Turn on the power switch, and the startup screen appears on the display.
After a few seconds, the main menu appears as shown below (Figure).
The specific operation instructions for the main menu are as follows:
l Line number: Press the "Function" key to move the cursor to "Line number", then press "OK" to enter.
l PT ratio: Press the "Function" key to move the cursor to "PT ratio".
l Test phase sequence: Press the "Function" key to move the cursor to "Test phase sequence", then press "OK" to enter; press the "Function" key to select the position to adjust, and a small cursor will appear at this position; press the "Increase" and "Decrease" keys to make selections. After all positions are adjusted, press the "OK" key. Among them, A, B, and C represent single-phase measurement, and Xrepresents three-phase simultaneous measurement.
l Compensation angle: The adjustment method is the same as above. Generally, the influence of interphase interference is about 2°~5°. Due to the difficulty in accurately calculating the interference amount, hard compensation is generally not recommended. Instead, it is set to 0.0°. According to the requirements of the regulations, the data change trend over a period of time can be compared longitudinally. If it is necessary to adjust the edge phase correction angle, refer to the relevant sections in "Measurement Principle" later. If three-phase simultaneous measurement is selected, the angle is automatically compensated.
l Date: The adjustment method is the same as above. Use the "Function" key to select the item to adjust (year, month, day, hour, minute, second), and use the "Increase" and "Decrease" keys to adjust. After all adjustments are completed, press the "OK" key. l Mode: Press "OK" to switch among wired, induction, and wireless modes.
l View: Press the "Function" key on the keyboard to move the cursor to "View", then press "OK" to enter (as shown in Figure 6); press the "Increase", "Decrease", and "Function" keys to select the data to view, and press "OK" to display that set of data.
l Measurement: Press the "Function" key to move the cursor to "Test", then press "OK" to enter measurement, and the measurement screen shown in Figure 7 appears. Press "OK".
Display: Switch the display screen to show all test information or a brief display. If testing three phases simultaneously, press "Increase" and "Decrease" to cycle through the information of the three phases.
Print: Can print the measured data, but does not store it.
Store: Store the current data. Select the storage location for the data and press "OK" to save.
Exit: Exit measurement and return to the system main menu.
7. Data upload: Install the data communication packaging software provided with the instrument on the computer, and use the serial communication cable to connect the instrument to the RS-232 serial port of the computer. Turn on the instrument power, run the communication program on the computer, and click the desired function on the computer to complete the relevant operations.
Principle
Edit
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 commonly used to evaluate the performance of the arrester.
The total current fundamental peak value Ix1p is projected in the direction of the voltage fundamental U1 (E1) as Ir1p, and in the perpendicular direction as Ic1p. φ is the phase angle between the current and voltage fundamentals, which includes the selected compensation angle (Figure 7). Therefore, both φ and Ir1p can be used to intuitively evaluate the performance of the MOA.
2. Interphase Interference
During on-site measurement, for arresters arranged in a line (Figure 8), the middle phase B affects the leakage currents of phases A and C through stray capacitance, causing the phase angle φ of phase A to decrease and the resistive current to increase, while the phase angle φ of phase C increases and the resistive current decreases or even becomes negative. This phenomenon is called interphase interference (Figure 9).
One method is to compensate for interphase interference: assuming that the phase difference between Ia and Ic is 120° without interference, and assuming that the interference of phase B on phases A and C is the same;
Take the voltage from phase B and the current from phase C, and measure φ1=φcb; then take the current from phase A, and measure φ1=φab; then the phase difference between the current of phase C and the current of phase A 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 phase sequence, the instrument will automatically perform angle compensation according to 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., set the compensation angle to 0) and judge the arrester performance from the change trend of the resistive current.
If conditions permit, power can be applied only to the phase under test to obtain absolute data. In laboratory measurements, interphase interference does not need to be considered.
3. Arrester Performance Judgment
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 | Fair | 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 a change of several times near 90°, and at this time it is more reasonable to directly check the angle.
4. Precautions in practical application:
Since this instrument can measure three phases simultaneously and automatically compensate, it is very convenient to use. The interphase interference issues mentioned above are automatically calculated by the instrument during three-phase simultaneous measurement, and no calculation by the test personnel is required. In short, when using this instrument, just connect the test leads, turn on the instrument, and start testing. All issues have been resolved by the instrument.
