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What can variable frequency speed control bring? Benefit Analysis of Energy-saving Retrofit of Motor System with Variable Freque

What can variable frequency speed control bring? Benefit Analysis of Energy-saving Retrofit of Motor System with Variable Freque

Classification:
Question and answer
Author:
2018/10/08 03:10

With the government's policy of building a resource-conserving and environment-friendly society, in recent years, the state and local governments have promulgated and implemented a number of policies and regulations aimed at promoting energy-saving technology, improving energy efficiency, and promoting energy conservation and pollution. Reduce emissions. Energy saving of motor system is one of the ten key energy-saving projects initiated by the state. National development planning requirements should promote the energy-saving technology of variable frequency speed regulation, that is, general mechanical systems such as fans, pumps and compressors adopt energy-saving measures of frequency conversion and speed regulation. AC motor frequency conversion process speed control technology. During the "Eleventh Five-Year" period, China will increase the operating efficiency of the motor system by 2 percentage points and form the goal of 20 billion kWh of annual energy-saving capacity.

1 motor system frequency conversion speed regulation energy saving background

The use of variable frequency speed control technology is an important way to save energy and reduce consumption. When the constant torque load such as water pump and fan is not regulated, when the flow rate is required to change, the valve opening angle can only be adjusted by mechanical adjustment. Although the flow rate drops, the outlet pressure of the pump or fan increases, and the power drop is not obvious. Approximate to a constant power load, resulting in extremely low power utilization (to overcome the resistance of the regulator). When using variable frequency speed regulation, if the flow demand is reduced, the speed of the pump or fan can be reduced to meet the requirements. The power of the pump or fan is proportional to the cube of the speed. As the speed decreases, the power will drop rapidly.

Most of the fan and pump load design has a large margin, and some of the equipment is considered for expansion. After the capacity is selected, the valve is not fully opened all the year round; the other part of the equipment should adjust the valve to control the flow according to the production situation; There are still some parts of the equipment that are constantly changing in the process of speed reduction and the motor is not adjusted. The power consumption of the above equipment is maintained at a high level for a long time, and waste is serious.

In the actual production field, in order to ensure the reliability of production, various production machines have a certain margin when designing with power drive. The motor can't run under full load. Except for the power drive requirement, the excess torque increases the consumption of active power, which causes waste of electric energy. When the pressure is high, the running speed of the motor can be reduced to make it at constant pressure. Save energy.

2 motor system frequency control principle of energy saving

According to the basic laws of fluid mechanics, fans and pumps are variable torque loads. The speed n is proportional to the flow rate q, the pressure p and the shaft power P. The flow rate is proportional to the speed and frequency, and the square of the pressure and speed. In proportion, the shaft power is proportional to the cube of the speed.

Q1/Q2 = n1/n2=f1/f2

H1/H2 = (n1/n2)2

P1/P2 = (n1/n2)3

It can be seen that reducing the motor speed can achieve a cubic energy saving effect. This is the principle of energy saving for inverter motor control for motor capacity reservation and production load phase adjustment.

After the inverter is turned on, the power factor of the motor system controlled by it can be increased, and the network loss of the power distribution system can be reduced.

Therefore, the use of reliable high- and low-voltage variable-frequency energy-saving technologies and products for the existing production systems in the factory to carry out the technical transformation of the inverter as the main energy-saving means, through the above-mentioned various types of high and low voltage motor driven fans, pumps, air compression The load of the machine is used to carry out the inverter control and transformation, so as to realize the energy saving and emission reduction and ensure the investment of the motor frequency conversion energy-saving renovation project, and achieve the expected economy.

3 motor system frequency conversion speed regulation energy saving

The following is a data analysis of various high- and low-voltage motor frequency conversion retrofit schemes and examples of effects to visually understand the economic benefits after the transformation.

1800kW high temperature fan

10kV1800kW high temperature fan operating status: the actual running current before the motor transformation is 116A, the current power consumption: 1.732× 10.5× 116× 0.85=1793KW, the original system uses hydraulic coupling speed regulation, speed regulation 78.5%, power converted by frequency conversion 0.7853×1800/0.96=908KW, saving power 1793-908=885KW, the hydraulic coupling is traditionally used for fluid machinery (such as fans and pumps) that require speed regulation, and has considerable power saving effect. The rate can reach 25%. Therefore, the actual power saving of the frequency conversion is about 437KW, so the frequency conversion can save 25% of the power. The annual operation is 7200 hours, the electricity fee is 0.50 yuan, the annual electricity saving fee is 437× 7200× 0.50=1.57 million yuan, according to the current domestic inverter price calculation, 2 years can be recycled inverter investment.

Modification method: It is planned to configure the frequency converter to be the function of frequency conversion, and the damper is fully open by the DCS given frequency.

Boiler blower (355KW)

Frequency conversion energy-saving calculation: Since the average opening degree of the damper is 50%, the actual flow rate is about 70% of the rated flow rate. From the above table curve, 36% of the rated power consumption when using variable frequency speed regulation is found, and the rated power is consumed by the blade adjustment. 64% of the two, compared to the frequency conversion adjustment can save 28% of the rated power consumption. 355× per hour when converting frequency; 0.95× 28%=94.4kw, 7200 hours per year, electricity cost 0.50 yuan, annual energy saving 94.4kw× 7200× 0.50=340,000 yuan, calculated according to current domestic inverter price , 1 year and a half can be recycled inverter investment.

Modification method: It is planned to configure the frequency converter to be the function of frequency conversion, and the damper is fully open by the DCS given frequency.

Feed pump (90KW)

Operating conditions: actual motor current 147A, pipe outlet pressure 5 kg

Frequency conversion energy-saving calculation: current actual power consumption of the motor 1.732× 380V×

147A×0.88=85.5KW

After the frequency conversion, the constant water supply pressure is about 3.95 kg, and the actual power consumption after the frequency conversion according to the formula;

(3.95/5) 1.5× 85.5KW/0.98=61.56KW

Power saving per hour: 85.5KW-61.56KW=23.94 degrees

Annual energy saving: 23.94 degrees & times; 8000 hours = 192,000 degrees

One and a half years of recyclable inverter investment.

Modification method: It is planned to configure 2 inverters, with the function of “inverter switching” and constant voltage control.

Normally, when the pressure reaches the maximum, the air compressor is depressurized and unloaded by the following method: closing the intake valve so that the air compressor does not need to compress the gas to do work, but the motor of the air compressor still drives the air compressor to move. It is estimated that the energy consumption of the air compressor when unloading accounts for about 10%-15% of the full operation of the air compressor. During the unloading period, the air compressor is doing nothing and consumes energy in vain. At the same time, the excess compressed air in the separation tank is emptied through the venting valve, and this adjustment method also causes a great waste of energy.

Modification method: It is planned to configure the frequency converter. The pressure transmitter converts the pressure signal of the gas storage tank into an electric signal and sends it to the PID regulator for comparison with the pressure set value, and according to the difference PID size according to the established PID control mode. The operation generates a control signal to control the output frequency of the inverter, and automatically adjusts the motor speed so that the actual pressure is always maintained at a given pressure. After the frequency conversion is reformed, the air compressor will not be unloaded most of the time. In addition, after adopting this scheme, the air compressor motor can be soft-started from the static to the stable speed by the inverter, avoiding the large current at the start and the mechanical shock to the air compressor at the start, see Figure 4.

Frequency conversion energy-saving calculation: According to the current meter, the actual power consumption of the motor is 225KW. Most of the time will not be unloaded after the frequency conversion transformation. The power-saving rate is estimated to be about 29% according to the current unloading time.

Annual energy saving: 225KW× 29%× 7920 hours = 51.67 million degrees, 1 year and a half recyclable inverter investment

4 motor system frequency conversion speed regulation energy saving other effects

4.1 After the frequency conversion is modified, the power factor is increased.

4.2 After the frequency conversion transformation, improve the automation level, reduce the labor intensity of workers, and improve the process level.

4.3 After the frequency conversion is changed, the motor will be soft-started without any impact on the power grid, motor and machinery, which greatly prolongs the service life of the equipment.

4.4 The inverter has over-current, over-voltage, overload, short-circuit, open circuit, and lack of multiple protection functions to effectively protect the motor and power grid, making it easier to find faults and maintenance.

5 conclusions

It can be seen from the above that the technical transformation of the relevant motor system in the industrial production field with the frequency converter as the main energy-saving means can achieve energy saving and emission reduction, and at the same time ensure that the investment of the motor frequency conversion energy-saving renovation project achieves the expected economy, generally within 2 years after being put into use. The investment can be recovered. At the same time, after the frequency conversion transformation, the power consumption will be greatly reduced, and the production cost of the enterprise will also be reduced, which will enable the enterprise to embark on a virtuous cycle.