ECET 211 Electric Machines & Controls Lecture 6 Contactors and Motor Starters. Lecture 6 Contactors and Motor Starters

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1 ECET 211 Electric Machines & Controls Lecture 6 Contactors and Motor Starters Text Book: Chapter 6, Electric Motors and Control Systems, by Frank D. Petruzella, published by McGraw Hill, Paul I-Hai Lin, Professor of Electrical and Computer Engr. Tech. P.E. States of Indiana & California Dept. of Computer, Electrical and Information Technology Purdue University Fort Wayne Campus Prof. Paul Lin 1 Lecture 6 Contactors and Motor Starters Part 1. Magnetic Contactor Part 2. Contactor Ratings, Enclosures, and Solid State Types Prof. Paul Lin 2 1

2 Part 1. Magnetic Contactor NEMA Definition - Magnetic Contactor A magnetically actuated device for repeatedly establishing or interrupting an electric power. Designed to make and break electric power circuit loads in excess of 15A without being damage. Figure 6-1 Typical magnetic contactor May be for switching AC motor load, not requiring overload protection Includes 3 main contacts, plus 1 auxiliary contact for 3- wire PB control Prof. Paul Lin 3 Part 1. Magnetic Contactor Figure 6-2 Three-pole magnetic contactor Connection for Two circuits Control Circuit Power Circuit Operating principle Voltage => Coil => Current => Magnetic field Coil => energize the stationary iron frame => Electromagnet Draw armature (plunger) => pulling the movable and stationary contacts together Power source => Main circuit current => Load side Prof. Paul Lin 4 2

3 Switching Loads Part 1. Magnetic Contactor Figure 6-3 Contactor used in conjunction with pilot devices Temperature and Liquid Level Control (non motor load) Liquid Level sensor Temperature sensor Heating element On/Off control Solenoid On/Off control Prof. Paul Lin 5 Switching Loads - Motor Load Part 1. Magnetic Contactor Figure 6-4 IEC contactor used in combination with an overload relay module to switch a motor load Two-wire control device: Automatic control applications for pumps, electric heating, air compressors Three-wire control Motor controlled by On/Off PB to initiate and terminate the system processes Prof. Paul Lin 6 3

4 Part 1. Magnetic Contactor Switching Loads High Voltage Load Kept the high voltage away from the operator to increase the safety Use Step-down transformer Primary-side voltage levels: 208, 220, 240, 460, 480, or 600V Secondary-side voltage levels: 12, 24 or 120V Figure 6-5 Heater circuit controlled by a magnetic contactor (page 152) Prof. Paul Lin 7 Figure 6-5 (page 152) Operation of the Circuit Part 1. Magnetic Contactor Prof. Paul Lin 8 4

5 Definite-purpose Contactors Figure 6-6 Electrically and mechanically held lighting contactors Mounted in enclosures Figure 6-7 Mechanically held lighting contactor Part 1. Magnetic Contactor Prof. Paul Lin 9 Part 2. Contactor Rating, Enclosures, and Solid State Types NEMA Ratings Figure 6-22 NEMA contactor size guide Order a contactor by the current, motor horse power, and voltage ratings Copper contact, Silver alloy contact The current rating for each size is an 8-hour open rating the contactor must be operated at least once every 8-hours to prevent copper oxide forming on the tips and causing excessive contact heating Prof. Paul Lin 10 5

6 Part 2. Contactor Rating, Enclosures, and Solid State Types NEMA Ratings Example 6-1. Use the table 6-22 to determine the NEMA size of an AC contactor required for a 480V heating element load with continuous current rating of 80A. Solution: Size 2 rated 45A Size 3 rated 90A NEMA rating 600 volts max Prof. Paul Lin 11 Part 2. Contactor Rating, Enclosures, and Solid State Types NEMA Ratings Load Utilization Categories: Nolinear loads tungsten lamps for lighting (large hot-to-cold resistance ratio: typically 10:1 or higher, current and voltage in phase) Resistive loads: heating elements for furnaces and ovens (constant resistance; current and voltage in phase) Inductive loads: industrial motors and transformers (current lags behind voltage) Capacitive loads: industrial capacitors for power factor correction (current leads voltage) Prof. Paul Lin 12 6

7 Part 2. Contactor Rating, Enclosures, and Solid State Types IEC Ratings Downsized to provide higher ratings in a smaller package IEC devices are 30 to 70 percent smaller than their NEMA counterparts Evaluated the contactor to meet the requirements of a number of defined applications. AC Categories AC-1: for all AC loads where the PF is at least 0.95; primarily for noninductive or slightly inductive loads AC-3: for squirrel-cage motors where the breaking of the power contacts would occur while motor is running. On closing, the contactor experiences an inrush current: 5 to 8 times the nominal motor current, and the voltage at terminals is approximately 20 percent of line voltage. AC-4: for the starting and breaking of a squirrel-case motor during an inch or plug reverse. Prof. Paul Lin 13 Part 2. Contactor Rating, Enclosures, and Solid State Types IEC Ratings DC Categories DC-1: This applies to all DC loads where the time constant (L/R) is less than or equal to 1 ms; primarily for noninductive or slightly inductive loads DC-2: This applies to the breaking of shunt motors while they are running. On closing, the contactor makes the inrush current around 2.5 times the nominal current DC-3: This applies to the starting and breaking of a shunt motor during inching or plugging. DC-5: This applies to the starting and breaking of a series motor during inching or plugging. Prof. Paul Lin 14 7

8 Part 2. Contactor Rating, Enclosures, and Solid State Types Contactor Enclosures Environmental factors: Expose to damaging fumes Operating in damp places Exposure to excessive dust Subject to vibration, shocks, and tilting Subject to high ambient air temperature NEMA Enclosures: Nonhazadous-location enclosure General purpose Watertight Oil-tight Dust-tight Hazadous-location enclosure Gaseous vapors (acetylene, hydrogen, gasoline, etc) Combustible dusts (meta dust, coal dust, grain dust, etc) Prof. Paul Lin 15 Part 2. Contactor Rating, Enclosures, and Solid State Types Figure 6-24 Typical contactor enclosure types NEMA Type 1 general purpose type NEMA Type 4 and 4X watertight and dust tight NEMA Type 12 provides a degree of protection from noncorrosive dripping liquids, falling dirt, and dust NEMA Type 7 and 9 for used in hazardous locations Prof. Paul Lin 16 8

9 Part 2. Contactor Rating, Enclosures, and Solid State Types Solid-State Contactor Solid-state switching refers to interruption of power by non-mechanical electronics means; Figure 6-25 Single-pole solid state contactor Figure 6-26 Silicon Controlled Rectifier switching semiconductor Prof. Paul Lin 17 Part 2. Contactor Rating, Enclosures, and Solid State Types SCR Theory and Biasing Prof. Paul Lin 18 9

10 Part 2. Contactor Rating, Enclosures, and Solid State Types Figure 6-29 SCR snubber circuit Figure 6-30 Solid-state contactor digital control Prof. Paul Lin 19 Magnetic Motor Starters Motor Overcurrent Protection Motor Overload Relays Thermal Overload Relays Electronic Overload Relays Dual Element Fuse NEMA and IEC Symbols Prof. Paul Lin 20 10

11 Magnetic Motor Starter Magnetic contactor - for switching power in resistance heating elements, lighting, magnetic brakes, and heavy industrial solenoids A contactor with an overload protective device (overload relay) Overload protective device protects motors from overheating and burning up. Figure 6-31 Magnetic Motor Starter (with some manufacturer installed control wiring) Prof. Paul Lin 21 Magnetic Motor Starter Two-, three, or four-pole magnetic contactor An overload relay Suitable enclosure Figure 6-32 Magnetic motor starter enclosure General-purpose sheet-metal Dust-tight Water-tight Explosion resisting Start/Stop PB may be mounted in the cover of the enclosure Prof. Paul Lin 22 11

12 Magnetic Motor Starter Figure 6-33 Magnetic motor starter with separately mounted start-stop pushbutton station Start/Stop PB may be mounted in the cover of the enclosure Prof. Paul Lin 23 Motor Overcurrent Protection Figure 6-34 Major functional blocks for motor operation Motor circuit and controller disconnecting means Motor branch short-circuit and ground-fault protection Motor controller and overload protection Sometimes motor disconnecting means, often referred to as the at the motor disconnecting means Prof. Paul Lin 24 12

13 Motor Overcurrent Protection Figure 6-35 Motor overcurrent protection Hot-circuit and ground-fault motor protection Overload protection Prof. Paul Lin 25 Motor Overcurrent Protection Figure 6-36 The basic difference between a contactor and motor starter is the addition of overload relays. Prof. Paul Lin 26 13

14 Motor Overload Relays Overload relays are designed to meet the special protective needs of motor control circuits. Overload relays are rated by a trip class define the length of time it will take for the relay to trip in an overload condition. Most common trip classes: Class 10: trip motor offline in 4-10 sec at 600 percent of the fullload amperes Class 20: trip in 6-20 seconds Class 30: trip in 9-30 seconds Prof. Paul Lin 27 Motor Overload Relays Overload protection devices have Trip Indicator Reset: manual/automatic Nominal current setting Figure 6-37 Overload relay trip indicator Prof. Paul Lin 28 14

15 Motor Overload Relays Thermal Overload Relays, Figure 6-38 A heater is connected in series with the motor supply. Two types Melting alloy Bimetallic Figure 6-39 Melting alloy-type thermal overload relay Prof. Paul Lin 29 Motor Overload Relays Figure 6-40 Bimetallic type of thermal overload relay Prof. Paul Lin 30 15

16 Motor Overload Relays Figure 6-41 Thermal overload relay circuit operation Figure 6-42 Typical motor overload heater selection chart Prof. Paul Lin 31 Electronic Overload Relays Figure 6-43 Thermal overload relay circuit operation Figure 6-44 Electronic solid-state overload relay Prof. Paul Lin 32 16

17 Electronic Overload Relays Figure 6-45 Microprocessor-based type modular overload relay Prof. Paul Lin 33 Dual Element Fuse Figure 6-46 Dual-element fuse Prof. Paul Lin 34 17

18 NEMA and IEC Symbols Figure 6-47 Comparison of NEMA and IEC symbols Prof. Paul Lin 35 NEMA and IEC Symbols Figure 6-48 Typical NEMA and IEC symbols found in a motor control schematic Prof. Paul Lin 36 18

19 Summary & Conclusion Questions? Contact Prof. Lin through: Prof. Paul Lin 37 19