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Energy saving analysis of MV300 converter in fan and pump applications

Introduction

In industrial production and product processing and manufacturing industries, fan and pump equipment are widely used, and their power consumption and throttling losses of related equipment and maintenance and repair costs account for 7% to 25% of production costs, as market competition intensifies Therefore, energy saving has become one of the important means to reduce production costs and improve product quality.
At the same time, the frequency converter has the characteristics of soft start, which greatly reduces the impact on other electrical equipment when the equipment is started, and can also increase the life of related electrical equipment and reduce the redundant capacity design of the entire power supply system.


Overview

Pump equipment also has a broad application space in the production field, such as the water supply and drainage system, industrial water and oil circulation system, heat exchange system of the water pumping station pool, centrifugal pump, axial pump, gear pump, plunger pump device.
Most of the fan and pump equipment are operated by asynchronous motor direct drive, which has the disadvantages of large starting current and poor mechanical protection characteristics of mechanical shock. Not only will it affect the service life, but when the load has a mechanical failure, the equipment cannot be protected instantly, and the pump often appears Damaged motor burned.
In recent years, due to the needs of energy saving and the continuous improvement of product quality requirements, coupled with the use of frequency converters (referred to as frequency converters), it is easy to operate, maintenance-free, high-precision control, and can achieve high functionality. Therefore, frequency conversion The drive-driven scheme began to gradually replace the control scheme of the damper flap valve.
The basic principle of variable frequency speed regulation technology is based on the relationship between the motor speed and the working power input frequency: n = 60f (1-s) / p, (where n, f, s, p represent the speed, input frequency, motor Slip ratio, motor pole pairs)


Energy saving calculation
For the energy-saving effect of fan and pump equipment after variable frequency speed regulation, the following two methods are usually used for calculation:
1. Calculate according to the flow load relationship curve of the known fans and pumps under different control modes and the load change on site. Take an IS150-125-400 type centrifugal pump as an example, with a rated flow of 200.16m3 / h and a head of 50m; equipped with a Y225M-4 motor with a rated power of 45kW. The flow-load curve of the pump during valve adjustment and speed adjustment is shown below. According to the operation requirements, the pump runs continuously for 24 hours, of which it runs at 90% load for 11 hours a day and 50% load for 13 hours; the annual operation time is 300 days.
Then the annual power saving is: W1 = 45 × 11 × (100% -69%) × 300 = 46035kW • h
W2 = 45 × 13 × (95% -20%) × 300 = 131625kW • h
W = W1 + W2 = 46035 + 131625 = 177660kW • h
Calculated at 0.5 yuan per kWh, it will save 88.83 million yuan per year.
2. According to the relationship between the square torque load of fans and pumps: P / P0 = (n / n0) 3 Calculate, where P0 is the power at rated speed n0; P is the power at speed n
Take the 22 kW blower used by an industrial boiler as an example. The operating condition is still running continuously for 24 hours, of which, it runs at 90% load for 11 hours a day (frequency is calculated at 46 Hz, and the motor power consumption is calculated at 98% during baffle adjustment), and runs at 50% load for 13 hours (frequency is calculated at 20 Hz , The power consumption of the motor is calculated as 70% when the baffle is adjusted); the annual operation time is 300 days as the basis for calculation.

Then the annual power saving during frequency conversion speed regulation is W1 = 22 × 11 × [1- (46/50) 3] × 300 = 16067kW • h
W2 = 221 × 3 × [1- (20/50) 3] × 300 = 80309kW • h
W = W1 + W2 = 46035 + 131625 = 177660kW • h 
The power saving when the baffle is opened is: W1 = 22 × (1-98%) × 11 × 300 = 1452kW • h
W2 = 22 × (1-70%) × 11 × 300 = 21780kW • h
Wd = W1 + W2 = 1452 + 21780 = 23232kW • h
Compared with the power saving: W = Wb-Wd = 96376-23232 = 73144kW • h
Each kilowatt hour is calculated at 0.5 yuan, and the frequency conversion can be used to save 36.57 million yuan per year.

The parameters of a factory centrifugal water pump are: centrifugal pump model 6SA-8, rated flow 53.5 L / s, head 50m;
Equipped with motor Y200L2-2 type 37 kW. The actual measured data recorded under the conditions of valve throttle control and motor speed control of the pump are as follows:
Flow L / s Time (h) Consumption of electrical energy output by the grid (kW • h)
Valve throttling adjustment motor frequency conversion speed regulation
47 2 33.2 × 2 = 66.4 28.39 × 2 = 56.8
40 8 30 × 8 = 240 21.16 × 8 = 169.3
30 4 27 × 4 = 108 13.88 × 4 = 55.5
20 10 23.9 × 10 = 239 9.67 × 10 = 96.7
Total 24 653.4 378.3
In contrast, the variable frequency speed regulation can save 275.1 kW · h of electricity compared with the throttle control of the valve in one day, and the power saving rate reaches 42.1%.


Conclusion
Practice has proved that the frequency converter used in the drive control of fans and pumps has achieved significant power saving effects, and is an ideal speed control method. It not only improves the equipment efficiency, but also meets the production process requirements, and therefore greatly reduces the equipment maintenance and repair costs, and also reduces the production shutdown period. The direct and indirect economic benefits are very obvious, and the one-time investment in equipment can usually be recovered in 9 to 16 months of production.