The AC Electric Motor

The AC electric motor is made up of a three-phase winding, which is composed of three single-phase windings spaced apart from each other by 120 °. AC motors are based on the principle of the rotating field and that to achieve this field there must be several windings, notably one per phase, around the magnetic cores in the stator that formed the pole pairs of an electromagnet.

If this winding is fed by a three-phase system, the currents I1, I2 and I3 will likewise create their own magnetic fields H1, H2 and H3. Thus, as they are proportional to the respective currents, they will also be time lagged by 120º between them and can be represented by a graph.

The resulting total field H will be equal to the graph sum of the three fields H1, H2 and H3 at that instant. We then check this graph sum for six successive instants and thus, when a three-phase winding is fed by three-phase currents, a rotating field is created, as if there were a single pair of rotating poles of constant intensity. As the rotating field rotates according to the maximum and minimum current flowing through each winding, the faster the current will alternate.

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The Buried Magnets

The rotors with buried magnets have circumferential magnetization and are installed in deep grooves. This setting is also referred to as “buried” or “spoke”. and in this configuration, a means must be used that prevents the flow from closing by means of the shaft. The use of a non-ferromagnetic material is essential.

With a ferromagnetic axis, much of the flow is located in a way to close without crossing the engine air gap and as a result this flow does not cause torque in the motor shaft.

With the principle of increasing the magnetic flux in the air gap, the axis must be non-ferromagnetic or a ring of non-ferromagnetic material should be applied between the magnets and the ferromagnetic axis. Because of this type of magnetization, the magnet height is in the tangential orientation and the effective arc coefficient is restricted by the groove.      Boston Gear SF-1 5/8

Thus, the synchronous reactance of the q-axis is greater than that of the d-axis and the thickness of the bridge between the axis and the adjacencies of the magnets must be meticulously chosen. This was the type of configuration that was selected for the design of this project.

Permanent Condenser Motor

Taking into account the construction factor, the permanent condenser electric motor has a smaller size and is generally free of the need for periodic maintenance, since they do not use contacts and moving parts, as in other types of engines found. However, the starting torque is significantly lower than that of the split-phase motor, which changes in average 50% and 100% of the nominal torque, a factor that can be definitive in case it is necessary to limit its application to equipment that generally does not need high starting torque.     Boston Gear BP5011T01

In this type of permanent condenser motor the auxiliary winding as well as the condenser are permanently active, the condenser being electrostatic. The effect of this capacitor is to operate in the creation of flow conditions considered very similar to those found in multiphase motors, increasing in this way the maximum torque, its efficiency and the power factor, thus having the ability to significantly reduce noise. Centrifugal pumps, grinders, drills, blowers, various office machines, fans, exhaust fans, small saws, air conditioners and sprayers, among other equipment, can be mentioned.

 

Induction Motor – Direct Start

The direct start is basically in the starting system, where the motor receives at its terminals, full voltage at the exact moment of departure. The squirrel cage rotor motor can split at full load and with the chain having the capacity to be raised from 4 to 8 times the rated current, according to the type and number of poles.

Electric motors can start directly from the grid only if they meet certain conditions and some of them are:

– the rated capacity of the network must be sufficiently high, making the motor starting current;

– the starting current of the low-value motor due to its low power;

– The starting of the motor must be done without load, which reduces the duration of the starting current, thus reducing the effects on the power system.      shaft collars boston

The torque at the start can reach on average 1.5 times the nominal torque and is considered as the simplest starting method in which no specific drive components of the motor are used. Only contactors, circuit breakers or switch switches are applied, which guarantee full voltage supply to the motor at the moment of starting.

 

The Useful Life of Insulators

The life of the insulating components can be reduced in the event of a considerable overheating of the motor. It is necessary to use the shutdown periods of the motors to clean the coils of the windings and if necessary, filters must be installed in the ventilation systems of the motors, making maintenance more exclusive.

Be careful when storing and installing the motors in a healthful place. Check for signs of smoke and periodically check the insulation conditions, equipping motors with alarm components and protection to avoid short circuits.

It is also necessary to check for possible noises, vibrations and overheating signals by periodically recording temperatures during operation. The main factors that lead to the degradation of insulators are factors such as line overvoltage, current overcurrent in the starters, the accumulation of dust that causes conductive bridges and attack by acid vapors or gases entrained by ventilation.    reelcraft

In order to prevent deterioration of these insulating components, it is recommended to take some measures, such as adequately providing power boards with suitable protective devices and controls, and periodically checking their operation.

 

 

The Departure Regime

In view of the high starting current value of the induction motors, the time taken to accelerate high inertia loads can result in a rapid rise in engine temperature. A starting with the electric motor heated, with the windings at regime temperature, simulating the case in which the first start of the motor is made, for example, by the shutdown of the protection, thus guaranteeing a second attempt.

The second starting condition occurs in the event of an accidental shutdown of the motor in normal operation, for example due to a lack of power in the mains, allowing to continue operation soon after the power is restored.    DUTF-B

If the interval between consecutive starts is very small, this factor will cause a rise in temperature in the winding, which can damage or reduce its durability. The official standards lay down a minimum starting system (S1), which engines, regardless of their category, must be able to meet. Two continuous starts, the first one being made with the engine cold, that is, with its windings at room temperature, and the second starting immediately after the engine has decelerated until the moment of rest.

 

The Two Types of Electric Motors

Over 90% of all electric motors applied in the industry are from AC induction motors because of their simplicity, strong construction and relatively lower manufacturing costs. They are adaptable to diverse environments and able to provide considerable power as well as variable speed control with a frequency inverter.

There are two different types of electric motors: the asynchronous (induction) and the synchronous electric motor.

The asynchronous (induction) electric motor: is designed with coils in its armature or stator and achieve the torque in the rotor through currents induced in these coils changing the magnetic field, that is, the voltage is “induced” in the rotor through electromagnetic induction , extinguishing the need for brushed or sliding ring switching.

The synchronous electric motor: this type of motor uses a coiled rotor reelcraft EA33112 M24D because coils of wire are placed in the grooves of this rotor. The rotor in turn is excited by an external direct DC power supply, employing sliding rings and brushes to supply current to the rotor. This motor is made to operate at a specific constant speed in accordance with the rotating magnetic field. A synchronous motor is applied where we need an exact speed.