Turn on the power switch, and the boot 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, Xrepresents three-phase simultaneous measurement.
l Compensation angle: The adjustment method is the same as above. Generally, the influence of inter-phase 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°. You can compare the data trend over a period of time longitudinally according to the regulations. If you need 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. OK"
Display: Switch the display screen to show all test information or a brief display. If it is three-phase simultaneous measurement, press "Increase" and "Decrease" to cyclically display 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, then 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 a serial communication cable to connect the instrument to the computer's RS-232 serial port. 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
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1. Measurement Principle
The input current and voltage are digitally filtered to extract the fundamental wave, and then the projection method is used to calculate the resistive current fundamental peak value 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 fundamental waves, which includes the selected compensation angle (Figure 7). Therefore, both φ and Ir1p can intuitively evaluate the performance of the MOA.
2. Inter-phase 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 inter-phase interference (Figure 9).
One method is to compensate for inter-phase 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 inter-phase interference (i.e., set the compensation angle to 0) and judge the arrester performance from the trend of the resistive current.
If allowed, you can energize only the phase to be tested to obtain absolute data. In laboratory measurements, inter-phase interference does not need to be considered.
3. Arrester Performance Judgment
The performance of the arrester can be judged from the resistive current fundamental peak value 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 inter-phase interference:
| Performance | <75° | 75°～ 79° | 79°～ 83° | 83°～ 89° |
| Φ | Poor | Fair | Good | Excellent |
With inter-phase interference, errors occur:
| Phase A | Phase B | Phase C |
| -2°～ -4° | (considered 0) | +2°～ +4° |
In actual measurement, this error should be considered. Although there is this inter-phase 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°. In this case, it is more reasonable to directly check the angle.
4. Precautions in practical application:
Because this instrument can perform three-phase simultaneous measurement and automatic compensation, it is very convenient to use. The above-mentioned inter-phase interference and other issues 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 and turn on the instrument to test. All problems have been solved by the instrument.
