Gas insulated disconnector

A circuit including arcing contacts is connected in parallel with main contacts of a disconnector to facilitate interruption of a loop current caused through the disconnector when switching main bus bars in a power station. A switching surge suppression resistor is adapted to be inserted in and removed from the circuit of the arcing contacts. Plural pairs of arcing contacts are provided in the circuit of arcing contacts.

BACKGROUND OF THE INVENTION 
This invention relates to a gas insulated connector capable of interrupting 
a loop current. 
Disconnectors in power station premises are usually installed adjacent to 
circuit breakers. They are used typically for isolating a circuit after 
interruption of current therein by a circuit breaker or for switching 
power transmission systems. The former function is the isolation of a 
no-load circuit by the disconnector. At the time of the isolation of the 
no-load circuit by the disconnector, re-arcing repeatedly takes place 
between the disconnecting switch contacts giving rise to a commonly termed 
switching surge having high sharpness. This occurs because of the fact 
that the switching speed of the disconnector is slow compared to the 
circuit breaker. It has been the practice to add a resistor to the 
disconnector in order to suppress such a switching surge. 
An example of the latter function of the disconnector is the switching of 
main bus bars in a power station by disconnectors. FIG. 1 shows the case 
of switching the connection of bus bars A and B in (a) to that in (b) by 
making use of a satisfactory interrupting capacity of SF.sub.6 gas. In 
this operation, a current which is close to the rated current in the 
circuit including the disconnectors A1 and B1 (which is referred to as 
loop current) is interrupted. 
The function of isolating a no-load circuit and the function of switching a 
loop current, as noted above, are often required for one disconnector in a 
power station. 
A prior art disconnector provided with a resistor for suppressing the 
switching surge as described above is shown in FIG. 2. The disconnector 
comprises a tank 1, which is filled with gas capable of extinguishing arc. 
The tank 1 is sealed by insulating spacers 2 and 3. Conductors 4 and 5 are 
secured to the respective insulating spacers 2 and 3. A shield member 6 
made of a conductor is secured to the conductor 4. The shield member 6a 
has an opening. A main contact 7 is disposed as a fixed contact in the 
shield member 6 such that it faces the opening 6a thereof. The main 
contact 7 is secured to and electrically connected to the shield member 6. 
A resistor 8 is secured at one end to the shield body 6. The resistor 8 
includes an insulating rod 8a and a resisting element 8b as shown in FIG. 
6 and as will be described later in detail. A cylindrical spring case 9 is 
secured to the other end of the resistor 8. A conductive support rod 10 is 
slidably supported in the spring case 9 and extends in the fixed contact 
7. The support rod 10 is provided at one end with a fixed arcing contact 
10a which is capable of withstanding arcing. It can be moved up to a 
position, at which the end of the arcing contact 10a projects from the 
shield member 6. The arcing contact 10a is connected to the other end of 
the resistor 8 through the spring case 9. A spring 11 biases the support 
rod 10 in such a direction that it projects from the shield member 6. 
Another shield member 12 made of a conductor is secured to the conductor 
5. The shield member 12 has an opening 12a. A movable main contact 13 is 
movably supported in the shield member 12. The main contact 13 is provided 
at one end with a movable arcing contact 13a which is capable of 
withstanding arcing. As the main contact 13 is moved to the right from the 
state of FIG. 2, it is broken apart from the fixed main contact 7 before 
the arcing contacts 10a and 13a are broken apart. A contact 14 which can 
be in sliding contact with the movable main contact 13 is connected to the 
shield member 12. An insulating operating rod 15 is coupled to the main 
contact 13. A link mechanism 16 transmits a driving force of a driving 
source (not shown) to the main contact 13 via the insulating operationg 
rod 15. 
In operation, with the rightward movement of the insulating operating rod 
15 in FIG. 2, the movable main contact 13 is broken apart from the fixed 
main contact 7. The arcing contact 10a is caused to follow the movable 
arcing contact 13a by the action of the spring 11. The arcing contact 10a 
can be moved up to a position, at which the electric field intensity at 
the end of the arcing contact 10a is higher than the electric field 
intensity at all parts of the shield member 6, i.e., at a position at 
which the end of the arcing contact 10a projects from the shield member 6. 
The main contact 13 can be moved beyond this position so that arcing is 
eventually produced between the arcing contacts 10a and 13a. The arcing 
contact 10a is stopped at a position, at which the electric field 
intensity at its end is higher than the electric field intensity at all 
parts of the shield member 6. Thus, a number of arc discharges (re-arcing) 
all occur between the arcing contacts 10a and 13a during the switching 
operation. In consequence, an abnormal voltage (i.e., switching surge) 
generated at the time of isolating the no-load circuit can be suppressed. 
FIGS. 3 and 4 are equivalent circuit diagrams showing a succession of 
states that occur when a loop current is interrupted using a disconnector 
provided with the surge suppression resistor shown in FIG. 2. In the state 
of FIG. 3, the disconnector is perfectly closed, and in the stage of FIG. 
4 only the main contacts have been broken apart. In FIGS. 3 and 4, the 
same reference numerals and symbols as in FIG. 2 designate corresponding 
parts. Indicated at Zm is the impedance of the main current path of the 
disconnector, indicated at Zl is the impedance of the loop established at 
the time of the switching of the system, and indicated at R is the 
resistance of the surge suppression resistor. These impedance values are 
generally related as 
EQU Zm&lt;&lt;Zl&lt;&lt;R (1) 
The equivalent circuit of FIG. 4 shows the state that results immediately 
after the start of operation of the disconnector with the surge 
suppression resistor shown in FIG. 2 to interrupt a loop current. At this 
time, R and Zm are related as Zm&lt;&lt;R from the inequality 1. If the 
resistance R is set to be considerably greater than the resistance offered 
to the arc produced between the main contacts 7 and 13, the loop current 
scarely flows through the path including the resistor 8, fixed arcing 
contact 10a and movable arcing contact 13a, that is, it substantially 
flows through the path including the main contacts 7 and 13. That is, most 
of the loop current i, for instance about 10 killoamperes, must be 
interrupted between the main contacts 7 and 13. 
In a disconnector capable of interrupting a large loop current, the arcing 
contacts 10a and 13a usually are capable of withstanding arcing so that an 
arc due to the loop current can be interrupted between the arcing contacts 
10a and 13a for ensuring a current-carrying performance after the 
interruption of the current. In other words, the main contacts 7 and 13 
usually are incapable of withstanding arcing. 
If the resistance R of the resistor 8 is set to be comparatively low with 
respect to the resistance offered to the arcing generated between the main 
contacts 7 and 13 when these contacts 7 and 13 are broken apart, a large 
current is caused to flow through the path including the resistor 8 and 
arcing contacts 10a and 13a with arcing generated between the main 
contacts 7 and 13 when the contacts 7 and 13 are broken apart. A voltage 
drop across the resistor 8 is thus applied between the main contacts 7 and 
13. In this case, the interruption of the loop current is extremely 
difficult compared to the case of absence of the resistor 8, i.e., the 
case where the voltage drop across the resistor 8 is zero. If the 
resistance R of the resistor 8 is set to be very low, even the function of 
surge suppression substantially cannot be obtained. 
For the above reasons, it has been thought difficult to add a function of 
interrupting loop current to the conventional disconnector with a surge 
suppression resistor. 
SUMMARY OF THE INVENTION 
The invention has been intended in the light of the foregoing, and its 
object is to provide a disconnector, which can interrupt loop current with 
bypass contacts provided to shunt a surge suppression resistor when 
interrupting the loop current. 
Another object of the invention is to facilitate the interruption of loop 
current and prevent wear of the main contacts.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 5 is an equivalent circuit diagram of the disconnector according to 
the invention, FIG. 6 is a longitudinal sectional view showing the 
construction of the disconnector of FIG. 5, and FIG. 7 is a fragmentary 
enlarged-scale sectional view showing part of the construction of FIG. 7. 
Referring to thse Figures, a pair of bypass contacts 10b and 20 are 
provided in series with the resistor 8. The bypass contact 20 is a fixed 
bypass contact. The bypass contact 10b is a movable bypass contact 10b 
which can be brought into contact with and broken apart from the fixed 
bypass contact 13. The movable bypass contact 10b is integral with the 
arcing contact 10a via the support rod 10. The bypass contacts 10b and 20 
are adapted to be broken apart after the arcing contacts 10a and 13a have 
been broken apart and be brought into contact again with each other after 
the arcing contacts 10a and 13a have been brought into contact. Designated 
at 22 and 23 are nozzles for controlling the operating speed of the arcing 
contact 10a. As a piston 10c which is moved by a biasing force of the 
spring 11 compresses gas in the spring case 9, the gas is discharged 
through the nozzles 22 and 23, thereby changing the speed of the arcing 
contact 10a. In FIG. 5, Zm is the impedance of the main current path of 
the disconnector, Zb is the impedance of the circuit including the arcing 
contact 10a, support rod 10 and bypass contact 10b, Zl is the impedance of 
the loop established at the time of the switching of the system, and 
indicated at R is the resistance of the resistor 8. 
Generally, Zm, Zb, Z and R are related as 
EQU Zb.perspectiveto.Zm&lt;&lt;Z1&lt;&lt;R (2) 
The function and operation of the disconnector according to the invention 
will now be described. 
FIGS. 8 to 11 show the state of the disconnector immediately after the 
start of the isolating operation when interrupting the loop current. As 
the main contact 13 is moved, the main contacts 7 and 13 are broken apart. 
At this time, the arcing contacts 10a and 13a and bypass contacts 10b and 
20 are in their closed state so that the resistor 8 is shunted by the 
bypass contacts 10b and 20. 
In this stage, Zm and Zb are related as Zb.perspectiveto.Zm from the 
inequality 2. Thus, when the main contacts 7 and 13 are broken apart, the 
loop current i turns to flow entirely through the path including the 
bypass contacts 10b and 20 and arcing contacts 10a and 13a. For this 
reason, no substantial damage is caused to the main contacts 7 and 13 due 
to the arcing. 
With further movement of the main contact 13, a state as shown in FIGS. 9 
and 12 results. In this state, the piston 10c which is integral with the 
arcing contact 10a has cleared the nozzle 22 formed in the spring case 9. 
Thus, as soon as this state is reached, the speed of the arcing contact 
10a is suddenly reduced. In consequence, the arcing contact 10a commences 
to be broken apart from the movable arcing contact 13a, producing an arc 
24 between both the arcing contacts 10a and 13a. 
The arc produced when interrupting the loop current as mentioned may be 
extinguished by making use of a flow of gas produced in a flow guide 28 by 
a puffer cylinder 28 and a piston 27 as shown in FIG. 6. 
With further movement of the main contact 13, a state as shown in FIGS. 10 
and 13 results. More particularly, after the arc produced between the 
arcing contacts 10a and 13a when interrupting the loop current has been 
extinguished, the movable bypass contact 10b integral with the arcing 
contact 10a commences to be broken apart from the fixed bypass contact 20. 
At this time, the main contacts 7 and 13 and arcing contacts 10a and 13a 
have already been broken apart, that is, it is not that a circuit carrying 
current is broken when the bypass contacts 10a and 20 are broken apart. 
When isolating a non-load bus bar, it is necessary to suppress the 
switching surge by inserting a resistor in series with the circuit 
including the disconnector as noted before. The switching surge is 
generally proportional to the potential difference between two contacts of 
the disconnector at the time of the re-arcing. The intercontact potential 
difference is proportional to the intercontact distance at the time of the 
discharge. Therefore, the high surge which is so high that it must be 
suppressed by inserting a resistor, occurs in case when an arc is produced 
with the main contact 13 at a certain distance from the arcing contact 10 
(the distance being specifically 1/4 of 1/3 of the full inter-contact 
distance although it depends on the apparatus). When the main contact 13 
is in a state in the initial stage of operation as shown in FIGS. 11 and 
12, the bypass contacts 10b and 20 are not broken apart yet, so that the 
surge suppression resistor 8 is in the shunted state. 
FIG. 13 shows the state in which the main contact 13 is broken apart from 
the arcing contact 10a. In this state, the resistor 8 is connected in 
series with the arcing contacts 10a and 13a since the bypass contacts 10b 
and 20 are broken apart. If re-arcing 25 is produced between the contacts 
at this time, the resultant switching surge can be effectively disposed 
with by the resistor 8. 
FIG. 14 shows the disconnector when the isolating operation is completed. 
When the re-closure of the no-load bus bar by the disconnector is started 
from the state of FIG. 14, re-arcing is produced before the arcing contact 
13a is brought into contact with the fixed arcing contact 10a. At this 
time, the surge suppression resistor provides effective action for all 
re-arcing. 
As has been described in the foregoing, the disconnector having bypass 
contacts according to the invention can interrupt a loop current in one 
case and suppress the switching surge generated at the time of the 
switching of the no-load bus bar with the resistor in the other case. 
The bypass contacts serve to insert the surge suppression resistor in the 
circuit of the arcing contacts or shunt the resistor. This means that with 
a disconnector which has the purpose of interrupting loop current and is 
not provided with any resistor, the bypass contacts may be used as the 
arcing contacts. That is, by providing two pairs of arcing contacts and 
causing these two pairs of contacts to be broken apart substantially 
simultaneously, it is possible to ensure reliable interruption of the loop 
current and prevent wear of the main contacts.