Mott Chapter 21 - Chapter 21 Electric Motors and Controls...

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1 Chapter 21 Electric Motors and Controls Electric Motors Electric motors are an efficient means of converting energy: – Electric motor = 50-80% efficient – Diesel engine = 40% efficient – Gasoline engine = 25-35% efficient Advantages Electric motors have many advantages: – Low cost and inexpensive to operate – Easy to start – Automatic/remotely controlled – Long life (35,000 hours) – Low noise, no exhaust – Compact
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2 Typical Applications in Agriculture 1. Blowers 2. Ventilation fans 3. Augers 4. Mixers 5. Irrigation pumps 6. HVACs Electric Motors Can operate in harsh environments – Dust and dirt – Moisture – Chemicals Common Motor Enclosures Open = indoor, free ventilation Drip proof = outdoor, protects 0-15 o from vertical, must be dust free, air exchange Splash proof = outdoor, 0-100 o from vertical, must be dust free, air exchange TEFC = no direct air exchange, cooling fan, not air tight Explosion proof = no direct air exchange, cooling fan, airtight
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3 AC Motor Principles Most farm motors are alternating current – Electromagnetic – Electromagnetic induction – Alternating current Motor has two main parts – Stationary part called stator – Rotating part called rotor Motor Power – Single-phase 110 V, 220 V – Three-phase 208 V, 230 V, 460 V Motor Selection Factors The following items must be specified for motors: – Motor type: DC, AC single-phase, three-phase, etc – Power rating and speed – Operating voltage and frequency – Type of enclosure – Frame size – Mounting details Motor Selection Factors con’t Special requirements may be communicated to the vendor: – Operating torque, operating speed, and power rating • Power = torque * speed – Starting torque – Load variations expected – Current limitations – Duty cycle – Environmental factors – Voltage variations expected – Shaft loading (side loads and thrust loads)
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4 Motor Size A rough classification of motors by size is used to group motors of similar design: – Subfractional horsepower: 1-40 millihorsepower (mhp) (0.75 to 30 W) – Fractional horsepower: 1/20 to 1.0 hp (37 to 746 W) – Integral horsepower: 1.0 hp (0.75 kW) and larger AC Power and General Info Alternating current (AC) power is produced by the electric utility and delivered to the industrial, commercial, or residential consumer in a variety of forms. In the United States, AC power has frequency of 60 HZ or 60 cycles/s. AC power is also classified as single-phase or three-phase. Most residential units and light commercial installations have only single-phase power carried by two conductors plus ground. AC Power and General Info con’t The waveform of the power appears like a single continuous sine wave at the system frequency whose amplitude is the rated voltage of the power. Three-phase power is carried on a three-wire system
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Mott Chapter 21 - Chapter 21 Electric Motors and Controls...

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