Understanding the Concepts of Induction Motors
The electric motor is a device whose main characteristic is to transform electrical energy into mechanical energy to move machines, equipment and equipment.
vehicles. Among the most diverse equipment, fundamental for the operation of an industry, it can be said that the electric motor is one of the main ones. After all, he is the great
responsible for providing the mechanical energy necessary for machines and equipment to perform their activities.
Electric motors are responsible for powering a wide range of equipment and processes, ranging from small electronic devices to large machines.
industrial. A correctly sized motor not only optimizes efficiency, but also reduces energy consumption and extends the life of the equipment.
However, given the various engine options available on the market, how can you determine which one is most suitable for a specific application? This article serves as a guide in understanding the fundamental concepts of electric motors, specifically for asynchronous motors, also known as induction motors, which operate based on electromagnetic induction.
The induction motor is the most used among all types of motors, as it combines advantages such as low cost, robustness, simplicity of control, in addition to having simple construction and less frequency between maintenance. In the industrial environment, applications with an alternating current (AC) electric motor together with a frequency inverter to vary the speed are very common.
Fundamental concepts
Choosing the most suitable electric motor is essential for proper operation in the application. Before selecting AC motors, it is essential to know some basic concepts.
Power (kW, hp or hp):
It refers to the work capacity of the engine, being the force that the engine generates to move a load at a given speed. Power can be expressed in kW (kilowatt), hp (horsepower) or in hp (horsepower). Choosing a motor with adequate power is important to ensure that it does not become overloaded.
The table below shows how to convert the values:
To convert power units, simply locate the unit you want to convert in the first column. Then, follow the same line to the desired unit column to find the conversion factor. Finally, it is necessary to multiply the initial value by this factor to obtain the result in the new unit.
Voltage (VCA):
The voltage, expressed in Volts in alternating current (VCA), varies depending on the application. While homes and businesses use 127 VAC or 220 VAC, industries and businesses can operate between 380 VAC and 760 VAC.
A small fluctuation in voltage can affect motor performance. Insufficient voltage reduces torque and can prevent the electric motor from maintaining its rated speed, while excessive voltage increases torque, which can cause starting damage.
There are two main types of voltage:
• Single-phase: is the voltage between phase and neutral. Usually at 127 VAC or 220 VAC, but there are exceptions that require motors with specific voltages.
• Three-phase: is measured between phases and is preferred due to its superior efficiency. In Brazil, the most common are 220 VAC, 380 VAC, 440 VAC and 760 VAC.
Efficiency (%):
It represents the relationship between the energy delivered to the engine and the useful energy. Motor efficiency indicates the percentage of input electrical energy that is converted to output mechanical energy. In practice, it means that high-efficiency motors consume less energy to perform the same work.
Frequency (Hz):
Expressed in Hertz (Hz), frequency indicates how many times a given event is repeated within a time interval. In North America and Brazil, 60 Hz is used, but the frequency most used worldwide is 50 Hz. Frequency is an important aspect as it has a direct influence on the rotation of the electric motor. Out of curiosity, in specific applications such as power engines for aerospace applications, the frequency of 400 Hz is used.
Rotation (rpm):
Motor speed refers to the number of shaft revolutions when the motor is supplied with its rated voltage and power. It is normally expressed in revolutions per minute (rpm). In synchronous motors, the rotor will rotate at the same speed as the stator field.
In asynchronous motors, the rotor will rotate at a speed lower than that of the stator field. In other words, there is what is known as slippage. Therefore, only asynchronous motors have slip.
Speed is related to the number of poles and frequency of a motor, as shown in the table below:
This article explored the essential concepts related mainly to induction motors, from power and voltage to efficiency and rotation, emphasizing the importance of choosing the correct motor for each application. Understanding these concepts not only aids in appropriate engine selection, but also contributes to
