Implement the traditional starter of variable frequency soft start asynchronous motor

The energy utilization rate of China's motor drive system is about 20% lower than that of foreign countries, and the total energy saving potential is about 100 billion kWh. Therefore, the energy-saving measures should be taken for asynchronous motors to tap potential energy. Optimize the motor structure and process, and develop high-efficiency motors to improve motor efficiency and save power. YX series high-efficiency motors are made of high-quality cold-rolled silicon steel sheets with good performance. Use a special winding machine to increase the slot full rate of the wires in the slot, change the winding method, shorten the end line length, adopt the optimal slot ratio and air gap value, and adopt advanced rotor processing and surface treatment new technology to improve the machining accuracy and assembly of the parts. Measures such as quality effectively reduce the iron loss, copper loss and stray loss of the motor, and improve the efficiency of the motor. At the same time, the air path structure is optimized, and the outer diameter of the fan is appropriately reduced, so that the noise and vibration of the motor are well suppressed. This series of motors has the advantages of high efficiency, low noise, low vibration, large temperature rise margin, long life and high reliability.

At the rated power point, the average efficiency of the YX high-efficiency motor is about 3.1 percentage points higher than that of the Y series, and the power factor is about 1.3 percentage points higher. In the non-rated load section, the average efficiency of the YX series high-efficiency motor is 3.9 percentage points higher than that of the Y series. The average is 1.9 percentage points higher.

An oil production plant replaced the ordinary Y series motors with the same capacity YX series high-efficiency motors on 8 oil wells, including 22kW1 units. Before and after the replacement, the measurement of liquid production and power consumption, the optimization of energy-saving measures for asynchronous motors analysis of Hunan University Hengyang Branch (421101) Lei Meiyan estimated that the oil plant can save about 4.3 million yuan per year after using high-efficiency motors. Crude oil production costs fell by 0.6 percentage points. At the same time, the high-efficiency motor is equipped with a grease nozzle for maintenance, which is easy to install and maintain, and has high work efficiency.

European and American countries actively promote motor energy conservation, and the United States enforces high-efficiency motors in the form of laws, making it possible for major motor manufacturers in the United States to introduce high-efficiency motor products in just one year. Only 5% of the motors currently manufactured in China are high-efficiency motors, and most are used for export. In view of this situation, China has put the development of high-efficiency motors on the agenda of the “10th Five-Year Plan”, requiring motor manufacturers to mass produce high-efficiency motors, implement energy efficiency standards, and implement efficiency certification systems. At the same time, effective measures are taken to encourage users to actively use high-efficiency motors.

Optimize the motor starting mode, implement the variable frequency soft start asynchronous motor. The traditional starting method is full pressure starting, Y-Y series series liquid production / m power consumption / kWh Table 1 "Motor Technology" 2004 (1) a subway station to centrifuge All the valves/gates of the main chiller of the chiller are adjusted to the fully open state, and the speed control method is adopted. The speed of the ABB ACS400 frequency converter is adopted. Under the requirement of the chiller starting, the data of Table 2 is measured, and the energy saving effect is obvious. The temperature rise basically conforms to national standards.

Δ step-down starting and self-decreasing step-down starting, the former has a large starting current, and the starting current of 5-7 times the rated current causes a huge loss of energy and a huge impact on the power grid and the transformer, affecting the service life of the motor itself and other control devices. The starting current of the latter two is reduced, but the inrush current is also present, the equipment failure rate is high, and the starting torque is reduced, and the starting time is prolonged.

At present, an electronic thyristor soft starter is a three-phase power supply line in which a thyristor voltage regulating circuit is connected in series to an electric motor. The conduction angle β is controlled by the microcomputer control system according to a predetermined mode, so that the starter adjusts the output voltage as needed to complete the process of stepping down the motor. After starting, short-circuit the thyristor voltage regulator circuit to let the motor run directly. The starter has good starting performance, can be adjusted according to the load demand, the starting current is small, no current impact, but the starting time is long, the cost is high, and there is harmonic pollution.

The new optimized starting method is to implement the inverter variable frequency soft start. The inverter rectifies the commercial frequency power supply into a DC voltage, and then inverts it into an AC power supply motor with variable voltage and variable frequency. The frequency converter adopts voltage regulation and frequency modulation mode, so that the slip power is greatly reduced, the starting current is almost rated current, the starting energy consumption is greatly reduced, there is no starting impact, and the starting torque can be provided 1 to 2 times, and the starting speed is controlled to make the starting speed The motor starts smoothly.

Optimize the operation mode of the motor and promote the equipment of the square-speed torque load of the variable frequency speed control fan and water pump. When the speed control is used, the flow rate can be adjusted according to the production needs, which greatly reduces the power of the input motor and achieves a large section. The purpose of electricity.

Frequency conversion speed regulation is the development trend of asynchronous motor speed regulation. Its operation is simple. As long as the inverter is connected between the power supply line and the AC asynchronous motor, it constitutes an AC variable frequency speed control system with automatic energy optimization (AEO) function and automatic Motor Adaptation (AMA) function and Automatic Voltage Adjustment (AVR) function. It has a sinusoidal pulse width modulation function, which fundamentally overcomes the harmonic problem of the thyristor voltage regulation control device, and has a high power factor, eliminating the reactive power local compensation device and improving the power quality.

The refrigerating pump is calculated for 16 hours per day and runs for 180 days per year. The inverter output frequency can meet the requirements of the chiller starting at 37 Hz. The electricity fee is calculated at 0.85 yuan/kWh, which saves electricity every year. Large, but the increased investment can be recovered in a short time, its performance price is relatively high, the use of frequency converter is very cost-effective, so we should actively promote the development of China's inverter industry, and seriously promote the AC motor's variable frequency speed control measures.

The optimal energy-saving measures for asynchronous motors are: vigorously develop high-efficiency motors, reduce the loss of the motor and improve its efficiency; secondly, implement variable frequency soft start to reduce energy consumption during start-up; third, actively promote variable frequency speed control to save motor drag power. The application of frequency converter speed regulation and starting is the first choice for asynchronous motor to optimize energy saving.