Induction furnaces are notorious “ผู้ก่อปัญหา” in industrial power grids. As typical non-linear loads, balancing melting efficiency with grid “สุขภาพ” is a constant battle for electrical engineers and facility managers.
Equipment Interference & Invisible Losses
Core Pain Point: Why is the transformer overheating even when not fully loaded? Why do the CNC machines in the adjacent workshop alarm for no apparent reason?
Mechanism of Harmonic Generation
The core of an induction furnace power supply lies in the การแก้ไข (AC to DC) และ การผกผัน (DC to AC) stages. When high-power Thyristors (เอสซีอาร์) or IGBTs perform high-frequency switching, the current waveform distorts. It ceases to be a standard sine wave, generating high-order harmonics (primarily 5th, 7th, 11th, and 13th orders).
The Damage Caused
- Transformer Overheating: High-frequency harmonic currents cause severe ผลกระทบต่อผิวหนัง in conductors, increasing winding resistance losses; they also increase hysteresis and eddy current losses in the iron core.
- Capacitor Explosions: If the factory’s compensation capacitor bank forms a Parallel Resonance with the system inductance at a specific harmonic frequency, voltage and current can amplify several times over, leading to capacitor breakdown or explosion.
- ความแม่นยำ Instrument Failure: Harmonic voltage interferes with zero-crossing detection in control circuits, causing CNC controllers, PLC, or relays to malfunction.
สารละลาย: Filter Selection
| สารละลาย | หลักการ | ข้อดี | ข้อเสีย | Applicable Scenario |
| Passive Filter | Uses Inductors (L) & ตัวเก็บประจุ (C) in series to form a low-impedance path for specific frequencies (เช่น, 5th, 7th). | Low cost, mature technology, simple structure. | Can only filter specific frequencies; susceptible to grid impedance; resonance risk exists. | Traditional factories with stable loads and limited budgets. |
| Active Power Filter (เอพีเอฟ) | Detects harmonic components in load current and injects a compensation current of equal amplitude but opposite phase. | Dynamically filters various frequencies; no resonance risk; ตอบสนองอย่างรวดเร็ว (microseconds). | Higher cost, relatively higher power consumption. | Modern factories requiring high power quality (containing sensitive CNC equipment). |
Reactive Power Compensation
Core Pain Point: ที่ “Power Factor Surcharge” (penalty) on the monthly electricity bill remains high, and transformer capacity seems insufficient.
The Root of Low Power Factor
Induction furnaces utilize electromagnetic induction for heating, meaning the load is essentially a massive Inductive Coil. Inductive loads cause current to lag behind voltage, generating significant Reactive Power (ถาม).
เพาเวอร์แฟกเตอร์ (พีเอฟ) = cosΦ = P (คล่องแคล่ว) / ส(Apparent)
If cosΦ is too low (เช่น, 0.6), it means the transformer is outputting a large amount of Apparent Power S, but performing very little useful Work P.
Compensation Strategy: Capacitor Banks
Capacitor banks connected to the busbar provide leading capacitive current to offset the lagging inductive current from the furnace.
- Avoid Penalties: Raising the power factor to above 0.95 directly eliminates utility fines and may even qualify for incentives.
- Release Transformer ความจุ:
- Case: A 2000kVA transformer with PF=0.6 can only support a 1200kW load.
- Improved: With PF=0.95, the same transformer can support a 1900kW load.
- บทสรุป: Compensating reactive power effectively adds “free” capacity to the transformer without requiring expensive upgrades.
บันทึก: In systems with severe harmonics, ธนาคารตัวเก็บประจุ with Series Reactors (detuned reactors) จะต้องถูกใช้. Otherwise, harmonic currents will surge into the capacitors, causing damage.
High-Current Transmission
Core Pain Point: The flexible connection cables (สายเคเบิลระบายความร้อนด้วยน้ำ) connecting the power cabinet to the furnace body are the highest failure zones. A break here means immediate production stoppage.
โครงสร้าง & อันตราย
Water-cooled cables typically consist of stranded copper wires with a central cooling water channel, wrapped in a rubber hose. They act as the “umbilical cord” of the เตาเหนี่ยวนำ, transmitting thousands or even tens of thousands of Amperes.
Common Failure Modes & การป้องกัน
- Broken Strands & Overheating (ความเหนื่อยล้า):
- Cause: Furnace tilting and electromagnetic vibration cause fatigue fracture of copper strands. Once broken, the effective cross-section decreases, resistance increases, leading to overheating.
- การป้องกัน: Measure DC resistance regularly. If the resistance of a cable increases by 10-15% compared to a new one, replace it immediately.
- Water Blockage:
- Cause: Poor water quality leads to scaling, reducing water flow and causing copper strands to burn out due to poor heat dissipation.
- การป้องกัน: Must use a closed-loop system with pure/distilled water and periodically back-flush the cable water lines.
- Friction & Shorting:
- Cause: Under high current, cables generate immense Lorentz Forces, causing them to swing violently and strike each other, wearing down the insulation.
- การป้องกัน: Use insulating spacers to fix and separate cables, and install abrasion-resistant outer sheaths (such as fireproof canvas).
