High-voltage switches with arc preventing or extinguishing devic – Arc preventing or extinguishing devices – Housing structure
Reexamination Certificate
1999-04-19
2001-06-19
Donovan, Lincoln (Department: 2835)
High-voltage switches with arc preventing or extinguishing devic
Arc preventing or extinguishing devices
Housing structure
C218S152000
Reexamination Certificate
active
06248971
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a circuit breaker at least one phase of which is formed by several poles mounted in parallel.
The circuit breaker rating, i.e. the value of the rated current of the circuit breaker, is, for a case of predetermined size, determined by the choice of the poles, i.e. essentially by the dimensions of the copper parts associated to the pole.
It is desirable to be able to extend a circuit breaker range by associating circuit breakers comprising a certain number of standard poles so as to obtain, for a minimum additional cost, a circuit breaker of higher rating than that of the conventional poles which make up the circuit breaker. For this purpose, it has been proposed, in the document EP-A-0,320,412, to connect two adjacent poles of a standard circuit breaker in parallel. At least one phase of the circuit breaker is then constituted by two poles, each comprising a stationary contact extended by a contact strip protruding out from the case, a movable contact connected by a flexible conductor to a second contact strip protruding out from the frame, and an arc extinguishing chamber. One connecting strip is fixed to the contact strips of the stationary contacts of the two poles and another connecting strip is fixed to the contact strips of the movable contacts, thus achieving twinning of the two poles.
Experience however shows that when breaking occurs under these conditions, the arcing current does not divide uniformly between the two twinned poles. Very quickly, the arcing current in fact only persists in one of the two breaking chambers. If the ultimate short-circuit breaking capacity assigned to the circuit breaker remains identical to that of the original standard circuit breaker, this phenomenon does not have any drawbacks. If on the other hand a higher breaking capacity is sought for, the arcing energy becomes too great for a single chamber. The twinned pole construction of the state of the technique therefore proves unsuitable for manufacture of a circuit breaker whose breaking capacity is higher than that of the individual circuit breakers which make it up. This is why circuit breakers with high breaking capacity of the state of the technique do not use standard chambers mounted in parallel.
SUMMARY OF THE INVENTION
One object of the invention is therefore to extend a circuit breaker range so as to form, from existing circuit breakers, a circuit breaker of higher rating and breaking capacity than the individual circuit breakers which make it up, with a minimum number of modifications. Another object is to increase the breaking capacity of a circuit breaker with twinned poles.
These objects are achieved according to a first feature of the invention by means of a circuit breaker comprising at least two contiguous pole compartments separated by a partition and juxtaposed inside an insulating case, in each compartment there are arranged an arc extinguishing chamber and a pair of separable contact parts, each contact part of one of the compartments being electrically connected in parallel with a corresponding contact part of the other compartment or able to be connected thereto, a circuit breaker which comprises means for distributing the arcing energy in the two compartments, comprising at least one communicating aperture between the two contiguous compartments, arranged in the partition. In other words, when the opening performances of the compartments connected in parallel with and without an aperture are compared, the distribution of the arcing energy between the two chambers is appreciably more balanced when the aperture exists than when it is absent.
According to a second feature of the invention, these objects are achieved with a circuit breaker comprising at least two contiguous pole compartments separated by a partition and juxtaposed inside an insulating case, in each compartment there are arranged an arc extinguishing chamber and a pair of separable contact parts. The circuit breaker also comprises an operating mechanism linked to the separable contact parts of the two compartments in such a way that their separation is either simultaneous or almost simultaneous. The corresponding contact parts in each compartment are electrically connected in parallel to form a single pole with an ultimate breaking capacity l
cu
for a given corresponding assigned voltage v
cu
and power factor k
cu
, wherein said partition comprises at least one communicating aperture between the two contiguous compartments, of dimensions and location such that, when a current of an intensity equal to 50% of the ultimate breaking capacity l
cu
of the pole for the voltage v
cu
and power factor k
cu
is flowing globally through the pole, the ratio between the arcing energy in the least solicited of the compartments and the arcing energy in the other compartment is greater than ⅙, the arcing energy being measured for each compartment by the integral
W
=
∫
t
0
t
4
v
(
t
)
·
i
(
t
)
ⅆ
t
where
v(t) is the instantaneous value of the voltage at the terminals of the contact parts
i(t) is the instantaneous value of the current intensity flowing through the contact parts
t
0
is the time when separation of the contact parts begins
t
4
is the time when the current intensity flowing through the contact parts is finally cancelled.
The physical phenomena generated by the aperture in the partition separating the two compartments are complex. The presence of the aperture first of all has a thermodynamic aspect: the hot ionized gases at high pressure generated in the compartment whose arc is greater enter the other compartment. This particle movement has various effects some of which are positive and others of which are not. From an energy point of view, the hot gases which have migrated can use the separators of the cooler chamber to cool down, which is beneficial. From an electrical point of view, the presence of ionized gas in the compartment whose arc is weakening or extinguishing tends to revive this arc. From an aerodynamic point of view on the other hand, the gas movements and possible pressure waves from one compartment to the other can have an influence on the movement of the arc foot, and elongation of the arc in each compartment, with a risk of hindering movement of the arc to the arc extinguishing chamber due to the effect of the electrodynamic forces. However this electrodynamic phenomenon, called blowing, is of prime importance to achieve breaking and it is not desirable that its effect be reduced. Likewise, from the point of view of the variation of the pressures in the two compartments, the orifice also appears counter-productive. In fact a pressure decrease occurs in the compartment whose arc is greater and a pressure increase occurs in the other compartment. But theory indicates that a high pressure enhances a decrease of the straight cross-section of the arcing column, and therefore an increase of its electrical resistance and of the arcing voltage. This is moreover one of the main reasons for the existence of arc extinguishing chambers which, by performing a confinement of the arc, enable a considerable increase of the pressure in which the arc is located. Decreasing the pressure in the compartment whose arc is greater therefore means decreasing the arcing voltage and favoring maintenance of the arc.
Globally, in surprising and unpredictable manner, it proves possible to position and calibrate the aperture in such a way that mutual restrikings of the two arcs occur during breaking, which enables the arcing energy to be distributed over the two chambers in significant proportions and a greater absorption capacity to be achieved globally. Naturally the energy distribution is not perfectly balanced, but the important thing is that the energy dissipated in each compartment be of the same order of magnitude, i.e. in a proportion better than 1 for 10. In practice it is about ⅓ to ⅔. This is sufficient to relieve the pole which is more affected by the arc and to increase the breaking capaci
Morel Robert
Rival Marc
Donovan Lincoln
Parkhurst & Wendel L.L.P.
Schneider Electric SA
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