Testing three phase systems application note 81 three phase systems a three phase system consists of three single phase ac supplies sharing its return path neutral conductor. For a three phase system multiply by three to get the total power. The windings are marked with tags u1 and u2, v1 and v2, w1 and w2. In many hermetic motor applications, a similar dynamic is at work. The contactor that switches supply to a three phase compressor motor operating a medium temperature cool room, is failing to close. Once you have tested a few 3phase motors, the process will come easily. Each of the three phases is separated by 120 shown below, giving the effect of constant power over each cycle. In this video you will find out how to test 3phase induction motor. Testing and commissioning procedure for electric motors eep. Thus from the working principle of three phase induction motor, it may be observed that the rotor speed should not reach the synchronous speed produced by the stator. To measure the inrush current when the motor starts. Threephase controlled rectifiers have a wide range of applications, from small rectifiers to large high voltage direct current hvdc transmission systems.
To find the power given current, multiply by the voltage and then the power factor to convert to w. The process is noninvasive, requiring only that a current transformer ampprobe or current clamp be placed around one conductor of the motor power supply cable. Wound rotor electric motor testing wound rotor motors have a threephase winding wound on the rotor which is connected to three phases of startup resistors in order to provide current and speed control on startup. Lets assume the meter youre using is designed for 3phase motors, and you are installing a 3phase motor. If the motor shaft still does not turn, the bearings are not turn frozen. The trick is knowing which leads to hold on to and which wires make no difference at all. Consider the working of a motor for a better understanding of these indicators. A threephase motor converts electricity into mechanical energy via an alternating current provided by three leading power wires. How to test a 3 phase motor windings with an ohmmeter. How to test three phase ac motors learning electrical.
In order to properly test the motor you must remove. There are two types of induction motors, one with wound type rotor, also called slipring motor and another one with squirrelcage rotor. Motor overheats motor is single basic electrical tester,check each of the three phase power lines for correct voltage. The most common configuration of a three phase motor is the delta. Testing a 3 phase motor is as simple as holding the leads of a volt ohmmeter. The basic steps in ascertaining the health of a threephase ac motor are given below. Once you have tested a few 3 phase motors, the process will come easily.
Ieee std 1122004, ieee standard test procedure for polyphase. A 3 phase induction motor can be used for different applications with various speed and load requirements. Threephase dualvoltage motor insulation resistance testing. Mar 28, 2018 in this video you will find out how to test 3 phase induction motor. If the motor does not start, turn it off and lock out the power.
Record all nameplate information for the induction motor. Well learn how to identify windings, check windings resistance and insulation resistance. Measurement of power characteristics in 3phase motor development u1 a3 communication wt333e threephase voltage, current and power can be displayed together with the frequency or harmonic distortion and other parameters at measurement speeds up to 100 ms. Apr 24, 2017 a three phase motor has two main parts. It should be less than the full load rating stamped on the nameplate only true for three phase motors. Testing a 3phase motor is as simple as holding the leads of a volt ohmmeter. If the speeds become equal, there would be no such relative speed, so no emf induced in the rotor, and no current would be flowing, and therefore no torque would be generated. Winding layout, single layer winding, induction motors, rewinding technique, three phase motor. By far the most commonly used ac motor is the induction motor.
Test interphase resistance by disconnecting the leads from each terminal with a flathead screwdriver, then touch any two terminals with the two probes. Dec 30, 2018 voltage is measured at the motor terminals and at the time of test, it should be approximately balanced. To this end, it will be assumed that the motor is a balanced three phase wye connected load and that you will therefore need to measure only one lineneutral voltage, only one line current, and only one phase power to characterize p in. The electricity is fed into the interior of the motor, where it creates a magnetic field that pushes the strator and makes it rotate, turning the motor shaft. With an ohmmeter, check the motor windings for any opens or shorts. Nov 27, 2019 thus from the working principle of three phase induction motor, it may be observed that the rotor speed should not reach the synchronous speed produced by the stator. Measurement of power characteristics in 3phase motor. Three phase dualvoltage motor insulation resistance testing three phase dualvoltage motors are used for most daytoday operations in todays industrial plants. For three phase motors, connection type is either star y or delta ac motor winding continuity test using a multimeter, check the continuity of motor winding from phase to phase u to v, v to w, w to u. The shaft should be rotated several revolutions about every month to maintain proper distribution of the grease within the. Determine the impact of rewindingrepair on motor effi ciency. What really matters is the trend in readings over a time period, showing lessening resistance and warning of coming problems.
Test inter phase resistance by disconnecting the leads from each terminal with a flathead screwdriver, then touch any two terminals with the two probes. How to test a threephase motor with a megger hunker. Waveform and harmonic measurement requires the harmonic measurement option g5. How to test a 3 phase motor windings with an ohmmeter custom search. After the load is disconnected, turn power on to try restarting the motor. The process is noninvasive, requiring only that a current transformer ampprobe or current clamp be placed around one conductor of the. In order to promote public education and public safety, equal justice for all, a better informed citizenry, the rule of law, world trade and world peace, this legal document is hereby made available on a noncommercial basis, as it is the right of all humans to know and speak the laws that govern them. It should be noted that the scope of motor testing depends upon the motor type and size, this being indicated on the inspection forms. Your meter has six leads on it, three on the load or motor side and three on the supply or line side. The temperature of the room is 5 degrees and the thermostat is set to close on a rise in temperature at 4 degrees, causing the compressor to energise.
Machine performance can be calculated by using average of the phase voltages. If a single phase motor is single voltage or if either winding is intended for only one voltage, the terminal marking shall be determined as follows. That is, with the same test connections and with the same test voltage applied for the same length of time. Star wye configuration with the delta side connected to supply voltage. An indepth troubleshooting guide to help you with your ac electric motor issues. This might result in unexpected motor failures when critical services from such motors are required affecting availability of plants. Electric motors are required in pumps, compressors, and blowers in typical heating, ventilation, air.
For instance, test equipment such as flukes 438ii power quality and motor analyzer uses algorithms to analyze not only threephase power quality but also torque, efficiency and speed to determine system performance and detect overloaded conditions. Motors are susceptible to the gradual failure of their insulation resistance. Home technical articles testing and commissioning procedure for electric motors. Insulation resistance test should be performed once every three months. Following data is taken from no load, locked rotor, and dc tests of a 3phase, wye connected 40 hp, 60 hz, 460 v, induction motor with a. The modes of sudden three phase shortcircuit at the motor terminals, sudden single linetoground fault at the highvoltage side of the power supply system and the motor starting process followed. How to test a 3 phase motor is discussed in this article. How to check the windings of a 3phase ac motor with an ohmmeter. One instrumentation rack with the usual test equipment. Some time ago i also had to figure out how to connect a 1. Another aspect in induction motor drives which has been researched recently is the use of multiphase induction motors where the number of stator phases is more. The first thing to do before testing the windings of the motor is to remove the links linking terminals w2u2v2 and the disconnect the motor from supply l1, l2, l3. The stator consists of a ring with three pairs of coils, evenly spaced around the rotor.
The torque developed at the shaft of a 3 phase motor is constant, less vibration in. When a three phase induction motor connected to a single phase power supply using the steinmetz connection operates in a practical noload condition, not all windings consume active power. One single phase wattmeter plus miscellaneous apparatus as needed. 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. The most common configuration of a threephase motor is the delta. Key insights into the motor manufacturers view of easa members. Set the voltage setting of the insulation resistance tester to 500v. How to test a 3phase motor gone outdoors your adventure.
A typical 3 phase squirrelcage motor has six connection leads in the electrical connection box for the three coils. The rotor is often called a squirrel cage because it consists of a circular network of bars and rings that look a bit like a cage connected to an axle. Motor shaft does disconnect the motor from the load. They can be quite different for one motor or machine tested three days in a row, yet not mean bad insulation. Load tests on a three phase induction motor and measurement of the inrush current objectives.
This final thesis will mostly be dedicated to induction motors but also to synchronous permanent magnet and reluctance motors. Basics, maintenance, and diagnostics vii contents continued page 4. Resistance it is necessary to check the ground resistance between the motor body and terminals of the machine. Claims that rewinding inevitably decreases the efficiency of induction motors are. Threephase dualvoltage motors are used for most daytoday operations in todays industrial plants. Every 3 phase motor has six 6 terminals with the supply voltage connected to three 3 of those terminals. The modes of sudden threephase shortcircuit at the motor terminals, sudden single linetoground fault at the highvoltage side of the power supply system and the motor starting process followed. A multimeter terminals placed across this matrix of terminals will indicate the following readings for a good 3 phase motor.
How to check the windings of a 3phase ac motor with an. Page 1 of 2 how to check the windings of a 3phase ac motor. The circuit diagram of load test on 3 phase squirrel cage induction motor. Wound rotor electric motor testing wound rotor motors have a three phase winding wound on the rotor which is connected to three phases of startup resistors in order to provide current and speed control on startup. Two digital multimeters and fluke power quality meter with banana cables from the. In the running configuration, the windings are joined with metal jumpers.
The torque developed at the shaft of a 3phase motor is constant, less vibration in machinery powered by 3phase motors. When the test is performed on other than threephase power, the equations shall be. Each phase to phase must have a continuity if winding is ok. If the motor is not in operation over three months, add grease to each bearing per lubrication nameplate. The complete guide to electrical insulation testing. Industries of today use three phase motors widely in highpower applications.
A three phase motor converts electricity into mechanical energy via an alternating current provided by three leading power wires. Instruments connected in the circuit serve the function indicated against each. Threephase ac current measurement using current transformer reference design 2 system description an electric motor is an essential moving element of any system. If a singlephase motor is single voltage or if either winding is intended for only one voltage, the terminal marking shall be determined as follows.
These motors run conveyor belts, pumps, fans, and many other applications. Three phase controlled rectifiers have a wide range of applications, from small rectifiers to large high voltage direct current hvdc transmission systems. Motor overheats motor is single basic electrical tester,check each of the threephase power lines for correct voltage. Threephase dualvoltage motor insulation resistance testing threephase dualvoltage motors are used for most daytoday operations in todays industrial plants. 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 order to promote public education and public safety, equal justice for all, a better informed citizenry, the rule of law, world trade and world peace, this legal document is hereby made available on a noncommercial basis, as it is the right of all humans to. Schematic diagram for load test on three phase induction motor 3 phase variac to limit the starting current of the motor ammeter to measure the current drawn by the stator. How to test a 3phase motor with a multimeter sciencing. To obtain the load performance characteristics of a three phase squirrelcage induction motor. For this motors, we require three phase power supply, whereas thus three phase power must be supplied in a sequence. Electric motor testing explained the electricity forum. Failed components in the resistor bank are common and often overlooked when troubleshooting.
Measurement of power characteristics in 3phase motor development. Stator resistance test of threephase induction motor. They are used for electrochemical process, many kinds of motor drives, traction equipment, controlled power supplies, and many other applications. Conduct locked rotor tests on 3 phase induction motors conduct noload tests on 3 phase induction motors. Jul 06, 2016 motor testing equipment newer more contemporary instruments make testing even easier.
253 790 425 189 581 558 1302 702 147 1555 462 672 216 1503 530 883 629 176 254 1485 495 1091 1385 699 692 289 647 36 1148 731 892 246 562 1044 608 478