FIELD OF THE INVENTION

The present invention relates to pump devices driven by an electric motor. Especially, the invention relates to pump devices with electric motors driven by an inverter. More specifically, the invention provides a device and a method of shielding to reduce high frequency electromagnetic (EM) radiation from the pump device, such as in the frequency range 30 MHz to 1 GHz.

BACKGROUND OF THE INVENTION

Pumps driven by electric motors are used in a wide range of applications and in a variety of setups where they have to comply with EMC regulations. In general, an electric motor generates electromagnetic radiation, but especially electric motors driven by an inverter operating at high switching frequencies will generate a significant EM radiation, unless effectively shielded.

The latest inverter technologies allow operation with high switching speed of the inverter, e.g., using Wide Band-Gap (WBG) semiconductors. Such inverters may operate with output voltage switching slopes high enough to generate significant EMI, e.g., within the frequency range 30 MHz to 1 GHz. This requires effective shielding to reduce the radiated EMI of the pump to an acceptable level, e.g. specified by the EMC standards, such as EN55014-1.

Further, for various reasons, a pump with a conduit box made of a composite material may be preferred, and such conduit box does not offer any EMC shielding in itself.

Hence, there is a need for effective shielding solution to provide a low EMI emission from a pump driven by a high frequency inverter, especially when a composite housing is used. OBJECT OF THE INVENTION

It may be seen as an object of the present invention to provide a pump device with an effective EMC shielding to allow application of a fast switching inverter to drive the electric motor driving the pump. It may be seen as a further object that the pump device can be made compact. It may be seen as a further object that the pump device can be made with a composite housing. It may be seen as a further object that the pump device is suited for low-cost mass production.

SUMMARY OF THE INVENTION

A first aspect of the invention provides a pump device comprising

- a rotational pump mechanism arranged for pumping a fluid between a fluid inlet and a fluid outlet,

- an electric motor with a shaft arranged to rotate the rotational pump mechanism, the electric motor comprising an electrically conductive motor casing electrically connected to Protective Earth, wherein a plurality of electric power wires penetrate the casing, and wherein the plurality of electric power wires are connected to provide electric power to drive the electric motor,

- an electric inverter arranged for connection to an electric power source, wherein electric output terminals of the electric inverter are connected to the electric power wires for powering the electric motor, and

- an electrically conductive shield arranged along the electric power wires at least at a part of a distance between the electrically conductive motor casing and the electric inverter, wherein one end of the electrically conductive shield is electrically connected to the electrically conductive motor casing and the opposite end of the electrically conductive shield is electrically connected to a DC electric potential different from Protective Earth via at least one electric capacitor.

Such pump device with the proposed electrically conductive shield has been found to significantly reduce electromagnetic (EM) radiation in the frequency range 30 MHz to 1 GHz to which allows use of an electric inverter based on Wide Band-Gap semiconductor technology which can involve high voltage slopes of more than 10 V/ns, or even 100 V/ns or more even at a rather low switching frequency of such as 10 kHz to 20 kHz of the inverter. The proposed EM shielding can be implemented within a very limited extra space, and it is possible to maintain composite as material for the housing enclosing the pump device.

Especially, it has been demonstrated in pump device prototypes that the radiated electromagnetic emission can be reduced by at least 20 dB in the range 30 MHz to at least 400 MHz compared to a non-shielded pump device. This has a significant influence of compliance with EMC regulations, for example radiated emission level requirements as stated in EN55014-1 QP.

The electrically conductive shield can be implemented with standard low-cost components and is thus suited for implementation in pump device designed for low-cost mass production.

In the following, preferred features and embodiments will be described.

In some embodiments, the electrically conductive shield is a one-sided shield, e.g., a plane sheet of metal. Especially, if the one-sided shield has a length so that it extends along the electric power wires the entire distance between the electrically conductive motor casing and the electric inverter, a significant EM shielding effect can be obtained with simple means. Preferably, the one-sided shield has a width corresponding at least to a distance covering a distance between the plurality of electric wires. Preferably, the one-sided shield is placed close to the electric power wires, so as to minimize a loop inductance between the shiled and the electric power wires.

The electrically conductive shield may form an electrically conductive duct enclosing the electric power wires. Preferably, the duct encloses the electric power wires along the entire distance between the electrically conductive motor casing and the electric inverter to provide optimal EM shielding effect, however at least 80% of said distance may suffice for effective shielding. Especially, the electrically conductive duct may be electrically connected to the electrically conductive motor casing along the entire circumference of said one end of the electrically conductive duct, or at least 50% of the entire circumference of said one end. This can be implemented e.g., by means of soldering, using conductive glue or electrical connector or the like, to provide an High Frequency (HF) tight or substantially HF tight connection between the motor casing and the electrically conductive duct to obtain optimal shielding. In one embodiment, the electrically conductive shield comprises first and second electrically conductive ducts enclosing the electric power wires with a layer of electric isolation in between, so as to form a combined electrically conductive shield and an electric capacitor. Specifically, these ducts may be first and second concentric shells, e.g., cylindrical shells. Preferably, one end of the first electrically conductive duct is electrically connected to the conductive casing of the motor, and wherein one end of the second electrically conductive duct is electrically connected to the DC electric potential different from Protective Earth, or to an electrical potential of an electrically conductive casing around the electric inverter. The first and second ducts preferably extend the entire distance between the electric motor casing and the electric inverter, e.g., between the electric motor casing and an electrically conductive casing enclosing at least part of the electric inverter. The first and second conductive ducts together form a capacitor, and by careful design, the capacitance of this capacitor can be tuned to a desired value.

The shield may, whether one-sided or completely enclosing the electric power wires, extend at least 50% of a distance between the motor casing and the electric inverter, such as at least 50% to 70% of a distance between the motor casing and the electric inverter, such as at least 80% of a distance between the motor casing and the electric inverter, such as 90% of a distance between the motor casing and the electric inverter. To obtain optimal shielding, the shield preferably extends at least most of a distance between the motor casing and the electric inverter, or at least more than 95% of this distance, most preferably 95- 100% of this distance. Especially, the shield extends the entire distance between the motor casing and the electric inverter for the most optimal shiedling effect. The shield may form a substantially or completely High Frequency tight electric shielding enclosing the electric power wires all the distance between the motor casing and the electric inverter, specifically between the motor casing and an electrically conductive casing enclosing the electric inverter components.

Said opposite end of the electrically conductive shield may be electrically connected via the at least one electric capacitor to a positive or a negative DC electric potential. Especially, it is preferred that said opposite end of the electrically conductive shield is electrically connected via the at least one electric capacitor to a positive or a negative DC electric input provided to the electric inverter and on which the electric inverter operates to generate power to the electric power wires. Specifically, the electrically conductive shield is electrically connected to both a positive and a negative DC electric potential via respective electric capacitors, i.e., to both of the positive and the negative DC electric inputs on which the electric inverter operates.

The electrically conductive shield can be implemented by a structure in various forms, e.g. a sheet, a plate, a perforated plate or a mesh, or a combination of any of these. To provide the most effective shielding, the electrically conductive shield is preferably High Frequency (HF) tight, i.e. provides a Faraday cage effect in the relevant HF frequency range.

One or more ferrite bead components may be provided on each of the electric power wires, preferably at the electric inverter end. Especially, a plurality of ferrite bead components with different electric characteristics may be connected to or provided on each of the electric power wires at the electric inverter end. The wires can also be fed through discrete ferrite beads, such as using ferrite bead components with one or more through-going holes. Hereby, it is possible to provide an optimalattenuation effect over a wide frequency band. The ferrite bead components may even be based on different technologies so as to allow different electric characteristics.

The electrically conductive shield may be electrically connected to the DC electric potential different from electric Protective Earth via a plurality of separate electric capacitor components, preferably spatially distributed electric capacitor components to provide optimal shielding. Especially, the plurality of electric capacitor components may comprise electric capacitor components having different electric characteristics, e.g., also including capacitor components based on different technologies. A combination of different capacitors may be necessary to keep an impedance of the capacitors low, especially in the region of the resonant frequency of the capacitor. Hereby, it is possible to provide an optimal shielding effect over a wide frequency band. In the present context, the term 'impedance' should be interpreted to mean the effective resistance of an electric circuit or component to alternating current, arising from the combined effects of ohmic resistance and reactance. Depending on the actual application, it is to be understood that the capacitor components may be components rated at an appropriate safety class, such as Yl, Y2 etc.

Preferably, the electrically conductive shield is made of a metal, preferably copper, however other metals may be used as well, including aluminium, steel or the like.

Specifically, the electrically conductive shield may have a thickness which is suitable and selected based on the shielding effect to be obtained as well as practical matters, such as space available etc. Especially, the thickness may be such as 1 pm to 10 mm, more preferably 10 pm to 1 mm, however it is to be understood that a thickness smaller or larger than the mentioned interval may be used, thus allowing e.g., various metal foils, sheets, meshes or casings to be used. The minimal thickness of the shield depends on the required impedance of the shield, i.e. how low an impedance is required to effectively feedback the electric noise from the stator of the electric motor to the electric inverter.

In some embodiments, an electrically conductive casing, such as a Faraday cage, at least partly encloses electric components of the electric inverter. Preferably, said electrically conductive casing is electrically connected to the electrically conductive shield via said at least one electric capacitor. In specific embodiments, the electric components of the electric inverter are arranged on a circuit board, and wherein a plurality of electric capacitor components are positioned at respective positions on the circuit board and electrically connected between the electrically conductive casing of the electric inverter and the electrically conductive shield. The electrically conductive casing may be formed by a metal, e.g., copper, e.g., following the options mentioned above for the electrically conductive shield.

Especially, the electric inverter may be implemented by Wide Band-Gap semiconductor components, e.g., such as Gallium Nitride (GaN) or Silicon Carbide (SiC) based semiconductor components. Such Wide Band-Gap semiconductor components may allow a high electric efficiency, but even at switching frequencies of such as 10 kHz to 20 kHz, the switching may involve high voltage slopes that generate high frequency electromagnetic radiation which can be remedied by the shield according to the present invention. Especially, the electric inverter may be arranged to generate a voltage slope at its electric output terminals which exceeds 10 V/ns, such as exceeding 50 V/ns, such as exceeding 100 V/ns, such as a voltage slope of 100 V/ns to 200 V/ns. Especially, the shield of the present invention is advantageous for reducing electromagnetic radiation in case of voltage slopes exceeding 5 V/ns to 10 V/ns.

The electric inverter may specifically operate at a switching frequency of 1 kHz to 1 MHz, such as 1-200 kHz, such as 2-100 kHz, such as 2-50 kHz, such as 5-30 kHz, such as 4-20 kHz, such as 4.5-18 kHz.

The electric inverter preferably comprises a plurality, such as 2 to 10, preferably at least 6, semiconductor switches electrically connected between a positive and a negative DC input voltage. Preferably, the pump device comprises a rectifier circuit arranged to generate the positive and negative DC input voltage to the electric inverter upon connection to an AC electric power source, e.g., an AC electric power source providing a 100 V AC to 500 V AC electric power input, e.g., the public grid. In some embodiments, e.g. for solar powering, the pump device may be configured to receive an electric power input in the form of a DC voltage, e.g. in the form of a positive and a negative DC voltage.

In specific embodiments, the electrically conductive shield may be implemented as at least two metallic parts assembled to form an electrically conducting duct around the plurality of electric power wires, such as a duct completely enclosing the electric power wires. E.g., this may involve two metal shells shaped to form a duct around the electric power wires, when assembled. More specifically, one or both of these metal shells may be shaped to allow soldering in one end to a circuit board where the electric inverter components are arranged.

The electric motor and the electric power inverter may be interconnected by at least three electric power wires, e.g., to allow a three-phase electric motor to be used. The electric motor may be any known electric motor technology involving a stator and a rotor to allow rotation of a shaft. The electric motor may be a permanent magnet electric motor, however the electric motor is not limited to that.

The rotational pump mechanism may be based on any known pump technology. E.g., the rotational pump mechanism may comprise an impeller arranged to rotate inside an impeller housing for pumping fluid, e.g., liquid such as water, from a fluid inlet to a fluid outlet, upon rotation.

The housing around the rotational pump mechanism may be partly or fully integrated with the electrically conductive motor housing.

The pump device may comprise a casing enclosing at least the electric inverter. The casing preferably encloses all electronic components of the pump device, however it may further enclose more components, e.g. part of or all of the electric motor, part of or all of the rotational pump mechanism. The casing preferably has openings to allow electric connection to an electric power source, e.g. it may have pipe connections for fluid inlet and fluid outlet. Especially, the casing may be made of a composite or another electrically non-conductive material.

It is to be understood that the invention is applicable to pump devices of various sizes. E.g., pumps with electric motors in the electric power range of 1 W to 100 W, however also to pump devices with electric motors in the electric power range 100 W to 1 kW, or larger pumps in the power range of 1-50 kW or even more.

The skilled person will know how to implement the invention based on the disclosure of the present description and the general knowledge in the technical field. E.g., the skilled person will know how to select specific capacitance values of electric capacitors and other parameters to be used for a specific application, e.g., based on inverter switching frequency, physical dimensions, and other parameters.

In a second aspect, the invention provides a method for reducing electromagnetic radiation from a rotational pump mechanism driven by an electric motor with an electrically conductive motor casing electrically connected to Protective Earth, wherein the electric motor is powered by electric power from an electric inverter via a plurality of electric power wires, the method comprising

- providing an electrically conductive shield along the electric power wires at least at a part of a distance between the electrically conductive motor casing and the electric inverter,

- electrically connecting the electrically conductive shield at one end to the electrically conductive casing of the electric motor, and

- electrically connecting the electrically conductive shield at the opposite end via at least one electric capacitor to a DC electric potential different from Protective Earth.

In a third aspect, the invention provides a system comprising one or more pump devices of the first aspect. The system may comprise a fluid pipe system to which the one or more pump devices are installed. The system may comprise a control system to control a function of the one or more pump devices. Specifically, the system may be a utility installation, e.g., a water, heat, or cooling installation.

The first, second and third aspects of the present invention may be combined. These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE FIGURES

The pump device according to the invention will now be described in more detail with regard to the accompanying figures. The figures show one way of implementing the present invention and is not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set.

FIG. 1 shows a diagram of components of a pump device embodiment.

FIG. 2a-2e show sketches of various physical configuration examples of the electrically conductive shield in relation to the electric power wires interconnecting electric inverter and electric motor.

FIG. 3 to FIG. 9 show diagrams of various electrical configuration examples of the electrically conductive shield in a three-phase example. FIG. 10 shows an example of an electrically conductive shield in the form of a double duct which itself forms a capacitor component.

FIG. 11 and FIG. 12 show sketches of a prototype.

FIG. 13 shows a graph indicating high frequency electromagnetic radiation for a pump device with and without the electrically conductive shield of the invention, as well as the EN55014-1 QP limit.

FIG. 14 shows steps of a method embodiment.

DETAILED DESCRIPTION OF AN EMBODIMENT

FIG. 1 shows a block diagram with basic components of a pump device embodiment with one composite casing H, a conduit box, for housing at least an electric inverter E_I and other electronic components. An electric motor MT is arranged to drive a rotational pump mechanism PMP to pump a fluid between an inlet F_I and an outlet F_O with connections to a pipe system external to the pump device. The electric inverter E_I is arranged to be electrically powered by an AC voltage AC_V from a power source outside the casing H.

The electric motor MT has an electrically conductive motor casing MTC enclosing the stator and rotor of the electric motor MT. The motor casing MTC is electrically connected to Protective Earth PE, such as it is normal practice within pump devices. A plurality of electric power wires W for driving the electric motor MT penetrate the motor casing, and these wires W are connected in the opposite end to an electric inverter E_I which generates electric power to drive the electric motor MT via the electric power wires W, here shown as three parallel wires.

An electrically conductive shield SLD, e.g., a metal sheet or the like, is arranged along the electric power wires W at least at a part of a distance between the electrically conductive motor casing MTC and the electric inverter E_I. One end of the electrically conductive shield SLD is electrically connected to the electrically conductive motor casing MTC, and the opposite end of the electrically conductive shield SLD is electrically connected via at least one electric capacitor Y2 to a DC electric potential DC_V which is different from Protective Earth PE. Especially, the electric inverter E_I operate at a positive and a negative DC voltage input, and the shield SLD can, via the capacitor Y2, be connected to either one of these positive or negative DC voltage inputs.

It is to be understood that the even though denoted "Y2" in FIG. 1 and the embodiments described below the electric capacitor connecting the shield SLD and the DC potential DC_V is not limited to capacitors complying with safety rating Y2, rather any safety rating can be selected for the capacitor component, depending on the actual application.

The shield SLD is here shown to shield the electric power wires W along such as 80% of the distance between the motor casing MTC and the electric inverter E_I, however it is to be understood that the shield SLD may occupy the full distance between motor casing MTC and the electric inverter E_I if maximum electromagnetic shield is required. Further, the shield SLD is more effective, if it forms a duct around the electric power wires W rather than forming only a onesided or open structure along the electric power wires W.

The electric inverter E_I may be housed within an electrically conductive casing, e.g., a Faraday cage, and this electrically conductive casing may be connected to either the positive or negative DC voltage on which the electric inverter E_I operates. Thus, especially the shield SLD may be electrically connected to such electrically conductive casing with the capacitor Y2.

FIG. 2a-2e show various examples of physical configurations of the shield SLD in relation to the electric power wires W. The illustrations show the electric power wires W as three parallel wires from the ends, i.e., in contrast to the illustration in FIG. 1, where the wires W are shown in side view.

FIG. 2a shows an example of the shield SLD being a one-sided sheet or plate, e.g., a plane sheet or plate, arranged with a size large enough to shield along one side of all of the electric power wires W, i.e., the shield SLD has a width exceeding a distance between the two far most wires of the plurality of power electric wires W. FIG. 2b show an example of the shield SLD fully enclosing all of the electric power wires W, i.e., the shield forms a duct around the electric power wires W.

FIG. 2c shows an example of the shield SLD which is in between the examples of FIG. 2a and 2b, i.e., where the shield SLD partly encloses the electric power wires W. Thus, the shielding is more effective than the one-sided example of FIG. 2a, but less effective than the fully enclosing example of FIG. 2b.

FIG. 2d shows yet another example, here with the shield SLD in the form of two one-sided sheets of plates arranged on opposite sides of the electric power wires W, e.g., two parallel plane sheets or plates.

FIG. 2e illustrates an implementation of the example of FIG. 2b, i.e., a duct enclosing the electric power wires W, but here formed by two electrically conductive shield elements SLD1, SLD2, which form the duct, when assembled.

FIG. 3-9 illustrate electric diagrams of various examples of electrically connecting the electrically conductive shield or duct for fully or partly shielding electric power wires interconnecting an output of the electric inverter and the casing of the electric motor. FIG. 3-9 show variants of the same principal circuit diagram with an electric inverter with three sets of controllable semiconductor switches, one set for each electric power wire which is connected to drive the motor. Especially, the semiconductor switches may be implemented with Wide Band-Gap semiconductor technology to allow a low power loss in the inverter. Each set of controllable semiconductor switches are connected between a positive DC voltage DC+ and a negative DC voltage DC-. These DC voltages DC+, DC- are generated by a rectifier circuit based on an AC voltage AC from an electric power source, e.g., a 100 V AC to 500 V AC power source. The switching operation of the semiconductor switches of the electric inverter are controlled by a micro controller, e.g., to operate at a switching frequency within the range of 4.5-18 kHz. The casing of the motor is electrically connected to Protective Earth PE, and in the motor end, the shield or duct is electrically connected to the casing of the motor and thus also to Protective Earth PE. In the following description of FIG. 3-9, only the variation specific for each variant will be described. It is to be understood that the specific circuit shown in FIG. 3-9 merely serves to illustrate various example of specific implementation of the shielding electric connections.

FIG. 3 shows a variant where the electrically conductive shield is a duct fully enclosing the electric power wires. At the motor end, the duct is preferably more or less integrated with the motor casing or at least the duct is electrically connected to the motor casing along a significant part of its periphery, or at least along more than 80%, such as more than 90%, such as 90-100%, of its periphery, to provide the most effective shielding. In some cases only 10%-50% of its periphery may be electrically connected to the motor casing. The electric inverter has an electrically conductive casing partly or fully enclosing its components including the semiconductor switches, e.g., forming a Faraday cage around all of the electric inverter components. The inverter casing is electrically connected to DC-, which alternatively could be DC+. The three power wires penetrate the inverter casing, and inside the casing, between the semiconductor switches and the inverter casing, each of the power wires is provided with a ferrite bead component at the electric inverter end serving in itself to reduce high frequency radiation. The inverter end of the shielding duct is electrically connected to the inverter casing, and thus to DC-, via a plurality of separate capacitor components Y2, here two capacitors Y2 are shown for simplicity. For optimal shielding effect, the shielding duct preferably extends all the distance between the motor casing to the inverter casing, leaving only a very short part of the power wires unshielded.

FIG. 4 shows a similar implementation as in FIG. 3 except that the ferrite beads have been left out, thereby providing a simpler solution but with a reduced electromagnetic shielding effect compared to FIG. 3.

FIG. 5 shows a variant without an inverter casing, but with a plurality of capacitors Y2 connected to the shielding duct at its end opposite the motor, and with the opposite ends of these capacitors Y2 connected to the negative DC voltage DC- on which the inverter operates. However, to improve shielding efficiency, each power wire is provided with a ferrite bead component between the inverter components and the shield duct.

FIG. 6 shows the same shielding design as in FIG. 5, except that the capacitors Y2 connected to the shielding duct are connected to the positive DC voltage on DC+ on which the inverter operates.

FIG. 7 shows a variant of the designs of FIG. 5 and 6, since here at least one capacitor Y2 is connected between the shielding duct and the positive DC voltage DC+ on which the inverter operates, and at least one capacitor Y2 is connected to the negative DC voltage DC- on which the inverter operates. This may help to spatially distribute capacitors which will improve the shielding effect.

FIG. 8 shows a variant of FIG. 5-7, where the plurality of capacitors Y2 connected to the shielding duct are connected to a DC voltage potential being between the negative and positive DC potential on which the inverter operates. As seen, the capacitors Y2 are in this variant connected at a midpoint of two series connected capacitors connected between the negative and positive DC voltages DC-, DC+ on which the inverter operates.

FIG. 9 shows a variant where the shield is one-sided, i.e., instead of a duct around the electric power wires between inverter and motor, the shield is a structure, such as a plate, foil, sheet or mesh, electrically connected at one end to the motor casing and extends along the electric power wires forming only a shield to one side. Preferably, the one-sided shield is placed close to the electric power wires, most preferably as close as possible, so as to minimize a loop inductance between the shield and the electric power wires. The shield is connected at the inverter end via one or more capacitors Y2 to a DC potential as shown in FIG. 5-8, here an example is shown where the capacitor Y2 is connected to the negative DC voltage on which the inverter operates.

FIG. 10 shows an electrically conductive shield design, where a metallic duct itself includes the capacitor to be connected to a DC potential different from Protective Earth, and thus a separate capacitor component can be eliminated. The metallic duct can be implemented by two metallic cylinders DI and D2 with a thin layer of isolation in between, thus forming a capacitor. One end of the first cylinder DI should be connected to the motor casing and the opposite end near the electric inverter drive should be floating. One end of the other cylinder D2 should be connected to the electrical potential of the electric inverter casing, or another DC potential different from Protective Earth, and the opposite end near the motor casing should be floating. The capacitor is hereby the capacitance between the two cylinders DI, D2 which can be calculated as known by the skilled person.

FIG. 11 and 12 show two sketches with different views of a prototype of a pump device which has been supplied with a metallic duct fully surrounding the power wires between the electric motor with a metallic motor casing and the circuit board on which the electric inverter components are located. A metal casing forms a Faraday cage around the electric inverter components, and on the illustrated embodiment, this inverter casing is locate on an opposite side of the circuit board than the shield. Several capacitors Y2_l, Y2_2 are distributed and connected between the shield and the inverter components. The electric inverter is implemented by WBG semiconductors, especially such as GaN or SiC, and these are capable of switching with voltage slopes up to 200 V/ns on the three-phase output to the electric motor. Furthermore, ferrite beads (not visible) are preferably applied on the output of the electric inverter.

FIG. 13 shows graphs indicating level of electromagnetic radiation versus frequency for the pump device prototype of FIG. 11 and 12 tested with and without the supplied shielding features. The upper curve is measured without shielding and the WBG semiconductors are switching up to 200 V/ns on the three- phase output to the motor. The lower curve is with shielding and still switching up to 200 V/ns on the three-phase output wires to the motor. As seen, the shielding provides a significant reduction of such as 20-30 dB from 30 MHz up to around 500 MHz, and still up to 1 GHz, an effect is seen. The electromagnetic radiation limit according to EN55014-1 QP is further indicated, and as seen the pump device exceeds this limit at frequencies up to 600 MHz, while the prototype with the shielding features is capable of complying with EN55014-1 QP.

FIG. 14 shows steps of a method embodiment, i.e., a method for reducing electromagnetic radiation from a rotational pump mechanism driven by an electric motor with an electrically conductive motor casing electrically connected to Protective Earth, wherein the electric motor is powered by electric power from an electric inverter via a plurality of electric power wires. The method involves providing P_SLD an electrically conductive shield, e.g., a metal duct, along the electric power wires at least at a part of a distance, preferably more than 80% of a distance, such as more than 90% of a distance, between the electrically conductive motor casing and the electric inverter. Further, electrically EC_SLD_MTC connecting the electrically conductive shield at one end to the electrically conductive casing of the electric motor, and further electrically EC_SLD_DC connecting the electrically conductive shield at the opposite end via at least one electric capacitor to a DC electric potential different from Protective Earth, such as the same positive or negative DC voltage on which the electric inverter operates. The method may further comprise providing an electrically conductive casing enclosing components of the electric inverter to provide further shielding effect, e.g., electrically connecting this casing to the same positive or negative DC voltage on which the electric inverter operates. Still further, the method may involve providing ferrite bead components s on the electric power wires.

Although the present invention has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. The scope of the present invention is set out by the accompanying claim set. In the context of the claims, the terms "comprising" or "comprises" do not exclude other possible elements or steps. The mentioning of references such as "a" or "an" etc. should not be construed as excluding a plurality. The use of reference signs in the claims with respect to elements indicated in the figures shall also not be construed as limiting the scope of the invention. Furthermore, individual features mentioned in different claims, may possibly be advantageously combined, and the mentioning of these features in different claims does not exclude that a combination of features is not possible and advantageous.