Partial Discharge (PD) testing is an essential method for evaluating and monitoring the insulation condition of GIS high-voltage switchgear and transformers. The main reasons and significance of PD testing include the following:
1.Early Defect Detection and Warning
Partial discharge is a localized weak discharge phenomenon within the insulation system, often caused by the presence of micro-bubbles, cracks, impurities, aging, or manufacturing defects. PD testing can detect these hidden issues at an early stage, preventing the long-term degradation of the insulation system and stopping minor defects from evolving into major failures.
2.Ensuring Insulation Performance
GIS high-voltage switchgear and transformers operate under high voltage, complex environments, and gas insulation conditions. If partial discharge is not controlled, it can lead to localized deterioration of insulation materials, accelerating insulation aging and even causing insulation breakdown. Regular PD testing helps assess the health of insulation materials, ensuring stable insulation performance and operational safety.
3.Preventive Maintenance and Lifespan Management
By monitoring partial discharge signals, operators can evaluate the condition of the equipment and schedule timely maintenance or replacement, achieving preventive maintenance. This not only prevents unexpected failures but also extends the service life of the equipment, ensuring the long-term stable operation of the power system.
4.Quality Control and Process Optimization
Conducting PD testing during the manufacturing and installation stages helps identify defects in design, production, or installation processes. Timely feedback and corrections improve product quality and overall process standards, reducing operational risks in the later stages.

GTPD-4C partial discharge comprehensive detector is the new generation of digital PD measurement and analysis instrument, it has a strong ability of comprehensive analysis of partial discharge and detection of partial discharge in small signal and strong interference environment. With different accessories, it can measure and locate the partial discharge in any high voltage electrical equipment. It can realize testing the transformer partial discharge by applying the voltage on the three phases simultaneously.

Functions and Feature:

1. Multi signal channel, desktop, TFT liquid crystal display, reliable system, low failure rate, strong anti- interference ability.

2. It integrates functions of measurement, diagnosis, location and on-line monitoring.

3. The location of fault position can be achieved by electro-acoustic and acoustic-sound.

4. According to the testing process, the test report can be generated automatically and the report can be read and printed.

5. The replay function can restore the saved data file to the waveform displayed on the screen.

6. Four channels electrical signal and four channels optical signal input port can simultaneously realize the measurement and analysis of multi-channel partial discharge signal.

GTPD-4C PD Tester Specification

Technical characteristics	Channels	Independent 4 one for external	Nonlinear error of this range	5%
	Sampling frequency	1M, 5M, 10M (optional)	Measuring range	0.1pC~1000nC
	Sampling accuracy	12bit	Sensitivity	0.1pC
	Measuring range	×1, ×10, ×100, ×1000, ×10000, ×100000	Capacitance range of specimen	6pF~250µP
	Measuring bandwidth	10kHz~1MHz (3dB Bandwidth)	External synchronous frequency  input range	30Hz~400Hz
	Digital filtering	10kHz~1MHz (Arbitrary choice)	External synchronous voltage input range	10V~400V
	Programmable filter segment	Low frequency:	Power supply	AC220V, Frequency: 50Hz (customized)
		10kHz, 20kHz, 40kHz, 80kHz OFF(10kHz)
		High Frequency:
		100kHz, 200kHz, 300kHz, 400kHz 800kHz,OFF(1MHz)
Display	Display screen	12 inch TFT true color touch LCD screen	resolution	1024×768
Interface	USB, Power interface, optical signal interface, electrical signal interface, RJ45 internet interface, grounding button
Common description	Operation system	Windows XP	CPU	1.6GHz
	Size	474×288×370mm	Memory	2.0GB
	Weight	15.8kg	Hard disc	128GB Solid state hard disk

GTPD-4C PD Tester Application

Infrared Thermography,UHF,TEV,HFCT,Ultrasonic sensors: Which test tells you more in PD Testing?

Infrared Thermography (IRT) and Partial Discharge (PD) testing are two widely adopted condition monitoring techniques in modern power systems, each with distinct applications and technical strengths. IRT detects surface temperature anomalies to identify potential faults caused by increased electrical resistance, such as loose connections, overloads, or deteriorated contacts. Based on passive thermal radiation measurement, IRT is simple to operate, allows for non-intrusive and live inspections, and is particularly effective for components like switchgear, busbars, and cable terminations. However, it has notable limitations: it can only detect faults that produce significant heat and cannot identify early-stage insulation degradation or internal defects. The results are also influenced by ambient temperature, surface emissivity settings, and operator experience. In contrast, PD testing detects small electrical discharges occurring within or on the surface of insulation systems. These discharges often indicate the onset of insulation breakdown, such as voids, cracks, surface contamination, or moisture ingress, allowing for much earlier detection of critical insulation failures.

PD testing employs various sensor technologies, including Ultra High Frequency (UHF), Transient Earth Voltage (TEV), High-Frequency Current Transformers (HFCT), and ultrasonic sensors. These systems analyze signal amplitude, phase, repetition rate, and waveform characteristics to assess discharge severity and type. PD signals typically exhibit short-duration, high-frequency pulses, and can propagate through metallic enclosures, making them suitable for metal-clad medium-voltage equipment. TEV measurements are effective for detecting internal discharges, while ultrasonic methods are better suited for surface or corona discharges. Unlike IRT, PD testing not only identifies defects before any heat is generated but also supports long-term condition-based monitoring and trending analysis. It is particularly applicable for critical equipment such as cable terminations, ring main units, GIS, and transformer windings. However, PD testing requires more sophisticated instrumentation and trained personnel to distinguish real signals from background noise and to minimize false positives.

According to international standards and industry best practices, IRT and PD testing should be used as complementary techniques. For instance, NFPA 70B in the United States recommends regular infrared and PD inspections for high-voltage equipment (>1000V). Similar guidelines are found in the UK and Australia for substations and critical assets. For metal-enclosed equipment, TEV and ultrasonic PD testing can be performed externally through the panel, while IRT is ideal for detecting heat-related issues in cable connectors, bus joints, and breaker contacts. In older systems or environments with significant electromagnetic interference, combined techniques (e.g., simultaneous TEV and ultrasonic monitoring) enhance diagnostic accuracy and confidence in results.

In summary, IRT is well-suited for identifying resistive faults and surface heating, while PD testing is more effective at detecting internal insulation degradation at an early stage. Integrating both methods enables a comprehensive asset monitoring strategy, combining surface thermal detection with internal dielectric diagnostics. Industry standards recommend joint application, and the reliability of the results depends heavily on the competency of the operators. Certified training (e.g., FLIR Level I/II for thermography or PD specialist training from EA Technology) is strongly recommended. By selecting the appropriate method based on asset type, voltage level, and environmental conditions, utilities and asset managers can significantly improve system reliability and reduce the risk of unplanned outages and catastrophic failures.

Kingrun Transformer Instrument Co.,Ltd.

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