The stator is the stationary part of the motor and consists of a housing with slots and a series of windings. This information can be used to assess the health of the motor compared to its intended design. How to test a squirrel cage motor.com. The growler test is the first test used to determine discontinuities of current through a rotor bar, caused by blown-out wires, loose laminations, or cracking. In this equation, the slip is very small. In this article, we'll specifically discuss three-phase systems and how to diagnose them when problems arise.
The test applies single-phase power to the motor and the tester slowly rotates the rotor, where an analog meter monitors one phase for any fluctuations in current draw. This article presented an understanding of the basics of electric motor testing. Light: 1 pound, hand-held. What is Motor Generator Set and How Does it Work? The No-load test of an induction motor is similar to the open-circuit test of a electrical transformer which is performed to determine the efficiency of motor and related circuit parameters of three phase electric motors. End Shields and Bearings. Next, examine the inside of the motor and the wires involved in the three-phase current. Induction squirrel-cage motors. Steps to prevent motor malfunctions should be given due consideration, especially when using a complex motor, as repairs can result in significant, costly delays and downtime. The voltage reading should be half of whatever voltage reading was received during the previous test. If the target voltage is achieved without any change in frequency on the graph, then the motor's turn-to-turn insulation is healthy, but any shifts in waveforms indicate weakness in that particular area. How to test a squirrel cage motor vehicles. The experiment is repeated for different values of load currents till the rated current of the machine is reached. The acceptance criteria shall be based on supplier approved motor routine testing procedure, but normally the calculated losses shall be less than of 110% of the theoretical loss.
The vector sum of the load and magnetising currents causes the voltage to lag, consequently yielding a low power factor. If this happens, it means that there is some issue with the generated magnetic field, and therefore some mechanical issue with the rotor. The Influence of Select Losses Components on Induction Squirrel-Cage Motor Efficiency. This article will go over the basics of motor testing and what types of motor testing are provided. Types of Testing For 3-Phase Motors. The overspeed test is performed to make sure that rotor speed can reach to the 1. Squirrel cages are typically made from copper or aluminium.
The starting current might be high, and the test normally is done at lower voltage and result of the test extrapolated to the rated voltage. Any shorts will manifest as "hot-spots" on the thermal image, which means that any current through the rotor will unevenly heat those points. So, the equivalent circuit of this test is shown in the figure below. Understanding the basics of electric motors can help you understand where the problem may be coming from, while proper diagnostic tools can help you identify and clarify the issue. There should be terminals on each side of the box that these wires are connected to. Each of the three phases of the motor must be correctly wired to the incoming supply. Stator windings are usually manufactured from copper, although other materials are available e. Testing of Induction Motor - Methods of regular testing. aluminium. Two-phase voltage can not start the motor, which often happens in the motor running state, will lead to the motor burning in a short time with heat and the power fuse fusing. It provides a test of the quality of insulation resistance (IR), which will start degrading as soon as the motor is in use due to temperature effects. Experience - 2-3 Years Experience - 10 to 15 positions. Bad cables or connections – broken or damaged, corroded or loose connections.
Induction Motor Rotor. One wattmeter will show negative reading. Patented Dynamic Stator and Rotor Signatures™. Motor Casing / Housing. Shaft Condition: Manually rotate the motor shaft to assess its condition. The leakage of current is plotted after each step, and the resulting graph will show an indication of the ground wall insulation condition. Stepper Motors vs. How to test a squirrel cage motor applications. Servo Motors - What's the Difference? There are also compared efficiencies obtained for three core losses values: -. The readings of the voltmeter, ammeter, wattmeters and spring balance are noted down. Patented Test Value Static™ (TVS™).
Short circuit fault. The reading must be taken as quickly as to avoid overheating. The reasons are bad contact of switch contact, too small contactor pressure, short circuit of one phase of the power supply line, etc. This can be accomplished by shunting conductors to ground and each other before reconnecting. When looking at the box, you should see six wires, three on each side. Field testing & inspection of 3-phase squirrel cage motors - Resource Library. Diagnose ground faults, test stator windings, test cables, and induction motor abnormalities and receive results all on one screen within minutes. The rotor core is constructed of steel laminations. © Copyright 2023 IEEE - All rights reserved. Best Value: Costs less than a good Meg-Ohm-Meter offering a quick return on your investment.
When installing, the rotor is sometimes cooled and the bearings heated in order to allow easy assembly (only for small motors). The meter now reads positive, but it is to be recorded as negative. I (Iph): line (phase) current. Subsequently, the voltage is decreased to 110%, and 1 more data point is taken. Disconnecting the motor from power: When you are ready, move the transformer's motor disconnect switch to take it off of power. Info - an overheated motor may melt the insulation around the windings and cause the motor to short circuit; this failure mode is unfortunately not uncommon but can easily be avoided providing adequate cooling is always provided. Batteries: They last for up to 10 hours of testing. When a motor fails to start, runs hot, continually trips or sputters, there are many possible causes.
Short circuit between poles. Therefore, the I2R loss in stator winding can be neglected as it varies with the square of the current. Three-phase systems are designed differently to fit different needs. The noise level normally should not be more than 80 dBA, but the measured value shall be checked aginst acceptance criteria indicated in datasheet or test procedure. If the value is less than 0. Squirrel cage induction motor is a three-phase asynchronous motor with rotor windings made of copper or aluminum strips instead of copper strips, welded with short-circuit rings. So, the core loss is very small and it can be ignored during this test. Each winding is energised in pairs and in sequence to produce a rotating magnetic field.
This test can also be used to balance 3 phase motors, as the phase-to-phase resistance of each winding can be compared to see how they differ from one another. At starting, zero voltage is supplied to the stator, and gradually increase the voltage in step with the help of an autotransformer. It's available FREE to members in an online format. Connection Quality: Look at all the connections within the motor for indications of wear or damage, and assess any wires outside of the motor for potential breaks.
It is still used in small devices and those that require low starting torque e. record players, projector fans, photocopying machine fans, hair dryers etc. For example, plain bearings require more space, a form of lubrication (oil usually), and do not use spring washers or c-clip retaining rings. Return to Induction Motor Inspection. This is a preview of subscription content, access via your institution. Applications of Electric Motors. The stator contains the insulated windings for the three phases of the motor.
But it cannot be ignored. Any broken wires should be handled and replaced with care. If no changes in amps are found, then there are no discontinuities, but any increase or decrease in stator current suggests one or more cracked rotor bars are present. Experience (1to 3 years)(3-male candidates required). The measured resistance values shall be verified aginst acceptance criteria provided in the test procedure. Self-starting - three-phase induction motors are inherently self-starting i. e. providing electrical current is supplied to the stator windings, the motor will rotate, no other external force is required. Block Rotor Test of Induction Motor. The intersecting point is A corresponds to the input power when the supplied voltage is zero. Automatic set-up of all measurement and evaluation procedures (parameter tolerances) via the selection and retrieval of the Master Parameter File (reference rotor).
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