The formula for calculation of electric effect in an electric system is P = V x I.P is effect in Watt
V is voltage in Volt
I is current in Ampere
n is efficiency
To calculate watts (P), you must multiply volts (V) by amperes (I). For a 3-phase motor, you also need to divide by the square root of 3. The formula then looks like this: P = (V x I) x √3, but we also need to include the motor's efficiency (n) in the calculation.
No motor operates at 100% efficiency. For example, the motor heats up when it is running, and some of the energy is lost in the form of heat. There are also other factors, such as the way the motor is designed, that can cause efficiency to vary with speed and load. This means that more energy is supplied to the motor than it outputs as mechanical work. In short, the efficiency of an electric motor is the ratio between the supplied power and the output power. Efficiency (n) is given as a fraction or percentage, for example, 0.90 or 90%.
Efficiency (n) is usually defined on the motor label. This is often the best efficiency for the motor, and in some cases, it can only be achieved at full load on the motor. Often, the motor is not run at full load, so it may be wise to consider the motor's current speed and load and check the motor data sheet to see what the current efficiency is. Efficiency (n) is given as a fraction or percentage, for example, 0.90 or 90%.
When we also take the efficiency into account, we have a formula that works and is usable, and the formula now looks like this: P=((VxI)x√3)xn.
Do you find the formula difficult? We understand. Let's take it one step at a time.
First, we need to multiply V and I, and we have parentheses around these two to show that this should be done as a separate calculation. Let's say the voltage (V) is 220 volts and the current (I) is 16 amperes. The answer to U x I is 3520.
Since this is a 3-phase motor, we need to multiply 3520 by the square root of 3. We also put parentheses around this calculation to calculate this separately, and the answer here is 6097. We now divide 6097 by the efficiency (n) to calculate the supplied power of the motor. If the efficiency (n) is 0.90, the answer is 6774 watts.
The supplied energy to the motor is 6.774 kW.
We can also calculate the supplied power with the nominal power for an electric motor. The nominal power is given on the motor label and in the data sheet in kilowatts (kW). This is a slightly simpler calculation that can be used if you don't need to calculate with voltage and current. Here, you simply divide the nominal power by the efficiency.
Let's take a new example where we calculate the supplied energy for a motor with a nominal power of 10 kW and an efficiency (n) of 0.9.
10 kW / 0.9 = 11.1 kW.
The supplied energy to the motor is 11.1 kW.
So, the motor consumes 11.1 kW to deliver 10 kW of work. That means there is an energy loss of 1.1 kW (11.1 kW - 10 kW = 1.1 kW).
An electric motor consists of several components such as the stator, rotor, windings, ball bearings, fan, and in some cases, permanent magnets. This article provides a detailed overview of key components and their functions, as well as in-depth information on how 3-phase electric motors, also called asynchronous motors, work. Some of the technical aspects are explained in greater detail later.
The stator is the stationary part of an electric motor and serves as the motor housing. It contains electrical windings that create the magnetic field necessary for the motor's operation. When electrical current flows through the windings, it generates a rotating magnetic field that causes the rotor to rotate. In many cases, the stator also has cooling fins, which help dissipate the heat generated during the motor's operation by increasing the surface area.
The windings in the stator generate the electromagnetic fields that cause the rotor to rotate. The windings can be made of materials like copper or aluminum, depending on the type of motor and desired efficiency. The number of poles in the windings determines how fast the electric motor runs. Simply put, a 2-pole motor rotates at about 3000 rpm, a 4-pole motor at about 1500 rpm, a 6-pole motor at about 1000 rpm, and an 8-pole motor at about 750 rpm, and so on. This is known as the nominal speed and is typically specified at 50 or 60 hertz (Hz).
The rotor is the rotating part of the motor, usually supported by ball or roller bearings. These bearings ensure that the rotor rotates smoothly with minimal friction and keeps the rotor centered in the stator. Choosing the wrong type of bearing for the application can lead to increased maintenance needs.
The choice of bearings depends on the motor's operating conditions. For example, if the motor is used to drive a pump with low axial load, ball bearings may be a good choice. If the motor drives a belt that needs to be tensioned, it will experience significant lateral load, and in this case, roller bearings are more suitable, as they are better at handling radial forces.
To secure the bearings and shaft (rotor) within the electric motor, bearing covers are mounted on each side of the stator. These covers, together with seals, help protect the motor's internals from contaminants like dust and moisture, which can damage the windings or bearings.
The connection box, or terminal box, contains the motor's electrical connections. This box is usually located outside the stator, allowing external cables to connect to the motor's internal windings and possibly other equipment, such as standstill heaters or PTC. The location may vary depending on the design and application but is usually on top or on the side of the stator.
The nameplate on an electric motor is a key source of information that provides essential technical data about the motor. Typically attached to the motor housing (stator), it includes details such as the motor’s brand, model number, serial number, power output (kW), speed (RPM), voltage, current, frequency (Hz), number of phases, number of poles, and other relevant specifications.
The fan is normally mounted directly on the motor’s shaft. This design ensures that the fan rotates in sync with the motor, providing cooling proportional to the motor's operating speed. As the motor speed increases, the fan speed also increases, resulting in additional cooling at higher operating temperatures.
For electric motors operating at lower speeds, or where constant cooling is required regardless of motor speed, it may be useful to have fans powered by a separate motor. These fans are independent of the electric motor’s operating speed and provide constant cooling when the motor speed is too low to ensure sufficient airflow. This is important at low speeds or in demanding industrial applications to prevent overheating.
Electric motors are machines that convert electrical energy into mechanical energy through magnetic interactions. The fundamental principle is based on the Lorentz force acting on current-carrying conductors within a magnetic field.
When electric current flows through the stator windings of an induction motor, it generates a rotating magnetic field. This magnetic field induces a current in the rotor's conductors, which are often made of aluminum. According to Lenz's Law, the induced current will oppose the change in magnetic flux that caused it. This creates a force on the rotor conductors, causing the rotor (shaft) to rotate.
The rotating magnetic field is generated because the current in the stator windings is phase-shifted, creating a sequence of magnetic pulses that rotate around the motor. This field interacts with the rotor's conductors, which also become magnetized. The interaction between these magnetic fields causes the rotor to turn, thereby driving the connected machinery.
There are several types of electric motors, each with its own characteristics and uses. The three main types are asynchronous motors, synchronous motors, and permanent magnet motors. Here, we explain the basics of how the different types work.
Asynchronous electric motors, also known as induction motors, are the most widely used motor types in industrial applications. They are robust, simple, and cost-effective. In these motors, the rotational speed of the rotor is slightly lower than the rotating magnetic field in the stator, which is called slip. This slip allows the motor to generate torque.
In synchronous electric motors, the rotor rotates in exact sync with the stator field without slip. These motors are used often in applications where precise speed control is required, and they can be adjusted to handle various loads without losing synchronization with the power supply. They often require more complex control systems compared to asynchronous electric motors.
Permanent magnet electric motors use permanent magnets to establish the rotor's magnetic field. This increases the motor's efficiency and reduces the physical size of the electric motor since they do not require electrical power to generate the magnetic field. These motors are ideal for applications where high efficiency and compact design are necessary, such as in electric vehicles. Permanent magnet electric motors utilize built-in magnets to maintain a constant magnetic field without the need for external power. This makes them more efficient and less complex, but they can also be more sensitive to high temperatures that can reduce their magnetic properties.
Synchronous speed is the speed of the magnetic field created by the motor’s stator windings and is crucial for determining how fast the rotor rotates. This speed depends on the frequency of the power supply and the number of poles in the motor. Synchronous speed can be calculated using the formula: 𝑛𝑠 = 120 × 𝑓/ P where 𝑛𝑠 is the synchronous speed in revolutions per minute (RPM), f is the frequency of the alternating current supply in Hertz (Hz), and P is the number of poles in the motor.
Example Speeds for Different Number of Poles:
2-pole motors: 𝑛𝑠 = 120 × 50 / 2 = 3000 revolutions per minute
4-pole motors: 𝑛𝑠 = 120 × 50 / 4 = 1500 revolutions per minute
6-pole motors: 𝑛𝑠 = 120 × 50 / 6 = 1000 revolutions per minute
8-pole motors: 𝑛𝑠 = 120 × 50 / 8 = 750 revolutions per minute
10-pole motors: 𝑛𝑠 = 120 × 50 / 10 = 600 revolutions per minute
Note: There is a wide variation among electric motors, and you should always check the actual rotational speed on the motor nameplate or in the data sheet.
Temperature tolerance is a critical factor in electric motors, especially for motors with permanent magnets that can lose their magnetic properties at high temperatures. Magnets can begin to permanently lose their magnetism when exposed to temperatures above their Curie temperature, which can vary between materials but often ranges between 80 °C and 250 °C for common magnet materials like neodymium. Although motor windings can normally withstand up to 150 °C before the insulation degrades, it is important to ensure that the temperature near the magnets stays well below their maximum tolerance to preserve their magnetic properties.
To ensure reliable operation and avoid damage due to overheating, several technologies are used to monitor and regulate the temperature in an electric motor. These can range from simple thermistors to advanced sensors. Here is an overview of the most commonly used technologies:
PTC Thermistors (Positive Temperature Coefficient)
PTC thermistors provide simple and reliable detection by increasing resistance when the temperature reaches a certain level. They can serve as a signal to a safety mechanism to cut off the power supply and/or activate an alarm system. The advantage of PTC thermistors is their simplicity and direct response to temperature changes.
NTC Thermistors (Negative Temperature Coefficient)
NTC thermistors operate in the opposite manner of PTC thermistors; their resistance decreases as the temperature rises. While they are not typically used for direct overheating protection in motors, they can be used for continuous temperature measurement.
Bimetallic Thermostats
Bimetallic thermostats utilize two metals with different coefficients of expansion that bend with temperature changes, leading to the opening or closing of an electrical circuit. They are robust, reliable, and often used in applications that require a mechanical, direct response at a specific temperature threshold.
Thermocouples and RTD Sensors (Resistance Temperature Detectors)
For applications requiring more accuracy, thermocouples and RTDs are used for advanced monitoring. Thermocouples produce a voltage proportional to temperature, while RTDs provide precise resistance measurements. Both types of sensors are suitable for fine-tuned control systems where precise temperature monitoring is important.
Microcontroller-Based Sensors
Microcontrollers connected to digital sensors can provide detailed and continuous monitoring of various operating parameters, including temperature. These systems can be programmed to make automatic decisions and can be part of an advanced form of temperature control and system management.
IP Classification (Ingress Protection) is a standard that indicates the degree of protection an electrical device has against intrusion of solid objects, including dust, and water. This classification is defined in the international standard IEC 60529.
Each IP code consists of two digits: the first digit indicates the level of protection against intrusion of solid objects or particles, while the second digit describes the protection against water. Here is a table that explains the meaning of each digit in an IP code:
| First Digit | Description |
| 0 | No protection |
| 1 | Protected against solid objects > 50 mm |
| 2 | Protected against solid objects > 12.5 mm |
| 3 | Protected against solid objects > 2.5 mm |
| 4 | Protected against solid objects > 1 mm |
| 5 | Dust-protected (limited intrusion allowed) |
| 6 | Dust-tight (no dust intrusion) |
| Second Digit | Description |
| 0 | No protection |
| 1 | Protected against dripping water |
| 2 | Protected against dripping water when the enclosure is tilted up to 15˚ |
| 3 | Protected against spraying water |
| 4 | Protected against splashing water from all directions |
| 5 | Protected against water jets from all directions |
| 6 | Protected against powerful water jets |
| 7 | Protected against temporary immersion in water |
| 8 | Protected against continuous immersion in water |
| 9K | Protected against water from high-pressure/steam cleaners |
Example: IP54
The number 5 in IP54 indicates that the equipment is dust-protected. This means that even though it is not completely dust-tight, the protection is sufficient to prevent harmful dust ingress.
The number 4 in IP54 means that the equipment is protected against splashing water from all directions, ensuring that water splashes will not damage the electrical equipment.
The IE classification refers to the energy efficiency classes for electric motors as defined in the IEC (International Electrotechnical Commission) standard IEC 60034-30-1. This standard applies to electric motors with a power output from 0.12 kW up to 1000 kW and classifies motors based on their energy efficiency. The goal of the standard is to promote the use of more energy-efficient motors in industrial and commercial applications to reduce energy consumption and environmental impact. Here is an overview and explanation of the different IE classes:
IE1 – Standard Efficiency
IE1 is the basic class for energy efficiency. This was the lowest acceptable standard for many markets, but many countries have now phased out IE1 motors in favor of more energy-efficient alternatives.
IE2 – High Efficiency
Electric motors in this class are significantly more energy-efficient compared to IE1 motors and are still widely used, although global efficiency requirements are shifting toward even higher classes.
IE3 – Premium Efficiency
IE3 requires higher energy efficiency compared to IE2. This class is now the minimum standard in many developed markets, including the EU and the USA, for new installations of certain types and sizes of electric motors.
IE4 – Super Premium Efficiency
These motors have the highest energy efficiency available on the market and are designed to provide maximum energy savings and significantly reduce operating costs.
IE5 – Ultra Premium Efficiency
Although not officially standardized under IEC 60034-30-1 in its latest edition, IE5 has been proposed and recognized in some documents and markets as a future class for ultra-premium efficiency. These electric motors will offer even better energy efficiency than IE4 motors.
To illustrate the differences in efficiency requirements across various classes, we have created this graph for a smaller portion of the power range. The dots on the lines represent data points specified in IEC 60034-30-1 for IE1, IE2, IE3, and IE4. However, we want to emphasize that this is primarily a pedagogical visualization.
The figure shows the efficiency of 4-pole motors at 50 Hz according to IEC 60034-30-1 for IE1, IE2, IE3, and IE4.
The transition to higher energy efficiency classes is driven by the need to reduce energy consumption and the associated greenhouse gas emissions. By choosing more efficient motors, companies can significantly reduce operating costs and CO₂ emissions. This is also in line with global legislation that is becoming increasingly stringent to promote sustainable development.
It is worth noting that even though the initial investment costs may be higher for motors with higher efficiency, the long-term savings in energy costs and reduced carbon emissions can be much greater.
