PART 1 VARIABLE SPEED DRIVE IN PUMPING STATIONS: ADVANTAGES PART 2 SPEED CONTROL IN INDUCTION MOTORS
Variable Speed Drives in Pumping Stations - Advantages
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PART 1
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SUMMARY – PART 1
1.
Introduction
2.
Criteria for the selection of the Variable Speed Drives
3.
Energy saving in pumps and fans with Variable Speed Drives 3.1 Typical pump and fan curves 3.2 Movement of the pump curve in accordance with the speed drop 3.3 Movement of the power and efficiency curves in accordance with the speed drop 3.4 Basic relationships for the power control 3.5 Efficiency of pumps with VSD
4.
Methods for flow control
5.
Needed information for a correct consulting in the energy saving field 3
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1. INTRODUCTION
1. Power Electronics offers to its clients optimization options for the production process through the application of variable speed drives and softstarters in a wide variety of industrial fields.
2. As a result of the application of variable speed drives and softstarters a spectacular raise of the quality of the product and an absolute improvement of the mechanical and electrical maintenance of the Company.
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Variable Speed Drives in Pumping Stations CRITERIA FOR THE SELECTION OF A VARIABLE SPEED DRIVE
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2. CRITERIA FOR THE SELECTION OF A VARIABLE SPEED DRIVE
A. Input Filters
[ SHOW ]
B. Input Chokes
[ SHOW ]
C. Protection Degree
[ SHOW ]
D. Ambient Temperature
[ SHOW ]
E. Constant and Variable Torque VSD?
[ SHOW ]
F. VSD Applications
[ SHOW ]
G. Technical Assistance
[ SHOW ] 7
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A. INPUT FILTERS WHAT IS ELECTROMAGNETIC COMPATIBILITY? It is a concept linked to any electronic device. This concept means the ability of a device to avoid the generation of interferences above a defined dB level. It means the measure of its immunity versus a defined dB level.
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A. INPUT FILTERS WHAT PHENOMENA PRODUCE THE RADIOFREQUENCIES IN A VSD?
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A. INPUT FILTERS RFI EMISSION SOURCES IN A VSD » The RFI can be radiated and conduced. » The conduction can be produced through the Motor Cables, through the Power Supply Cables and through the Earth Connections.
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A. INPUT FILTERS CABLE LENGTH » 40 meters of screened cable.
Vcc = Ve · 1,41
= 380 · 1,41 = 534 = 500 · 1,41 = 720 = 690 · 1,41 = 972,9
» 150 meters of screened cable.
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B. INPUT CHOKES USE OF INPUT CHOKES FOR HARMONIC REDUCTION.
» Power electronics for SD700 series: 90A – 170A. [ BACK TO THE CRITERIA ]
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B. INPUT CHOKES USE OF INPUT CHOKES FOR HARMONIC REDUCTION.
» Power electronics for SD700 series: 210A – 2200A. [ BACK TO THE CRITERIA ]
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C. PROTECTION DEGREE PROTECTION DEGREE FOR EXTRA PROTECTION » IP54 protection impedes that dust or any other particles damage the devices. » In this case, splashing occurred near the motor don’t damage our products.
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D. AMBIENT TEMPERATURE OVER-HEATING CHARACTERISTICS OF THE SD700 SERIES
Drive Current (%)
Over-heating Characteristics for SD700 Series
Overload peak for 1 sec.
200 175
Overload for 60 sec. at 40º Overload for 30 sec. at 50º
150
Operation current at 40º Operation current at 45º
125 100
Overload peak 1 sec. Overload 30 sec. at 50º Operation current at 40º Operation current at 45º Operation current at 50º
Operation current at 50º
75 50 25 0 0
25
50
75
400
Hz
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D. AMBIENT TEMPERATURE ENVIRONMENTAL TEMPERATURE Power Electronics Variable Speed Drives are prepared to resist the hardest environmental working conditions. They CAN RESIST TILL 50º 50ºC AMBIENT TEMPERATURE WITHOUT OVER-SIZING THE VARIABLE SPEED DRIVE.
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E. CONSTANT TORQUE AND VARIABLE TORQUE
Temperature 80ºC
VARIABLE TORQUE 15 kw Temperature 60ºC
THERMAL SHOT (85ºC)
THERMAL SHOT (85ºC) OVERLOAD 1.1In (40ºC)
CONSTANT TORQUE 11 kw
» Competitors
Temperature 70ºC OVERLOAD 1.5In Temperature 60ºC (40ºC)
VARIABLE TORQUE 15 kw
OVERLOAD 1.25 In (40ºC) OVERLOAD 1.5In (50ºC)
CONSTANT TORQUE 11 kw
» Power Electronics
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E. CONSTANT TORQUE AND VARIABLE TORQUE
MODEL A MODEL B
POWER AT CONSTANT TORQUE
POWER AT VARIABLE TORQUE
P.V.P
11 15
15 18,5
100 115
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F. VARIABLE SPEED DRIVE APPLICATIONS CONTROL The Variable Speed Drives extend the regulation field with regard to: Flow fluctuation Pressure control Temperature control Level control… APPLICATIONS Several applications can be considered: Pumping stations Pressure groups Irrigation systems High concentration of carbonic monoxide, oxygen… Heating and Air conditioning…
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Variable Speed Drives in Pumping Stations ENERGY SAVING IN PUMPS AND FANS
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3. ENERGY SAVING IN PUMPS AND FANS WITH VSD 3.1 TYPICAL PUMPS AND FANS CURVES.
HEIGHT, POWER AND EFFICIENCY
H (m)
FLOW
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3. ENERGY SAVING IN PUMPS AND FANS WITH VSD 3.2 MOVEMENT OF THE PUMP CURVE IN ACCORDANCE WITH THE SPEED DROP. H
nnom
16 14 12 10 8
0.9 n nom 0.8 n nom 0.7 n nom
6 4 2 20
40
60
80
100
120
140
Q (l/s) 22
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3. ENERGY SAVING IN PUMPS AND FANS WITH VSD 3.3 MOVEMENT OF THE POWER AND EFFICIENCY CURVES IN ACCORDANCE WITH THE SPEED DROP. p
Power Efficiency
Q 23
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3. ENERGY SAVING IN PUMPS AND FANS WITH VSD 3.4 BASIC RELATIONSHIPS FOR THE POWER CONTROL.
POWER (W) = r x g x H x Q x ŋ-1 r = Density (Kg/m³) g = Gravity (9.81m/s²) H = Height (m) Q = Flow (m³/s) ŋ = Efficiency
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3. ENERGY SAVING IN PUMPS AND FANS WITH VSD 3.5 EFFICIENCY OF PUMPS WITH VARIABLE SPEED DRIVE. 80
N = 1480 RPM 1Xn
30%
50%
60% 70%
70
80% 85% 87%
0.9 X n
60
88% 50
0.8 X n
40
0.7 X n
87% 85% 80%
30 0.6 X n
20
0.5 X n
Efficiency curves
0.4 X n
10
Curves H – Q System curves
0
10
20
30
40
Q flow m3/min
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Variable Speed Drives in Pumping Stations METHODS FOR FLOW CONTROL
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4. METHODS FOR FLOW CONTROL A. Valve Control
[ SHOW ]
B. By – Pass Control
[ SHOW ]
C. Start – Stop Control (On / Off)
[ SHOW ]
D. Variable Speed Drive
[ SHOW ]
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4. METHODS FOR FLOW CONTROL A. VALVE CONTROL. CHARACTERISTICS. » Pumps always work at maximum speed. » The transversal section of the conduct or pipe. » Pressure increases when pipe cross section is reduced. » Problems with the over-heating of the fluids. » Cavitation, turbulences.
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4. METHODS FOR FLOW CONTROL A. VALVE CONTROL. GRAPHIC. 80
Height in m H2O
FLOW
1Xn
STATIC height 20 meters
70 0.9 X n 60
50
40
30
20
0.8 X n
0.7 X n
0.6 X n 0.5 X n
n = 1480 RPM Efficiency curves H-Q curves System curves
0.4 X n 10
0
80% 60% 100% 50% 90% 70%
10
20
50% Flow
30
100% Flow
40
Q Flow m3/min 29
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4. METHODS FOR FLOW CONTROL A. VALVE CONTROL. GRAPHIC.
BOTTLENECK INCREASES
H 3
HEIGHT
2 1
OPERATIONAL POINT WITHOUT BOTTLENECK
Q KW
POWER
7
FLOW
Q
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4. METHODS FOR FLOW CONTROL B. BY - PASS CONTROL. H
HEIGHT
OPERATIONAL POINT WITHOUT BY-PASS
BY-PASS EFFECT
Q
System curves Pump H – Q curves POWER
Efficiency curves
» This is the least efficient method with regard to the energy consumption. » The pump always works at maximum power without taking into account the flow level.
KW
Q FLOW
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4. METHODS FOR FLOW CONTROL C. START – STOP CONTROL (On / Off). CHARACTERISTICS. » It is recommendable for those systems in which the pumping flow is constant. » It leads to mechanical and electrical stress. » It does not allow to maintain constant parameters, a small or big variation always exists. » Over-pressure during the starting. » Water hammering during the stop.
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4. METHODS FOR FLOW CONTROL D. VARIABLE SPEED DRIVE CONTROL. CHARACTERISTICS. » It allows to keep constant those parameters to be controlled. »It provides a reduction of absorbed power by the motor. » Compensation of reactive power of the motor. » Reduction of mechanical and electrical failures. » Reduction of civil construction cost in pumping systems.
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4. METHODS FOR FLOW CONTROL D. VARIABLE SPEED DRIVE CONTROL. GRAPHIC. 80 Height in m H2O 1Xn
60 490 kPa
STATIC height 20 meters
70 637 kPa
0.9 X n
50 0.8 X n 0.7 X n
40
PID
REFERENCE
30 0.6 X n 20 0.5 X n 10 0
n = 1480 RPM Efficiency curves H – P curves
0.4 X n
System curves
0
10
20
30
40
Q Flow m3/min
1400 RPM 34
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4. METHODS FOR FLOW CONTROL D. VARIABLE SPEED DRIVE CONTROL. TABLE. H
HEIGHT
OPERATIONAL POINT AT FULL LOAD
8
SPEED DROP
9 Q
7
KW
POWER
8 9 Q
FLOW
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4. METHODS FOR FLOW CONTROL D. VARIABLE SPEED DRIVE CONTROL. ENERGY MISUSE.
HEIGHT
VALVES SYSTEM
FREQUENCY CONVERTER
POWER LOSSES
MISUSED POWER
STATIC HEIGHT
USEFUL POWER SET POINT
REDUCED SPEED 36
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4. METHODS FOR FLOW CONTROL D. VARIABLE SPEED DRIVE CONTROL. COMPARATIVE CURVES AND POWER REQUIREMENTS. POWER (%)
A: Control using Variable Speed Drive. B: Control using valve adjusting.
FLOW (%)
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4. METHODS FOR FLOW CONTROL D. VARIABLE SPEED DRIVE IN WELLS.
SUMMER
WINTER 38
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Variable Speed Drives in Pumping Stations NEEDED INFORMATION FOR A CORRECT CONSULTING IN THE ENERGY SAVING FIELD
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5. NEEDED INFORMATION FOR A CORRECT CONSULTING IN THE ENERGY SAVING FIELD
ANALYSIS OF EXISTING SYSTEMS A. Type of control B. Height curves and flow of the system PUMP OR FAN DATA A. Pump and fans efficiency curves B. Fan or pump power C. Motor curves PROCESS INFORMATION A. Fluid or gas density B. Flows and required duty cycles C. Static and dynamic height values
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5. NEEDED INFORMATION FOR A CORRECT CONSULTING IN THE ENERGY SAVING FIELD
IF WE DO NOT HAVE COMPLETE INFORMATION, THE FOLLOWING DATA COULD BE USEFUL A. B. C. D. E.
HEIGHT / FLOW CURVES OR CHARACTERISTICS OF THE SYSTEM REQUIRED FLOWS AND OPERATION CYCLES FLUID OR GAS DENSITIES VALUES OF STATIC AND DYNAMIC HEIGHT PUMP OR FAN POWER
MINIMUM INFORMATION REQUIRED (GRAPHICS USE) A. REQUIRED FLOWS AND OPERATION CYCLES B. PUMP OR FAN POWER (DIFFERENT FLOWS)
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Speed Control in Induction Motors VARIABLE SPEED DRIVE & SOFTSTARTERS
PART 2
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Speed Control in Induction Motors INTRODUCTION
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SUMMARY – PART 2
1. Introduction 2. Induction motors Control Outlines 3. Speed control in a Squirrel Cage Motor 4. Electronic Outlines for A.C. Motor Control
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1. INTRODUCTION
1. Induction motor control outlines: variable speed drive and softstarters 2. Power Electronics technology and experience in power electronics
3. Basic Outlines: - To know the outlines of the induction motors - Variable speed drives performance - Softstarters performance - Harmonics in industrial provisions - Electromagnetic compatibility of VSD - Energy saving in pumps and fans - Applications and control 45
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Speed Control in Induction Motors INDUCTION MOTORS CONTROL OUTLINES
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2. INDUCTION MOTORS CONTROL OUTLINES INDUCTION MOTORS The induction motor (asynchronous or squirrel cage), is made up of two main parts: The ROTOR , fixed along an axis The STATOR
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2. INDUCTION MOTORS CONTROL OUTLINES INDUCTION MOTORS The rotor is built with electronically short-circuit bars through rings at the edges, which form the squirrel cage
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2. INDUCTION MOTORS CONTROL OUTLINES INDUCTION MOTORS Connecting the motor to a 3-phase power supply, a rotational magnetic field it is generated in the stator (flux). This is due to: ¾The physical position of the stator windings: 3 coils separated physically 120º. ¾The current in those windings diphase 120º electrically.
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2. INDUCTION MOTORS CONTROL OUTLINES INDUCTION MOTORS The flux lines (arrows) induce currents on the rotor bars. When a magnetic field acts over a conductor in which a current flow, the resultant is a force which produce the torque and therefore the motor rotation. ROTATING FIELD
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Speed Control in Induction Motors SPEED CONTROL IN A SQUIRREL CAGE MOTOR
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3. SPEED CONTROL IN A SQUIRREL CAGE MOTOR SPEED CONTROL A squirrel cage motor is a constant speed motor. But speed can be controlled acting on the number of poles of the motor and the frequency supply. supply TORQUE – SPEED RELATIONSHIP
MOTOR CURRENT STARTING CURRENT
MOTOR TORQUE MAXIMUM TORQUE
STARTING TORQUE
NO LOAD CURRENT
MOTOR SPEED
MOTOR SPEED » Torque – Speed curve in a induction motor
» Current – Speed curve
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3. SPEED CONTROL IN A SQUIRREL CAGE MOTOR SPEED CONTROL Method used by electronic speed controllers Î To vary the frequency supply of the motor. WHY IS VARYING THE FREQUENCY SUPPLY THE BEST METHOD? ¾ A high performance in the whole range of speeds is obtained ¾ This method disposes of a continuous variation of the speed, that might be electrically through control signals such as 0-10VDC o 4-20mA. This makes VSD for A.C. motors to be the best option for process automation. ¾ The available motor torque is constant even at low speeds. This offers the possibility to work with any load. ¾ It is possible to work with frequencies above 50Hz.
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Speed Control in Induction Motors ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL
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4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL FREQUENCY SUPPLY VARIATION Torque – speed curve evolution when the frequency supply varies.
% OF NOMINAL TORQUE
MOTOR SPEED
» Torque – Speed curve
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4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL WHY V/Hz CONSTANT? Equivalent circuit per phase can be represented according to: IR: Component of load. “Real” component that flows through the rotor. This current generates the torque and therefore increases as the load of the motor increases.
IM: “Imaginary” component, 90º diphased regarding to the “real” component. Magnetizing current responsible of the motor flux. It is convenient to keep it constant as the load varies. 56
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4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL WHY V/Hz CONSTANT?
Imaginary current (Magnetizing)
» At full load
IT Cu rre nt
cos φ = Power factor
To tal
Real current (Torque)
ent tal IT Cu rr To
Real current (Torque)
Vector diagram of the motor current.
Imaginary current (Magnetizing)
» At medium load
Magnetizing current IM is constant regardless of the load. It is this current which generates the magnetic field in the stator, affecting to the motor capacity of producing torque.
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4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL WHY V/Hz CONSTANT? Controlling the voltage applied to the stator (E1) it is possible to control the magnetizing current (IM) and therefore the flux.
IM =
E1 = f = LS =
E1 2·π · f ·LS
Supply voltage Supply frequency Magnetizing inductance of the stator
In a electronic speed controller, the motor voltage supply must be adjusted proportionally to the frequency, so that the magnetization current remains constant. Increasing the motor speed, the slip (S) decreases and the relative frequency decreases too. Then the cosϕR improves, the losses inductance is reduced and e Ir decreases.
Ir =
E2 .S R 2 r + ( X 2 ·S ) 2
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4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL RELATIONSHIP VOLTAGE – FREQUENCY IN A VSD. VOLTAGE COMPENSATION AT REDUCED SPEEDS Voltage increase. It is necessary when the load requires a high starting torque (transport bands, high inertia load, …). 100% OUTPUT VOLTAGE
AREA WHERE THE MAGNETIC FIELD MAKES WEAKER
OUTPUT VOLTAGE
100%
STARTING VOLTAGE
50Hz
OUTPUT FREQUENCY
» Voltage – Frequency relationship in the drive
50Hz
OUTPUT FREQUENCY
» Voltage compensation at reduced speeds
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4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL DIAGRAM BLOCK FOR A VARIABLE SPEED DRIVE
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4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL INVERTER CIRCUIT
Output waveforms of the inverter bridge
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4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL CURRENT IN THE MOTOR WITH SEMI-SQUARED VOLTAGE
» Output voltage (quasi-rectangular wave) Transistor Free flow current current
» Output motor current
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4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL MODULATION AND WAVE SHAPES. OUTPUT VOLTAGE
CARRIER WAVE SINUSOIDAL WAVE REFERENCE SIGNAL SUPERIOR TRANSISTOR ON INVERTER OUTPUT VOLTAGE (REGARDING TO THE MIDDLE POINT IN THE DC BUS) INFERIOR TRANSISTOR ON OUTPUT VOLTAGE BETWEEN PHASES PWM
» Modulation and waveforms of the output voltage
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4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL OUTPUT WAVES MODULATION
NOMINAL FREQUENCY – NOMINAL VOLTAGE
A triangular signal is compared to a senoidal one in the sinusoidal modulation. The wave shape of the current produced in the motor is very similar to the senoidal one, with a very long distortion.
MEDIUM LEVEL FREQUENCY – MEDIUM LEVEL VOLTAGE » Output voltage modulation
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4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL OUTPUT WAVES MODULATION The width and the number of hollows are electronically adjusted in order to reduce the output voltage as long as the frequency diminishes. NOMINAL FREQUENCY – NOMINAL VOLTAGE
New technology: vector space modulation Î better wave shapes and less commutations.
MEDIUM LEVEL FREQUENCY – MEDIUM LEVEL VOLTAGE » Output voltage modulation
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Speed Control in Induction Motors VARIABLE SPEED DRIVE & SOFTSTARTERS
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4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL VECTOR SPACE MODULATION A system of 3-phasic senoidal waves can be represented through three rotating vectors (phasors).
VA
Rotation speed (rev/sec) Î Frequency Instantaneous position Î Status in a cycle Vector length Î Voltage amplitude
N V C
VE
» 3-Phase vector
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4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL ADVANTAGES OF VECTOR SPACE MODULATION VERSUS SINUSOIDAL MODULATION 9
Small content of harmonics in the motor
9
Small pulsate pairs
9
Constant frequency modulation
9
Better use of voltage supply
9
Adapted to the wave generation using microprocessor
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Speed Control in Induction Motors VARIABLE SPEED DRIVE & SOFTSTARTERS
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4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL ELECTRONIC DEVICES BASED ON COMMUTATION THYRISTORS Î Power semiconductor with PNPN structure. Currently not used. BIPOLAR TRANSISTORS Î Based on NPN or PNP structure. ISOLATED GATE BIPOLAR TRANSISTORS (IGBT) Î the latest generation; control realized by mean of voltage, the commutation is done by the application of voltage to the gate. Advantages of the IGBT: IGBT • Less voltage saturation • Higher commutation frequencies • Higher overload capability • Less power demand in the motor circuit 68
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Speed Control in Induction Motors VARIABLE SPEED DRIVE & SOFTSTARTERS
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4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL ELECTRONIC CONTROL Î THE BRAIN OF THE DRIVE Functioning: It receives the required speed signal. It receives user commands: stop, start…etc. It generates waveforms modulated in vector space technology. It commutates the switches. It controls the current in the motor to protect the drive and the motor from overloads. It allows to do the necessary adjustments for one application: acceleration and deceleration ramps, maximum and minimum speed…etc. It offers output information: motor current, frequency, start, stop, failure indication…etc.
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Speed Control in Induction Motors VARIABLE SPEED DRIVE & SOFTSTARTERS
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4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL MONOPHASIC DEVICES Small motors are designed with windings of 230Vac. Drive with 3-phasic input of 400V Î Control configured with the voltage and the frequency of the motor.
WIRING FOR 230V MOTOR CONNECTION
DELTA CONNECTION OF THE TERMINALS
WIRING FOR 400V MOTOR CONNECTION
STAR CONNECTION OF THE TERMINALS
Drive with singlephase input of 230Vac. » Wiring connections for 230/400V motors
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4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL
Current operation
+ve
REGENERATION
Motor operation
Generator operation
torque Motor Torque -ve
N2
N1
speed
+ve
0 Generator torque
slip 2
1
0
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4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL LOADS TYPES. CONSIDERATIONS Before choosing the size of the motor and VSD, it is necessary to understand the torquespeed characteristics for every single load. Constant Power
TORQUE
POWER
TORQUE
200%
TO RQ UE
PO WE R
50%
Magnetic field makes weaker
100%
Available TORQUE peak PO WE R
Constant Torque 100%
Continuous Torque (limited due to the motor cooling)
63%
100%
200% Motor speed
» Relation (%) between torque and power
50Hz
100Hz Motor speed
» Torque loss due to motor cooling 72
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4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL BASIC LOADS TYPES Constant power load Î The torque required by the load increases as the speed decreases. Constant power (mills, winding machines)
TORQUE
Area for intermittent Area for continuous operation operation
Available torque peak
TORQUE
Constant load torque Î Constant torque at any speed (transport bands, presses of printers, crane and hoist, …etc) Area for intermittent operation
Area for continuous operation
Available torque peak Area for intermittent operation
Continuous torque Required resistant torque Required resistant torque
» Load at constant power
Continuous torque
» Load at constant torque 73
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4. ELECTRONIC OUTLINES FOR A.C. MOTOR CONTROL TORQUE – SPEED RELATIONSHIP
Area of continuous operation
Available torque peak Area of intermittent operation
TORQUE
TORQUE
Available torque peak
Area of continuous operation
Area of intermittent operation
Continuous torque ue torq ant t s i Res
d uire req
Speed
» Torque proportional to the Speed
R
orq nt t sta esi
ue
req
d uire
Continuous torque
Speed
» Torque proportional to the Square of the Speed
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Thanks for your attention
Presentation Variable Speed Drives in Pumping Systems: Advantages Speed Control in Induction Motors
Realization Pilar Navarro
Organization Marketing Department
www.power-electronics.com ©2006 Power Electronics España, S.L.
