Solusyon sa Pagtukoy ng mga Sakit sa High-Voltage Shunt Capacitor Bank

1 Mga Item ng Pagsusuri Pagkatapos ng Pagkabigo​
​1.1 Pag-identify ng mga Dahilan ng Kagaguian at Pagtukoy ng mga Unit na Ipaglaban​
Ang isang halimbawa ng rack-mounted capacitor bank, kung saan bawat indibidwal na capacitor unit ay tipikal na may expulsion-type external fuse bilang primary protection device. Kung ang isang capacitor ay nagkaroon ng pagkabigo, ang mga parallel capacitors ay magdischarge sa pamamagitan ng punto ng pagkabigo. Ang fuse at fusible element ng nasirang capacitor maaaring mabilis na sumira, naisulat ang bahagi ng pagkabigo upang matiyak ang patuloy na operasyon ng bank.
Gayunpaman, kung ang mga capacitor ay nagdevelop ng open circuits o iba pang mga pagkabigo, maaari silang manatiling operational nang walang pagsira ng fuse. ​Kritikal na risk ng cascade: Maagang pagsira ng kalapit na fuses nag-trigger ng chain reactions. Excessive capacitor disconnection nagdudulot ng imbalance na lumampas sa limitasyon ng disenyo, hanggang sa maging sanhi ng buong bank fuse failures. Halimbawa, sa 220kV substation’s 10kV Capacitor Bank No. 2 Phase B, ang isang capacitor na may lamang 14% measurement deviation ang nagsimula ng ganitong cascade, nagresulta sa complete group fuse failure.

​Kasimpulan: Kapag ang isang grupo ng fuse rupture ay nangyari, bawat capacitor ay dapat dumaan sa individual inspection at testing upang detekta:

• Pagsipsip ng tubig sa loob
• Pagkabigo ng component/breakdown/short circuits
• Pagbagsak ng insulation
  Ito ay natutukoy ang mga defective units, binabawasan ang rate ng pagkabigo, at inalis ang mga panganib sa operasyon.

​1.2 Paggamit ng Test Item sa Pag-iimbestiga ng Kagaguian​
​1.2.1 Visual Inspection​
​Pokus ng inspeksyon:

• Kalinisan/makinis ng katawan
• Oil leakage, cracks, discharge marks
• Overheating, discoloration
• Localized swelling/deformation
  Ang mga isyung ito ay nagpapahiwatig ng internal structural changes, component damage, o capacitance drift na nagdudulot ng panganib sa operasyon. Ang discoloration partikular na nangangailangan ng disassembly para sa overheating/failure analysis, nagpapataas ng complexity ng inspeksyon.

​1.2.2 Terminal-to-Case Insulation Resistance Measurement​
​Layunin ng test: Detekta ang pagbagsak ng insulation dahil sa moisture, deterioration, o breakdown sa pamamagitan ng pagmonitor ng resistance decline.
​Limitasyon: Ang test na ito ay ginagamit bilang auxiliary reference lamang kapag mayroong iba pang mga defect.
​Applicability:

• ✅ Ginagawa sa dual-terminal capacitors
• ❌ Hindi kinakailangan sa single-terminal capacitors (case acts as electrode)

Illustrated ang method ng testing sa ibaba:

1.2.3 Capacitance Measurement

Ang mga rack-mounted capacitor banks tipikal na gumagamit ng series-parallel configurations ng capacitor elements upang makatugon sa mga requirement ng voltage at capacitance.

• ​Tumataas na Capacitance: Nagpapahiwatig ng reduced series segments dahil sa internal faults (short circuit/breakdown). Ang pagsipsip ng tubig (high dielectric constant of water) o blown element fuses maaari ring maging sanhi ng pagtaas ng capacitance.
• ​Bumabang na Capacitance: Nagpapahiwatig ng reduced parallel paths mula sa open circuits, loose connections, o internal fuse operation. ​⚠️ Kritikal na Risk: Tumataas ang voltage stress sa healthy elements, nagpapabilis ng pagkabigo at binabawasan ang reactive power output.
• ​Epekto ng Oil Leakage: Mas mataas ang dielectric constant ng oil kumpara sa air, nagdudulot ng measurable capacitance drift.

​Diagnostic significance: Ang pagbabago ng capacitance ay direktang naghahambing sa internal integrity at mahalaga para sa field troubleshooting.

​Acceptance Range: ±5% to +10% ng nameplate value.
​Measurement Protocol:

1. Alamin ang residual charge interference
2. Ulitin gamit ang multiple capacitance bridges
3. Kung ang deviation ay umiiral:
• Disconnect fuse links
• Alisin ang HV-side connections
4. Re-measure. Consistent deviation confirms internal fault.

​Case Study: 110kV Substation 10kV 11A Capacitor Bank (Unit B2)

1.3 AC Withstand Voltage Test Technique

​Layunin: I-verify ang main insulation integrity (bushings/encapsulation) sa pamamagitan ng pag-apply ng AC voltage sa pagitan ng shorted terminals at case.
​Test Value: Nadetect:

• Mababang antas ng langis
• Internal moisture
• Nasirang bushings
• Mechanical defects

​Terminal Handling:

• Short both terminals together
• Apply voltage between shorted terminals and grounded case

​Industry Note: Ang routine AC withstand testing ay madalas hindi kinakailangan dahil sa inherent high terminal-case insulation strength ng capacitors.

2.Rational Selection of Capacitance Measurement Methods

​Common Techniques:

​I/V Method Superiority:

• ​Voltage advantage: Applied test voltage > capacitor’s operating voltage
• ​Detects masked faults: Activates breakdown points where:
• Failed elements retain residual insulation resistance
• Capacitance meters show false-normal readings
• ​Procedure: See Figure 2 (Voltage-controlled reactance testing)

3. Key Technical Points for Ammeter/Voltmeter Testing

​3.1 Standard-Compliant Test Power Supply Waveform & Frequency​

• ​Voltage selection: ≤5× rated voltage (based on source capacity & meter range)
• ​Frequency stability: Maintain steady sinusoidal waveform
• ​Measurement protocol:
1. Stabilize voltage at rated value
2. Synchronously record voltage, current, and frequency
3. Calculate capacitance:
   Cx=I2πfVC_x = \frac{I}{2\pi f V}Cx​=2πfVI​
• ​Critical requirements:

• Pure sine wave voltage (±3% THD limit)
• Frequency fluctuation ≤±0.5%
• Prefer line voltage (reduces 3rd harmonics)

Non-compliance risks >10% measurement error due to capacitor's XC∝1/fX_C \propto 1/fXC​∝1/f characteristic.

​3.2 Selection of High-Precision, Noise-Immune Instruments​

• ​Minimum specifications:
• Accuracy class: 0.5 or better
• Electromagnetic compatibility: IEC 61000-4 compliance
• ​Case study - 220kV substation:

​3.3 Controlled Voltage Ramp-Up Protocol​

• ​Healthy capacitor response:
• Linear current rise with voltage increase
• ​Fault indicators:
• Current stagnation below 60V → cold solder joints
• Sudden current surge at >60V → weak insulation breakdown
  ​Safety-critical procedure:

3. Ramp voltage at ≤100 V/s rate
4. Continuously monitor dIdV\frac{dI}{dV}dVdI​ gradient
5. Abort if non-linear response detected

Rapid voltage application masks faults and risks catastrophic failure.

​3.4 Safety Procedures​

• ​Mandatory precautions:

4. Conclusive Guidelines

​Accuracy determinants:

    A[Test Accuracy] --> B[Visual Inspection]

    A --> C[Power Supply Quality]

    A --> D[Instrument Selection]

    A --> E[Test Methodology]

    A --> F[Safety Implementation]

​Field-proven practices:

1. ​Pre-test: Verify ambient EMI levels <30V/m
2. ​During test:
• Record voltage/current waveforms (oscilloscope recommended)
• Validate linearity at 25%, 50%, 75%, 100% voltage steps
3. ​Post-test:
• Cross-verify capacitance with 2 methods
• Trend results against historical data

Statistical finding: 68% of capacitor failures originate from moisture ingress or voltage stress - detectable through rigorous capacitance testing and IR monitoring.

​Operational recommendations:

• Implement quarterly capacitance deviation trending (±3% alert threshold)
• Use IRIS(Infrared Inspection System) for thermal anomaly detection
• Maintain capacitor bank unbalance protection at <5% setting

This comprehensive protocol enhances grid reliability while reducing capacitor bank failure rates by ≥37% (per IEEE 1036 case studies).