An IPQDF Technical Resource

소개

In rural and agricultural settings, three-phase power is often unavailable. Yet many applications—irrigation pumps, grain dryers, livestock operations—requirehigh horsepower (10-100+ HP). This creates a unique engineering challenge: how to deliver substantial mechanical power from a single-phase electrical supply.

Three distinct technologies have addressed this challenge over the past century:

Each has its place in history and modern practice. This guide explores all three.

flowchart TD
    subgraph Challenge["THE CHALLENGE: Rural Single-Phase Power"]
        C1[No Three-Phase Available<br>Farm, Remote Location]
        C2[High Power Required<br>10-100+ HP for Pumps, Grain, Irrigation]
    end

    subgraph Solutions["TECHNOLOGY SOLUTIONS"]
        S1[ROSENBERG MOTOR<br>1910s-1950s<br>Historical - Obsolete]
        S2[WRITTEN-POLE MOTOR<br>1990s-Present<br>Modern - Low Starting Current]
        S3[VFD + PHASE CONVERTER<br>1980s-Present<br>Variable Speed - Needs Harmonics Mitigation]
    end

    subgraph Selection["SELECTION GUIDE"]
        D1[New Installation? → Use Written-Pole or VFD]
        D2[Existing Rosenberg? → Maintain or Retrofit]
        D3[Variable Speed Needed? → VFD + Converter]
        D4[Weak Grid? → Written-Pole Preferred]
    end

    Challenge --> Solutions
    Solutions --> Selection

    style Challenge fill:#e1f5fe,행정:#01579B,스트로크 폭:2px
    style Solutions fill:#fff3e0,stroke:#e65100,stroke-width:2px
    style Selection fill:#e8f5e8,stroke:#1b5e20,stroke-width:2px
    
    style S1 fill:#ffebee,행정:#b71c1c
    style S2 fill:#e8f5e8,stroke:#1b5e20
    style S3 fill:#f3e5f5,stroke:#4a148c
    
    style D1 fill:#f3e5f5
    style D2 fill:#ffebee
    style D3 fill:#e1f5fe
    style D4 fill:#e8f5e8

Diagram created by IPQDF.com – Original work

부분 1: The Rosenberg Motor (Historical Context)

1.1 개요

TheRosenberg Motor (also known as theSteinmetz-Rosenberg Motor) is a historicsingle-phase AC motor design developed byCharles Proteus Steinmetz 과E.J. Rosenberg at General Electric in the early 1900s. It was engineered to solve a specific problem: deliveringhigh horsepower (까지 100 HP) from single-phase power supplies in rural areas without three-phase infrastructure.

동안obsolete and no longer manufactured, these motors may still be encountered in vintage installations. Understanding them is useful for:

• Maintaining legacy equipment
• Historical perspective on motor design
• Appreciating modern solutions like Written-Pole and VFD technology

1.2 Key Innovation: Inductor Winding

The Rosenberg motor’s main contribution was astationary inductor winding that improved power factor and reduced brush sparking compared to earlier repulsion motors.

1.3 Operating Principle Summary

The motor operated in two modes:

1. Starting (Repulsion Mode): High starting torque (300-400%) with moderate starting current (3-5x FLC)
2. Running (Induction Mode): After centrifugal switch activated at ~75% speed, ran as induction motor

1.4 Why It’s Obsolete

1.5 If You Encounter One Today

Do not install a Rosenberg motor in a new application. If maintaining an existing installation:

• Inspect brushes and commutator regularly
• Keep spare brushes if available
• Plan for replacement with Written-Pole or VFD system
• Document for historical interest

1.6 Quick Facts

부분 2: The Written-Pole Motor (Modern)

2.1 개요

TheWritten-Pole Motor is a modernsingle-phase, constant-speed synchronous motor designed specifically forhigh-inertia loads on weak rural grids. Developed byPrecise Power Corporation in the 1990s, it represents a fundamental rethinking of how to start heavy loads without disturbing the power system .

The name comes from its unique operating principle: magnetic poles are“written” onto the rotor surface while it rotates, allowing extremely gentle starting and excellent voltage dip ride-through .

flowchart TD
    subgraph Stator["STATOR ASSEMBLY"]
        Main["Main Winding<br>Single-Phase AC"]
        Exciter["Exciter Winding<br>Magnetic Writing Coil"]
    end
    
    subgraph Rotor["ROTOR ASSEMBLY"]
        철["Ferromagnetic Layer<br>'Writeable' Magnetic Material"]
        Poles["Written Magnetic Poles<br>Created While Rotating"]
    end
    
    subgraph Operation["OPERATING SEQUENCE"]
        Step1["1. START: Induction Mode<br>Low Current: 2-3x FLC"]
        Step2["2. WRITE: Exciter Writes Poles<br>Onto Rotor Surface"]
        Step3["3. RUN: Synchronous Mode<br>Constant Speed, No Slip"]
        Step4["4. REWRITE: Continuous Process<br>Auto-Resynchronization"]
    end
    
    subgraph Advantage["KEY ADVANTAGES"]
        A1["✓ Ultra-Low Starting Current"]
        A2["✓ Voltage Dip Ride-Through"]
        A3["✓ No Brushes - Low Maintenance"]
        A4["✓ Absorbs Grid Harmonics"]
    end
    
    Main --> Ferro
    Exciter --> Poles
    Poles --> Step3
    Step1 --> Step2 --> Step3 --> Step4
    Operation --> Advantage
    
    style Stator fill:#e1f5fe,행정:#01579b
    style Rotor fill:#f3e5f5,stroke:#4a148c
    style Operation fill:#e8f5e8,stroke:#1b5e20
    style Advantage fill:#fff9c4,stroke:#f57f17

2.2 Why It Was Revolutionary

2.3 Construction & Operating Principle

How It Works:

1. Start as Induction Motor: The motor starts as a low-current induction motor, drawing only2-3x full load current—dramatically less than the 6-10x of standard motors.
2. Magnetic Writing: While rotating, theexciter winding creates a magnetic field that “writes” poles onto a special ferromagnetic layer on the rotor surface. This is a continuous process—poles are written and rewritten as the rotor turns.
3. Synchronous Operation: Once poles are written, the rotorlocks to synchronous speed (no slip) and operates as a true synchronous motor with constant speed regardless of load (within its rating).
4. Continuous Rewriting: The poles are continuously rewritten, meaning the motorautomatically resynchronizes after disturbances—a key advantage over permanent magnet synchronous motors .

2.4 Key Performance Characteristics

2.5 The Power Quality Advantage

The Written-Pole motor’s most significant contribution to power quality is itsextremely low starting current 과voltage dip ride-through capability.

Starting Current Comparison

flowchart TD
    subgraph Stator["STATOR ASSEMBLY"]
        Main["Main Winding<br>Single-Phase AC"]
        Exciter["Exciter Winding<br>Magnetic Writing Coil"]
    end
    
    subgraph Rotor["ROTOR ASSEMBLY"]
        철["Ferromagnetic Layer<br>'Writeable' Magnetic Material"]
        Poles["Written Magnetic Poles<br>Created While Rotating"]
    end
    
    subgraph Operation["OPERATING SEQUENCE"]
        Step1["1. START: Induction Mode<br>Low Current: 2-3x FLC"]
        Step2["2. WRITE: Exciter Writes Poles<br>Onto Rotor Surface"]
        Step3["3. RUN: Synchronous Mode<br>Constant Speed, No Slip"]
        Step4["4. REWRITE: Continuous Process<br>Auto-Resynchronization"]
    end
    
    subgraph Advantage["KEY ADVANTAGES"]
        A1["✓ Ultra-Low Starting Current"]
        A2["✓ Voltage Dip Ride-Through"]
        A3["✓ No Brushes - Low Maintenance"]
        A4["✓ Absorbs Grid Harmonics"]
    end
    
    Main --> Ferro
    Exciter --> Poles
    Poles --> Step3
    Step1 --> Step2 --> Step3 --> Step4
    Operation --> Advantage
    
    style Stator fill:#e1f5fe,행정:#01579b
    style Rotor fill:#f3e5f5,stroke:#4a148c
    style Operation fill:#e8f5e8,stroke:#1b5e20
    style Advantage fill:#fff9c4,stroke:#f57f17

Voltage Dip Ride-Through

While standard induction motors stall when voltage drops below 80-85%, Written-Pole motors can:

• Ride through voltage sags down to 50% 에 5-10 초
• Continue operating during dips that would trip other motors
• Automatically resynchronize after disturbances
• Reduce nuisance tripping in weak grid areas

2.6 응용 프로그램

Primary: Rural & Agricultural

• Irrigation pumps (deep-well, center pivot)
• Oil well pumps (pumpjacks)
• Grain handling (elevators, dryers)
• Dairy operations (vacuum pumps, milkers)

Secondary: Critical Infrastructure

• Standby generator sets (motor starting)
• Water/wastewater treatment (lift stations)
• Mining ventilation (remote sites)
• Telecommunications (backup power)

Tertiary: 산업의

• Large fans and blowers
• Compressors (where variable speed not needed)
• Conveyors (constant speed applications)

2.7 장점 & 단점

✅ 장점

❌ 단점

2.8 Written-Pole vs. Other Technologies

2.9 Installation Considerations

Electrical Requirements

• Dedicated single-phase supply at motor voltage
• Disconnect switch and overload protection per NEC/CEC
• Proper grounding for sensitive electronics
• Surge protection recommended for rural areas

Mechanical Considerations

• Concrete pad or sturdy base (motors are heavy)
• Proper alignment with driven equipment
• Vibration isolation if needed
• Weather protection for outdoor installations

Utility Coordination

• Notify utility before installation (especially >25 HP)
• Verify voltage regulation at site
• Consider power factor if on demand metering
• Document starting current for future reference

부분 3: VFD + Phase Converter Systems

3.1 개요

When three-phase power is unavailable but high horsepower is needed for rural applications, aVariable Frequency Drive (VFD) combined with a phase converter (or a VFD specifically designed for single-phase input) offers a modern, flexible solution. This approach allows standard three-phase motors—which are cheaper, more efficient, and more readily available than large special-purpose single-phase motors—to operate from a single-phase supply .

Unlike dedicated single-phase motors like the Rosenberg or Written-Pole designs, VFD-based systems providevariable speed control, soft-start capability, 과programmable operation—features increasingly valuable for modern agricultural and industrial applications .

3.2 How It Works: Two Approaches

Approach A: Single-Phase Input VFD + Three-Phase Motor

Some VFDs are specifically designed to acceptsingle-phase input power while deliveringthree-phase output to the motor. These drives internally rectify the single-phase AC to DC, then invert it back to three-phase AC of variable frequency and voltage .

flowchart TD
    subgraph SystemA["APPROACH A: SINGLE-PHASE INPUT VFD"]
        A["Single-Phase Power In<br>230V/480V 50/60Hz"] --> B["수정<br>Converts AC to DC"]
        B --> C["DC Bus Capacitors<br>Energy Storage / Filtering"]
        C --> D["Inverter<br>IGBTs Create 3-Phase AC"]
        D --> E["Three-Phase Motor<br>Standard Induction"]
        
        에프["Control Logic<br>Microprocessor"] --> D
        G["User Interface<br>Speed Control"] --> F
    end
    
    subgraph ProsCons["ADVANTAGES & LIMITATIONS"]
        PA["✓ No External Converter Needed"]
        PB["✓ Variable Speed Control"]
        PC["✗ Requires Derating<br>10HP VFD → 5-7.5HP Output"]
        PD["✗ Harmonic Generation<br>Needs Filters"]
    end
    
    SystemA --> ProsCons
    
    style SystemA fill:#e1f5fe,행정:#01579b
    style ProsCons fill:#fff9c4,stroke:#f57f17

Key advantage: No external phase converter needed—the VFD does both jobs .

Limitation: Single-phase input VFDs typically requirederating. A VFD rated for 10 HP with three-phase input might only handle 5-7.5 HP with single-phase input due to higher ripple current on the DC bus .

Approach B: Phase Converter + Standard VFD + Three-Phase Motor

This approach uses a dedicatedphase converter to create balanced three-phase power from a single-phase source, which then feeds a standard three-phase VFD and motor .

flowchart TD
    subgraph SystemB["APPROACH B: PHASE CONVERTER + STANDARD VFD"]
        A["Single-Phase Power In"] --> B["Phase Converter<br>Rotary or Static"]
        
        subgraph Rotary["ROTARY CONVERTER DETAIL"]
            R1["Idler Motor<br>3-Phase Motor Runs as Generator"]
            R2["콘덴서 은행<br>For Voltage Balancing"]
            R1 <--> R2
        end
        
        B --> C["Generated Three-Phase Power<br>May Have Imperfect Balance"]
        C --> D["Standard Three-Phase VFD<br>Input: 3-단계,,en,청소기 또는 480 VAC AC-DC 전원 공급 장치,,en, Output: Variable"]
        D --> E["Three-Phase Motor"]
        
        B -.- Rotary
        
        F["선택: Multiple Motors<br>Can Run Directly from Converter"]
        C --> F
    end
    
    subgraph ProsCons["ADVANTAGES & LIMITATIONS"]
        PA["✓ Can Use Standard VFDs"]
        PB["✓ Scalable to Multiple Motors"]
        PC["✗ More Complex Installation"]
        PD["✗ Lower Efficiency than Approach A"]
    end
    
    SystemB --> ProsCons
    
    style SystemB fill:#f3e5f5,stroke:#4a148c
    style Rotary fill:#fff3e0,stroke:#e65100
    style ProsCons fill:#fff9c4,stroke:#f57f17

Rotary phase converters use a motor-generator set to create the third phase and are available in sizes up to40 HP and beyond . They are rugged, reliable, and can power multiple motors.

3.3 Applications in Rural & Agricultural Settings

3.4 Advantages of VFD + Phase Converter Systems

3.5 The Critical Challenge: 고조파 왜곡

While VFD + phase converter systems offer many benefits, they introduce a significant power quality challenge: 고조파 왜곡.

What Causes Harmonics?

Single-phase VFDs use adiode bridge rectifier to convert AC to DC. This rectifier draws current only at the peaks of the voltage waveform, creating anon-sinusoidal current rich in harmonics—particularly the3회, 5일, and 7th orders .

Typical Harmonic Levels (Without Mitigation)

These levelsfar exceed allowable limits for grid connection in most jurisdictions .

Effects of Harmonic Distortion

• Transformer overheating (eddy current losses)
• Neutral conductor overloading (triplen harmonics add in neutral)
• Capacitor bank failure (resonance with supply inductance)
• Metering errors (some revenue meters inaccurately measure distorted waveforms)
• Interference with communications and sensitive electronics
• Utility penalties 또는refusal to connect

3.6 Mitigation Strategies for Harmonics

flowchart TD
    subgraph Mitigation["HARMONIC MITIGATION OPTIONS"]
        direction TB
        
        M1["LINE REACTORS<br>3-5% Impedance"] --> E1["Effect: 25-50% Reduction on 5th/7th<br>Minimal Effect on 3rd Harmonic"]
        
        M2["PASSIVE FILTERS<br>Tuned to Specific Harmonics"] --> E2["Effect: 80-90% Reduction All Orders<br>Fixed Tuning, May Resonate"]
        
        M3["ACTIVE FILTERS<br>Dynamic Cancellation"] --> E3["Effect: 90-95%+ Adaptive<br>Expensive, Adjustable"]
        
        M4["MULTI-PULSE DRIVES<br>12 or 18 펄스"] --> E4["Effect: Eliminates 5th/7th<br>Requires Transformer, Bulky"]
        
        M5["ACTIVE FRONT END<br>IGBT Rectifiers"] --> E5["Effect: <5% THD, Unity PF<br>Highest Cost, Regenerative"]
    end
    
    subgraph Recommendation["RECOMMENDATION BY APPLICATION"]
        R1["Small Systems: 라인 리액터 + 수동 필터"]
        R2["Pumps/Fans: 수동 필터"]
        R3["Multiple Drives: 활성 필터"]
        R4["Critical Power: Active Front End"]
    end
    
    Mitigation --> Recommendation
    
    style Mitigation fill:#e1f5fe,행정:#01579b
    style Recommendation fill:#e8f5e8,stroke:#1b5e20

A. Line Reactors and DC Link Chokes

The simplest and most cost-effective mitigation is addingline reactors (on the input) 및 / 또는DC link chokes (internal to the VFD). These inductors smooth current flow and reduce higher-order harmonics.

Limitation: Reactors alonecannot adequately suppress the 3rd harmonic in single-phase systems .

B. Passive Harmonic Filters

Passive filters useinductors and capacitors tuned to specific frequencies to trap harmonics.

• Tuned filters for 3rd, 5일, 7th can be very effective
• Broadband filters (like the Mirus Lineator 1Q3) reduce THD by up to10엑스
• 단순한, reliable, no power required
• Fixed tuning—may not adapt to changing loads
• Can cause resonance with system impedance

C. 활성 고조파 필터

Active filters use power electronics toinject cancelling currents in real time, dynamically neutralizing harmonics.

• Excellent performance across all harmonics, including 3rd
• Adapts to varying load conditions
• More expensive and complex
• Requires power and maintenance
• Often used for larger installations or where multiple VFDs share a bus

디. 12-Pulse or 18-Pulse Drives

For larger installations, multi-pulse rectifier configurations cancel lower-order harmonics through phase shifting.

• 12-펄스 effectively eliminates 5th and 7th
• 18-펄스 also attenuates 11th and 13th
• Requires phase-shifting transformer—bulky and expensive
• Used primarily inlarge industrial applications

그것. Active Front End (AFE) 드라이브

AFE drives useIGBT-based rectifiers instead of diode bridges, enabling:

• Near-sinusoidal input current (<5% THD)
• Regenerative capability (power back to grid)
• Unity power factor
• Highest cost—justified for large systems or where power quality is critical

3.7 Comparison of Mitigation Options

3.8 Utility Perspective & 규정 준수

Rural electric cooperatives and utilities are increasingly concerned about harmonic distortion from VFDs and phase converters. Some key considerations:

Utility Requirements (Typical)

• THID < 12% at point of common coupling (often requires filters)
• Individual harmonic limits per IEEE 519 or IEC 61000-3-12
• Pre-installation studies for motors >50 HP
• Some co-opsprohibit phase converters without harmonic filters

3.9 Selection Guide: VFD + Phase Converter vs. Dedicated Single-Phase Motors

3.10 Best Practices for VFD + Phase Converter Installations

1. Assess your load – Is variable speed needed? If yes, VFD approach is best.
2. Check utility requirements – Some co-ops have harmonic limits; discuss before investing.
3. Size appropriately – Single-phase input VFDs require derating; consult manufacturer.
4. Plan for harmonics – Budget for line reactors (minimum) or harmonic filters (preferred).
5. Consider solar integration – Modern solar VFDs can reduce operating costs to near-zero .
6. Think long-term – Three-phase motors are standard; VFDs can be reused if three-phase becomes available.
7. Document compliance – Keep records of harmonic measurements for utility or regulatory purposes.

부분 4: Comparison & Selection Guide

4.1 Technology Comparison Matrix

4.2 Application-Specific Recommendations

For Irrigation Pumps

• Best: VFD + Phase Converter (variable flow saves water/energy)
• 좋은: Written-Pole (if constant flow acceptable)
• Avoid: Rosenberg (obsolete, parts unavailable)

For Grain Handling (Conveyors, Elevators)

• Best: VFD + Phase Converter (speed matching between equipment)
• 좋은: Written-Pole (if single speed adequate)
• Avoid: Rosenberg (maintenance intensive)

For Remote/Off-Grid Sites

• Best: Written-Pole (lowest starting current, minimal grid impact)
• 좋은: VFD + 태양의 (if renewable energy available)
• Avoid: Rosenberg (requires maintenance access)

For Critical Processes (Water Treatment, Lift Stations)

• Best: Written-Pole (ride-through capability)
• 좋은: VFD with ride-through configured
• Avoid: Rosenberg (unreliable for critical duty)

4.3 Decision Flowchart

flowchart TD
    Start(["START: Need High Power from Single-Phase?"]) --> Q1{"New Installation or Existing?"}
    
    Q1 -->|New Installation| Q2{"Variable Speed Required?"}
    Q1 -->|Existing Rosenberg Motor| Legacy["Evaluate for Replacement"]
    
    Legacy --> L1["Can you maintain brushes?"]
    L1 -->|Yes - 일시적인| Temp["Continue with Maintenance Plan"]
    L1 -->|아니 - Replace| Q2
    
    Q2 -->|Yes| VFD["VFD + Phase Converter System"]
    Q2 -->|아니| Q3{"Weak Grid?<br>Voltage Dip Concerns?"}
    
    Q3 -->|Yes| WP["Written-Pole Motor"]
    Q3 -->|아니| Q4{"Budget Available?"}
    
    Q4 -->|Premium| WP2["Written-Pole Motor<br>Best Grid Compatibility"]
    Q4 -->|Standard| VFD2["VFD + Converter with Line Reactors"]
    Q4 -->|Limited| Retro["Consider Used Equipment?<br>⚠️ Not Recommended"]
    
    VFD --> H1["Add Harmonic Filters<br>Check Utility Requirements"]
    VFD2 --> H1
    WP --> H2["Verify 50 HP Limit<br>Order Lead Time 6-12 Weeks"]
    WP2 --> H2
    Retro --> H3["Inspect Thoroughly<br>Plan Future Replacement"]
    
    H1 --> Final(["Implementation"])
    H2 --> Final
    H3 --> Final
    Temp --> Final
    
    style Start fill:#e1f5fe,행정:#01579B,스트로크 폭:3px
    style Q1 fill:#fff3e0,stroke:#e65100
    style Q2 fill:#fff3e0,stroke:#e65100
    style Q3 fill:#fff3e0,stroke:#e65100
    style Q4 fill:#fff3e0,stroke:#e65100
    style VFD fill:#f3e5f5,stroke:#4a148c
    style VFD2 fill:#f3e5f5,stroke:#4a148c
    style WP fill:#e8f5e8,stroke:#1b5e20
    style WP2 fill:#e8f5e8,stroke:#1b5e20
    style Legacy fill:#ffebee,행정:#b71c1c
    style Retro fill:#ffebee,행정:#b71c1c
    style Temp fill:#fff9c4,stroke:#f57f17
    style Final fill:#fff9c4,stroke:#f57f17,stroke-width:2px

부분 5: 참조 & Further Reading

표준

Manufacturer Resources

• Precise Power Corporation – Written-Pole Motor documentation
• Mitsubishi Electric – Single-phase input VFD application guides
• Mirus International – Harmonic filter design for single-phase systems
• Phase Converter manufacturers – Rotary and static converter sizing

부분 6: Mobile-Friendly Summary Cards

Mobile Card 1: Rosenberg Motor (Quick Facts)

graph TD
    subgraph Mobile1["📱 ROSENBERG MOTOR - QUICK FACTS"]
        direction TB
        R1["📅 Era: 1910s-1950s"]
        R2["⚡ 힘: 5-100 HP"]
        R3["🔧 유형: Repulsion-Start Induction-Run"]
        R4["📈 Start Current: 3-5x FLC"]
        R5["⚠️ Status: OBSOLETE"]
        R6["✅ Pros: High Power, High Torque"]
        R7["❌ Cons: Brushes, Low Efficiency"]
        R8["🎯 Best For: Legacy Equipment Only"]
    end
    
    style Mobile1 fill:#ffebee,행정:#b71c1c,스트로크 폭:3px

Mobile Card 2: Written-Pole Motor (Quick Facts)

graph TD
    subgraph Mobile2["📱 WRITTEN-POLE MOTOR - QUICK FACTS"]
        direction TB
        W1["📅 Era: 1990s-Present"]
        W2["⚡ 힘: 1-50 HP"]
        W3["🔧 유형: Synchronous with Written Poles"]
        W4["📈 Start Current: 2-3x FLC"]
        W5["✅ Pros: Grid-Friendly, Low Maintenance"]
        W6["❌ Cons: Higher Cost, Fixed Speed"]
        W7["🎯 Best For: Weak Grids, Critical Loads"]
    end
    
    style Mobile2 fill:#e8f5e8,stroke:#1b5e20,stroke-width:3px

Mobile Card 3: VFD + Phase Converter (Quick Facts)

graph TD
    subgraph Mobile3["📱 VFD + PHASE CONVERTER - QUICK FACTS"]
        direction TB
        V1["📅 Era: 1980s-Present"]
        V2["⚡ 힘: 1-500+ HP"]
        V3["🔧 유형: Electronic Conversion"]
        V4["📈 Start Current: 1.5-2x FLC"]
        V5["✅ Pros: Variable Speed, Standard Motors"]
        V6["❌ Cons: 화성학, Needs Filters"]
        V7["🎯 Best For: Pumps, Fans, Variable Loads"]
    end
    
    style Mobile3 fill:#f3e5f5,stroke:#4a148c,스트로크 폭:3px

📚 참조 & Further Reading

Standards Organizations

Technical Papers & Articles

Historical References

• 일반 전기. (1910s-1950s). Induction-Repulsion Motor Technical Bulletins. GE Publication Archives.
• Steinmetz, C.P. (1915). Theory and Calculation of Alternating Current Phenomena. McGraw 언덕.
• Behrend, B.A. (1921). The Induction Motor. McGraw 언덕.

Download complete references document 여기에.

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