The measuring instrument of electrical safety performance is developing rapidly in contemporary science and technology. All kinds of electrical and electronic equipment have entered all fields of social life and become an important symbol of social civilization progress. All kinds of electrical and electronic equipment are rapidly spreading in urban and rural areas across the country, bringing great convenience to production. However, the widespread use of various types of electrical and electronic equipment has led to a significant increase in personal accidents. Harm to life and property, electric shock and electrical fire are common examples. Therefore, the important issue of the safety of the use of electrical appliances and electronic equipment has become the primary factor in determining the quality of products. Safety standards have become one of the most important technical standards.
Electrical safety performance tests mainly include withstand voltage test, insulation resistance test, leakage current test and grounding resistance test. The following is a brief introduction to these types of tests.
The withstand voltage test is one of the main methods for testing the overvoltage capability of electrical appliances, electrical equipment, electrical equipment, electrical circuits and electrical safety appliances. There are two types of power frequency withstand voltage test and DC withstand voltage test. The test voltage of the power frequency withstand voltage test is more than double the rated voltage of the equipment under test, not less than 1000V. The pressurization time is 1 minute for equipment with ceramic and liquid as the main insulation, 5 minutes for equipment with organic solids as main insulation, 3 minutes for voltage transformers, and 10 minutes for oil-immersed power cables. Electrical equipment can be found to have local defects, moisture and aging of the insulation through the withstand voltage test. AC withstand voltage test: 2.5 times or more of the voltage of the equipment to be tested, from the viewpoint of thermal breakdown of dielectric loss, the weakness of local free defects and insulation aging can be effectively found. Since the voltage is divided mainly by the capacitance at the alternating voltage, the insulation defects of the device can be effectively exposed.
It mainly achieves the following purposes:
1. Detect the ability of the insulation withstand voltage to be affected by the operating voltage or overvoltage.
2. Check the quality of electrical equipment insulation manufacturing or overhaul.
3. Eliminate the damage to the insulation caused by raw materials, processing or transportation, and reduce the early failure rate of the product.
4. Verify the electrical clearance and creepage distance of the insulation.
Insulation resistance measurement
Insulation resistance is the most basic insulation indicator for electrical equipment and electrical wiring. Insulation resistance refers to the resistance between two conductors separated by insulating material. Insulation resistance is called insulation resistance between different conductors (different phases) or between conductors and enclosures. The insulation resistance presents a minimum requirement.
By measuring the insulation resistance of electrical equipment, the following objectives can be achieved:
1. Understand the insulation properties of the insulation structure. A reasonable insulation structure (or insulation system) composed of high-quality insulating materials should have good insulation properties and high insulation resistance;
2. Understand the quality of insulation treatment of electrical products. The insulation treatment of electrical products is not good, and its insulation performance will be significantly reduced;
3. Understand the moisture and contamination of the insulation. When the insulation of the electrical equipment is damp and contaminated, the insulation resistance will usually drop significantly.
4. Verify that the insulation is subjected to withstand voltage test. If the withstand voltage test is performed when the insulation resistance of the electrical equipment is below a certain limit, a large test current will be generated, causing thermal breakdown and damaging the insulation of the electrical equipment. Therefore, in general, various test standards stipulate that the insulation resistance is measured before the withstand voltage test.
Ground resistance measurement
The grounding resistance is the resistance encountered when the current flows from the grounding device into the earth and then flows through the earth to another grounding body or spreads to a distant place. It includes the resistance of the grounding wire and the grounding body itself, and the contact resistance between the grounding body and the earth's resistance. And the resistance of the earth between the two grounding bodies or the earth resistance of the grounding body to infinity. The magnitude of the grounding resistance directly reflects the degree of contact between the electrical device and the "ground" and also reflects the scale of the grounding grid.
The leakage current refers to the current formed between the metal parts with electrical insulation in the electrical insulation, or between the live parts and the grounded parts in the absence of a fault applied voltage, and the current formed by the surrounding medium or the insulating surface is called leakage current.