Insulation resistance 19 spot or timed insulation resistance test 20 polarisation index pi 21 dielectric absorption ratio dar 22 temperature correction 24 guard terminal 25 three phase test 28 voltmeter28 phase rotation 28 continuity28 diode test 29. Jul 06, 2016 the insulation resistance tester or megohmmeter, generally known by its trade name megger, can provide critical information regarding the condition of motor insulation. The measurement of insulation resistance is carried out by means of a. Defects in turntoturn, coiltocoil, and phase to phase that cannot be detected by other methods will be revealed. The measurement of insulation resistance is a common routine test performed on all types of electrical wires and cables. The problem of course is that on a tncs the neutral and earth are combined at the intake position. Insulation resistance or ir test is carried out by maintenance engineers to ensure the healthiness of the overall insulation system of electrical equipment it reflects the presence or absence of harmful contamination, dirt, moisture, and gross degradation. A typical 3phase squirrelcage motor has six connection leads in the electrical connection box for the three coils.
It differs from an ohmmeter in that, unlike the ohmmeter, it is able to measure resistances in ohm values of more than one million. The megger test is checking the condition of the ground wall insulation of the motor. Standard for acceptance testing specifications for. Insulation resistance should indicate 1 megohm or more.
Aug 16, 2014 it is unnecessary to perform the insulation resistance test of transformer per phase wise in a three phase transformer. When measured through the drop cable, the resistance of the drop cable must be subtracted from the ohmmeter readings to get the winding resistance of the motor. With one probe still connected to ground, connect the other test probe to a motor terminal. The complete guide to electrical insulation testing. Motor guide february 2014 low voltage motors motor guide. What equipment is necessary for conducting insulation. Our two videos listed below will properly demonstrate how to conduct these tests correctly. Dc voltage of 500 or v is applied between the windings and the ground of the motor.
How to megger a motor also known as an insulation test. These motors run conveyor belts, pumps, fans, and many other applications. 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. If someone works with ac 3 phase motors, then it is important to know how to connect these motors in star and delta connection, and how to detect an electrical problem. In an industrial facility, the recommended procedure is to perform periodic tests and record the results so that damaging trends can be detected and corrected to prevent an outage. If there is a 4 pole isolator,the neutral can be isolated,so no problem but most isolators are 3 pole. This magnetic field causes a metal bar inside the coil to rotate and power the motor. Threephase dualvoltage motors are used for most daytoday operations in todays industrial plants. To accomplish this, a test procedure should be established and used consistently over time. How to meg a motor with a megohmeter checking motor condition. Test interphase resistance by disconnecting the leads from each terminal with a flathead screwdriver, then touch any two terminals with the two probes. Figure 4typical record of insulation resistance of a mill motor.
Curve d indicates a good insulation with an excellent polarization index of 5. Tests using multivoltage megger insulation testers 42. The test measures the insulation resistance between the phases andor between phase and ground. 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. It is commonly used in the industry for acceptance testing prior to energizing the cable and for maintenance testing programs. Figure 2 absorption curve of test conducted on 350 hp motor. Irp with small discharges starting at about seven minutes, indicating an aging insulation system the irp was performed at 2500 vdc and resulted in only a few small capacitive discharges. The sharp fall at b indicates there was an insulation fault. How to use a megger to measure and test motor insulation. The insulation resistance test is an electrical test which uses a certain type and level of voltage 500v d. Pdf measurement of winding resistance and insulation. How to test a threephase motor with a megger hunker.
On a 3 phase motor, what resistance would you like to see. How to check the windings of a 3phase ac motor with an. Wb82 i work in a power plant of a large utility company. If someone works with ac 3phase motors, then it is important to know how to connect these motors in star and delta connection, and how to detect an electrical problem. Megging a motor presented by katie nyberg for galco tv. In an industrial facility, the recommended procedure is to perform periodic tests and record the results so damaging trends can be detected and corrected to prevent an outage. If all readings are within one percent of each other, then they are acceptable. There are two schools of thought regarding the voltage to test insulation at. Ir value will be usually high several hundred megaohms for a dry insulation system. If there are no checks, a motor with poor insulation, for example, may not only be dangerous to touch when voltage is applied, but also be subject to burn out. Megger mit1020 10kv insulation resistance testers are all. At c, the fault has been repaired rewinding of the motor so the insulation resistance has returned to. Insulation testing on 3 phase board electrical inspection.
Threephase dualvoltage motor insulation resistance testing. Loop testing firstly, you must establish which type of supply you are testing. The following sections of the ansineta standard for acceptance testing specifications for electrical power equipment and systems must be incorporated by reference as part of any subsection. As a production test, this test is often used as a customer acceptance test, with minimum insulation resistance per unit length often specified by the customer. Well learn how to identify windings, check windings resistance and insulation resistance. Insulation resistance values are taken between the windings collectively as because all the windings on the hv side are internally connected together to form either star or delta. Standard for acceptance testing specifications for electrical. The measurement of insulation resistance is carried out by means of a megohmmeter high resistance range ohmmeter. How to test a 3 phase motor windings with an ohmmeter. A spot test should be performed at regular intervals every six months, for example to track the changes in insulation integrity. Regardless of the configuration, either star or delta, the measurements are normally made phase to phase and comparisons are made to determine if the readings are comparable. Keep in mind that the purpose of the test is not to.
I was wondering how others do insulation testing on a 3 phase board,in particular,neutral to earth and phase and neutral combined to earth. In order to successfully test and tag a 3 phase appliance, there are three tests you can perform. Feb 26, 2014 this is a basic explanation about insulation resistance and what it means and how to apply it to every day electrical work. Insulation resistance test insulation resistance failure of an electric motor is one of the first signs that the motor is about to fail.
If the insulation resistance of a new, cleaned or repaired motor. Even though this test was developed 80 years ago, surge testing still forms a part of testing a 480v motor to find whether it is good or bad. How to check the motor winding resistance it still runs. Surge comparison test and pd test of the 300 horsepower motor figure 3.