WO2013054301A2

WO2013054301A2 - A pump for pumping waste water

Info

Publication number: WO2013054301A2
Application number: PCT/IB2012/055545
Authority: WO
Inventors: Tanja Hedberg
Original assignee: Itt Manufacturing Enterprises Inc
Priority date: 2011-10-14
Filing date: 2012-10-12
Publication date: 2013-04-18
Also published as: WO2013054301A3

Abstract

The invention relates to a pump (1) comprising a motor (2), a drive shaft (3) and an impeller connected to the drive shaft (3), said motor (2) comprising a stator (4) and a rotor (6) of hybrid type, wherein the hybrid rotor (6) comprises a rotor core comprising an annular radially outer section of asynchronous type and an annular radially inner section of synchronous type, wherein the inner section comprises a number of permanent magnets. The hybrid rotor comprises two poles, wherein the total permanent magnet area per pole is in the range 500 to 600 square millimeters, and the total rotor slot area per pole is in the range 400 to 600 square millimeters, or four poles, wherein the total permanent magnet area per pole is in the range 200 to 350 square millimeters, and the total rotor slot area per pole is in the range 100 to 300 square millimeters.

Description

A PUMP FOR PUMPING WASTE WATER

Technical field of the Invention

The present invention relates generally to the field of pump for pumping liquid, such as waste water. Further, the present invention relates specifically to the field of motors for submersible pumps, which motor is smaller and more

powerful than prior art motors, without having to adversely affect the durability of the motor/pump. The pump comprises a motor, a drive shaft and an impeller connected to the drive shaft, the impeller in operation being driven by the motor for rotation about an axially extending axis. Thereto, said motor comprises a stator and a rotor of hybrid type, wherein the hybrid rotor comprises a rotor core comprising an annular radially outer section of asynchronous type and an annular radially inner section of synchronous type arranged radially inside said outer section, which inner section comprises a number of permanent magnets.

Background of the Invention

The market, together with tougher laws and regulations regarding efficiency, has raised an increased demand for high efficiency motors, and the new motor is designed to address this increased demand.

The International Electrotechnical Commission (IEC) standards are being addressed on a global scale. The IEC standards are part of an effort to unify motor testing

standards, efficiency requirements and product labelling requirements. IEC/EN 60034-30 defines energy efficiency (IE code) classes based on the test methods specified in IEC/EN 60034-2-1. IEC 60034-30 Super Premium Efficiency class is denominated IE4, IEC 60034-30 Premium Efficiency class is denominated IE3, IEC 60034-30 High Efficiency class is

denominated IE2 and IEC 60034-30 Standard Efficiency class is denominated IE1. The ICE 60034-30 standard covers for example: Single speed, three-phase 50 and 60 Hz motors; 2, 4 and 6-pole motors; Rated power output from 0,75kW to 375 kW; and Rated voltage up to 1000 V.

This chart with efficiency classes discloses how difficult it is to reach the premium efficiency class IE3 for motors with lower power. For high power motors the step is minimal, and thus it is easy to rise to the Premium efficiency class for larger motors with a traditional induction motor

technology while for pumps comprising low power motors it is more difficult to rise to the Premium Efficiency class. The motor size needs to be drastically enlarged which will have a negative impact on service and maintenance, and also entail that the entire pump design need to be changed. Thus, a traditional induction motor is not option for pumps comprising low power motors (i.e. up to about 15 kW pump), with regard to the ability to reach the Premium Efficiency class IE3.

The inventive pump comprises a new Line Started Permanent Magnet (LSPM) motor, which is the world's first LSPM motor for waste water pumping applications. It should be pointed out that it is possible to upgrade an existing pump to a higher motor efficiency level, i.e. international efficiency class 3 of motors, by exchanging the present motor with a LSPM motor according to the invention.

Object of the Invention

The present invention aims at providing an improved pump of the initially defined type.

Summary of the Invention

According to the invention at least the primary object is attained by means of the initially defined pump having the features defined in the independent claim. Preferred

embodiments of the present invention are further defined in the dependent claims.

According to the present invention, there is provided a pump of the initially defined type, which is characterized in that in that the hybrid rotor comprises:

two poles, wherein the total permanent magnet area per pole, in a radially extending plane, is in the range 500 to 600 square millimeters, and the total rotor slot area per pole, in a radially extending plane, is in the range 400 to 600 square millimeters,

or

four poles, wherein the total permanent magnet area per pole, in a radially extending plane, is in the range 200 to 350 square millimeters, and the total rotor slot area per pole, in a radially extending plane, is in the range 100 to 300 square millimeters.

Thus, the present invention is based on the insight that the LSPM motor combines the benefit of an induction motor and of a Permanent Magnet Synchronous Motor (PMSM) motor, by starting direct on line with a squirrel cage (induction motor) and having higher efficiency, lower stator current and higher power factor (than similar size pure induction motor) when the motor is run by permanent magnets in synchronous duty, i.e. almost no rotor losses in the synchronous duty. Thus, a LSPM motor is a PMSM motor (synchronous motor) that can be started like an asynchronous motor, or is an induction motor that in steady state runs in synchronous duty. The LSPM motors use permanent magnets located in the rotor unit and operate at synchronous speed in steady state. Since there are no rotor current losses during synchronous duty, almost all rotor losses are eliminated. Almost all of the motor losses are concentrated in the stator where the

resulting heat can be readily cooled by the surrounding liquid or by the use of an integral closed-loop motor cooling

system. LSPM motor losses are as much as 50% lower than conventional motors, resulting in lower motor operating temperatures and extended bearing and motor lifetime.

Further advantages with and features of the invention will be apparent from the other dependent claims as well as from the following detailed description of preferred embodiments.

Brief description of the drawings

A more complete understanding of the abovementioned and other features and advantages of the present invention will be apparent from the following detailed description of preferred embodiments in conjunction with the appended drawings, wherein :

Fig. 1 is a cross sectional side view of a part of a waste water pump,

Fig. 2 is a partial cross sectional side view of a rotor unit comprising two poles,

Fig. 3 is a view from above of the rotor unit according to figure 2,

Fig. 4 is a cross sectional view from above of the rotor unit according to figure 2,

Fig. 5 is a partial cross sectional side view of a rotor comprising four poles,

Fig. 6 is a view from above of the rotor unit according to figure 5, and

Fig. 7 is a cross sectional view from above of the rotor unit according to figure 5.

Detailed description of preferred embodiments of the invention Reference is now made to figure 1, disclosing an inventive pump, generally designated 1, without a hydraulic unit, which is removed for sake of simplicity.

The pump 1 comprises a motor, generally designated 2, a drive shaft 3 and an impeller (not shown) connected to the drive shaft 3. The impeller in operation is driven by the motor 2 for rotation about an axially extending axis, in order to transport a liquid through the pump 1.

The motor 2 comprises a stator 4, which preferably is the same as is used in the comparable prior art pump, i.e. the inventive pump assembly comprises the same stator as the prior art pump that comprises a fully asynchronous motor. However, it should be pointed out that a synchronous stator and an asynchronous stator are equivalents regarding to the inventive pump assembly. The stator 4 comprises a number of annular stator plates stacked onto each other, which are made of a magnetic material, e.g. metal such as iron. The stack of stator plates comprises a number of axially extending teeth, which are protruding inwards and which are separated by stator slots. Stator coiling 5 is arranged in the stator slots in a conventional way, such that magnetic fields will rotate along the stator 4 about the axially extending drive axis, when the pump 1, i.e. the stator coiling 5, is connected to the power mains. The stator coiling 5 may be constituted by distributed winding or concentrated winding, i.e. overlapping windings.

Reference is now also made to figures 2-7. In addition to the stator 4 the motor 2 comprises a hybrid rotor, generally designated 6. The hybrid rotor 6 and the drive shaft 3 constitute a rotor unit. The hybrid rotor 6 comprises a rotor core 7, which may be a stack of several rotor plates, or which may be cast in one piece. The rotor core 7 is made of a magnetic material, e.g. metal such as iron. It is essential that the rotor core 7 comprises an annular radially outer section of asynchronous type 8 and an annular radially inner section of synchronous type 9 arranged radially inside said outer section 8. See figure 4 in which the width of each annular section is indicated. The annular outer section 8 of asynchronous type is arranged to be active only at startup of the motor 2 and the annular inner section 9 of synchronous type is arranged to be positively active after the hybrid rotor 6 has obtained a rotating motion and during normal operation, i.e. steady state.

According to the shown embodiments of the invention, the annular radially outer section 8 of the rotor core 7 of the hybrid rotor 6 comprises a number of rotor slots 10 arranged therein. The number of rotor slots 10 per pole is preferably in the range 10 to 15. In the embodiments shown in figures 2- 7, each rotor slot 10 is oval-shaped having a bottle neck in the radially outer end. The rotor slots 10 are axially

arranged adjacent and distributed along an envelope surface of said rotor core 7. Upon manufacturing of the rotor core 7, each rotor slot 10 is preferably fully delimited by the rotor core 7, in order to facilitate the manufacturing of the rotor core 7, e.g. by means of punching of the rotor plates. The finished hybrid rotor 6 comprises a material bridge 11, arranged between the radially most outer part of the rotor slot 10 and the envelope surface of the rotor core 7. The final width of said material bridge 11 is achieved by means of machining, e.g. turning of the hybrid rotor 6, which machining also is made to balance the hybrid rotor. Thus, during normal operating of the pump 1 when a material bridge is lacking or a thin material bridge 11 exists between the radially outer most part of the rotor slot 10 and the envelope surface of the rotor core 7, the magnetic field will be prevented from leaking. Either due to the lack of a material bridge of due to the fact that a thin material bridge will be saturated, which prevents the magnetic field to leak. The rotor slots 10 are separated by rotor teeth 12, connecting the annular inner section 9 with the envelope surface of the rotor core 7.

The rotor slots 10 are filled with rotor slot fillings, made of a non-magnetic material, e.g. aluminum or copper, in which an electric current may be induced. In the upper and lower ends of the hybrid rotor 6, the rotor slot fillings are joined by means of an upper ring 13 and a lower ring 14, of the same material as the rotor slot fillings. The upper ring 13, the lower ring 14 and the rotor slot fillings are jointly also known as a rotor cage. The rotor cage may be cast in one piece, or the rotor slot fillings may be pre-cast bars, which are inserted into the rotor slots 10 and joined by the upper ring 13 and the lower ring 14, respectively.

Reference is now especially made to figures 2-4, which discloses one preferred embodiment of a two pole hybrid rotor 6. The annular radially inner section 9 of the rotor core 7 of the hybrid rotor 6 comprises a two sets of air-slots 15 arranged therein, see figure 4. Each air-slot may be consti- tuted by three separate straight sub slots separated only by means of a thin material bridge. The sub slots of the air- slots 15 are axially arranged in the rotor core 7 and are oriented to follow the curvature of the envelope surface of the rotor core 7. The air-slots 15 are arranged adjacent the radially outer part of the annular radially inner section 9.

The two air-slots 15 are diametrically arranged in relation to the axially extending drive axis.

In the above embodiment of the hybrid rotor 6, the annular radially inner section 9 of the rotor core 7 of the hybrid rotor 6 comprises a number of permanent magnets 16, which are inserted into said air-slots 15 such that each air-slot 15 constitute one pole of the hybrid rotor 6. The permanent magnets 16 are cuboids, and in the preferred embodiment two, three or more axially arranged permanent magnets 16 are inserted into each sub slot of the air-slot 15. The use of several permanent magnets 16 in each sub slot of the air-slot 15 comes from the difficulty to make long, thin and wide permanent magnets 16. It should be pointed out that the outer ends of each sub slot of the air-slots 15 are filled with air, or any other suitable gas. One pole is "positive" and one pole is "negative". In the shown embodiment the hybrid rotor 6 comprises two poles, this result in that during normal

operation of the pump 1, the hybrid rotor 6 and thus the impeller will rotate at 3000-3600 rpm when powered directly from the power mains having a frequency of 50-60 Hz. It should be pointed out that when the supply power has another

frequency the impeller will rotate at a different speed. The present invention relates to a so-called Line Start Permanent Magnet Motor (LSPM-motor) , but it shall be pointed out that a variable frequency drive unit (VFD) may be used.

According to the invention the total permanent magnet area per pole, in a radially extending plane, is in the range 500 to 600 square millimeters, and the total rotor slot area per pole, in a radially extending plane, is in the range 400 to 600 square millimeters.

According to the invention the total rotor slot area per pole in relation to the total permanent magnet area per pole effects the ability for the stator 4 to induce currents in the rotor slot fillings 10 upon start up of the motor 2, which induced currents are strong enough to generate magnetic fields strong enough to follow the rotating magnet field of the stator 4, without obstructing the normal synchronous duty of the motor 2. Thus, the rotor slots 10, i.e. the annular radially outer section 8, are used to get the hybrid rotor 6 to start to rotate asynchronously with the supplied power. Thereafter, the permanent magnets 16, i.e. the annular

radially inner section 9, gets the hybrid rotor 6 to rotate synchronously with the supplied power.

Reference is now especially made to figures 5-7, which discloses one preferred embodiment of a four pole hybrid rotor 6. The annular radially inner section 9 of the rotor core 7 of the hybrid rotor 6 comprises a four sets of air-slots 15 arranged therein, see figure 7. Each air-slot may be consti^¬ tuted by three separate straight sub slots separated only by means of a thin material bridge. The sub slots of the air- slots 15 are axially arranged in the rotor core 7 and are oriented in a U-shape, open towards the envelope surface of the rotor core 7. The four air-slots 15 are equidistantly arranged about the axially extending drive axis.

In the above embodiment of the hybrid rotor 6, the annular radially inner section 9 of the rotor core 7 of the hybrid rotor 6 comprises a number of permanent magnets 16, which are inserted into said air-slots 15 such that each air-slot 15 constitute one pole of the hybrid rotor 6. The permanent magnets 16 are cuboids, and in the preferred embodiment two, three or more axially arranged permanent magnets 16 are inserted into each sub slot of the air-slot 15. The use of several permanent magnets 16 in each sub slot of the air-slot 15 comes from the difficulty to make long, thin and wide permanent magnets 16. It should be pointed out that the outer ends of each sub slot of the air-slots 15 are filled with air, or any other suitable gas. Every second pole is "positive" and every other second pole is "negative". In the shown embodiment the hybrid rotor 6 comprises two poles, this result in that during normal operation of the pump 1, the hybrid rotor 6 and thus the impeller will rotate at 1500-1800 rpm when powered directly from the power mains having a frequency of 50-60 Hz. It should be pointed out that when the supply power has another frequency the impeller will rotate at a different speed. The present invention relates to a so-called Line Start Permanent Magnet Motor (LSPM-motor) , but it shall be pointed out that a variable frequency drive unit (VFD) may be used.

According to the invention the total permanent magnet area per pole, in a radially extending plane, is in the range 200 to 350 square millimeters, and the total rotor slot area per pole, in a radially extending plane, is in the range 100 to 300 square millimeters.

Feasible modifications of the Invention

The invention is not limited only to the embodiments described above and shown in the drawings, which primarily have an illustrative and exemplifying purpose. This patent application is intended to cover all adjustments and variants of the preferred embodiments described herein, thus the present invention is defined by the wording of the appended claims and the equivalents thereof. Thus, the mixer assembly may be modified in all kinds of ways within the scope of the appended claims.

It shall also be pointed out that even thus it is not explicitly stated that features from a specific embodiment may be combined with features from another embodiment, the

combination shall be considered obvious, if the combination is possible .

Claims

1. A pump (1) for pumping liquid such as waste water, the pump assembly comprising a motor (2), a drive shaft (3) and an impeller connected to the drive shaft (3) , the impeller in operation being driven by the motor (2) for rotation about an axially extending axis, said motor (2) comprising a stator (4) and a rotor (6) of hybrid type, wherein the hybrid rotor (6) comprises a rotor core (7) comprising an annular radially outer section (8) of asynchronous type and an annular radially inner section (9) of synchronous type arranged radially inside said outer section (8), which inner section (9) comprises a number of permanent magnets (16), characterized in that the hybrid rotor comprises:

or

2. The pump according to claim 1, wherein the outer section (8) of the rotor core (7) of the hybrid rotor (6) comprises a number of rotor slots (10) arranged therein filled with a non- magnetic and electric conducting material, which rotor slots

(10) are axially arranged adjacent and distributed along an envelope surface of said rotor core (7) .

3. The pump according to claim 2, wherein the number of rotor slots (10) per pole is in the range 10 to 15.

4. The pump according to any of claims 1-3, wherein the hybrid rotor, in a radially extending plane, comprises at least three permanent magnets (16) per pole.