Analiz na Bi 10kV SF₆ Ring Main Unit Faalawa da Testin Zan Iya Tafiya

Ana ɗi Biyu 10kV SF₆ Ring Main Unit Failures da Live Testing​

​1 Bayanin 10kV SF₆ Ring Main Units​
A 10kV SF₆ ring main unit (RMU) tana da gas tank, an operating mechanism compartment, da kuma cable connection compartment.

• ​Gas Tank: Wani abu mai muhimmanci, wanda yake da load switch busbar, switch shaft, da SF₆ gas. An load switch ya shafi hanyar switch na biyu, wadanda suka da isolating blade da arc-extinguishing shield.
• ​Operating Mechanism Compartment: An operating mechanism ya haɗa zuwa load switch da grounding switch ta hanyar switch shaft. Ana iya saka operating rod zuwa access hole don in yi closing, opening, ko grounding operations. Saboda haka ba a fahimta switch contacts ba, ana amfani da position indicator da take haɗa zuwa shaft don in nuna yadda ake kara load da grounding switches a lokacin. Mechanical interlocks bayan load switch, grounding switch, da kuma front panel suna daidaito a yi "five preventions" safety requirements.
• ​Cable Connection Compartment: Yana cikin RMU don in yi karin cable connection. Cable terminations sun amfani da touchable ko non-touchable live silicone rubber cable accessories don in haɗa zuwa RMU’s insulating bushings.

​2 Ana ɗi Biyu 10kV SF₆ Ring Main Unit Failures​
​2.1 SF₆ Gas Leakage Failure​
An yi ƙasa ɗaya ɗaya 10kV line saboda abu mai zafi. An samu da ɗaukan yanayi daga Yangmeikeng RMU. Ba da kusa ƙwarewa, #2 switch cable terminal an yi jiragen, da gas an yi ƙwarewa daga tank. Idan an yi ƙaramin elbow connector, an samu cewa double-ended stud for bushing installation bai da shiga tsari a lug hole, wanda ya faɗa lalacewar da gine da bushing da ya yi cracking a root.
Wannan nau'o'i na ƙwarewa gas tank-to-terminal interface da SF₆ leakage yana faru a cable terminals saboda babban rike, wanda ya yi cracking gas tank-to-terminal interface da SF₆ leakage. Kuma abubuwa masu sayayi da aka yi a dukkar tana iya faɗa ƙwarewa.

​2.2 Cable Termination Failure in RMU​
A lokacin da ake yi routine inspection, an samu da ƙwarewa a 10kV RMU cabinet door, wanda ya nuna discharge. Four-unit RMU’s fourth unit ita ce spare. Post-outage inspection an samu da discharge mai yawa a second and third units:

• ​Unit 2: Phase C stress cone an samu da discharge marks da blackening a wall of the cabinet.
• ​Unit 3: Phase B cable elbow an samu da discharge burns.
  Disassembly an samu cewa:
• ​Unit 2: Stress cone an yi jiragen, entirely below the cable semiconductive break. Poor contact at both ends caused electric field concentration, leading to breakdown and discharge against the cabinet.
• ​Unit 3: An amfani da outdoor cable lug (smaller size) instead of the original. Spacers were illegally inserted between the lug and bushing copper core, causing poor contact and overheating. An oversized elbow failed to seal the stress cone, allowing moisture ingress, insulation degradation, and tracking.
  Cable termination quality is crucial in compact RMUs. Substandard conductor, shielding, or semiconductive layer treatment reduces creepage distance, risking breakdown. Strict quality control during termination minimizes failure risks.

​3 Live Testing Analysis​
​3.1 Live Testing Findings​
A Oktoba, partial discharge (PD) testing on 10kV RMUs detected abnormally high signals (TEV ≈18dB, AE ≈20dB) in units from one manufacturer. Subsequent tests on 15 units revealed similar discharges in 7. Observation windows showed tracking marks on cable terminations, with T-heads exhibiting burns. Disassembly confirmed severe discharge damage:

• Surfaces of plugs, surge arresters, epoxy bushings, and seals showed tracking burns.
• Loose interfaces between plugs and seals allowed moisture ingress, corroding metal parts and degrading insulation.
  After replacing components, PD levels returned to normal.

​3.2 Testing Methodology Summary​
PD assessment combines "listening," "smelling," "observing," and "testing":

• ​Preparation: Verify equipment safety, calibrate PD instruments, and cross-check system IDs.
• ​Preliminary Checks:
• Monitor gas pressure.
• Listen for abnormal sounds (if present, evacuate and report).
• Smell for burnt odors before opening doors.
• Visually inspect via windows: tree-like discharge traces on T-heads or white melting on insulation plugs indicate faults.
• ​Testing Procedure:
  ① Measure background TEV on non-energized metal doors to gauge overall PD levels.
  ② TEV testing: Press sensors firmly against metal doors; locate PD sources by signal attenuation.
  ③ AE testing: Scan door gaps.
• ​Result Criteria (Shenzhen Utility Standard)​:

​4 Conclusion​
Key insights:
① SF₆ RMUs are increasingly deployed at critical nodes in distribution networks due to their advantages.
② 10kV SF₆ RMU failures often stem from poor cable termination craftsmanship. Rigorous quality control, on-site supervision, and pre-commissioning tests are essential to reduce faults.
③ Live PD testing enables non-disruptive health assessments, facilitating defect mitigation and minimizing outage risks.