Partial Discharge Detector

 

What is Partial Discharge Detector？

A partial discharge detector is a specialized instrument used to identify potential insulation hazards in high-voltage electrical equipment; it is one of the core tools for preventive maintenance in power systems. By capturing and analyzing the faint signals generated by partial discharges (PD) within the equipment, it assesses the condition of the insulation and determines the risk of failure.

 

A Partial Discharge Detector is a precision instrument specifically designed to collect, detect, quantify, and analyze partial discharge signals from high-voltage equipment; it can measure discharge charge (pC), discharge phase, and discharge frequency to determine whether the insulation has latent faults.

 

Main Targets for Partial Discharge Detection

I. High-Voltage Switchgear

• High-voltage switchgear / Medium-voltage switchgear / Ring main units
• GIS (Gas-Insulated Switchgear)
• SF6-filled switchgear, load break switches, circuit breakers

II. Substation Equipment

• Power transformers, dry-type transformers, oil-immersed transformers
• CTs (Current Transformers), PTs (Voltage Transformers)
• High-Voltage Bushings, Wall-Penetrating Bushings

III. Power Cables

• High-Voltage Cross-Linked Power Cables
• Cable Joints, Cable Terminations
• Long-Distance Power Transmission Cable Lines

IV. Insulation and Hardware

• High-Voltage Insulators (Ceramic, Composite Insulators)
• High-Voltage Surge Arresters
• High-Voltage Insulation Poles, Insulation Components

V. Other High-Voltage Electrical Equipment

• High-Voltage Motors, Generators
• High-Voltage Frequency Converters, Reactors
• Pre-assembled Substations, Prefabricated Substations

1. Ultra-High Frequency (UHF) Method

Detection Signal: Electromagnetic waves ranging from 300 MHz to 3 GHz.

Working Principle: An antenna sensor captures the ultra-high frequency electromagnetic waves generated during partial discharge, effectively avoiding common low-frequency interference signals.

Key Advantages: Strong interference resistance, high sensitivity (up to 0.1 picocoulombs), and high localization accuracy (up to 5 centimeters), making it highly suitable for online monitoring.

Key Limitations: If the equipment has a fully enclosed metal housing (such as GIS), a non-metallic window must be provided to enable measurement; susceptible to interference from high-frequency signals in the environment, such as 5G; relatively high equipment costs.

Typical Applications: Precise diagnosis and online monitoring of fully enclosed high-voltage equipment such as GIS (Gas-Insulated Switchgear), GIL (Gas-Insulated Lines), and UHV transformers.

2. Ultrasonic Method (AE)

Detection Signal: Acoustic waves (ultrasonic waves) in the 20 kHz to 200 kHz range.

Principle of Operation: Utilizes piezoelectric sensors to convert ultrasonic signals generated by partial discharges into electrical signals.

Key Advantages: Sensors are completely electrically isolated from high-voltage circuits, providing inherent resistance to electromagnetic interference; highly sensitive to surface discharges and corona discharges; convenient and flexible installation.

Key Limitations: Ultrasonic waves attenuate rapidly as they propagate through the medium, affecting detection sensitivity; susceptible to interference from environmental noise such as mechanical vibrations of the equipment.

Typical Applications: Oil-immersed transformers, reactors, switchgear, and cable joints. Often used in conjunction with the UHF method; suitable for live-line inspections.

3. High-Frequency Current Method (HFCT)

Detection Signal: High-frequency pulse currents ranging from hundreds of kHz to tens of MHz.

Principle of Operation: A Rogowski coil (high-frequency current transformer) is clamped onto the equipment’s grounding conductor to capture high-frequency ground current pulses generated by partial discharges.

Key Advantages: It is the only recognized method capable of absolutely quantifying discharge levels (in the pico-coulomb range), strictly adhering to the IEC 60270 standard; particularly suitable for cable lines; moderate cost.

Main Limitations: Relatively weak resistance to on-site interference, potentially low signal-to-noise ratio; applicable only to equipment with a complete ground loop; poor localization accuracy, typically only capable of identifying the approximate fault section.

Typical Applications: High- and medium-voltage power cables, transformers, and surge arresters; serves as the core solution for online monitoring of cable lines.

4. Transient Earth Voltage Method (TEV)

Detection Signal: High-frequency voltage pulses ranging from 5 MHz to 100 MHz.

Working Principle: A capacitive sensor is attached to the surface of the equipment’s metal enclosure to capture the transient earth voltage generated on the enclosure during partial discharge.

Key Advantages: Non-invasive operation; simple and convenient; fast detection speed; low cost; supports live testing without powering down the equipment.

Main Limitations: Low signal-to-noise ratio and slightly lower sensitivity; only applicable to equipment with metal enclosures.

Typical Applications: Switchgear, ring main units, distribution panels, etc. It is a common method for efficient on-site screening (rapid inspection).

5. Chemical Detection Method (DGA)

Detection Signal: Decomposition products of insulating oil or sulfur hexafluoride (SF₆) gas.

Working Principle: Uses methods such as gas chromatography to detect characteristic gases produced by the decomposition of insulating materials under partial discharge conditions, as well as their concentrations.

Key Advantages: Completely immune to electromagnetic interference; capable of reflecting the dynamic process of long-term cumulative degradation of insulating materials.

Key Limitations: Slow response time (cannot monitor in real time); insensitive to sudden faults; and unable to precisely locate the source of discharge.

Typical Applications: Oil chromatography analysis for oil-immersed transformers; analysis of decomposition products in SF₆ gas-insulated equipment.

6. Acoustic Imaging Method

Detection Signals: Audible and ultrasonic sounds in the 2 kHz to 100 kHz range.

Working Principle: Utilizes a microphone array to receive sound waves; algorithms overlay the location of the sound source in real time as a color image (acoustic image) on a visible light image.

Key Advantages: Provides intuitive, “what-you-see-is-what-you-get” visualization; enables non-contact, rapid scanning of large areas from a distance.

Key Limitations: Difficulty in providing quantitative analysis of discharge levels; limited positioning accuracy for discharge sources located deep within equipment or in complex structures.

Typical Applications: Live-line inspection of switchgear, insulators, and cable terminations, as well as leakage point detection in GIS equipment.

I. Safety Precautions

Strictly adhere to high-voltage safety regulations during on-site testing, maintain a safe distance, and never touch live parts.

The instrument, sensors, and grounding wires must be reliably grounded; poor grounding can introduce interference and pose an electric shock hazard.

Outdoor testing is prohibited during thunderstorms, strong electromagnetic interference, or other adverse weather conditions.

Never approach equipment for testing if severe flashover or breakdown faults have not been isolated to prevent sudden accidents.

Do not disassemble the unit or modify internal circuits without authorization. Under no circumstances should sensor connectors be plugged in or unplugged while live at high-voltage sites.

II. Wiring and Installation Precautions

Sensors must be placed or installed in accordance with specifications, away from interference sources such as variable frequency drives, mobile phones, walkie-talkies, and high-power motors.

Signal cables should be as short and straight as possible, without coiling, and should avoid running parallel to high-voltage leads and power cables.

Do not misconnect TEV, UHF, ultrasonic, or HFCT sensors to the corresponding interfaces, as this may result in no signal or channel damage.

The HFCT transformer clamp must be securely closed and locked, and attached to the cable shield or a dedicated ground wire.

III. Instrument Calibration and Parameter Settings

Allow the instrument to warm up before powering on, then enter the measurement interface. First, measure environmental background interference, followed by partial discharge in the equipment.

Set gain, threshold, and frequency bandwidth appropriately to avoid excessive gain causing a screen full of noise, or insufficient gain leading to missed weak partial discharges.

When on-site interference is high, promptly enable digital filtering, phase filtering, and interference suppression functions.

Do not arbitrarily modify the system’s factory calibration parameters to prevent measurement inaccuracies.

IV. Precautions During Testing

During testing, personnel should stay as far away as possible from the sensor and high-voltage equipment; do not place your body close to the sensor to avoid interfering with the signal.

It is recommended to take multiple samples at the same location and compare the spectra to avoid misjudgment from a single measurement.

Distinguish between external interference signals and actual partial discharges from the equipment; do not rely solely on numerical values, but make a comprehensive judgment by combining PRPD spectra and waveforms.

During prolonged continuous monitoring, monitor the instrument’s temperature and battery level to prevent unexpected shutdowns that could interrupt the test.

V. Post-Use, Storage, and Maintenance

After testing, remove the sensor before turning off the main unit, and neatly coil and store the cables.

Avoid storing the device in environments subject to heavy pressure, drops, rain, or humidity.

Calibrate and clean the sensor probe regularly to maintain sensitivity.

If the device will not be used for an extended period, disconnect the power, remove the battery, and store it in a dry, well-ventilated area.

I. Classification by Detection Principle / Detection Method

Ultra-High Frequency (UHF) Partial Discharge Detector

Detects using ultra-high frequency electromagnetic waves in the 300 MHz to 3 GHz range;

Suitable for: GIS, high-voltage switchgear, ring main units, and gas-insulated switchgear.

Ultrasonic Partial Discharge Detector

Captures ultrasonic signals above 20 kHz generated by discharges;

Suitable for: Insulators, bushings, transformers, and corona and surface discharge on exposed high-voltage equipment.

TEV Ground Wave Partial Discharge Detector (TEV Type)

Detects transient ground waves on the surface of metal enclosures;

Suitable for: Medium- and high-voltage metal-enclosed switchgear and prefabricated substations; allows for inspection without opening the enclosure or interrupting power supply.

HFCT High-Frequency Current Partial Discharge Detector (HFCT Type)

Detects partial discharge pulses on grounding wires via high-frequency current transformers;

Suitable for: high-voltage cables, cable joints/terminals, transformers, CTs/PTs.

Combined 4-in-1 Partial Discharge Detector

Integrates four detection methods: UHF, Ultrasonic, TEV, and HFCT;

Handles all high-voltage equipment with a single unit—the market’s leading best-seller.

II. Classification by Application Scenario

Offline Partial Discharge Detector (Offline Type)

Used with a partial discharge-free high-voltage test system for synchronous partial discharge testing during withstand voltage tests in laboratories, enabling precise pC quantification.

On-site Portable Partial Discharge Detector (On-site Portable Type)

Portable and handheld, designed for live, uninterrupted inspections and defect surveys at substation sites.

Fixed Online Partial Discharge Monitoring System (Fixed Online Monitoring Type)

Sensors are permanently installed in GIS, switchgear, or cables for 24/7 real-time online monitoring and remote alarm notification.

 

III. Classification by Number of Channels

Single-Channel Partial Discharge Detector

An entry-level model for single-point detection, offering excellent value for money.

Multi-Channel Partial Discharge Detector

Available in 4-channel, 8-channel, and 16-channel configurations, enabling simultaneous multi-point data acquisition and comparative analysis.

 

IV. Classification by Structural Type

Handheld Portable

Lightweight and portable with touchscreen operation, suitable for on-site inspections.

Desktop Lab Type

High precision and advanced algorithms, suitable for factory testing, type testing, and scientific research.

Cabinet Type

Integrated into a monitoring cabinet for online partial discharge monitoring of entire substations.

I. Domestic Prices:

1. Handheld (Inspection / Single-point, TEV / Ultrasound / UHF)

Basic models (single-function, e.g., ultrasound only): 6,000–20,000 RMB

Goldhome HM9001: approx. 6,000 RMB

Mainstream models (2-in-1 / 3-in-1, TEV + Ultrasound): 28,000–60,000 RMB

High-end models (4-in-1: TEV + UHF + ultrasonic + HFCT): 65,000–120,000 RMB

Goldhome HMJFS-03: approx. 80,000–100,000 RMB

 

2. Benchtop / Portable (laboratory / field precision, multi-channel)

Dual-channel (0.1 pC sensitivity): 78,000–150,000 RMB

Goldhome HM9102: Approx. 90,000–120,000 RMB

Four-channel (high precision, IEC 60270): 150,000–300,000 RMB

Goldhome HMPD-9104: Approx. 180,000–250,000 RMB

 

3. Online Monitoring Systems (GIS / Transformers / Switchgear, Long-term Deployment)

Single Bay (GIS / Switchgear): 200,000–500,000 RMB

Multi-Bay / Full-Station Integration: 500,000–1,500,000 RMB

Goldhome GIS Online Monitoring System: Approx. 300,000–800,000 RMB

II. International Brand Prices

1. Handheld

OMICRON (MPD Handheld): 180,000–250,000 RMB

Megger (PD Scan): 150,000–220,000 RMB

EA Technology (UltraTEV Plus²): 120,000–180,000 RMB

 

2. Benchtop / Portable

OMICRON (MPD 600/800): 350,000–600,000 RMB

ABB (TXpert): 400,000–700,000 RMB

Haefely (PD 700): 300,000–500,000 yuan

 

3. Online Monitoring Systems

OMICRON (CableScout+): 800,000–1,500,000 yuan

Siemens Energy (TEC Series): 600,000–1,200,000 yuan

Doble (PDMonitor): 500,000–1,000,000 yuan

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