History Protection - Relaying in Japan

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

Introduction
No article on the history of protection relaying in Japan would be complete without a brief introduction to some of the unique attributes of the Japanese power system. The peak demand in Japan is around 180GW and as illustrated in Figure 4, Japan comprises four main islands Hokkaido, Honshu, Shikoku and Kyushu along with Okinawa and many other smaller islands. The main islands are connected via AC/DC converters with the exception of the connection between Kyushu and Honshu,  which is connected via a 500kV AC transmission line rated at 5570MW. The undersea DC links from Honshu to Hokkaido and Shikoku to Honshu are rated at 600MW and 1400MW respectively. Shikoku is also connected to Honshu via a 500kV 2400MW overhead transmission line.
There is also an AC/DC 300MW back-to-back converter located in Minami-Fukumitsu in the center of Japan to improve power system stability in the area of the Hokuriku-Kansai-Chubu interconnection. Frequency converters are installed approximately in the center of Honshu Island to connect the 50Hz and 60Hz systems, each one serving half of Japan. The frequency conversion stations are located in Sakuma 300MW and Shin-Shinano 600MW. There is a third frequency 300 MW converter  also in Chubu in Higashi-Shimizu (not shown in Figure 4.)
Japanese engineers are often asked why Japan is separated into 50Hz and 60Hz systems. The reason is quite logical and of historic interest. Prior to 1890 the Tokyo area was served by a DC network owned and operated by Tokyo-Dentou ho began to supply electric power in 1887. In the early 1890s they purchased an AC generator from AEG Germany. The generator was a 3-phase machine rated at 3kV and 265kW operating at 50Hz and was installed in the Tokyo area. In Osaka, in the west of Japan, Osaka-Dentou purchased a 60Hz generator rated at 2.3kV and 150kW from GE in the United States. The network grew up around these first installations into the system found in Japan today. Another interesting feature of the Japanese power system is that the topography evolved from that of a radial network and today features many multi-terminal and double circuit lines which explains the widespread use of current differential protection and multi-phase auto-reclosing described later in the article.

Early Beginnings
The advent of protection relaying in Japan began more than 100 years ago, in 1907 with the manufacture of the first plunger type protection relay shown in Figure 2. The first application was for the 55kV Yatsuzawa line in Tokyo.
This was followed by the introduction of the induction disc type overcurrent protection shown in Figure 1, which was manufactured in 1920. The sensitivity of operation and the accuracy of the operating time were dramatically improved compared to that of the plunger type relay.
During this period the construction of large power plants was widespread in response to an increase in the demand for power which resulted in the rapid expansion of the transmission network. A large number of parallel line configurations were adopted to meet the requirement for high reliability power transmission. With regard to protection, great importance was attached to selectivity and therefore in the early 1920s a transverse differential type protection relay was adopted - an advanced protection scheme at the time giving much improved selectivity to that of overcurrent protection.
The transverse differential relay utilizes the phenomenon that the currents in parallel lines flow at almost the same level under both normal and external fault conditions, however under internal fault conditions the balance between the parallel lines collapses as shown in Figure 5, because a larger current will flow in the faulted line. This type of protection has been applied in other countries such as the U.S. as early as 1938 but is now so widely applied in Japan that it can be considered a characteristic feature of protection relay engineering in Japan. The principle has since been implemented in numerical protections and is typical of the protection schemes used for 66/77kV applications to this day.
Cultivated through the development of the plunger and induction disc type relays the technology employed in electromechanical relays advanced rapidly and resulted in a high performance induction cylinder device offering faster operation, better accuracy and increased sensitivity for the post-war period.
The arrangement of the induction cylinder or induction cup type relay is shown in Figure 6. This relay has magnetic poles which consist of iron cores and coils surrounding a rotating cylinder in the center. The rotating flux generated in the magnetic poles causes the cylinder to rotate. A high operating speed can be achieved because the rotating cylinder is hollow and the moment of inertia is small. Following earlier experience in overcurrent applications, the induction cylinder arrangement was adopted in the "Mho type distance relay'" developed in 1951.
Network Expansion
Following the increase in power demand in the post war period, planning for the construction of the EHV system began and the 275kV 320km trunk line between Narude power station in Toyama prefecture and Hirakata substation in Osaka prefecture went into operation in 1951. The protection scheme was the first directional comparison carrier scheme using a Mho type distance relay as shown in Figure 10.
A directional comparison scheme using power line carrier communication is illustrated in Figure 9.  The scheme isolates the faulted section of the power system when the protection terminals judge that a fault has occurred within the protected section. Therefore, this scheme requires that each terminal has the means of transmitting the result of the directional decision to the opposite terminal. For transmission line applications, power line carrier communication was used to transmit the information using a high frequency signal over the transmission line itself.  The scheme was installed in the Kansai area in 1952 on the Shin Hokuriku trunk line which used single phase auto-reclosing for the first time in Japan.
The directional comparison scheme was in use for many years in Japan for the protection of trunk power system EHV transmission lines. Microwave transmission was adopted for the Kushiro trunk line in Hokkaido in 1958 for the first time providing a new means of communication between protection terminals. Following experience gained with vacuum tube technology in a phase comparison carrier relay system in 1956 the protection relay advanced through innovations in peripheral technology.  A protection relay using transistors was developed in 1959. This was referred to as a static type relay when compared with the aforementioned relays which were all various forms of electromagnetic mechanical relays with moving parts. In 1962 the first transistor based distance protection was launched using germanium transistor technology. This was a physically large device with a high power consumption with limited popularity. However by 1971 subsequent evolutions had led to smaller, lower power consumption devices and transistorized distance protection was in widespread use.

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