Last Updated on October 22, 2023 by Kevin Chen
We all know that transformers have a wide range of applications in various fields. As a result, it’s even more important to delve into the notion of transformer maintenance, which includes equipment testing, oil tests, and a variety of other tasks. More concentration is required to undertake dissolved gas testing, which analyzes the transformer’s complete electrical condition. Because transformer oil is used in circuit breakers, wires, and switches, it must be tested for the condition. Because oil improves dielectric characteristics, the Tan Delta Test determines the state of the transformer’s oil. This page explains the Tan Delta Test, its principle, multiple procedures, and distinct modes in a clear and informative manner.
What Is the Tan Delta Testing?
For electrical devices, the Tan Delta Test is crucial. This test provides information that can be combined with the results of other tests. This device determines the temperature of the equipment’s windings and insulation. This information is necessary for establishing whether or not a motor is faulty.
At zero speed, the method measures the voltage of a motor’s windings. The process is then repeated at full speed without any load. The formula for determining the maximum permissible delta voltage is:
Delta Voltage = (V2-V1)/(10 * RPM * K)
V1 is the voltage when no load is applied and V2 is when the load is applied fully.
The K factor is a number determined by the motor’s insulation and structure. A lower K factor is needed for a motor with better insulation. A lower K factor is required for a building with less insulation.
The delta voltage should not exceed 20% of V1’s maximum rating in either situation. If it doesn’t, an issue with the device’s insulation or winding needs to be addressed.
Tan Delta testing can be performed on which instruments?
Tan testing can be performed on transformers, windings, current transformers, potential transformers, transformer bushings, cables, and generators, among other power types utilized in substations. It is used to measure the insulation quality and in conjunction with other tests such as WRM and TTR.
Reasons for doing Tan δ testing?
The tan delta test ensures that the transformer continues to perform safely and reliably. The result of the insulation behavior of bushings and windings can be calculated using the capacitance values and dissipation factor.
Variations in capacitance, for example, imply partial bushing breakdowns and automated winding movement. Heat is produced due to a lack of insulation, equipment aging, and an increase in energy levels. The dissipation factor is used to determine the number of losses in these.
Using the tan delta testing procedure, one can quickly understand the capacitance values and the dissipation factor athe the needed frequencies level. So, any aging factor can be identified earlier, and the corresponding action can be implemented.
Understanding Tan Delta Testing Results
A 20 percent delta isn’t huge, and it’s easily achievable even when the motor is operating at maximum capacity. As a result, it’s critical to proceed with caution when measuring voltage.
If feasible, take at least one measurement with the motor turned off. This ensures that as current is pulled from the windings, the voltage of the windings rises, indicating faulty winding insulation.
When taking measurements on a motor, it’s also a good idea to avoid reversing the load and voltage connections. For example, test without a load first, then without voltage. This might lead to erroneous data points and harm to the measurement equipment or electrical device.
For motors, the tan delta test is crucial. This test identifies whether or not there is a problem that could result in high maintenance costs, downtime, or decreased productivity.
Principle of Tan Delta Test
When the earth and the line are connected, a pure insulator acts as a capacitor. Because the insulating substance serves as a dielectric that is completely pure in an ideal insulator form, the current passing through the material only carries capacitive material. Because there are no impurities in the insulating component, there’ll be no resistive component for the electric current traveling from the line to the ground via the insulator. The circuit schematic for the tan delta test looks like this:
The capacitive current in a pure capacitive material is 900 times higher than the voltage level. In general, the insulating substance is completely clean, although contaminations like moisture and dirt may be introduced due to the aging qualities of the components. These contaminants provide a current with a conductive route. As a result, resistive elements are held in the leakage current that passes from the line to the ground via the insulator.
As a result, claiming that the leakage current within the resistive element is equally modest for a decent insulator quality is meaningless. The proportion of the resistive element to the capacitive element, on the other hand, may provide insight into an insulator’s behavior. This fraction is known as tan or tan delta, which is proportional to the quality of the insulator. This is also known as a dissipation factor in some situations. It can be figured out by looking at the vector diagram below.
The x-axis shows the level of system voltage, which is the resistive element of leakage current IR, and the y-axis represents the level of system voltage. This capacitive element of the leakage current IC is taken across the y-axis because it precedes 900.
IL(IC + IR) now represents the total leakage current.
And tan is (IR /IC) according to the diagram.
tanδ = (IR /IC)
Tan Delta Testing Process
The procedure outlined below walks you through the steps of tan delta testing.
- The components required for this test, such as the potential transformer, cable, current transformer, bushings, and winding on which the testing is performed, must first be isolated from the system.
- The instrument where the insulation is to be analyzed is used in conjunction with the lowest frequency level of test voltage.
- The voltage levels are initially applied at typical levels. The applied voltage level is increased by two times the applied voltage level when the tan delta values are as expected at this voltage level.
- The tan delta controller keeps track of the values of the tan delta.
- A loss angle analyzer is coupled to the tan delta calculating component, and it relates tan delta values at general and higher voltage levels, delivering precise results. It has to be noted that the testing procedure is to be carried out at very minimal frequency levels.
It is preferable to conduct testing at low frequencies because when the applied voltage level increases, the capacitive reactance of the insulator device decreases, and the capacitive element of the current increases. Because the resistive element is nearly constant, it is determined by the applied voltage level and the conductivity value of the insulator.
When the current frequency is raised, the capacitive current increases, and the amplitude of the vector amount of either the capacitive or resistive portions of the current increases. As a result, the tan delta tests required level of power increases, which appears unacceptable. As a result of the power constraint, only a very low-frequency test voltage is necessary for dissipation factor analysis.
Predicting the Test Results
There are primarily two techniques to analyze the insulating method’s situation during tan delta testing. The first step is to assess previous test results to see whether the insulation conditions have deteriorated due to the aging effect. The second example involves determining the insulation behavior straight from the tan value. In this case, there is no need to evaluate previous outcomes using those tan test values.
If the insulation results are correct, the full test voltage range loss factor numbers are almost identical. However, when the insulation results are incorrect, the tan values are increased for higher voltage levels. In insulation, increased tan corresponds to the presence of a high resistive current element. These results could be compared to those of previously tested insulators to make the best judgment about whether or not the equipment should be replaced. This is how tan delta testing is carried out.
What are the Tan Delta Test’s Different Modes?
There are three kinds of power factor assessment regarding the tan delta test. That is it.
The amount of current that leaks to the ground is calculated using this method. Current leakage across red or blue leads is eliminated using this technique. Because calculation of the grounded edges are not done in UST, the ground is called the guard. The current measurement is solely through red or blue leads when the device uses the UST method. The current flowing via the ground lead is automatically bypassed and consequently not included in the computation.
This is used to calculate the insulation between the equipment’s ungrounded leads. Here, the individual part of isolation must be detached and analyzed without being attached to any other insulation.
The test device calculates both leakage paths in this last phase of operation. The UST, capacitance values, current, GST guards, and the loss in watts must all match the GST test criteria.
This describes the test’s whole behavior.
When the summing value of UST and GST Guard does not equal the GST parameters, it is possible that the test set is crashing or that the test terminal is not built correctly.
The Tan Delta Test is explained in full in this article. In this post, we will learn everything there is to know about the tan delta test, including its premise, purpose, testing technique and procedures.
For more details on Tan delta testing and purchase of quality electrical components to use, contact us at ICRFQ. We manufacture the best electrical components in China.
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