An Optimum Solution for Telemetry of Distributed. Wells in South of Tehran

Transcription

1 An Optimum Solution for Telemetry of Distributed Wells in South of Tehran ESMAIL FATHI LOSHANI Engineering Faculty, Shahid Beheshti University, Daneshjoo Boulevard-Evin-Tehran, IRAN MARYAM SHARIFKHANI Automation and Communication Department, Pars Oil and Gas Company, No. 132,Fatemi Ave,Tehran,IRAN Abstract: Some distributed wells located in south of Tehran planned to be controlled locally and also from control center. One safe control method is designed for each well by means of PLCs. For overall process purposes one main controller designed for control center and wells data are logged in a server. Two operators can control and monitor wells from control center by means of two operating station. Communication backbone to exchange data between wells and control center is studied. Offline dial up solution using polling and interrupting method is chosen for this purpose. The most important part of our design is software layers and interfaces used for easy and optimum communication. Keywords: Offline, Modbus, Standard Modem, OPC Server, Monitoring, PLC, Multiport, Interrupt, Polling. 1 Introduction Helping farmers and solving high level Aquifer problems in the south region of Tehran, government decided to do a project to drill some wells and lead exploited water to farms located outside of the city. First 100 deep wells drilled and submersible pumps installed for each well. In order to supply pumps, a MCC Cabinet containing Current indicator, Voltage Indicator, Main Power Switch and some other necessary instruments for each pump was installed. Exploited water of each well finally leaded to farms by means of a canal. The most important note that should be considered is that wells are distributed in an overcrowded area of the city. In section 2 control and communication problems is discussed. In section 3 system design and solution is explained. In section 4 concluding remarks are made. 2 Control and Communication To have a good operation in an overcrowded area of the city there aren't many choices. Distributed clients make it difficult to operate each well manually by means of local operators. More over if we choose this method, at least 20 operators are needed. The best method is trying to have wells data in a control center and be able to monitor and control wells from remote in addition to local control. Data exchange between center and local is needed. Hence a safe and sufficient communication backbone has to be chosen. ISSN: ISBN:

2 3 System Design 3.1 Local Control For controlling wells, SCADA (Supervisory Control And Data Acquisition) system has been applied and a SIEMENS PLC S7222 DC with 256 kb memory cartridge is needed. The memory cartridge is for saving data. We also need an input module EM231, a modem compatible with analog line EM241 and a power supply 24VDC/4A all made by SIEMENS. In each RTU cabinet one alarm reset button, some fuses, 3 relays for outputs, light and one door micro switch are installed Instrumentation For each well in this project, we need instruments explained below. Current Transducer A current transducer with range 0 to 5 Ampere and standard output 4-20 ma is used for measuring pomp current. In warning limits PLC announces and in alarm limit sends pump stop command. Then overload message will be send to communication center. Voltage Transducer It converts pump input voltage to a 4-20 ma signal. Working range is between 0 to 400 AC volts. Pressure Transducer Pressure sensor with 4 to 20 ma output with 0 to 25 bar working range has low, high and ultra high limits. Outlet Water Volume Pulse Sensor This sensor is located in outlet well water counter and for every cubic meters volume of water it sends one pulse to control system. These pulses acquire in PLC.Equation 1 is used for calculating the flow rate (1) Limit Switch Two limit switches for high and low limits of the water in manhole has been installed List s sent to the center are water pressure, pump voltage and current, Remote/Local mode, pump off/on status, manhole water level, security signal and fault voltage signal. The control signals coming from the Control Center Room are pump On/Off command, Horn and Horn reset command. Totally there are 14 input and output signals (Table 1). In addition to input and output signals mentioned above, there are some internal signals (logical signals) like set points and alarm messages. These signals stored in PLC memory, are used in logical calculations and exchange between Control Center Room and wells. Table 1: List Function Type ZS-xxx04 Security DI LSL-xxx05 Well Low Level DI LSL-xxx06 Manhole Low Level DI FS-xxx07 Flow meter Pulse DI XR-xxx12 Auto/Manual DI XSR/S-xxx13 On/Off Pump Status DI XA-xxx15 Pump Voltage Fault DI XA-xxx16 Overload Fault DI PT-xxx01 Pressure AI CT-xxx02 Current AI VT-xxx03 Voltage AI XCR/Sxxx11 Pump on/off Command DO Horn Horn Command DO Horn_Reset Horn Reset Command DO Where t is the time interval between upcoming edges of two pulses. ISSN: ISBN:

3 3.2 Remote Control As we mentioned each well is controlled locally by PLC. In addition to that local control, one overall process controller is needed which is installed in Control Center Room. This controller controls wells with total output water flow and some other parameters. In Control Center Room One computer is used as server. There are also two S7-412 PLCs one is standby to another. This means it has software redundancy. These PLCs are installed for automatic control. Moreover there are two client computers in control room for monitoring all data, alarms and sending commands to wells (Fig 1, 2). PLC programming software for the control room is Simatic Step7 and monitoring programming software is WinCC all made by SIEMENS. Fig 3 shows system network configuration. Fig 3: system network configuration 3.3 Communication There are several communication methods to send and receive data from wells. Some of them are discussed below [1], [2],[6]: Fig 1: Monitoring software overview page Communication Backbones Radio communication method In this method radio frequencies will be used to communicate with client. Radio modems should be installed both in center and clients and frequency band license have to be taken from the RF license office to interchange data [4]. Considering to location of the project (overcrowded areas in the city) there is no available frequency band and absolutely this method does not work. GSM Communication method Fig 2: Monitoring software one Well page GSM communication method needs GSM Modems in both sides and the clients should be well covered by this network [5]. Our clients are under ground and it is clear that it is not a safe way to use this method. More over ISSN: ISBN:

4 controllers and accessories are a bit expensive. So this method is not affordable. Leased Line Method This method is using Iranian Telecommunication Center dedicated lines to exchange data. As other methods we need modems. The modems in this method are expensive so it is not economic. In addition, Iranian Telecommunication Center facilities are not suitable for taking such services. In experimental projects (for Traffic Light Controller) there were many errors and sometimes disconnections occur. So it may be not safe. Online Dialup Line method This method is using ITC dial up analog lines for exchanging data. In this method we need 100 modems in clients and 100 modems in the control center (or E1 line with necessary facilities). The main problem is the operation expenses. Each line has to be connected 24 hours in a day and it will be very expensive. Offline dialup Line Method Facilities in this method are similar to online method but functionally they are different. We have 15 lines in the center and 100 lines in clients. 10 lines are for communicating from center to clients and 5 lines are dedicated for communicating from well to center when fault occur in well clients such as overload and so on [7] Offline Design For transmitting data between wells and Control Center Room, one telephone line has been installed in each well which means 115 in total. 10 lines in control room receive data from well with polling method. So 100 well divided to 10 groups of 10 wells and these groups acquire data of 10 wells. The time interval between two connections from control center is calculated 17 minutes. If any alarm in each well occurs, the well PLC reports it with interrupt method by means of 5 other free lines. So connection is in two modes: Polling and Interrupting. Fig 4 shows the offline configuration with hardware details. Fig 4: Offline configuration There are 20 bytes data, including internal and external signals, in each moment. These data should be sampled in order to be recorded. Here the sampling time is one second. Therefore in each 17 minutes all data saved are about or 20 Kbyte. Considering data transmitting speed between PLC well and the server is about 19.2 Kbyte per second, all data will send to the center less than two seconds. Iranian Telecommunication Center counts one pulse for each connection. One pulse is 1.7 minutes. So whether the connection cut or continues it charges like 1.7 minute continuing call.hence it is beneficial this connection not to be cut and that is why 17 minutes takes for next connection Hardware Connection The idea in this design which makes it different is using most common standard modems for transmitting and receiving data with Modbus. It first seems that Standard modems that are generally transmit data with Ethernet, cannot connect to industrial modems with Modbus protocol. But this ability tested and it works. One Multiport card with 16 channels connected to the server and with the software called DialoutEZ, 16 Com port modified in the system. Ten standard modems connected to ports number 3 to 13 [8]. ISSN: ISBN:

5 3.3.4 Interface Software Some communication solutions has been studied and offline dial up line including Interrupting and Polling method is found the optimum method. Here 20 Kbytes data could be exchanged between the control center and the wells every 17 minutes. This means that with 15 phone line we can control 100 wells. There are many problems when connection between software and hardware is needed. In many cases OPC (OLE for Process Control) software is good solution. In this case, we installed OPC software called KEPServer on server that transfers needed tags for controlling modem to monitoring software WinCC. These tags are well line numbers, connection status, Dial Up and disconnect commands. PLC tags are addressed like Modbus in this software and after connecting they are transmitted from the PLC memory to the server [3]. Fig 5 shows Software layers and their connection. Standard modems that are generally transmit data with Ethernet; can connect to industrial modems with Modbus protocol. OPC (OLE for Process Control) is proper software for connecting software (WinCC) and hardware (Server). All estimated expenses of control room are 250 Euros per month for communication and 1000 Euros for two operators. Comparing with local operator method in which 20 operators are needed and total expenses are Euros per month, 8750 Euros per month are saved. References: [1] Deon Reynders, Steve Mackay, Edwin Wright, Practical Industrial Data Communication, Elsevier, NOV-2004 [2] Steve Mackay, Edwin Wright, Deon Reynders, John Park, Practical Industrial Data Network, Elsevier, FEB Fig 5: Software Layers [3] Siemens S7-200 Addressing, V4.x 10/1/01 Document v1.01, Kepware Technologies Co. 4 Conclusion [4] David Bailey, Practical Radio Engineering and Telemetry for Industry (IDC Technology), Jun 2003 There are 100 distributed wells in an overcrowded area of the city and the main problem is to acquire data from these centers on a safe communication backbone and control the process in proper way. For local controlling a control system is designed for each well. Moreover one overall process controller is needed so one computer used as a server in Control Center Room for acquiring data, controlling and monitoring the whole process. [5] Andy Dornan, the Essential Guide to Wireless Communications Applications, Prentice Hall PTR, 2001 [6] Dr. Frank Carden, Dr. Robert Henry, Dr. Russ Jedlicka, Telemetry Systems Engineering, Artech House, 2002 [7] Siemens Micro Industrial Solutions, SIEMENS, 2001 [8] Using DialoutEZ with cisco Access Server, CISCO, 2004 ISSN: ISBN: