More than five years of experience with an automatic meter reading system has benefited many customers and the system at Sola Energi AS (SE), Sola, Norway. SE is a municipal distribution utility with about 7600 customers, of which 10-15% are industrial or commercial. SE receives power at 50 kV and distributes it at primary voltages of 15 kV and 5 kV. Secondary voltages are 400 V and 230 V. Yearly load is 420-425 GWh, with a maximum load 70-75 MW.
When the demand side management (DSM) project was initiated in 1992, the majority of SE's energy meters were at least 20 years old, and a major refurbishment program was required. For the industrial and commercial customers, more cost-efficient meter reading and accounting services were needed to improve operational economy and improve customer relations in a deregulated market.
The purpose of the project was to automate the meter reading and energy accounting services for SE's customers, and to provide enhanced services for tariff management and maximum energy consumption accounting for the industrial and commercial customers. The system also was to facilitate more efficient streetlight management and provide ground-fault detection and energy-saving services to customers. In addition, we had to respond to demands from the authorities to provide hourly energy accounting based on customer options obtained in the deregulated market that contained additional consumption fees when usage exceeded a certain limit.
The automatic meter reading system, a DSM 100, is manufactured by ABB Network Partner, Vasteras, Sweden. SE uses the medium-voltage and low-voltage distribution network for communication between the master control unit (MCU) in its headquarters and the load point units (LPU) at the customer sites. The MCU defines the communication method to each LPU. All LPUs are polled from the MCU since the distribution lines have only one communication carrier line and allow just one signal to communicate at a time.
The signal goes from the MCU to the LPUs on medium-voltage and low-voltage networks by a communication carrier unit (CCU). From the MCU to the CCU the communication is via fixed lines, or by telephone when fixed lines are not available.
The system uses a specialized phase modulation technique, allowing the communication signals to propagate on the medium-voltage network through the distribution transformer and further down to the LPUs on the low-voltage distribution network. Medium-voltage and low-voltage repeaters (RPT) assure sufficient communication quality even under difficult loading and network conditions.
All LPUs continuously listen for a network call, but only the terminal with the requested address responds. Then the LPU replies with the requested data through the CCU back to the MCU. The MCU does a quality control of the incoming data and stores it in the correct register.
The MCU may also communicate changes to all the parameters in the LPU. This means that normally it is not necessary for personnel to go out to the LPU. All servicing of the LPU is done by headquarters personnel.
For meter readings the LPUs have two digital SO-impulse inputs that normally are connected to the energy consumption meter. The hourly energy consumption is stored in circuitry that can take up to 40 days of data for each channel. This means that the meters must be contacted daily at SE because of the rules in the Norwegian energy market.
The digital signals on the distribution lines have a 12.5-kHz carrier frequency. The CCU has a 350 W capacity. It is then normally easy to get the signals down to the LPUs but not always that easy to get the response back from the LPUs to the CCU. That is why all the terminals may be used as a repeater to each other if it is necessary. All this makes the system trustworthy and robust against disturbances on the lines.
Ground Fault Detection The system can be used for ground-fault detection. The two digital inputs in the LPU may be connected to a ground-fault detector. When the CCU asks the terminals for metering values, it may ask for ground fault at the same time. That kind of ground-fault detection depends on the possibilities in the software. The status at the whole substation under a transformer is then covered with one detector per substation.
In addition, the DSM 100 can control streetlights. All the terminals may be grouped in different user groups. If all the streetlights are grouped in the same user group, they may be turned on and off after a pre-specified schedule. The lights can be turned off after midnight and are energized earlier during the winter than during the summer. The light can be controlled by the relay at one of the digital outputs in the LPU. This can give a signal to a conductor out at the circuit for streetlights that turns the light on and off.
All this is controlled by MCU and works automatically when the user groups and the coupling scheme are registrated. Load control at the customer level can be done by the same routine.
At all customer installations, a LPU is connected to the energy meter to accumulate consumption according to downloaded tariff schemes (time of use) or as hourly energy counters. For the industrial and commercial customers, the maximum energy consumptions are calculated and stored.
All of the LPUs allow for monitoring of service quality, in terms of end-point voltage, the number of service outages and the accumulated outage time. The LPUs and meters are remotely configured from the MCU at SE's headquarters, allowing for efficient and flexible customization of customer pricing strategies.
The MCU includes functionality for configuration and automatic reading of the customer LPUs as well as data management and reporting features. Automatic export of data from the MCU to SE's Customer Information Systems for energy accounting and billing is possible today without adjustments.
The DSM 100's commissioning began in mid 1992 with the installation of communication equipment in SE's Sande transformer station and the commissioning of 50 LPUs at industrial and commercial customers. By the end of 1994, approximately 650 units were installed, including about 50 LPUs dedicated to streetlight management.
In 1996, SE had four medium-voltage repeaters installed and approximately 50 LPUs configured as repeaters to assure the required communication quality.
Main Benefits For the DSM 100 installation SE has identified the following economical benefits: - Automation of the meter reading, tariff management and maximum energy consumption accounting for industrial and commercial customers. - Monitoring and accounting of reactive energy consumption is not only a system dependent function. - Pre-payment schemes and service disconnection for bad payers. - Documentation of voltage profiles in the distribution network. - Enhancement of customer service quality by providing better statistics and presentation on energy usage and energy saving potentials. - Service connection and disconnection of customers in units with frequent customer shifts. - Possibilities for faster and more flexible energy pricing strategies to win and conserve customers in a deregulated market. - Assessment and documentation of service quality for the industrial customer. - More efficient meter system management through continuous monitoring of meter performance.
Conclusion About three years of operational experience have verified the feasibility and capabilities of the DSM 100 system. A meter is set up for reactive accounting and connected to a LPU. Then, standard procedure is followed. Through the automated data export functionality, SE has accomplished an efficient and flexible flow of energy usage data from the meter at the customer site through the energy accounting database and back to the customer as an energy usage invoice.
Acknowledgement The author wishes to thank Knut Godager, sales manager, ABB Kraft AS, Billingstad, Norway, for supplying additional technical details to this article.
Lars Lima is an electrical engineer with the Sola Energi municipal utility, Sola, Norway, which he joined in 1995. He has the engineering degree from Stavanger Polytechnical School. His current responsibilities include mainly network facilities and metering. Lima is a member of NITO and NEF, Norwegian technical organizations.