Uhaba wa THD: Kutoka Grid hadi Vifaa
Mfano wa uharibifu wa harmoniki THD kwenye mifumo ya umeme lazima kutathmini kutoka kwa viwango vya mbadala: "THD halisi ya grid zinazozingatia hatari (kivuvi cha harmoniki kinachohesabika)" na "matako katika utafiti wa THD (ujifunzaji usio sahihi)" — chache kwanza unaharibu vifaa vya mfumo na ustawi, na pili inaleta matumizi bila hesabu kwa sababu ya "tafsiri za kosa au kusikia." Wakati wanajumuisha, viwango hivi vinazidi hatari za mfumo. Mfano unafanana na mzunguko wote wa umeme — kuundwa → kutuma → kutambua → kutumia — kuhusu ustawi, ustawi, na uchumi.
Mfano Mkuu 1: Uharibifu Mkuu wa THD Halisi (Kivuvi Kikubwa)
Wakati THDv (ujuzi wa harmoniki wa umeme) unaelekea kiwango cha kimataifa (≤5% kwa mitandao ya umma) au THDi (ujuzi wa harmoniki wa umeme) unaelekea kiwango cha vifaa (mfano, transforma ≤10%), hii huongeza uharibifu wa vifaa vya mfumo, ustawi wa kazi, na vifaa vya watumiaji wa mwisho.
Mifumo ya Kutuma: Zingatia na Kuongezeka
Zingatia Za Copper Za Kiwango Kikubwa: Umeme wa harmoniki huchangia "mtazamo wa ngozi" kwenye mistari ya kutuma (mfano, kabali la 110kV), kufanya umeme wa kiwango kikubwa kuonekana kwenye pembeni la mtaro, kuboresha upinzani na zingatia za copper kwa kiwango cha harmoniki.
Mfano: Wakati THDi inaongezeka kutoka 5% hadi 10%, zingatia za copper zinaongezeka kwa asilimia 20%-30% (hisiwa kwa I²R). Kazi iliyofanyika kwa muda mrefu huchangia majalela ya mtaro (mfano, kutoka 70°C hadi 90°C), kukuza ukosefu wa usafi na kupunguza muda wa kazi (kutoka 30 hadi 20 miaka).Uharibifu wa Umeme Ukubwa: Umeme wa harmoniki huchangia umeme wa msingi, kufanya mizizi yake kukosa kwenye vipimo vya mchakato. Watumiaji wenye hisia (mfano, mashamba ya semiconductors) wanaweza kupata kusita vifaa kwa sababu ya umeme usio sahihi, na tukio moja kunaweza kupata gharama za daraja la elfu.
Vifaa vya Kutambua: Kuongezeka, Uharibifu, na Muda wa Kazi Unapunguza
Hatari za Transforma:
Umeme wa harmoniki huchangia "zingatia za iron za ziada" (zingatia za eddy current zinazoungana kwa mraba wa kiwango cha harmoniki). Wakati THDv=8%, zingatia za iron za transforma zinaongezeka kwa asilimia 15%-20% kulingana na kiwango cha kimataifa, kuboresha joto la core (mfano, kutoka 100°C hadi 120°C), kukuza ukosefu wa mafuta ya usafi, na kutokumbuka kwa kutosha, inaweza kuongeza kuvunjika au kusita (mfano, stesheni moja imepoteza transforma ya 10kV kutokana na harmoniki ya 5th, na gharama zisizodhibiti zaidi ya elfu moja).Uharibifu wa Capacitor Bank:
Capacitors hawana upinzani mdogo kwa harmoniki, kwa urahisi kuunda "resonance ya harmoniki" kwenye inductance ya grid (mfano, resonance ya 5th harmoniki inaweza kuboresha umeme wa capacitor hadi 3–5× kiwango cha kimataifa), kufanya kuvunjika au kusita. Chumba cha biashara moja limeharibu tatu capacitor banks za 10kV kwenye mwezi moja kutokana na resonance ya 7th harmoniki, na gharama za magari zaidi ya 500,000.
Vifaa vya Kutengeneza: Uharibifu wa Mchango na Upunguaji wa Matumizi
Synchronous Generator Output Limitation:
Grid harmoniki hurejesha kwenye windings ya stator ya generator, kufanya "torque ya harmoniki," kuboresha vibra (msingi wa muda wa ±0.5%), kupunguza mchango (mfano, kitengo cha 300MW kumpunguza hadi 280MW wakati THDv=6%), na kuboresha joto la stator, kuhusu muda wa kazi ya generator.Renewable Inverter Grid-Connection Failure:
PV/wind inverters ni wenye hisia sana kwa THD. Ikiwa THDv ya point-of-connection > 5%, inverters hutukia "protection ya harmoniki" na kutoka (kulingana na GB/T 19964-2012), kutoa renewable curtailment (mfano, shamba la wind limempoteza zaidi ya 100,000 kWh kwenye siku moja kutokana na harmoniki ya 3rd).
Mifumo ya Kumiliki: Malfunction Leading to System Faults
Relay Protection Misoperation:
Umeme wa harmoniki huchangia saturation ya kisasa kwenye current transformers (CTs), kufanya sampling isiyosahihi katika overcurrent au differential protection. Mfano, superimposed 5th harmonic current huchangia umeme wa CT wa pili, kufanya overcurrent protection kuamini "line short circuit" na kutoka, kufanya kusita kwa kawaida (mfano, mifumo ya distribution imepata 10 feeder trips kutokana na THDi=12%, kuhusu 20,000 nyumba).Automation System Communication Interference:
Harmoniki huchangia electromagnetically kwenye mistari ya communication ya control (mfano, RS485, fiber), kuboresha gharama za data (kutoka 10⁻⁶ hadi 10⁻³), kutokosea au kuharibu amri za dispatch (mfano, amri ya "trip fault line" haipatikani, kuboresha hatari).
Vifaa vya Watumiaji: Uharibifu na Uharibifu wa Mara Kwa Mara
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)
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.
