JiangDoor Motor Quick Facts: Risks to Be Aware Of When Using Industrial Frequency Motors Under Variable Frequency Conditions
Jiangmen Electric Motor produces standard asynchronous motors in compliance with...Heng frequency, constantVoltageThe operation scheme designed allows for high-speed operation within a relatively narrow operational region near the rated working point, generally not suitable for wide-range variable frequency speed control. Some customers, considering cost, directly use standard asynchronous motors as variable frequency motors, leading to frequent motor failures orService LifeNo Chinese content provided.
In fact, many electric motor companies have designed and developedWideband Motor, specifically designed for wide-range variable frequency speed control applications.So, to get back to the topic..."Is the application of a standard asynchronous motor as a variable-frequency motor really as simple and粗暴 as it seems? What are the potential dangers involved, and is there a need for an upgrade?"Wideband MotorNecessity? Today, we delve into theoretical analysis to clarify the intrinsic reasons behind frequent failures.Mechanism.Briefly, state the issue.
Efficiency DecreasedWen Sheng Zeng
All variable-frequency drives generate varying degrees of...Harmonic Voltage and CurrentThere is no Chinese content provided for translation. Please provide the text you wish to have translated into American English.Sine Voltage, CurrentThe inverter is now operational.High-order harmonicsThese losses will increase the copper consumption of the stator and rotor, iron consumption, and additional losses, with the rotor copper consumption being particularly notable. These losses will cause the motor to generate extra heat, decrease efficiency, and reduce output power.If a standard three-phase asynchronous motor is used under inverter conditions,*The direct increase is the rise in temperature, especially for...The IP23 series motors are affected more severely.。
Cooling efficiency decreases at low speeds.
Initially, the impedance of asynchronous motors is not ideal, particularly when the power frequency is low, leading to significant losses due to higher-order harmonics in the power supply. Furthermore, as the speed of a standard asynchronous motor decreases, the cooling air volume decreases proportionally to the cube of the speed, worsening the low-speed cooling conditions and causing a sharp increase in temperature rise, making it difficult to achieve a constant torque output. Additionally, when the power frequency is low, the losses caused by higher-order harmonics in the power supply are more pronounced. Moreover, as the speed of a standard asynchronous motor decreases, the reduction in cooling air volume is evident, affecting the motor's performance.Cooling ConditionsDeteriorate, the direct result is:Wen ShengRapidly increasing, yet difficult to achieve a constant torque output.
Insulation strength insufficient
The carrier frequency of inverters is very high (ranging from several thousand to tens of thousands of hertz), which can cause the stator windings of the motor to bear a high voltage, thus making the motorInsulation IntervalSubject to rigorous testing, and the motor...Ground InsulationThreateningThe final result was that the motor was due to inter-turn Intercircuit and earth faults, which can be severe, manifest as winding overloads. Due to the relatively large design margin for both intercircuit insulation and earth insulation, motors typically exhibit more turn-to-turn and overload issues. However, for stators without intercircuit blocks in automated winding machines, relative failures are relatively more frequent.
Electromagnetic noise and vibration issues
When a general asynchronous motor is powered by a variable-frequency inverter, it complicates the vibration and noise issues caused by electromagnetic, mechanical, and ventilation factors. The various time harmonics in the variable-frequency power supply interfere with the inherent spatial harmonics of the motor's electromagnetic part, resulting in various...Electromagnetic Excitation ForceWhen the frequency of the electromagnetic wave is in harmony or close to the natural vibration frequency of the motor body, it will produce...Resonance PhenomenonSevere electromagnetic high-frequency noise will occur, accompanied by a certain degree of vibration.
Structural Fatigue and Insulation Aging
Our motor operates with an inverter-powered supply, allowing it to run at very low frequencies and voltages.Start without surge currentThe use of variable-frequency drives enables various braking methods for rapid braking, thus creating conditions for frequent start-ups and braking. However, the mechanical and electromagnetic systems of the motor are subjected to cyclic alternating forces, which cause fatigue and accelerated aging of the mechanical and insulation structures.
The application of high-performance variable-frequency drives has brought a revolutionary change to the motor industry, with most motor testing equipment replacing transformers and variable-frequency generators with static adjustable variable-frequency power supplies. However, since most end-users are supplied with power at a fixed frequency, this inevitably leads to an overlooked risk: while motors can run normally with the static adjustable variable-frequency power supply, they may fail to start properly with fixed-frequency power supply.
Motor's adaptability to frequent starts and stops
Due to the use of variable frequency drives for power supply, motors can start with minimal current shock at very low frequencies and voltages. Additionally, they can utilize various braking methods provided by the variable frequency drives for rapid braking, which creates conditions for frequent starts and stops. As a result, the mechanical and electromagnetic systems of the motor are subjected to cyclic alternating forces, leading to fatigue and accelerated aging of the mechanical and insulation structures.
In light of the above situation,Variable frequency motor incorporates the following design:
1. Minimize the stator and rotor resistance as much as possible to reduce fundamental copper loss, in order to compensate for the increased copper loss caused by higher-order harmonics.
2. The main magnetic field design avoids saturation by considering two factors: first, higher-order harmonics can exacerbate magnetic circuit saturation, and second, to increase the output torque at low frequencies, the inverter's output voltage can be appropriately elevated.
3. Structural design focuses primarily on improved insulation ratings; thoroughly considers issues related to motor vibration and noise; employs forced ventilation cooling, with the main motor's cooling fan driven by a separate motor for enhanced cooling, ensuring effective cooling at low speeds.
4. Variable frequency motor windings have a smaller distributed capacitance, and silicon steel sheets have a higher resistance, which reduces the impact of high-frequency pulses on the motor, improving the motor's inductive filtering effect.
5. Standard motors, or line-frequency motors, only require consideration of the starting process and a single point of operation at line frequency for design; however, variable-frequency motors necessitate evaluating the starting process and all points of operation within the variable-frequency range before designing the motor.
6. To accommodate the PWM modulated sine AC output with a high harmonic content from inverters, a special-purpose variable-frequency motor has been designed. Its function can be understood as a combination of an inductor and a standard motor.
How to differentiate between standard motors and variable frequency motors?
No Chinese content provided.The structural differences between standard motors and variable-frequency motors
Higher insulation grade requirements
Typically, the insulation grade of variable-frequency motors is:F-grade or higher, enhance ground insulation and wire coil insulation strength, particularly considering the insulation's ability to withstand impulse voltage.
02. Higher vibration and noise requirements for variable frequency motors
Variable frequency motors require careful consideration of both the rigidity of the motor components and the overall structure.(Public Channel: Pump Manager), striving to enhance its inherent frequency to avoid resonance with various force waves.
03. Different Cooling Methods for Variable Frequency Motors
Variable-frequency motors generally employ forced ventilation cooling, meaning the main motor's heat dissipation fan is driven by a separate motor.
04. Protection Measures Vary
Please provide the Chinese content that needs to be translated.160KW variable frequency motors should implement bearing insulation measures. This is primarily due to the potential for magnetic circuit asymmetry, which can also generate shaft current. When combined with the current produced by other high-frequency components, the shaft current significantly increases, leading to bearing damage. Therefore, insulation measures are generally required. For constant power variable frequency motors, when the speed exceeds 3000/min, a special high-temperature-resistant lubricant should be used to compensate for the increased bearing temperature.
05. Different Cooling Systems
The variable frequency motor cooling fan is powered by an independent power supply, ensuring continuous cooling capability.
TwoThe Differences in Design Between Standard Motors and Variable Frequency Motors
Electromagnetic Design
For conventional asynchronous motors, the primary performance parameters considered during design are overload capacity, starting performance, efficiency, and power factor. In contrast, variable-frequency motors, due to the critical slip being inversely proportional to the power frequency, can operate with the critical slip approaching...The system directly starts in 1 second, so the overload capacity and startup performance are not primary concerns. The key issue to address is how to enhance the motor's adaptability to non-sinusoidal power sources.
02. Structural Design
During structural design, it is primarily necessary to consider the impact of non-sinusoidal power characteristics on the insulation structure, vibration, noise, and cooling methods of variable-frequency motors.
