Our Services

1. Offline Testing (Cable De-energized)

These tests require the cable to be taken out of service.

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A. Insulation Resistance (IR) Test

• Uses a megohmmeter (Megger)
• Measures resistance between conductor and ground
• Indicates gross insulation problems
• Quick but not very diagnostic for aging

B. Very Low Frequency (VLF) Testing

• Applies AC voltage at ~0.1 Hz
• Used for:
  • Withstand testing
  • Tan Delta (dissipation factor) measurement
• Common for medium-voltage cables (e.g., 11 kV, 33 kV)
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C. Tan Delta (Dissipation Factor) Test

• Measures dielectric losses
• Detects:
  • Water trees
  • Insulation aging
  • Contamination
• Widely used for XLPE cables

D. Partial Discharge (PD) Testing – Offline

• Detects localized insulation defects
• Identifies:
  • Voids
  • Cracks
  • Termination/joint defects
• Can pinpoint defect location with time-domain reflectometry

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2. Online Testing (Cable Energized)

Performed while the cable is in service.
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A. Online Partial Discharge Monitoring

• Uses:
  • HFCT (High-Frequency Current Transformers)
  • TEV sensors
• Continuous or periodic monitoring
• Ideal for critical feeders

B. Thermal Imaging

• Uses infrared cameras
• Detects:
  • Hot joints
  • Poor connections
  • Overloading
• Often used in substations

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3. Diagnostic vs Withstand Testing

Modern best practice favours diagnostic testing (PD, Tan Delta) over purely withstand testing.

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4. Typical Test Selection by Cable Type

XLPE Cables

• VLF Tan Delta
• Offline PD
• Sheath testing

PILC (Paper Insulated Lead Covered)

• DC testing (limited use now)
• Tan Delta
• PD testing

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5. Additional Specialised Tests

• Sheath Integrity Testing – Detects jacket damage
• Time Domain Reflectometry (TDR) – Locates faults
• Dielectric Spectroscopy (FDS) – Detailed insulation analysis

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