【2026 Motor Issue】Motors rated at 60Hz cannot be used with a power supply operating at 50Hz
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Why can’t a 60Hz motor be connected to a 50Hz power supply? In motor design, silicon steel sheets are generally made to operate in the saturation region of the magnetization curve. When the supply voltage remains constant, reducing the frequency increases the magnetic flux and the excitation current, which in turn leads to an increase in motor current and copper losses. This results in an elevated temperature rise in the motor; in severe cases, the motor may even be damaged due to overheating of the coils.
The following motor knowledge is provided for reference: 1. When a single-phase transformer is operating without a load, the current is out of phase with the main magnetic flux; there is a phase angle difference of aFe due to the existence of iron loss current. The no-load current has a sharp peak waveform due to the presence of significant third harmonics.
2. An alternating current also flows in the armature winding of a DC motor. However, direct current flows through its excitation winding. The excitation methods for DC motors include separately excited, shunt excited, series excited, and compound excited types.
3. The back EMF expression for a DC motor is E = CEΦn； The electromagnetic torque expression is then Tem = CTFI.
4. The number of parallel branches in a DC motor is always in pairs. The number of parallel branches in the alternating current winding, on the other hand, is not necessarily fixed.
5. In DC motors, the elements of a single-layer winding are connected in series one on top of another. Whether it is a single-wave winding or a single-layer winding, the commutator connects all the components in series to form a single closed circuit.
6. An asynchronous motor, also known as an induction motor, is so named because the rotor current in such motors is generated through electromagnetic induction.
7、When an asynchronous motor is started with reduced voltage, the starting torque decreases, and it decreases in proportion to the square of the starting current in the windings.
8. When the amplitude and frequency of the primary side voltage remain constant, the degree of saturation of the transformer’s core remains essentially unchanged, as does the excitation reactance.
9. The short-circuit characteristic of a synchronous generator is a straight line; in the case of three-phase symmetrical short circuit, the magnetic circuit remains unsaturated； During a three-phase symmetric steady-state short circuit, the short-circuited circuit consists of a purely demagnetizing direct-axis component.
10. The current in the excitation winding of a synchronous motor is direct current, and the main methods of excitation include excitation by an excitation generator, excitation by a static rectifier, and excitation by a rotating rectifier.