Distributed control and measurement system for natural gas metering application

Distributed control and measurement system for natural gas metering application

Abstract Application of a natural gas distribution system, using distributed control and management methods, layered on 2 management levels, each applying closed loop control methods on the batch available for control. Local controlled processes include gas quality determinations, gas flow and pressure measurement and regulation, filtering and overcompensation. Central controlled processes include data gathering from all local processing nodes, data processing and inferring of data, high level control of general gas network parameters.

Introduction

The gas distribution networks have been using local/manual control of the pipe lines to oversee the fiscal metering process, pressure control and safety standards. For this purpose, a 3-shift operation for each metering point was organized in order to keep under control the process.

2 System description; Architecture

The system provides automated and independent functioning of all local processes taking into consideration general gas delivery requirements on each region covered by the network.

The low level management takes care of each stations control zones: inlet and filtering, metering, regulation, outlet and auxiliary systems (electrical system, diesel generator, UPS, hydraulic unit, smoke detection, ESD and odorizing unit). At this level the process data acquisition is done via open communication protocols from specific instruments like flow computers with ultrasound and turbine metering, gas chemical composition analysis, water dew point, temperature and pressure transmitters. The local operator has access to controls, measured data, reports, trends, GSM alarming. All supervisory control and acquisition on each station is completely redundant in both hardware and software components.

The higher level management is done by controlling set-points and parameters of each distributed node. These set-points are calculated and estimated depending on cost calculus and gas delivery requirements and estimations of the consumers. Also at this level, all data acquisitioned at the lower level is centralized in one point. The central point operator can audit the actions of the local operators and systems and give macro-commands that have higher priority in execution than any other commands.

The whole system is based on a 4 layer design: 3 local layers and one regarding centralized control and acquisition.

The first local layer, process layer, is handling all I/O and metering instrumentation integration from the process to the control system. So here the measured physical values are read, and the output signals are controlling the actuators on each station.

The control layer role is to independently control al local processes via PLC: sequential, regulation and safety logic and algorithms. At this level the specific gas measurements (flow, energy, chemical composition) are encapsulated in a standard gas data protocol DSfg and sent to the SCADA and Fiscal servers.

The third layer is the local supervisory level. Here all data from the process is recorded and stored for a period of minimum 6 months in a circular designed buffer. This data can be viewed and interpreted by the operators. The operator can give macro-commands (start/shutdown station, close/open metering line, configure regulation parameters and set-points, set general parameters of the process) to the local control system from local or remote location via the SCADA server present on each station. Also the important concept of authorization, authentication and audit is implemented within the SCADA server software. At this critical level all hardware and software are functioning in a redundant environment.

The highest layer of the system is the central supervisory level at which all data from the distributed stations is gathered and stored. The gas measurement data coming via DSfg is connected to the Fiscal server where it is interpreted for use in the commercial activities and for statistic and estimation calculus. The process data is connected to the DCS and SCADA server which is responsible in generating of control strategy for all stations. The DCS and SCADA server stores local processes data, and intelligently controls the stations network by starting or shutting downs stations, opening and closing meter lines, configuring set-point for the gas flow. All these decisions are made by monitoring and predicting the flow needs through the network.

2.1 Local controlled processes

Procesele reglate local:

Masurare componente gaz, presiune, temperature

The basic philosophy for the fiscal measurement is to have a separate system for fiscal in order to segregate the dates (fiscal and process). Controlling and watching the fiscal measurement by MSFS (include the fiscal data transmission).

Reglare debit, presiune si calitate gaz

Suprareglare

Filtrare gaz

The Control System principles:

The basic philosophy for the Metering Station operation is to automate the process as extended as necessary.

The main processes are:

Controlling and watching the process by MSCS (include the process data transmission);

Concerning the above items, Metering Station could be operated through three different operating modes:

the manual mode: this mode shall be used only to start and stop processes and for equipment maintenance;

the auto/local mode: this mode shall be used to control the process;

the auto/central mode: this mode will be used for process observation and in future for the process control.

Diagrame

2.2 Central controlled processes

Procesele reglate central:

Preluare date de la nivelul local

The installed Metering Station Fiscal System shall satisfy the centralized networking requirements, the recording of fiscal data, centralized monitoring measurement and fiscal data transmission. The functions shall be made in order to have a secure measurement data.

In order to harmonize the recording of fiscal data, volume converters and gas chromatographs shall be equipped with a serial interface pursuant to DVGW G485 'Digital interface for gas metering devices' (DSfG interface). All thus equipped gas meters shall be connected to a measurement recorder via the DSfG data bus.

Procesare date si integrare process

Comenzi macro catre nivelul local

Diagrame

3 Methods and implementation examples of local/central control

Diagrame logice + explicarea lor in cuvinte

Exemplu de implementare; print screen din IDE

Print screen ecrane operator.

Results

Rapoarte

Screen shot cu control

5. Conclusions

Informatii fiscale despre masurare; crestere randament la distributie; reduceri pierderi; automatizare totala, statii autonnome;

Inferare rezultate si concluzii referitoare la eficienta investitiei

Adaptare:

►The local equipment for energetic data acquisition (LDAqE) is a component element of a complex supervision system for the electrical energetic flow which is implemented in an electrical station from Craiova.

►The system offers the possibility of real-time monitoring of the electrical measures, energetic consumptions on the supply lines, total station and also flaws monitoring.

►Through the possibilities that it offers, the system can work interconnected with other monitoring systems and also with other computational systems in the network, allowing this way access to information, at different decisional levels.