Abstract

 At present, the existing water supply system in the town of Mospino is not automated, i.e. controllers use remote control devices to start up and shut down the pumps supplying  water to the water towers,  thereby, generating pressure in the water supply network. At the  outlet  of the water towers, the pressure which is determined by their height,  is limited and inconsistent.  Under these operating conditions of the pumps  the pressure remains either constant  throughout the day,  or sharply decreases when the pumps are shut down.  Besides, it is important to note, that the pumps  begin to operate in the mode of direct starting up,  which may result in serious failures, such as hydraulic shock and mechanical shock loads onto the pump engines.  The need to control the pump efficiency in water supply systems  is  determined, first of all, by a variable schedule of water consumption during the day. [2]

The objective of the present work is to conduct research into the dynamic properties of the automated control water supply system, when using a regulated frequency drive for the pump unit.

The  main  objectives of the research:

1. To analyse the existing methods and solutions in terms of automation of the water supply process in small towns.

2. To  study  ways of controlling  the asynchronous engine by using frequency converters and equipment  implementation of the system.

3. To develop and do research into the mathematical model and the structural scheme of the control system based on the above model for the municipal water supply.

4. To substantiate the parameters and structure of the system and do research into its dynamic properties.

The anticipated scientific innovation is water consumption control,  based not on daily schedules, but on actual water consumption, the consumption data coming from the sensors and being transmitted to the frequency converter, which, in its turn, will control the speed of the asynchronous pump engine.

To develop the structural scheme of the system and automated control of the municipal water supply, to do research into its work and show that with its implementation there will be achieved positive feasibility results. Namely, reduction of electrical energy  consumption   due to replacement of the unregulated pump drive with the variable frequency one and uninterrupted supply of necessary amount of water for water consumers.

The NGOs ELLAT company is Latvia's largest manufacturer of automation equipment for water supply enterprises. For efficient management and control, NGOs ELLAT proposes  the system which is unique and has been proven at numerous enterprises. The system ensures  collection of  information from cotrol sites, its analysis and output of issue control signals agreed with an operator or automatically.

The introduction of the control system for the municipal water supply  makes it possible to  reduce electrical energy consumption by 10  to 15percent,  decrease emergency loss, quickly respond to instant changes in water consumption, reduce the cost of maintenance and detection of  troubleshooting. Economical mode of pump operation is achieved by installation of frequency regulators. The main functions, apart from optimization of pump operation and  control systems, include pump alternation, hooking up to the reserve unit,  the possibility to operate several pressure installations  –  for every certain time of the day,  control of the frequency converter and the electrical parameters of the pumps. To automate the second rise pump stations, the pump control station is produced. The operation control is performed by the control system for pump units SUNA-B. The station includes a frequency control, a switchgear, a controller, and means of communication with the controllers`  center. The controller makes it possible to program the sequence and order of pump operations, as well as regulation modes [5].

The stations and automated control systems designed by the DK-Electro company , have been   installed and are successfully operating in Ukraine, the total power of the frequency converters  being  more than 15 MW. Below are just  a few examples of the installed  automated control systems, which will help to estimate the level of the produce  manufactured by this enterprise, as well as the quality of its  assembly.

 The site is presented by  the automated control system which includes the four pumping stations  of the second rise at the CE "Chernigovvodokanal",  in the  framework of realizing the project for  the municipal infrastructure development.

The automated control system for pump stations sites  is designed to maintain the set pressure by controlling the rotation speed of pump units, to ensure regular and timely water supply to the sites of Chernigov, efficient and economical use of energy resources, while supplying water to the sites of Chernigov; integrated automation control, collecting, processing, storage and display of protection information; using it as an accomplished cotrol unit in the automated water supply system.

The automated control system (ACS) ensures:

•    automatic maintenance of the operating pressure in the discharge pipeline with the operation mode from the frequency  converter;

•    control mode:  from the main control panel (LGU); from the local control panels (PMU); from the central control cabinet (TSSHU);

•    mode of operation: "Manual", "Automatic."

Remote control,  management and visualization is performed by means of the main control module MCM, the microprocessor device PLC with a color graphic display TFT LCD 5.7 inch resistive TouchScreen being mounted on it.

The possibility of operation in the mode of  frequency converter, as well as in the mode of  starting up is also ensured.

Protection functions are performed by the complex set of automatic switches,  ultra-fast fuses, and a frequency converter, whereas in the mode of direct starting up by MPZK microprocessor devices [6].

The operation site is the automation system for pump units of the second rise in a residential area. The control site is presented by the 5 pump units (NA) with different capacity values:

•    D -500-63 with capacity 160kW  – 1 unit;

•    D-800-56 with capacity 200kW  – 2 units;

•    D-1250-65 with capacity 315kW – 2 units.

The automated control system ACS-SM-DC-5NA 315 kW, which is shown on fig.1, is designed to maintain the set pressure by controlling the rotation speed of any two of the five pump units.

 The possibility of operation in the mode of  frequency converter, as well as in the mode of  start-up is ensured [6].

To solve the task under review, it is necessary to use a regulated electric drive for the pump  station of the first rise. An important distinction of the operation technology is that the pumps work not for the water supply network, but for the water towers. However, it should be noted that nowadays there is a tendency to avoid using water towers. In modern direct-flow "non-tower" water supply systems, the main thing is  a frequency converter that controls the pump engine.  The method of water supply without using  water towers can be successfully  applied for supplying water  to small communities. [1]

In this system, it is proposed  to  turn a water tower into a reserve as an emergency source  of water supply  and pump water directly into the water supply network. In this case, the pressure value will be reduced, since there will be no  regular need to raise  water to the tower at a height of 15-25 m, and it will be more efficient to supply water directly into the water pipeline. In case of lack of pressure in the water supply network  or electricity failures, it will be possible to open the valve at the outlet of the reservoir  to make water supply  available for consumers.

Pic. 2 –  General scheme of water supply system

Pic. 2  shows the following designations: FI – frequency inverter, FS – water flow sensor. Animation on pic. 3 shows the principle of operation of the system.

Pic. 3 – Animation changing the water flow under the influence of the FC to the submersible pump motor (SP). Animation parameters: count of frames – 5, size – 168 kB, the number of repetitions – 5

At the next stage of the research,  there was developed a model of asynchronous engine  adjusted to the frequency converter, the Matlab Simulink package (pic. 4)

By using the Lookup Table block, the engine control has been achived in accordance with  the  exponential law of alternating voltage and frequency; by using the  Sine Wave Function block  a three-phase voltage source has been generated. From the frequency converter,  voltage is supplied through the Controlled Voltage Source blocks to the three-phase asynchronous engine, the characteristics of which are specified in the Asynchronous Machine block.

     It will be necessary to add to this scheme the control site – the water supply system,  and to adjust the speed of the engine with regard to the actual water consumption, its data being obtained  from the consumption sensor. In the mathematical model of the system, there will be achieved the dependence of the consumption value on the voltage value brought by the frequency converter to the asynchronous engine.

By the time of having written this research paper,  the master's  diploma work  had not yet been completed. The date of completion is December 2013. The full text of the paper and materials on the subject can be obtained from the author or her research supervisor after the above date.

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