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IEC TR 62836:2013 – Measurement of Internal Electric Field in Insulating Materials – Pressure Wave Propagation Method
🔌 IEC TR 62836 establishes a standardized procedure for measuring internal electric field distribution in insulating materials using the pressure wave propagation (PWP) method. This is critical for HVDC cable development and qualification.
⚠️ Space charge accumulation in HVDC cable insulation can lead to electric field distortion and premature failure. The PWP method provides a direct measurement tool for evaluating this phenomenon.
1. Scope and Principle of the PWP Method
IEC TR 62836:2013 contains an efficient and reliable procedure for testing the internal electric field in insulating materials used for high-voltage applications using the pressure wave propagation (PWP) method. It is suitable for homogeneous insulating materials with electric fields higher than 1 kV/mm, depending on sample thickness and pressure wave generator characteristics.
The principle (Clause 3) involves applying a pressure pulse wave to a dielectric sample. Space charges and interface charges are forced to move by the pressure wave, inducing an electrical signal in the measuring circuit that represents the charge distribution. The fundamental equation is: i(t) = C0 integral [B E(x) dp(x,t)/dt] dx, where E(x) is the electric field distribution, p(x,t) is the pressure wave, and C0 is the sample capacitance.
2. Measurement Setup and Methods
Two main PWP techniques are described: LIPP (Laser Induced Pressure Pulse) where a powerful pulse laser generates the pressure wave (high sensitivity, recommended energy 300-500 mJ per pulse with 3-7 ns duration), and PIPP (Piezoelectric Induced Pressure Pulse) using a piezoelectric device (better spatial resolution). The pressure pulse should have 20-50 ns duration with 1-10 MPa amplitude.
Sample conditions (Clause 4) recommend homogeneous dielectric materials like polyethylene, 1-2 mm thickness, planar plaque samples with sufficient diameter to avoid edge discharges (typically >20 cm for 60 kV). Electrode materials (Clause 5) depend on the generation method – semi-conductive electrodes with EVA+carbon black or PE+carbon black are common, with suitable thickness of about 0.5 mm for LIPP method. The measurement setup (Clause 7) specifies cable lengths (<0.5 m connections), 50-ohm characteristic impedance, amplifier specifications (40 dB, 200 MHz bandwidth), and input impedance matching requirements.
3. Engineering Applications and Data Analysis
Clause 8-10 cover calibration, measurement procedure, and data processing. Calibration uses a charge-free sample under intermediate voltage to determine the integral of the pressure wave. The measured short-circuit current signal is deconvolved to obtain the electric field distribution E(x).
Clause 11 provides measurement examples with real data. Results show internal electric field distributions under applied voltages of -5.8 kV and -46.4 kV, demonstrating how field distortion evolves over time (1.5 hours under high voltage). The residual field after voltage removal indicates trapped charge, a critical parameter for HVDC cable insulation design. For engineers designing HVDC cable systems, this method enables quantitative comparison of different insulating materials and formulations, supporting the development of cables with reduced space charge accumulation and improved DC breakdown strength.
PWP Method Key Parameters
| Parameter | Specification | Recommendation |
|---|---|---|
| Sample thickness | 1-2 mm | Polyethylene or similar homogeneous dielectric |
| Pressure pulse duration | 20-50 ns | Amplitude 1-10 MPa |
| Laser energy (LIPP) | 300-500 mJ/pulse | Pulse duration 3-7 ns |
| Cable impedance | 50 ohms | Connection length <0.5 m each |
| Amplifier | 40 dB gain | 200 MHz bandwidth |
| Electric field range | >1 kV/mm | Depends on sample and generator |
Frequently Asked Questions
Q1: Why is measuring the internal electric field in insulators important?
High-voltage DC cables suffer from space charge accumulation that can distort the internal electric field and cause premature breakdown. The PWP method enables direct measurement of this field distribution, allowing material comparison and qualification for HVDC applications.
Q2: What is the difference between LIPP and PIPP methods?
LIPP uses a powerful pulsed laser to generate pressure waves, offering higher measurement sensitivity. PIPP uses a piezoelectric device, providing better spatial resolution. Both are variants of the PWP method and follow the same analysis principles.
Q3: What types of materials can be tested with this method?
The method is designed for homogeneous dielectric insulating materials, typically polymer-based materials like polyethylene used in power cable insulation. The sample must be a planar plaque with thickness of 1-2 mm and sufficient diameter to avoid edge discharges.
