Pinsala sa THD: Gikan sa Grid Hangtod sa Equipment
Ang impacto sa mga sistema sa kuryente sa harmonic THD errors kinahanglan isipahan gikan sa duha ka aspeto: "actual grid THD nga nagsobra sa limit (excessive harmonic content)" ug "THD measurement errors (inaccurate monitoring)" — ang una direkta nga nagdulot og pinsala sa mga equipment ug estabilidad sa sistema, samtang ang ikaduha nahimong dili maayo nga pagpangandoy tungod sa "false o missed alarms." Kon ipakilid ang duha ka aspeto, mas mapasabot ang mga risks sa sistema. Ang impacto mahimong mabati sa tanang chain sa kuryente — generation → transmission → distribution → consumption — naaapektuhan ang seguridad, estabilidad, ug ekonomiya.
Core Impact 1: Direct Harm of Excessive Actual THD (High Harmonic Content)
Kon ang grid THDv (voltage total harmonic distortion) gibabaw sa national standards (≤5% para sa public grids) o ang THDi (current total harmonic distortion) gibabaw sa tolerance sa equipment (e.g., transformers ≤10%), nagdulot kini og pisikal nga pinsala sa system hardware, operational stability, ug end-user equipment.
Transmission Systems: Increased Losses and Overheating
Increased Copper Losses: Ang harmonic currents magdudulot og "skin effect" sa transmission lines (e.g., 110kV cables), nagconcentrate ang high-frequency currents sa surface sa conductor, nagpadayon sa resistance ug copper losses uban ang harmonic order.
Example: Kon ang THDi mumataas gikan sa 5% hangtod sa 10%, ang line copper losses mumataas ngadto sa 20%-30% (calculated via I²R). Sa pagpatag sa operasyon, mumataas ang temperatura sa conductor (e.g., gikan sa 70°C hangtod sa 90°C), nag-accelerate ang aging sa insulation ug nagsunod sa pagshorten sa line life (gikan sa 30 hangtod sa 20 years).Worsened Voltage Sag: Ang harmonic voltages superimpose sa fundamental voltage, distorting waveforms sa load ends. Ang sensitive users (e.g., semiconductor plants) mahimong mogamit og shutdown sa equipment tungod sa irregular voltage, na ang single incident magdulot og hundreds of thousands.
Distribution Equipment: Overheating, Damage, and Reduced Lifespan
Transformer Failure Risks:
Ang harmonic currents mag-increase sa "additional iron losses" (eddy current losses rise with the square of harmonic frequency). Sa THDv=8%, ang transformer iron losses mumataas ngadto sa 15%-20% kon ihap sa rated conditions, nagpadayon sa core temperature (e.g., gikan sa 100°C hangtod sa 120°C), nag-accelerate ang degradation sa insulation oil, potentially causing partial discharge or burnout (e.g., a substation lost a 10kV transformer due to excessive 5th harmonic, with direct losses over one million).
Unbalanced three-phase harmonics also increase neutral wire current (up to 1.5× phase current), risking neutral overheating and breakage, leading to three-phase voltage imbalance.Capacitor Bank Resonance Damage:
Ang capacitors adunay low impedance sa harmonics, easy na makabuo og "harmonic resonance" sa grid inductance (e.g., 5th harmonic resonance can cause capacitor current to reach 3–5× rated value), resulting in insulation breakdown or explosion. One industrial workshop damaged three 10kV capacitor banks within a month due to 7th harmonic resonance, with repair costs exceeding 500,000.
Generation Equipment: Output Fluctuations and Efficiency Drop
Synchronous Generator Output Limitation:
Ang grid harmonics back-feed into generator stator windings, creating "harmonic torque," increasing vibration (speed fluctuation ±0.5%), reducing output (e.g., a 300MW unit drops to 280MW at THDv=6%), and raising stator temperature, affecting generator lifespan.Renewable Inverter Grid-Connection Failure:
PV/wind inverters are sensitive to grid THD. If point-of-connection THDv > 5%, inverters trigger "harmonic protection" and disconnect (per GB/T 19964-2012), causing renewable curtailment (e.g., a wind farm lost over 100,000 kWh in one day due to excessive 3rd harmonic).
Control Systems: Maloperation Leading to System Faults
Relay Protection Misoperation:
Ang harmonic currents magdudulot og transient saturation sa current transformers (CTs), leading to inaccurate sampling sa overcurrent o differential protection. For example, superimposed 5th harmonic current distorts secondary CT current, causing overcurrent protection to falsely detect "line short circuit" and trip, resulting in widespread outages (e.g., a distribution network experienced 10 feeder trips due to THDi=12%, affecting 20,000 households).Automation System Communication Interference:
Ang harmonics couple electromagnetically into control communication lines (e.g., RS485, fiber), increasing data error rates (from 10⁻⁶ to 10⁻³), delaying or corrupting dispatch commands (e.g., a "trip fault line" command fails to deliver, expanding the fault).
End-User Equipment: Performance Degradation and Frequent Failures
Industrial Motor Overheating and Burnout:
Asynchronous motors under harmonic voltage generate "negative sequence torque," causing speed fluctuations, increased vibration, and higher stator copper losses. At THDv=7%, motor efficiency drops by 5%-8%, temperature rises by 20–30°C, and lifespan is halved (e.g., a steel plant burned two rolling mill motors within six months due to 7th harmonic, with repair costs over 2 million).Precision Equipment Accuracy Loss:
Sensitive equipment like semiconductor lithography machines and medical MRI systems require extremely clean voltage (THDv≤2%). Excessive THDv increases measurement errors — e.g., a lithography machine’s etching precision drops from 0.1μm to 0.3μm due to voltage harmonics, reducing product yield from 95% to 80%.
Core Impact 2: Indirect Risks of THD Measurement Errors (Inaccurate Monitoring)
Ang THD measurement errors (e.g., actual THDv=6%, measured as 4%, error = -2%) lead to "false compliance" or "over-treatment," exacerbating risks or causing economic waste — essentially, "data distortion leading to poor decisions."
Missed Detection of Excess: Delayed Mitigation, Escalated Harm
If measured THD is lower than actual (e.g., actual THDv=6%, measurement error -1%, displayed as 5%), it falsely indicates "harmonic compliance," delaying filter installation (e.g., APF). This allows long-term harmonic accumulation:
Short-term: Accelerated aging and higher failure rates of transformers, capacitors, etc.
Long-term: Risk of system resonance, potentially causing regional grid collapse (e.g., a regional grid experienced resonance after two years due to missed 3rd harmonic detection, resulting in 5 substations offline).
False Alarm of Excess: Over-Investment, Wasted Costs
If measured THD is higher than actual (e.g., actual THDv=4%, measurement error +1%, displayed as 5%), it falsely indicates "harmonic excess," leading to unnecessary filter installation:
Economic waste: A 10kV/100A APF costs ~500,000; if no mitigation is needed, the equipment sits idle (with annual maintenance of 20,000).
System disturbance: Excess filters may create new resonance points (e.g., installing a 5th harmonic filter triggers 7th harmonic resonance), introducing new risks.
Data Distortion: Affects Grid Planning and Dispatch
THD measurement errors distort harmonic distribution data, impacting long-term planning:
Example: A region’s monitoring shows average THDi=8% (actual 6%), leading to over-provisioning of harmonic mitigation capacity (building 2 extra filter stations, investment over 10 million).
In dispatch, inaccurate THD data prevents precise harmonic source identification (e.g., wrongly blaming a PV plant, limiting its output), affecting renewable energy integration.
Core Impact 3: Economic Loss — From Direct Costs to Indirect Losses
Harmonic THD errors (including excess and measurement inaccuracies) cause significant economic losses through equipment damage, increased energy consumption, and production downtime, quantifiable in three cost categories:
| Loss Type | Specific Performance | Quantification Example (Taking a 10kV Industrial User as an Example) |
| Direct Equipment Cost | Burnout/replacement of equipment such as transformers, capacitors, motors | When THDv=8%, the annual equipment replacement cost increases by 5-20 million yuan (calculated based on 2 transformers + 3 sets of capacitors) |
| Additional Energy Consumption Cost | Increase in copper loss/iron loss of lines and transformers | When THDi=10%, the annual additional electricity consumption increases by 100,000 - 500,000 kWh (calculated based on an annual electricity consumption of 10 million kWh and an electricity price of 0.6 yuan/kWh, the annual additional electricity fee is 60,000 - 300,000 yuan) |
| Production Stop Loss | Shutdown of sensitive equipment and interruption of production lines | A semiconductor factory’s lithography machine shuts down for 1 hour due to harmonics, resulting in a loss of wafer output value exceeding 500,000 yuan |
Summary: The Core Impact Chain of THD Errors on Power Systems
The fundamental impact of harmonic THD errors follows a cascading chain: "waveform distortion → equipment damage → system instability → economic loss." Measurement errors act to amplify or misjudge this chain:
Excessive actual THD is the "primary hazard", directly damaging power system hardware and compromising stability;
THD measurement error is the "decision interference", leading to improper mitigation—either worsening risks or wasting resources;
Ultimately, both lead to safety risks (equipment burnout, system collapse) and economic losses (repair costs, energy waste, production downtime).
Therefore, power systems must adopt a dual approach: "precise monitoring (controlling THD measurement error ≤ ±0.5%) + effective mitigation (keeping actual THDv below 5%)" to comprehensively avoid these risks.
