A Must Course for All Engg

Concept of Insulation Resistance

Leakage Current & Its Component

Insulation Resistance Test

d Insulation Resistance test

Di-Electric Absorption Ratio Test , Reading at 30 Sec & 1 Min

Polarization Index Test

Die-Electric Discharge Test

Variable Voltage Range

Ramp Test

What Causes Insulation Resistance to Degrade

How Insulation Resistance Test Set work

Understanding Insulation resistance distribution

Understanding Leakage Current

Direction of Leakage Current

Principle of measurement for Insulation Resistance

Equivalent Circuit of Insulation Resistance

Formula to calculate insulation Resistance

Understanding types of leakage current Conductive Leakage Current Capacitive Leakage Current Polarization / Absorption Leakage Current Surface Leakage Current

Understanding Chag Current

Capacitance Distribution

Capacitance Equivalent circuit of three phase circuit

How Cable Chag works Chag Constant Calculating 5T Effect of Chag Current on reading of IR Polarization / Absorption Current Die Electric absorption in detail Understanding Current Curves ( Conduction, Capacitive, Polarization)

Selection of Applied Voltage as per IEEE standard 43 Application of IR Test How to make connections & different combinations to test Understanding Test Connection Proof Testing / Installation Testing Maintenance Testing Spot / Short resistance test d Resistance Test

Step Voltage test Analyzing Step Curve Di-Electric Absorption Test Analyzing Curve for Di-Electric Absorption Test Various Insulation Resistance Test

Temperature correction for testing rotating machines Analyzing curve for Temperature Co-efficient Factor Testing Wiring Mr Testing Calculation Example Connection Diagram of Cable testing Connection Diagram of Motor testing Connection Diagram of Generator testing Connection Diagram of Circuit Breaker Testing Connection Diagram of Bushing testing

Understanding Voltage Characteristics for IR Tester Analyzing Curve for IR Tester Guard Teal Guard Teal Connection Guard Teal Equivalent Circuit Example of using Guard connection for accuracy The Guard Teal as Diagnostic Tool

Basic Understanding

Content of Course

Definition of Insulation Resistance

What Causes Insulation Resistance to Degrade

How Insulation Resistance Test Set work

Understanding Insulation resistance distribution

Understanding Leakage Current

Direction of Leakage Current

Principle of measurement for Insulation Resistance

Equivalent Circuit of Insulation Resistance

Formula to calculate insulation Resistance

Understanding types of leakage current

Conductive Leakage Current

Capacitive Leakage Current

Polarization / Absorption Leakage Current

Surface Leakage Current

Understanding Chag Current

Capacitance Distribution

Capacitance Equivalent circuit of three phase circuit

How Cable Chag works

Chag Constant

Calculating 5T

Effect of Chag Current on reading of IR

Polarization / Absorption Current

Die Electric absorption in detail

Understanding Current Curves ( Conduction, Capacitive, Polarization)

Selection of Applied Voltage as per IEEE standard 43

Application of IR Test

How to make connections & different combinations to test

Understanding Test Connection

Proof Testing / Installation Testing

Maintenance Testing

Spot / Short resistance test

d Resistance Test

Step Voltage test

Analyzing Step Curve

Di-Electric Absorption Test

Analyzing Curve for Di-Electric Absorption Test

Various Insulation Resistance Test

Temperature correction for testing rotating machines

Analyzing curve for Temperature Co-efficient Factor

Testing Wiring

Mr Testing Calculation Example

Connection Diagram of Cable testing

Connection Diagram of Motor testing

Connection Diagram of Generator testing

Connection Diagram of Circuit Breaker Testing

Connection Diagram of Bushing testing

Understanding Voltage Characteristics for IR Tester

Analyzing Curve for IR Tester

Guard Teal

Guard Teal Connection

Guard Teal Equivalent Circuit

Example of using Guard connection for accuracy

The Guard Teal as Diagnostic Tool

Introduction to ANSI/IEEE Std 95-1977

Demonstration of Mr Video

Video How to Test Cable

Video How to Test Transformer

Video How to Test Motor

insulation resistance

An insulation resistance (IR) test measures the total resistance between any two points separated by electrical insulation. The test, therefore, detees how effective the dielectric (insulation) is in resisting the flow of electrical current

Insulation Resistance / Mr Test

Most commonly referred to as simply a "mr," the insulation resistance test set (or Megohmeter) is used to detee the condition of insulation on various types of electrical equipment like cables, transformers and switchgear.

Tests are typically conducted by applying a direct current (dc) voltage to the conductor under test and measuring the current that flows through insulation (called the "leakage current") and into the non-current carrying metal parts of equipment. Contaminated insulation can be deteed by observing the absorption current - or current absorbed by the insulation - over a specified period of .

What Causes insulation to Degrade?

Electrical Stress

Mechanical Stress

Chal Attack

Thermal Stress

Environmental Contamination

How an Insulation Resistance Tester Operates

The Mr insulation tester is essentially a high-range resistance meter (ohmmeter) with a built-in dc generator.

The instrument's generator, which can be hand-cranked, battery or line-operated, develops a high dc voltage that causes several small currents through and over surfaces of the insulation being tested.

The total current is measured by the ohmmeter, which has an analog indicating scale, digital readout or both

Insulation Resistance / Mr Test Record keeping

Insulation-resistance test data may be used to establish a trending pattern with deviations from the baseline information pe evaluation of insulation. The results of these tests (typically expressed in Megohms) are dependent on the temperature of the insulating material and the humidity of the surrounding environment at the of testing; therefore all readings must be corrected to a base temperature, such as 20°C.

How much voltage can a be produced?

Insulation testers come in a variety of sizes and output voltages depending on its specific application. A handheld 1000V Megohmeter is usually sufficient for 600V class equipment while larger sets for use on high voltage apparatus can output up to 15,000V or more.

Mr Test Connections

There are three test teals on an insulation resistance tester marked positive (+), negative (-) and Guard (G). Most basic measurements utilize only the positive and negative teals, such as in cases when there is little possibility of adverse current paths that could affect the result.

When testing at higher voltages, such as with cable or transformers, the guard teal can be used to divert surface leakage from the measuring circuit. Not all insulation testers are equipped with a guard teal.

Note: Handheld megohmeters with outputs of 1000V or less may not be equipped with a Guard teal.

What is Insulation Resistance

No insulation is ideal and hence there will be always some leakage current from insulation to ground, when voltage is applied.

Leakage Current Direction

How to Measure Insulation Resistance

Insulation Resistance is measured by Ohm's Law

Insulation Resistance = Applied Voltage / Leakage Current

Applied Voltage = 1000 V

Measure Leakage Current = 0.001Amp

Measured Insurance Resistance = 10 Mega Ohms

Understanding Insulation Resistance Equivalent Circuit

finding Insulation Resistance value by using formula

Leakage Current Types

There are two types of leakage current

1.Conductive Leakage Current

2.Capacitive Chag leakage Current

3.Polarizing / Absorption Current

4.Surface Leakage Current

Different types of leakage Currents & its effect on readings

The total current is the sum of these components. (Leakage current is shown as one current.) It is this current that can be measured directly by a microammeter or, in terms of megohms, at a particular voltage by means of a Mr insulation tester. Some instruments offer the alternatives of displaying a measurement in terms of current or as a resistance.

Because the total current depends upon the that the voltage is applied, Ohm's Law (R = E/I) only holds, theoretically, at an infinite (that implies waiting forever before taking a reading). It is also highly dependent upon starting from a base level of total discharge. The first step in any insulation test is, therefore, to ensure that the insulation is completely discharged

Conduction current

Conduction current is steady through the insulation and is usually represented by a very high value resistor in parallel with the capacitance of the insulation. It is a component of the Leakage Current, which is the current that would be measured when the insulation is fully charged and full absorption has taken place. Note that it includes surface leakage, which can be reduced or eliminated by the use of the guard teal (to be discussed later).

The graph in Figure 2 shows the nature of each of the components of current with respect to .

Surface Leakage Current

The surface leakage current is present because the surface of the insulation is contaminated with moisture or salts. The current is constant with and depends on the degree of ionization present, which is itself dependent on temperature. It is often ignored as a separate current, being included with the conduction current below as the total leakage current.

Capacitive chag leakage current (IC )

When two or more conductors are run together in a raceway, they act as a capacitor. Due to this capacitive effect, a leakage current flows through conductor insulation. This current lasts only for a few seconds as the dc voltage is applied and drops out after the insulation has been charged to its full test voltage. In low-capacitance equipment, the capacitive current is higher than conductive leakage current, but usually disappears by the we start recording the data. Because of this, it is important to let the reading "settle out" before recording it. On the other hand, when testing high capacitance equipment the capacitive chag leakage current can last for a very long before settling out.

Polarization / absorption leakage current (IA )

Absorption current is caused by the polarization of molecules within dielectric material.

The positive and negative charges in molecules separate, causing an increase in the state of polarization P. A chag state of polarization corresponds to charge movement and so is equivalent to a current, hence the term "polarization current".

Absorption current is actually made up of up to three components, which decay at a decreasing rate to a value close to zero over a period of several minutes. The first is caused by a general drift of free electrons through the insulation under the effect of the electric field.

Components of test currents

Capacitor Chag Behavior

Capacitance of cable is distributed along cable.

Capacitance is added in parallel hence it will be added

Longer is the cable more will be the capacitance

Capacitance Equivalent circuit of three phase circuit

Capacitor Chag

Chag

Chag Current will decay when Capacitor is charged

After cable / equipment is charged Capacitive chag current reduces to zero.
Constant = T = RC

Capacitor Charge in 5T

Effect of Chag Current on Reading of Insulation Resistance

Insulation Resistance can be defined as

IR = V applied / I conductive resistive leakage current

But in practical there is Capacitive Leakage current is also available due to capacitance of cable.

Tester Read IR = V / ( I R + I C )

I C decays to Zero after 5T and reading become stable.

Initially Tester will show low reading and with it will increase & become stable

Testing of IR

During the testing procedure, the high dc voltage generated by pressing the test button will cause a small (micro-amps) current flow through the conductor and the insulation. The amount of current depends on the amount of voltage applied, the system's capacitance, the total resistance, and the temperature of the material. For a fixed voltage, the higher the current, the lower the resistance (E=IR, R=E/I). The total resistance is the sum of the internal resistance of the conductor (small value) plus the insulation resistance in MΩs

Dielectric polarization

Dielectric polarization is the term given to describe the behavior of a material when an external electric field is applied on it. A simple picture can be made using a capacitor as an example. ... The charges in the material will have a response to the electric field caused by the plates

Absorption current

Absorption current is actually made up of up to three components, which decay at a decreasing rate to a value close to zero over a period of several minutes.

The first is caused by a general drift of free electrons through the insulation under the effect of the electric field. A Guide to Diagnostic Insulation Testing Above 1 kv 7

The second is caused by molecular distortion whereby the imposed electric field distorts the negative charge of the electron shells circulating around the nucleus toward the positive voltage.

The third is due to the alignment of polarized molecules within the electric field applied. This alignment is fairly random in a neutral state, but when an electric field is applied, these polarized molecules line up with the field to a greater or lesser extent.

Polarization

How Much Voltages should be applied for different insulations

Application of IR Test

Installation Test

The most important reason for testing insulation is to insure public and personal safety

By perfog a high dc voltage test between de-energized current-carrying (hot), grounded, and grounding conductors, you can eliminate the possibility of having a life-threatening short circuit or short to ground.

Maintenance Test

The second most important rea- son for insulation testing is to protect and prolong the life of electrical systems and motors.

Over the years, electrical systems are exposed to environmental factors such as dirt, grease, temperature, stress, and vibration. These conditions can lead to insulation failure, resulting in loss of production or even fires. Periodic maintenance tests can provide valuable information about the state of deterioration and will help in predicting possible failure of the system.

Installation Test / Proof Testing

To Check Healthiness of installed equipment / Cables

The proof test is a simple, quick test used to indicate the instantaneous condition of insulation.

It provides no diagnostic data and the test voltages used are much higher than the voltages used in predictive maintenance tests. The proof test is somes called GO/NO GO TEST because it tests cable systems for maintenance errors, incorrect installation, serious degradation, or contamination.

The installation is declared acceptable if no breakdown occurs during testing.

Choosing the test voltage

Choosing the test voltage

Proof test procedure

Proof Testing

Predictive maintenance tests

Spot-reading/short- resistance test

Selection of Voltage level

Formula to apply voltages

Insulation Resistance test curve

IR over period of

Step Voltage Curve

Step voltage test

Step Voltage Curve

Analyzing Good V/s Poor Insulator after step voltage test

Dielectric-absorption/ -resistance test

Dielectric absorption test, Dielectric Absorption Ratios, Various Insulation test Chart, Dielectric Discharge Test, Polarization Index , D.A. and PI Comparison, Temperature correction for testing rotating machines, How to make connections & different combinations, Testing generators and motors, Testing transformers, Testing wiring and cable installations, Calculation Example, Pre-Testing Requirement How to setup connections, Work safely, Connection Diagram for Motor, Transformer, Cable, Generator, Voltage Characteristics, The Guard Teal, Introduction to ANSI/IEEE Std IEEE Std P43-2000, Demonstration of Mr Test

Student, Eeer, Professionals



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