Milestones:Kurobe River No. 4 Hydropower Plant, 1956-63

Kurobe River No. 4 Hydropower Plant, 1956-63

Kansai Electric Power Co., Inc., completed the innovative Kurobe River No. 4 Hydropower Plant, including the subterranean power station and Kurobe Dam, in 1963. The 275kV long-distance transmission system delivered the generated electric power to the Kansai region and solved serious power shortages, contributing to industrial development and enhancing living standards for the population.

In May 1951, almost six years after the end of the World War II, the Kansai Electric Power Co., Inc. was
established by the Electricity Utility Industry Law, as one of the nine monopolistic electric power
companies of Japan, with a capital of 1,690 million yen (cf. 1,460 million yen of the Tokyo Electric) and
a total power capacity of 2,284 MW, with 1,130 MW by 130 hydropower plants and 1,154 MW by 16
thermal power plants (cf. 1,786MW=1,441MW+345MW of the Tokyo Electric), each the greatest of all
power companies. As for 130 hydropower plants, the numbers of pondage-type and reservoir-type
plants were 32 and 1, respectively, and hence its hydroelectric generating capacity was heavily
vulnerable to drought. On the other hand, as for 16 thermal power plants, all of them were built mainly to
supplement the shortage of hydroelectric capability in the drought season of winter, and moreover they
could not output any more than 70% of the installed capacity due to cumulative mechanical degradation
during the postwar confusion as well as lack of coal caused by the Korean War in 1950-1953.
In August 1951, just after the establishment, the Kansai Electric suffered from exceptional drought, and
the power shortage became suddenly worse in the service area of the Kansai Region to such a serious
extent that the worst case in Japan occurred there in September 1951 through March 1952, in which two
and three days’ power cut per week had to be imposed on industrial/commercial and residential
customers, respectively[2]. Furthermore, to satisfy the power demand that was growing rapidly with the
vigorous progress of postwar reconstruction, the Kansai Electric had to make every effort to construct
new hydropower plants as well as to reinforce the generating capability of thermal power plants.
To overcome such terrible power shortage, the Kansai Electric started large-scale geographical surveys
for constructing the Kurobe River No.4 Hydropower Plant, henceforth referred to as the Kuroyon, a well known Japanese alias. The upper basin of the Kurobe River (see Fig. 1) originating in the Northern Japan
Alps of 3,000m order altitude has an annual precipitation of 3,800mm, an average river slope of 1/40,
and an average snowfall of 5m, and therefore it had long been regarded as an ideal site for hydropower
generation. Eventually, Mr. Shiro Ohtagaki, the President of the Kansai Electric, announced in autumn
1955 a big project of constructing the 250 MW class Kuroyon that would harness a huge reservoir
created by a dome-shaped arch dam, called the Kurobe Dam, at an elevation of 1,448m in the midst of
rugged Kurobe Gorge in the Chubu-Sangaku National Park.

Subsequently, the postwar Japan’s largest-class project of constructing the Kuroyon and the Kurobe Dam
began in July 1956. The long-awaited concrete placing began in September 1959, and partial reservoir
filling started in October 1960. Immediately after that, the Kuroyon began partial power generation of
154MW output in January 1961, using two Pelton turbines, each with the world’s largest output among
those of the same type, and then increased output to 234MW in August 1962, using additionally a third
Pelton turbine. The combined project of the Kuroyon and the Kurobe Dam was completed in June 1963,
after a total investment of 51.3 billion yen (142.5 million 1963 US dollars) and a labor output of 10 million man-days. The Kuroyon’s generating capacity was finally expanded to 335MW in June 1973 with the addition of a fourth Pelton turbine at a cost of 1.4 billion yen (5 million US dollars).

The construction of the Kuroyon and the Kurobe Dam paved the way for a new phase of downstream
development by means of huge controlled water storage. Specifically,
(i) the total hydroelectric capacity in the Kurobe River Basin has since grown from 273MW to 969MW,
by building a total of six new hydropower plants for more effective use of river flow as well as by
reinforcing the generating capability of existing plants through efficient flow control, and
(ii) the agricultural utilization of water resources has since been performed by the irrigation drainage and
alluvial soil improvement in the Kurobe River Basin.
In parallel with the construction of the Kuroyon and the Kurobe Dam, the Japan’s first 275kV long
distance power transmission system covering 350km from the Kurobe River Basin to the Kansai Region
was repeatedly reformed, and finally completed in October 1973 by installing the Japan’s first 275kV
series capacitor banks at the Johana Switching Station in Toyama Prefecture, as shown in Fig. 3.
Consequently, the pioneering works dedicated to developing and operating huge facilities of the Kuroyon,
the Kurobe Dam, and related facilities in July 1956 through October1973, as summarized in Table 1,
contributed greatly not only toward the stable power supply against serious power shortages and growing
peak power demands, but also toward the postwar development of industries and the enhancement of the
quality of life.

One of the most distinctive features of the Kuroyon is the perfect harmony with nature. In order to fulfill
the nationwide requirements of rigorous preservation for the natural environment and the scenic beauty
of the Chubu-Sangaku National Park as well as to avoid snowfall and avalanches in winter, all of huge
facilities of the Kuroyon, such as Powerhouse (2.043m2), Substation (3,043m2), Switchyard (3,120m2),
and supporting equipments, were constructed completely underground at a depth of 150m.

Pelton Turbines
As soon as the concrete placing of the Kurobe Dam began in September 1959, partial reservoir filling
started in October 1960, and the Kuroyon began partial generation of 154MW output in January 1961,
using two Pelton 6-nozzle vertical shaft turbines, as shown in Fig. 5, each with output of 95,800kW
(60Hz) and 90,100kW(50Hz), the largest in the world among those of the same type. Then the Kuroyon
increased output to 234MW in August 1962 and to the maximum of 258MW in July 1969, by using
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additionally a third Pelton turbine with output of 95,000kW(60Hz) and 90,000kW(50Hz)[3]. The
Kuroyon’s generating capacity was finally expanded to 335MW in June 1973 with the addition of a
fourth Pelton turbine.
It should be noticed that the adoption of the first two German Pelton turbines manufactured by Voith
promoted the development of Japanese casting technology, resulting in the employment of the last two
Hitachi’s Pelton turbines, the first domestic products.

275kV Oil-Filled Cables
The 275kV oil-filled cables of a total length of 180m and a height of 68m were successfully installed in
the Kuroyon for the first time in Japan for the underground transmission from the switchyard to the
outgoing of transmission lines, as indicated by ⑦ in Fig. 4 and as illustrated in Fig. 6.
In 1950s there was no actual achievement of the 275kV oil-filled cable in Japan, and therefore the
development of the cable technology was faced with numbers of difficulties in design, manufacturing,
and cable laying. Hence, the Kansai Electric established a ‘Study Group on Kuroyon Extrahigh Voltage
Cable’ jointly with Sumitomo Electric Industries. After numbers of trial-and-error experiments of
prototype manufacturing, performance improvement and test, and cable laying in inclined passages, the
joint project team succeeded in installing the Japan’s first 275kV oil-filled cables in the Kuroyon[9,10].
The Kansai Electric opened up the application of 275kV oil-filled cables to the underground transmission,
and moreover the oil-filled cable technologies have since been widely spread in Japan. In fact, the total
length of the cables used for the underground transmission in the Kansai Region is more than 150km.

275kV Transmission System
Before the construction of the Kuroyon, 154kV power transmission systems were used for hydropower
transmission throughout Japan, which could not stabilize the long distance transmission. At that time, the
Kansai Electric was using five 154kV transmission trunk lines from main power generation cites to the
Kansai Region, any of which could no more cope with growing generating power due to lack of
transmission capacity. Hence the Kansai Electric had to take account of adopting the 275kV transmission
system.

The Kansai Electric began to develop the Japan’s first 275kV power transmission system in order to
cover stably 350km from the Kuroyon to the Kansai Region by means of substituting the conventional
arc-suppressing technology for a new neutral grounding technology. Since at that time there was very few
technical information on switch surge in Japan, the project team encountered difficulties in insulation
design, protection for ground/short-circuit faults, etc. Hence, this team conducted large-scale field tests
using one of the old 154kV transmission trunk lines, and built up on a step-by-step basis a solution
technique for insulation design and protection relay. Unifying these technologies, the Kansai Electric
succeeded in operating the Japan’s first 275kV long distance transmission system in January 1961, as
shown in Fig. 7, which transmitted the power that the Kuroyon just began to generate.
It should be added that this 275kV long distance transmission system enabled the installation of large
scale power plants far away from the electric load center.

Series Capacitor Bank
When a pair of the New Kurobe River No.3 and No.2 Hydropower Plants of output 107MW and
74.2MW were planned to be built to harness the water flowing from the Kuroyon and the New Kurobe
River No.3 Plant, respectively, a technical issue arose as to how to reinforce the additional transmission
capability of the existing power transmission system. To cope with this difficulty, the Kansai Electric
started to develop the ‘series capacitor bank’ jointly with Mitsubishi Electric and Nissin Electric. The
joint project team investigated the Japan’s first ‘post reinsertion transient voltage limiters’ to limit subsynchronous
voltages across series capacitors[13]. After numbers of steady/transient analysis and field
tests including intentional fault tests, the series capacitor banks were successfully installed in October
1973 at Johana Switching Station (Fig. 3) in the existing 275kV power transmission system for
the first time in Japan, resulting in the increase of the transmission capability by 28% enough to supply
stably the combined generating power to the Kansai Region.
The installation of the series capacitor banks in the existing 275kV transmission system in October 1973 increased the transmission capability, and hence the total generating power, by more then 150MW. The technologies so far attained for developing this transmission system laid the base of 275kV transmission technology in Japan, and contributed greatly to the development of higher capacity transmission systems of 500kV and 1,100kV.

Civil Engineering Innovations
Numbers of civil engineering innovations were achieved as follows:
(1) The Kurobe Dam is 186m tall (the highest in Japan now, and the world’s fourth highest at that time)
and has crest length of 492m and storage capacity of approximately 200Mm3. A
significant characteristics of this dam is the economical use of concrete, applying the method of
supporting the water pressure by the wing dams on both sides.

(2) Large-scale geographic surveys and rock tests were conducted, involving 67 drilling holes (total
length; 5,000m) and 49 adits (total length; 2,700m), in parallel with the excavation of the Kurobe Dam,
[4,5,6,7].
(3) High-precision systems were constructed for long-term measuring of static and dynamic behaviors of
the dam [8].
(4) Ultrahigh pressure penstock tunnels with a gradient of 47 degrees and 20 minutes were of bandedtype
utilizing a large number of bonds on pipes to support ultrahigh pressure.
g.3 Social Significance
The construction of the Kuroyon and the Kurobe Dam made possible a new phase of downstream
development through controlled water storage and flow adjustment. Specifically, the combined project
contributed to social development as follows:
g.3.1) Enlargement of Generating Capacity in Kurobe River Basin
Before the construction of the Kurobe Dam, the total generating capacity in the Kurobe River Basin was
273MW by 12 hydropower plants, and after the construction it has grown to 969MW by 18 plants, as
stated in g.1. Thus the Kurobe Dam contributed to the increase of the total generating capacity and the
number of plants by 696MW and 6, respectively, by harnessing more efficiently the water flowing from
it.
Power Supply for Growing Peak Demand
Due to unprecedented economic boom beginning in the late 1950s, the Japanese economy continued to
achieve double-digit growth in the 1960s. Accordingly, Japanese electric home appliance industry
embarked on a dramatic expansion. For example, as of 1963 the penetration rates in the Kansai Region of
home appliances of TV, washing machine, electric ‘kotatsu’ (table heater), refrigerator, rice cooker, and
vacuum cleaner, grew to 93%, 71%, 62%, 53%, 53%, and 34%, respectively. Moreover, since the spread
of air conditioners was very drastic, the power demand for them grew rapidly from 11% in 1962 to 18%
in 1966, and hence the maximum power demand which used to be in winter turned to be in summer in
1966.
In this way, the power demand structure was so radically changed that the Kansai Electric had to shift the
power supply policy such that the basis and peak power demands could fall back on the thermal-power
and hydropower generation, respectively. Consequently, the Kuroyon and the Kurobe Dam
contributed greatly to the supply for the growing peak demand caused by the huge boom of home electrification
in the 1960s and 1970s.

Social Contribution
The Kurobe Dam brought a new phase of developing the Kurobe River Basin in such a way that
(i) the total generating power capacity has since grown from 273MW to 969MW, 
(ii) an agricultural reformation was achieved by installing facilities to discharge irrigation water as well
as to improve alluvial soil in the basin plain, and
(iii) tourism resources of the Northern Japan Alps were developed by opening to the public the accessing
routes of (i) the ‘Tateyama-Kurobe Alpine Route’, which consists of the bus route between
Ohmachi and the Kurobe Dam and the ropeway route between the Kurobe Dam and Mt. Tateyama
of 3,015m altitude, and still attracts 1,025 thousand tourists per year, and (ii) the ‘Kurobe Gorge
Railway’ between Unazuki and Keyakidaira, which also attracts 490 thousand tourists per year.
Thus in the postwar Japan, the Kuroyon has become a landmark to achieve the persistently stable electric
supply by large-scale power generation with long distance transmission systems. It is safe to say that the
success of the Kuroyon laid the foundations of the rapid growth of the Japanese economy in the 1960s.
Even now the Kuroyon plays an important role to supply electricity to the Kansai Region, and has made a
great contribution to the welfare of people’s lives and the evolution of industries.
h.2 Technical Innovation
Before the Kuroyon was constructed, 154kV power transmission systems were used for hydropower
transmission throughout Japan, which could not stabilize the long distance transmission. The Kansai
Electric developed the Japan’s first 275kV long distance power transmission system to supply stably the
generating power from the Kurobe River Basin to the Kansai Region, which involved the employment of
the Japan’s first 275kV oil-filled cables, the technical reformation of the long distance power
transmission by substituting the conventional arc-suppressing technology for a new neutral grounding
technology, and the enhancement of power system protection. Furthermore, when a pair of the New Kurobe River No.3 and No.2 Hydropower Plants of output 107MW and 74.2MW, respectively, were built to harness the water flowing from the Kuroyon, the existing power system had to suppress the transmission power less than the thermal transmission capacity in order to reinforce the additional transmission capability. To this end, Kansai Electric decided to develop ‘series capacitor banks’ to decrease the transmission impedance, which were successfully installed in the
existing 275kV transmission system, resulting in the increase of the transmission capability by 28%
enough to supply stably the combined generating power to Kansai Region. Thus, Kansai Electric succeeded in the stable operation of the 275kV long distance power transmission system for the first time in Japan.
Conquest of Financial Obstacles
In an early survey the total construction cost of the Kuroyon and the Kurobe Dam was estimated at 50
billion yen, almost 30 times of the company’s capital. Therefore, soon after the decision of this huge project, the Kansai Electric entered into loan negotiations with the World Bank, which at last promised in June 1958 to extend loans worth 37 million US dollars (13.32 billion yen), almost one fourth of the total estimated cost.
Unfortunately, however, in the midst of constructing the Kurobe Dam, a dam of the same type in France
broke in December 1959, and more than 450 people died in the catastrophe. Hence the engineering staff
of the World Bank strongly recommended the Kansai Electric to reduce the dam height from 186m to
150m. Such a severe reduction would affect the whole project so fatally that the Kansai Electric
continued insistently financial and technical negotiations with the World Bank for two years in
Washington, Kurobe, Paris, Milan etc., until the insistence of the Kansai Electric was admitted in
principle, but with the collateral condition that rigorous requirements of the redesign for structural
reinforcement and the large-scale geographic surveys and rock tests had to be fulfilled.
Kansai Electric performed its duties of (i) the structural reinforcement by the gravity wing dams at both
sides of the arch portion, (ii) the execution of large-scale geographic surveys and rock tests[4-7], and (iii) the installation of a long-term high-precision measuring system for static and dynamic behaviors of the dam[8]. As a result, the expected construction cost of 50 billion yen was expanded to 51.3 billion yen.

Victory over Geographic Difficulties
The Kurobe River originating in the Northern Japan Alps has an annual precipitation of 3,800mm, an
average river slope of 1/40, and an average snowfall of 5m, and hence it had long been regarded as an
ideal site for hydropower generation. To harness these precious power generation resorces, different efforts had been attempted since the 1920s, on which numbers of dramatic stories were written in several nonfiction novels.
Actually, the project of the Kuroyon and the Kurobe Dam confronted serious obstacles due to (a) the
nationwide requirements of rigorous conservation for the natural environment and the scenic beauty of
the Chubu-Sangaku National Park, (b) terribly hard access due to rugged Kurobe Gorge, and (c)
exceptional snowfall and frequent avalanches in winter. In view of (a) and (c), all facilities of
powerhouse, substation, switchyard, and supporting equipments, were built completely underground, On the other hand, in terms of (b) and (c), a tunnel of 5.4km length, called the ‘Kanden

 Location(s) of Milestone plaque(s):
(i) At the entrance of the Kurobe River No.4 Hydropower Plant:
Address: Unazuki-machi, Kurobe-shi, Toyama, 938-0200 Japan
GPS: N 36.64486 E 137.68964
(ii) In front of the Kurobe Dam:
Address: Ashikuraji, Tateyama-machi, Nakaniikawa-gun, Toyama, 930-1406 Japan
GPS: N 36.56644 E 137.66213