In many heavy industry enterprises, the water supply system is a large energy-consuming household, and more than 90% of them are used for pumping water. How to improve the operating efficiency of the pump and reduce energy consumption in a reasonable and effective way is an important part of improving the economic efficiency of the enterprise. There are many ways to regulate the amount of water in a water supply system. The frequency conversion speed regulation technology is due to its high reliability. The advantages of better energy-saving effect and low price are gradually accepted by the majority =5.

1 The basic conditions for water pump speed regulation In the water supply system, the flow in the pipe network changes frequently, and the change in the flow in the pipe network will cause a large change in the water supply pressure. Can not meet the needs of water users 3 The methods of controlling flow changes have traditionally been the following two.

1.1 Adopt the adjustment of the opening degree of the outlet valve to control the change of the water delivery volume, which is to adapt to the change of the flow in the pipe network by changing the shape of the pipeline characteristic curve.

The change of the shape of the pipeline characteristic curve is obtained by increasing or decreasing the transmission resistance of the outlet valve. A pressure difference AH is generated on both sides of the outlet valve. The product of this AH and the instantaneous water delivery Q. AHQ is the energy loss of the outlet valve during the adjustment: this part of the energy loss is charged by the motor to the power supply. Therefore, when the flow rate is adjusted small, the power drawn by the motor does not decrease proportionally, because the outlet valve is in this In this case, a considerable amount of electrical energy is consumed = the relevant data shows that when the flow adjustment range is 50% 90%, the power consumed on the outlet valve can reach 20% 60% of the motor input power, obviously. This is a very uneconomic control method.

1.2 Adopt Taiwan education to change the parallel operation of water supply units to control the changes of pipeline network and pressure: In general, several units are set in the flood pump room, and their water volume can be different. But the rated head is basically the same: a variety of different ways to set up to full. Different flow requirements: This control method also has its drawbacks, that is, when the number of running units is less than the set value, the working head of the running machine pump will be lower than its rated head, so that it is in a low-efficiency operating state. Changes in water supply will cause changes in pump operating conditions. Especially when the transmission loss on the pipeline occupies a large proportion, the change of the operating point is more obvious, and the water chestnut falls into the low-efficiency zone. The operation will be deeper: for the above situation, the use of speed control device for adjustment can effectively improve the pump The operating efficiency of the group. At present, there are mainly three kinds of speed regulating devices used in large systems: (1) thyristor cascade speed regulation 2) frequency conversion speed regulation; hydraulic coupler speed regulation. Among them, the speed regulation of the hydraulic coupling is a mechanical speed regulation. Due to its complicated mechanical structure and poor speed regulation effect, it has been gradually eliminated: cascade speed regulation, especially internal feedback cascade speed regulation, is mainly used in some high-voltage equipment with low speed regulation accuracy requirements and small speed regulation range. = On small and medium-sized low-voltage motors, frequency conversion speed regulation technology is gradually widely used because of its wide speed range, high precision, and easy automatic control. This article mainly analyzes the frequency conversion speed regulation device.

2 Determination of the number of frequency conversion speed regulating water pumps The application of metallurgical automation and microcomputer application of variable speed regulation technology in water supply system The number of speed regulating water pumps is mainly determined by the specific operating conditions of the water supply system itself. The main points are as follows: The capacity should be the largest capacity of the water supply unit of the pumping station.

The range of water pump speed regulation should consider that it still runs in the high-efficiency area after speed regulation. The speed regulation ratio of the water pump should meet the requirements of the following formula.

Kn- due speed control ratio H-full pump head before speed regulation; Hmax-upper limit of full head in the working area recommended by the pump; Hmin-full head in the working area recommended by the pump lower limit.

After the speed regulation ratio is determined according to the above formula, the flow adjustment value of the corresponding pump has also been determined. If the flow that needs to be adjusted in the pipe network is greater than this value, the number of adjustment pumps should be increased accordingly. The calculation formula is: n- the number of adjustment pumps; the required adjustment flow in the AQ pipe network; Q,-each The flow adjustment value of a speed regulating pump in the high-efficiency speed regulation range.

3 Energy-saving principle and benefit analysis of frequency conversion speed-regulating water pump Energy-saving of frequency conversion speed-regulating water pump is reflected in the following aspects.

3.1 Compared with the power frequency pump, after the speed of the water pump is adjusted, the working point of the water pump changes and enters the high-efficiency area, so the efficiency of the water pump becomes higher.

3.2 On the premise of satisfying the supply pressure, the water supply of the pump due to the speed regulation is the head-flow curve corresponding to its speed, and uk2 and k3 are the trajectory curves of the equivalent point of the pump. According to the similarity law, the ratio is: H= k, Q2. Therefore, for any point on the rated curve, the trajectory of its similar operating point (equivalent point) is a parabola passing through this point and the origin. For the pipeline resistance curve, H., the required net water supply pressure. In fact, due to the complexity of the water supply network, there is generally no such ideal resistance curve. Here, the users are treated in a centralized manner, and the network is simplified into a main line.

It can be seen that when the flow rate is Q, the water chestnut head is H, and the operating efficiency is when the flow rate becomes, if the pump is operated at power frequency, the operating head is, the efficiency is the operating point a); if the speed is adjusted to n3, then When the flow rate is changed, the running head of the pump is H, and the operating efficiency is the working point c).

For the flow rate of Q:, the difference between the energy consumption before and after the speed regulation is: (H2-H,) Q: the flow unit is l3m3/d, the head unit is MPa. N, multiplied by the running time, set at the flow operating time Power.

When the flow rate drops to Qh, if constant pressure water supply is used, the speed is adjusted down, and the water supply head is still H at this time. Obviously, under the premise of ensuring the water supply pressure, the constant pressure water supply takes into account the surplus pressure caused by the increase of the pump head due to the reduction of the flow rate (middle ah section), but does not consider the reduction of the pipe head loss caused by the reduction of the water volume to increase the surplus Water pressure. Therefore, for the case where the pipeline transmission loss in the water supply system accounts for a considerable proportion, it is best to set the pressure point at the end of the water supply line.

The loss of the frequency conversion speed regulating device itself is generally 4%-5%, and this factor should also be considered when performing benefit analysis.

4 Some points to be noted when using frequency conversion speed regulation device 4.1 Use frequency conversion speed regulation device to determine the reasonable plan according to the characteristics of each water supply system process, try to avoid the speed regulation pump running outside the high-efficiency zone for a long time or the investment recovery period is over Long (generally should not exceed 5 years).

4.2 In actual operation. The parameter values set by the frequency converters used in each water supply system should be determined according to their different process characteristics. For example, for the constant pressure water supply of the water supply line, the set acceleration and deceleration time should not be too small, otherwise the motor will often work in an overload condition when the water supply fluctuation range is large, and the constant level water supply for the pump station suction well , The acceleration and deceleration time can be appropriately reduced, thereby reducing the speed adjustment time to minimize the fluctuation of the water level.

4.3 In the water supply systems of many heavy industry enterprises, the working environment of the equipment is poor, and dust, ambient temperature, and ambient humidity will have a greater impact on the service life of the inverter, and these problems should be paid attention to in use.