.LYYB-3000 Measurement Principle
1. Measurement Principle
After digital filtering of the input current and voltage, the fundamental wave is extracted, and then the projection method is used to calculate the peak value of the resistive current fundamental wave Ir1p=Ix1p.cosφ. Since the fundamental wave value is stable, Ir1p is currently widely used to evaluate the performance of the arrester.
The peak value of the total current fundamental wave Ix1p is projected in the direction of the voltage fundamental wave U1 (E1) as Ir1p, and in the perpendicular direction as Ic1p. φ is the phase angle between the current and voltage fundamental waves, including the selected compensation angle (Figure 10). Therefore, both φ and Ir1p can intuitively measure the performance of the MOA.
Figure 10, Projection Method Figure 11 Arrangement of Arresters in a Row Figure 12 AC Phase Affected by B Phase
2. Interphase Interference
During on-site measurement, for arresters arranged in a row (Figure 11), the middle B phase affects the leakage currents of A and C through stray capacitance, causing the φ of phase A to decrease and the resistive current to increase, while the φ of phase C increases and the resistive current decreases or even becomes negative. This phenomenon is called interphase interference (Figure 12).
One method is to compensate for interphase interference: assuming that without interference, the phase difference between Ia and Ic is 120°, and assuming that the interference of B phase on A and C phases is the same;
Take the voltage from phase B and the current from phase C, measure φ1=φcb; then take the current from phase A, measure φ1=φab; then the phase difference between C phase current and A phase current is φca=φcb-φab;
Select the correction angle Dφ=(φca -120°) / 2, and enter this value into the instrument in the main menu;
After selecting the correct phase sequence, the instrument will automatically perform angle compensation based on the selected phase sequence (add Dφ to phase A, no compensation for phase B, i.e., select 0, and subtract Dφ from phase C).
It is also possible not to compensate for interphase interference (i.e., compensation angle of 0), and judge the arrester performance from the trend of the resistive current.
If permitted, power can be applied only to the phase under test to obtain accurate data. In laboratory measurements, interphase interference need not be considered.
3. Arrester Performance Evaluation
The performance of the arrester can be judged from the peak value of the resistive current fundamental wave Ir1p, but it is more effective to judge from the current-voltage angle Φ, because 90°-Φ is equivalent to the dielectric loss angle. If it is specified that the resistive current is less than 25% of the total current, the corresponding φ is 75°;
Without interphase interference:
Performance <75° 75°～ 79° 79°～ 83° 83°～ 89°
Φ Poor Medium Good Excellent
With interphase interference, errors occur:
Phase A Phase B Phase C
-2°～ -4° (considered 0) +2°～ +4°
In actual measurement, the influence of this error should be considered. Although there is this interphase interference error, it is still feasible to judge the performance of the MOA. If only Ir1p is used for judgment, there will be several times of change near 90°, and it is more reasonable to directly check the angle at this time.
7. LYYB-3000 Precautions
1. When taking the reference voltage from the secondary side of the PT, carefully check the wiring to avoid a short circuit on the PT secondary side.
2. Do not reverse the voltage signal input line and the current signal input line. If the current signal input line is connected to the PT secondary side or the test transformer measurement terminal, the instrument may be burned out.
3. Do not plug or unplug the measurement cables when there is input voltage and current, to avoid burning the instrument.
4. If the instrument is damaged, stop using it immediately and notify our company. Do not open the case for repair by yourself.
5. The LYYB-3000 should not be placed in humid or excessively high temperature environments.
10. Packing List
1 Zinc oxide arrester tester One unit
2 Voltage isolator (wireless transmitter) One unit
3 Current input cables Three pieces
4 Voltage input cables Two pieces
5 Ground wire One piece
6 Chargers Two pieces
7 Antennas Two pieces
8 Product manual One copy
9 Factory test report One copy
10 Certificate of conformity One piece
Note: The above information and technical parameters are compiled and released by Yangzhou Darui Electric Co., Ltd.
