163:
When fixed-speed pumps are used, the pumps are set to start when the level of the liquid in the wet well reaches some high point and stop when the level has been reduced to a low point. Cycling the pumps on and off results in frequent high surges of electric current to start the motors that results in electromagnetic and thermal stresses in the motors and power control equipment, the pumps and pipes are subjected to mechanical and hydraulic stresses, and the sewage treatment process is forced to accommodate surges in the flow of sewage through the process. When adjustable speed drives are used, the pumps operate continuously at a speed that increases as the wet well level increases. This matches the outflow to the average inflow and provides a much smoother operation of the process.
378:. Power proportional to the slip speed times operating torque is dissipated as heat in the clutch. While it has been surpassed by the variable-frequency drive in most variable-speed applications, the eddy current clutch is still often used to couple motors to high-inertia loads that are frequently stopped and started, such as stamping presses, conveyors, hoisting machinery, and some larger machine tools, allowing gradual starting, with less maintenance than a mechanical clutch or hydraulic transmission.
366:) and an eddy current clutch. The clutch contains a fixed-speed rotor and an adjustable-speed rotor separated by a small air gap. A direct current in a field coil produces a magnetic field that determines the torque transmitted from the input rotor to the output rotor. The controller provides closed loop speed regulation by varying clutch current, only allowing the clutch to transmit enough torque to operate at the desired speed. Speed feedback is typically provided via an integral AC tachometer.
38:
116:
either four or eight pole pairs, giving two speeds - at 60 Hz, these would be 1800 RPM and 900 RPM. If speed changes are rare, the motor may be initially connected for one speed then re-wired for the other speed as process conditions change, or, magnetic contactors can be used to switch between the two speeds as process needs fluctuate. Connections for more than three speeds are uneconomic.
437:
156:
196:, reciprocating or turbine steam engines, water wheels, and others) have a range of operating speeds which can be varied continuously (by adjusting fuel rate or similar means). However, efficiency may be low at extremes of the speed range, and there may be system reasons why the prime mover speed cannot be maintained at very low or very high speeds.
66:, describes equipment used to control the speed of machinery. Many industrial processes such as assembly lines must operate at different speeds for different products. Where process conditions demand adjustment of flow from a pump or fan, varying the speed of the drive may save energy compared with other techniques for flow control.
447:, the AC motor's voltage-to-frequency ratio can be maintained constant, and its power can be varied, between the minimum and maximum operating frequencies up to a base frequency. Constant voltage operation above base frequency, and therefore with reduced V/Hz ratio, provides reduced torque and constant power capability.
172:
flow in the process. However, this additional pressure drop represents energy loss. Sometimes it is economically practical to put in some device that recovers this otherwise lost energy. With a variable-speed drive on the pump or fan, the supply can be adjusted to match demand and no extra loss is introduced.
171:
Fans and pumps consume a large part of the energy used by industrial electrical motors. Where fans and pumps serve a varying process load, a simple way to vary the delivered quantity of fluid is with a damper or valve in the outlet of the fan or pump, which by its increased pressure drop, reduces the
162:
An adjustable-speed drive can often provide smoother operation compared to an alternative fixed-speed mode of operation. For example, in a sewage lift station sewage usually flows through sewer pipes under the force of gravity to a wet well location. From there it is pumped up to a treatment process.
406:
large pumps and fans, wind turbines, shipboard propulsion systems, large hydro-pumps andgenerators and utility energy storage flywheels. Early slip energy recovery systems using electromechanical components for AC/DC-AC conversion (i.e., consisting of rectifier, DC motor and AC generator) are termed
130:
that is used to adjust the motor's operating speed. The combination of a constant-speed motor and a continuously adjustable mechanical speed-changing device might also be called an "adjustable speed motor drive". Power electronics-based variable frequency drives are rapidly making older technologies
401:
controls speed by varying motor slip via rotor slip rings either by electronically recovering slip power fed back to the stator bus or by varying the resistance of external resistors in the rotor circuit. Along with eddy current drives, resistance-based WRIM drives have lost popularity because they
373:
based drives. The motor develops the torque required by the load and operates at full speed. The output shaft transmits the same torque to the load, but turns at a slower speed. Since power is proportional to torque multiplied by speed, the input power is proportional to motor speed times operating
405:
Slip energy recovery systems return energy to the WRIM's stator bus, converting slip energy and feeding it back to the stator supply. Such recovered energy would otherwise be wasted as heat in resistance-based WRIM drives. Slip energy recovery variable-speed drives are used in such applications as
115:
of the alternating current supply. AC motors can be made for "pole changing" operation, reconnecting the stator winding to vary the number of poles so that two, sometimes three, speeds are obtained. For example a machine with eight physical pairs of poles, could be connected to allow running with
52:
means a system that includes a motor. An adjustable speed motor drive means a system that includes a motor that has multiple operating speeds. A variable speed motor drive is a system that includes a motor and is continuously variable in speed. If the motor is generating electrical energy rather
260:
A hydroviscous drive consists of one or more discs connected to an input shaft pressed against a similar disc or discs connected to an output shaft. Torque is transmitted from the input shaft to the output shaft through an oil film between the discs. The transmitted torque is proportional to the
199:
Before electric motors were invented, mechanical speed changers were used to control the mechanical power provided by water wheels and steam engines. When electric motors came into use, means of controlling their speed were developed almost immediately. Today, various types of mechanical drives,
344:
is often applied to the controller without the motor. In the early days of electric drive technology, electromechanical control systems were used. Later, electronic controllers were designed using various types of vacuum tubes. As suitable solid state electronic components became available, new
353:
DC drives are DC motor speed control systems. Since the speed of a DC motor is directly proportional to armature voltage and inversely proportional to motor flux (which is a function of field current), either armature voltage or field current can be used to control speed.
217:
transmit power through metal rollers running against mating metal rollers. The input-output speed ratio is adjusted by moving the rollers to change the diameters of the contact path. Many different roller shapes and mechanical designs have been used.
233:
consists of a hydraulic pump and a hydraulic motor. Since positive displacement pumps and motors are used, one revolution of the pump or motor corresponds to a set volume of fluid flow that is determined by the displacement regardless of speed or
175:
For example, when a fan is driven directly by a fixed-speed motor, the airflow is designed for the maximum demand of the system, and so will usually be higher than it needs to be. Airflow can be regulated using a
146:
are the two primary reasons for using an adjustable-speed drive. Historically, adjustable-speed drives were developed for process control, but energy conservation has emerged as an equally important objective.
119:
The number of such fixed-speed-operation speeds is constrained by cost as number of pole pairs increases. If many different speeds or continuously variable speeds are required, other methods are required.
450:
Regenerative AC drives are a type of AC drive which have the capacity to recover the braking energy of a load moving faster than the motor speed (an overhauling load) and return it to the power system.
123:
Direct-current motors allow for changes of speed by adjusting the shunt field current. Another way of changing speed of a direct current motor is to change the voltage applied to the armature.
340:
drives. Each of these general types can be further divided into numerous variations. Electric drives generally include both an electric motor and a speed control unit or system. The term
184:, for 50% of the airflow, the variable-speed motor consumes about 20% of the input power (amps). The fixed-speed motor still consumes about 85% of the input power at half the flow.
369:
Eddy current drives are slip-controlled systems the slip energy of which is necessarily all dissipated as heat. Such drives are therefore generally less efficient than
238:. Speed is regulated by regulating the fluid flow with a valve or by changing the displacement of the pump or motor. Many different design variations have been used. A
838:
582:
1236:
316:
device, (which is more resistant to dust and grease) or it can also be automatically controlled, for example, by using a rotational detector such as a
362:
An eddy current drive (sometimes called a "Dynamatic drive", after one of the most common brand names) consists of a fixed-speed motor (generally an
60:(VFD) or variable speed drive (VSD) describes the electronic portion of the system that controls the speed of the motor. More generally, the term
374:
torque while the output power is output speed times operating torque. The difference between the motor speed and the output speed is called the
1241:
473:
253:
use oil to transmit torque between an impeller on the constant-speed input shaft and a rotor on the adjustable-speed output shaft. The
292:
282:
1246:
551:
519:
500:
1018:
1256:
575:
967:
752:
111:
AC electric motors can be run in fixed-speed operation determined by the number of stator pole pairs in the motor and the
1100:
226:
There are three types of hydraulic drives, those are: hydrostatic drives, hydrodynamic drives and hydroviscous drives.
1110:
823:
796:
468:
127:
211:
Variable-pitch drives are pulley and belt drives in which the pitch diameter of one or both pulleys can be adjusted.
1226:
1120:
1115:
568:
193:
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813:
791:
270:
31:
1231:
1064:
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411:
288:
230:
57:
42:
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or motor in which the swash plate angle can be changed to adjust the displacement and thus adjust the speed.
1105:
656:
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833:
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923:
661:
641:
621:
177:
53:
than using it – this could be called a generator drive but is often still referred to as a motor drive.
261:
pressure exerted by a hydraulic cylinder that presses the discs together. This effect may be used as a
1054:
947:
696:
671:
463:
73:. If the output speed can be changed without steps over a range, the drive is usually referred to as
69:
Where speeds may be selected from several different pre-set ranges, usually the drive is said to be
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426:
143:
1251:
1185:
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200:
hydraulic drives and electric drives compete with one another in the industrial drives market.
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977:
769:
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515:
496:
243:
239:
112:
106:
45:, showing capacitors (top cylinders) and inductors attached which filter the regenerated power
402:
are less efficient than AC/DC-AC-based WRIM drives and are used only in special situations..
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266:
254:
443:
When changing VFD frequency in standard low-performance variable-torque applications using
93:
refers to a drive used to control a motor and therefore gets interchanged with VFD or VSD.
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208:
There are two types of mechanical drives, variable-pitch drives, and traction drives.
37:
17:
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1180:
848:
309:
295:" when they are used in vehicles, farm equipment and some other types of equipment.
181:
1205:
1140:
828:
333:
155:
982:
436:
313:
873:
843:
714:
676:
180:
but it is more efficient to directly regulate fan motor speed. Following the
1155:
908:
686:
317:
421:
In general, a VFD in its most basic configuration controls the speed of an
937:
781:
737:
329:
82:
1013:
1008:
126:
An adjustable-speed motor drive might consist of an electric motor and
80:
Adjustable and variable speed drives may be purely mechanical (termed
691:
615:
287:
Mechanical and hydraulic adjustable speed drives are usually called "
262:
235:
560:
345:
controller designs incorporated the latest electronic technology.
154:
257:
in the automatic transmission of a car is a hydrodynamic drive.
564:
435:
308:
Control can mean either manually adjustable - by means of a
167:
Saving energy by using efficient adjustable-speed drives
328:
There are three general categories of electric drives:
839:
Dual-rotor permanent magnet induction motor (DRPMIM)
1088:
1027:
1001:
956:
887:
728:
705:
630:
539:
433:the frequency of the power supplied to the motor.
86:), electromechanical, hydraulic, or electronic.
576:
8:
269:, or as a variable-speed drive, such as the
583:
569:
561:
135:Reasons for using adjustable speed drives
277:Continuously variable transmission (CVT)
36:
542:Electrical Control Systems in Industry
531:Controlling Power Transmission Systems
474:Regenerative variable-frequency drives
7:
293:continuously variable transmissions
283:Continuously variable transmission
25:
1237:Electric power systems components
495:. Instrument Society of America.
410:, with more recent systems using
222:Hydraulic adjustable speed drives
514:. New York: Marcel Dekker, Inc.
299:Electric adjustable speed drives
510:Campbell, Sylvester J. (1987).
968:Timeline of the electric motor
546:. New York: McGraw-Hill, Inc.
1:
1242:Mechanical power transmission
753:Dahlander pole changing motor
512:Solid-State AC Motor Controls
445:Volt-per-Hertz (V/Hz) control
538:Siskind, Charles S. (1963).
533:. Cleveland, OH: Penton/IPC.
414:(VFDs) being referred to as
395:slip-controlled wound-rotor
30:For use in photography, see
797:Brushless DC electric motor
529:Jaeschke, Ralph L. (1978).
469:Doubly fed electric machine
194:internal combustion engines
1273:
491:Spitzer, David W. (1990).
280:
100:
29:
27:Piece of machine equipment
814:Switched reluctance (SRM)
792:Brushed DC electric motor
598:
412:variable-frequency drives
271:Beier variable-ratio gear
43:variable frequency drives
32:Motor drive (photography)
1247:Mechanical power control
1002:Experimental, futuristic
919:Variable-frequency drive
58:variable frequency drive
1019:Superconducting machine
657:Coil winding technology
390:speed control systems.
249:Hydrodynamic drives or
1257:Electric motor control
440:
159:
46:
18:Adjustable-speed drive
1060:Power-to-weight ratio
924:Direct torque control
493:Variable Speed Drives
439:
158:
40:
1055:Open-loop controller
948:Ward Leonard control
672:DC injection braking
464:DC injection braking
416:static Kramer drives
151:Acceleration control
958:History, education,
604:Alternating current
371:AC/DC-AC conversion
358:Eddy current drives
192:Some prime movers (
144:energy conservation
1121:Dolivo-Dobrovolsky
1080:Voltage controller
1035:Blocked-rotor test
973:Ball bearing motor
943:Motor soft starter
897:AC-to-AC converter
758:Wound-rotor (WRIM)
720:Electric generator
441:
160:
47:
41:Line regenerative
1227:Robotics hardware
1214:
1213:
1050:Open-circuit test
889:Motor controllers
770:Synchronous motor
592:Electric machines
320:optical encoder.
244:axial piston pump
242:drive employs an
231:hydrostatic drive
204:Mechanical drives
107:synchronous motor
16:(Redirected from
1264:
1065:Two-phase system
1045:Electromagnetism
993:Mouse mill motor
960:recreational use
834:Permanent magnet
763:Linear induction
616:Permanent magnet
585:
578:
571:
562:
557:
545:
534:
525:
506:
324:Types of drives
304:Types of control
267:Hele-Shaw clutch
255:torque converter
71:adjustable speed
21:
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1232:Electric motors
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997:
988:Mendocino motor
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883:
743:Induction motor
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701:
647:Braking chopper
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479:Scherbius Drive
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397:induction motor
384:
364:induction motor
360:
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326:
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285:
279:
251:fluid couplings
224:
215:Traction drives
206:
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188:Types of drives
169:
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140:Process control
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103:Induction motor
99:
97:Electric motors
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1040:Circle diagram
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1028:Related topics
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978:Barlow's wheel
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902:Cycloconverter
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632:Components and
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386:AC drives are
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281:Main article:
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75:variable speed
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502:1-55617-242-7
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408:Kramer drives
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310:potentiometer
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182:affinity laws
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399:(WRIM) drive
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334:eddy current
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55:
49:
48:
983:Lynch motor
748:Shaded-pole
634:accessories
427:synchronous
336:drives and
314:hall effect
240:swash plate
131:redundant.
91:motor drive
50:Motor drive
1221:Categories
879:Axial flux
869:Ultrasonic
844:Servomotor
824:Doubly fed
819:Reluctance
715:Alternator
707:Generators
677:Field coil
662:Commutator
622:commutated
620:SC - Self-
485:References
376:slip speed
312:or linear
128:controller
101:See also:
89:Sometimes
1252:Variators
1196:Steinmetz
1111:Davenport
909:Amplidyne
809:Universal
787:Homopolar
775:Repulsion
687:Slip ring
431:adjusting
429:motor by
423:induction
382:AC drives
349:DC drives
318:Gray code
113:frequency
83:variators
1201:Sturgeon
1131:Ferraris
1116:Davidson
938:Metadyne
854:Traction
802:Unipolar
782:DC motor
738:AC motor
642:Armature
458:See also
388:AC motor
338:AC motor
332:drives,
330:DC motor
1191:Sprague
1186:Siemens
1161:Maxwell
1126:Faraday
1075:Starter
1014:Railgun
1009:Coilgun
849:Stepper
697:Winding
1181:Saxton
1166:Ørsted
1151:Jedlik
1146:Jacobi
1136:Gramme
1101:Barlow
1089:People
914:Drives
829:Linear
730:Motors
692:Stator
550:
518:
499:
291:" or "
263:clutch
236:torque
178:damper
1206:Tesla
1176:Pixii
1141:Henry
1106:Botto
1096:Arago
682:Rotor
652:Brush
614:PM -
608:DC -
602:AC -
342:drive
63:drive
1171:Park
1156:Lenz
874:TEFC
548:ISBN
516:ISBN
497:ISBN
142:and
105:and
425:or
1223::
418:.
393:A
273:.
229:A
77:.
56:A
584:e
577:t
570:v
556:.
524:.
505:.
34:.
20:)
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