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The dielectric loss factor (dielectric loss factor) refers to a parameter that measures the degree of dielectric loss. Dielectric loss refers to the energy loss caused by the insulating material under the electric field due to the hysteresis effect of dielectric conductance and dielectric polarization. Also called media loss, referred to as dielectric loss.
1, dielectric lossWhat is the dielectric loss: the energy loss caused by the insulation material under the electric field due to the hysteresis effect of the dielectric conductance and dielectric polarization. Also called media loss, referred to as dielectric loss.
2. Dielectric loss angle δThe residual angle (δ) of the angle between the current phasor flowing through the dielectric and the voltage phasor (power factor angle Φ) under the action of an alternating electric field. Referred to as the dielectric loss angle.
Detailed description of dielectric loss factor1, dielectric loss tangent value tgδ
The dielectric loss factor atlas, also known as the dielectric loss factor, refers to the dielectric loss tangent, referred to as the dielectric loss tangent. The dielectric loss factor is defined as follows:
If the current phasor and voltage phasor of the sample are obtained: the total current can be decomposed into a combination of the capacitor current Ic and the resistance current IR, so this is the tangent of the loss angle δ=(90°-Φ). Therefore, the current digital instrument essentially obtains the dielectric loss factor by measuring δ or Φ. Measuring dielectric loss is a traditional and very effective method for judging the insulation of electrical equipment. The decrease in insulation capacity is directly reflected in the increase in dielectric loss. Further, it is possible to analyze the causes of the drop in insulation, such as: insulation moisture, insulation oil contamination, aging deterioration, and the like. While measuring the dielectric loss, the capacitance of the sample can also be obtained. If one or several of the multiple capacitive screens are short-circuited or open-circuited, the capacitance changes significantly, so the capacitance is also an important parameter.
2. The power factor cos Φ power factor is the cosine of the power factor angle Φ, which is the proportion of the active power P in the total apparent power S of the tested product.
The power factor is defined as follows: Some dielectric loss testers are used to display the power factor (PF:cosΦ) instead of the dielectric loss factor (DF:tgδ). Generally cosΦ "tgδ, the two values are very close when the loss is very small.
3, high-voltage capacitor bridge high-voltage capacitor bridge standard channel input standard capacitor current, test channel input sample current. The test piece capacitance was measured by the ratio of the current amplitude by measuring the tg δ of the current phase difference. Therefore, measuring the dielectric loss with a bridge also requires carrying a standard capacitor, boost PT and voltage regulator. Wiring is also very cumbersome.
Hydrogen generator stator bar dielectric loss factor synthesis calculation study Atlas 4, high-voltage dielectric loss measuring instrument referred to as dielectric loss instrument, refers to the use of the bridge principle, the application of digital measurement technology, the dielectric loss tangent and capacitance A new type of instrument for automatic measurement. It generally consists of three parts: high voltage bridge, high voltage test power supply and high voltage standard capacitor. AI-6000 uses the principle of frequency conversion anti-interference and uses Fourier transform digital waveform analysis technology to calculate the standard current and sample current, which has strong interference suppression capability and accurate and stable measurement results. 5, external application using external high-voltage test power supply and standard capacitors for testing, the value of the dielectric loss meter is calculated according to a certain proportional relationship to obtain the measurement results.
6. The internal application method is carried out by using a high-voltage power supply and a standard device in the dielectric loss meter to directly obtain the measurement result.
7. Positive wiring is used to measure the method of ungrounded test sample. When measuring, the dielectric loss measuring circuit is at ground potential.
8. The reverse wiring is used to measure the method of grounding the test sample. When measuring, the measuring circuit of the dielectric loss meter is at a high potential, and the test voltage is withstand between the outer casing and the outer casing.
9. Classification of commonly used dielectric loss devices The commonly used dielectric loss devices are Xilin type and M type. QS1 and AI-6000 are Xilin type.
10. Common anti-interference methods There are three common anti-interference methods in dielectric loss measurement: phase inversion method, phase shift method and frequency conversion method. The AI-6000 uses an inverter method to resist interference and supports phase-inversion measurement.
11. Accuracy representation method tgδ: ±(1%D+0.0004)Cx:±(1%C+1pF)+ is expressed as relative error, and + is expressed as absolute error. The small relative error means that the linearity of the range of the instrument is good, and the small absolute error means that the error starting point of the instrument is low. The difference between the reading and the standard value during calibration shall be less than the above accuracy, otherwise it will be the excess.
12. Anti-interference index The anti-interference index is the maximum ratio of interference current to test current under the premise of satisfying the accuracy of the instrument. The larger the ratio, the better the anti-interference performance. The AI-6000 can still achieve the above accuracy under 200% interference (ie, I interference / I sample ≤ 2).
3. Calculation formula of dielectric lossThe dielectric loses power under the action of a constant electric field.
W=U2/R=(Ed)2S/ρd=σE2Sd
Defining the dielectric loss per unit volume as the dielectric loss rate
ω=σE2
Under the action of alternating electric field, the electric displacement D and the electric field strength E both become complex vectors. At this time, the dielectric constant also becomes a complex number, and the imaginary part represents the amount of energy loss in the dielectric.
Phase relationship diagram between D, E, and J
As shown, from a circuit point of view, the current density in the dielectric is
J=dD/dt=d(εE)/dt=Jτ+iJe
Where Jτ is in phase with E. It is called active current density, which leads to energy loss; Je, which is 90° ahead of E, is called reactive current density.
definition
Tanδ=Jτ/Je=ε〞/εˊ
In the formula, δ is called the loss angle, and tan δ is called the loss tangent.
The loss tangent is the amount of energy that is consumed to obtain a given stored charge, and is an important evaluation parameter when the dielectric is used as an insulating material. In order to reduce dielectric loss, it is desirable for the material to have a smaller dielectric constant and a smaller loss tangent. The reciprocal of the loss factor Q = (tan δ) - 1 is called the quality factor of the dielectric under high frequency insulation application conditions, and it is expected that its value is high.
Tan δ is called the tangent of the dielectric loss angle. It is the ratio of the active component to the reactive component in the dielectric under AC voltage. It is a dimensionless number that reflects the amount of energy loss per unit volume in the dielectric.
Dielectric loss 
The dielectric loss is proportional to the applied voltage, the power supply frequency, the dielectric capacitance C, and the dielectric loss factor tan δ. However, it is inconvenient to use the dielectric loss P to indicate the quality of the medium, because the P value is related to the test voltage, the size of the medium (shape, size, thickness, etc.), etc., and it is difficult to compare the different devices, so it is not accurate. Reflects the insulation of the dielectric. When the applied voltage and frequency are constant, the dielectric loss is only related to the equivalent capacitance and dielectric loss factor of the medium. For a certain structure and the formed dielectric, the equivalent capacitance is a fixed value, so tan δ completely reflects the dielectric loss. It is used to evaluate the insulation level of high-voltage power equipment, which is a physical quantity that is independent of the material size depending only on the characteristics of the material. Therefore, in the engineering, the value of the tangent tan δ of the dielectric loss angle is used to judge the quality of the medium and characterize the loss of the dielectric.
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