Technical field
The invention relates to a puffer circuit breaker having
an overpressure valve.
Puffer circuit breakers generate a high pressure buildup
in their puffer volume at very high current levels. The pressure depends on contact
speed, puffer volume, current asymmetry and contact system dimension. While it is
desirable to achieve a certain pressure level in the circuit breaker, a too high
pressure is not desired since the force generated by the pressure acts against the
contact movement, reduces the contact distance in the moment of interruption and/or
makes it necessary to use a stronger breaker drive.
Background
It has therefore been known to use overpressure valves
for limiting the pressure in the puffer volume. However, such overpressure valves,
which are mounted as separate units to the support of the movable contact assembly,
are expensive. In addition, they require space or, if they are of small design,
they have small diameters only, which reduces the gas flow therethrough.
Summary of the invention
Hence, the object of the present invention is to provide
a puffer circuit breaker that addresses these problems. This object is achieved
by the circuit breaker of claim 1.
Accordingly, the support comprises an integrated valve
cavity for receiving the spring of the valve. Furthermore, it comprises an integrated
valve inlet opening that opens into the puffer volume and that can be closed by
the piston of the valve.
Since the valve cavity and inlet opening are integrated
into the support, the support itself forms the walls of the same. In contrast to
this, the conventional design uses a separate valve unit forming the valve cavity
and the valve inlet opening, which valve unit has, in turn, to be held by the support,
e.g. in a threading, which requires more space.
Advantageously, the support comprises an integral, single-piece
body surrounding the driving rod of the moveable contact assembly and the valve
cavity and valve inlet opening are integrated therein.
Brief description of the drawings
Further embodiments, advantages and applications of the
invention are disclosed in the dependent claims as well as in the following description,
which makes reference to the figures. These show:
- Fig. 1 is a sectional view of a circuit breaker and
- Fig. 2 is an enlarged section of Fig. 1 showing a single overpressure valve.
Embodiments of the invention
The circuit breaker of Fig. 1 is a high voltage circuit
breaker designed for voltages of e.g. at least 72.5 kV. It comprises a stationary
contact assembly 1 and a moveable contact assembly 2. Moveable contact assembly
2 is moveably held in a stationary support 3. A rod 4 comprising a base member 4a
and a tube 4b is connected to moveable contact assembly 2 for moving the same along
a direction of displacement that generally coincides with the longitudinal axis
5 of the circuit breaker.
Stationary contact assembly 1 comprises a series of first,
stationary contacts 6 arranged to contact a mating second contact 7 of moveable
contact assembly 2. When the circuit breaker is operated, second contact 7 disengages
from the first contacts 6 and an arc is formed in an arc volume. The pressure generated
in the arc volume feeds back, in part, into a puffer volume 9 (also called "buffer
volume") formed between moveable contact assembly 2 and support 3. Puffer volume
9 is formed between a front plate 11 of support 3 and a cylinder housing 12 of moveable
contact assembly 2. Front plate 11 is slideably arranged in the cylinder housing
12.
Support 3 comprises an integral tubular body 10 made from
a single piece of cast metal. Body 10 is of tubular, approximately cylindrical shape
and extends around rod 4. It forms front plate 11 at one end, a cylindrical base
section 13a at the opposite end, and a valve section 13b located between front plate
11 and base section 13a. Rod 4 is located in an axial cavity 14 of body 3 and guided
therein by frictional bearings 15.
Overpressure valves 16 are mounted in valve section 13b
of the integral tubular body 10 of support 3. In the present embodiment, a total
of four such overpressure valves 16 are provided in two pairs at angular positions
of e.g. 0°, 45° and 180°, 225°. Two of these overpressure valves
16 can be seen in Fig. 1. The purpose of these valves 16 is to release gas from
puffer volume 9, if the pressure therein exceeds a given threshold of e.g. 45 bar.
As can best be seen in Fig. 2, each overpressure valve
16 comprises a moveable piston 17 with a rear end 17a extending into a valve cavity
18 formed by a bore in valve section 13b of the tubular body 10. A valve spring
19 surrounds rear end 17a of piston 17 and extends, in a slightly compressed state,
between a shoulder 20 of piston 17 and a rear wall 21 of valve cavity 18.
A head 22 at the forward end of piston 17 extends into
a valve inlet opening 23. Valve inlet opening 23 is formed by a bore through front
plate 11 of support 3.
A stop member 24 formed by a screw projects laterally from
piston 17 into an elongate hole or recess 25. The stroke could also be limited by
any other means, e.g. by a centered screw or a Seeger-ring.
The tubular body 10 further comprises at least one window
26 forming a duct from a region between valve cavity 18 and valve inlet opening
23 to an exhaust space of the circuit breaker. In the embodiment shown here, the
window 26 opens into the exhaust space 27 located outside the tubular body 10 as
well as into the axial cavity 14, with the axial cavity 14 being connected to the
exhaust space 27 by means of large openings (not visible in the figures) in the
tubular body 10.
In operation in the absence of overpressure in puffer volume
9, spring 19 urges piston 17 forwards such that its head 22 extends into the valve
inlet opening 23, thereby closing the valve 16. When the pressure in puffer volume
9 exceeds the threshold pressure of the valve 16, the piston 17 is pushed backwards
to release the valve inlet opening 23, thereby opening the valve 16 such that gas
from puffer volume 9 can pass through window 26. The maximum displacement of piston
17 is limited by the stop member 24 abutting against a rear end 25a of the hole
or recess 25 or by the rear end 17a of the piston 17 abutting against the rear wall
21 of the valve cavity 18. This limitation prevents an excessive, potentially damaging
compression of the spring 19 even if the pressure in the puffer volume 9 is very
high.
Piston 17 is displaceable along a direction of displacement
parallel to longitudinal axis 5 of the circuit breaker (see Fig. 1). Its head 22
has a constant cross-section, i.e. the cross-section perpendicular to the direction
of displacement does not change along the direction of displacement. Similarly,
at least an end section 23a of the valve inlet opening 23 has a constant cross-section.
Both said cross-sections match for forming a seal when the head 22 extends into
the end section 23a. The head 22 ends in an end surface 28 of piston 17 that extends
perpendicular to said direction of displacement. Similarly, the end section 23a
of valve inlet opening 23 ends in a surface 29 of support 3 that extends perpendicular
to said direction of displacement. All these measures contribute, individually and
in combination, to reducing the hysteresis of the overpressure valve 16.
As can be seen e.g. in Fig. 2, piston 17 closes a forward
end of the cavity 18. In order to allow a gas exchange between the cavity 18 and
its surroundings during a movement of piston 17, a duct 30 connects the valve cavity
18 to the exhaust space 27 (or to any other volume much larger than the valve cavity
18). Duct 30 is dimensioned such that the gas passing therethrough experiences sufficient
friction for damping the movement of piston 17 in cavity 18.
The overpressure valve 16 according to the design shown
here is very compact. Hence, it is inherently fast. To increase its speed even further,
piston 17 is made of aluminum, thereby reducing its weight.
Even though the overpressure valve 16 is very compact,
it can open a channel of comparatively large cross-section, thereby depleting the
puffer volume 9 quickly. To further expedite such a depletion, a window 26 opens
towards an axial cavity 14 and a window 26, preferably the same window 26, opens
towards an exhaust space 27. Preferably, the windows 26 are large, each one connecting
two neighboring overpressure valves 16, which again increases the available cross-section
of the passage.
The design of the overpressure valve 16 shown here is simple
and compact. Since it is an integral part of support 3, the costs for its assembly
are low. Still it reacts quickly, has low hysteresis, and is able to deplete the
puffer volume 9 quickly.
List of reference numbers
- 1: stationary contact assembly
- 2: moveable contact assembly,
- 3: support
- 4: rod
- 4a: base member
- 4b: tube
- 5: longitudinal axis
- 6: first contacts
- 7: second contact
- 9: puffer volume
- 10: body
- 11: front plate
- 12: cylinder housing
- 13a: base section
- 13b: valve section
- 14: axial cavity
- 15: frictional bearings
- 16: overpressure valves
- 17: piston
- 17a: rear end of piston 17
- 18: valve cavity
- 19: valve spring
- 20: shoulder
- 21: rear wall of valve cavity 18
- 22: head of piston 17
- 23: valve inlet opening
- 23a: end section of valve inlet opening
- 24: stop member
- 25: hole or recess
- 26: window
- 27: exhaust space
- 28: end surface
- 29: surface
- 30: duct
