SOLUSYON SA PAG-DIAGNOSIS NG MGA SAKIT SA HIGH-VOLTAGE SHUNT CAPACITOR BANK

1 Mga Item ng Pagsusuri pagkatapos ng Pagkabigo​
​1.1 Pagtukoy sa mga Dahilan ng Pagkabigo at Pagtukoy sa mga Unit na Ipaglaban​
Sa isang halimbawa ng rack-mounted capacitor bank, bawat indibidwal na capacitor unit ay karaniwang mayroong expulsion-type external fuse bilang primary protection device. Kung ang iisang 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 ma-breakdown nang mabilis, na nag-iisolate ng bahagi ng pagkabigo upang tiyakin ang patuloy na operasyon ng bank.
Gayunpaman, kung ang mga capacitors ay nagkaroon ng open circuits o iba pang mga pagkabigo, maaari silang magpatuloy sa operasyon nang walang pag-rupture ng fuse. ​Kritikal na panganib ng cascade: Ang maagang pag-rupture ng mga kalapit na fuses ay nag-trigger ng chain reactions. Ang sobrang pag-disconnect ng mga capacitor ay nagdudulot ng imbalance na lumampas sa limitasyon ng disenyo, na sa huli ay nagdudulot ng buong pagkabigo ng mga fuse ng bank. 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, na nagresulta sa buong group fuse failure.

​Kasimpulan: Kapag nagkaroon ng group fuse rupture, kailangan ng bawat capacitor na mag-undergo ng individual inspection at testing upang matukoy:

• Internal moisture ingress
• Component breakdown/short circuits
• Insulation degradation
  Ito ay nakakatukoy ng mga defective units, binabawasan ang rate ng pagkabigo, at inililipat ang mga operational hazards.

​1.2 Piliin ang Mga Item ng Pagsusuri para sa Fault Investigation​
​1.2.1 Visual Inspection​
​Pokus ng inspeksyon:

• Kalinisan/luwagan 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 mga operational risks. Ang discoloration partikular na nangangailangan ng disassembly para sa overheating/failure analysis, na nagdudulot ng mas komplikadong inspeksyon.

​1.2.2 Terminal-to-Case Insulation Resistance Measurement​
​Layunin ng test: Matukoy ang insulation degradation mula sa moisture, deterioration, o breakdown sa pamamagitan ng pag-monitor ng pagbaba ng resistance.
​Limitasyon: Ang test na ito ay ginagamit bilang auxiliary reference lamang kapag may kasama pa ring iba pang mga defect.
​Applicability:

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

Ang paraan ng pagsusuri ay ipinapakita sa ibaba:

1.2.3 Capacitance Measurement

Ang rack-mounted capacitor banks karaniwang gumagamit ng series-parallel configurations ng capacitor elements upang matugunan ang mga requirement ng voltage at capacitance.

• ​Tumaas na Capacitance: Nagpapahiwatig ng bawas na series segments dahil sa internal faults (short circuit/breakdown). Ang moisture ingress (high dielectric constant of water) o blown element fuses maaari ring magdulot ng pagtaas ng capacitance.
• ​Bumabang Capacitance: Nagpapahiwatig ng bawas na parallel paths mula sa open circuits, loose connections, o internal fuse operation. ​⚠️ Kritikal na Panganib: Ang voltage stress sa mga healthy elements ay tumaas, nag-accelerate ng pagkabigo at binabawasan ang reactive power output.
• ​Epekto ng Oil Leakage: Ang mas mataas na dielectric constant ng oil kaysa sa hangin ay nagdudulot ng measurable capacitance drift.

​Diagnostic significance: Ang deviation 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 maraming capacitance bridges
3. Kung ang deviation ay patuloy:
• I-disconnect ang fuse links
• Alisin ang HV-side connections
4. I-re-measure. Ang consistent deviation ay nakukumpirma ng 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: Nakakadetect:

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

​Terminal Handling:

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

​Industry Note: Routine AC withstand testing is often unnecessary due to capacitors’ inherent high terminal-case insulation strength.

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).