History Protection - Relaying in Japan

Authors: Phil Beaumont, Toshiba, UK, Tadashi Nakamura and Noriyoshi Suga, Toshiba, Japan

Digital Relaying

Digital Relaying
The advent of the microcomputer began to influence protection relaying and in the 1970s a digital relay that would use a microcomputer was actively researched in Japan.  In order to gain experience with this new technology, field tests were arranged in 1968 with participating manufacturers and utilities using a current differential relay for application on long-haul multi-terminal transmission lines. Digital data transmission using high-quality, high-accuracy pulse code modulation was employed in this relaying system as a means for transmitting the current waveform from one terminal to the other. However, the demodulated analogue waveform was used as the relay input quantity. Although the relay was extensively tested in the field, it did not directly result in the practical use of the system, but the tests did provide valuable experience for manufacturers and utilities to aid further development of the digital relay. The experience gained highlighted the need for high-quality, high-accuracy analogue-to-digital conversion techniques, digital transmission techniques, and how disturbances in the microwave network affect data transmission for digital relaying.
In 1973 Japanese manufacturers commenced with the full-scale development of digital relays using a new element; - the microprocessor. Two approaches were adopted for the digital relaying algorithm:
  One was based on the fundamental wave
   The other on travelling wave phenomena
Extensive simulation studies were also conducted to develop an algorithm which had both high computation efficiency, and excellent protection capability.
In terms of hardware, the development of a high speed microcomputer using bit slice type bipolar microprocessors was adopted because of the requirement for high speed computation. Around this time the technology of optical data transmission was introduced with its associated immunity to interference.
Based on these developments in July 1977 a field test of a current differential relay for EHV transmission lines commenced, and in 1978 the field test was extended to include a digital distance protection. The first digital relays went into service in the early 1980s (Figure 17), when a PCM current differential relay was applied to a 275kV transmission line and a digital distance protection was applied at 66kV. The use of digital relays increased, and in the mid-1980s protections using 16-bit multiprocessor designs with sampling rates of 600/720Hz for 50/60Hz devices became available. Digital transformer protections were now commercially available and in 1990 decentralized digital busbar protections entered into service. These busbar protections employed distributed bay units from multiple vendors featuring a countermeasure for CT saturation. The current data and binary status information was retrieved over a dedicated fiber-optic LAN using IEEE 802.4 (Token Bus), a level of interoperability being achieved by unifying the data format and the characteristics of the analog filters used by the various vendors.
Before moving on, it is also worth mentioning the introduction of the fault recording function to digital protection relays in 1989. Today this function is making a major contribution to the analysis of relay operations and is implemented in IEDs all over the world.
The next step in technology came in the mid-1990s with the move to high performance microprocessors such as 32-bit devices along with the adoption of 16-bit A/D converters. Higher sampling rates were introduced typically 4800/5760Hz for 50/60Hz devices. The rest you might say is history. Product ranges expanded to provide new solutions and features covering the entire spectrum of substation protection, control and automation. New technologies and techniques were embraced such as IEC61850 enabling interoperability, and along the way continuous improvements were made to reliability and cost effectiveness.

Before we conclude it is briefly worth mentioning the development of Special Integrity Protection Schemes or SIPS in Japan. The story began in 1968 with the implementation of a fault cascading prevention relay employing operational amplifiers. In 1978 a digital System Stabilising Controller SSC went into service for system frequency control. As the power system evolved and digital technology advanced, the development of other types of SIPS such as islanded operation systems and transient/voltage stability countermeasure systems took place throughout the 1980s, culminating in an Islanding Protection System providing active and reactive power balancing control. In 1999, the benefits of one such system were called upon when on the 29 of November one of the sub-power systems within the Metropolitan power system owned and operated by Tokyo Electric Power Company was separated from the main power system in an accident involving an Air Self-Defence Force jet training plane, which severed the 275kV tie transmission lines. The successful operation of the Islanding Protection System ensured that the most important customers in the metropolitan area were not affected by the power failure. The latest systems provide Transient Stability Control and Integrated Stability Control SPS/FACTS, (STATCOM).

Today Japan boasts digital products covering microprocessor technologies spanning more than 30 years, from the bit-slice MPU to the typical devices that we see today that utilize 64-bit high performance MPUs.
If this article has inspired anyone to learn more about the history of the development of Japanese relaying technology we would be pleased to share the technical papers that we used in the preparation of this review. 

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