Polyphase high-voltage circuit breaker

Abstract: The invention relates to a three-pole high-voltage circuit breaker with a device for synchronous closing or opening in relation to the phase position of voltage or current in the respective poles. The breaker has an operating mechanism with a rotary shaft (5) which is common to all the poles. The necessary time-lag between the instants of closing or opening in the different phases is brought about by mechanical means by connecting the movable contact (2) in each pole to the common rotary shaft (5) via an operating rod (3) and a crank lever (4) fixed to the shaft, the angle (α R , α S α T ) between the crank lever and the direction of movement of the movable contact in one of the breaker poles differing in magnitude from the corresponding angle (α R , α S α T ) in at least one of the other poles. By mutual adaptation of the lengths of the three crank levers (4), the same length of contact travel (s₁) in the different breaker poles can be obtained.

Description: The invention relates to a polyphase, preferably three-phase, high-voltage circuit breaker according to the precharacterising part of claim 1. More particularly the invention relates to a device for synchronous closing or opening of such a breaker. By "synchronous closing or opening" is meant that a defined time-lag between the instants of closing or opening of the breaker's poles (breaker units) in the different phases is obtained. The instants of closing or opening of the breaker units are usually selected in relation to the phase position of voltage or current in the respective phase. When certain electric apparatus, such as transformers, reactors or shunt capacitors, are switched into a high-voltage network by a circuit breaker which closes the circuit at an arbitrary point on the voltage wave, transient inrush currents with a large amplitude and rate of rise may occur. These currents may be detrimental to the apparatus and may cause mains interference. To reduce the above-mentioned inrush currents, it is known to use a circuit breaker with closing (preinsertion) resistors, whereby the apparatus in question is first connected to the network via these resistors, which are thereafter short-circuited by the main contacts of the circuit breaker. However, this is a relatively expensive solution, which requires a complicated operation mechanism, which in turn involves reduced reliability. It is known that the closing transients can be considerably reduced if, during connecting of apparatus of the above-mentioned kind via a three-phase circuit breaker to the network, a closing impulse is supplied to the operating device of the circuit breaker at such a time that the contact make in the three phases occurs at a certain point on the respective phase voltage wave. The most favourable time for contact make depends on what type of apparatus (load impedance) is to be switched in. For transformers and reactors the most favourable time of closing is often at the peak value of the respective phase voltage, whereas shunt capacitors in networks with a grounded neutral point should be switched in at the zero passage of the respective phase voltage, which means that there should be a 3.33 ms time interval between the instants of contact make in the three breaker poles, provided the mains frequency is 50 Hz. When connecting shunt capacitors to networks with an insulated neutral point, two phases should be switched in simultaneously at an instant when the voltage between them is near zero, whereas the third phase should be switched in when its voltage passes through zero 5 ms later. Equipment for achieving synchronous closing in the manner described above is described in IEEE Transactions on Power Apparatus and Systems, Vol. PAS-104, Sep. 1985 (R W Alexander: "Synchronous closing control for shunt capacitors"). In this equipment, an electronic control device is used which supplies separate tripping impulses in the different phases. This requires a separate operating device for each breaker pole, that is, in total three operating devices. From SE-A-457 582 a device for synchronous closing or opening of three-pole circuit breakers is previously known, in which the required time-lag between the instants of contact make or contact break in different phases is brought about by mechanical means. In this way it is possible, among other things, to use only one single operating device for synchronous switching of the three phases. In this device the movable contact in each breaker pole is connected, by means of a plurality of arms and links, to an operating rod common to poles of all phases. This operating rod is axially displaceable between a closed and an open position with the aid of the operating device. The invention aims at developing a polyphase, preferably threephase, high-voltage circuit breaker of the afore-mentioned kind arranged for synchronous closing or opening, which in comparison with corresponding prior art circuit breakers is less expensive and more reliable. To achieve this aim the invention suggests a polyphase, preferably threephase, high-voltage circuit breaker according to the introductory part of claim 1, which is characterized by the features of the characterizing part of claim 1. A further development of the invention is characterized by the features of claim 2. Like the device described in the above-mentioned SE-A-457 582, the circuit breaker according to the invention is designed for polyphase operation with an operating device, in which the time-lag between the instants of contact make or contact break in different phases is also brought about by mechanical means which links up contacts and operating device. However, in the design according to the invention, a considerable simplification of the mentioned mechanical means is achieved by the use of a rotary shaft which is common to all the breaker poles and which, via only one crank lever and an electrically insulating operating rod, is connected to the movable contact in the respective pole (breaker unit). The drawing schematically shows, in perspective, an embodiment of a threephase high-voltage circuit breaker according to the invention. The contacts and operating mechanism in the three poles (breaker units) of the circuit breaker are intended to be switched into a respective one of the phases R, S, T in a high-voltage network. The breaker may, for example, be an SF 6 circuit breaker of the kind described in ASEA Journal 1983, No. 3, pp. 16-21, and it is intended for three-pole operation, that is, the movable contacts in the three poles of the circuit breaker are mechanically connected to a common operating device. Each breaker pole comprises one fixed contact 1 and one rod-shaped or tubular, axially movable contact 2. The movable contact 2 is connected via an electrically insulating operating rod 3 and a crank lever 4, to a shaft 5, which is common to all the poles. The current path through the circuit breaker passes via the fixed contact 1, the movable contact 2 and a sliding contact 6. For alignment of the movable contact, a guide bearing 7 is provided. The operating shaft 5 is connected via a crank lever 8 and an operating rod 9, to an operating device which is able to rotate the operating shaft through a certain angle β. Opening of the circuit breaker is performed by displacing the rod 9 downwards (direction of arrow D), and closing is performed by displacing the rod upwards (direction of arrow E). The movable contact 2 then moves between the closed position, where the contact tip lies on the line C, and the open position, where the contact tip lies on the line A. The position of the contact tip at the instant of contact make or contact break is marked in the drawing by the line B. For synchronous closing of the circuit breaker, the operating device receives a closing impulse from an electronic control device which may be of conventional design. The operating shaft 5 is then rotated to the closed position. With knowledge of the closing time of the circuit breaker, the closing impulse can be chosen such that synchronous closing of the contacts in phases R, S, and T is obtained. Since the operating system in the three poles is mechanically connected through the operating shaft 5, a distinct time difference upon contact make or contact break between the three breaker units is always ensured. The time difference can be arbitrarily chosen by a suitable choice of the angles α R , α S and α T between the respective crank lever when the circuit breaker is in the closed position and the direction of movement of the movable contact. In the embodiment shown, α R is greater than α S , which in turn is greater than α T . By mutual adaption of the effective lengths of the crank levers 4, which lengths are marked in the drawing by the radii r R , r S and r T , the same length of contact travel s 1 and the same contact path s 2 can be obtained in the three poles. In the drawing, contacts and link mechanisms in the three poles are shown in the position in which contact make has just occurred in phase S. The movable contact 2 in phase T has then already passed the position of contact make by the length x 2 , whereas the corresponding contact in phase R still has to cover the distance x 1 before contact make occurs. The crank levers 4 are suitably fixed to the shaft 5 by splines, whereby the angles α R , α S and α T can be easily adapted to the use of the circuit breaker.

Claims: Poly-phase, preferably three-phase, high-voltage circuit breaker with at least one breaking unit per phase, said breaking units each comprising a rod-shaped or tubular, axially movable contact (2) which is connected via a operating rod (3) to an operating shaft (5) which is common to the breaking units of all phases and which is rotatable back and forth between a closed and an open position, characterized in that the connection between each operating rod (3) and the operating shaft (5) takes place via a crank lever (4), whereby the angle (α R , α S , α T ) between the crank lever (4) and the direction of movement of the movable contact (2) in the breaker unit(s) of one phase differs in magnitude from the corresponding angle (α R , α S , α T ) in the breaker unit(s) of at least one of the other phases to such an extent that synchronous closing or opening of the breaker unit(s) in relation to current or voltage in the respective phases is obtained. High-voltage circuit breaker according to claim 1, characterized in that said crank lever (4) of the breaker unit(s) in one phase has a length different from that of the corresponding crank lever (4) of the breaker unit(s) in at least one of the other phases.

Inventors: AKESSON ULF, AKESSON,ULF
Applicants: ASEA BROWN BOVERI, ASEA BROWN BOVERI AB
Application year: 1992
Main classification: H01H1
IPC codes: H01H9