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5 | on their rated power and other characteristics. The legislation means that the EU is the first body to mandate IE4 as a minimum level of efficiency for motors in the scope of the regulation. Motor Operation and Types At its most basic level, the electric motor is a simple machine that converts electrical energy into mechanical motion. This process is possible because of the interaction of magnetic fields, where opposite poles attract and similar poles repel. In most motors, the magnetic fields are created by permanent magnets and/or electromagnets. When constructing a basic electric motor, the electromagnet is wound around a core on an axle at the center of the construction. The permanent magnet is on the outside of the structure with poles on directly opposite sides. As shown in Figure 1, when power is supplied to the rotor, an electric field is created, and the north pole of the electromagnet is repelled by the north pole of the permanent magnet while being attracted to its south pole. It rotates to match the opposing pole of the permanent magnet. When it gets to that position, its power supply is reversed, which also reverses the magnetic field, and the rotor is repelled from the magnet that it is near and attracted by the magnet on the opposite side of the device; when it gets there, the polarity is again reversed to keep the rotation going. This type of device is known as a DC motor, as the current supplied to the electromagnet is DC. Figure 2 shows the main constituent parts of a DC motor. The electromagnet windings, also known as the armature, are part of the rotor construction, which usually also contains a core, bearings, and an axle to allow it to rotate freely. The permanent magnet's north and south poles, respectively, on the left and right of the rotor, make up the stator. In a motor, poles always come in pairs, and the pole count of a motor is the number of permanent magnetic poles. Therefore, a single permanent magnet would be used in a two-pole motor, such as the one shown in Figure 2. Depending on the number of poles in the motor, there is a trade-off between speed and torque. A two-pole motor will be capable of rotating roughly twice as fast as a four- pole motor of the same size, but the four-pole motor will have more torque. A split-ring commutator switches the polarity of the current every time the rotor reaches its opposite pole. The brushes are electrical contacts that conduct current from the power supply to the rotor. More sophisticated motor designs may use an electromagnet on both the rotor and stator or have the permanent magnet on the rotor and the electromagnet on the stator. The other main category of electric motors is the AC motor, which, as the name suggests, works off an AC power supply. AC motors are like DC motors in that they use a rotor and a stator. However, the stator has multiple coils that energize in pairs in a set sequence to produce a magnetic field that rotates around the outside of the motor. Because the stator powers Figure 1: The most basic operation of a DC motor. (Source: "HASSANE/stock.adobe.com")