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

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1 ECET 211 Electric Machines & Controls Lecture 6 Contactors and Motor Starters (2 of 2) 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 Engineering and 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 1. Magnetic Contactor Part 2. Contactor Ratings, Enclosures, and Solid State Types Prof. Paul Lin 2 1

2 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 3 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 4 2

3 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 5 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 6 3

4 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 7 Motor Overcurrent Protection Figure 6-35 Motor overcurrent protection Hot-circuit and ground-fault motor protection Overload protection Prof. Paul Lin 8 4

5 Motor Overcurrent Protection Figure 6-36 The basic difference between a contactor and motor starter is the addition of overload relays. Prof. Paul Lin 9 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 10 5

6 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 11 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 12 6

7 Motor Overload Relays Figure 6-40 Bimetallic type of thermal overload relay Prof. Paul Lin 13 Motor Overload Relays Figure 6-41 Thermal overload relay circuit operation Figure 6-42 Typical motor overload heater selection chart Prof. Paul Lin 14 7

8 Electronic Overload Relays Figure 6-43 Thermal overload relay circuit operation Figure 6-44 Electronic solid-state overload relay Prof. Paul Lin 15 Electronic Overload Relays Figure 6-45 Microprocessor-based type modular overload relay Prof. Paul Lin 16 8

9 Dual Element Fuse Figure 6-46 Dual-element fuse Prof. Paul Lin 17 NEMA and IEC Symbols Figure 6-47 Comparison of NEMA and IEC symbols Prof. Paul Lin 18 9

10 NEMA and IEC Symbols Figure 6-48 Typical NEMA and IEC symbols found in a motor control schematic Prof. Paul Lin 19 Summary & Conclusion Questions? Contact Prof. Lin through: lin@ipfw.edu Prof. Paul Lin 20 10