GB2196794A

GB2196794A - Electric circuit

Info

Publication number: GB2196794A
Application number: GB08725003A
Authority: GB
Inventors: Kari Luoma
Original assignee: Stromberg Oy AB
Current assignee: ABB Stromberg Oy
Priority date: 1986-10-27
Filing date: 1987-10-26
Publication date: 1988-05-05
Anticipated expiration: 2007-10-26
Also published as: SE8704180L; FI78195C; IT8767902A0; FR2605796B1; FI864340A; DE3736165A1; GB2196794B; GB8725003D0; DE3736165C2; IT1211430B; SE462881B; FR2605796A1; FI864340A0; SE8704180D0; FI78195B

Description

GB2196794A 1 SPECIFICATION current breaking capacity within the whole cur

rent range. This is because with low currents An electric circuit-breaker magnetic forces alone are not able to shift the base point of the arc to the annular arc elec The invention relates to an electric circuittrode, i.e. an arc ring.

breaker in which breaking means are provided The object of the present invention is to in a breaking housing containing an insulation improve the advantageous basic structure dis and extinguishing medium, said breaking closed in the above-mentioned European Pa means comprising: a first fixed contact con- tent Specification 11,972 in such a way that a nected to a first portion of the current path; a 75 reliable breaking is provided within the whole second movable knife contact one end of current range. For the achievement thereof, which is hinged to be pivotable in such a way the basic structure described in the beginning that a tip of the knife contact moves along a is characterized in that the knife contact is so circular path, and which knife contact is con- arranged with respect to the arc electrode that nected to a second portion of the current 80 the tip thereof gets into galvanic contact with path; and an annular arc electrode surrounded the arc electrode between the ON and OFF by a coil connected electrically in series be- positions of the circuit- breaker.

tween the arc electrode and the first contact, The inventive basic idea is thus to ensure whereby the tip of the knife contact makes that the base point of the arc is shifted even contact with the first fixed contact in the ON 85 with low currents from the fixed contact to position of the circuit-breaker, and during the the arc ring so that the tip of the knife con opening of the circuit-breaker, an arc is first tact makes contact with the arc ring when formed between the fixed contact and the passing it.

knife contact and thereafter between the knife According to one preferred embodiment of contact and the arc electrode, so that the 90 the invention, the arc ring is provided with an magnetic field created by the coil causes the outwardly projecting commutation block of arc to rotate so that it is extinguished. tungsten copper with which the tip of the It is generally known to provide electric cir- knife contact makes contact during the move- cuit-breakers with a coil which causes the arc ment thereof.

to rotate. This is particularly useful in circuit- 95 A contact structure as inexpensive and relia- breakers in which sulphur hexafluoride (SFJ is ble as possible is obtained by using parallel used as an insulation and extinguishing me- knives in the knife contact. Therefore the out dium in the housing. wardly projecting commutation block in It has been difficult in circuit-breakers utiliz- another preferred embodiment of the invention ing the principle of rotating arc to reliably en- 100 is narrower than the fixed contact, i.e. nar sure that the arc is put into rotation and sirower than the interspace between the parallel multaneously provide the apparatus with a knives in the ON position of the contact.

structure as simple and as economically profi- It is further to be preferred that the knife table as possible. To solve these problems, a contact is so positioned with respect to the circuit-breaker structure is previously known in 105 arc ring that the hinge point thereof is outside which the movable contact is hinged at one the central axis of the coil, and that the knife end, so that the path of the contact can be contact is parallel to the central axis of the easily determined by means of the hinge po- coil in the ON position of the circuit-breaker.

int, whereby no additional operating devices In this way the tip of the knife contact is are needed. The operating means moving the 110 positioned remote from the arc ring in the OFF contact can thereby also be simplified. position. This improves considerably the die- However, this kind of prior circuit-breakers lectric strength of the clearance between open have the drawback that in the ON position of contacts and the breaking capacity of low cur the contacts the current flows through the rents so that the diameter of the coil need not coil, thus warming it. 115 be increased when a higher voltage is applied.

Europea n Patent Specification 11,972 dis- The outer dimensions of the circuit-breaker are closes a circuit-breaker in which this thereby also reduced.

drawback, too, has been eliminated. The cir- In the following the invention will be de- cuit-breaker thereby comprises a knife-like scribed in more detail with reference to the contact which is hinged at one end thereof 120 examples shown in the attached drawings, and the tip of which moves along a circular wherein path. The coil creating a magnetic field is po- Figure 1 is a side view of a circuit-breaker sitioned outside the current path when the structure according to the invention in the ON contacts are in the ON position. When shifted position, to the OFF position, the knife-like contact 125 Figure 2 is a top view of the circuit-breaker moves towards the axis of the coil so that it structure seen in the direction of the line 11-11 passes the arc electrode close thereto and re- shown in Figure 1, mains parallel to the axis of the coil in the Figure 3 shows the circuit- breaker structure OFF position thereof. However, a drawback of in a side view similarly as in Figure 1 but in a this structure is that it possesses a deficient 130 position in which a knife contact is in -galvanic 2 GB2196794A 2 contact with an arc electrode, and In the following the operation of the circuit- Figure 4 is likewise a side view of the cir- breaker structure according to the invention cuit-breaker structure when the circuit-breaker will be described with reference to both Fig is in the OFF position thereof. ures 1 and 2 and to Figures 3 and 4. In the The figures show only parts relevant to the 70 ON position of the circuitbreaker a tip 4c of invention; the housing structure, for instance, the knife contact 4 makes contact with the is shown in Figure 1 only. fixed contact 2 as shown in Figures 1 and 2, Figure 1 shows a circuit-breaker structure so that current flows from the first portion 3a arranged in a housing 1. The housing is gas- of the current path to the second portion tight and contains an extinguishing and insula- 75 thereof through the fixed contact 2 and the tion medium, preferably sulphur hexafluoride knives 4a and 4b. The opening of the circuit (SF,). The circuit-breaker structure comprises breaker is effected by the above-mentioned an elongated fixed contact 2 connected to a operating means by the action of the guide first portion 3a of a current path, and a mov- arms 10 and 11. At the beginning of the able knife contact 4 comprising two parallel 80 breaking process, the knives 4a and 4b are knives 4a and 4b (Figure 2). The knife contact disengaged from the main contact 2, so that 4 is connected to a second portion 3b of the an arc is formed between the knives and the current path. An annular arc electrode, i.e. an fixed contact 2. When the knives have been arc ring 5, is arranged on the fixed contact 2, disengaged from the fixed contact 2, the and a coil 6 is arranged around the arc ring. 85 springs 12 allow them to approach each The coil is narrower than the arc ring 5 and other, so that the tip 4c thereof gets into electrically in series therewith, so that the arc galvanic contact with the commutation block current passes from the arc ring 5 through the 8, which is narrower than the fixed contact.

coil 6 into the fixed contact 2. The arc ring 5 The operational stage for this opening move is fastened to the fixed contact 2 by means 90 ment is shown in Figure 3. Part of the current of an insulation block 7. Further, a commuta- passes now through the coil 6, generally ex tion block 8 projecting from the end plane of tinguishing the arc between the knives or the the arc ring 5 is arranged in the lower part of commutation block and the fixed contact 2 the arc ring 5. The knife contact 4 is hinged already at this stage. While the opening at the end thereof close to the second portion 95 movement of the knife contact 4 is continued 3b of the current path by means of a hinge as shown with the arrow D in Figure 3, it is pin 9 so that the knives 4a and 4b are pi- disengaged from the commutation block 8, so voted round a hinge axis A (Figure 2) in a that the proper arc is formed between the manner described below. The hinge point of knife contact 4 and the arc ring 5 (the com the knives is also positioned in the mid plane 100 mutation block 8), i.e. one base point of the C of the fixed contact 2, and in the ON posi- arc has now shifted from the fixed contact 2 tion of the circuit-breaker, shown in Figure 1, to the arc ring 5. The arc current passes now the knives 4a and 4b are substantially in par- through the coil 6, so that the magnetic field allel with the central axis B of the coil 6. A created by the coil causes the arc to rotate in guide arm 10 is jointed substantially in the 105 a known manner so that it is extinguished. By middle of the knives, and the guide arm, in attaching the arc ring 5 to the fixed contact 2 turn, is jointed on another guide arm 11. By by means of the insulation block 7 as de means of the guide arms 10 and 11, operat- scribed above, the rotation of the arc ring 5 ing means positioned outside the housing 1 under the influence of the magnetic forces is cause the knife contact 4 to move in a man- 110 prevented and it is thus ensured that the com ner described below. The operating means are mutation block 8 stays in its proper place. At not shown separately, because they are not the same time the strains exerted on the coil relevant to the basic idea of the invention. 6 are reduced.

Figure 2 shows schematically springs 12 by The knife contact 4 further continues to means of which the knives 4a and 4b are 115 move towards the OFF position of the circuit pressed against each other for obtaining a breaker shown in Figure 4, in which the tip 4c suitable contact force on the contact surfaces. of the contact has clearly risen above the cen Since the current causes the parallel knives 4a tral axis B of the coil 6. The arc is extingu and 4b to be drawn towards each other when ished either as early as during the movement it passes therethrough, it increases the con120 of the knife contact 4 or not until thereafter tact force when this is required. So it is pos- when the knife contact has reached the OFF sible to use springs providing a small contact position thereof. The extinguishing point de force and the contacts will have a long me- pends on the phase of the current, i.e. on the chanical life time. It further appears from Fig- position of the zero point of the current with ure 2 that the commutation block 8 made of 125 respect to the breaking moment. In the OFF tungsten copper and projecting from the end position the tip 4c of the knives is remote face of the arc ring 5 is narrower than the from the arc ring, so that a high dielectric interspace between the knives 4a and 4b in strength is obtained in the clearance between the transverse direction of the knives in the open contacts.

ON position of the circuit-breaker. 130 Even though the invention has been de- 3 GB2196794A 3

Claims

scribed above with reference to the examples Claim 1 or 3, characterised in that the hinge of the attached drawings, it is to be under- point of the knife contact (4) is outside the stood that the invention is not restricted central axis (B) of the coil (6), and that the thereto, but it can be modified within the in- knife contact (4) is parallel to the central axis ventive idea defined in the attached claims. So 70 (B) of the coil in the ON position of the circuit- e.g. the spring(s) drawing the knives towards breaker. each other may as well be positioned between 5. An electric circuit breaker comprising a the knives. The knife contact can also be fixed contact, a movable contact, movable formed by a single knife, whereby the commu- into and out of engagement with the fixed tation block 8 would be provided with e.g. 75 contact, and an arc electrode supporting an projecting branches between which the knife arc extinguishing electromagnetic coil which is would extend. However, this kind of structure connected across the movable and fixed con will not provide all the above-described advan- tacts, the locus of the movable contact being tages of the structure. such that it makes contact with the arc electrode as it moves into and out of engagement CLAIMS with the fixed contact.

1. An electric circuit-breaker in which break- 6. An electric circuitbreaker substantially as ing means are provided in a breaking housing hereinbefore described with reference to Fig (1) containing an insulation and extinguishing ures 1 and 2 or Figures 3 and 4.

medium, said breaking means comprising:

- a first fixed contact (2) connected to a Published 1988 at The Patent Office, State House, 66/7 1 HighHolborn, London WC 1 R 4TP. Further copies may be obtained from first portion (3a) of the current path; The Patent Office, Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD.

- a second movable knife contact (4) one Printed by Burgess & Son (Abingdon) Ltd. Con. 1/87.

end of which is hinged to be pivotable in such a way that a tip (4c) of the knife contact (4) moves along a circular path, and which knife contact (4) is connected to a second portion (3b) of the current path; and - an annular arc electrode (5) surrounded by a coil (6) connected electrically in series be tween the arc electrode (5) and the first con tact (2), whereby the tip (4c) of the knife contact makes contact with the first fixed contact (2) in the ON position of the circuit-breaker, and during the opening of the circuit-breaker, an arc is first formed between the fixed contact (2) and the knife contact (4) and thereafter between the knife contact (4) and the arc electrode (5), whereby the magnetic field created by the coil (6) causes the arc to ro tate so that it is extinguished, characterized in that the knife contact (4) is so arranged with respect to the arc electrode (5) that the tip (4c) thereof gets into galvanic contact with the arc electrode (5) between the ON and OFF positions of the circuit-breaker.

2. An electric breaker according to claim 1, characterized in that the annular arc electrode (5) comprises a commutation block (8) which projects outwardly from the end plane of the ring and with which the tip (4c) of the knife contact makes contact.

3. An electric circuit-breaker according to Claim 2, wherein the knife contact (4) is formed by two parallel knives (4a, 4b) pro vided with springs, characterised in that the width of the commutation block (8) is smaller than the interspace between the knives (4a, 4b) in the ON position of the circuitbreaker, whereby the knife contact does not make contact with the commutation block (8) until it is completely disengaged from the fixed con tact (2).

4. An electric circuit-breaker according to