Technical Field

[001] The invention relates to the field of electrical machinery. It is applicable to the cooling of fast neutron nuclear reactors, metallurgical plants, metal foundries and metal production plants, where the transportation of liquid, electrically conductive metals is required, as well as it can be incorporated into magnetohydrodynamic research equipment

Background Art

[002] In hydraulic circuits where a constant flow of liquid metal with constant parameters is required, mechanical pumps with rotating blades in direct contact with the liquid are usually used. However, these pumps have two major drawbacks: low operational safety and the need for regular maintenance due to the rotating parts in the fluid and the gaskets.

[003] Cooling systems for liquid, sodium (Na) cooled fast neutron nuclear reactors have particularly high safety requirements. Because of the chemically aggressive nature of molten sodium, there it is tend to opt out of mechanical pumps in fast neutron reactors and to switch to electromagnetic pumps.

[004] The mechanical pump and its electric drive system are known (Fig. 1) [1, 2], The liquid metal pumping function is provided by blades that via a shaft are connected to the motor rotor. The joint is sealed. The motor speed can be controlled and regulated by a frequency converter mounted on the motor. The known solution does not allow to ensure complete tightness of the duct; the mechanical pump has a low service life as well there is low work safety.

[005] An electromagnetic induction pump [4] is known, comprising a motor, a shaft functionally connected to the motor and permanent bipolar magnets functionally connected to the shaft; arranged around a circumference with variable poles and mounted with the possibility of rotation relative to a channel for the flow of molten metal, wherein the permanent bipolar magnets with the axial direction of magnetization are arranged symmetrically on both opposite sides with respect to the channel for the flow of molten metal, and the opposite poles of the magnets on each side are located opposite each other. Compared to the known solution, the proposed one allows: to concentrate the field in the direction of the channel; to change the position of the channel in relation to the rotor. There is only one direction in the known solution, but in the proposed variant other directions are possible, for example, radial. The proposed solution allows to change the ferromagnetic properties of the field source, ensuring that the magnetic permeability of the source is significantly higher than one, thus improving the flow stability.

Disclosure of the Invention

[006] The object of the invention is to overcome the drawbacks of the prior art The object is achieved by offering an electromagnetic pump for the transport of a liquid, electrically conductive medium with a specific electrical conductivity of 5 to 9 MS/m, comprising an electric motor with a rotor and a magnetic system connected to the rotor with the possibility of rotation relative to the hydraulic channel, to guide the flow of the electrically conductive environment; wherein the magnetic system comprises permanent magnets arranged around the circumference of the rotor and made in the form of sectors which, when assembled, form a disk, characterized in that inserts made of ferromagnetic material or non-magnetic material are mounted between the permanent magnets so as the configuration of permanent magnets has a periodically variable magnetization, which is designed to obtain a running magnetic field in the azimuthal direction. The magnetic system can be located on one side or on both sides of the hydraulic channel. According to another manifestation of the invention, the inserts mounted between the permanent magnets may be formed of one or more permanent magnets having a different magnetization direction comparing with the adjacent magnets, i.e. so that the magnetization direction of the magnets arranged around the rotor circumference is different in each subsequent magnet [007] According to the invention, the rotor is connected to a magnetic system which makes it possible to obtain a magnetic field which rotates in an azimuthal direction. The magnetic system is designed as a permanent magnet configuration with periodically changing magnetization. This means that the direction of magnetization of the magnets arranged around the rotor circumference is different in each subsequent magnet; moreover, there are sector-shaped inserts between the magnets, which can be made of ferromagnetic or non-magnetic materials, or of permanent magnets

[008] The principle of operation of the invention provides that the hydraulic power of the pumping to be developed is directly proportional to the electrical conductivity. Thus, as the controllability of the working body decreases, the hydraulic power will decrease accordingly.

Brief Description of Drawings

[009] The present invention is illustrated by appropriate drawings, in which:

Fig. 1 shows a prior art solution - a mechanical pump with an electric drive system;

Fig. 2 - principal scheme of one manifestation of the proposed equipment;

Fig. 3 - an accelerometer to be mounted on the pressure sensor;

Fig. 4 - energy diagram of the electromagnetic pump on permanent magnets, in which Ap mag - magnetic losses in the stator; Ap el - electrical losses in the stator; Ap e2 - electrical losses in the rotor; Ap meh - mechanical losses; Ap pap - additional losses of asynchronous motor (losses from higher harmonics, field pulsations in teeth, etc); Ap wall - losses due to induced currents in the walls of the stainless steel channel of the pump; Ap Na - losses due to currents induced in liquid metal; Pl - supplied electric power; P2 - hydraulic power to be developed;

Fig. 5 - p-Q curves of the proposed device, recorded on the Na contour, and demonstrable operating modes of the controller p = const and Q = const;

Fig. 6 - a diagram showing the operation of the invention in the mode p = const;

Fig. 7 - a diagram showing the operation of the invention in the mode Q = const; Fig. 8 - a scheme of one manifestation of the proposed pump rotor magnetic system.

[010] The schematic diagram of the proposed device is shown in Fig. 2. The device comprises an electric motor with a rotor (1) and a magnetic system connected to the rotor with the possibility of rotation relative to a hydraulic channel (2) for directing the flow of liquid, electrically conductive medium. The magnetic system comprises permanent magnets (3) arranged around the circumference of the rotor (1) and designed in the form of sectors which, when assembled, form a disk. Inserts (4) are mounted between the permanent magnets (3). The inserts (4) can be made of ferromagnetic material, nonmagnetic material or one or more permanent magnets. The configuration of the permanent magnets (3) has a periodically variable magnetization, which is designed with the possibility to obtain a running magnetic field in the azimuthal direction.

[011] The magnetic system can be arranged on one side or on both sides of the hydraulic channel (2), forming discs on both sides of the hydraulic channel (2), respectively (Figs. 2 and 8). The inserts (4) mounted between the permanent magnets (3) are formed by one or more permanent magnets, the direction of magnetization of which differs from the direction of magnetization of the permanent magnets (3) in the magnetic system. According to one embodiment of the invention, the direction of magnetization of these inserts (4), which are formed of permanent magnets, is perpendicular to the direction of magnetization of the permanent magnets (3) in the magnetic system. This allows significantly amplify the magnetic field by concentrating it in the direction of the channel.

[012] According to a preferred embodiment of the invention, the electromagnetic pump is connected to a proportional integral (PI) regulator for stabilizing the flow parameters, which is designed with the possibility to separately set the required maintenance pressure and flow without a differential part

[013] The electromagnetic pump may further comprise a pressure sensor (7) operatively connected to the hydraulic channel (2) and a three-axis accelerometer (8) which can be mounted on the pressure sensor (7), in addition to a pressure sensor (7) and a three-axis accelerometer (8). The sensitive elements are placed as close to each other as possible. This is done in order to be able to monitor possible pressure fluctuations. This is done from the accelerometer (8) reading by observing the displacement of the manometer diaphragm with the corresponding coordinate component in the normal direction of the diaphragm plane.

Example of Implementation of the Invention

[014] In the embodiment of the invention, an electric motor with a synchronous speed of 1500 revolutions per minute was used as the drive element and the electric motor of the device was started through a frequency converter.

[015] It follows from the principle of operation of the pump that energy is transferred: stator-rotor-liquid metal. Thus, unlike the design of the prior art device, there are two separate slides in the proposed device. The first is the normal slip of an asynchronous electric motor, as the proportional ratio of the rotational frequency of the relative rotor to the rotational frequency of the magnetic field. The second is the relative lag of the flow rate of liquid metal in relation to the faster rotating rotor.

[016] According to these two slides, a sequential pump frequency circuit can be distinguished: the angular frequency of rotation of the electric motor stator, or the main magnetic field, which is determined by the applied voltage; electric motor rotor; the angular frequency of rotation of the pump magnet and, consequently, the electromagnetic field of the pump; and the flow rate of the liquid metal, which is determined by the angular frequency of rotation of the magnets through the pump slide.

[017] The load curve of an electromagnetic pump characterizes a new type of mechanical load. The mentioned curve - torque dependence of the motor slip - was taken in various cases in the hydraulic pumping experiment [018] In the specific example of the embodiment of the invention, the dependences of the supplied electric power on the flow at a constant frequency were also taken. It was proved that at almost all points the power consumption of the electric motor at reduced voltage is lower than at the nominal voltage of 400V.

[019] In a similar way, changes in efficiency and power factors were taken as the voltage changed, and for both of these energy parameters, the maximum value was reached at a lower voltage than the nominal one.

[020] The optimal mode is defined as the conditions when the change of the adjustable parameter is on the one hand fast enough and on the other hand - minimizing the possibility of exceeding the desired value and minimizing fluctuations.

[021] The choice of the control factors of the device was made based on the following parameters: the characteristic response time of the hydraulic circuit must be less than the time constant of the control system. The corresponding calculation of the reaction time for one specific case is shown below. Comparing the result with the curves of the PI controller. As can be seen from the calculations and measurement graphs below, the condition is fulfilled.

[022] Characteristic parameters of Na contour:

V = 0,04 m ³ = 40 L p = 915,5 kg/m ³ m = p • V = 0,04 • 915,5 = 36,62 kg

P = 5 bar = 500000 Pa

Typical reaction time to reach a pressure of 5 bar from

[023] Demonstration of the operation of the invention is shown in Fig. 4. For demonstration purposes the dependence of the pressure developed by the pump on the capacity at different electric motor rotation frequencies, as well as the specific values of the stabilized pressure and flow selected here are shown.

[024] Experimental results with two identical permanent magnet pumps connected in a cascade, in two variants respectively: in parallel and in series are shown in Fig. 5, where one of the pumps is the proposed invention and the other is an electromagnetic pump without electric drive control and regulation system.

[025] As can be seen from Figs. 6 and 7, the proposed pump design allows to effectively reduce both the unevenness of the supplied fluid and the unevenness of the drive power, using the proposed combination of permanent magnet system with the dimensions of the pump channel, and a control system with feedback. In this design, the number of rotor poles of the pump magnetic system is matched to the length and shape of the enclosing channel, as well as the shape and dimensions of the magnetic conductor, so that the electromagnetic forces generated by the magnets in the liquid metal and in the magnetic conductor on both the inlet and outlet sides of the channel are balanced and their changes are coordinated. The important principle here is that if the load on the outlet side of the duct falls, the load on the inlet side of the duct must increase proportionally. These load changes must take place at the same speed. In addition, the control system collects data on the flow, vibration level and power consumption of the pump. The following are the basic principles for choosing a particular geometry.

[026] The geometry, number, location, and configuration of the electromagnetic pump on permanent magnets are selected to provide maximum pumping capacity. The losses of the pumping part for the given pump - according to the right-hand side of the energy diagram - are quadratic depending on the motor rotation frequency. This means, for example, that by reducing the rotational frequency twice, the losses increase four times. Consequently, the part of the pump energy diagram loss related to the frequency reduction is very significant The effective hydraulic power of the pump, in turn, is proportional to the first stage of the frequency. Therefore, the control of the pump is purposefully implemented by choosing the lowest possible frequency to ensure the required hydraulic power. Once this frequency has been reached, the U / f ratio of the electric motor is further selected. This, in turn, is chosen in an effort to ensure maximum pump efficiency. Therefore, the most rational operating mode is chosen as the optimum between these two parameters mentioned above.

References:

[1] https: //www.northridgepumps.com/p 1071 calpeda-mxh-el-series-horizontal- multistage-pump-with-variable-speed-drive

[2] https://www.researchgate.net/figure/Photograph-of-experiment al-setup-with- printed-centrifugal-pump-placed-inside-stator fig4 335984048

[3] J. Dirba, K. Ketners, Elektriskas mašīnas, RTU, 2009.

[4] RU 164336 Ul.