3 phase motor winding failure

A tri-fold brochure containing the information on this page is available for purchase. This makes the perfect handout for your employees! Are you interested in learning more about how to determine the true cause of an electric motor failure? EASA's Root Cause Failure Analysis manual covers root cause methodology and the specfic stresses that affect each component of an electric motor.

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All rights are reserved. Reproduction of these photographs by print or electronic means is prohibited. The life of a three-phase stator winding can be shortened dramatically when the motor is exposed to unfavorable operating conditions — electrical, mechanical or environmental. The winding failures illustrated here are typical of what can happen is such circumstances.

A single-phased winding failure is the result of an open in one phase of the power supply to the motor. The open is usually caused by a blown fuse, an open contactor, a broken power line or bad connections. This type of insulation failure is typically caused by contaminants, abrasion, vibration or voltage surge. Thermal deterioration of insulation in one phase of the stator winding can result from unequal voltage between phases.

Unequal voltages usually are caused by unbalanced loads on the power source, a poor connection at the motor terminal, or a high resistance contact weak spring.

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Thermal deterioration of the insulation in all phases of the stator winding typically is caused by load demands exceeding the rating of the motor. Severe thermal deterioration of the insulation in all phases of the motor normally is caused by very high currents in the stator winding due to a locked rotor condition. It may also occur as a result of excessive starts or reversals.

Insulation failures like this usually are caused by voltage surges.

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Voltage surges are often the result of switching power circuits, lightning strikes, capacitor discharges and solid-state power devices. Order copies A tri-fold brochure containing the information on this page is available for purchase. Learn more about failure analysis Are you interested in learning more about how to determine the true cause of an electric motor failure?

Winding single-phased wye-connected A single-phased winding failure is the result of an open in one phase of the power supply to the motor. Winding single-phased delta-connected A single-phased winding failure is the result of an open in one phase of the power supply to the motor.

Winding shorted phase-to-phase This type of insulation failure is typically caused by contaminants, abrasion, vibration or voltage surge. Winding shorted turn-to-turn This type of insulation failure is typically caused by contaminants, abrasion, vibration or voltage surge. Winding with shorted coil This type of insulation failure is typically caused by contaminants, abrasion, vibration or voltage surge.

Winding grounded at edge of slot This type of insulation failure is typically caused by contaminants, abrasion, vibration or voltage surge. Winding grounded in the slot This type of insulation failure is typically caused by contaminants, abrasion, vibration or voltage surge.

Shorted connection This type of insulation failure is typically caused by contaminants, abrasion, vibration or voltage surge. Phase damage due to unbalanced voltage Thermal deterioration of insulation in one phase of the stator winding can result from unequal voltage between phases.

Winding damaged due to overload Thermal deterioration of the insulation in all phases of the stator winding typically is caused by load demands exceeding the rating of the motor. Damage caused by locked rotor Severe thermal deterioration of the insulation in all phases of the motor normally is caused by very high currents in the stator winding due to a locked rotor condition. Winding damaged by voltage surge Insulation failures like this usually are caused by voltage surges.Check for burnt, damage to body or cooling fan or shaft.

Look out for smooth and free shaft rotation.

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If shaft rotation is free and smooth, bearing is possibly in good condition, otherwise consider replacing, repair or carry out further diagnosis.

Examine the name plate thoroughly and compare values of running amps test see below with name plate value Earth Continuity and Resistance Test With a multimetermeasure the resistance between motor frame body and earth. A good motor should read less than 0. Any value greater 0. Check that the correct voltage is applied to the motor using a multimeter. Ensure the terminal for power supply is in good condition. Check the connection bar for terminal U, V, and W.

3 phase motor winding failure

Each phase to phase must have a continuity if winding is OK. If any particular phase fails the continuity test, your motor is probably burnt. Please see how to identify three phase windings for proper winding identification.

U, V, W is a European winding designation. The ohms reading for each winding must be the same or nearly the same.

How to Testing Motor Windings

Remember that the three phases have identical windings or nearly so! Insulation Resistance Test Insulation resistance failure of an electric motor is one of the first signs that the motor is about to fail. 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. Set the voltage setting of the insulation resistance tester to V. See how to measure insulation resistance of Electric Motor Running Amps Test With the motor running, check the full load amps FLA with a suitable meter or preferably a clamp on meter and compare with the name plate FLA.

Deviations from rated FLA could signify problems with the motor under test. Labels: Electric Motors.Since sales nassarelectronics. Remember me. Lost your password? Image Credit: Wikimedia Commons. Three-phase motors must be connected to a nominal voltage to function properly. If for any reason any of the phases that supply the motor are disconnected, the motor continues to operate with the remaining 2 phases.

Rewinding 3 Phase Motor

This is called phase failure or single phasing. If a three-phase motor is operating and loses one of the phases, the motor will continue to operate at a reduced speed and experience vibrations. The current will also increase considerably in the remaining phases, causing an internal heating of the motor components.

If the motor is not disconnected quickly, it will break down as a result of this increase in temperature. This failure can be harmful even if it occurs when the engine is not in operation because, depending on the load, sometimes the engine is able to start even when only two phases are connected. In short, a phase failure is never a desirable condition for the operation of an induction motor and appropriate measures should always be taken to protect it.

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3 phase motor winding failure

Phase failure is a very common electrical fault experienced by three-phase motors.A phase failure is an interruption of a single conductor. The motor then continues running with two phases and can suffer damage.

The cause is, for example, blown fuse. Small to medium sized motors are mostly stator critical — this means that only the stator can be damaged. These motors are not put at risk by a phase failure. As shown in Figure 1, the currents in the motor windings, during disturbed and undisturbed operation at the failure of a single conductor, equal the currents in the other two.

Due to the increasing current, a higher power loss occurs in both live windings. On the whole, the motor is running coolsince the third cold winding causes a temperature compensation. In case of an overcurrent, a protective current detector trips in time. Small to medium sized stator critical motors in star connection are usually not put at risk during a phase failure. This phenomenon occurs because the motor keeps the power transmitted to the shaft practically constant.

The absolute current increase in the windings and in both intact phases depends on the load applied. Since the currents in the windings are not equal, they do not warm up equally either.

Since heat is exchanged between individual windings and between windings and the iron body, the warming up of the stator is proportional to the sum of all losses in all windings. In this case, the warming up is, at the most equal, to the warming up during a symmetrical, three-phase load.

3 phase motor winding failure

Besides electrical protection, the fast cut-out also contributes to reduced stress on the bearings. For a single phase feed of the stator, the rotor losses are considerably higher compared to a symmetrical feed.

This can represent an additional danger, especially for rotor critical motors. Good Day. Thank you for this article. I found another article on the same topic below and I am trying to find out how they calculated the winding current.

For example, when there is an open on one of the phases, the line current increases by 1. How exactly can we calculate the winding current in the delta connected motor?

In general, how long can a motor continue run without causing damages when one phase fails? Would it be fine to run for 1 — 2 minutes as an example? They have different operating and over-temperature range. This will directly affect how long a motor can operate in one phase fault condition. The run time would be interrupted by eventual burn out.

The speed would be decreased from that of the normal three-phase operational cycle. Great site. Yes it would still run, but not as fast as when three phase supply is still intact. If let you run the motor during this condition, it would get damage. Performing necessary tests is advise.Every 3 phase motor has six 6 terminals with the supply voltage connected to three 3 of those terminals.

The terminal configuration of a 3 phase motor is shown below:. The 3 phase motor is a rugged piece of equipment but as with everything man made, there comes a time when this beautiful piece of machinery fails either due to old age, misapplication, mal-operation or any other adverse cause. The most common failure mode of a 3 phase AC motor is burnt winding or shorted winding leading to the damage of the motor. Often it is required to test the winding of the 3 phase windings with the aid of a multimeter or ohmmeter to determine whether the motor is still good or burnt or shorted.

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. 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:. 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.

A multimeter terminals placed across this matrix of terminals will indicate the following readings for a good 3 phase motor:.

E should indicate open for a good motor. Labels: Electric Motors. Newer Post Older Post Home. You May Also Like:. Terminals Configuration of a 3 Phase Motor. How to test the windings of a 3 Phase Motor with an Ohmmeter.The rotor of a squirrel-cage motor. This is why we call this type of connection "Star" or Y. A star connection is accomplished simply by bridging one horizontal row in the connection box.

This is a photo from the connection box of a motor connected in Star. A Delta connection is easily accomplished by bridging the 3 columns in the connection box vertically. This is a photo from the connection box of a motor connected in Delta. Continue reading. But if you have questions please use the forum instead to post it. Thank you. Today my all doubts are clear abt motor connection.

Very helpful. Really good. Thanks At 2 Novemberuser M. My husband cut the wires and took some resistance readings. It has 4 wires.

Three-phase Y and Delta Configurations

There was no reading between any of the wires and the green one which he assumes is the ground. Do these reading point to a problem with the motor. Just a great piece of technical writing! At 18 Novemberuser Michael L.

Rappaport] Beautifully written and illustrated article. It would be good if material could be added about the result of not having one phase in both the Y and delta configurations. White] Do you have same information for 12 lead 3 phase motor? I found out my windis are not da same while doing continuity test with my meter. Now I had to balance the windings, I had I could not calculate my percentage difference becouse onfinity is too big it has mo value. My qiestion what was I surpose to do??

Whts infinity value?? Concise and easy to understand, although not what I was looking for. How can i find the high and low speed windings.??

3 phase motor winding failure

C:F part number The machine is indicating Error motor too hot after running for 4minutes. The winding resistance is 1.This configuration of voltage sources is characterized by a common connection point joining one side of each source. Figure below. The three conductors leading away from the voltage sources windings toward a load are typically called lineswhile the windings themselves are typically called phases.

In a Y-connected system, there may or may not Figure below be a neutral wire attached at the junction point in the middle, although it certainly helps alleviate potential problems should one element of a three-phase load fail open, as discussed earlier.

Line voltage refers to the amount of voltage measured between any two line conductors in a balanced three-phase system. With the above circuit, the line voltage is roughly volts.

Phase voltage refers to the voltage measured across any one component source winding or load impedance in a balanced three-phase source or load. For the circuit shown above, the phase voltage is volts. The terms line current and phase current follows the same logic: the former referring to the current through any one line conductor, and the latter to the current through any one component.

Y-connected sources and loads always have line voltages greater than phase voltages, and line currents equal to phase currents. If the Y-connected source or load is balanced, the line voltage will be equal to the phase voltage times the square root of Take close notice of the polarity for each winding in the figure below. At first glance, it seems as though three voltage sources like this would create a short-circuit, electrons flowing around the triangle with nothing but the internal impedance of the windings to hold them back.

If they do, then there will be no voltage available to push current around and around that loop, and consequently, there will be no circulating current.

Motor Winding Check Technical Tip

Starting with the top winding and progressing counter-clockwise, our KVL expression looks something like this:. Indeed, if we add these three vector quantities together, they do add up to zero. Another way to verify the fact that these three voltage sources can be connected together in a loop without resulting in circulating currents is to open up the loop at one junction point and calculate the voltage across the break: figure below.

Sure enough, there will be zero voltage across the break, telling us that no current will circulate within the triangular loop of windings when that connection is made complete.

Conversely, because each line conductor attaches at a node between two windings, the line current will be the vector sum of the two joining phase currents. With each load resistance receiving volts from its respective phase winding at the source, the current in each phase of this circuit will be


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