Electrical high speed circuit breaker with explosive charges including ablative arc extinguishing material

A simple high-speed circuit breaker which is cheap to produce is specified for alternating currents which have to be switched off, which switches such currents off within one half-cycle at the current zero crossing, by means of a gas-generating explosive charge (4). In this case, a switching piston (2) which makes a sliding contact with a consumable contact pin (K1) of a first electrode (E1) when the high-speed circuit breaker is closed, moves in the direction of a hollow electrode (E2). The switching piston (2) has a contact tube (2') with an exhaust opening (3) which is closed by the hollow electrode (E2) when the high-speed circuit breaker is closed, and is open to an exhaust chamber (8) when the high-speed circuit breaker is open (left-hand half of the figure). The contact tube (2') moves in a sliding manner in a cutout in the hollow electrode (E2). A plurality of explosive charges (4) may be accommodated in the first electrode (E1). In addition, rated current contacts which are provided between the first electrode (E1) and the switching piston (2) carry a continuous current when switched on. The high-speed circuit breaker is particularly suitable as a circuit breaker in addition to a power breaker, in which case the high-speed circuit breaker is tripped if the power breaker fails.

FIELD OF THE INVENTION
 This invention relates to electrical high-speed circuit breakers of the
 type having a gas generating explosive charge for quenching an arc.
 The invention also relates to use of the high-speed circuit breaker.
 BACKGROUND OF THE INVENTION
 Patent No. DE 35 37 314 A1 discloses an apparatus for interrupting current
 in which an electrical connection is disconnected by the explosion of an
 explosive charge. A tubular bridging contact composed of ductile material
 between a first and second electrode has notches internally as weak
 points, and has an explosive charge externally, inside a pressure chamber.
 If the current to be monitored exceeds a current limit value which can be
 determined, the explosive charge is detonated. An arc produced in this
 case is blown by the mixed gas emerging from the pressure chamber, and is
 quenched at the next current zero crossing. A disadvantage in this case is
 that, apart from the explosive charge, the electrodes and the bridging
 contact also have to be replaced after each disconnection process. As a
 result of the arc, electro-negative gas is released, as a component of the
 mixed gas, from the lining of the inner wall of the pressure chamber,
 leading to consumption of the latter.
 DE 19 613 568 A1 discloses a power breaker for operating voltages up to 30
 kV, in which first and second electrodes are electrically conductively
 connected, when closed, by means of a moving, circular-cylindrical
 switching pin as a bridging contact. Between the electrodes, the switching
 pin is surrounded circumferentially by a pressure chamber. A rated current
 path, which is provided with moving rated current contacts, may be
 arranged in parallel with the power current path. When the power breaker
 is switched off, the rated current path is interrupted first of all, as a
 result of which the current commutates onto the power current path.
 Afterwards the power current path is interrupted. An arc is formed in the
 process, and is then quenched. The drive for the switching pin, which can
 reach a speed in the range of 10 m/s-20 m/s during switching, is not
 quoted in any more detail. The switching pin, which is connected to a
 relatively complex switching drive for a rated-current contact finger, is
 subjected to a high load during switching.
 SUMMARY OF THE INVENTION
 The invention achieves the object of further developing an electrical
 high-speed circuit breaker of the type mentioned initially, in such a
 manner that the design complexity for lines and switching devices is
 reduced.
 One advantage of the invention is that there is no need to replace
 electrodes and the bridging contact after each switching operation. The
 simple design leads to cost savings.
 The high-speed circuit breaker according to the invention can
 advantageously be used as a reserve circuit breaker for a main power
 breaker.

DETAILED DESCRIPTION OF THE INVENTION
 FIG. 1 shows, schematically, a cross-sectional view through the contact
 regions of a high-speed circuit breaker having an axis of symmetry or
 circuit-breaker axis (A), in the switched-on state on the right, and in
 the switched-off state on the left.
 A first electrode (E1) having a consumable contact or consumable contact
 pin (K1) and having a gas-generating charge or explosive charge (4) on
 which a firing apparatus (4') is fitted, is arranged in the upper part of
 a circular-cylindrical circuit-breaker enclosure (1) such that it is
 gas-tight with respect to a high-pressure chamber (6) located underneath.
 A second electrode or hollow electrode (E2) is located in the lower region
 of the circuit-breaker enclosure (1), having a vent line (9) for venting a
 low-pressure chamber or piston chamber (7) into an exhaust chamber (8)
 underneath the hollow electrode (E2). When the high-speed circuit breaker
 is switched on, a tubular bridging contact or switching piston (2) on the
 one hand makes an electrically highly conductive sliding connection with
 the consumable contact pin (K1) via a current contact element (K2), and on
 the other hand makes the sliding connection with the inner wall of the
 circuit-breaker enclosure (1). This switching piston (2) has an axial,
 electrically highly conductive contact tube (2') which is arranged such
 that it can move in a central opening 20 in the hollow electrode (E2) and
 makes an electrically highly conductive contact with the wall of this
 central opening. In its lower region, the contact tube (2') has a gas
 outlet opening or exhaust openings (3), which are located underneath the
 upper surface of the hollow electrode (E2) when the high-speed circuit
 breaker is switched on, and are thus closed by said hollow electrode (E2).
 It is not possible for gas to escape from the high-pressure chamber (6)
 through the exhaust openings (3) in this switched-on position.
 Detonation of this explosive charge (4) causes a chemical reaction in a
 similar way to that of a safety airbag in a motor vehicle, briefly
 releasing a large amount of gas, which flows through openings or explosion
 gas inlet openings (5) in the first electrode (E1), into the high-pressure
 chamber (6) where it produces a pressure in the range from 5 MPa to 10
 MPa. This pressure drives the tubular switching piston (2) downwards in
 the movement direction of an arrow (B). In the process, the electrical
 contact between the consumable contact pin (K1) and the current contact
 element (K2) is interrupted, so that an arc (10) is formed between the
 consumable contact pin (K1) and the inner wall of the contact tube (2'),
 which arc (10) is lengthened as the piston continues to move. Once the
 switching piston (2) has reached its lower position, see the left-hand
 side of FIG. 1, then the exhaust openings (3) are exposed to the exterior,
 and the explosion gases can escape from the high-pressure chamber (6) into
 the exhaust chamber (8). In the process, the arc (10) is blown, and is
 caused to extinguish within one half-cycle of the alternating current to
 be interrupted, at the next current zero crossing. The vent line (9) in
 the hollow electrode (E2) ensures that the movement of the switching
 piston (2) is not braked by the gas that is compressed in the piston
 chamber (7).
 Suitable design of the gas-generating explosive charge (4) allows the
 pressure in the high-pressure chamber (6) to be set such that
 1. the movement of the switching piston (2) and thus the disconnection of
 the consumable contact pin (K1) from the current contact element (K2) take
 place within the desired short time of a few ms and
 2. the blowing of the arc (10) which is produced when the explosion gas
 flows out is sufficient to interrupt the current and, possibly to produce
 a desired high arc voltage.
 Pressures in the range of 5 MPa to 10 MPa can easily be reached; these
 allow contact disconnection times of a few ms, with a distance of about 10
 cm between the first electrode (E1) and the hollow electrode (E2).
 The volume of the exhaust chamber (8) is designed such that the residual
 pressure in the high-pressure chamber (6) is sufficient to ensure the
 desired dielectric strength of the open contact path.
 After a switching operation, the high-speed circuit breaker can be made
 ready to switch again by resetting the contact tube (2') and replacing the
 gas-generating explosive charge (4). In the simplest case, this is done by
 manual servicing. However, the readiness for disconnection can also be
 automated by means of a mechanical resetting drive and an automatic
 reloading apparatus for the explosive charge (4) (not shown).
 FIG. 2 shows, schematically, a cross-sectional view of a first electrode
 (E1') having a plurality of gas-generating explosive charges (4a, 4b, 4c)
 which can be detonated separately and successively as required, and which
 are connected to the high-pressure chamber (6) via separate supply
 channels. There is thus no need for an automatic reloading apparatus for
 applications when switching operations occur rarely.
 FIG. 3 shows, schematically, a cross-sectional view of the right-hand half
 of the contact regions of a high-speed circuit breaker, in which a
 plurality of finger contacts or rated current contacts (11), only one of
 which can be seen, are connected in parallel with arc quenching contacts
 (K1', K2) in order to increase the rated current carrying capacity. These
 rated current contacts (11) are arranged at the edge between a stationary
 first electrode (E1") and the moving switching piston (2) and are forced
 into contact by in each case one compression spring (12). The moving
 switching piston (2) is thus used to carry the rated current. The current
 is passed from this switching piston (2) via a plurality of webs (2a)
 which are rigidly connected to the switching piston (2) and one of which
 is illustrated in cross section, to a sliding contact (13), from where it
 is transmitted to the stationary hollow electrode (E2). The large radii on
 which the contact junctions are made allow high rated currents to be
 carried.
 In order to ensure safe commutation from the rated current contacts (11) to
 the consumable contact pin (K1'), the latter is lengthened by an overlap
 distance (a) of, for example, 1 cm in comparison with the consumable
 contact pin (K1) in FIG. 1.
 Instead of the sliding contacts (13), rated current contacts (11) may be
 used for the second rated current junction from the switching piston (2)
 to the hollow electrode (E2), as for the 1.sup.st first rated current
 junction from the first electrode (E1") to the switching piston (2).
 It is self-evident that the current contacts may be designed other than as
 illustrated. Thus, for example, instead of a consumable contact pin (K1)
 projecting from the first electrode (E1), it is possible to provide a
 cutout in the first electrode (E1) which makes an electrically conductive
 sliding connection (not shown) at the edge with a current contact element
 (K2) of the switching piston (2). Such a contact cutout could also be
 provided in the consumable contact pin (K1).
 The high-speed circuit breaker according to the invention may be used as an
 additional or back-up circuit breaker for a power breaker (not shown)
 whose switching capacity is not sufficient for the maximum short-circuit
 current to be expected. In such a situation, the high-speed circuit
 breaker could, for example, divert a portion of the short-circuit energy
 fed in in the center of a busbar, right at the start of a short-circuit,
 so that the existing power breaker need not be switched until after the
 end of the switching process in the high-speed circuit breaker, and is no
 longer overloaded by the reduced short-circuit current.
 The high-speed circuit breaker according to the invention may also be used
 as a protective circuit breaker or back-up circuit breaker for a cheap
 "intelligent" power breaker designed for a relatively low rating, which
 switches off when the phase conditions of the current to be switched off
 are advantageous. If such a power breaker fails, as can be identified, for
 example, by the arc duration being too long, the high-speed circuit
 breaker is detonated and tripped. This allows the reliability of
 overcurrent protection to be improved considerably using cheap
 "intelligent" power breakers. Since such a failure of the power breaker
 occurs very rarely, the high-speed circuit breaker need be designed for
 only a few switching operations in this case. In most cases, single
 operation with subsequent servicing will be sufficient.
 A high-speed circuit breaker used as a back-up circuit breaker is
 preferably tripped independently of the normal system protective system,
 for example by a tripping apparatus which is fed from the local current
 profile (not shown) that is to say independently of a tripping signal for
 the power breaker. If it is impossible to interrupt very high
 short-circuit currents at the right time, for example close to a
 generator, due to an imbalance and the resultant lack of zero crossings of
 the current to be switched off, then a high-speed circuit breaker which
 has built up a high arc voltage can force a premature current zero
 crossing to occur, and can thus ensure that the current is interrupted at
 the right time.
 The high-speed circuit breaker according to the invention and of simple
 design may also be used as a recloseable protective element in
 high-voltage systems since, at the same time, it has a high rated current
 carrying capacity and a high response sensitivity. It can be designed for
 the maximum possible short-circuit current in the system to be protected
 and can switch this system off, if necessary, after one half-cycle.
 The time delay between the occurrence of a tripping signal and the start of
 the movement of the switching piston (2) can be kept considerably shorter
 than one half-cycle owing to the high-speed electrical detonation and the
 high-speed chemical reaction.