TECHNICAL FIELD
[0001] The invention concerns a sealing apparatus for a liquid-filled electrical equipment
comprising a cavity filled with a dielectric liquid. The invention also concerns an
assembly comprising a sealing apparatus and an electrical equipment.
[0002] The invention applies to the field of electric power generation and transmission,
and more precisely to electric power systems.
BACKGROUND ART
[0003] In the field of electric power generation and transmission, it is known to use liquid-filled
electrical equipment, such as a liquid-filled power transformer or a shunt reactor.
Such an equipment comprises a casing defining a cavity, said cavity being filled with
a dielectric liquid such as mineral oil or alternative insulation liquids like natural
or synthetic ester.
[0004] Generally, a liquid-filled electrical equipment is provided with a conservator (also
called "expansion tank") to enable expansion and contraction of the dielectric liquid
due to temperature changes. Such temperature changes result, for instance, from daily
and seasonal temperature variations of the environment surrounding the electrical
equipment or from variations in loading.
[0005] However, if the conservator is not hermetically sealed, the electrical equipment
is free breathing with the external environment. As a result, moisture and oxygen
can ingress into the dielectric liquid, thereby changing its performance (for example
by reducing the breakdown voltage capability or accelerating ageing due to oxidation)
and affecting nominal operation of the electrical equipment. Moreover, moisture and
oxygen may also be absorbed within a paper insulation system used in the electrical
equipment, which may affect the performance and accelerate cellulose ageing (for example
by oxidative or hydrolytic aging).
[0006] To prevent such a problem, it has been suggested to seal the conservator, from the
surrounding air, with an elastic membrane (also referred to as "rubber bag", "hydro-compensator",
"bladder" or "air bag") configured to expand and contract to absorb thermal expansion
and contraction of the dielectric liquid.
[0007] However, such rubber bags are not satisfactory.
[0008] Indeed, these rubber bags are generally not robust and are subject to tearing, their
lifetime expectancy being only about ten years. Such tears may result in dielectric
liquid leakage, as well as ingress of oxygen and moisture within the electrical equipment.
Since the aforementioned electrical equipment are generally designed to last at least
thirty years, repair or replacement of the rubber bag is required on a regular basis,
which is costly.
[0009] A purpose of the invention is to provide a sealing apparatus that is simpler and
more robust and cost-efficient than such rubber bags.
SUMMARY OF THE INVENTION
[0010] To this end, the present invention is a sealing apparatus of the aforementioned type,
comprising a conservator and a breather device,
the breather device comprising a main port, an input port and an output port, and
being configured to allow:
- a first fluid flow from the main port to the output port if a pressure difference
between the main port and the output port is higher than a predetermined overpressure
threshold; and
- a second fluid flow from the input port to the main port if a pressure difference
between the main port and the input port is lower than a predetermined under-pressure
threshold,
the conservator comprising an enclosure including a first port for connection to the
cavity of the liquid-filled electrical equipment, and a second port, distinct from
the first port, fluidically connected to the main port of the breather device, the
enclosure defining an internal volume in fluid communication with each of the first
port and the second port.
[0011] Indeed, using such a sealing apparatus, the need for a rubber bag similar to that
used in the prior art is eliminated. As a result, the claimed sealing apparatus is
simple and robust.
[0012] Such a sealing apparatus is designed so that, within a predetermined temperature
range, corresponding to a predetermined nominal pressure range of the dielectric liquid
in the electrical equipment, the electrical equipment is hermetically sealed. As an
example, such a temperature range corresponds to the -25 °C to 100 °C range prescribed
by the International Electrotechnical Commission (IEC) 60076 series standards.
[0013] Moreover, the claimed sealing apparatus has a pressure release capability, whereby
breathing of the electrical equipment is allowed if a pressure within the cavity of
the electrical equipment, that is to say a pressure at the main port of the breather
device, is outside the nominal pressure range. This enhances safety.
[0014] The inventors have found that, using the claimed sealing apparatus, breathing of
the electrical equipment can be reduced to approximately less than 10% of the breathing
occurring if the liquid-filled electrical equipment were left free breathing.
[0015] Moreover, due to its simple architecture, the claimed sealing apparatus can be designed
so that it can be accessed, from ground level, while the liquid-filled electrical
equipment is in service, thus allowing an operator to easily perform inspections.
[0016] According to other advantageous aspects of the invention, the sealing apparatus includes
one or more of the following features, taken alone or in any possible combination:
- the breather device comprises a first non-return valve and a second non-return valve,
the first non-return valve being arranged between the main port and the output port
and being configured to allow the first fluid flow if the pressure difference between
the main port and the output port is higher than the overpressure threshold, and the
second non-return valve being arranged between the main port and the input port and
being configured to allow the second fluid flow if the pressure difference between
the main port and the input port is lower than the under-pressure threshold;
- the sealing apparatus further comprises a controller configured to control the breather
device, preferably the overpressure threshold and/or the under-pressure threshold,
based on at least one predetermined control parameter;
- the input port and the output port form a same common port;
- the breather device comprises a bidirectional valve arranged between the main port
and the common port and configured:
- to allow the first fluid flow if the pressure difference between the main port and
the common port is higher than the overpressure threshold; and
- to allow the second fluid flow if the pressure difference between the main port and
the common port is lower than the under-pressure threshold;
- the sealing apparatus further comprises a safety valve including an inlet and an outlet,
the inlet being fluidically connected to the second port of the conservator, in parallel
to the breather device, the safety valve being configured to allow a third fluid flow
from the inlet to the outlet if a pressure difference between the inlet and the outlet
is higher than a predetermined safety threshold, the safety threshold being higher
than or equal to the high pressure threshold;
- the sealing apparatus further comprises a gas drying part connected to the input port
of the breather device and configured to at least partly remove moisture from the
second fluid flow;
- the sealing apparatus further comprises a gas supply fluidically connected to the
input port of the breather device;
- the conservator further comprises an elastic membrane arranged within the enclosure
to provide a hermetic seal between the first port and the second port;
- the sealing apparatus further comprises a pressure gauge arranged upstream with respect
to the first flow and configured to measure a pressure within the sealing apparatus,
preferably the pressure at the main port.
[0017] The invention also relates to an assembly comprising an electrical equipment and
the sealing apparatus as defined above, the electrical equipment being a liquid-filled
electrical equipment comprising a cavity filled with a dielectric liquid, the first
port of the conservator of the sealing apparatus being connected to the cavity of
the liquid-filled electrical equipment so that the internal volume is partially filled
with dielectric liquid when a temperature of the dielectric liquid is within a predetermined
nominal temperature range.
[0018] Advantageously, the assembly further comprises a Buchholz relay arranged between
the first port of the conservator and the cavity of the liquid-filled electrical equipment.
[0019] The invention also relates to an assembly comprising an electrical equipment and
a sealing apparatus, the electrical equipment being a blanketed-tank electrical equipment
comprising a cavity, a dielectric liquid and a blanketing gas being provided in the
cavity, the blanketing gas forming a gas blanket arranged on top of the dielectric
liquid, the sealing apparatus comprising a breather device including a main port,
an input port and an output port, and configured to allow:
- a first fluid flow from the main port to the output port if a pressure difference
between the main port and the output port is higher than a predetermined overpressure
threshold; and
- a second fluid flow from the input port to the main port if a pressure difference
between the main port and the input port is lower than a predetermined under-pressure
threshold,
the main port of the breather device being connected to the cavity of the blanketed-tank
electrical equipment so that, when a temperature of the dielectric liquid is within
a predetermined nominal temperature range, the main port leads to the gas blanket,
the gas blanket confining the dielectric liquid in the cavity.
[0020] According to other advantageous aspects of the invention, the assemblies defined
above include one or more of the following features, taken alone or in any possible
combination:
- the electrical equipment is a power transformer or shunt reactor;
- the electrical equipment comprises a pressure gauge configured to measure a pressure
within the electrical equipment.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] The invention will be better understood with the attached figures, in which:
- figure 1 is a schematic view of an assembly comprising a liquid-filled electrical
equipment provided with a first embodiment of a sealing apparatus according to the
invention; and
- figure 2 is a schematic view of an assembly comprising a blanketed-tank electrical
equipment provided with another embodiment of a sealing apparatus according to the
invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0022] An assembly 2 comprising a liquid-filled electrical equipment 4 connected to a sealing
apparatus 6 according to the invention is shown on figure 1.
[0023] As an example, the liquid-filled electrical equipment 4 is a transformer, such as
a three-phase transformer, or a shunt reactor.
[0024] The liquid-filled electrical equipment 4 comprises a casing 8 defining a cavity 10,
the cavity 10 being filled with a dielectric liquid 12. For instance, the dielectric
liquid 12 is mineral oil.
[0025] The sealing apparatus 6 is configured to provide hermetic sealing to the cavity 10
within a predetermined nominal pressure range inside the cavity 10, corresponding
to a predetermined nominal temperature range (for instance -25 °C to 100 °C), while
allowing for thermal expansion and contraction of the dielectric liquid 12. The sealing
apparatus 6 is also configured to allow for breathing of the liquid-filled electrical
equipment 4 when the pressure within the cavity 10 is outside the nominal pressure
range.
[0026] The sealing apparatus 6 comprises a conservator 14 and a breather device 16 connected
to each other through a tubing 17.
[0027] The conservator 14 comprises an enclosure 18 defining an internal volume 20. The
enclosure 18 further comprises a first port 22 and a second port 24, distinct from
the first port 22, the internal volume 20 being in fluid communication with each of
the first port 22 and the second port 24.
[0028] As shown on figure 1, after connection of the sealing apparatus 6 to the liquid-filled
electrical equipment 4, the first port 22 of the conservator 14 is connected to the
cavity 10 of the liquid-filled electrical equipment 4. As a result, during normal
operating conditions (that is to say within the nominal temperature range), the enclosure
18 is partially filled with the dielectric liquid 12, a level of the dielectric liquid
within the enclosure 18 rising and dropping with the thermal expansion and contraction
of the dielectric liquid 12.
[0029] Preferably, a Buchholz relay 25 is arranged between the first port 22 and the cavity
10.
[0030] Moreover, the second port 24 is fluidically connected to the tubing 17.
[0031] The breather device 16 comprises a main port 26, an input port 28 and an output port
30.
[0032] The main port 26 is fluidically connected to the tubing 17, so that the main port
26 of the breather device 16 and the second port 24 of the conservator 14 are fluidically
connected to each other.
[0033] The breather device 16 is configured to allow a first fluid flow from the main port
26 to the output port 30 if a pressure difference between the main port 26 and the
output port 30 is higher than a predetermined overpressure threshold which is, for
instance, equal to 200 mbar (millibar).
[0034] The breather device 16 is further configured to allow a second fluid flow from the
input port 28 to the main port 26 if a pressure difference between the main port 26
and the input port 28 is lower than a predetermined under-pressure threshold which
is, for instance, equal to -200 mbar.
[0035] The output port 30 is, for instance, in fluid communication with an exhaust environment,
such as the atmosphere surrounding the assembly 2.
[0036] Preferably, the input port 28 is fluidically connected to a gas supply 32 of the
sealing apparatus 6.
[0037] Alternatively, the input port 28 is in fluid communication with a gas reservoir,
such as the atmosphere surrounding the assembly 2, preferably through a gas drying
part 32 (also referred to as "dehydrating breather") connected to the input port 28
of the breather device 16 and configured to at least partly remove moisture from the
second fluid flow.
[0038] For instance, the gas drying part 32 is a known silica gel dryer.
[0039] Alternatively, the input port 28 and the output port 30 form a single common port.
[0040] It results from the foregoing that communication between the cavity 10 and an environment
outside the casing 8 can only occur through the breather device 16.
[0041] According to the embodiment of the invention shown on figure 1, the breather device
16 comprises a first non-return valve 34 (also referred to as "check valve" or "unidirectional
valve") and a second non-return valve 36. In this case, the first non-return valve
is arranged between the main port 26 and the output port 30 and is configured to allow
the first fluid flow if the pressure difference between the main port 26 and the output
port 30 is higher than the overpressure threshold. Moreover, the second non-return
valve 36 is arranged between the main port 26 and the input port 28 and is configured
to allow the second fluid flow if the pressure difference between the main port 26
and the input port 28 is lower than the under-pressure threshold.
[0042] Advantageously, the sealing apparatus 6 further comprises a controller (not shown)
configured to control the breather device 16 based on at least one predetermined control
parameter. More precisely, the controller is configured to control the overpressure
threshold and/or the under-pressure threshold, or a delay in the occurrence of the
first fluid flow and/or the second fluid flow (if the corresponding condition relating
to pressure difference is met), based on said at least one control parameter.
[0043] For instance, the control parameter is a weather forecast (that is, a forecast of
environmental conditions), or a load forecast.
[0044] Indeed, the overpressure threshold and/or the under-pressure threshold typically
include a safety margin to avoid any damage to the electrical equipment 4. With knowledge
of the control parameter, the controller may control the breather device 16 to adjust
the overpressure threshold and/or the under-pressure threshold, or to apply a timely
delay to the occurrence of the first fluid flow and/or the second fluid flow.
[0045] As an example, using such a controller, a first fluid flow can be prevented in case
of overpressure in the electrical equipment 4 when it is already known that pressure
might drop again very soon (because of a drop in load or in temperature, for instance).
[0046] As a result, breathing can be further reduced.
[0047] Each of the first non-return valve 34 and the second non-return valve 36 is, for
instance, a spring-operated valve.
[0048] Advantageously, the sealing apparatus 6 further comprises a safety valve 38.
[0049] The safety valve 38 comprises an inlet 40 and an outlet 42.
[0050] The inlet 40 is fluidically connected to the second port 24 of the conservator 14,
for instance to the tubing 17, in parallel to the breather device 16. Moreover, the
outlet 42 is, for instance, in fluid communication with the exhaust environment.
[0051] The safety valve 38 is configured to allow a third fluid flow from the inlet 40 to
the outlet 42 if a pressure difference between the inlet 40 and the outlet 42 is higher
than a predetermined safety threshold, the safety threshold being higher than or equal
to the high pressure threshold.
[0052] The safety valve 38 acts as a protective device that prevents unacceptable excessive
overpressure which could damage the casing 8 of the liquid-filled electrical equipment
4, and which may result from a failure of the breather device 16.
[0053] Preferably, a pressure gauge 44 is also connected to the tubing 17 to provide a visual
indication of the pressure within the sealing apparatus 6, preferably the pressure
at the main port 26. Alternatively or additionally, a pressure gauge (not shown) is
connected to the casing 8 to provide a visual indication of the pressure within the
liquid-filled electrical equipment 4.
[0054] Alternatively, the breather device 16 comprises a bidirectional valve (not shown)
replacing the first non-return valve 34 and the second non-return valve 36. In this
case, the input port and output port are combined, forming a same common port. Nonetheless,
operation of the breather device 16 remains unchanged, the bidirectional valve being
arranged between the main port 26 and the common port and being configured:
- to allow the first fluid flow from the main port 26 to the common port if the pressure
difference between the main port 26 and the common port is higher than the overpressure
threshold; and
- to allow the second fluid flow from the common port to the main port 26 if the pressure
difference between the main port 26 and common port is lower than the under-pressure
threshold.
[0055] Alternatively, the conservator 14 further comprises an elastic membrane (not shown)
arranged within the enclosure 18 to provide a hermetic seal between the first port
22 and the second port 24. In this case, the sealing apparatus 6 is preferably configured
so that, after connection to the liquid-filled electrical equipment 4, the dielectric
liquid 12 is in contact with a face of the elastic membrane that is on the side of
the first port 22.
[0056] A second embodiment of an assembly 102 comprising an electrical equipment 104 connected
to a sealing apparatus 106 according to the invention is shown on figure 2. In this
figure, numeral references that are identical to those of figure 1 refer to the same
parts.
[0057] More precisely, the electrical equipment of the assembly 102 is a blanketed-tank
electrical equipment. The blanketed-tank electrical equipment 104 of figure 2 differs
from the liquid-filled electrical equipment 4 of figure 1 in that its casing 8 defines
a cavity 10 which is not completely filled with the dielectric liquid 12. On the contrary,
a gas blanket 113 is provided in the cavity 10, on top of the dielectric liquid 12.
[0058] The gas blanket 113 is made of a blanketing gas 114, generally a dry inert gas, such
as nitrogen or dry air, which advantageously acts as a buffer layer that prevents
air and moisture from coming into contact with the dielectric liquid 12.
[0059] In this case, and contrary to the embodiment of figure 1, the sealing apparatus 106
does not comprise a conservator. The main port 26 of the breather device 16 is directly
connected to the cavity 10 (through the tubing 17) and leads to the gas blanket 113.
More precisely, the assembly 102 is configured so that, within the nominal temperature
range, the dielectric liquid 12 does not flow from the blanketed-tank electrical equipment
104 in the sealing apparatus 106, but only the blanketing gas 114 does. In other words,
within the nominal temperature range, the dielectric liquid 12 is confined by the
gas blanket 113 in the cavity 10 of the blanketed-tank electrical equipment 104.
1. A sealing apparatus (6) for a liquid-filled electrical equipment (4) comprising a
cavity (10) filled with a dielectric liquid (12), the sealing apparatus (6) comprising
a conservator (14) and a breather device (16),
the breather device (16) comprising a main port (26), an input port (28) and an output
port (30), and being configured to allow:
- a first fluid flow from the main port (26) to the output port (30) if a pressure
difference between the main port (26) and the output port (30) is higher than a predetermined
overpressure threshold; and
- a second fluid flow from the input port (28) to the main port (26) if a pressure
difference between the main port (26) and the input port (28) is lower than a predetermined
under-pressure threshold,
the conservator (14) comprising an enclosure (18) including a first port (22) for
connection to the cavity (10) of the liquid-filled electrical equipment (4), and a
second port (24), distinct from the first port (22), fluidically connected to the
main port (26) of the breather device (16), the enclosure (18) defining an internal
volume (20) in fluid communication with each of the first port (22) and the second
port (24).
2. The sealing apparatus (6) according to claim 1, wherein the breather device (16) comprises
a first non-return valve (34) and a second non-return valve (36),
the first non-return valve (34) being arranged between the main port (26) and the
output port (30) and being configured to allow the first fluid flow if the pressure
difference between the main port (26) and the output port (30) is higher than the
overpressure threshold; and
the second non-return valve (36) being arranged between the main port (26) and the
input port (28) and being configured to allow the second fluid flow if the pressure
difference between the main port (26) and the input port (28) is lower than the under-pressure
threshold.
3. The sealing apparatus (6) according to claim 1 or 2, comprises a controller configured
to control the breather device (16), preferably the overpressure threshold and/or
the under-pressure threshold, based on at least one predetermined control parameter.
4. The sealing apparatus (6) according to any one of claim 1 to 3, wherein the input
port and the output port form a same common port.
5. The sealing apparatus (6) according to claim 4, wherein the breather device (16) comprises
a bidirectional valve arranged between the main port (26) and the common port and
configured:
- to allow the first fluid flow if the pressure difference between the main port (26)
and the common port is higher than the overpressure threshold; and
- to allow the second fluid flow if the pressure difference between the main port
(26) and the common port is lower than the under-pressure threshold.
6. The sealing apparatus (6) according to any one of claims 1 to 5, further comprising
a safety valve (38) including an inlet (40) and an outlet (42), the inlet (40) being
fluidically connected to the second port (24) of the conservator (14), in parallel
to the breather device (16), the safety valve (38) being configured to allow a third
fluid flow from the inlet (40) to the outlet (42) if a pressure difference between
the inlet (40) and the outlet (42) is higher than a predetermined safety threshold,
the safety threshold being higher than or equal to the high pressure threshold.
7. The sealing apparatus (6) according to any one of claims 1 to 6, further comprising
a gas drying part (32) connected to the input port (28) of the breather device (16)
and configured to at least partly remove moisture from the second fluid flow.
8. The sealing apparatus (6) according to any one of claims 1 to 6, further comprising
a gas supply fluidically connected to the input port (28) of the breather device (16).
9. The sealing apparatus (6) according to any one of claims 1 to 8, wherein the conservator
(14) further comprises an elastic membrane arranged within the enclosure (18) to provide
a hermetic seal between the first port (22) and the second port (24).
10. The sealing apparatus (6) according to any one of claims 1 to 9, further comprising
a pressure gauge (44) arranged upstream with respect to the first flow and configured
to measure a pressure within the sealing apparatus (6), preferably the pressure at
the main port (26).
11. An assembly comprising an electrical equipment (4) and the sealing apparatus (6) according
to any one of claims 1 to 10,
the electrical equipment being a liquid-filled electrical equipment (4) comprising
a cavity (10) filled with a dielectric liquid (12),
the first port (22) of the conservator (14) of the sealing apparatus (6) being connected
to the cavity (10) of the liquid-filled electrical equipment (4) so that the internal
volume (20) is partially filled with dielectric liquid (12) when a temperature of
the dielectric liquid (12) is within a predetermined nominal temperature range.
12. The assembly according to claim 11, further comprising a Buchholz relay (25) arranged
between the first port (22) of the conservator (14) and the cavity (10) of the liquid-filled
electrical equipment (4).
13. An assembly comprising an electrical equipment (104) and a sealing apparatus (106),
the electrical equipment (104) being a blanketed-tank electrical equipment (104) comprising
a cavity (10), a dielectric liquid (12) and a blanketing gas (114) being provided
in the cavity (10), the blanketing gas (114) forming a gas blanket (113) arranged
on top of the dielectric liquid (12),
the sealing apparatus (106) comprising a breather device (16) including a main port
(26), an input port (28) and an output port (30), and configured to allow:
- a first fluid flow from the main port (26) to the output port (30) if a pressure
difference between the main port (26) and the output port (30) is higher than a predetermined
overpressure threshold; and
- a second fluid flow from the input port (28) to the main port (26) if a pressure
difference between the main port (26) and the input port (28) is lower than a predetermined
under-pressure threshold,
the main port (26) of the breather device (16) being connected to the cavity (10)
of the blanketed-tank electrical equipment (104) so that, when a temperature of the
dielectric liquid (12) is within a predetermined nominal temperature range, the main
port (26) leads to the gas blanket (113), the gas blanket (113) confining the dielectric
liquid (12) in the cavity (10).
14. The assembly according to any one of claims 9 to 13, wherein the electrical equipment
(4; 104) is a power transformer or shunt reactor.
15. The assembly according to any one of claims 9 to 14, wherein the electrical equipment
(4; 104) comprises a pressure gauge configured to measure a pressure within the electrical
equipment (4; 104).