Over the past 10 years and longer in China, electronic electricity meters have developed from almost nothing to their current level of maturity, and now are moving forward to network meters. Accordingly, Chinese national meter standards and industry standards have gradually been established, through the efforts of both local utilities and meter manufacturers. Wasion Electronics was extensively involved in the development of the technical specification that local utilities are using, and was prominent in the push for its wider acceptance.
This article presents a brief introduction to the history in China of the communications interface in electricity meters and the communication protocol in electric power applications.
Local comunication interface – RS485 1993-1997
In the period 1993 to 1997 locally designed and manufactured electronic multi-function meters and electromechanical meters were equipped only with a pulse output interface. At that time Wasion introduced the RS232 interface, mainly for the manufacturing process and accuracy adjustment. Due to the limited needs at that time, parameter setting and meter data collecting were performed by Data-key and IC memory card.
Under a policy of schemed power consumption, wireless load control systems and related equipment have become widely used since 1995, in order to ease the stress on China’s electricity system. The traditional way to collect meter data was by fitting mechanical meters with load control terminals, but this exposed many technical defects when collecting data via pulse output interface, in particular the differences of the values in the mechanical meter’s registers and in the local control terminals. This led to disputes between the utilities and their customers.
As a result the demand grew for an electricity meter with data communication interface. Given the large investment required it was also felt that combining a wireless control system with a meter reading function would increase the life cycle of the meter and the multi-functional electronic meter was considered the best for this approach.
As a result the RS485 communication device was interfaced with the load control terminals in conjunction with meters featuring a master/slave structure and one port to multi-port communication function. Wasion’s early multi-functional meters were designed with an A/D+MCU structure, providing active energy, reactive energy, power energy and demand energy, as well as three phase real-time voltage and current, which could replace the CT and PT on the load control terminals and make whole system cost effective.
Data accuracy could be assured while delivering data from the meters to the communication equipment and control devices in data communication mode, and the implementation was readily realised on the multi-function electronic meters. As a result electronic meters rapidly came to be widely used in load control systems, which further sped the maturity of new electronic meters in terms of design, manufacturing and technical applications. In recent years the demand for dual RS485 communication interface has increased, reflecting the improvements utilities are bringing to the automation of power management and meter management.
Meter communication protocol
In the early years, the meter communication protocol was too basic to adapt for the multi-functional meter application, because it was drafted based on the requirements of meter data collection via the load control terminal. In 1995, with the introduction of the RS485 interface, Wasion Electronics drafted a Wasion Meter Communication Protocol to initiate application in electric power load control systems. In 1998, the official industry standard, DL/T645-1997: Multifunctional Meter Communication Protocol, was released by the Chinese ministry of the power industry, which initiated the gradual regulation of the activities of local meter manufacturers and system suppliers and stimulated competition.
To date this remains the standard protocol, indicating its major influence on meter applications and developments in China. Today the application of the meter communication function is becoming more mature and widespread.
Though there are still some concerns due to the limitation of the MCU technology and cost, as well as the awareness of communication security and efficiency in the initial development stage, the standard continues to prove practical after more than 10 years of experience.