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GPRS solution of remote power meter reading system
For more than a hundred of years, meter readers of Power Company knocked the doors one by one to record the meters. This is a trouble for both the power company and the customers. Nowadays, many customers pay for the power through electronic prepayment card, which releases the staff of Power Company from meter reading door by door. However, data statistic and real-time supervising are still problems for power companies.

I. Solution introduction
Through the GPRS network system of China mobile, power companies can transmit the power system data, both from industries and civilian, to supervise center of a city or province.
Thus, by the simplicity and efficiency of GPRS network, power companies can realize centered supervisory control and distributed management of power measuring equipments.
China mobile GPRS system supports wireless IP connection in WAN. Building remote meter reading systems based on the GPRS service platform is a good solution that effectively
utilizes the networks to transmit wireless data, cuts down the construction cycle, reduces the construction costs and easily to install and maintain the equipments.
GPRS remote meter reading system comprised of two components: the power distribute center at power company and the power meter sampling station at residents. The data from power meter are transmitted through the GPRS/GSM network..

All customers’ KWH meters transmit power data to the meter concentrator by RS485. The concentrator connects to the GPRS transparent data terminal by RS232. The meter data, after packaged under protocol, are sent to China Mobile GPRS networks through which the data package arrive at the power distribution center eventually. In such a matter, there is a real-time connection between meter data and power distribution center.

II. Advantages of solution
GPRS remote meter reading systems take advantages as follows:

1. Hard Real-time
GPRS, as an always online communication, has no delay when transmitting data. What’s more, GPRS can receive and process multiple requests from all data centers synchronously without polling. All these features satisfy the real-time requirement in data sampling and transmitting.

2. Remote control
Through the bidirectional system of GPRS, Power Company can realize remote control of the KWH meters such as parameters adapting and switch control, etc.

3. Low cost
Based on the GPRS public wireless network platform, the only thing a power company needs to do is installing the terminal. Without layout of special connection, the system need less
investment in early stage and can be updated easily in future. So, this system features as fast cost-recovering and low cost in maintenance.

4. Covering wide area
GPRS is a kind of WAN. As long as the meters are under the cover of GSM/GPRS, the power company can control and manage the procedure of meter reading. In addition, there are
no limits on expansion and tie-in places, which satisfy the requirements of country towns, mountain areas and inter-area connection.

5. Huge transmission capacity
The power distribution needs to keep real-time connection with each meter reading concentrators. For there are a lot of concentrators, the system should have the capacity to deal with data outburst. Beyond the question, GPRS is an expert in this aspect.

6. High transmit rate
The data transmit rate from each concentrator requires ≥10Kbps. At present, GPRS data transmit rate is about 40Kbps (with a theoretical rate up to 171.2Kbps) and can easily reach
such requirement.

7. Low communication cost
By calculating communication fees per month, the operational cost is reduced to a low level.

III. System Construction
For GPRS is a data packet communication network based on IP address, the host computer at power distribution center are assigned fixed IP. All meter concentrators communicate with this host by GPRS module.

(1) system composition
1. User terminals
All customers’ KWH meters transmit power data to the meter concentrator by RS485. The concentrator connects to the GPRS transparent data terminal by RS232. The meter data, after packaged under protocol, are sent to China Mobile GPRS networks through which the data package arrive at the power distribution center eventually. In such a matter, there is a
real-time connection between meter data and power distribution center.
A concentrator connects to the meters by RS485 connector. A concentrator can connect to single meter as well multi-meters. It samples, saves, preprocesses or transmits the meter
data to distribution center. At the same time, a concentrator can execute control operations according to the remote instructions from distribution center.

2. Distribution center
Servers at distribution center are configured fixed IP and connect to GPRS network through DDN supplied by a province branch of China Mobile. For DDN is of high bandwidth, distribution center need not to expand bandwidth even when the concentrator number increased.
Data received by the RADIUS server at distribution center through GPRS network are AAA authenticated first, then transmitted to the host computer where they are decoded, processed and displayed.

The host computer manages the service and accounting operations, accomplishes data verification, computing, saving, analysis and management etc. At the same time, a host computer supervises the use of customers real-time to assure the benefits of Power Company as well as alerts when exceptions occur.

3. GPRS/GSM mobile data transmission network
Data from meter concentrators are decoded to the format that can be transmitted on the public network by the GSM connector module. After that, the data are transmitted to the IP address at distribution center through China Mobile GPRS network.

For GPRS is a data packet communication network based on IP address, the host computer at power distribution center are assigned fixed IP. All meter concentrators communicate with this host by GPRS module.

(2) System solution
Power meters, by GPRS transparent data transmission terminal, connect to the distribution center through GPRS network.
China Mobile’s STK card is used in all meters. In order to identify customers and maintain their materials, distribution center registers all meter concentrators. Each concentrator runs system software to support data sampling and transmission real-time and 24 hours a day.
All concentrators authorized by the power company can adopt this system:
 1) Concentrators must use the China Mobile uniformed STK card which only used to communicate data with distribution center.
 2) WIXUM tech. offers GPRS mobile data communication terminal.
 3) Customer registration: match the requirement of Power Company

We recommend that province level distribution uses VPN through public network to tie-in mobile GPRS network.. This solution is featured as low cost and high safety, speed and QoS
are assured as well. Other solution, such as by using GPRS dedicated line to tie-in GPRS network, is also safe and stable, but with high cost.

(3)Product features
WIXUM series GPRS wireless transparent data transmit unit are used in the system. The terminals, based on China Mobile’s GPRS network, take advantages with high quality and
stability. The terminals can connect to computers, RTU, PLC, GPS receiver, digital camera, and data terminal by standard 232 connector 171Kbps. The terminals have capacities of remote diagnosis, test and supervise, which satisfy the control center to sample data and control remote concentrators.
 1) Support three GSM/GPRS frequency at 900/1800/1900.
2) Connector: RS232, RS484, PCMCIA.
 3) Practical transmit speed at 40Kbps and theoretical speed up to 171Kbps.
4) Support operating systems such as Windows95/98/2000/XP and Linux.
 5) Support transparent data transmit and protocol translation.
 6) Support VPN security.
 7) Flexible installation and easily and robust to use.

(4)Security solutions
The power meter remote reading system requires extreme safety and stability. Safety means to protect the system from intended or natural destroy. Stability means the system can run all 7×24 hours without break even though there are faults of either hardware or software.
 1) APN private network: As SIM card are unique ID, customers are authorized to join the VPN to avoid illegal invasion. By using the China Mobile’s APN and binding SIM cards to it, only the authorized customers with the SIM cards can access the VPN. Other common GPRS terminal on cell phones can not access the APN.
 2) For special customers, specific user ID and password are assigned to their mobile terminals. Other customers without such ID and passwords can not log in the system, which enhanced the security.
3) Firewall software are installed to filter data to assure safety.

IV. Conclusion
Remote meter reading has been a headache for power companies long ago. For there are many transformer substations distributed in large areas, the power companies had to invest a lot of money and human resources. The solution is using the GPRS based remote meter reading system. By this system, the power center can sample and analysis data from customers as well as control and maintain the remote equipments, which saves a lot of cost of materials and human resources.
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