Online Partial Discharge Measurement Service

Online Partial Discharge (PD) measurement is the cornerstone of modern predictive maintenance for power systems. It is a specialized, non-intrusive service performed on high-voltage (HV) and medium-voltage (MV) electrical assets—such as switchgear, transformers, and cables—while they remain fully energized and under normal operating load.

Unlike traditional testing methods that require costly shutdowns, this technique detects, locates, and analyzes insulation degradation in real-time. For facility managers looking to move beyond simple visual inspections to a comprehensive Electrical System Assessment, online PD monitoring is the most effective tool available.

Why Is Online PD Measurement Critical?

Drawing from over 20 years of field experience, we observe that Partial Discharge (PD) is the leading cause of long-term insulation failure in HV equipment, accounting for approximately 85% of disruptive switchgear failures. PD is a localized electrical discharge that only partially bridges the insulation between conductors. It is a “cancer” within your electrical system—often silent, invisible, and progressively destructive.

By the time PD becomes audible to the naked ear (crackling) or visible (ozone smell/corrosion), the damage is often irreversible, necessitating emergency replacement. Online PD testing services provide early warning signs, often months or years in advance, shifting your asset management strategy from reactive (fixing after failure) to predictive (fixing before failure).

Strategic Benefits for Facility Management

• Zero Downtime (Business Continuity): The primary advantage is the ability to perform a complete health check without isolating the equipment. Testing is conducted during normal operating hours under actual load conditions. This mirrors the non-intrusive approach of modern Motor Monitoring Solutions.
• Enhanced Personnel Safety: Catastrophic arc flashes often start as undetected PD. By detecting hazardous insulation defects without requiring physical contact with live conductors, we significantly reduce the risk of workplace accidents.
• Data-Driven Maintenance Decisions: The service provides quantitative data (amplitude in dB/pC) and qualitative analysis (PRPD patterns). This allows asset managers to prioritize budgets effectively, similar to how we utilize Energy Monitoring Solutions.
• Compliance and Insurance: Regular non-intrusive testing helps meet requirements for Condition-Based Monitoring (CBM) standards like IEEE 1434 and IEC 60270.

Core Measurement Technologies and Sensor Application

A professional online partial discharge measurement service does not rely on a single “magic wand.” It utilizes a multi-physics approach, combining different detection technologies to identify specific types of discharge phenomena.

1. Transient Earth Voltage (TEV) – For Switchgear

TEV sensors are the industry standard for detecting internal discharge activity within metal-clad switchgear panels. This is essential for maintaining the integrity of Medium Voltage Cabinet Maintenance.

• Target Defects: Internal insulation voids, dry termination faults, breakdown of solid dielectrics in RMUs and switchgear.
• Methodology: The engineer places a magnetic TEV sensor on the outside of the switchgear panel. The magnitude is measured in dBmV.
• Interpretation: A rise of 10dB over the background noise, or readings exceeding 20-29dB, typically indicates developing discharge activity requiring investigation.

2. Airborne Ultrasonic Detection – For Surface Discharge

While TEV detects internal faults, it is effectively blind to surface issues. Surface tracking, arcing, and Corona discharge emit acoustic energy. This technology is often paired with Thermal Scanning Services to provide a complete picture of connection health.

• Target Defects: Surface tracking on polluted insulators, loose mechanical connections causing arcing, and corona discharge on HV bushings.
• Methodology: Scanning air vents, door gaps, and cable boxes. The signal is heterodyned (frequency shifted) into the audible range for the engineer to listen via headphones.

3. High Frequency Current Transformer (HFCT) – For Cables

The HFCT is the most reliable method for assessing the condition of XLPE and PILC cables. It is also a vital technique when assessing grid components like Reclosers.

• Target Defects: Water treeing evolving into electrical trees in XLPE, void discharges in cable joints, and poor workmanship in cable terminations (stress cones).
• Methodology: Non-intrusive clamping on ground wires without disconnecting the ground.

The Service Workflow: A Strict Engineering Protocol

Executing a safe and effective Online PD survey requires more than just handheld equipment; it requires a rigorous procedure to ensure data integrity and personnel safety.

Deep Dive: Interpreting the Data (PRPD & Severity)

The raw value (e.g., 25dB or 500pC) is meaningless without context. The core expertise of an Online Partial Discharge Measurement Service lies in the interpretation of the PRPD (Phase Resolved Partial Discharge) pattern.

Risk Assessment Levels

• 🟢 Acceptable (Green): No significant PD detected. Readings are within background noise levels. Action: Continue routine monitoring.
• 🟡 Investigate (Amber): PD activity detected with stable amplitude. Insulation is degraded but not in immediate danger. Action: Increase monitoring frequency to track trends.
• 🔴 Critical (Red): High-amplitude PD detected with steep repetition rates or clear evidence of arcing. Action: Immediate intervention required. Schedule a planned outage.

Comparing Online vs. Offline Testing

Online and Offline testing are complementary. While offline testing is often part of a major Transformer Station Maintenance shutdown, online testing fills the gap between these major events.

When Should You Schedule a PD Survey?

1. Baseline Survey (Pre-Commissioning): Conduct a survey 24 hours after energizing new equipment to validate installation quality.
2. Before Warranty Expiry: A strategic scan 1-2 months before the manufacturer’s warranty ends allows you to claim replacements for defective assets.
3. Annual Health Check: Integrate into your standard Preventive Maintenance program.
4. Aging Assets (>15 Years): Equipment approaching the end of its design life should be tested more frequently (every 6 months), especially for heavy Transformer lifecycles.

William

Senior Industrial Electrical Specialist

With over 12 years of hands-on experience in the industrial electrical sector, I specialize in delivering optimized technical solutions for factories. My core expertise includes Power System Design, Substation Installation, and Heavy-Duty System Maintenance.