The variable frequency dielectric loss tester starts measurement, the high voltage set value is sent to the variable frequency power supply, which uses PID algorithm to slowly adjust the output to the set value. The measurement circuit sends the actual high voltage to the variable frequency power supply, fine-tuning the low voltage to achieve accurate high voltage output. According to the positive/reverse wiring settings, the measurement circuit automatically selects input and switches range based on the test current. The measurement circuit uses Fourier transform to filter out interference, separate the fundamental wave of the signal, perform vector operations on the standard current and test sample current, calculate capacitance from amplitude, and calculate tgδ from phase difference. Multiple measurements are repeated, and a middle result is selected after sorting. At the end of measurement, the measurement circuit issues a voltage reduction command, and the variable frequency power supply slowly reduces voltage to 0.
Precautions and Others
Precautions
1. This instrument can only be used on equipment that is de-energized; the grounding terminal should be reliably connected to the grounding grid,
The instrument should be used in a spacious, safe, and reliable place as much as possible.
2. The equipment under test should be disconnected from the high-voltage leads from the running state to the maintenance state, cleaned, and after a preliminary insulation test is good, the instrument can be used for testing to prevent damage to the instrument during voltage application due to poor insulation of the equipment under test.
3. Determine which wiring method to use based on the installation situation of the equipment, and select the wiring method in the corresponding menu options.
4. Correctly select the test voltage level according to different equipment, and select the required voltage in the corresponding menu options.
5. If a special situation endangering safety occurs during the test, the main power can be urgently turned off.
6. Only after disconnecting the power switch on the panel and clearly disconnecting the 220V test power supply can wiring changes be made or work be completed; when repeating a test on the same test equipment, press reset and then measure again, or choose to repeat after the previous test is completed.
7. To ensure measurement accuracy, especially when the loss of small capacitance test samples is small, it is necessary to ensure that the low-voltage end (or secondary end) of the equipment under test has good insulation, and measure in an environment with relatively low humidity.
8. When conducting experiments with large capacitance test samples, the grounding of the instrument and the grounding of the test sample should not be at the same grounding point, to prevent counter-voltage or traveling waves from affecting the safety of the instrument during grounding discharge.
9. The instrument comes with a voltage boosting device; attention should be paid to the insulation distance of the high-voltage lead and personnel safety; 10. The instrument should be reliably grounded; poor grounding may cause machine protection or danger.
10. After the instrument is started, except for special circumstances, it is not allowed to suddenly turn off the power, to avoid overvoltage damage to the equipment;
11. Although the special high-voltage wire (HVx) provided with the instrument has been tested and qualified at the factory, it still needs to be kept away from the human body and the low-voltage test line (Cx) during measurement; both the high-voltage core wire and the high-voltage shield wire are not allowed to be grounded or contact the low-potential part of the test circuit.
The core wire and shield wire of the CX input line are not allowed to contact the high-voltage part of the test circuit.
12. The instrument should be protected from moisture and severe vibration.
13. When there is significant on-site interference and a definite result cannot be obtained with power frequency, use variable frequency measurement; in other cases, use power frequency measurement.
14. After issuing a measurement command, if the measurement result does not appear on the screen for a long time (1 minute), it may be due to the test sample capacitance being too large or a crash; restart the machine and lower the measurement voltage before measuring again.
15. Short circuit of the test sample will prevent measurement, and the instrument will automatically protect. When a section extends from the paper outlet above the machine head, press the button to stop paper feeding. The printing paper is allowed to be pulled outward.
Instrument Structure
Measurement circuit: all calculations such as Fourier transform, complex number operations, range switching, and variable frequency power supply control.
Control panel: printer, keyboard, display, and communication relay.
Variable frequency power supply: uses SPWM switching circuit to produce high-power sine wave stabilized output.
Step-up transformer: boosts the variable frequency power supply output to the measurement voltage, with maximum reactive power output of 2KVA/1 minute.
Standard capacitor: internal Cn, measurement reference.
Cn current detection: used to detect the current of the internal standard capacitor, 10μA～1A. Input resistance <2Ω.
Cx positive wiring current detection: only used for positive wiring measurement, 10μA～1A. Input resistance <2Ω.
Cx reverse wiring current detection: only used for reverse wiring measurement, 10μA～1A. Input resistance <2Ω.
Reverse wiring digital isolation communication: uses precision MPPM digital modem to transmit the reverse wiring current signal.
