Partial discharge (PD), abbreviated as PD, is the core indicator and precursor signal of insulation degradation in high-voltage electrical equipment. Accurate detection of PD signals is a critical method for assessing the operational condition of equipment insulation and preventing sudden insulation failures. Since the electrical signals generated by partial discharges are extremely weak—measured only in picocoulombs (pC)—they are highly susceptible to interference and masking from complex external electromagnetic environments. The primary function of a partial discharge shielded room is to create a clean testing environment with low background noise and minimal electromagnetic interference, ensuring the accuracy and reliability of measurement data.
I. Application Scope
The application of partial discharge shielded rooms spans the entire lifecycle of high-voltage power equipment, including research and development, manufacturing, commissioning, and operation and maintenance. Their core value lies in providing standardized, repeatable PD testing environments for various high-voltage electrical products. Specific application scenarios cover four main areas:
1. Factory Testing of High-Voltage Equipment: For high-voltage products such as transformers, reactors, instrument transformers, power cables and accessories, gas-insulated switchgear (GIS), and bushings, partial discharge testing is a key item in verifying insulation quality at the factory. Shielded rooms effectively isolate strong electromagnetic interference caused by overhead cranes, welding operations, and other workshop activities, ensuring accurate and reliable test results.
2. Maintenance and Diagnostic Testing in Field Operations: In real-world operating environments such as substations and converter stations, mobile or semi-enclosed shielding facilities can eliminate complex electromagnetic interference during handover tests and preventive maintenance, providing precise data support for condition-based maintenance and fault diagnosis.
3. Certification Testing and Research Applications: Professional testing and research institutions can use shielded rooms to conduct type tests, arbitration tests, and fundamental research on insulation technologies. This not only delivers impartial and authoritative test results but also supports performance evaluation and technological development of new insulation materials.
4. Testing in Complex Industrial Environments: In industrial settings such as electrified railways, metallurgy, and chemical plants where strong electromagnetic interference exists, shielded rooms enable accurate PD testing of critical high-voltage equipment like traction transformers and high-voltage motors by effectively eliminating environmental disturbances, ensuring measurement precision, and meeting testing requirements under special conditions.
II. Core Functions and Components
A fully functional partial discharge shielded room is designed around two core objectives: external electromagnetic isolation and test safety. The overall system consists of three main components: the electromagnetic shielding enclosure, interference purification systems, and supporting safety systems.
(1) Electromagnetic Shielding Function
Electromagnetic shielding is the most fundamental and essential function of the shielded room. The structure is built using high-quality conductive steel plates forming a fully enclosed six-sided shell. Relying on the Faraday cage effect, it effectively attenuates and blocks external electromagnetic radiation—including broadcast signals, industrial electrical noise, and lightning-induced electromagnetic pulses—preventing external electromagnetic signals from coupling into the test circuit and interfering with measurements. Industry standards specify minimum shielding effectiveness: greater than 60 dB in the frequency range of 14 kHz to 1 MHz, and greater than 90 dB in the higher frequency band from 1 MHz to 1000 MHz.
(2) Power Supply and Environmental Purification Function
External electromagnetic interference can enter the test system not only through spatial radiation but also via power lines. Therefore, shielded rooms are equipped with power line filters and double-shielded isolation transformers to efficiently suppress conducted interference such as power harmonics and voltage spikes, thereby purifying the power supply environment. To ensure consistent and stable test conditions and comparable test data, dedicated temperature and humidity control systems are installed inside the room, maintaining the test environment within a standard range of 20°C ±5°C and relative humidity below 80%.
(3) Safety and Supporting Auxiliary Systems
High-voltage PD testing involves risks of electric shock, so the shielded room must be equipped with a comprehensive safety protection system. The core safety features include a low-resistance grounding system (with a standard grounding resistance requirement of less than 0.5 Ω), emergency shutdown devices, door interlock protection structures, and audiovisual alarm systems, comprehensively mitigating potential safety risks during testing. To meet the demands of routine testing operations, auxiliary facilities such as video surveillance, ventilation waveguides, dedicated lighting, and soundproofing noise reduction systems are also integrated, ensuring both test safety and operational convenience.
III. Key Performance Indicators
The performance of partial discharge (PD) shielding rooms is primarily evaluated by two core indicators: background noise level and shielding effectiveness, which directly determine detection accuracy and environmental adaptability.
(1) Background Noise Level
This indicator serves as the primary criterion for assessing shielding room performance, representing the total sum of all ambient stray signals detected by the measurement system when no test voltage is applied and no discharge occurs in the specimen. The background noise level directly defines the minimum detectable PD charge quantity, forming the foundation for high-precision PD detection. According to IEC 60270 standards, the background noise level of a shielding room must be at least 6 dB lower than the specified PD limit value, ensuring that actual PD signals can be accurately identified. High-performance shielding rooms typically maintain a stable background noise level within 1–2 pC.
(2) Shielding Effectiveness
Shielding effectiveness is the key physical parameter indicating the ability of a shielding room to attenuate electromagnetic waves in space, measured in decibels (dB). Higher values indicate stronger electromagnetic shielding and better interference rejection. The fundamental principle of shielding effectiveness lies in reducing external electromagnetic field intensity—for example, a shielding effectiveness of 100 dB at 1 GHz reduces the external electromagnetic field strength at that frequency to one hundred-thousandth of its original value. There is no single fixed threshold; instead, this metric requires full-frequency-range measurements conducted across different locations and frequency bands within the shielding room, according to industry standards, to ensure compliance with shielding performance requirements throughout the entire space and frequency spectrum.
IV. Construction and Acceptance Standards System
The entire process of design, construction, commissioning, and acceptance of partial discharge shielding rooms follows standardized, systematic industry norms, ensuring overall performance, test environment, and inspection procedures meet regulatory requirements. Core standards fall into three main categories.
(1) Shielding Effectiveness Measurement Standards
GB/T 12190 “Method for Measuring Shielding Effectiveness of Electromagnetic Shielded Rooms” is the national standard for shielding room acceptance, equivalent to the international IEEE Std 299. It clearly defines the testing procedures, methods, and evaluation criteria for shielding effectiveness, serving as the essential reference for construction and acceptance.
(2) Fundamental Standards for Partial Discharge Measurement
IEC 60270 / GB/T 7354 “High-Voltage Test Techniques – Partial Discharge Measurements” is the foundational and authoritative standard in the field of PD testing. It not only unifies testing methods and operational procedures for various high-voltage equipment but also explicitly specifies critical technical requirements for the test environment—such as background noise levels and environmental conditions—making it the core guideline for shielding rooms designed for PD testing.
(3) Specialized Testing Standards for Electrical Equipment
Various product-specific standards for high-voltage electrical equipment include clauses related to PD testing, indirectly defining requirements for test environments. For instance, GB 1094.3, GB/T 11017, and GB 1207 specify PD limits and test environmental conditions for power transformers, high-voltage cross-linked polyethylene power cables, and voltage transformers, respectively, serving as important references for specialized shielding room applications.
V. Common Terminologies for Equipment
In the industry, partial discharge shielding rooms are referred to by several common names, though they all refer to the same core equipment. Typical terms include: PD shielding room, high-voltage PD shielding room, high-voltage shielding room, PD laboratory, high-voltage PD laboratory, shielded test hall, fully shielded PD test lab, and high-voltage PD shielding chamber.
Post time: Jul-13-2026