Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02825938 2013-08-28
RESTRICTED BREATHING ENCLOSURE
TECHNICAL FIELD
[0001] The following relates to restricted breathing enclosures.
BACKGROUND
[0002] It is sometimes necessary to install electrical equipment in a
hazardous location
where explosive gas may be present. If the electrical equipment creates a
spark when explosive
gas is present, an explosion can result. One method to prevent an explosion is
to ensure that the
explosive gas can never come into contact with the spark. In locations where
explosive gas is
present very rarely and for short periods, restricted breathing enclosures
have been used to keep
the explosive gas away from the sparking electrical equipment.
[0003] Restricted breathing enclosures may only be used if the average
temperature of
the air inside the enclosure may rise by a maximum of about 10 C when compared
with the
ambient temperature of the air outside the enclosure, when all internal
equipment is operating. In
a traditional restricted breathing enclosure, the internal temperature rise
may be kept below the
maximum value only if the internal electrical equipment dissipated very low
power. Any power
generated by the internal equipment must be conducted through the wall of the
enclosure. The
rate of heat transfer must equal or exceed the rate of heat dissipation by the
internal electrical
equipment so that the average internal temperature rises less than the
maximum.
[0004] Previously, restricted breathing enclosures were not used to
enclose circuit
breakers in hazardous locations where explosive gas might be present. Instead,
other methods of
protection such as explosion proof enclosures have typically been used for
circuit breakers
installed in hazardous locations. Circuit breakers dissipate significant heat,
especially when they
are operating near their trip point. This heat dissipation made it impractical
to transfer the heat
from the inside to the outside of the enclosure without exceeding maximum
allowable internal
temperature rise.
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SUMMARY
[0005] The present restricted breathing enclosure is designed to alleviate
this problem.
[0006] In a preferred embodiment, the electrical apparatus comprises a
restricted
breathing enclosure having an interior cavity; and a temperature regulator
having at least an
interior sensing portion within the interior cavity, the temperature regulator
including a processor
responsive to the interior sensing portion to send control signals to a heat
transfer portion of the
temperature regulator.
[0007] In an exemplary embodiment, the interior sensing portion and the
heat transfer
portion may both comprise a Peltier junction (also known as a thermoelectric
module) located
within the interior cavity, the Peltier junction being operable in a sensing
mode to act as the
interior sensing portion and a heat transfer mode to act as the heat transfer
portion.
[0008] In another embodiment, the heat transfer portion comprises a
Peltier junction
located within the interior cavity, and the interior sensing portion may be
any temperature
sensing device.
[0009] In a further embodiment, an ambient sensing portion is provided.
The ambient
sensing portion may be located exterior to the interior cavity. The processor
may be responsive
to the ambient sensing portion.
[0010] The processor may be located exterior to the interior cavity. The
Peltier junction
may be connected to the processor by electrical conductors that pass through a
restricted
breathing seal in the restricted breathing enclosure.
[0011] In another embodiment, there is a heat producing electrical
apparatus within the
interior cavity, the heat producing electrical apparatus having leads for
connecting into an
exterior circuit. The heat producing electrical apparatus may be a circuit
breaker. A sealed
actuator mechanism may be connected to the circuit breaker for controlling the
circuit breaker
between an on position and an off position.
[0012] The Peltier junction may have a hot side and a cold side. The hot
side may be
affixed to a wall of the electrical apparatus, and the cold side may be
exposed to the interior
cavity. An interior heat sink may be provided in the interior cavity to
transfer heat from the
interior cavity to the cold side of the Peltier junction. An exterior heat
sink may be provided
exterior from the interior cavity to radiate heat from the hot side.
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[0013] The restricted breathing enclosure may have steel walls. The
interior cavity may
be hermetically sealed from the exterior.
[0014] These and other aspects of the device and method are set out in the
claims, which
are incorporated here by reference.
BRIEF DESCRIPTION OF THE FIGURES
[0015] Embodiments will now be described with reference to the figures, in
which like
reference characters denote like elements, by way of example, and in which:
[0016] Fig. 1 is a perspective view of an embodiment of a restricted
breathing enclosure,
in which a Peltier junction comprises an interior sensing portion and a heat
transfer portion.
[0017] Fig. 2 is a perspective view of a restricted breathing enclosure,
in which an
interior sensing portion is distinct from a heat transfer portion.
[0018] Fig. 3 is a block diagram of a restricted breathing enclosure, in
which a Peltier
junction comprises an interior sensing portion and a heat transfer portion.
[0019] Fig. 4 is a block diagram of a restricted breathing enclosure, in
which an interior
sensing portion is distinct from a heat transfer portion.
DETAILED DESCRIPTION
[0020] Immaterial modifications may be made to the embodiments described
here
without departing from what is covered by the claims.
[0021] Referring to Fig. 1, an electrical apparatus 10 comprises a
restricted breathing
enclosure 12 having an interior cavity 14; and a temperature regulator 16
having at least an
interior sensing portion 18 within the interior cavity 14, the temperature
regulator 16 including a
processor 20 responsive to the interior sensing portion 18 to send control
signals to a heat
transfer portion 22 of the temperature regulator 16. Thus, the temperature of
the interior cavity
14 of the restricted breathing enclosure 12 may by actively controlled.
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[0022] As shown in the embodiment of Fig. 1, the interior sensing portion
18 and the
heat transfer portion 22 may both comprise a Peltier junction 24 located
within the interior cavity
14. The Peltier junction 24 may be operable in a sensing mode to act as the
interior sensing
portion 18 and in a heat transfer mode to act as the heat transfer portion 22.
An ambient sensing
portion 26 may be provided to measure the ambient temperature. The processor
20 may be
responsive to the ambient sensing portion 26.
[0023] As shown in Fig. 3, a current source 30 may power the processor 20.
The ambient
sensing portion 26 may send signals to the processor 20. The processor may
also send signals to
the heat transfer portion 22 and the interior sensing portion 18 of the
Peltier junction 24. The
interior sensing portion 18 of the Peltier junction 24 may in turn send
signals to the processor 20.
In some embodiments, when the Peltier junction 24 switches from the heat
transfer mode to the
heat sensing mode, it may be necessary to wait for the temperature of the
external heat sink 41
and the interior heat sink 40 to equalize to the temperature of the ambient
air and the interior air,
respectively, before taking temperature readings.
[0024] In the embodiment of Fig. 2, the heat transfer portion may comprise
a Peltier
junction 24A located within the interior cavity 14. The interior sensing
portion 18A may be
separate from the Peltier junction 24A. The interior sensing portion 18A may
be any suitable
temperature sensing device, such as a thermistor, a thermocouple, resistance
thermometer, or
other such means. An ambient sensing portion 26 may be provided to determine
ambient
temperature. The processor 20 may be responsive to the ambient sensing portion
26.
[0025] The processor 20 may use the difference in temperature between the
interior
cavity (as determined by the interior sensing portion 18 or 18A) and the
ambient temperature (as
determined by the ambient sensing portion 26) in a feedback control loop to
regulate the interior
cavity temperature.
[0026] In the embodiment of Fig. 4, both the interior sensing portion 18A
and the
ambient sensing portion 26 may send signals to the processor 20. The processor
may be powered
by a current source 30, and the processor 20 may send signals to the Peltier
junction 24A.
[0027] As in Figs. 1 and 2, the Peltier junction 24, 24A may be powered by
a current
source 30. The processor 20 may control the current through the Peltier
junction such that the
temperature of the air inside the enclosure 12 remains as close to the
temperature outside the
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enclosure 12 as desired and to limit the temperature range within the
enclosure 12 within a
predefined range, such as may be established by regulation. Both the current
source 30 and
processor 20 may be provided within a box 32.
[0028] In some embodiments such as that of Fig. 1, the Peltier junction 24
may comprise
a hot side 34 and a cold side 36. The hot side 34 may be affixed to a wall 38
of the electrical
apparatus 10, such that the wall 38 dissipates heat from the hot side 34 of
the Peltier junction 24
and radiates it to the air outside the interior cavity 14. In some embodiments
it may be necessary
to provide an exterior heat sink 41 to radiate heat from the hot side 34. The
cold side 36 may be
exposed to the interior cavity 14. An interior heat sink 40 may be provided in
the interior cavity
14 to transfer heat from the interior cavity 14 to the cold side 36 of the
Peltier junction 24, and
enhance heat transfer from the internal air to the cold side 36 of the Peltier
junction 24.
[0029] The processor 20 may be located exterior to the interior cavity 14.
The Peltier
junction 24 may be connected to the processor by electrical conductors 42 that
pass through a
restricted breathing seal 44 in the restricted breathing enclosure 12.
Similarly, in some
embodiments such as in Fig. 2 where the interior sensing portion 18A is
distinct from the Peltier
junction 24A, the interior sensing portion 18A may be connected to the
processor 20 by electrical
conductors 42A that pass through the restricted breathing seal 44 in the
restricted breathing
enclosure 12.
[0030] The restricted breathing enclosure 12 may be constructed with steel
walls, to
enhance heat dissipation and radiation.
[0031] Referring to Fig.1, there may be a heat producing electrical
apparatus 46 within
the interior cavity 14, the heat producing electrical apparatus 46 having
input and output leads 45
for connecting into an exterior circuit. The heat producing electrical
apparatus 46 may be a
circuit breaker 48.
[0032] A sealed actuator mechanism 50 may be connected to the circuit
breaker 48 for
controlling the circuit breaker between an on position and an off position, in
order to open and
close the circuit breaker from outside the restricted breathing enclosure
without allowing leaking
of air into or out of the enclosure 12. The shaft 52 of the sealed actuator
mechanism may be
sealed with an 0 ring or a U cup seal, to allow the shaft 52 to move without
allowing air to leak
along the shaft 52. The shaft 52 may transfer the motion of a handle 54
attached to outside the
CA 02825938 2013-08-28
enclosure 12 to an actuator 56 inside the enclosure 12 to move the on/off
lever 58 of the circuit
breaker 48.
[0033] In a preferred embodiment, the restricted breathing enclosure is
hermetically
sealed. The seal may in part be created through at least in part a door seal
59 on the door 61 of
the restricted breathing enclosure 12. It may be desirable to connect external
wires (not shown)
to the input and output leads 45 on the circuit breaker 48, without allowing
leakage of air into or
out of the enclosure 12. This may be accomplished by connecting wires to the
leads 45 on the
circuit breaker 48 inside the restricted breathing enclosure 12. These wires
may be routed to a
separate field termination enclosure 60 through a sealed coupling 62 such as a
Killark Model
ENY-3-T wherein the coupling 62 is completely sealed with epoxy after the
wires are routed
through, to prevent the leakage of air. The field termination enclosure 60 may
contain field
terminal blocks 64 such as Weidmuller W Series DIN Rail Terminals. The wires
from the
restricted breathing enclosure 12 may be connected to one side of the field
terminal blocks 64.
The external wires may be connected to the other side of the field terminal
blocks 64, so that
electrical connections may be made from the external wires to the terminals on
the circuit
breaker 48 without the need to open the restricted breathing enclosure 12. An
area 66 may be
provided for connecting external field wiring (not shown). Because there are
no components in
the field termination enclosure 60 that may create a spark under normal
conditions, it may not be
necessary to keep explosive gas out of the field termination enclosure 60.
This method may
allow field electricians to install the restricted breathing circuit breaker
assembly, without
concern for maintaining the seal on the restricted breathing enclosure.
[0034] This system of active temperature regulation may allow the heat
producing
electrical apparatus to dissipate much more power without exceeding maximum
allowable
temperature rise, compared to a passive system where heat transfer occurs only
due to the
temperature difference between the air inside the enclosure wall and the
ambient air outside.
[0035] By installing an active temperature regulator in a restricted
breathing enclosure as
described herein, it may now be possible to install one or more circuit
breakers in a restricted
breathing enclosure without violating the maximum temperature rise limitation.
[0036] In the claims, the word "comprising" is used in its inclusive sense
and does not
exclude other elements being present. The indefinite articles "a" and "an"
before a claim feature
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do not exclude more than one of the feature being present. Each one of the
individual features
described here may be used in one or more embodiments and is not, by virtue
only of being
described here, to be construed as essential to all embodiments as defined by
the claims.
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