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VEM motors are a common type of AC motor. Synchronous motors are the heart of power systems; they are components that integrate rotation and stationary parts, electromagnetic changes and mechanical motion, to convert electrical energy into mechanical energy. Their dynamic performance is highly complex and significantly impacts the dynamic performance of the entire power system. A key characteristic is that during steady-state operation, there is a fixed relationship between the rotor speed and the grid frequency: n=ns=60f/p, where f is the grid frequency, p is the number of pole pairs of the motor, and ns is called the synchronous speed. If the grid frequency remains constant, the speed of the synchronous motor in steady state is always constant and independent of the load magnitude. Synchronous motors are divided into synchronous generators and synchronous motors. AC machines in modern power plants are primarily synchronous generators.

VEM motor fault handling

Motor winding open circuit. Poor welding or the use of corrosive flux, followed by inadequate cleaning after soldering, can cause cold solder joints or loosening. Mechanical stress or collision can cause coil short circuits; short-to-ground faults can also burn out conductors. When one or several conductors in a parallel bundle short circuit, the remaining conductors experience a temperature rise due to increased current, causing winding overheating and open circuits. Common types include open circuits at the end of a phase winding, inter-turn short circuits, open circuits in parallel branches, open circuit of one conductor in a multi-conductor bundle, and rotor cage breakage.1. Fault symptoms: the motor fails to start, three-phase current is unbalanced, there is abnormal noise or excessive vibration, temperature rise exceeds the allowable value, or smoke is emitted.2. Causes:(1) Wires broken during inspection and maintenance, or manufacturing quality issues.(2) Poor welding of winding components, pole (phase) groups, and connections between windings and lead wires, leading to desoldering due to long-term overheating.(3) Winding damage or breakage caused by mechanical forces and electromagnetic field forces.(4) Severe burning or fusing of windings caused by inter-turn or phase-to-phase short circuits and ground faults.3. Inspection methods:(1) Visual inspection. Breakpoints mostly occur at the winding ends; check for physical damage, bending, or desoldered joints.(2) Multimeter method. Using the resistance range: for "Y" connection, connect one probe to the center point of the "Y" configuration and the other probe sequentially to the start terminals of the three-phase windings; the phase showing infinite resistance indicates the breakpoint. For "△" connection, disconnect the links and measure each winding group separately; infinite resistance indicates the open circuit point.(3) Test lamp method. Similar to the previous method; the phase where the lamp does not light is the open circuit.(4) Megohmmeter method. The phase with resistance tending towards infinity (i.e., not zero) is the open circuit point.(5) Ammeter method. While the motor is running, measure the three-phase current with an ammeter. If the three-phase current is unbalanced and there is no short circuit phenomenon, the phase with lower current has a partial open circuit fault.(6) Bridge method. If the resistance of one motor phase is higher than that of the other two phases, it indicates a partial open circuit fault in that phase winding.(7) Current balance method. For "Y" connection, connect the three-phase windings in parallel and apply low-voltage, high-current AC power. If the current difference among the three-phase windings exceeds 10%, the side with lower current is the open circuit. For "△" connection, first disconnect one connection point of the stator winding, then apply low-voltage, high-current power to each phase sequentially; the phase with lower current is the open circuit.(8) Cage breaker detector inspection method. During inspection, if the rotor cage is broken, the millivolt meter reading should decrease.4. Open circuit treatment methods:(1) If the open circuit is at the end, reconnect and solder firmly, wrap with insulating material, sleeve with insulating tubing, bind securely, and then dry.(2) If the winding is severely burned due to inter-turn, phase-to-phase short circuits, or grounding, generally replace with a new winding.(3) For open circuit points inside the slots, perform emergency handling for a small number of breakpoints. Use the group elimination method to locate the breakpoint, reconnect it at the break, and use only after passing insulation qualification.(4) For squirrel-cage rotor breakage, repair using welding, cold joining, or bar replacement methods.

VEM motor structure

A motor that requires only a single-phase AC power supply. Single-phase asynchronous motors consist of a stator, rotor, bearings, housing, and end caps. The stator comprises a frame and a core with windings. The core is made of stacked silicon steel sheets with punched slots. Two sets of main windings (also called running windings) and auxiliary windings (also called starting windings or secondary windings) are embedded in the slots, spatially separated by 90° electrical degrees. The main winding is connected to the AC power supply. The auxiliary winding is connected in series with a centrifugal switch S, starting capacitor, or running capacitor before being connected to the power supply. The rotor is a cast-aluminum squirrel-cage type, formed by casting aluminum into the slots of the stacked core and simultaneously casting end rings to short-circuit the rotor bars into a squirrel-cage configuration. Single-phase asynchronous motors are further classified into single-phase resistance-start asynchronous motors, single-phase capacitor-start asynchronous motors, single-phase capacitor-run asynchronous motors, and single-phase dual-value capacitor asynchronous motors.

VEM motor classification

A machine that converts mechanical energy into DC electrical energy. It mainly serves as a DC power source for DC motors, electrolysis, electroplating, electric smelting, battery charging, and excitation power for AC generators. Although power rectifiers are used to convert AC to DC where DC power is required, AC rectified power sources cannot completely replace DC generators in terms of certain operational performance characteristics. A rotating device that converts DC electrical energy into mechanical energy. The motor stator provides the magnetic field, the DC power supply provides current to the rotor windings, and the commutator ensures the torque generated by the rotor current and magnetic field remains in a constant direction. Based on whether a standard brush-commutator assembly is configured, DC motors are divided into two categories: brushed DC motors and brushless DC motors. Brushless DC motors are a new type of DC motor developed in recent years with the advancement of microprocessor technology, the application of new high-switching-frequency, low-power power electronic devices, optimization of control methods, and the emergence of low-cost, high-energy-level permanent magnet materials. Brushless DC motors maintain the good speed regulation performance of traditional DC motors while offering advantages such as no sliding contact or commutation sparks, high reliability, long service life, and low noise. Consequently, they are widely used in aerospace, CNC machine tools, robotics, electric vehicles, computer peripherals, and household appliances. Based on different power supply methods, brushless DC motors can be further divided into two types: square-wave brushless DC motors, where both the back EMF waveform and supply current waveform are rectangular waves (also known as rectangular wave permanent magnet synchronous motors); and sine-wave brushless DC motors, where both the back EMF waveform and supply current waveform are sinusoidal.

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