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1
Content available Problemy związane z doborem pomp w instalacjach pompowych w celu powiększenia efektywności energetycznej
Zieliński W. G.
Maszyny Elektryczne : zeszyty problemowe
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2013
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Nr 1(98)
127-130
PL
Zmniejszenie energochłonności procesów produkcyjnych ma na całym świecie priorytetowe znaczenie. Praca przepompowni, instalacji wodociągowych i kanalizacyjnych, oczyszczalni ścieków i ciepłowni miejskich wiąże się z zastosowaniem pomp, wśród których najbardziej rozpowszechnionymi są pompy wirowe. W instalacjach tych występują duże straty, które należy eliminować, aby uzyskać większą efektywność energetyczną. W artykule przedstawiono rodzaje strat występujące w instalacjach pompowych i wprowadzono pojęcie efektywności energetycznej oraz możliwość jej zwiększenia. Kryteria doboru pompy omówiono na podstawie przebiegu charakterystyk: przepływu, poboru mocy oraz sprawności z uwzględnieniem zmian parametrów obiektu pompowego. Dotyczy to dobowych lub sezonowych zmian statycznej wysokości podnoszenia oraz zmian wydajności obiektu. Ponadto zamieszczono przykład instalacji pompowej zastosowanej w rzeczywiście istniejącej elektrociepłowni.
EN
Reducing the energy consumption of production processes has priority meaning worldwide. Work of the pump station, water systems and sewer, sewage treatment plant and municipal thermal power stations are being combined with applying pumps, amongst which the most spread there are rotary pumps. Heavy losses should be eliminated are appearing in these installations in order to get the greater energy efficiency. The article presented loss of energy appearing in pump installations and implemented the concept of energy efficiency and the possibility of its increase. Pump selection criteria are discussed on the basis of the course of characteristics: flow, power consumption and performance, the power consumption and the efficiency including changes of parameters of the pump object. This applies to daily or seasonal changes in static head and changes in building performance. In addition, pump system is an example used in actually existing Power plants.
2
Content available Wpływ nasycenia obwodu magnetycznego i wypierania prądu na przebiegi momentu elektromagnetycznego i prądu podczas rozruchu wysokoobrotowych silników klatkowych
Zielińska M.J., Zieliński W.G.
Maszyny Elektryczne : zeszyty problemowe
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2011
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Nr 3(91)
183-186
EN
High speed squirrel-cage motors are a relatively unknown group of machines, mainly due to their particular application. High rotational speed is achieved by supplying the motors with 400-1500Hz frequency voltage. Their operation in special conditions results in the fact that their structure and some properties differ from those of squirrel-cage induction machines supplied with 50Hz frequency voltage. The use of closed rotor slots causes strong saturation of the magnetic circuit for the slot leakage flux. Changes in the current in the slot causes a varying state of saturation and thus rotor leakage inductance is not a constant parameter. When determining the rotor winding leakage inductance for classic induction motors supplied with 50Hz frequency voltage, the influence of the saturation of the magnetic circuit for the leakage flux is usually omitted. This is a standard approach and an equivalent scheme, mentioned in literature, is used in such a case. Identification of the inductance in motors supplied with high frequency voltage, in which the phenomenon of core saturation occurs, is a relatively complex issue due to the complicated distribution of magnetic flux, and especially the leakage flux. The value of leakage inductance was determined experimentally. The paper presents differential equations describing a mathematical model and transients of the current and electromagnetic torque, obtained by simulating the start-up of a squirrel-cage high-speed motor.
3
Content available Porównanie wskaźników energetycznych przy energooszczędnej pracy silnika klatkowego, realizowanej przez skokową regulację napięcia
Zieliński W.G.
Maszyny Elektryczne : zeszyty problemowe
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2011
|
Nr 3(91)
187-190
EN
Economic effectiveness of the operation of a propulsion system depends on energy indices of motors. Along with the type of operation, the load can vary greatly. Most induction motors operate at load which is considerably lower than their nominal load. Operation at small load or idle run has an adverse effect, when energy indices of the motor, such as power factor and energy efficiency, are very low. There is a need to improve these indices and establish conditions for optimum motor operation. If the motor's load is lower than its nominal load, supply voltage should be lowered to make the energy indices as high as possible. Thus, supplying the motor with voltage which varies depending on the degree of load brings positive results. At nominal load, the motor must by supplied with nominal voltage, however, as the load decreases, the voltage should be accordingly lowered. Lowering the supply voltage will result in decreased energy losses, which are connected with it, as well as increased energy efficiency and power factor. This leads to lower power consumption and thus to saving electric energy. The paper presents transients of current supplied from the mains, the power factor, and motor energy efficiency for various degrees of voltage changes ensuring the motor,s low-energy operation.
4
Content available Opracowanie algorytmów regulacji napięcia zasilania wysokoobrotowych silników klatkowych celem zapewnienia zadanego momentu krytycznego lub rozruchowego
Zielińska M.J., Zieliński W.G.
Maszyny Elektryczne : zeszyty problemowe
|
2010
|
Nr 86
247-250
EN
Obtaining a high value of the breakdown or starting torque in an asynchronous motor is a very important issue from the point of view of improving its operational properties. These values can be determined based on data of a typical equivalent scheme. This refers to motors without the skin effect in the cage bar or those in which the phenomenon has been omitted. In a high-speed motor, the phenomena of core saturation and skin effect influence the parameters of the equivalent scheme, which are not constant values and depend on the frequency of supply voltage and the value of the current in the bar of the rotor's cage. In consequence, an equivalent scheme valid for classic motors should not be used for analysis of the performance of a high-speed motor. Based on an equivalent scheme which takes into account the influence of frequency on its parameters, the article describes how supply voltage was selected in order to guarantee the preservation of the given breakdown or starting torque. The calculations were made for three motors representing low, medium and high power machines.
5
Content available Metoda wyznaczania poślizgowych charakterystyk admitancji wysokoobrotowego silnika klatkowego
Zielińska M.J., Zieliński W.G.
Maszyny Elektryczne : zeszyty problemowe
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2010
|
Nr 86
251-254
EN
High speed squirrel-cage induction motors are supplied with a high frequency voltage ranging from 400 to 1500Hz. The highest frequencies, i.e., the highest rotation speeds, arise from technological needs and are limited by manufacturing possibilities. These motors have a structure and electromagnetic properties that differentiate them from classic machines. In particular, they are distinguished by the high frequency of supply voltage, intensive cooling introduced to reduce the size of the motor, and closed rotor slots used to minimize vibrations and noise. The paper presents how slip characteristics of admittance of a squirrel-cage motor were determined on the basis of laboratory measurements conducted with current of variable frequency. This characteristic is the geometric locus of motor admittance with the slip ranging from + ∞ to - ∞ and an assumed constant frequency of supply voltage. The image of these characteristics differs considerably from a typical pie chart and it evidences the differences in electromagnetic properties in comparison with typical induction motors. Changes in the current in the slot causes a varying state of saturation and thus rotor leakage inductance is not a constant parameter.
6
Content available Przebiegi nieustalone prądu i momentu elektromagnetycznego podczas rozruchu w silnikach indukcyjnych wysokoobrotowych
Zielińska M.J., Zieliński W.G., Zieliński W.
Maszyny Elektryczne : zeszyty problemowe
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2009
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Nr 82
249-252
EN
High-speed motors are produced in Poland outside the machine-building industry. Only a few motors, adapted to specific purposes, are manufactured, for example, by plants that produce rolling-element bearings. These motors have found their application in driving high-speed grinders in bearing ring raceway production lines. The properties of motors fed with high-frequency voltage result mainly from the use of a closed slot in the rotor and the high frequency of supply voltage. The use of the closed rotor slot causes strong saturation of the magnetic circuit by the leakage flux around the slot. Taking account of the phenomenon of saturation of the magnetic circuit due to the leakage flux around the closed rotor slots is a complex issue. In the present article, this phenomenon was taken into consideration by introducing into the mathematical model of the motor, derived for a linear magnetic circuit, rotor leakage inductance dependent on rotor current. The relation was determined experimentally.
7
Content available Wyznaczanie prądu rozruchowego i momentu rozruchowego dla silników asynchronicznych
Zieliński W.G.
Maszyny Elektryczne : zeszyty problemowe
|
2008
|
Nr 80
147-150
EN
Calculation of the starting parameters for three-phase asynchronous motors is a very important issue as these parameters determine whether a motor can be satisfactorily used in a driving system and characterize it from the point of view of supply mains. The article discusses methods of determining initial starting current and initial starting torque with the omission of issues connected with electromagnetic transient processes, the influence of thermal states, and the effect of parasitic torques. Direct determination of these parameters is relatively complex, which is why they are often determined in an indirect way. Two methods are described, which allow to establish the aforementioned parameters: the tangent method and the short-circuit reactance distribution method. The methods consist in an extrapolation of short circuit characteristics obtained at reduced voltage. The results of research and the comparison of parameter calculations refer to two induction motors: squirrel cage and slip ring.
8
Content available Wykorzystanie metody pośredniej do określania momentu krytycznego silnika indukcyjnego
Zieliński W.G., Zielińska M.J., Zieliński W.
Maszyny Elektryczne : zeszyty problemowe
|
2008
|
Nr 80
151-154
EN
Pull-out torque and the corresponding pull-out slip of induction motors is determined, with a fair degree of accuracy, by measurements in the short-circuit and idle-running states. This refers to motors without the skin effect in the cage bar or those in which the phenomenon has been omitted. The paper compares analytical methods for determining pull-out torque based on the method of equivalent graphs and a simplified Kloss formula. The analysis was carried out for two induction motors: squirrel cage and slip ring. Pull-out slip and torque diagrams were used. An advantage of this method is the fact that determination of pull-out torque does not require the knowledge of pull-out slip.
9
Content available Metoda wyznaczania rezystancji wirnika z uwzględnieniem wypierania prądu dla silników szybkoobrotowych
Zielińska M.J., Zieliński W.G.
Maszyny Elektryczne : zeszyty problemowe
|
2008
|
Nr 80
155-157
EN
High speed motors are supplied with 400-1500Hz frequency voltage. They operate in special conditions and have a structure and properties that differentiate them from classic machines. In particular, they are distinguished by the high frequency of supply voltage, intensive cooling introduced to reduce the size of the motor, and closed rotor slots used to minimize vibrations and noise. In the discussed motors, the closed rotor slot was replaced with an open slot due to saturation of the magnetic circuit by the slot leakage flux. The resistance increase coefficient for rotor cage bar as a function of current flowing through the bar was estimated and then total rotor resistance was determined. Subsequently, the resistance calculated on the basis of geometric dimensions with skin effect taken under consideration was verified against results obtained from measurements. It was proved that short-circuit resistance is not a constant and depends on the value and frequency of current. It also includes a component which derives from additional losses occurring in solid construction elements and in rotor cage bars. The paper also presents descriptions showing changes in short-circuit resistance as a function of the motor's current determined on the basis of measurements with parametrically variable frequency.
10
Content available Racjonalna praca silników asynchronicznych klatkowych przy zmianie skojarzenia uzwojeń z trójkąta w gwiazdę
Zieliński W.G.
Maszyny Elektryczne : zeszyty problemowe
|
2007
|
Nr 77
125-128
EN
Three-phase asynchronous motor with a squirrel-cage rotor that is the most often applied in the industry has its disadvantages, which get revealed at a low-load motor operation or at its idling. High current input and low power factor at idling are among the disadvantages. Electrical energy saving is possible owing to the increased energy indices such as efficiency or power factor. The power factor value to a considerable degree depends on the load. Hence, in cases when the load varies within a wide range an adequate voltage reduction causes its increase. When voltage is reduced such quantities as: torque overload capacity, slip, rotor current and total power losses increase. The motor supply voltage can be varied in a continuous or a step mode. In some cases in order to considerably enhance energy indices and obtain significant energy savings it is enough to apply a two-step voltage regulation. It is mostly when the time-load run of the motor approaches intermittent running with idling breaks. The paper presents a solution that makes possible to enhance energy indices that is to make the motor operation more efficient with the application of a delta-to-star change of the winding connection. The method consists in that at the startup and full-load phase the motor operates at the delta connection of the windings, while at lower load values a switch to the star connection is performed. Additionally, runs of quantities that are characteristic for an efficient motor operation (power factor, efficiency, slip, current input) and have been obtained based on laboratory measurements performed at the delta-to-star switch of the stator winding connection have been determined.
11
Content available Ocena oszczędności energii elektrycznej przy skokowej regulacji napięcia w silniku asynchronicznym klatkowym
Zielińska M.J., Zieliński W.G.
Maszyny Elektryczne : zeszyty problemowe
|
2007
|
Nr 77
121-124
EN
In order to enhance energy indices and obtain electrical energy savings for an asynchronous squirrel-cage motor operating on a long-time basis at a load lower than the rated load it needs to reduce its supply voltage. Efficient operation obtained that way can apply to a single motor or a set of motors driving the same machines. Motor load can vary within a wide range depending on the operation kind. Particularly disadvantageous is operation at little load or at idling, when energy indices of the motor are very low. In such a case it is necessary to apply voltage that can be varied depending on the load factor. When voltage is changed simultaneously with a load change the motor runs at higher values of the indices that decide over electrical energy consumption. At the rated load a motor should be supplied with rated voltage and when the load gets reduced the supply voltage should also be adequately decreased. The lowest voltage is required at the idle run. Relative value of the voltage is then of ca 0.3. Voltage reduction brings about a decrease of voltage-dependent energy losses and an increase of efficiency and the power factor, which leads to the power input reduction and consequently to electrical energy savings. The paper presents motor operation conditions that should be met at a sudden voltage change and rules for enhancing energy indices on the basis of algorithms that maintain such parameters as: minimal current, maximal power factor and maximum efficiency at a preset level. Additionally, runs of the basic motor quantities such as: current input, power factor, efficiency, and slip at step-regulated supply voltage have been determined
12
Content available Wpływ rodzaju wymuszenia na wybór struktury sterowania wektorowego
Zieliński W.G., Michałowska J.
Maszyny Elektryczne : zeszyty problemowe
|
2006
|
Nr 75
41-45
EN
Vector control of induction motor torque and speed yields very good static and dynamic properties. Systems that apply such control become a standard solution that is widely used even for drives of high requirements. When vector control is applied aside with amplitudes and frequencies phases of rotational vectors of motor currents and flux linkages are determined. Correct orientation of the vectors can be maintained due to the control system both in steady and transient states. In the paper field-oriented vector control is discussed and kinds of input signals for that type of control are determined. Kind of an input signal is important for the motor operation as its dynamic properties get essentially changed then. Particular attention has been paid to voltage and current signals and control possibilities have been determined for each of them. Additionally, attention has been paid to the selection of control orientation with respect to the vector of magnetic field in the motor.
13
Content available Poślizgowa charakterystyka admitancji stojana silnika indukcyjnego uzyskana przy zastosowaniu symulacji komputerowej
Zielińska M.J., Zieliński W.G.
Maszyny Elektryczne : zeszyty problemowe
|
2006
|
Nr 75
47-51
EN
Slip characteristic of induction motor admittance is the admittance locus at varied slip and constant frequency of feeding voltage. Circle diagram can graphically represent the characteristic only in the case when electromagnetic parameters of a machine are constant. Circle diagram makes an important tool at the evaluation of an asynchronous motor operation. Based on the diagram it is possible to find for an arbitrary slip not only values of electrical parameters but also mechanical parameters such as torque, mechanical power and rotational speed. The paper presents a comparative analysis of classical methods for circle diagram elaboration and of their accuracy. Computer simulation of an admittance slip characteristic has been performed with the Matlab-Simulink software, based on dependences that determine admittance of a motor. The analysis concerns conditions when equivalent network parameters of an asynchronous motor are constant and the characteristic is represented by a circle. When electromagnetic parameters of a motor are not constant then the characteristic essentially differs from a typical circle diagram. It mainly concerns a squirrel-cage motor with closed slots in the rotor, fed with high-frequency voltage. In the mentioned case saturation of the closure occurs under the influence of a leakage flux. It has been shown that a shape of the characteristic depends on many parameters of a motor as well as on the way the leakage reactance changes.
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