I Overview
The GHJS-A variable frequency fully automatic dielectric loss tester is a high-precision testing instrument used in power plants, substations, and other field or laboratory settings to measure the dielectric loss tangent and capacitance of various high-voltage power equipment..The instrument features an integrated structure, incorporating a dielectric loss test bridge, variable frequency voltage regulating power supply, step-up transformer, and SF6 high-stability standard capacitor. The test high-voltage source is generated by the internal inverter and stepped up by the transformer for testing the specimen. The frequency can be varied to 50Hz, 47.5Hz, 52.5Hz, 45Hz, 55Hz, 60Hz, 57.5Hz, 62.5Hz, 55Hz, and 65Hz. It employs digital notch technology to avoid interference from power frequency electric fields, fundamentally solving the problem of accurate measurement under strong electric field interference. It is also suitable for testing with generator power supply after a complete power outage. The instrument can be equipped with an insulating oil cup and temperature control device to test the dielectric loss of insulating oil.
The instrument mainly has the following features:
l Large LCD Chinese display
Simple operation: the instrument is equipped with a high-end full touch LCD screen, with a large full touch operation interface. Each process is very clear and understandable, and operators can use it without additional professional training. A simple tap can complete the entire measurement process, making it an ideal intelligent dielectric loss measurement device.
l Massive data storage
The instrument is equipped with a calendar chip and large-capacity storage, saving up to 200 sets of data. Test results can be saved in chronological order, and historical records can be viewed at any time and printed out.
l Scientific and advanced data management
Data can be exported via USB drive and can be viewed and managed on any PC using our company's dedicated software.
l Multiple test modes
The instrument can test using various modes such as internal high voltage, external high voltage, internal standard, external standard, positive connection, reverse connection, and self-excitation method. Under external standard and external high voltage conditions, it can perform high-voltage (greater than 10kV) dielectric loss tests.
l One-step CVT testing
The instrument can also test the dielectric loss and capacitance of fully sealed CVT (capacitor voltage transformer) C1 and C2, achieving simultaneous testing of C1 and C2. It can also test CVT ratio and voltage phase difference.
l Measure CVT without disconnecting high-voltage leads
The instrument can accurately measure the dielectric loss and capacitance of CVT without disconnecting the high-voltage leads.
l CVT reverse connection shielding method to measure C0
The instrument can use the reverse connection shielding method to measure the dielectric loss and capacitance of the upper end C0 of the CVT.
l High-speed signal sampling
The internal inverter and sampling circuit are fully digitally controlled, and the output voltage is continuously adjustable.
l Fully automatic LCR measurement
Fully automatic measurement of inductance, capacitance, and resistance, with angle display.
l Multiple protections for safety and reliability
The instrument has multiple protection measures such as input voltage fluctuation, high voltage current, output short circuit, power supply failure, overvoltage, overcurrent, and temperature, ensuring the safety and reliability of the instrument. It also has a grounding detection function to ensure that ungrounded equipment cannot be boosted.
II Working Principle
Under the action of AC voltage, the dielectric consumes part of the electrical energy, which is converted into heat energy and causes loss. This energy loss is called dielectric loss. When AC voltage is applied to the dielectric, there is a phase angle difference ψ between the voltage and current in the dielectric. The complementary angle δ of ψ is called the dielectric loss angle, and the tangent of δ, tgδ, is called the dielectric loss tangent. The tgδ value is a parameter used to measure dielectric loss. The instrument's measurement circuit includes a standard circuit (Cn) and a test circuit (Cx), as shown in Figure 2-1. The standard circuit consists of a built-in high-stability standard capacitor and the measurement circuit, while the test circuit consists of the test object and the measurement circuit. The measurement circuit is composed of a sampling resistor, a preamplifier, and an A/D converter. The measurement circuit separately measures the amplitude and phase difference of the current in the standard circuit and the test circuit. Then, the digital signal processor uses digital real-time acquisition methods and vector operations to obtain the capacitance and dielectric loss tangent of the test object. The instrument has built-in anti-interference measures to ensure accurate measurement under external electric field interference.
