Tadacin ƙarshen kasa na turancin jama'a mai tsarki da ke 35 kV

Mutuwar da tsakiyar (PTs) suna da kofin feri da kofin kirkiro, wadanda suke yi aiki a matsayin mutuwar da tsakiyar amma da sarrafa yau. Suke kawo tasirin mafi girma zuwa mafi gadi don hanyar inganci, cutar da kuma bayyana ayyukan abubuwan sauran, tare da masu aikinsa a kan wurare/wurare. An sanya da kyau saboda hanyoyin kwalbar: na fata (≤6 kV), na kasa (indoor 3 - 35 kV), na taili (outdoor ≥35 kV), da gas SF₆ (don abubuwan da suka haɗa).

A lokacin da aka yi aiki a wuraren, ana iya samun nasarorin daga resonance da kuma kwalbar da take yaɓe. Misali, a Watan Maris 2015, an yi shiga ɗaya 35 kV PT mai karfin magunguna saboda kwalbar da take yaɓe, wanda ya ba ƙarin ɗaya 35 kV Bus I & II. Bincike a cikin ƙasar:

1 Aiki a Kafuwar Gara

Hali na systemen bayan gara ta shahara a Figure 1.

An kawo takarda ne a wuraren da biyu ɗaya 35 kV (Jingdian 390 Line, Jingre 391 Line). An yi shiga su, suke kawo zuwa 35 kV Section I & II busbars. Waɗannan busbars suna da wiring na kasa. Arziki masu juyin magungunan; babu juyin da ke cika a karkashin magungunan. Rukunin takarda:

• 35 kV Section I busbar → 3# main transformer → 10 kV Section I busbar.

• 35 kV Section II busbar → 4# main transformer → 10 kV Section II busbar.

• 10 kV Section I & II busbars run in parallel.

2. Bincike a Cikin Ƙasar & Tabbacin Gara

Masu aiki/masana'antu suka samun labaran shiga:

• 35 kV Jingdian 390 Line-side PT3: Yana nemo tasirin Phase A/B line. An yi shiga karshe, akwai lalace.

• 35 kV Jingdian 390 Line Incoming Switch: Tasirin current da ke shiga ya yi shiga. Akwai lalace a fata-fata, maɗaɗin kasa suka yi shiga.

2.1 Binciken Tasirin 35 kV Section II Busbar

An kawo data fault recording 35 kV Section II busbar don kawo tasiri, waveforms, da electrical parameters a lokacin gara. Binciken data mai daidai yana ba da damar gara, tare da dalilai muhimmanci don tabbatar da sababin gara.

2.2 Tabbacin Gara & Binciken Electrical
(1)Tasirin Tsari Daga Gara

• 19.6ms daga gara: 35kV Section II busbar ta da tasirin uku na gida, zero-sequence voltage mafi gadi → abubuwan da suke daidai.

• 13.6ms daga gara: Tasirin Phase A/B ta zama 49.0V/43.1V; Phase C ta zama 71.8V; zero-sequence voltage ta zama 22.4V → kwalbar da PT yaɓe.

• 1.6ms daga gara: Tasirin Phase A/B ta zama 11.9V/7.4V; Phase C ta zama 44.5V; zero-sequence voltage ta zama 23.5V → kwalbar da yaɓe yana ci.

 (2)Gara & Hanyar Inganci

A lokacin gara: Kwalbar da Phase A/B yaɓe (short to ground); tasirin Phase C ta zama. 3ms later, tasirin uku ta zama zero; PT ta yi shiga → an tabbatar da shi a matsayin three-phase short-circuit to ground.

Bayani: Tasirin busbar daga gara ta daidai (babu lightning/misoperation → resonance overvoltage excluded). Amfani da lokaci mai tsari ya yi kwalbar da PT → kwalbar da take yaɓe a cikin → inter-turn short circuit → an yi shiga zuwa three-phase insulation breakdown/short-circuit → line tripped.

(3)Hanyar Inganci & Hanyar Inganci

Incoming line switches (Jingdian 390, Jingre 391) babu incoming protection. Main station has protections with identical settings:

• Differential protection: 5A setting, 0s operation.

• Time-limited quick-break protection: 21.2A setting, 1.1s operation.

• Over-current protection: Further analysis needed (ref. Figure 2 for incoming current recording data, not provided).

Ba gara, currents a duk waɗannan lines suka ƙare. Ba transients, suke zaune zuwa steady-state:

• 35 kV Jingdian 390 Line: 14,116 A (steady-state primary fault current);

• 35 kV Jingre 391 Line: 10,920 A (steady-state primary fault current).

Hanyar inganci:

• Jingdian 390 Line (remote main station side): Differential protection tripped 268 ms post-explosion. Fault not isolated as 35 kV Sections I & II busbars were looped.

• Jingre 391 Line (remote main station side): Time-limited quick-break protection tripped 1,173 ms post-explosion, isolating the fault.

3 Binciken Sababtaka & Hanyoyin Da Nake So

The fully-insulated electromagnetic voltage transformer, commissioned in 2008, had no outage maintenance/electrical tests. Long-term operation caused internal insulation failure. Key causes:

• Product Defects: Substandard design → insufficient insulation, short service life.

• Environmental Contamination: Dirt on porcelain sleeves → sharp insulation resistance drop in rainy seasons, flashovers, and long-term insulation damage.

• Insulating Oil Deterioration: Poor sealing → moisture ingress, electric field distortion, reduced oil withstand voltage/dielectric properties.

• Aging & External Impacts: Thermal aging (ambient conditions, long-term use); mechanical aging (switching overvoltage, short-circuit currents damaging insulation).

3.2 Binciken Kwalbar Da Yaɓe

Regular insulation resistance tests prevent failures:

• Primary Winding: Use 2,500 V meter during handover/overhaul → insulation resistance ≥ 3,000 MΩ. In preventive tests, resistance drop ≤ 50% of initial value.

• Secondary Winding: Use 1,000 V meter during handover/overhaul → insulation resistance ≤ 10 MΩ.

3.3 Common Fault: Resonance Overvoltage
Conditions for Occurrence :

• Electromagnetic voltage transformers are nonlinear inductors. Excitation current increase causes ferromagnetic saturation → inductance drop (main resonance cause).

• Resonance requires matched capacitance/inductance (inductive reactance ≤ 100× capacitive reactance).

• Trigger conditions: no-load bus switching, sudden ground-fault clearance, lightning, switching overvoltage, etc.

Preventions: Ground voltage transformer neutrals via harmonic eliminators + small resistors; install harmonic elimination devices at bus voltage transformer open deltas.

4. Bayani

Kwalbar da yaɓe a voltage transformers yana ba da gara da bus outages – common in grids. Follow preventive test regulations strictly, test/replace unqualified equipment. In this accident, unprotected thermal power plant incoming lines and failed #1 35 kV bus tie switch widened the fault. Regularly check protection configuration/reliability. Accident analysis helps quickly identify issues, take targeted actions, reduce fault risks, and boost substation reliability.