Electric motors are quite complex mechanisms that can develop a lot of power, due to which they provide 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 only to living 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 the breakdown is limited only by discomfort, then on an industrial scale this leads to forced interruptions in the operation of electrical equipment. And such delays in production are extremely undesirable, therefore, it is necessary to identify the cause of the malfunction in a timely manner and eliminate it as soon as possible.
Electric motor device
Going into details does not make sense, so we will limit ourselves to a short course. From a structural point of view, any electric motor consists of two main parts:
- Stator - is a stationary part that is mounted on the mechanism body.
- The rotor is the rotating part, due to which the operation of the devices is carried out.
In this case, the rotor is located in the stator cavity and does not have any mechanical contact with it, but at the same time it can come into contact through bearings. When analyzing for troubleshooting a fan motor or any other device, the ability to rotate the rotor is first checked. To do this, first of all, the voltage is completely removed from the power circuit and only after that it is possible to manually rotate the rotor.
For the operation of an electric power unit, two important conditions are necessary. Firstly, the rated voltage must be applied to its winding (there are several of them for multiphase electric motors). Secondly, both the electrical and magnetic circuits must be completely in good condition.
DC motors
These mechanisms have a fairly wide range of uses:
- fans of computer devices;
- vehicle starters;
- powerful diesel stations;
- combine harvesters, etc.
The stator magnetic field of these mechanisms is created by two electromagnets, which are collected on special cores (magnetic cores). Around them are coils with windings.
The magnetic field of the movable element is formed by a current that passes through the brushes of the collector assembly along the winding laid in the slots of the armature. We will definitely touch upon the issue of the rotor of the electric motor, but a little later.
AC motors
These mechanisms can be either asynchronous or synchronous. It is possible to identify some similarities 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). In the people, such a design received a rather sonorous name - "squirrel wheel". In addition, in such engines there is a different principle for the arrangement of stator turns.
In synchronous power units, the coil windings on the stator are located at the same offset angle between each other. Due to this, the force lines of the electromagnetic field are formed, which rotate with a certain speed.
Inside this field is the rotor electromagnet. Under the influence of the applied magnetic field, it also begins to move in accordance with the frequency of the synchronous rotation speed of the applied force.
Rotor Rotation Estimation
Troubleshooting an AC motor involves various rotor manipulations. Often the ability to evaluate the degree of rotation of this movable element is complicated by the connected drive. For example, the power unit of a vacuum cleaner can be unwound without problems by hand. And in order to rotate the working shaft of the punch, you need to make some effort. But if the shaft is connected to the worm gear, then in this case, due to the peculiarities of this mechanism, it will not work at all.
It is for this reason that the rotation of the rotor is checked only when the drive is off. But what can hinder its rotation? There are several reasons for this:
- Slip pads are worn out.
- There is no grease in the bearings or the wrong composition was used. In other words, an ordinary solid oil, which is used to fill ball bearings, thickens at a strong negative temperature. This may cause a poor start of the electrical mechanism.
- The presence of dirt or foreign objects between the stator and the rotor.
As a rule, the cause of the motor failure in relation to the bearing is not difficult to determine. A broken part starts to make noise, which is additionally accompanied by backlash. To identify this, it is enough to sway the rotor in a vertical or horizontal plane. You can also try to slide and pull the rotor along its axis. It should be borne in mind that a slight backlash for most models of the power unit is the norm.
Checking the brushes
The collector plates, in fact, are the contact connection of the part of the continuous winding of the armature. Through this connection, an 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 capable of exerting any significant influence on the operation of the mechanism.
How to determine the malfunction of the motor? Those power units that are subjected to heavy loads during operation, usually collector plates become dirty. In addition, graphite dust can accumulate in the grooves, which adversely affects the insulating properties.
The brushes themselves are pressed to the plates under the influence of springs. During the operation of the electric motor, graphite is gradually erased, the length of the brush shaft is reduced, and the force created by the spring is reduced. As a result, the contact pressure weakens, which leads to an increase in transient electrical resistance. Because of this, the collector begins to sparkle.
Ultimately, this leads to increased wear of the brushes, including copper collector plates. In turn, it all ends in engine failure. For this reason, it is important to regularly check the brush assembly, carefully inspecting the cleanliness of the surfaces. When searching for the causes of a motor malfunction, one should also not forget about the development of graphite brushes themselves, including the operating conditions of the springs.
Detected contaminants should be cleaned with a piece of soft cloth, previously moistened with a solution of industrial alcohol. The gaps between the plates must be cleaned with burnished hard non-resinous wood. You can walk on the brushes themselves with fine-grained emery paper.
If potholes or burned-out areas are found on the collector plates, the assembly itself undergoes mechanical processing, including polishing, until all irregularities are eliminated.
The main causes of motor damage
After collecting the electric motors in the factory, they undergo various testing. And upon completion, they are considered to be fully operational and delivered to the market or directly to the customer. Subsequently, all the malfunctions that arise are detected during the further operation of the power units.
Among the causes of the main malfunctions of electric motors, a violation of the conditions of transportation from the manufacturer to the destination can be attributed. In most cases, failure can occur during the loading or unloading phase of electric motors. Also, not every company is responsible for the transportation of goods, in particular not observing the recommendations regarding the transportation of electric motors.
Another reason is a violation of 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.
Malfunctions of the electric motor and methods for their elimination
Among a large number of breakdowns, cases that are most often observed can be distinguished:
- The anchor does not rotate when the power is connected, which may be due to low current or its complete absence.
- Does not develop the necessary speed. Here, the cause of the malfunction may be a worn bearing.
- Overheating of electric motors. In this case, there are quite a few reasons - from overloading the device to disturbing ventilation.
- Strong buzz of the mechanism during operation, as well as the appearance of smoke. Perhaps closed coils of certain coils.
- The mechanism vibrates violently - caused due to imbalance in the fan wheel or other part of the power unit. This can be detected during a visual inspection.
- The shutdown button refuses to work. This usually happens when the contacts on the magnetic starter “stick”.
- Extraneous noise due to overheating of the bearing. Such damage 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 arise during the operation of electric power plants. Identify other breakdowns can only an experienced specialist. We will analyze in more detail some equally common malfunctions.
Uniform overheating of the stator
In some cases, the active steel of the stator of electric motors begins to overheat, although the load has nominal parameters. In this case, the heating can be uniform or uneven. In the first case, the cause may be a voltage that is higher than the rated value or the whole thing is in 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 determining 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:
- For low values, the triangle connection is used.
- For higher voltage, a star connection is provided.
In other words, for the “triangle” it is 220 V, and for the “star” - 380 V. Otherwise, the power unit may overload, which is fraught with overheating.
Uneven stator overheating
In 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, this can be facilitated by locking between some of the plates caused by burrs. In addition, touch of the rotor to the stator housing cannot be ruled out. In this case, troubleshooting the motor will be reduced to cutting out the defective elements, removing burrs. After this, it is necessary to isolate the sheets from each other by means of mica or special cardboard.
If there is too much damage, a stitching of the active steel of the stator is done with reinsulation of all the sheets. The stationary part itself is rewound.
It's all about the rotor
With the following characteristic signs, the cause of the rotor malfunction should be sought in the poor-quality soldering of its circuit:
- rotor overheating;
- buzz
- braking;
- asymmetric readings of currents in phases.
Before starting to repair the rotor, you should examine how well the soldering of its windings was performed. If necessary, it is worth soldering, the same must be done with those areas that cause concern.
There may also be cases where a motor failure is caused by the fact that the rotor is motionless and open, although the voltage on the three rings is the same. In this case, the cause of the malfunction is most likely due to a 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 attract to the stator. Rotor repair is the replacement of liners, as well as the adjustment of bearing shields.
In addition, brushes and a collector can spark or heat up. This can happen for several reasons:
- the brushes are worthless;
- incorrect installation of brushes;
- the dimensions of the brushes do not correspond to the dimensions of the holder holder;
- poor connection of brushes with fittings.
In this case, it is enough to precisely set the brushes along with the holders.
Increased vibration
From a technical point of view, this phenomenon can also be considered a malfunction of the electric motor. Typically, strong vibrations occur due to imbalance of the rotor, clutch or pulley. Also, this phenomenon can be promoted by inaccurate centering of the device shafts, curvature of the connecting coupling halves.
First of all, it is necessary to balance the rotor, for which it is necessary to balance the coupling halves with the 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 connection or break, and then repair the breakdown.
Expert Advice
The installation of an electric motor does not end there, which is confirmed by many experts. It is necessary to take all necessary measures to extend the life of electric power plants.
In particular, on the part of the staff, it is necessary:
- Protect electric motors with special devices.
- Install the soft starter motor. This will increase the service life of not only the power unit, but also its drive.
- Install a thermal relay. With its help, thermal overloads can be avoided, which is very important for electric motors.
- Prevent moisture from entering the engine housing and its cavity. Thus, it is possible to ensure its operability, since this factor negatively affects the internal components of the electric motor.
- Regular maintenance is required. This is cleaning the engine itself from contamination, lubricating the bearings, tightening the contacts.
- Do not repair power electrical installations without the proper experience and skills. This work is best entrusted to specialists.
In addition, it is important to timely detect the malfunction of the electric motor and eliminate it, since the delay in production depends on this. And it, as you know, is worth its weight in gold, if not even more valuable.