Switchgear Partial Discharge Online Monitoring System: Principle and Advantages in Detail

Date: November 19, 2025 09:26:37

  • Core definitions: The Switchgear Partial Discharge Online Monitoring System is a professional diagnostic equipment for real-time, continuous detection of the internal insulation status of medium and high voltage switchgear. Its core function is to capture and analyze Partial Discharge (PD) signals generated by insulation degradation, in order to realize early warning and condition assessment of potential insulation defects.
  • Need for monitoring:: Switchgear has a compact internal structure and a small insulation margin, so once insulation breakdown occurs, it is very easy to cause phase-to-phase short circuit or even arc explosion. On-line monitoring is a key technology to prevent such catastrophic failures and ensure the safety of personnel and equipment.
  • Working Principle:: The system is based on the detection of multiple physical signals accompanying partial discharges, mainly transient earth voltages (TEV), ultra-high frequency (UHF) electromagnetic waves, acoustic emission (AE) ultrasound, and high frequency currents (HFCT). By fusing and analyzing these signals, the severity of PD can be identified and assessed.
  • Core Benefits: Significantly improve operational safety, increase supply reliability through early warning, enable a shift from planned maintenance to condition-based maintenance (CBM) to optimize O&M costs, and provide quantitative health status data for asset management.
  • system configuration:: A complete monitoring system consists of non-invasive sensors at the front-end, a data acquisition unit (DAU) in situ, a communication network and intelligent diagnostic master software at the back-end.

Table of Contents for this article

1. What is switchgear partial discharge?

Partial discharge (PD) in switchgear refers to a bounded discharge inside a medium- to high-voltage switchgear where the electric field strength is too high in a localized area of the insulating structure (e.g., basin insulators, cable terminals, busbar insulating supports, voltage/current transformers, etc.), resulting in the occurrence of a binding discharge in the insulating medium in that area that does not result in the formation of a penetrating channel. Although the energy of this discharge is weak, its long-term existence will cause irreversible cumulative damage to the insulating material (e.g., carbonization, formation of electrical dendrites), which is the main cause of the eventual insulation failure of the switchgear and the occurrence of phase-to-phase or ground-to-ground short circuits.

2. Why is switchgear localized emission monitoring critical?

Medium- and high-voltage switchgear is a key node in the power system, and once insulation breakdown occurs within it, the consequences are often catastrophic, mainly reflected in:

  • Arc explosion risk:: Phase-to-phase short circuits caused by insulation breakdown can generate high-energy arcs that instantly vaporize metal and generate huge pressure waves that can cause switchgear doors to burst open, creating an “arc explosion” that can be devastating to personnel and adjacent equipment.
  • blackout: As the centerpiece of power distribution and control, the failure of a single switchgear can result in the interruption of power to an entire feeder or even an entire region.
  • High maintenance costs: Arc faults usually result in complete destruction of the switchgear's internal components (circuit breakers, busbars, transformers, etc.), which can be extremely costly to repair or replace.

Partial discharges are the most important, and most measurable, of all the serious faults mentioned above before they occurprecursor signal. Therefore, capturing and analyzing them through on-line monitoring system is currently recognized as the most effective technical means to prevent malignant accidents in switchgear.

3. Principles of monitoring: detection and analysis of PD signals

Switchgear partial discharge online monitoring systems are based on the integrated detection of multiple physical signals accompanying PD events. Mainstream monitoring technology principles include:

3.1 Transient Earth Voltage (TEV) method

Working PrincipleWhen a PD occurs inside a switchgear cabinet, the current pulse generated by the discharge induces a weak, transient voltage pulse in the surrounding metal cabinet, which propagates along the surface of the cabinet towards the earth, i.e. the “transient-to-ground voltage”. These voltage signals can be coupled by attaching a capacitive TEV sensor to the metal enclosure of the switchgear cabinet.
specificities: The TEV method is particularly sensitive to PD signals from inside the switchgear and is an effective means of determining the presence of discharge activity inside the cabinet.

3.2 UHF (Ultra-High Frequency) method

Working Principle: The PD source acts as a miniature antenna, radiating electromagnetic waves with an extremely wide bandwidth (typically 300MHz-3GHz) to the surrounding area. These UHF signals can be received by installing UHF antenna sensors in switchgear vents, viewing windows or specially opened media windows.
specificities:: The high frequency of the UHF signal effectively avoids low-frequency interference from corona and radio broadcasts and has an extremely high signal-to-noise ratio. Its signal characteristics are strongly correlated with the PD type, making it a powerful tool for defect type diagnosis.

3.3 AE - Acoustic Emission

Working Principle:: The rapid release of energy during the PD process generates mechanical stress waves in the ultrasonic band. By attaching highly sensitive acoustic sensors (usually piezoelectric ceramic) to the switchgear enclosure, it is possible to “hear” the sound generated by the PD directly.
specificities: The AE method has good directionality, and the joint analysis of signals from multiple AE sensors enables three-dimensional spatial localization of the PD source inside the cabinet, which is an effective method to accurately locate defective parts.

3.4 High Frequency Current Transformer Method (HFCT)

Working Principle:: Primarily used to monitor PD at the terminals of incoming and outgoing cables, when PD occurs at the cable terminals, its pulsed current flows through the cable's grounding wire to earth. These high-frequency current signals can be measured non-intrusively by clamping an open-ended HFCT sensor to the ground wire.
specificities: A specialized and efficient means of diagnosing defects in cable terminal insulation.

Data Processing and Intelligent Diagnostics

The collected signals are sent to the backend system for analysis. The signal is analyzed through thePRPD (Phase Resolved Partial Discharge) mapping,PRPS (pulse sequence) mappingAs well as the analysis of the time-of-flight difference of the signal, the system is able to automatically filter out noise interference, identify the type of PD, assess the severity and trend alarms.

4. Core benefits of the system

  1. Significantly improves operational safety: By providing early warning of insulation failure at its incipient stage, vicious personal and equipment safety accidents, such as arc explosions, can be effectively avoided.
  2. Significantly improve power supply reliability:: Changing from reactive emergency repairs to proactive preventive maintenance reduces unplanned outages due to sudden switchgear failures and directly improves power supply reliability indicators (SAIDI/SAIFI).
  3. Optimize O&M strategy and costs: Achieve accurate “condition repair”, avoiding unnecessary and excessive preventive testing and dismantling, and reducing whole-life operation and maintenance costs.
  4. Provide quantitative status data:: Create digital health profiles for switchgear assets so that condition assessment, risk ranking and replacement decisions are supported by objective, quantitative data.
  5. Non-intrusive installation and operation: All sensors are externally mounted without the need to open cabinet doors or de-energize the equipment, making the installation process safe and convenient.

5. System components

A typical switchgear local line monitoring system consists of the following components:

  • Front-end sensors:: TEV sensors, UHF sensors, AE sensors and HFCT sensors configured as required.
  • Data Acquisition Unit (DAU): Installed near the switchgear cabinet, it is responsible for the simultaneous acquisition, digitization and preliminary processing of multi-channel signals.
  • communications network: Aggregate and transmit data from the collection unit to the monitoring master station via fiber optic or wireless.
  • Diagnostic Master Software: Deployed on servers or in the cloud, it provides data visualization, intelligent diagnostics, alarm management, trend analysis and report generation.

6. Frequently Asked Questions (FAQ)

1. What is the difference between on-line monitoring and traditional off-line local discharge testing?

Offline testing is a “static physical examination” conducted under power outage and external power supply, with accurate data but not reflecting the real operating conditions. Online monitoring is a “dynamic electrocardiogram” under actual voltage and load, which can capture the real insulation deterioration signals related to temperature, humidity and load.

2. How does the system distinguish between real PD signals and noise interference in the field?

This is the core technology of the system. It is mainly used to effectively suppress and reject noise from sources such as corona, radio, poor contact, etc. by 1) fusion of multiple sensing technologies (e.g., UHF and TEV signals at the same time); 2) synchronization of the signal with the phase of the IF voltage (PRPD mapping); 3) analysis of the characteristics of the pulse waveforms; and 4) intelligent algorithms (e.g., clustering analysis, AI recognition).

3. Can the system locate which specific component is at fault?

Can. Higher precision localization can be achieved by joint analysis of multiple sensors. For example, the amplitude comparison of TEV signals at different locations on the cabinet can initially locate the area; the directionality of the UHF antenna can point to specific compartments; and an array of AE sensors can achieve more accurate 3D spatial localization.

4. How many sensors need to be installed on one side of the switchgear?

This depends on the structure and importance of the switchgear cabinet. A typical configuration is: 1-2 TEV sensors on the surface of the cabinet for overall screening, 1 UHF sensor in the circuit breaker compartment or busbar compartment for high-precision diagnostics, and HFCT sensors on the ground wire at the termination of the incoming and outgoing cables.

5. Can this system be retrofitted to switchgear already in operation?

Completely. All sensors of the system are of non-intrusive design and can be installed directly on the outside of the switchgear cabinet in operation. The whole installation process is safe and quick without power failure.

6. What should be done when the system issues an alarm?

The system will issue different levels of alarms (e.g. “Attention”, “Serious”) according to the severity of the PD. After receiving the alarm, the O&M personnel should first combine the defect type and location information given by the diagnosis software, and then can use the portable PD inspector to conduct on-site review, and based on the comprehensive judgment results, formulate the next step of overhaul or outage inspection plan.

Why choose Inotera's switchgear localized emission monitoring solution?

INNOTD (Fuzhou) Sales Limited (INNOTD) Dedicated to providing world-class online monitoring technology for critical power assets.

  • Multi-technology integration and complementarity: Our system is capable of convertingTEV, UHF, AE, HFCTA variety of monitoring technologies are seamlessly integrated under one platform, realizing cross-validation and fusion diagnosis of multi-dimensional information, which greatly improves the accuracy and reliability of diagnosis.
  • Advanced intelligent diagnostic algorithms: The system is built-in with a massive sample base based on theIntelligent PRPD mapping recognition engineand noise suppression algorithms that can automatically identify defect types and transform complex raw data into clear, actionable diagnostic conclusions.
  • Highly reliable industrial grade hardware: All of our sensors and acquisition units are designed for strong electromagnetic environments in substations, have passed the most stringent EMC electromagnetic compatibility tests, and have excellent environmental adaptability to ensure long-term stable operation.
  • Professional full-process services: Inotera provides you with end-to-end professional services from the initial project site survey, measurement point optimization design, to system installation and commissioning, technical training, as well as continuous data analysis and diagnostic support at a later stage.

Choosing Inotera is choosing an all-weather, highly intelligent insulation state safety guard for your switchgear assets.

The content of this article is only a general technical science and does not represent the performance and specifications of any specific product of our company. For detailed product information, solutions and quotations, please be sure to contact us for...].

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