In the power system, the measurement of dielectric loss for components such as transformers, transformers, reactors, capacitors, bushings, and lightning arresters is the most fundamental method for evaluating their insulation performance. The dielectric loss tester breaks away from the traditional bridge measurement method and adopts variable-frequency power supply technology. It utilizes single-chip microcomputers and modern electronic technology for automatic frequency conversion, analog-to-digital conversion, and data calculation; achieving strong anti-interference ability, fast testing speed, high accuracy, full automation and digitalization, and simple operation.
The power supply adopts a high-power switching power supply, providing pure sine waves of 45Hz and 55Hz. It automatically boosts the voltage and can offer a high voltage of 10 kilovolts. It automatically filters out 50Hz interference and is suitable for on-site testing in environments with strong electromagnetic disturbances such as substations. It is widely applicable to the measurement of dielectric loss of facilities in the power industry, such as transformers, current transformers, bushings, capacitors, and lightning arresters.
Safety measures
Before using this instrument, you must carefully read the user manual.
2. The operator of the instrument should have knowledge of the use of general electrical facilities or instruments.
3. The dielectric loss tester can be used both indoors and outdoors. However, it should not be used in places exposed to rain, corrosive gases, excessive dust, high temperatures, or direct sunlight.
4. The instrument should be free from severe vibrations.
5. The maintenance, care and adjustment of the instrument should be carried out by professionals.
6. Before any connection is made, the grounding terminal of the instrument must be reliably connected to the ground using a grounding cable.
7. Due to the high voltage generated by the testing facilities, the testers must strictly follow the safety operating procedures to prevent others from coming into contact with the high-voltage components and circuits. The personnel directly involved in the testing must fully understand the high-voltage testing lines and the key points of instrument operation. Non-testing personnel must stay away from the high-voltage testing area, and the testing area must be clearly marked with fences, ropes, warning signs, etc.
8. The adjustment, repair and maintenance of the dielectric loss tester must be carried out without power supply. If power supply is necessary, the operator must be very familiar with the high-voltage dangerous components of this instrument.
9. When the fuse is damaged, it is essential to replace it with the same type of fuse. It is strictly prohibited to replace it with a different model or to use the fuse in a short-circuit manner.
Precautions for On-site Testing of Dielectric Loss Tester
If the test data during use appears to be obviously unreasonable, please look for the reasons from the following aspects:
1. Poor contact of the hooks
When conducting on-site measurements using clamps to connect the test samples, the clamps must make a proper contact with the samples. Otherwise, the discharge at the contact points will cause significant fluctuations in the data! Especially when the oxide layer on the lead wires is too thick, or when the wires are swayed by the wind, it is prone to cause poor contact.
2. Poor grounding contact
Poor grounding can cause instrument protection issues or severe fluctuations in data. The paint and rust on the grounding points should be removed thoroughly, and ensure a 0-ohm resistance connection!
3. Direct measurement of CVT or measurement using the terminal shielding method for electromagnetic PT
Direct measurement of the coupling capacitor of the lower section of the CVT will result in negative dielectric loss. Therefore, the self-excitation method should be adopted instead. When measuring the electromagnetic PT using the terminal shielding method, negative dielectric loss occurs due to moisture, and drying out the lower three skirts of porcelain and the connection terminal plate will solve the problem. The conventional method or the terminal voltage application method can also be used for measurement.
4. Excessive air humidity
The dielectric loss measurement values of the air humidity tester show abnormal increase (or decrease or even negative values) and are unstable. In such cases, a shielding ring can be added. Due to the addition of the shielding ring by humans, the electric field distribution of the test sample has been changed. This method is controversial and can be referred to in accordance with relevant regulations.
5. Generator power supply
When the generator is supplying power, the input frequency is unstable. In this case, the device can operate in the fixed 50Hz mode.
6. Test Line
Due to long-term use, the test cable is prone to hidden short circuits, or core wires and shielding short circuits, or poor contact of the plug. Users should frequently maintain the test cable: When testing standard capacitor samples, a fully shielded plug should be used for connection to eliminate the influence of additional stray capacitance; otherwise, the instrument’s accuracy cannot be reflected. When measuring CVT using the self-excitation method, non-specific high-voltage cables should be suspended and left open; otherwise, the additional stray capacitance and dielectric loss to ground will cause measurement errors.
7. Selection of Work Mode
After connecting the wires, please select the correct measurement mode (positive, reverse, and CVT) correctly. Do not make any mistakes. Especially in a disturbed environment, the anti-interference mode should be adopted.
8. Influence of Test Methods
Since dielectric loss measurement is greatly influenced by the test method, it is necessary to distinguish whether the error is due to the test method or the instrument. When a problem occurs, one should first check the wiring, and then determine if it is an instrument fault.
9. Instrument malfunction
Use a multimeter to check if the test line is open-circuited, or if the core wire and the shielding are short-circuited; check if the input power is too high or too low at 220V; verify if the grounding is professional. Test the standard capacitor or the capacitor sample with known capacitance and dielectric loss using positive and reverse wiring. If the results are correct, it can be concluded that the instrument is not faulty; remove all test leads and perform a no-load test to apply voltage. If it does not work properly, the instrument may have a fault. After starting the CVT measurement, measure the low-voltage output. A voltage of 2 to 5V should be present; otherwise, the instrument is faulty.
Post time: Apr-14-2026