What are the GST, GST Guard, and UST test modes for dielectric loss (tan δ) measurement?

dielectric loss tester (Tan Delta Tester) is generally used in substations, power plants, workshops, laboratories, scientific research units and other environmental sites, the instrument is mainly for a variety of high-voltage power equipment dielectric loss tangent and capacitance measurement.

The working principle of this instrument is that after starting the measurement, the high voltage set value will be sent to the variable frequency power supply, the frequency conversion power supply uses the PID algorithm to adjust the output slowly to the set value, and the measurement circuit sends the measured high voltage to the variable frequency power supply, fine-tune the low voltage, and achieve accurate high voltage output.

According to the forward and reverse wiring settings, the measurement circuit will automatically select the input and switch the range according to the test current, the measurement circuit uses Fourier transform to filter out interference, separate the signal fundamental, perform vector operation on the standard current and sample current, calculate the capacitance of the amplitude, and calculate the angular difference.

Multiple measurements are repeated and the intermediate value is selected from the measurement result data. After the measurement, the measurement circuit issues a step-down command to slowly step down the conversion power supply to 0.

What are the Different Modes of the Tan Delta Test?

When it comes to tan delta test, there are essentially three modes of power factor testing. Those are:

GST Guard – This calculates the amount of current leakage to the ground. This method eliminates the current leakage through red or blue leads. Whereas in UST, the ground is termed to be guard because grounded edges are not calculated. When the UST method is applied on the device, then the current measurement is only through blue or red leads. The current flow through ground lead gets automatically bypassed to the AC source and thus excluded from the calculation.

UST – This is employed for the calculation of insulation in between ungrounded leads of the equipment. Here the individual portion of isolation has to be separated and analyze it having no other insulation connected to it.

GST – In this final mode of operation, both the leakage pathways are calculated by the test apparatus. The current, capacitance values, UST, and GST guards, loss in watts need to be equal to the GST test parameters. This provides the entire behavior of the test.

When the summing value of GST Guard and UST is not equal to the GST parameters, then it can be known that there is some crashing in the test set, or might the test terminal are not correctly designed.

FAQs:

• What does the Tan Delta value indicate?
  The Tan Delta value provides information about the quality of the insulation. Higher tan δ values suggest poorer insulation, while lower values indicate better insulation condition.
• When is the Tan Delta Test typically performed?
  The test is performed during the manufacturing, commissioning, and maintenance of electrical equipment, as well as during routine diagnostic assessments to monitor the condition of insulation over time.
• What are the applications of the Tan Delta Test?
  The Tan Delta Test is commonly used for assessing the condition of power cables, transformers, bushings, circuit breakers, and other high-voltage equipment with insulating materials.
• What are the advantages of the Tan Delta Test? Early Detection: It can detect insulation problems in their early stages, allowing for timely maintenance and preventing catastrophic failures.
• What are acceptable Tan Delta values?
  The acceptable Tan Delta values vary depending on the type of equipment and insulation material. Generally, lesser values than 0.7% indicate better insulation quality. Acceptable values should be defined by equipment standards or manufacturer guidelines.
• Is it necessary to perform the Tan Delta Test regularly?
  Regular testing is recommended, especially for critical equipment, as it helps to track the insulation’s condition and plan maintenance activities accordingly.
• Can the Tan Delta Test be used for oil-filled equipment?
  Yes, the Tan Delta Test is commonly used for assessing the insulation condition of oil-filled transformers and bushings, where it helps identify issues like moisture or contamination in the oil.
• How this Test is conducted on site?
  On-site testing involves using specialized test kit that applies high voltage at a specific frequency to the equipment under test, measuring the phase angle difference between current and voltage. The results are then compared to reference values.
• Can this Test predict the remaining lifespan of equipment?
  While the Tan Delta Test provides valuable data about insulation condition, it cannot predict the exact remaining lifespan of equipment. It helps in making informed decisions regarding maintenance and repair.
• Is it safe to perform this Test on energized equipment?

  No, it is not safe to perform on energized equipment. The equipment being tested should be properly de-energized and grounded to ensure the safety of the testing personnel.

• 
  

• Transformer Tan Delta Tester （JYC）

  

  

  
  

  
  

Kingrun Transformer Instrument Co.,Ltd.

More Transformer Testers from Kingrun