Electricity: measuring and testing – Electromechanical switching device – Circuit breaker
Reexamination Certificate
2001-11-08
2004-05-04
Pert, Evan (Department: 2829)
Electricity: measuring and testing
Electromechanical switching device
Circuit breaker
Reexamination Certificate
active
06731115
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-341100, filed on Nov. 8, 2000; the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
This invention is related to a current transducer (CT) system for measuring high-voltage main circuit AC current in a gas-insulated switchgear (GIS) for AC power supply system, the switchgear with the current transducer system and a method for measuring the AC current.
In general air-insulated substations, switchgears are sometimes replaced by new ones, while busbars and steel towers are rarely replaced since their life spans are relatively long. Therefore, in most replacement works, the switchgears are replaced by new ones of higher performance and higher reliability utilizing installed older air-insulated busbars. For those purposes, some integrated gas-insulated switchgears have been proposed.
Referring to
FIGS. 1 and 2
, typical line bay construction of an air-insulated substation of double busbar scheme of the prior art is described now. The air-insulated substation has a circuit breaker (CB)
1
which is connected to busbars
101
a
and
101
b
via bus side disconnecting switches (DSs)
2
a
and
2
b
, respectively. The substation also has a pair of current transformers
102
a
and
102
b
on both sides of the circuit breaker
1
. The substation also has a line side disconnecting switch
2
c
, an instrument transformer (or a voltage transformer: VT)
103
and a lightning arrester (LA)
104
.
Those components of the substation are supported on insulating supporting structures. The output AC current is sent out of the substation through over-head lines (OHLs)
130
. The current transformers
102
a
and
102
b
are typically of oil-filled insulator types.
FIG. 3
shows an exemplary construction of components of a conventional substation replaced with new integrated gas-insulated switchgears and conventional current transformers. The component groups surrounded by dot-dash lines
105
and
106
shown in
FIG. 1
might be replaced by integrated gas-insulated switchgears
107
and
108
, respectively, as shown in FIG.
3
.
The component group surrounded by a dot-dash line
109
shown in
FIG. 3
is now described referring to FIG.
4
. The integrated gas-insulated switchgear
107
may have a metal box
13
a
containing a driving connector
121
e
. The metal box
13
a
may be supported by and disposed on top end of a vertically standing supporting hollow insulator
11
a.
An operation device
12
a
may be disposed at the bottom end of the supporting hollow insulator
11
a
. Hollow insulators
14
e
and
14
f
may be supported by the metal box
13
a
on their ends and contain the disconnecting switches
2
a
and
2
b
, respectively. The disconnecting switches
2
a
and
2
b
may be operable by the operation device
12
a
via the driving connector
121
e.
Likewise, the integrated gas-insulated switchgear
108
may have a metal box
13
b
containing a driving connector
121
. The metal box
13
b
may be supported by and disposed on top end of a vertically standing supporting hollow insulator
11
b
. An operation device
12
b
may be disposed at the bottom end of the supporting hollow insulator
11
b.
Hollow insulators
14
a
and
14
c
may be supported by the metal box
13
b
on their ends and contain the circuit breaker
1
and the disconnecting switch
2
c
, respectively. The circuit breaker
1
and the disconnecting switch
2
c
may be operable by the operation device
12
b
via the driving connector
121
.
The disconnecting switches
2
a
and
2
b
, the circuit breaker
1
and the disconnecting switch
2
c
may be electrically connected each other in series in the metal boxes
13
a
and
13
b
, respectively.
Thus, the components surrounded by the dot-dash line
105
shown in
FIG. 1
would be replaced by the integrated gas-insulated switchgear
107
having the two disconnecting switches
2
a
and
2
b
, and the components surrounded by the dot-dash line
106
would be replaced by the integrated gas-insulated switchgear
108
having the circuit breaker
1
and the disconnecting switch
2
c
as shown in
FIGS. 3 and 4
.
Now replacement of current transformers is discussed. The line side current transformer
102
b
shown in
FIGS. 1 and 2
can be replaced by a penetrating-type current transducer, which is of the same type used in conventional gas-insulated switchgears, in the integrated gas-insulated switchgear if the line-side (e.g. the metal box
13
b
shown in
FIG. 4
) is grounded. However, the bus side current transformer
102
a
shown in
FIG. 1
cannot be replaced by a penetrating-type current transducer for either of the integrated gas-insulated switchgears
107
or
108
shown in
FIG. 4
, since the replaced current transformer would be on the high-voltage side.
Therefore, oil-filled insulator type current transformers must be used. Thus, if the air-insulated substation shown in
FIG. 1
is replaced with an integrated gas-insulated switchgear shown in
FIG. 3
, the current transformers used there would be a combination of current transformers of oil-filled insulator-type and of penetrating-type.
General line bay construction of air-insulated substation of double busbar scheme have been discussed, whereas combination of oil-filled insulator-type current transformers and penetration-type current transformers may have to be utilized in other facilities such as bus section or bus coupler constructions, line bay constructions of single busbar scheme substations, line bay constructions of one and half busbar scheme substations, and so on.
As discussed above, a penetration-type current transformer which is generally used in conventional gas-insulated switchgears cannot be disposed at the high-voltage side for the integrated gas-insulated switchgear
108
shown in
FIG. 4
due to the insulation difficulty, so that the circuit breaker cannot have current transformers on its both sides. Therefore, in practice, disposing current transformer on one side of the circuit breaker may be omitted, or an independent oil-filled insulator-type current transformer may be installed if current transformers on both sides of the circuit breaker would be necessary.
Oil-filled insulator-type current transformers themselves are expensive, and would require extra area and ground construction for setting up, which would spoil the advantage of reduced required area for substations and the total cost-down which would be generally obtained by applying integrated gas-insulated switchgears.
In addition, in an oil-filled insulator-type current transformers, internal burnout accident could cause increased pressure in the tank which could develop into a severe accident with a tank explosion. Therefore, the oil-filled insulator-type current transducers would be demanded to be replaced by penetrating-type current transformers when the substations are replaced.
However, the penetrating-type current transformers used in conventional gas-insulated switchgears with analog current output, the rated secondary output of which may be 1 Ampere or 5 Amperes, can be installed only in ground voltage side, and cannot be disposed on both sides of the circuit breaker of integrated gas-insulated switchgears such as the ones shown in FIG.
3
.
BRIEF SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an improved current transformer which can be disposed on either side of the circuit breaker of an integrated gas-insulated switchgear.
There has been provided, in accordance with an aspect of the present invention, a current transducer system for measuring AC current in a high-voltage main circuit having a circuit breaker and a disconnecting switch in an integrated gas-insulated switchgear, the system comprising: a current sensor for detecting the AC current and outputting an analog electric signal representing the AC current, the current sensor disposed near the circuit breaker; a sensor unit including an analog
Kabushiki Kaisha Toshiba
Nguyen Trung Q.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Pert Evan
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