Electric motors are rather complex mechanisms that are capable of developing high power, due to which they ensure the operation of many devices. The scope of their application is extensive - they can be found in a vacuum cleaner, meat grinder, washing machine. But everything is not limited to domestic conditions, and these mechanisms can be part of industrial equipment, where they are capable of much more functionality. In this case, sooner or later, but there are malfunctions of electric motors.
If in everyday life a breakdown is limited only to discomfort, then on an industrial scale this leads to forced interruptions in the operation of electrical equipment. And such delays in production are extremelyare undesirable, therefore, it is necessary to identify the cause of the malfunction in a timely manner and eliminate it as soon as possible.
Electric motors
It doesn't make sense to go into details, so we will limit ourselves to a short course. From a constructive point of view, any electric motor consists of two main parts:
- Stator - is a stationary part, which is fixed on the body of the mechanism.
- Rotor is the rotating part, due to which the devices work.
In this case, the rotor is located in the stator cavity and does not mechanically contact it in any way, but at the same time it can come into contact through the bearings. When analyzing for malfunctions of a fan motor or any other device, the ability of the rotor to rotate is first checked. To do this, the first step is to completely remove the voltage from the power circuit, and only after that you can manually turn the rotor.
There are two important conditions necessary for the operation of an electric power unit. Firstly, the rated voltage must be applied to its winding (there are several of them for multi-phase electric motors). Second, both the electrical and magnetic circuits must be in perfect working order.
DC motors
These mechanisms have a fairly wide range of uses:
- computer fans;
- vehicle starters;
- powerful diesel stations;
- combine harvesters, etc.
Magnetic field of the statorof these mechanisms is created by two electromagnets, which are assembled on special cores (magnetic cores). Coils with windings are located around them.
The magnetic field of the moving element is formed by the current that passes through the brushes of the collector unit along the winding laid in the grooves of the armature. We will definitely touch on the topic of a malfunction of the rotor of the electric motor, but a little later.
AC motors
These mechanisms can be either asynchronous or synchronous. Some similarities can be identified between asynchronous models and DC motors. However, there are design differences. The rotor of asynchronous power electrical installations is made in the form of a short-circuited winding (there is no direct current supply to it from the electrical installation). Among the people, such a design received a rather sonorous name - "squirrel wheel". In addition, in such engines, a different principle for the arrangement of stator turns.
In synchronous power units, the windings of the coils on the stator are located at the same offset angle between themselves. Due to this, electromagnetic field lines are formed, which rotate at a certain speed.
Inside this field is the electromagnet of the rotor. Under the influence of the applied magnetic field, it also begins to move in accordance with the frequency, synchronous with the rotation speed of the applied force.
Rotor rotation estimate
Troubleshooting AC Motorincludes various manipulations with the rotor. Often the ability to assess the degree of rotation of this moving element is complicated by the connected drive. For example, at the power unit of a vacuum cleaner, it can be untwisted by hand without any problems. And in order to turn the working shaft of the perforator, you need to make some effort. But if the shaft is connected to a worm gear, then in this case, due to the peculiarities of this mechanism, it will not be possible to turn it at all.
It is for this reason that the rotation of the rotor is checked only when the drive is turned off. But what can make it difficult to rotate? There are several reasons for this:
- Sliding pads worn out.
- The bearings are missing lubrication or the wrong compound has been used. In other words, ordinary grease, which is used to fill ball bearings, thickens at a strong negative temperature. This may cause the electrical mechanism to start poorly.
- Dirty or foreign objects between the stator and rotor.
As a rule, the cause of a motor failure in relation to a bearing is not difficult to determine. The broken part begins to make noise, which is additionally accompanied by play. To identify this, it is enough to shake the rotor in a vertical or horizontal plane. You can also try pushing and pulling the rotor along its axis. It should be noted that a slight play for most models of the power unit is the norm.
Checking brushes
Platescollectors, in fact, are a contact connection of a part of a continuous armature winding. Through this connection, electric current is supplied to the brushes. While the power unit is in good condition, a transient electrical resistance is formed in this node. Fortunately, it is not able to have any significant effect on the operation of the mechanism.
How to determine the malfunction of the electric motor? For those power units that are subjected to heavy loads during operation, the collector plates are usually contaminated. In addition, graphite dust can accumulate in the grooves, which adversely affects the insulating properties.
The brushes themselves are pressed against the plates under the influence of springs. During the operation of the electric motor, the graphite is gradually erased, the length of the brush rod is reduced, and the force generated by the spring is reduced. As a result, the contact pressure weakens, which leads to an increase in the transient electrical resistance. This causes the collector to spark.
Ultimately, this leads to increased wear on the brushes, including the copper commutator plates. In turn, everything ends up with a breakdown of the engine. For this reason, it is important to regularly check the brush assembly, carefully inspecting the cleanliness of the surfaces. When looking for the causes of a motor failure, one should also not forget about the development of the graphite brushes themselves, including the operating conditions of the springs.
Detected dirt should be removed with a piece of soft cloth previously moistened withtechnical alcohol solution. The gaps between the plates must be cleaned with a crow made of hard, non-resinous wood. You can go over the brushes themselves with fine-grained sandpaper.
If potholes or burnt areas are found on the collector plates, the assembly itself will be machined, including polishing, until all irregularities are eliminated.
Main causes of motor failures
After the assembly of electric motors in the factory, they are subjected to various tests. And upon their completion, they are considered fully serviceable and are delivered to the market or directly to the customer. Subsequently, all malfunctions that occur are detected during the further operation of the power units.
Among the causes of the main malfunctions of electric motors can be attributed to a violation of the conditions of transportation from the manufacturer to the destination. In most cases, a breakdown can occur during the loading or unloading of electric motors. Also, not every company is responsible for the transportation itself, in particular, not following the recommendations regarding the transportation of electric motors.
Another reason is a violation of the storage rules. As a result, the main components of power units are destroyed due to the effects of temperature changes, humidity levels and other external factors.
Electric motor malfunctions and solutions
Among the large number of breakdowns, there are cases thatseen most often:
- The armature does not rotate when the mains is connected, which may be due to low current or its complete absence.
- No RPM needed. Here, a worn bearing may be the cause of the failure.
- Overheating of electric motors. In this case, there are quite a few reasons - from overloading the device to ventilation failure.
- Strong buzz of the mechanism during operation, as well as the appearance of smoke. The turns of certain coils may be shorted.
- Mechanism vibrates a lot - caused due to imbalance of the fan wheel or other part of the power unit. This can be identified during a visual inspection.
- The shutdown button refuses to work. This usually happens when the contacts on the magnetic starter “stick”.
- Extraneous noises due to overheating of the bearing. Such a breakdown is usually caused by severe contamination of the part or its wear.
This is not the whole list of malfunctions of asynchronous electric motors (and others) that may occur during the operation of electric power plants. Only an experienced specialist can determine other breakdowns. Let's take a closer look at some equally common malfunctions.
Uniform stator overheating
In some cases, the active steel of the stator of electric motors starts to overheat, although the load has the nominal parameters. In this case, heating can be uniform or uneven. In the first case, the cause may be a voltage that is higher than the nominal valueOr is it the fan. The cause of such a malfunction is easily eliminated - for this it is necessary to reduce the load or strengthen the fan motor.
When identifying motor faults, it is also important to pay attention to how the stator windings are connected. Usually it all depends on the value of the rated voltage:
- Delta connection is used for low values.
- Wye connection available for higher voltage.
In other words, for the “triangle” it is 220 V, and for the “star” it is 380 V. Otherwise, the power unit may be overloaded, which is fraught with its overheating.
Uneven stator overheating
In the case of uneven overheating, there are several reasons. This may be a breakdown in the stator winding, a short to the housing. Because of this, the teeth not only burn out, but can also melt.
Also, shorting between some plates caused by burrs can also contribute to this. In addition, contact of the rotor with the stator housing cannot be ruled out. In this case, the troubleshooting of the electric motor will be reduced to cutting out faulty elements, removing burrs. After that, it is necessary to isolate the sheets from each other using mica or special cardboard.
If there is too much damage, the active steel of the stator is remixed with reinsulation of all sheets. The stationary part itself is rewound.
It's all about the rotor
With the followingcharacteristic signs, the cause of a rotor malfunction should be sought in poor-quality soldering of its circuit:
- rotor overheating;
- hum;
- braking;
- asymmetric readings of currents in phases.
Before you start repairing the rotor, you should examine how well the soldering of its windings was performed. If necessary, it is worth resoldering, the same should be done with those areas that cause concern.
There may also be cases where the failure of the electric motor is due to the fact that the rotor is stationary and open, although the voltage on the three rings is the same. In this case, the cause of the malfunction, most likely, lies in the break in the wires connecting the rotor to the starting rheostat. As a rule, this is due to wear of the liners, shift of the bearing shields, due to which the rotor begins to be attracted to the stator. Rotor repair is the replacement of liners, as well as adjustment of bearing shields.
In addition, the brushes and commutator may spark or heat up. This can happen for several reasons:
- brushes are out of order;
- Incorrect brush setting;
- brush sizes do not match the dimensions of the holder holder;
- Poor-quality connection of brushes with fittings.
In this case, it is enough to precisely set the brushes together with the holders.
Increased vibrations
From a technical point of view, this phenomenon can also be considered a malfunction of the electric motor. Usually strong vibrations are caused byimbalance of the rotor, clutch or pulley. Also, this phenomenon can be facilitated by inaccurate centering of the shafts of the device, the curvature of the connecting halves.
First of all, you need to balance the rotor, for which you need to balance the coupling halves with pulleys. You also need to center the engine. Put the coupling half in the correct position, but for this it must first be removed. Find the point of poor-quality connection or break, and then fix the breakdown.
Expert Tips
The installation of the electric motor alone does not end, which is confirmed by many experts. All necessary measures must be taken to extend the life of electric power plants.
In particular, on the part of the staff it is necessary:
- Provide motor protection with special devices.
- Install the motor soft starter. This will increase the service life of not only the power unit, but also its drive.
- Install a thermal relay. With it, you can avoid thermal overload, which is very important for electric motors.
- Exclude the ingress of moisture on the motor housing and in its cavity. In this way, its performance can be ensured, since this factor negatively affects the internal components of the electric motor.
- Regular maintenance required. This is cleaning the engine itself from contamination, lubricating the bearings, tightening the contacts.
- Notengage in the repair of power electrical installations without proper experience and skills. It is better to entrust this work to specialists.
In addition, it is important to detect the malfunction of the electric motor in time and eliminate it, since the production delay time depends on it. And, as you know, it is worth its weight in gold, if not even more valuable.
