1、PDF外文：http:/ DESIGN AND IMPLEME.NTATION OF A VARIABLE FREQUENCY REGULATORY SYSTEM FOR WATER SUPPLY ABSTRACT The designs of the variable frequency constant pressure water supply for a single hydraulic pump and high power multiple hydraulic motors systems are presen
2、ted in this paper. This system can save energy by controlling the speed of the pipe motors which depend upon the number of consumers in use. This system was also uccessfully implemented in most of the modern buildings in. Shanghai, China. Finally, the choice criteria for variable frequency regulator
3、s for water supply system will be discussed. INTRODUCTION It is inevitable to install high level water storage systems or reservoirs for a multiple story building or residential areas. This kind of system results in increasing construction cost and cleaning problems. Nevertheless, hydraulic pumps ar
4、e used to raise the energy level of the water. The conventional high level reservoir system is in fact a pressure regulatory system. This pressure (head) is proportional to the height of the reservoir. Resistance of pipes is varying from time to time. When number of users increases, that means numbe
5、r of relief valves to be open is increased. It in turn reduces the resistance of the pipes. In order to reduce the construction cost, eliminate the cleansing problem of the high level reservoirs, and make the system simple, a variable frequency constant pressure closed loop system is presented to co
6、ntrol the speeds of the hydraulic pumps. In this paper, the designs of the variable frequency constant pressure water supply for a single hydraulic pump and high power multiple hydraulic motors systems are presented. From static characteristics of water flow system, the critical point can be obtaine
7、d to achieve the minimization of energy consumed. The implementation of this system is also discussed. The choice of variable frequency regulators for water supply system is finally presented. ADVANTAGESOFTHEPROPOSEDSYSTEM In short, the advantages of this proposed variable frequency constant pressur
8、e system for water supply are 1. In a 3 hydraulic motors system, the capacity of the variable frequency regulator is just one-third of the capacity of the overall system. The cost is much reduced. 2. Since the system consists of multiple pumping motors, they can be controlled by PLC such
9、 that the system is more reliable. 3. Energy saving can be achieved by controlling the speed of pump motors, pressure can be kept constant no matter what water flow is (from zero to its maximum capacity) 4. Each pumping imotor can be started smoothly by using this variable frequency regulator, it re
10、duces pulse current. This kind of water supply system could become a new trend in modern multiple-story building design. PRINCIPLE OF OPERATION The principle of operation was initially illustrated by a single pump system. Fig. 1 shows a block diagram of a variable frequency constant pressure system
11、which is suitable for single pump or small scale water flow system. The model type is JS.5-P1. The pressure sensor (PS) transducers the water pressure in pipes to e1ectrical signals. This signal will go to pressure regulator (PR) through an amplifier (A) and a comparator compared with the set value
12、of water pressure. The difference will come to the PID control to regulate the output frequency as well as the speeds of electric motors and hydraulic pumps. The constant pressure can then be achieved. Fig. 2 shows static characteristics of this constant pressure water supply system. Curves 1
13、 and 2 represent relationship between the pressure head (H) and flow rate (Q) for different speeds of the pump. Curves 3 and 4 represent for different values of resistance of pipe. To simply the exposition, per unit values are adopted in the Fig. 2. Hence, H*=H/HN, Q*=Q/QN where HN and
14、QN are the set values of head and flow rate. In this system, both flow rate and the resistance of pipes are varying because the flow rate is proportional to number of valves to be opened. Curve 3 represents the resistance of pipe when the flow rate reaches the maximum point. It intercepts with
15、 the H* - Q* at point a , which is the set point for operation. Curve 4 is for resistance of pipe when the flow rate is less and only part of valves to be opened. If there is no frequency regulator, it works at point b' only. At this moment, the head pressure exceeds the set value. The flo
16、w rate Q is proportional to the speed of the pump, n. Head pressure H is thus proportional to the square of the speed, n2. The speed of the pump can be controlled by the frequency regulator. It becomes the curve 2, which intercepts curve 4 at point b, it is a new set (working) point. At this time, t
17、he set speed should be n* = n/nN = K (K<l). Obviously, the point b is lower than point b'. It in turn means that H at point b is less than that at point b'. Hb < Hb' It achieves the purpose of energy saving. FURTHER MODIFICATION This JSS-P1 model was suitable for single
18、 pump water supply system. When the flowrate is little, the pressure can be much reduced. For example, Hp* varies from 1 to Hp-* which is less than 1 (Hp-* < 1). It is able to save much energy. From this working principle, it was modified to suit a large scale multiple pumping water supply system
19、. A new model of JS5-P2 was then developed. Fig. 3 shows a block diagram of a variable frequency constant pressure system consisting of 3 same capacity pumps. It was modified from the JSS-P1 model. It is designed for multi- pumps water supply system which programmable logic control (PLC) is involved
20、 such that the number of hydraulic motors in operation can be determined by the flow rate. The rest of motors are in stand-by mode and the energy saving can be realized. From Fig. 3, the system was composed of pressure sensor (PS), pressure amplifier (A), pressure regulator (AP), signal identifier (
21、AI), programmable logic control (PLC), and frequency regulator. The main feature of this system is that one set of variable frequency regulator is in use to control one hydraulic motor. The rest is idling at starting. If the water flow is within the preset range. This motor is running according its
22、characteristic curve. When the flow rate is increased, The second motor will be smoothly started. The preset value of pressure in pipes can be maintained. There are three values for operating these motors, 0-33.3%, 33.3-66.6% and 66.6-100%. In brief, the first pump motor will work if the flow rate f
23、alls within 33.3% of operation. The operating region is within curves 1 and 4 in the Fig. 4. When the flow rate increases, beyond 33.3%, frequency regulator keeps the output frequency at 50 Hz, PLC will control of on-off state of the motors such that the first pump motor is supplied by the mains. Th
24、e speed of the first pump motor runs at rated speed. The frequency regulator also set the second pump motor in stand-by mode. The operating region of the second motor is within curves 2 and 5 in the Fig. 4. When the flow rate is continuously increased and beyond 66.6%, and the frequency regul
25、ator reaches its rated frequency 50 Hz, PLC will command the second motor to connect to the mains again and the third one at stand-by mode. The operating region of the third one falls within curves 3 and 6 in the Fig. 4. If the flow rate is reduced from 66.6% to 33.3%, PIX will command to one of the
26、 pump motors cut off from the mains. When the flowrate further reduces, and less than 33.3%, there will be only one motor connected to the mains. From the working principle, the three pump motors are operated in turn to meet the requirement of energy saving. CRITERIA FOR FREQUENCY, REGULATOR F
27、or the load of the hydraulic pump, the torque is proportional to the square of the motor speed, it is also proportional to the square of the supply frequency, f2. To a electric motor, the torque is equal to Cm *m*I2*cos, where Cm, is a constant, m, is the magnetic flux of rotating field, I2 is the r
28、otor current, and cos is the power factor of rotor circuit. I2 normally cannot exceed its rated value.If the voltage drop in the stator is negligible, $, will be proportional to supply voltage V. In order to maintain, the supply voltage V should be required to be proportional to the square of the fr
29、equency. Therefore, the characteristic of V versus f should be set to be a quadratic relationship. CONCLUSION This type of variable frequency constant pressure closed loop system for water supply was designed and implemented in Shanghai, China. The performance was proven satisfactory. A copy of a photograph of this system was shown in Fig. 5. All four advantages of this proposed system were fully realized. This system is one of the energy saving methods in tall building design.
