Effectively Improving the Safety and Efficiency of Impulse Testing Laboratories
Impulse testing laboratories generate large currents of several thousand amperes during testing, with current rate of change ranging from 107 A/s to 109 A/s. Without proper measures, flashover or damage to control devices may occur, posing a risk to personal safety. To address these issues, the grounding system plays a crucial role in ensuring the safety and accurate measurement of pulse test laboratories.
Effective Grounding Solutions
In pulse testing laboratories, where high currents and rapid current changes occur, proper grounding is essential. Copper strips are preferred over round conductors to minimize inductance, reducing the risk of flashovers and equipment damage. Additionally, a metal grid embedded in the concrete floor enhances the ground circuit's efficiency, especially when using large-sized strips with close spacing.
Key Grounding System Conditions
To ensure an effective grounding system, the following conditions must be met:
- Defects in the grounding system should be avoided as they can cause excessive voltage differences between points and lead to flashover, damage, or endanger personal safety.
- Defects can cause excessive loop current in the measurement cable shield, introducing errors in the measurement.
- The grounding system should avoid voltage drops along the grounding system, voltages at circuit junctions, and circulating currents in the circuit.
Metal Conduits and Expanded Metal Sheets
Metal conduits for measuring and control cables are recommended to avoid neutral inductance effects. Furthermore, incorporating expanded metal sheets, particularly copper ones, proves highly effective in grounding systems. These sheets, with their large surface area and interconnected structure, contribute to minimizing resistance and improving overall safety.
Optimal Earthing System Design
A typical good earthing system includes a copper network with 1m width meshes laid below ground around the impulse test area. This network extends over the entire equipment area, connecting to metallic frames and reinforcing iron. The impulse test area features a spread copper grid on the floor, further enhancing the overall grounding effectiveness.
Ionization Measurements and Electromagnetic Shielding
For ionization measurements, the earthing system should maintain the RIV level from external sources at the lowest value. To address high-frequency energy produced during impulse tests, considerations for electromagnetic shielding become crucial. Building the entire laboratory into a Faraday cage ensures optimal protection.
Electromagnetic Shielding and Earth Return
In high voltage laboratories of any size, screening against electrostatic and electromagnetic field interference is essential. Imperfect screening may lead to interference, highlighting the need for effective attenuation. Testing the screening using a portable radio can identify potential issues, emphasizing the importance of proper screening materials like expanded metal wire mesh.
Measurement Considerations and Reference Grounding Points
Establishing reference grounding points is critical for accurate measurements. Potential differences during impulse testing can be minimized by reducing impedance on the Grounding of Impulse Testing Laboratories side of the test circuit. The use of a return conductor in the form of a metal sheet, especially expanded metal sheets, proves highly effective in reducing voltage differences.
Ensuring Safety and Equipment Protection
Proper earthing is essential to protect equipment against lightning strokes and short circuits inside the laboratory. Without adequate grounding, potential differences may arise, posing unnecessary danger to human life and causing damage to equipment.
In conclusion, integrating copper expanded metal sheets into the grounding system of pulse testing laboratories enhances safety, minimizes errors in measurements, and ensures the efficient operation of high voltage equipment. Careful consideration of grounding conditions, optimal earthing system design, and the use of shielding materials contribute to a robust and reliable testing environment.
