TAN DELTA & CAPACITANCE MEASUREMENTS TEST

 

TAN DELTA & CAPACITANCE MEASUREMENTS  

SOFTWARE : DIGITAL LOSS AND PARTIAL DISCHARGE ANALYZER 10-100HZ-V2-2.1

 

THIS TEST WILL BE PERFORMED BY APPLYING AC VOLTAGE IN STEP OF 20% OF THE RATED PHASE TO GROUND VOLTAGE TO EACH PHASE SEQUENTIALLY. THE MAX. VOLTAGE WILL BE LIMITED TO 100% OF THE RATED PHASE TO GROUND VOLTAGE . THE FOLLOWING PARAMETERS WILL BE MESSURED AND CACULATION.

A.TAN-DELTA & TAN-DELTA TIP-UP

B.CAPACITANCE & CAPACITANCE TIP-UP

 

PROCEDURE:

CONNECTION

R-PHASEàEARTH

Y-B PHASE SHORT àEARTH

THEN ANOTHER SAME SEQUENCE FOLLOW

 

RESULT:

 

Temp: 40°C

KV	PHASE – U		PHASE – V		PHASE - W		PHASE – UVW
	TAN d %	CAP (pF)	TAN d %	CAP (pF)	TAN d %	CAP (pF)	TAN d %	CAP (pF)
1.20	3.23	71980	3.08	72040	2.98	71850	2.35	208700
2.60	3.31	72080	3.13	72110	3.12	71970	2.39	208900
3.90	3.37	72070	3.21	72130	3.19	71960	2.43	209000
5.10	3.40	72090	3.21	72130	3.24	71990	2.51	209100
6.30	3.88	72370	3.68	72420	3.69	72230	2.96	209900

 

 

For what reason to know the TAN DELTA unequivocally?

 

What is the Tan Delta Test?

A pure insulator when is connected across line and earth behaves as a capacitor. In an ideal insulator, as the insulating material which acts as dielectric too, is 100 % pure, the electric current passing through the insulator, only have a capacitive component. There is no resistive component of the current, flowing from line to earth through the insulator as in ideal insulating material, there is zero per cent impurity.

In a pure capacitor, the capacitive electric current leads the applied voltage by 90o.

In practice, the insulator cannot be made 100% pure. Also due to the aging of insulators, the impurities like dirt and moisture enter into them. These impurities provide the conductive path to the current. Consequently, an electric leakage current flowing from line to earth through the insulator has a resistive component.

 

Purpose

The main purpose of the tan delta test is to make sure of maintaining a secure and reliable functioning of the transformer. With the calculation of dissipation factor and capacitance values, it provides the result of insulation behavior of bushings and in windings too.

Variation in the capacitance value, for instance, it indicates partial kind of breakdowns in bushings and automated movement of windings. Insulation deprivation, aging of the equipment, enhancement in the energy levels is transformed into heat. The amount of losses in these is calculated as the dissipation factor.

With the tan delta testing method, one can easily know the dissipation factor and the capacitance values at the required level of frequencies. So, any kind of aging factor can be identified earlier and the corresponding action can be implemented.

 

Principle of Tan Delta Test

When a pure insulator has a connection between the earth and the line, then it performs like a capacitor. In an ideal kind of insulator, as the insulating substance functions as a dielectric, which is totally pure, then the passage of current through the material holds only capacitive material. There will be no resistive element for the electric current that is flowing from the line to the earth via insulator as in the insulating component, there will be no presence of impurities. The tan delta test circuit diagram is shown as follows:

Tan Delta Test Circuit

In a pure capacitive material, the capacitive current precedes the voltage level by 900. As a general, the insulating material is totally pure, and even because of the aging properties of the components, the contaminations such as moisture and dirt might get added. These contaminations create a conductive path for the current. As a result, leakage current that flows from line to earth via the insulator holds resistive elements.

 

Therefore, it is pointless to claim that, for a good quality of insulator, this resistive element of leakage current is correspondingly minimal. In the other aspect, the behavior of an insulator might be known by the proportion of the resistive element to that of the capacitive element. For good quality of insulator, this proportion is correspondingly less and this is termed as tanδ or tan delta. In a few cases, this is also expressed as a dissipation factor. With the below-depicted vector diagram, it can be known.

Tan Delta Test Vector Diagram

Where the x-axis represents the level of system voltage which is the resistive element of leakage current IR. As this capacitive element of leakage current IC precedes by 900, it is taken across the y-axis.

And now, the whole leakage current is given by IL(IC + IR)

And from the diagram, tanδ is (IR /IC)

tanδ =  (IR /IC)

 

Tan Delta Testing Process

The below process explains the method of tan delta testing in a step-by-step manner.

The requirements necessary for this test such as cable, potential transformer, bushings, current transformer, and winding on which this testing is conducted has to be initially separated from the system.

The minimal frequency level of test voltage is applied along with the equipment where the insulation to be analyzed.

At first, normal voltage levels are applied. When the tan delta values are as expected at this voltage level, then the applied voltage level is increased by 2 times as of applied voltage.

The values of the tan delta are recorded by the tan delta controller.

To the tan delta calculating component, a loss angle analyzer is connected which compares tan delta values at higher and general voltage levels and delivers accurate results.

It has to be noted that the testing procedure to be carried out at very minimal frequency levels.

It is more recommended to conduct testing at minimal frequency levels, because when the applied voltage level is more, then the capacitive reactance of the insulator device reaches very minimal, therefore the capacitive element of the current reaches more. As the resistive element is practically constant; it is based on the applied voltage level and the insulator’s conductivity value.

Whereas at increased frequency level the capacitive current, is more, and then the amplitude of the vector amount of both the capacitive and resistive elements of the current reaches very high. So, the necessary level of power for the tan delta test would become more that seems to be not acceptable. Because of this, the power constraint for dissipation factor analysis, very minimal frequency test voltage is required.

Predicting the Test Results

These exist mainly two approaches to analyze the situation of the insulation method at the time of tan delta testing. The first is, evaluating the past test results to know the worsening of insulation conditions because of the aging effect. Whereas the second scenario is to verify the insulation behavior directly from tanδ value. Here, there is no necessity of assessing past results with that tanδ test values.

When the insulation results are accurate, then the loss factor values are nearly similar for the entire test voltage values. But, in the case when the insulation results are not accurate, then the tanδ values get increased for a higher level of voltages. The increasing tanδ corresponds that, high resistive current element, happens in insulation. These outcomes might be matched with the outcomes of past tested insulators, to go with the appropriate decision either the equipment has to be substituted or not.

This is the way that how to test the result tan delta testing can be done.

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 Mode – 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 Mode – 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.

On the whole, this is a detailed explanation of the Tan Delta Test. Here, in this article, we are completely aware of what is a tan delta test, its principle, purpose of it, methods, and testing technique. Also know about what are LV to earth test, HV to earth test, and LV-HV tan delta testing methodologies?

 

 

WHAT IS DISSIPATION FACTOR?

 

Dissemination Factor Tan Delta is the proportion of futile flow in the Electrical framework to a helpful flow in it. That implies this is the proportion of Wattloss current to the Reactive current in it.

 

i.e tan = IR/Ic

 

For the voltage applied V

 

tan = Watt-misfortune (Active) Power

 

Thus tan delta is considered as the proportion of nature of protection in dielectric material.

 

In certain nations Cos is estimated to know the Insulation Quality.

 

Watt misfortune in Power System

 

It is needed to screen the watt misfortune through the protection of Power System, A Generator, Transformer, Cable even a Power Capacitor utilized in the Electric circuit of Generation, Transmission and Distribution will have exceptionally low influence misfortune.

 

Eg1 . The Capacitors, that to be utilized for Power Factor Correction, or a Power Cable that is utilized in Electric Power Circuit are extremely fundamental to have exceptionally low wattloss.

 

for example 0.2/kVAR for Power Capacitors and tan delta of 0.0005 for Power Cables.

 

The Dissipation Factor tan is the immediate proportion of watt misfortune (VAcos) in the absolute reactance of the Power Capacitor. for example The ostensible tan delta worth of 0.0002 will be saved for Power Capacitor under use.

 

To guarantee the right wattloss/KVAR, the tan delta will be estimated with high accuracy i.e with the precision 0.00005 or better and this estimating framework will create repeatable outcomes for a long time.

 

Eg2 All over the world for a really long time together the information on Dielectric Material have been recorded and checked. Ordinarily the Insulating Oil contributes significant part as the dielectric material, in an Electrical Power Appliance. Subsequently it is exceptionally fundamental to exactly know the diverse Electrical and Chemical properties of Insulating Oil.

 

To know the electrical properties of the Insulating Oil, the tan delta test and to know the compound debasements the Dissolved Gas Analysis (DGA) of the oil is led. These two tests are considers similar to the ideal measuring stick for Failure Analysis and furthermore for Aging Effect of the Power Equipment under use.

 

For crisp protecting Oil the Dissipation Factor is noted utilizing exceptionally exact instrument. For this situation the Dissipation Factor is just about as less as 0.0001 and this estimation will be with precision of 0.00005 (0.005%) of perusing (according to IEC 250).

 

This table was genuine tan delta test on generator after fixed from flooded of seal oil. The test outcome ought to be less that 2 %.