A gas-insulated switchgear apparatus comprises, PA1 (a) first and second grounded tanks filled therein with insulating gas, PA1 (b) a circuit breaker unit enclosed in the first tank, PA1 (c) a disconnecting switch unit connected to an axial extension of the first tank and enclosed in the second tank partitioned off the first tank through a gas, PA1 (d) a third grounded tank having a connecting conductor filled therein insulating gas and connected to an axial extension of the second tank as partitioned off the second tank through a gas, PA1 (e) a grounding switch connected to the third tank in an opposite side of the disconnecting switch unit, and PA1 (f) a lightning arrester connected to the third tank.

BACKGROUND OF THE INVENTION 
The present invention relates to a gas-insulated switchgear and, more 
particularly, to a gas-insulated switchgear for which a constitution of a 
composite gas-insulated switchgear is improved. 
A composite gas-insulated switchgear with an increasing production lately 
is constituted generally as shown in FIG. 1. In the drawing, 1 denotes a 
breaker enclosing a breaking unit together with SF.sub.6 gas in a grounded 
horizontal tank, 2 denotes an air bushing, which is placed on one end of 
the breaker at one terminal part of the switchgear. It is also placed on a 
tank of a disconnector 3 provided on the other end of the breaker 1 at the 
other terminal part. The terminal part of each air bushing 2 is connected 
to an air bus part insulated atmospherically or a lead for line circuit. 
One terminal part 4 of the disconnector 3 and a terminal part 4a of the 
breaker 1 are connected through a window type current transformer 5 
intermediately. A terminal part 8 of a grounding switch 7 is provided on a 
terminal part 6 connected to the bushing 2 of the disconnector 3. Then, a 
lightning arrester 9 is provided for coordination of insulation between 
the gas-insulated switchgear and a lightning surge, a terminal part 9a of 
the lightning arrester 9 is connected to the terminal part 6 of the 
disconnector 3 with a conductor 10, and an electrostatic capacity type of 
intermediate electrode 11 to detect a voltage on the line side by means of 
said conductor 10 is arranged cylindrically as coaxial with the conductor 
10. 
In such constitution, since the grounding switch 7 is arranged on a portion 
coming comparatively upper at the disconnector 3, its operation involves a 
producing of various metal powders through sliding, and such powders drop 
into the tank of the disconnector 3 and thus come to deposit on an 
insulating spacer 12 to support the one terminal part 4 of the 
disconnector 3. The situation that the metal powders stick to the 
insulating spacer 12 may invite a deterioration, after all, in insulating 
performance of the gas-insulated switchgear. Particularly of late, a large 
scale and large capacity transmission (550 KV/12 KA transmission line 
being 200 km or longer) is being realized, a switching duty of a grounding 
switch used for the gas-insulated switchgear to be employed for such 
transmission system becomes severe as compared with that of conventional 
one accordingly, and the situation is such that a 90 KV/1,500 A induced 
current breaking is required as an example for the switching ability. To 
allow the grounding switch to operate in such switching ability, a gas 
spray function, i.e. puffer spray will be employed on the contact part. 
However, a large switching mechanism 13 will have to be provided to 
enclose such grounding switch 7 in the tank of the disconnector 3, which 
may involve a hardship in consequence. Moreover, the quantity of dusts 
produced at the time of induced current breaking will increase inevitably 
to deposit on the insulating spacer 12, which deteriorates a dielectric 
strength of the insulating spacer 12, therefore an employment of a 
pollution-proof insulating spacer with a long creeping distance or a 
spacer somewhat larger in size will have to be taken into consideration. 
Then, the grounding switch 7 is mounted comparatively at high position, 
and hence a special operating floor must be prepared for operation and 
inspection. 
SUMMARY OF THE INVENTION 
In view of what has been pointed out as above, an object of the present 
invention is to improve a check working efficiency of the grounding 
switch, integrate each equipment further in good condition, thereby 
providing a gas-insulated switchgear capable of improving a reliability to 
cope with the large capacity transmission age. 
Briefly, in accordance with one aspect of this invention, a gas-insulated 
switchgear is provided which includes 
(a) first and second grounded tanks filled therein with insulating gas, 
(b) a circuit breaker unit enclosed in the first tank, 
(c) a disconnecting switch unit connected to an axial extension of the 
first tank and enclosed in the second tank partitioned off the first tank 
through a gas, 
(d) a third grounded tank having a connecting conductor filled therein 
insulating gas and connected to an axial extension of the second tank as 
partitioned off the second tank through a gas, 
(e) a grounding switch connected to the third tank in an opposite side of 
the disconnecting switch unit, and 
(f) a lightning arrester connected to the third tank.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The invention will now be described for one preferred embodiment with 
reference to the accompanying drawing FIG. 2. In the drawing, 21 denotes a 
breaker enclosing a breaking unit with its one end connected to a bushing 
21a provided on a tank inside a horizontal grounded tank and charged with 
an insulating gas, and a terminal part 22 is provided to project on its 
one end axial of said tank. Then, 23 denotes a current transformer 
arranged in a line of the terminal part 22. And, 24 denotes a disconnector 
arranged on the other end of said breaker 21, enclosing a disconnecting 
unit in the tank and charged with an insulating gas, and its one terminal 
part 25 is connected to the one terminal part 22 of the breaker 21. Then, 
the other terminal part 26 is led into a bushing support tank 28 on which 
an air bushing 27 is provided through an insulating spacer 24b. Further, 
24a denotes a kinematic part of the disconnector 24. The bushing support 
tank 28 is provided on an axial extension of the disconnector 24 provided 
on an axial extension of the breaker 21, and thus it can be pointed out 
that said breaker 21, disconnector 24 and bushing support tank 28 are 
coupled to each other linearly. The bushing support tank 28 is given in a 
longitudinal shape extending perpendicularly to the axial direction of the 
tank of the breaker 21 with said bushing 27 provided on its upper end. Two 
openings 32, 33 orthogonal to the axis given by the center conductor 30 of 
said bushing 27 are provided on the side of bushing support tank 28, which 
is counter to the disconnector 24. Particularly the one opening 32 is 
provided at a position where it coincides with the axis of the tank of the 
breaker 21, and a grounding switchgear 34 is coupled to the opening 32 
through an insulating spacer 35 for gas partitioning. A fixed 
contact-maker 34a of the grounding switchgear 34 is connected to the 
center conductor 30 of the bushing 27 through a conductor 36. The center 
conductor 30 is connected to the other terminal part 26 of the 
disconnector 24 through a conductor 29. The grounding switchgear 34 is 
charged with an insulating gas in the tank, and a moving contact driven by 
a switching kinematic part 37 and an operating kinematic part 38 is 
arranged opposite to the fixed contact-maker 34a. A lightning arrester 40 
is coupled to the other opening 33 through an insulating spacer 39 for gas 
partitioning in parallel with said grounding switchgear 34. The lightning 
arrester 40 has an internal element 40a enclosed in the tank together with 
insulating gas, and the internal element 40a is led into the bushing 
support tank 28 through a conductor 40b. On the other hand, said bushing 
center conductor 30 has a conductor 31 on its extended axis, and a free 
end of the conductor 31 is supported by an insulator 41. The conductor 31 
and the conductor 40b of said lightning arrester 40 are connected through 
a detachable conductor 42. Then in the drawing, A, B and C denote manholes 
each, which are provided for inspection of the fixed contact-maker 34a of 
the grounding switchgear 34 and also for replacement of the detachable 
conductor 42. Further, 43 denotes an intermediate electrode arranged on 
the circumference of the conductor 31 concentrically therewith, and a 
voltage detecting function is secured through capacity type potential 
division by said conductor and electrode 43. 
The above way of constitution is effective enough to cope with the breaker 
21 remarkably improved of late to work on large capacity. Namely, the 
number of breaking points may be reduced to half by an improvement of the 
breaking performance. For example, the situation is such that the number 
of breaking points is reduced from 2 to 1 for 300 KV class and from 4 to 2 
for 550 KV class. This suggests that the axial length of the tank of the 
breaker 21 is shortened. However, when the breaker is particularly 
considered stand-alone, the bushings 21a, 27 will have to be mounted on 
the tank slantwise to secure a clearance of insulation between heads of 
both the bushings. However, in a composite switchgear, the bushings need 
not be provided slantwise, as each component will be arranged reasonably. 
Namely, it is easy to provide the bushings perpendicularly to the breaker 
tank axis for aseismatic strength and also for strength of openings for 
the bushings to provide, and further a manufacture of the tank is 
facilitated. Then, a necessary clearance between the bushings can be 
secured by arranging the disconnector in the middle of the bushings. For 
example, when the bushings are provided on the disconnector in 550 KV and 
2-point breaking class, the clearance is given at 4.5 m or so, which is 
shorter than the minimum requirement in 5 m for insulation, however, when 
the bushings are provided on the bushing support tank 28 according to the 
invention, the clearance may cover 6 m or so to comply with the 
requirement. Then, the disconnector 24 and the grounding switchgear 34 are 
isolated in separate vessels according to the constitution, and hence the 
switching duty of the grounding switchgear 34 applied to a large capacity 
transmission network is rather severe as described hereinabove, the 
breaking dust may increase consequently, however, since it is isolated 
from the disconnector 24, the dust will never pollute the insulator 
surface. A reliability of the insulating performance will upswing 
accordingly. Then, the grounding switchgear 34 or the lightning arrester 
40 is arranged to come linearly with breaker 21, disconnector 24 and 
bushing support tank 28, therefore a supporting level of the bushing 27 
can be lowered, and a better aseismatic strength is obtainable 
consequently. Further, the conductor 42 through which to connect the 
lightning arrester 40 is provided in the bushing support tank 28, which is 
made detachable, therefore a severe voltage stress can be prevented from 
being impressed on the element 40a of the lightning arrester 40 by 
demounting the conductor 42 at the time of withstand voltage test to be 
carried out in a shop and after installation at a site, thus preventing 
the element 40a from deterioration. Moreover, the lightning arrester 40 is 
arranged in the lower space of the bushing support tank 28, i.e. below the 
grounding switchgear 34, thereby simplifying a support on the weighty 
lightning arrester 40 and rationalizing the space for arrangement. 
According to the constitution given by the present invention, in case a 
breaker superior in insulation characteristic and miniaturized is employed 
as a composite switchgear to work for a large capacity transmission 
system, a necessary distance of insulation between the bushings is 
secured, a bus part is not particularly required, the system can be 
miniaturized as a whole, the bushings on both ends are arranged linearly, 
which is preferable in respect of arrangement for a substation generally. 
As described above, according to the invention, a clearance of insulation 
between the bushings can be secured satisfactorily enough to cope with an 
operation of the breaker further miniaturized without interposing a 
special bus unit therefor, and the disconnector and the grounding 
switchgear are partitioned through gas, therefore a gas working only at a 
portion of the grounding switchgear is recovered when the grounding 
switchgear reaches the number of necessary operating times (200 times, for 
example, as an inspection criterion of a grounding switchgear with current 
switching ability), and contact can be checked easily through manholes 
provided in the grounding switchgear. Further, each equipment can be 
arranged linearly, the bushing supporting level can be kept lower, thereby 
improving an aseismatic strength. Namely, it can be kept lower by the 
interpole distance of insulation of the disconnector according to the 
constitution of the preferred embodiment. Then, there is a merit to obtain 
easily a structure whereby a breaking dust produced according to current 
switching of the grounding switchgear is hard to deposit on an insulating 
spacer. In addition, an actuator for each equipment can be set at 
comparatively low level, therefore a special operating floor is not 
particularly required for maintenance and inspection and manual operation 
of the actuator. On the other hand, at the time of withstand voltage test 
to be carried out in a shop and after installation at a site, it is 
desirable that the lightning arrester be detached to avoid an operation of 
the lightning arrester and also to prevent the arrester element from being 
deteriorated by overvoltage; a disconnector for the lightning arrester is 
provided particularly therefor hitherto and is stopped functioning at the 
time of normal operation so as to function only as a connecting conductor, 
which is uneconomical indeed, however, a conductor is provided detachably 
in the bushing support tank according to the invention, which is 
reasonably detached only at the time of withstand voltage test, thus 
giving an economical constitution. 
Obviously, many modifications and variations of the present invention are 
possible in light of the teachings of the present invention. It is 
therefore to be understood that within the scope of the appended claims, 
the invention may be practiced otherwise than as specifically described 
herein.