FR2529965A1 - MOTOR-PUMP GROUP WITH SPEED ADJUSTMENT - Google Patents

Abstract

IN A MOTOR-PUMP UNIT CONSISTING OF AN ELECTRIC MOTOR AND A CENTRIFUGAL PUMP DRIVEN BY THE LATTER, THE ROTATION SPEED CAN BE ADJUSTED IN STEPS ACCORDING TO THE OPERATING CHARACTERISTICS SELECTED BY THE UNIT WITHIN A DIAGRAM OF CHARACTERISTICS DETERMINED ON THE ONE HAND BY THE TWO THROTTLE CURVES FOR THE MAXIMUM AND MINIMUM ROTATION SPEEDS AND, ON THE OTHER HAND, BY THE DISCHARGE HEIGHT AND FLOW RATE COORDINATES. A DEFINED PARTIAL SECTION CAN BE DETERMINED RESPECTIVELY ON THE THROTTLE CURVES VALID FOR CONSTANT SPEEDS. A SWITCHING OF THE SPEED IS TRIGGERED AS SOON AS THE OPERATING CHARACTERISTICS OF THE GROUP WHICH ARE REPRESENTATIVE FOR THE EXTREME VALUES OF THE PARTIAL SECTIONS ARE REACHED, THE SPEED IS REDUCED WHEN, ON A PARTIAL SECTION, THE EXTREME VALUE WITH THE SUPERIOR HEIGHT OF LOWER FLOW IS REACHED, AND INCREASED WHEN, ON THE CORRESPONDING PARTIAL SECTION, THE OTHER EXTREME VALUE WITH THE LOWER DISCHARGE HEIGHT AND THE UPPER FLOW IS REACHED.

Description

252996;

  The invention relates to a speed-controlled motor-pump group comprising an electric motor and a centrifugal pump driven by the latter, the speed of which is

  rotation N is adjustable in steps depending on the character

  selected operating characteristics of the group within a characteristic diagram whose limits

  are determined on the one hand by the two foreign curves

  setting H (Q) for the maximum and minimum speeds of rotation and, on the other hand, by the coordinates delivery head H and flow rate Q. As we know, the operating point of a

  pumping installation coincides with the point of intersection

  tion of the HA installation characteristic curve (Q)

  and the throttling curve of the pump H (Q)

  fications of this operating point therefore require

  a modification of the characteristic curve of the installation

  lation, the characteristic curve of the pump or

two curves.

  As we know, the variation of the characteristic curve

  of the installation by closing a tap or

  by opening a bypass leads to energy losses

  gie On the other hand, the adaptation of the characteristic curve

  of the pump by varying the speed in the operating state

  Desired operation of the installation can be carried out almost without loss In addition to the lower energy consumption, it is often advantageous that the speed-controlled pump provides only the pressure difference necessary for the installation in such a way that flow noises can be avoided. The manufacturer of installations therefore requires a motor-pump unit whose throttling curve can be adapted over a wide range.

  measurement with good yield at different charac-

  installation specifications and which also makes installation as simple as possible.

  This is why we have already expressed and discussed more

  Several times the desire to have pumps whose characteristic curves can be placed arbitrarily by trying as much as possible to operate the

  pump outside the specification network which

  otherwise lead to listening noises

  Also in systems filled with water and poor

setting behavior.

  There are pumps on the market designed with this in mind and whose short-circuited three-phase armature motor can rotate with continuous speed control via a frequency converter. The differential pressure produced and measured by the pump and the volumetric flow also measured are then compared with a preprogrammed characteristic curve of the group and adjusted on this curve via the speed of rotation However, taking into account metrological expenses, of the motor-driven pump groups controlled from this

  are very expensive In addition, their order is complicated.

  quée and very sensitive because of the considerable work for the installation This is why these groups are generally reserved for the great powers and

  must be installed by specialists.

  The object of the present invention is to create a motor-pump unit with simple and inexpensive speed adjustment.

  whose characteristic curve can be chosen, mainly

  cipe, at will During the operation of the group, this characteristic curve must be able to be reached to a very large extent by stepwise switching of the speed of rotation without the need for recourse

costly metrology.

  According to the invention, this object is achieved by the fact that the pump set of the aforementioned type is produced in 3 - such that on the valid throttling curves H (Q)

  for speeds n const we can define respective-

  ment a determined partial section and a speed changeover is triggered when reaching the electrical or hydraulic operating characteristics of the group representative for the extreme values of the partial sections so that the speed is reduced when, on a partial section, the extreme value with

  the upper head H and the flow Q in-

  lower is reached, and it is increased when the other extreme value with the delivery head H lower and the flow Q higher is reached We can draw an imaginary adjustment characteristic HR (Q) arbitrarily preselected for the respective practical application of the group and cutting the partial sections in such a way that when the characteristics of

  electrical or hydraulic operation of the group represented

  sensitive for extreme values from partial sections the speed switching is triggered, the speed being reduced for an extreme value located, in the network of characteristics, above the group characteristic, and increased as soon as a value is reached extreme

  located below this feature.

  The predetermined adjustment characteristic H R (Q) therefore cuts a series of throttling curves, each of these points of intersection being placed between the extreme values of the considered partial section of the curve

  throttling, which then allows you to use the

  electrical or hydraulic functionalities which

  are decisive for the extreme values for the commu-

  speed and approach the preselected characteristic of the installation by the juxtaposition of the

  partial sections of corresponding throttling curves.

  at different rotational speeds.

  Fig 1 shows a series of corner curves-

  ment H (Q) for constant velocities n For an instal-

  unchanged lseltin N 1 / n 2, H / H 2 2 2 unchanged lation, the relationships Q 1 / Q 2 N 1 / n 2, H 1 / H 2 = N 1 / n 2 _ 4- and P / P n, 3 / n 3 called affinity laws are valid, Qi Q 2 i 2

  Q being the flow rate, H the delivery head, P the

  electric drive and N the speed of rotation

of the motor pump group.

  Since in the H-Q diagram the abscissa varies linearly while the ordinate varies quadratically with the speed n, the associated points of the different throttling curves are located on parabolas R 1 to R

  whose vertex coincides with the origin of the coordinates.

  All the intersections of such a parabola R with the throttling curves H (Q) are characterized by

  similar speed triangles and by pulse states-

  identical nels In addition, they present almost the same efficiency provided that the ratio between the speed

  maximum and minimum speed is not too large.

  For all the points of intersection of a parabola with the throttling curves, we thus obtain well determined numerical values k, - "namely Q / n = k Qy H / n 2 k H or P / n 3 = k P It is the same for the electrical data which must be fixed, during the operation of the motor-pump unit, on the aforementioned points of intersection,

  for example for the intensity of the drive motor current

  The voltage at the motor capacitor, the voltage at the windings, etc. As already mentioned, the parabolas R to R ix divide all the throttling curves H (Q) into specific partial sections and associate the ends of these sections partial of the defined and representative operating characteristics for the parabola considered in such a way that the characteristic field is covered with a network of unambiguously defined points Each of these points can be used as the end point of a partial section to be selected , namely in such a way

  that the speed is reduced when, on a section

  tial, the extreme value with the higher delivery head H or even with the lower flow rate Q is reached and

  that it is increased as soon as it is reached, on the section par-

  tial, of the other extreme value with the discharge height

  H lower and with higher Q flow.

  By plotting an adjustment characteristic H (Q) R

  imaginary arbitrarily preselected for the application

  respective practice of the group and cutting the partial sections, the process described above means in other words that each end point of the network located above or to the left of the adjustment characteristic can be used for lowering of speed and that each end point placed below or to the right of the

  adjustment feature can be used to increase

speed.

  It will be further explained how it

  choose these end points or even commu-

  In any case, the decisive data for these points are stored as a control program for

  so as to be able to approach the adjustment characteristic-

  through the sawtooth exploration of partial sections

  on the throttling curves for different speeds.

  The particular advantage of this solution lies in the fact that it is no longer necessary to enter and use hydraulic control data, for example differential pressure and flow rate, which can only be measured with expensive devices, but that we use electrical quantities much simpler to measure such as the current and the voltage at the service capacitor, at the motor windings, etc. which, combined with or even related to the known or measured speed ,

  then provide the switching signals.

  In addition, it should be noted that the width of the meshes of the aforementioned network constituted by the throttling curves H (Q) and by the parabolas R can be staggered according to an arithmetic or geometric progression In the second case, one works with a number lower speeds, and the adjustment characteristic is always approached with

the same percentage accuracy.

  Another advantage is that the pump unit can be combined with the control system.

  required in a set ready for assembly, the branch of which

  electric and assembly is done as for any other motor pump group not adjusted because all the control signals are taken from the group and processed

  in the control unit located on the engine.

  In the diagram represented in fig 1, the throttling curve H (Q) 1 is associated with the most rapid

  weak N 1, while the throttling curve H (Q) 7 cor-

  responds to the highest speed N 7 These two curves delimit, with the delivery head H as the ordinate and with the flow rate Q as the abscissa, the field within which the operating points of the pump may be located For reasons practical, that is to say if we

  wish, for example, to operate with a good return

  ment or a good suction behavior of the pump, we will limit ourselves to choosing as limits not the coordinate axes but some affinity parables In fig 1, these are the curves R 1 and R 9

  To facilitate discussion, each point of inter-

  section of an affinity dish R with a curve of strangeness

  settlement H (Q) is designated by the numbers of the curves A

  as examples, the number 97 designates the point of intersection

  tion of the parabola R 9 and the throttling curve H (Q) 7 and the number 26 designates the point of intersection of the parabola R 2 and the throttling curve H (Q) 6 The field

  of application that can be envisaged for the moto- group

  pump considered is therefore a quadrilateral with angles 97-17-11-91; you have to take into account that the

  group can also operate on the choke curve-

  ment H (Q) 2 up to zero flow and on the throttle curve-

  up to zero discharge head, which is indicated in the figure by the arrows from the points

17 and 92.

  However, if the facility designer prescribes a

  adjustment characteristic HR (Q) which, in the example shown

  felt in fig 1, must be a straight line passing through the

  points x and y, this line cuts certain sections by-

  on the throttling curves H (Q) in such a way

  that on both sides of the characteristic of the installation

  There are selected end points from the partial sections, for example points 37 and 57 for speed N 7, end points 35 and 65 for speed N 5, etc. During operation of the pump,

  the adjustment characteristic HR (Q) can then be approximated

  by exploring the partial sections of the throttling curves valid for different speeds Furthermore, it does not matter here that the characteristic of the installation for the operation of the group is chosen as lower or upper limit or, as shown in the figure, as mean value, being

  given that, in principle, this decision is left to the

  precaution of the designer of installations.

  To allow a better understanding of an example of adjustment, let us consider the diagram represented in fig 2 which reproduces an enlarged portion of the network of characteristics of fig 1 The installation is designed, for example, for a flow Qx and a height of discharge H For the partial load regime, the points of x

  function must be oriented in relation to the character-

  ristic of adjustment HR (Q) which was chosen here as an average value In addition, it is considered that it is, in the case of the installation in question, a system of

  central hot water heating with thermostatic valves

ticks on radiators.

  The operating point x calculated for the

  maximum sance is located on the throttling curve H (Q) 7

  between the affinity parabolas R 3 and R 4 In case of clos-

  of some of these thermostatic valves, the pressure

  differential pressure or even delivery head H increases and the operating point x moves in

direction of the point of the network 47.

  The question whether the speed N 7 can be reduced when the switching point 47 is reached is regulated by a stability condition. An oscillation of the group is not possible if, when the speed is reduced from neither to nor 11 flow Q is less than flow

  Q 1 when increasing the speed from neither 1 to nor.

  -8- I-l emerges from fig -2 that the flow at point 47 is

  equal to the flow at point 36 which is provided as an increase point

  speed statement To fulfill the aforementioned condition Qi C Qi 19, the next higher network point 57 is chosen as the speed increase point. In this case, Qi <Q ic l, that is to say Q 57 c Q 36 and pumping of the adjustment is excluded The following meshes of the network can be considered in an analogous manner It is advisable to choose as upper limits points 57-56-65-84-83 for speed reduction and points 53-44- 35-36 for

increasing speed.

  It is easy to understand that the differences between the real operating points and the desired values located on the characteristic H R (Q) are all the more

  weak-that the meshes of the network are tighter, that is

  that is, the points selected for the commutations

  are closer to the imagi-

  However, in many installations the precision required is not very high, which makes it possible to be satisfied with a small number of speeds and parabolas

  affinity This is so, for example, for instal-

  Hot water central heating lations Here, an appro-

  coarse ximation is sufficient because, in the same installation, the same calorific value can be

  obtained with a larger current of water and a different

  lower temperature between the supply duct

  tation and return of the heating water or vice versa.

  In this case, it is only important that the pressure differs

  the supply supplied by the pump is large enough to guarantee sufficient water distribution in the system and to avoid the occurrence of values at all speeds

  causing flow noises in the valves.

  Below it is explained how the different points marking the ends of the partial sections

  -possibles can be found and fixed Stretch curves-

  settlement H (Q) for determined speeds ni = const are recorded in the usual manner on the test bench for

  a given type of pump In addition to the delivery head

  ment H and flow Q, then we also measure all

  electrical quantities which must be used later-

  For speed switching With regard to these quantities, these are, for example, the motor current consumption, the voltage applied to the motor capacitor or also other values which vary with the speed In addition, it is also possible to retain for this use characteristic quantities of

  service such as differential pressure on the pump.

  By writing in the same diagram of the throttling curves of the arbitrarily predetermined affinity parabolas, it is possible to associate with each point of intersection a throttling curve with an affinity parabola of the electrical data in addition to the values H and Q. The points of intersection form a network and receive specific order numbers, for example those indicated in fig 1 The electrical data associated with the points constitute the basis of all possible control programs and they are memorized. is then

  possible to arbitrarily associate the instruction with each point

  tion for speed increase as well as

  instruction for speed reduction.

  In addition, there will be essentially two possibilities.

  capabilities for the application or practical use of the solution according to the invention The first possibility is that the manufacturer programs beforehand and in a fixed manner certain partial sections on the throttling curves which are characteristic and useful for

  often repeated applications of the motor-pump unit considered

  d In the heating technique, one will thus orient oneself by a report to a series of partial sections for which flow noises are improbable in the field

  of action selected but which nevertheless guarantees a dis-

  uniform distribution of water in the heating system.

  We will therefore give the group a "negative characteristic" which corresponds approximately to the characteristic of

  setting H (Q) or even to the right xy indicated in the figures.

  -o 10 -2529965 The slope and the position of several xy characteristics usable with the associated partial sections can be predetermined differently for a type of pump in such a way that a single motor-pump group represents, in principle, a whole range of pumps with different characteristics The heating contractor must then choose from the respective characteristics the one that is suitable

for its application case.

  Another possibility consists in leaving the choice of the partial sections to the heating engineer himself. For this, it is however necessary to be able to select the different points in the network of characteristics, for example by means of a keyboard Taking into account the condition of mentioned stability, it is then also necessary to determine the selected end points of the partial sections at which the speed must be

reduced or increased.

  il 2529965 Re v e N d i c a t i on s

  1 Motor-pump group with speed adjustment

  nant an electric motor and a centrifugal pump driven by the latter, whose speed of rotation N is adjustable

  in stages according to the operating characteristics

  selected from the group within a characteristic diagram whose limits are determined on the one hand by the two throttling curves H (Q) for the maximum and minimum rotational speeds and, on the other hand, by the coordinates delivery head H and flow rate Q, because ac etered in that respectively a defined partial section can be determined on the curves

  throttling valve H (Q) valid for 'speeds n const.

  and that a speed switching is triggered as soon as the electrical or hydraulic operating characteristics of the group which are representative for the extreme values of the partial sections are reached, the speed being reduced when, on a partial section,

  the extreme value with the delivery head H greater than

  lower and the lower flow rate Q is reached, and increased when, on the corresponding partial section, the other extreme value with the delivery head H lower

  and the Q-higher rate is reached.

  2 motor-pump unit according to claim 1, characterized in that a de-setting characteristic HR (Q)

  imaginary arbitrarily preselected for the application

  the respective group can be traced so as to cut the partial sections and the speed changeover is triggered as soon as the hydraulic or electrical operating characteristics of the group which are representative for the extreme values of the partial sections are reached, the speed being reduced for

  an extreme value located in the network of characteristics

  ticks, above the setting characteristic, and increased as soon as an extreme value located in

  below the setting characteristic.

-12 _ 2529965

  3 Motor-pump unit according to one of the claims

  1 and 2, characterized in that all the points of ex-

  possible ends of the partial sections are located on parabolas of affinity Rx which divide the network of the throttling curves H (Q) into partial sections.

  4 Motor-pump unit according to one of the claims

  1 to 3, characterized in that the end points on the throttling curves HIQ) i which cause the speed reduction are located, in the network of characteristics, to the left of the end points on the curve d '' throttle H (Q) for the immediately lower speed so that the relation Q <Qi 1 is

still valid.