U.S. patent application number 16/277142 was filed with the patent office on 2019-08-15 for apparatus and method for the production of foods.
The applicant listed for this patent is ALBERT HANDTMANN MASCHINENFABRIK GMBH & CO. KG. Invention is credited to Daniel BETTINGER, Wolfgang SCHRADER, Kurt STROHM.
Application Number | 20190248519 16/277142 |
Document ID | / |
Family ID | 61231079 |
Filed Date | 2019-08-15 |
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United States Patent
Application |
20190248519 |
Kind Code |
A1 |
STROHM; Kurt ; et
al. |
August 15, 2019 |
APPARATUS AND METHOD FOR THE PRODUCTION OF FOODS
Abstract
The invention relates to an apparatus and a method for the
production of foods, in particular, a stuffing machine for the
production of sausages, with a load circuit that generates a
leakage current IA and with a filter, a frequency converter, a
motor cable and a motor. The apparatus comprises a leakage current
compensator with a device for detecting a leakage current and a
device for generating a compensation current that is directed
opposite to the leakage current and is superimposed with the
leakage current, such that the leakage current is reduced, is in
particular substantially eliminated.
Inventors: |
STROHM; Kurt; (Attenweiler,
DE) ; BETTINGER; Daniel; (Maselheim, DE) ;
SCHRADER; Wolfgang; (Biberach, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ALBERT HANDTMANN MASCHINENFABRIK GMBH & CO. KG |
Biberach |
|
DE |
|
|
Family ID: |
61231079 |
Appl. No.: |
16/277142 |
Filed: |
February 15, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A22C 5/00 20130101; A22C
11/02 20130101; A22C 7/00 20130101; A22C 15/00 20130101; B65B 31/02
20130101; B65B 25/001 20130101; B65B 57/10 20130101; A22C 11/00
20130101; A22C 17/00 20130101; B65B 3/34 20130101; A22C 9/00
20130101; B65B 31/04 20130101; B65B 3/18 20130101; A22C 18/00
20130101 |
International
Class: |
B65B 3/18 20060101
B65B003/18; B65B 31/02 20060101 B65B031/02; B65B 25/00 20060101
B65B025/00; B65B 31/04 20060101 B65B031/04; B65B 57/10 20060101
B65B057/10; B65B 3/34 20060101 B65B003/34 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 15, 2018 |
EP |
18156940.1 |
Claims
1. An apparatus for the production of foods, comprising: a load
circuit that generates a leakage current; an EMC filter; a
frequency converter; a motor cable; a motor; a leakage current
compensator with a device for detecting said leakage current; and a
device for generating a compensation current that is directed
opposite to said leakage current and is superimposed with said
leakage current, such that said leakage current is reduced.
2. The apparatus according to claim 1, wherein said leakage current
is substantially eliminated when superimposed with said
compensation current.
3. The apparatus according to claim 1, wherein said compensation
current is shifted in its phase relative to said leakage current by
180.degree. and has substantially a same amplitude as said leakage
current.
4. The apparatus according to claim 1, wherein said device for
generating said compensation current comprises an amplifier and a
capacitor network via which said compensation current is supplied
to individual phases of a multi-phase system.
5. The apparatus according to claim 4, wherein the individual
phases of the multi-phase system comprises at least one of three
phases of a three-phase system.
6. The apparatus according to claim 4, wherein said leakage current
compensator is arranged between a ground fault interrupter and said
EMC filter.
7. The apparatus according to claim 4, wherein said leakage current
compensator is installed in a device upstream of said
apparatus.
8. The apparatus according to claim 7, wherein said apparatus
further comprises a plug connected to said leakage current
compensator by way of an outlet.
9. The apparatus according to claim 8, wherein a power supply of
said leakage current compensator is effected via a power supply of
said apparatus.
10. The apparatus according to claim 8, wherein said apparatus
further comprises a delay device configured such that said
compensation current is superimposed in a time-delayed manner.
11. The apparatus according to claim 10, wherein said compensation
current is superimposed in the time-delayed manner only when all
phases of said plug have contacted when said apparatus is plugged
in, and further wherein said delay device is optionally configured
such that said capacitor network is switched on only when all
phases of said plug have contacted when said apparatus is plugged
in.
12. The apparatus according to claim 1, wherein said leakage
current compensator is integrated into said apparatus and is
supplied via a separate auxiliary power supply.
13. The apparatus according to claim 12, wherein said apparatus can
be unplugged and is movable.
14. The apparatus according to claim 1, wherein said apparatus is
at least one apparatus from the following group: a stuffing machine
for the production of sausages, a clipper, a spooling unit, a
driven suspension unit, a cutter, a separation unit, a grouping
unit, a conveyor belt, a charging system, and a packaging machine
for food products.
15. A method for the production of foods with an apparatus
comprising a load circuit that generates a leakage current, the
method comprising: detecting said leakage current during operation
of said apparatus; generating, with a leakage current compensator,
a compensation current directed opposite to said leakage current;
and superimposing said compensation current onto said leakage
current, whereby said leakage current is reduced and substantially
eliminated.
16. The method according to claim 15, wherein said leakage current
compensator comprises an amplifier and a capacitor network, the
method further comprising switching on said compensation current
via said capacitor network in a time-delayed manner, when said
apparatus is plugged in and only when all phases of a plug of said
apparatus have contacted when plugged in.
17. The method according to claim 16, wherein a power supply of
said leakage current compensator is effected via a power supply of
said apparatus, wherein said leakage current compensator is
integrated into said apparatus and is supplied via a separate
auxiliary power supply.
18. The method according to claim 17, wherein said apparatus is
unplugged, moved to another production location, and plugged in
again.
19. The method according to claim 17, wherein said leakage current
compensator is arranged between a ground fault interrupter and an
EMC filter of said apparatus.
20. The method according to claim 19, wherein said apparatus is
supplied with voltage via a three-phase mains with three phases,
further comprising: detecting a current in the three phases;
feeding corresponding signals to an amplifier comprising an
evaluation unit; determining, with the evaluation unit, a
respective leakage current by subtraction; and generating, with the
evaluation unit, a compensation current which is fed via a
capacitor network to at least one of the three phases.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims priority to European Patent
Application No. 18156940.1 entitled "APPARATUS AND METHOD FOR THE
PRODUCTION OF FOODS", and filed on Feb. 15, 2018. The entire
contents of the above-listed application are hereby incorporated by
reference for all purposes.
TECHNICAL FIELD
[0002] The invention relates to an apparatus and a method for the
production of foods from pasty or liquid masses, in particular a
stuffing machine for sausage production.
BACKGROUND AND SUMMARY
[0003] Machines and equipment in food production, in particular
stuffing machines, such as vacuum stuffing machines, spooling
lines, clippers, etc., often use switch-mode power supplies and
electronically commutated drives. In order to satisfy the legal
requirements for electromagnetic compatibility (EMC), filter
measures against electrical faults are necessary. These EMC filters
cause leakage currents that can trigger ground fault interrupters
(GFIs)--in particular where they serve operator protection. This
makes operation at outlets with a ground fault interrupter for
operator protection impossible. With a ground fault interrupter
having higher tripping thresholds, however, the machines and
buildings are only protected against fire. The machines and systems
are therefore often either fixedly connected to the mains, equipped
with an isolating transformer, or operated at special outlets
without ground fault interrupters. Another option is to lead the
leakage currents--possibly--to the neutral conductor. Operator
protection is achieved by way of the grounding conductor (PE).
[0004] However, the aforementioned measures have significant
drawbacks.
[0005] In particular in food production, compact and mobile
machines are needed that can be employed in a flexible manner. This
includes e.g., that the machines can easily be moved out of
production areas to another location for cleaning purposes.
Attachments, such as a spooling line, clippers, a suspension
device, etc., are often used in a flexible manner in particular in
filling lines, so that the individual machines must be movable for
the production. This is not possible with fixedly connected
machines.
[0006] Machines with a built-in isolating transformer become larger
and heavier, which also hampers mobility--just like isolating
transformers which are mounted in external housings and can be
connected upstream of the machine. In the isolating
transformations, the leakage currents and therefore also the
insulation fault current remain on the secondary side of the
transformer. The detection of whether a compensation current flows,
however, can only be measured and detected by the ground fault
interrupter on the primary side of the transformer. Therefore, no
protection is ensured by the ground fault interrupter. Especially
in wet rooms, however, this protection is highly desired. The
placement and marking of special outlets which are not protected
with ground fault interrupters also increase the complexity and
reduces the flexibility and safety.
[0007] If the filter currents are to be dissipated via the neutral
conductor, special filters and inverters are required. The leakage
currents of the cable shields continue to dissipate through the
grounding conductor because the shields can be connected to the
neutral conductor. A separate neutral conductor is not present in
all types of mains, so this solution cannot be employed worldwide.
Furthermore, with more comprehensive EMC filtering (larger and
oversized filters), the high-frequency leakage currents can be
reduced. For example, more efficient EMC input filters can be used
in combination with additional output filters, but at higher costs.
Another drawback of this measure against leakage currents is the
space problem that arises especially when retrofitting larger and
additional filters.
[0008] The use of ground fault interrupters with a high tripping
threshold is also conceivable, but involves considerable risks
since the higher leakage currents cause shifts in the potential and
the permissible contact voltage of at most of 50 VAC can be
exceeded. In addition, damage to the individual components of the
system is possible.
[0009] Starting from there, the present invention is based on the
object of providing an improved apparatus and an improved method
for food production which can be employed in a flexible manner and
at the same time can be operated safely.
[0010] According to the invention, this object is satisfied with an
apparatus and a method for the production of foods as described
further herein.
[0011] The apparatus for the production of foods is, in particular,
a stuffing machine for the production of sausages with a load
circuit that generates a leakage current. The apparatus comprises a
motor to drive, for example, the conveyor of a stuffing machine. In
order to satisfy the legal requirements for electromagnetic
compatibility, filter measures against electrical faults are
required. The apparatus also comprises, in particular, a frequency
converter. Due to this at least one filter and a cable to the
motor, leakage currents can arise that could trigger a ground fault
interrupter. For this reason, a leakage current compensator is
provided according to the present invention with a device for
detecting a leakage current and a device for generating a
compensation current that is directed opposite to the leakage
current and is superimposed with the leakage current, such that the
leakage current is reduced, is in particular substantially
eliminated. The leakage current is there at least reduced to the
extent that it is below the threshold for triggering a GFI ground
fault interrupter. The leakage current is optionally completely
eliminated.
[0012] This entails the advantage that the currents cancel each
other and the ground fault interrupter is no longer tripped due to
increased leakage currents. Only insulation faults or dangerous
body currents can be detected and lead to tripping, for example, a
frequency range of 100 Hz to 300 kHz should be covered. The
frequency range 50-60 Hz may not be compensated so that operator
protection remains in effect. The invention has the advantage that
full operator protection is ensured and the apparatus can
nevertheless be moved since it does not have to be fixedly
installed and no large and heavy isolating transformer needs to be
integrated. This also entails, inter alia, better hygiene due to
simplified cleaning of the machine and great flexibility with
regard to the assembly of the individual machines of a stuffing
line. The leakage current compensator is inexpensive and can also
be easily retrofitted into existing machines. In comparison to
isolating transformer, high energy efficiency arises. With the
present invention, a wide voltage range can be covered such that
the apparatus can be used worldwide. Insulation faults or device
faults are detected 100% with upstream ground fault interrupters.
With the present invention, currents up to 1 A can be
compensated.
[0013] The compensation current can be shifted in its phase
relative to the leakage current by 180.degree. and have
substantially the same amplitude. The leakage current can then be
completely compensated. Since it is sufficient to have the leakage
current be below the threshold for triggering the ground fault
interrupter, the leakage current can be e.g. at approx. 40% of the
switching threshold of the ground fault interrupter. It is
essential that the leakage current is e.g. lower than the trigger
threshold.
[0014] The device for generating a compensation current
advantageously comprises an amplifier and a capacitor network (as
filter capacitors) via which the compensation current can be
supplied to individual phases of a multi-phase system, in
particular to at least one of the three phases, optionally all
three phases of a three-phase system. For example, the current can
be detected in all three phases and the leakage current of each
phase can be determined by calculating the difference, and a
respective compensation current is conducted to the corresponding
phases in terms of symmetrical load distribution.
[0015] Advantageously, the compensation current generated by the
amplifier is distributed to the three phases in such a manner that
the leakage current is overall compensated or sufficiently
reduced.
[0016] The leakage current compensator is optionally located
between a ground fault interrupter (GFI) and the EMC filter, i.e.
the EMC input filter. The leakage currents generated by the filter
can then be compensated, but also other leakage currents generated
in the load circuit by parasitic coupling, in particular due to
long motor leads and/or a frequency converter.
[0017] According to one preferred embodiment, the leakage current
compensator is installed in a device upstream of the apparatus. The
apparatus comprises in particular a plug which is connectable to
the leakage current compensator by way of an outlet, in particular
an industrial outlet. The apparatus therefore then comprises this
device which in turn can be connected via an outlet, in particular
an industrial outlet, to the mains by way of a plug, in particular
an industrial plug. This entails the advantage that the apparatuses
can be flexibly plugged in at various locations and a respective
device can be easily retrofitted. A respective upstream device
could then also be used for various apparatuses. But it is also
possible that the apparatus is fixedly connected to the upstream
device by use of a cable, and then connectable to an outlet, in
particular an industrial outlet, using a plug.
[0018] Power supply for the leakage current compensator, in
particular the amplifier, can be effected with the power supply of
the apparatus, i.e. via the mains voltage. For example, if the
leakage current compensator is installed in the upstream device,
there may be a problem that the ground fault interrupter trips when
this device is plugged into the industrial outlet. This is for the
reason that the phases do not contact exactly at the same time
during the plug-in action and asymmetric charging currents then
arise through the Y-capacitors which can trigger the upstream GFI.
In order to prevent this, the apparatus comprises a delay device
which is configured in such a manner that the compensation current
is superimposed with a time delay, i.e. in particular only when all
the phases of the plug have contacted when the apparatus is
connected to the mains. This means that the capacitor network is
switched on optionally only when all phases of the plug have
contacted when the apparatus is plugged in. The delay circuit can
there be formed, for example, as a switching relay, a semiconductor
relay, a time relay or as a software solution, or be implemented in
the form of a mechanical solution in that the power supply for the
compensation device is effected by way of plug contacts in a plug
which, when plugged together, are located farther back than the
contacts for the power supply of the apparatus, so that the
contacts of the compensation device only contact after the power
contacts have already contacted.
[0019] It is also possible that the leakage current compensator is
integrated in the apparatus and is supplied by a separate auxiliary
power supply, so that the leakage current compensator is already
supplied before a leakage current is generated in the load circuit
when the apparatus is switched on. It is advantageous and
space-saving to have the leakage current compensator be integrated
into the machine. No extra space outside the machine is then
required if the leakage current compensator is integrated into the
machine, it would be possible that the ground fault interrupter
(GFI) triggers unintentionally if leakage currents already arise
once the apparatus is switched on, but the compensator is not yet
operational. To prevent this, the leakage current compensator is
supplied with the separate auxiliary voltage that is applied before
the load circuit generates the leakage current. The system can then
compensate the current before the ground fault interrupter
triggers. In this solution, it is no longer harmful if the phases
of the load circuits are switched on in a non-symmetric manner.
Therefore, no expensive protection with contacts contacting
simultaneously is required.
[0020] As already described above, the present invention enables
the apparatus to be disconnected and therefore be movable. If the
apparatus comprises the external device with the leakage current
compensator, this device has a mains plug.
[0021] The apparatus is advantageously an apparatus of at least a
group: stuffing machine, clipper, spooling unit, driven suspension
unit, cutter, separation unit, grouping unit, conveyor belt,
charging system, packaging machine for food products, etc.
[0022] In the method according to the invention for the production
of foods, in particular with the apparatus for the production of
foods described herein including a load circuit generating a
leakage current, the leakage current is detected during operation
of the apparatus and a compensation current directed opposite to
the leakage current is generated using a leakage current
compensator. The compensation current is superimposed onto the
leakage current, whereby the leakage current is reduced, in
particular substantially eliminated.
[0023] The leakage current compensator comprises an amplifier and a
capacitor network. When the apparatus is plugged in, the
compensation current is advantageously switched on via the
capacitor network with a time delay only when all the phases of a
plug of the apparatus have been contacted during the plug-in
action, i.e., are connected to the mains.
[0024] It is also possible that the power supply of the leakage
current compensator is effected via the power supply of the
apparatus or that the leakage current compensator is integrated
into the apparatus and supplied by a separate auxiliary power
supply such that the compensation current is already applied before
a leakage current is generated in the load circuit. The system can
then compensate the current before the ground fault interrupter
triggers.
[0025] According to the present invention, the apparatus can
therefore now be unplugged, i.e. be disconnected from the mains by
way of a mains plug, be moved to another production location, and
finally plugged in again. This enables increased flexibility while
maintaining safety.
[0026] The leakage current compensator is advantageously located
between a ground fault interrupter and an EMC filter. When the
leakage current compensator is located upstream of the EMC input
filter, all the leakage currents of the load circuit can be
compensated.
[0027] It is particularly advantageous if the apparatus is supplied
with power via three-phase mains and the current is detected in the
three phases and the leakage current is determined by subtraction,
corresponding signals are fed to an amplifier, comprising an
evaluation unit, for generating a compensation current which is fed
via a capacitor network to at least one, optionally all three
phases, whereby the leakage current is substantially
eliminated.
BRIEF DESCRIPTION OF THE FIGURES
[0028] FIG. 1 shows a simplified schematic representation of an
apparatus according to the invention with a leakage current
compensator;
[0029] FIG. 2 shows a simplified schematic representation of an
embodiment of an apparatus according to the invention with an
external leakage current compensator;
[0030] FIG. 3 shows a simplified schematic representation of an
equivalent circuit diagram of a leakage current compensator for the
embodiment shown in FIG. 2;
[0031] FIG. 4 shows a simplified schematic representation of a
further embodiment of the present invention with an integrated
leakage current compensator;
[0032] FIG. 5 shows a simplified schematic representation of an
equivalent circuit diagram of a leakage current compensator for the
embodiment shown in FIG. 4;
[0033] FIG. 6 shows a simplified schematic representation of a
stuffing machine according to the present invention; and
[0034] FIG. 7 shows a further embodiment according to the present
invention.
DETAILED DESCRIPTION
[0035] FIG. 6 shows a simplified schematic representation of an
apparatus 1 for the production of foods, presently in the form of a
stuffing machine 1. Stuffing machine 1 comprises a hopper 20 into
which the pasty substance, e.g. sausage meat, is filled and passes
downwardly into a conveying mechanism, no shown, for example, into
a rotary vane pump, via which it is ejected into a stuffing tube
21, for example, into a sausage casing, not shown. The apparatus
can also comprise, for example, a lifting device 22 which raises a
sausage meat carriage 23 upwardly by way of a lifting arm 24 and
empties it into hopper 20. The stuffing machine can comprise a
motor 2, as shall be explained below, which drives, for example,
the conveying mechanism. The stuffing machine can further comprise
a separate motor for lifting device 22.
[0036] FIG. 1 shows a simplified schematic representation of a load
circuit for motor 2. FIG. 1 shows a simplified schematic
representation of a drive system, for example, for a rotary vane
pump, which substantially comprises an EMC input filter 3, a
frequency converter 4, a motor cable 5 and a motor 2. The EMC
filter as well as frequency converter 4 and the long motor cable
and motor 2 can produce leakage currents that would trigger a
ground fault interrupter 5. According to the present invention, a
leakage current compensator 6 is provided upstream of EMC filter 3
and generates a compensation current I.sub.K, which is directed
opposite to leakage current I.sub.A. The leakage current can thus
be compensated, i.e. be eliminated, at least be reduced so that it
is below the threshold for triggering GFI ground fault interrupter
5, for example, below the tripping threshold of 30 mA for currents
in the frequency range <100 Hz, of 300 mA for currents with a
frequency >1000 Hz.
[0037] Leakage current I.sub.A is the sum of all individual present
leakage currents, the sum of
I.sub.Filter+I.sub.Frequency-coverter+I.sub.Cabel+I.sub.Motor.
According to the present invention, a frequency range between 100
Hz and 300 kHz is to be covered. The frequency range of 50 to 60 Hz
may not be compensated so that operator protection remains in
effect. In practice, compensation currents up to 1 A are required.
Compensation current I.sub.K is optionally shifted in its phase by
180.degree. relative to leakage current I.sub.A and has
substantially the same amplitude and optionally the same
frequency.
[0038] FIG. 2 shows an embodiment according to the present
invention with an external leakage current compensator 6 arranged
outside of the machine housing. FIG. 2 shows a power supply 14, for
example, three-phase mains, as well as an industrial outlet 18 via
which an apparatus with a mains plug 19 can be plugged on. In this
embodiment, leakage current compensator 6 is installed in an
upstream device 11 which comprises a further industrial outlet 13
into which an industrial plug 12 of apparatus 1 can in turn be
plugged. Industrial plug 12 is connected via a corresponding line
to main switch 25 of the apparatus. A motor protection switch 26
can be provided thereafter, and a main contactor 27 without
"symmetrical contacts", i.e. without snap-action contacts.
Thereafter, a mains line choke 28 can be provided, followed by an
EMC filter 3 and a frequency converter from which motor 2 can be
supplied. After main switch 25, a line can branch off to a
transformer protection switch 38 which is connected to a control
transformer 29 and supplies a control unit 30. Control unit 30 is
connected to the main contactor in order to switch on the main
contactor. As shown in FIG. 2, leakage current compensator 6 is
supplied with power in the same load circuit as the motor by way of
power supply 14 i.e. the mains voltage. The leakage current
compensator is therefore located upstream of main switch 25.
[0039] FIG. 3 shows an equivalent circuit diagram of leakage
current compensator 6 for the embodiment shown in FIG. 2. FIG. 3
shows three-phase mains. Leakage current compensator 6 comprises a
device for measuring a leakage current 7 as well as a device for
generating a compensation current 8. The device for generating a
compensation current 8 comprises an amplifier 9 which is connected
to the device for measuring the leakage current 7 and comprises an
evaluation unit which can determine a leakage current I.sub.A and a
compensation current I.sub.K on the basis of the values measured.
The device for detecting a leakage current 7 can comprise, for
example, a measuring caliper. The currents of the three phases can
be detected, and the leakage current from the respective
differences. This means that, if the sum of the currents in the
three phases L1, L2, L3 is not 0, a leakage current I.sub.A is
present. Compensation current I.sub.K is calculated e.g. such that
it is shifted in its phase by 180.degree. relative to leakage
current I.sub.A and has substantially the same amplitude as the
leakage current. FIG. 3 shows in a simplified representation that
amplifier 9 feeds the compensation current to the three phases
based on compensation current I.sub.K determined such that the sum
of the currents of the individual phases L1, L2, L3 is e.g. again 0
and the leakage current is thus compensated, is at least located
below a triggering threshold of the GFI switch.
[0040] For example, the respective current I.sub.L1, I.sub.L2,
I.sub.L3 can there be measured.
[0041] For example, a leakage current and an opposite compensation
current, which is then distributed to the three phases L1, L2, L3,
are determined by subtraction.
[0042] However, it is also possible to determine a separate leakage
current for each phase by measuring the currents in each individual
phase and to then determine corresponding compensation currents for
the individual phases and to supply them accordingly to each
phase.
[0043] In this embodiment, the leakage current compensator is
supplied with power from power supply 14 via two of the phases of
the three-phase system, as already explained.
[0044] The apparatus advantageously comprises a delay device 15.
Delay device 15 is configured such that compensation current
I.sub.K is superimposed with a time delay, in particular only when
all phases of plug 19 have contacted when the apparatus is plugged
in. This means that capacitor network 10 is switched on only when
all phases of the plug have contacted when the apparatus is plugged
in. It can thus be prevented that the GFI can already trigger when
apparatus 1 is plugged in. This problem arises from the fact that
phases L1, L2, L3 do not contact at exactly the same time and
asymmetric charging currents then arise through the Y-capacitors of
capacitor network 10 which can trigger the upstream GFI. This can
be prevented by delay circuit 15. Delay circuit 15 can be
implemented, for example, as a time relay, a semiconductor relay,
or as a software solution. Furthermore, there is also the
possibility of a mechanical delay device 15, such that leakage
current compensator 6 is supplied with power in a time delayed
manner, for example, in that plug 19 is configured such that the
contacts supplying leakage current compensator 6 with power are
located further back so they only contact after the power contacts
have already contacted. This can be realized, for example, by
shorter pins.
[0045] FIG. 4 shows a further embodiment according to the present
invention. Leakage current compensator 6 is there installed
directly into the apparatus i.e. is integrated. As can be seen,
leakage current compensator 6 is located between industrial plug 12
and EMC mains filter 3. In order to here as well prevent that the
GFI ground fault interrupter triggers unintentionally, leakage
current compensator 6 is supplied with a separate auxiliary voltage
16 and not via mains voltage 14 like in the first embodiment.
Different separate auxiliary power supplies 16 can there be used.
In the embodiment shown in FIG. 4, for example, current is branched
off downstream of the main switch to a circuit breaker for
transformers and supplied to leakage current compensator 6. This
avoids the problem that the GFI triggers unintentionally when
leakage currents already arise once the machine is switched on but
the compensator is not yet ready for operation. To prevent this,
the compensator is supplied the separate auxiliary voltage that is
applied before the load circuits generate the leakage current. The
system can then compensate leakage current I.sub.A before the GFI
ground fault interrupter triggers. In this solution, it is no
longer harmful if the phases of the load circuits are switched on
in a non-symmetric manner. Therefore, no expensive protection with
contacts contacting simultaneously is required.
[0046] FIG. 7 shows a further embodiment according to the present
invention. The embodiment shown in FIG. 7 corresponds to the
embodiment shown in FIG. 4. In this embodiment, multiple motors are
present in the apparatus. This means that a further motor for
another functional unit, for example for a lifting device and/or a
spooling device are provided in a stuffing machine, in addition to
a motor for the rotary vane pump. According to a first alternative,
for example, a further frequency converter for further motor 2 can
be provided downstream of the EMC mains filter and/or downstream of
the mains line choke and a further frequency converter can be
provided for a further motor. These load circuits can therefore be
protected as well, i.e. several motors by only one leakage current
compensator 6.
LIST OF REFERENCE NUMERALS
[0047] 1 apparatus [0048] 2 motor [0049] 3 EMC filter [0050] 4
frequency converter [0051] 5 ground fault interrupter [0052] 6
leakage current compensator [0053] 7 device for measuring leakage
current [0054] 8 device for generating a compensation current
[0055] 9 amplifier [0056] 10 capacitor network [0057] 11 upstream
device [0058] 12 plug [0059] 13 outlet [0060] 14 power supply
[0061] 15 delay device [0062] 16 separate power supply
* * * * *