Have you ever been curious about how "durable" the insulation materials we use every day, such as plastic, rubber, and ceramics, are? In power equipment or high-voltage cables, the quality of insulation is directly related to safe and stable operation, and "dielectric loss" is a key indicator to measure their insulation performance. Today, let's talk about a special "stethoscope" - ultra-low frequency dielectric loss tester, and see how it "understands" the low-frequency "whispers" inside the material.
What is dielectric loss? The culprit causing the material to 'heat up'!
Before delving into the testing equipment, we need to first understand what "dielectric loss" is. Simply put, dielectric loss refers to the phenomenon in which a dielectric converts a portion of electrical energy into thermal energy under the action of an alternating electric field. You can imagine that when we apply an electric field to a material, the charge or polarity inside the material will move or flip with the change of the electric field. During this process, there will always be some "friction" and "resistance", and these energy losses are known as dielectric losses.
The dielectric loss is not better with more or less, but needs to be controlled within an appropriate range. Excessive dielectric loss means that the material will generate severe heat during operation, be prone to aging, and even breakdown, greatly affecting the lifespan and safety of the equipment. For example, in the insulation layer of high-voltage cables, excessive dielectric loss can accelerate insulation aging, increase leakage current, and ultimately lead to insulation failure.
The meaning of "ultra-low frequency": why isn't it better to be higher?
You may ask, why is it "ultra-low frequency"? In the years of practice at Wuhan Ultra High Voltage Power Technology Co., Ltd., we have found that for many high-voltage insulation materials, conducting dielectric loss testing in the ultra-low frequency range (usually below 0.1Hz) can more sensitively reflect the performance changes of the materials under long-term operating conditions, especially some early defects and aging signs.
Early defect detection: Many material defects, such as small bubbles, impurities, moisture intrusion, etc., may not be obvious at high frequencies, but at ultra-low frequencies, their loss changes will be more prominent and easier to detect.
Simulate long-term operation: In actual power systems, power frequency (50Hz or 60Hz) is the mainstream, but the insulation performance of materials will change with time and environmental changes. Ultra low frequency testing can to some extent better simulate the loss characteristics of materials under long-term and complex electric fields, and predict their future performance.
Exclude high-frequency interference: Some losses at high frequencies may be due to the charge response of the material, which is not completely the same as the heat loss mechanism at actual power frequencies. Ultra low frequency testing helps us to strip away the interference of these high-frequency effects and focus more on the real loss situation.
What are the 'behind the scenes' factors that affect dielectric loss?
There are many "secrets" inside materials, and there are various factors that affect dielectric loss, mainly including:
The properties of the material itself: the molecular structure, polarity, and charge carrier mobility of different materials are different, which directly determines their inherent dielectric loss level.
Temperature: An increase in temperature usually accelerates the movement of charges and increases dielectric losses.
Humidity: Moisture is the "enemy" of dielectrics, as it greatly increases the conductivity of materials, thereby significantly increasing dielectric losses.
Electric field strength: Within a certain range, as the electric field strength increases, the dielectric loss will also increase accordingly.
Frequency: As mentioned above, the response mechanism of materials is different at different frequencies, and the dielectric loss will also vary greatly.
Impurities and defects in materials: tiny bubbles, cracks, impurity particles, etc. can become places for charge accumulation, increasing energy loss.
The secret of the stethoscope: the working principle of the ultra-low frequency dielectric loss tester
How does the ultra-low frequency dielectric loss tester work? It works like a precision "stethoscope" by applying a stable ultra-low frequency AC voltage and accurately measuring the phase difference between the current and voltage flowing through the measured material.
Applying voltage: The instrument generates a low distortion ultra-low frequency AC voltage and applies it to the tested sample.
Measuring current: At the same time, the instrument will accurately measure the current flowing through the tested sample.
Calculate phase difference: The key is that it calculates the phase difference between the applied voltage and the measured current (usually represented by tg δ or tan δ, which is the tangent of the dielectric loss angle).
Obtain loss value: Based on the measured voltage, current, and phase difference, combined with the capacitance value of the material, the dielectric loss tangent (tg δ) and dielectric constant can be calculated.
Wuhan Ultra High Voltage Power Technology Co., Ltd. has a profound technical accumulation in this field and is committed to providing high-precision and high stability ultra-low frequency dielectric loss testing solutions.
How to make auscultation more accurate? Master these skills!
To obtain more valuable information through ultra-low frequency dielectric loss testing, we can start from the following aspects to make "auscultation" more accurate and effective:
Selected testing frequency: Select appropriate ultra-low frequency testing points based on the tested material and actual application scenarios. For example, frequencies such as 0.01Hz, 0.02Hz, 0.05Hz, and 0.1Hz are commonly used.
Control environmental factors: The temperature and humidity of the testing environment have a significant impact on the measurement results. It is necessary to conduct the test in a constant temperature and humidity environment and keep records.
Ensure sample quality: The surface smoothness, thickness uniformity, and the presence of visible defects of the tested sample will all affect the measurement results. Ensure that the sample meets the testing requirements.
Proficient in operating instruments: Master the various functions and operation steps of the instrument, understand the testing logic in different modes, and avoid misoperation.
Comprehensive analysis of data: Do not view the TG δ value in isolation. A more comprehensive judgment can only be made by combining the dielectric constant of the material, the loss curve at different frequencies, and comparing it with historical data.
Regular calibration of instruments: In order to ensure the accuracy of measurement results, it is necessary to regularly calibrate the ultra-low frequency dielectric loss tester. Wuhan Ultra High Voltage Power Technology Co., Ltd. provides professional instrument calibration and maintenance services to ensure that your equipment is always in the best working condition.
Related applications and extensions: More than that!
The application range of ultra-low frequency dielectric loss testing is very wide. It is not only an important means of evaluating the performance of insulation materials, but also plays a key role in the following fields:
High voltage cable diagnosis: used to evaluate the health status of cable insulation, predict lifespan, and guide maintenance plans.
Transformer oil testing: testing the insulation performance of transformer oil to determine whether it needs to be replaced or treated.
Overall insulation assessment of electrical equipment, such as GIS (gas insulated switchgear), bushings, etc.
New material research and development: Evaluate the performance of new insulation materials and guide material design.
At Wuhan Ultra High Voltage Power Technology Co., Ltd., the ultra-low frequency dielectric loss tester we provide is designed to meet these stringent testing requirements. Through ultra-low frequency dielectric loss testing, we can detect problems earlier and evaluate materials more accurately, thereby ensuring the safe and stable operation of the power system.
Frequently Asked Questions (FAQ)
Q: Why choose "ultra-low frequency" instead of power frequency (50Hz/60Hz) for dielectric loss testing? A: The "ultra-low frequency" test (such as below 0.1Hz) can more sensitively reflect the early defects and aging signs of insulation materials, especially suitable for long-term performance prediction of high-voltage insulation materials, while the power frequency test mainly reflects the loss of materials in stable working conditions.
Q: What is the normal range of "dielectric loss tangent" (tg δ)? A: The normal range of TG δ depends on the specific material, voltage level, and application scenario. Generally speaking, the better the insulation performance, the lower the TG δ value. In the power industry, there are usually corresponding standards to specify the allowable range of TG δ values for different equipment and materials.
Q: What is the impact of temperature and humidity on dielectric loss? A: Temperature and humidity are two very important factors that affect medium loss. An increase in temperature will accelerate charge migration and increase losses; The invasion of moisture will significantly improve the conductivity of the material, leading to a sharp increase in losses. Therefore, temperature and humidity must be strictly controlled during testing.
Q: What other methods can be used to evaluate the performance of insulation materials besides ultra-low frequency dielectric loss testers? A: In addition to dielectric loss testing, various methods such as insulation resistance testing, withstand voltage testing, partial discharge testing, and thermal stability testing can be used to comprehensively evaluate the performance of insulation materials.
Q: What are the advantages of Wuhan Ultra High Voltage Power Technology Co., Ltd. in the field of dielectric loss testing? A: Wuhan Ultra High Voltage Power Technology Co., Ltd. has years of industry experience and profound technical accumulation, providing high-precision and high stability ultra-low frequency dielectric loss testing instruments, as well as professional solutions and technical support, to meet the customized needs of different customers.