ECET 211 Electric Machines & Controls Lecture 4-1 Motor Control Devices: Lecture 4 Motor Control Devices

Transcription

1 ECET 211 Electric Machines & Controls Lecture 4-1 Motor Control Devices: Part 1. Manually Operated Switch Part 2. Mechanically Operated Switch Text Book: Electric Motors and Control Systems, by Frank D. Petruzella, published by McGraw Hill, Paul I-Hai Lin, Professor of Electrical and Computer Engineering Technology P.E. States of Indiana & California Dept. of Computer, Electrical and Information Technology Purdue University Fort Wayne Campus Prof. Paul Lin 1 Lecture 4 Motor Control Devices Chapter 4. Motor Control Devices Part 1. Manually Operated Switches Part 2. Mechanically Operated Switches Part 3. Sensors Part 4. Actuators Prof. Paul Lin 2 1

2 Part 1. Manually Operated Switches Primary and Pilot Control Devices Toggle Switches Push Button Switches Pilot Lights Selector Switch Drum Switch Prof. Paul Lin 3 Manually Operated Switches Primary and Pilot Control Devices Control device A component that governs the electric power delivery to an electrical load Must be capable of handling the voltage and current to be switched Two classes of control devices: Primary control and Pilot control device Primary control device: Motor contactor, Starter, or Controller that connect the load to the line Contactor can also be used as pilot control device Pilot control device: Relay, Switch contact that used to activate the primary control device Should not be used to switch horsepower load Prof. Paul Lin 4 2

3 Manually Operated Switches Push Button SW Figure 4-1 Primary and Pilot Control Devices A typical motor control switch that include both a Primary Control (contactor), and a Pilot Control device (toggle switch) Theory of operation 1. Turn toggle switch on to complete the control circuit: Power source (L1, L2) Toggle switch Contactor s coil M 2. Contactor energized => close the M s NO contacts => Deliver power to the Motor 3. Turn toggle switch off => Contact M de-energized => the M s NO contacts open => Motor stop Prof. Paul Lin 5 Manually Operated Switches Toggle Switches Types of toggle switch SPST Single pole, single throw SPDT Single pole, double throw DPST Double pole, double throw DPDT Double pole, double throw Figure 4-2 Toggle switches Electrical Rating for Switches Maximum interrupting voltage and current AC rating higher than DC rating for an equivalent amount of voltage AC current is at zero level twice during each cycle Prof. Paul Lin 6 3

4 Volts AC 120V 60Hz Since Wave % sine120v.m % MATLAB simulation % 2014/1/13 % By Paul Lin f = 60; %Frequency in Hz T = 1/f; %Period in Second dt = T/100; %Samlping time interval Vrms = 120; % Root Mean Square voltage t = 0: dt: 2*T; % Time vector theta = 0; % Initial offset angle e = 120*sqrt(2)*sin(2*pi*f*t + theta); % Voltage equation % e = 120*1.414*sin(2*pi*f*t + theta); % Voltage equation plot(t, e), grid on; %Plot the voltage waveform xlabel('time Second'), ylabel('volts') time Second Prof. Paul Lin 7 Manually Operated Switches Push Buttons NO Push button (Normally open) START NC Push button (Normally close) STOP Break-Make Push button NC contact on the top section, NO contact on the bottom section Application example2 1) Motor starting/stopping control 2) Control and override process functions Figure 4-3 Pushbutton symbols and switching action Figure 4-5 Pushbutton station NEMA type 1 Prof. Paul Lin 8 4

5 Manually Operated Switches Pushbutton SW Figure 4-4 Break-make push button and typical motor control circuit Jogging Application Momentary operation to give small movement of a driven machine. 1) Start PB pushed => M coil energized => Motor running; contact M is closed and remembering the Start operation 2) Push down the Jog PB momentary, M coil de-energized, Motor stopped; 3) Then when Jog PB is pressed all the way down, it then energize M coil again and contact M is also closed again Prof. Paul Lin 9 Manually Operated Switches Pushbutton SW Figure 4-6 Typical pushbutton assembly Figure 4-7 Flush pushbutton operator: used for start button that need to be protected from accidental initiation Figure 4-8 Extended pushbutton operator: Prof. Paul Lin 10 5

6 Manually Operated Switches Pushbutton SW Figure 4-9 Mushroom head pushbutton operator: easily seen and actuated, used as emergency stop PBs E-Stop Emergency Stop Pushbutton White Paper, 2012, com/idc/groups/literature/document s/wp/800-wp008_-en-p.pdf Prof. Paul Lin 11 Manually Operated Switches Pushbutton SW Figure 4-10 Half-rounded pushbutton operator Figure 4-11 Illuminated pushbutton operator: LED integrated Figure 4-13 Pushbutton assembly Legend Plates (Labels) for Pushbuttons: START, STOP, FWD, REV, JOG, UP, DOWN, ON, OFF, RESET, and RUN Prof. Paul Lin 12 6

7 OSHA Safety Requirement: Emergency Stop Pushbutton OSHA requirements on Emergency Stop: Requires that once the emergency stop switch has activated, the control process cannot be started again until the actuating stop switch has been reset to the on position. Safeguarding Equipment and Protecting Employee from Amputation, 2007, Section IV: Chapter 4 Industrial Robots and Robot System Safety, OSHA Technical Manual, Other References Electrical Requirements, Safeguarding Cutting and Turning Machine The Safety Library, Prof. Paul Lin 13 Emergency Stop Pushbutton Figure 4-14 Emergency Stop Pushbutton motor control circuit Theory of Operation An Emergency Stop PB is added (in series) with the typical START/STOP motor control circuit The normally closed maintained contacts of the Emergency Stop push button will open when the push button is pressed and remain open until its is manually reset. Motor will not operate To restart the motor, you must first reset the emergency PB, and then press the Start button Prof. Paul Lin 14 7

8 Mechanically Operated Switches Pilot Lights Pilot Lights provide visual indication of the status for many motor-controlled processes permitting personnel at remote locations to observe the current state of the operation. Full-voltage type with transformers (Figure 4-16) Low-voltage type operate at 6 to 24 V, AC or DC Figure 4-15 Remote start/stop station with run pilot light Prof. Paul Lin 15 Mechanically Operated Switches Pilot Lights Figure 4-17 Push-to-test pilot light Designed to reduce the time required to troubleshoot a suspected faulty lamp. Theory of Operation 1) Normal operation R light on 2) If R light out, push and release the Push-to-test light to see if the R light is at fault rather that the motor control circuit. Prof. Paul Lin 16 8

9 Selector Switch A rotated switch for opening and closing contacts of the attached contact block Operator knob: turning right or left May have two or more selector positions Selector Switch Figure 4-17 Three-position selector switch: Pump Control Hand it allows for manual control via Manual Control Switch Auto It allow only for pump to be control via Liquid-level switch Off Prof. Paul Lin 17 Drum Switch A drum switch consists of a set of moving contacts and a set secondary contacts that open and as close as the shaft is rotated Figure 4-19 Drum switch used for reversing the direction of rotation of a three-phase motor FWD position T1 L1 T2 L2 T3 L3 REV position T1 L1 T2 L3 T3 L2 Prof. Paul Lin 18 9

10 Part 2 Mechanically Operated Switches Limit Switches A mechanically operated switch is one that is controlled automatically by factor such pressure, position, and temperature Designed to operate only when a predetermined limit is reached Often used in the control circuits of machine processes to govern the Starting, Stopping, or Reversal of motors Temperature Control Devices Pressure Switches Float and Flow Switches Prof. Paul Lin 19 Part 2 Mechanically Operated Switches Limit Switches Two parts: the body and the operator head (actuator) Contact types NO, NC, Momentary (spring returned), Maintainedcontact type Prof. Paul Lin 20 10

11 Figure 4-12 Limit switch symbols and configuration NEMA Symbols IEC Symbols A limit switch with both NO and NC contacts, you must wire the Load on the same side of line; and be sure to form a COM on the line side Limit Switches COM Prof. Paul Lin 21 Limit Switches Figure 4-12 Limit switch operator Level type Fork type Wobble stick Push roller COM Prof. Paul Lin 22 11

12 Common Applications for Limit Switches To limit the travel of electrically operated Doors, Conveyors, Hoists, Machine tool worktables, and similar device Figure 4-12 Limit switches providing over travel protection operator Forward Direction Movement 1) Push Forward PB, energize F coil that control the motor to rotate in one direction, F s NO contact maintained; F s NC contact open to provide interlock that prevent the reverse director of motor 2) If it is overtravel in FWD direction, FWD LS is pushed Open, deenergized the F coil, and then turn off the motor Reverse Direction Movement 1) Push Reverse PB, energize R coil that control the motor to rotate in the reverse direction, R s NO contact maintained; R s NC contact open to provide interlock that prevent the reverse director of motor 2) If it is overtravel in REV direction, REV LS is pushed Open, deenergized the R coil, and then turn off the motor Prof. Paul Lin 23 Limit Switches Micro Limit Switch (Figure 4-24) Provide rapid closing and/or opening action Single-pole double throw that has COM, NO, and NC Offers a limit amount of electrical insulation and physical protection for contacts Normally mounted within encloses with lower risk of physical damage Rotating Cam Limit Switch (Figure 4-25) Senses angular shaft rotation within 360 and the activates contacts Used with machinery having a repetitive cycle of operation Prof. Paul Lin 24 12

13 Part 2 Mechanically Operated Switches Temperature Control Devices Monitoring temperature or changes in temperature for a particular process Temperature switch (Thermostats), Figure 4-26 Used in heating or cooling applications where temperature must be maintained within preset limits Figure 4-27 Capillary tube temperature switch Temperature-sensitive liquid will expand and contract with a change in temperature Pressure in the system changes in proportion to temperature and is transmitted to the bellow through a bulb and capillary tube Prof. Paul Lin 25 Temperature Controlled Fan Motor Application Figure 4-28 Temperature switch utilized as part of a motor control circuit 230 V fractional HP fan motor Selector Switch: Auto, OFF, Hand In Auto position, Temperature sw actuated Prof. Paul Lin 26 13

14 Part 2 Mechanically Operated Switches Pressure Switches Used to monitor and control the pressure of liquids and gases Pressure => activate electrical contacts Three types Positive pressure Vacuum (negative pressure) Differential pressure Figure 4-29 Pressure switch symbols Prof. Paul Lin 27 Part 2 Mechanically Operated Switches Theory of Operation 1) Pressure sw with high cut off and low turn on differential setting (dean band) is preselected 2) System on/off sw is set to on position => energize Compressor motor starter coil => Motor is on 3) Compressor system pressure is reached, Pressure sw off, de-energize M coil => Motor stopped 4) Compressor system pressure dropped below the low level => Pressure sw On, M coil energized again => Motor start to run again 5) Repeat step 3 through 4 Figure 4-30 Pressure switch used as part of air-compressor control system Prof. Paul Lin 28 14

15 Part 2 Mechanically Operated Switches Float Switches A float-level switch is used to sense the height of a liquid Applications: providing automatic control for motors that pump liquid from a sump or into a tank Figure 4-31 Float switch symbols and circuit Motor stop level => Float SW Off => M coil de-energized => Pump Motor Off Motor start level => Float SW On => M coil energized => Pump Motor On Prof. Paul Lin 29 Part 2 Mechanically Operated Switches Flow Switches A flow switch is used to detect the movement of air or liquid through a duct or pipe Applications: providing automatic control for motors that pump liquid from a sump or into a tank Figure 4-32 Flow switch symbols and circuit Paddle-type flow SW moves to close the electrical contacts of flow SW when the flow is sufficient to overcome the spring tension on the paddle When flow stops, the contacts open Prof. Paul Lin 30 15

16 Summary & Conclusion Questions? Contact Prof. Lin through: LINE Group discussion forum Prof. Paul Lin 31 16