The dielectric loss tester (also known as dielectric loss measuring instrument, anti-interference dielectric loss tester) is an advanced instrument for measuring dielectric loss and capacitance. It is mainly used to measure the dielectric loss tangent (tgδ) and capacitance of various insulating materials, insulating bushings, power cables, capacitors, transformers, and other high-voltage equipment under power frequency high voltage.
The following is a detailed introduction to the dielectric loss tester:
1. Working Principle
Under the action of AC voltage, the dielectric will consume part of the electrical energy and convert it into heat energy. This energy loss is called dielectric loss. When AC voltage is applied, there is a phase angle difference between the voltage and current in the dielectric, and its tangent value (tgδ) is the key parameter to measure the dielectric loss.
Modern testers contain a standard circuit and a test circuit. The current amplitude and phase difference of both are measured separately through digital control circuits, and then the capacitance value and dielectric loss tangent value of the test object are obtained by vector operation.
2. Core Features
Strong anti-interference ability: Using frequency conversion technology (such as outputting 45Hz, 55Hz and other different frequency signals), it fundamentally avoids the interference of the power frequency electric field (50Hz) on the test object, and can maintain accurate measurement in a strong electric field environment.
Easy operation: Adopting Chinese menu and microcomputer control, it automatically completes the whole measurement process. Some equipment is equipped with a full touch LCD screen, no complex conversion is required.
Multiple test modes: Supports positive wiring, reverse wiring, internal/external standard capacitor, internal/external high voltage, CVT self-excitation method, etc., suitable for ungrounded or directly grounded high-voltage electrical equipment.
High safety: Built-in high-voltage step-up transformer, with multiple protection measures such as zero-crossing closing, lightning protection, overvoltage, overcurrent, short circuit and grounding detection. The test voltage is "slowly rising and slowly falling", effectively protecting the test object and personnel safety.
Data management: Built-in large-capacity memory, can save hundreds of sets of test data, supports micro-printer printing or uploading to computer via U disk, Bluetooth, RS232 interface.
3. Main Technical Parameters (Reference)
High voltage output: Usually between 0.5kV and 10kV, adjustable in multiple gears.
Accuracy: tgδ error is usually between ±(reading 1.0%+0.04%) and ±(reading 1.0%+0.08%); capacitance (Cx) error is about ±(reading*1.5%+5PF).
Resolution: tgδ can reach 0.01% or 0.001%, Cx can reach 1pF or 0.1pF.
Operating conditions: Working temperature is generally -15℃ to 50℃, relative humidity <80%.
4. Application Fields
Widely used in on-site commissioning and preventive tests in power plants, substations, etc., as well as in workshops, laboratories, and scientific research units for testing the insulation performance of high-voltage equipment such as transformers, transformers, reactors, capacitors, bushings, and arresters.
5. Usage Precautions
Must be used in a power-off state: This instrument can only be tested on equipment that is powered off, but other non-tested equipment can remain powered.
Reliable grounding: The grounding terminal of the instrument must be reliably connected to the grounding grid. If the grounding is poor, the instrument usually refuses to start the test.
Pay attention to high voltage safety: The instrument has a built-in voltage boosting device. During operation, special attention should be paid to the insulation of the high-voltage lead and the safety of on-site personnel.
6. Related Industry Standards
The development, production, and testing of this instrument need to follow relevant power industry standards, for example:
DL/T 962-2005 "General Technical Conditions for High Voltage Dielectric Loss Testers" (Note: This standard has been abolished, and the current relevant standards such as DL/T 846.17—2025, etc.
