Test method for power frequency dielectric constant

GHP-3ATest method for power frequency dielectric constantCharacteristics of electric bridge:

Potential tracker and zero point indicator attached to the bridge body, peripheral wiring and few

The bridge adopts a ten way switch with low contact resistance and long mechanical life to ensure measurement stability

The instrument has dual shielding, which can effectively prevent interference from external electromagnetic fields

The internal resistance and capacitance components of the instrument have undergone special aging treatment to ensure stable and reliable technical performance

Internal high-voltage power supply with an accuracy of 3%

Attached standard capacitor loss<0.00005, nominal value 100pF

1、 Technical indicators

1. Measurement range and error

Under the conditions of an ambient temperature of 20 ± 5 ℃ and a relative humidity of 30% -80%, this bridge should meet the technical specifications listed below.

When Cn=100 pF R4=3183.2 (Ω)

When Cn=100 pF R4=318.3 (Ω)

2. Sensitivity of bridge measurement

During the use of the bridge, the sensitivity directly affects the resolution of the bridge balance. To ensure measurement accuracy, it is hoped that the sensitivity of the bridge can reach a certain level. Under normal circumstances, the sensitivity of a bridge is directly proportional to the measured voltage and standard capacitance.

In the following calculation formula, users can estimate the sensitivity level of the bridge based on actual conditions, and even small changes in capacitance and dielectric loss factor at this level can be reflected.

ΔC/C或 Δtgδ=Ig/UωCn(1+Rg/R4+Cn/Cx)

Where:

U is the measured voltage: volts (V)

ω is angular frequency 2 π f=314 (50Hz)

Cn standard capacitor capacity: Farad (F)

The current of Ig universal zero meter is 5 × 10-10 amperes (A)

The Rg balance zero meter has an internal resistance of approximately 1500 ohms (Ω)

R4 bridge arm R4 resistance 3183 ohms (Ω)

Cx Tested capacitance value: Farad (pF)

3. Operating Voltage Description

In use, the maximum voltage at point V on the top A and B of this bridge shall not exceed 11V, and the current at each plate of the R3 bridge arm shall not exceed the following regulations:

10×1kΩ 1max≤15mA

10×100Ω 1max≤120mA

10×10Ω 1max≤150mA

Users should pay attention to the above issues before use. If not clear, the approximate operating current can be calculated based on the experimental voltage and standard capacitance using the following formula.

I=ω V C

4. Technical characteristics of auxiliary bridge:

Non distortion tracking voltage 0-11V (effective value)

5. Technical characteristics of the zero device:

At 50Hz, the voltage sensitivity shall not be less than 1 × 10-6V/grid

Current sensitivity not less than 2 × 10-9A/grid

The second harmonic reduction shall not be less than 25dB

The third harmonic reduction shall not be less than 50dB

IIGHP-3ATest method for power frequency dielectric constantWorking principle of electric bridge

The high-voltage bridge adopts a typical Xilin bridge circuit. At the basic range, the C4 bridge arm is connected in parallel with the R4 bridge arm, and the measured value is a positive loss factor. The structure adopts double-layer shielding. And through the auxiliary balance of the auxiliary bridge, eliminate the influence of parasitic parameters on the balance of the bridge. The auxiliary bridge consists of an automatic potential tracker and an inner shield (S). Automatic trackers are composed of electronic components. It takes an input voltage at the top B of the bridge, amplifies it, and generates a voltage equal to the B potential through the inner shield (S). When the bridge is in balance, the potentials of points A, B, and S must be equal, thus achieving automatic tracking. During the balancing process of this bridge, the auxiliary bridge adopts automatic potential tracking. While the main bridge is balancing, the auxiliary bridge also automatically tracks and remains in a balanced state. Users only need to operate the main bridge balance to obtain reliable required data. At the same time, it effectively suppresses the impact of voltage fluctuations on balance. In the zero point section, a pointer type electric meter is used for indication, which is visually intuitive and clearly distinguishable, overcoming the shortcomings of traditional vibrating ammeters.

1. Composition of the bridge body

Composition of each arm of the bridge

First arm: Z1 is composed of the tested object Cx.

Second arm: Z2 is composed of high-voltage standard capacitors Cn.

Third arm: Z3 is composed of a ten pin resistor 10 x (1000+100+10+1+0.1) ohms and a sliding line resistor (0-0.13) ohms.

Fourth arm: Composed of a ten pin capacitor arm 10 × (0.1+0.01+0.001+0.0001) uf and a variable capacitor 100pF, C4 is connected in parallel with electrical group R4 to form Z4.

2. Calculation formula

Cx=R4×Cn/R3 R4[Ω] R3[Ω] Cn[pF] Cx[pF]

tgδ=ω·R4·C4 R4[Ω] C4[F]

当 R4=10K/π

tgδ=C4

当 R4=1K/π

tgδ=0.1C4

We adopt a relatively fixed R4 resistor and adjust R3 and C4 separately to balance the bridge heel, in order to measure the capacitance value Cx and dielectric loss tg of the test sample. In order to directly read the loss value of this bridge, the resistance value of resistor R4 is taken as several times the angular frequency (f=50Hz).

3. Formula Explanation

The positive formula for frequency to dielectric loss:

The rated operating frequency of this bridge is f=50Hz. When the actual operating frequency deviates from the rated frequency, a correction formula can be used for correction:

tg=f’·tgδ/f

In the formula: f is the rated operating frequency (f=50Hz)

F 'is the actual working frequency

The loss value measured by the TG δ bridge

TG is the actual value of the tangent of the dielectric loss angle of the tested product

3、 Safety operating procedures

1. This instrument must be kept and used by a dedicated person. Non dedicated operators should understand and familiarize themselves with this manual before use to avoid unnecessary losses and accidents.

2. Before each use, carefully check whether the grounding wire is intact to ensure that it can be powered on for use in the future.

Before connecting the power, the sensitivity switch should be set to the low position.

Before measuring the test sample, a high-voltage test should be conducted to prove that there is no noise, ionization, or other phenomena under the working voltage of the bridge. Only then can the test be carried out (if the test sample has already undergone a high-voltage test, this item does not need to be done every measurement).

5. When applying high voltage to the test sample, slowly increase it and do not apply sudden voltage changes.

During testing, operators must concentrate and make all necessary preparations before starting work. There should be clear markings or metal shields around the testing site to form a high-voltage danger zone to prevent non operators from entering.

7. During the measurement process, if the discharge tube emits light, the power must be cut off in a timely manner, and the wiring and test sample must be carefully checked for no breakdown. After the fault is eliminated, high-voltage measurement work can be carried out.

4、 Operation method

1. Preparation before testing

① Connect the standard capacitor Cn (with the Cn switch placed in the OUT position when selecting an external standard capacitor), connect the measured capacitor Cx, and keep the standard capacitor and the measured capacitor as far apart as possible to prevent interference between each other. When selecting an external connection method, simply turn on the main power switch and do not start the built-in high voltage. If using an internal standard capacitor (with the Cn switch on the back placed in the IN position), simply connect the tested product.

② Check if there is strong electromagnetic field interference around and try to avoid it as much as possible.

③ Check if the grounding wire is secure to ensure the safety of operators, and check if the (⊥) on the bridge is in good contact with the ground.

④ Check if the sensitivity switch of the bridge has returned to another position.

⑤ The insulation strength of the test sample should meet the standard of greater than 2U+1.

⑥ Apply test voltage to the test sample (according to departmental standards or international professional standards).

2. Testing of test samples

① When the approximate capacity and loss of the tested product are unknown, a small voltage can be applied first to find the rough balance point, then the working voltage can be raised to the desired value, and then the fine balance point can be found.

② When measuring, the sensitivity switch is adjusted according to the law from small to large.

③ During measurement, the R3 switch is adjusted in a left to right pattern.

④ During measurement, the C4 switch is adjusted in a right to left pattern.

⑤ The entire measurement process: First, check that the wiring is correct before conducting the power on test. The second step is to raise the test voltage and adjust the sensitivity switch so that the UA meter has a clear indication. At this point, it indicates that the bridge is not balanced. Adjust the R3 switch in order from left to right. At this point, observe the balance of the bridge by observing the meter head. If the header has already changed, the sensitivity can be increased again. The balance of the bridge should always be clearly observable when adjusting R3. At a certain point, users will find that adjusting R3 no longer allows the header to return to another position. At this point, the C4 switch can be adjusted in sequence from right to left, adjusting the meter pointer to the minimum position. The fifth user may find that they cannot return the pointer to another position when adjusting C4 to a certain point. At this point, it is necessary to adjust the R3 switch again. The number of adjustment bits is the last bit of the previous adjustment of R3, and then the problem with the fourth point will occur. Therefore, it is necessary to adjust the C4 switch again and again. This way, adjust the R3 and C4 switches back and forth until the sensitivity switch is at its maximum, and the pointer returns to the other (or the other instrument indicates the minimum). Indicates that the bridge has reached equilibrium.

⑥ After the measurement is completed or when the measurement is paused, the sensitivity switch of the other instrument should be lowered to "0", then the measurement voltage should be lowered to another and the power switch should be cut off. According to the calculation formula, the capacity and dielectric loss value of the tested product should be calculated.

5、 Equipment completeness

1. One high-voltage bridge

3. One double shielded measurement cable

4. One copy of the user manual

5. One power cord