ECET 211 Electric Machines & Controls Lecture 6 Contactors and Motor Starters (1 of 2) Lecture 6 Contactors and Motor Starters

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1 ECET 211 Electric Machines & Controls Lecture 6 Contactors and Motor Starters (1 of 2) Text Book: Chapter 6, Electric Motors and Control Systems, by Frank D. Petruzella, published by McGraw Hill, 2015 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 6 Contactors and Motor Starters Part 2. Contactor Ratings, Enclosures, and Solid State Types Part 3. Motor Starters Prof. Paul Lin 2 1

2 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 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 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 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 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 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 Prof. Paul Lin 9 Definite-purpose Contactors Figure 6-8 Single-operatingcoil mechanically held lighting contactor Prof. Paul Lin 10 5

6 Contactor Assemblies Figure 6-9 Typical Operating mechanisms for magnetic contactors Bell-crank Horizontal-actions Clapper Prof. Paul Lin 11 Contactor Assemblies Figure 6-10 Contactor coil Operational limit: 85 to 110 percent of the rated coil voltage. A coil voltage variation of greater than ±5 percent will maximize the contact wear, minimize life Higher voltage => increase closing speed Lower voltage => decrease closing speed Specification: Rated voltage Pick-up voltage overcome mechanical forces Hold-in voltage Drop-out voltage Prof. Paul Lin 12 6

7 Contactor Assemblies Figure 6-11 Deenergized coil air gap The inrush current for an AC coil may range from 5 to 20 times that of the sealed current. Figure 6-12 RC suppression module Voltage spike suppression Prof. Paul Lin 13 Contactor Assemblies Figure 6-13 Shading coils or rings Prevent humming noise and wear on the AC contactor s moving parts Prof. Paul Lin 14 7

8 Contactor Assemblies Figure 6-14 Contactor assembly alignment Figure 6-15 Typical contactor replacement kit Figure 6-16 Contactor auxiliary contact blocks Prof. Paul Lin 15 Arc Suppression Figure 6-17 Electric arc occurs when contacts are open Figure 6-18 DC contactors Prof. Paul Lin 16 8

9 Arc Suppression Figure 6-19 Arc chute Figure 6-20 Magnetic blowout coil (assist arc suppression) Figure 6-21 Vacuum contactor Prof. Paul Lin 17 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 18 9

10 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 19 Part 2. Contactor Rating, Enclosures, and Solid State Types NEMA Ratings Load Utilization Categories: Nonlinear 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 20 10

11 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 non-inductive 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 21 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 non-inductive 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 22 11

12 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: Non-hazardous-location enclosure General purpose Watertight Oil-tight Dust-tight Hazardous-location enclosure Gaseous vapors (acetylene, hydrogen, gasoline, etc) Combustible dusts (meta dust, coal dust, grain dust, etc) Prof. Paul Lin 23 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 24 12

13 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 25 Part 2. Contactor Rating, Enclosures, and Solid State Types SCR Theory and Biasing Prof. Paul Lin 26 13

14 Part 2. Contactor Rating, Enclosures, and Solid State Types Figure 6-27 SCR testing circuit Figure 6-28 SCR connection for singlephase contactor Prof. Paul Lin 27 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 28 14

15 Summary & Conclusion Questions? Contact Prof. Lin through: LINE Group Discussion forum Prof. Paul Lin 29 15