3.measuring and testing equipment.ppt

MEASURING AND TESTING INSTRUMENTS MEASURING AND TESTING INSTRUMENTS (ELECTRICAL):(ELECTRICAL):

Types & Applications

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Introduction• Testing is an essential activity in the power utility

industry. Whatever your role in the industry - electrical designer, purchase engineer, manufacturer, installation contractor, technician or maintenance engineer, a solid knowledge of electrical tests to be carried out on a given piece of HV and MV electrical equipment and interpretation of results obtained, is a necessity.

• This presentation is designed to familiarize you with some of the most common measuring instruments and some of the most common tests conducted and used for various aspects of installing and testing general electrical equipment.

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The Need for and Purpose of Testing:

• Electrical Safety Testing is essential to ensure safe operating standards for any product that uses electricity. Various governments and agencies have developed stringent requirements for electrical products that are sold world-wide. In most markets it is mandatory for a product to conform to safety standards. To conform to such standards, the product must pass safety tests such as the high voltage test (also called dielectric voltage-withstand test or high potential test), Insulation Resistance Test, Ground (Earth) Bond & Ground Continuity Test & Leakage Current Test (also called Line Leakage Test, Earth Leakage Current Test, Enclosure Leakage Current Test or Patient Leakage Current Test).

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Some Common Safety Tests:

• High Voltage Test (Dielectric Voltage-withstand Test): Also called a Hipot test, this test is carried out by applying a significantly higher than operating voltage to the device under test. In this test, the insulation of a product, stressed to a greater extent than under normal operating conditions, should not be breached for the product to pass. In most cases, the device is stressed to twice its normal operating voltage. DDielectric strength is the maximum voltage a ielectric strength is the maximum voltage a dielectric can withstand without rupturing.dielectric can withstand without rupturing.

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Some Common Safety Tests:

• Insulation Resistance Test: This test is to measure the total resistance of a product’s insulation by applying a minimum acceptable voltage. The minimum acceptable value of resistance for a product must be met for it to pass an insulation resistance test. The test therefore, determines how effective the dielectric(insulation) is in resisting the flow of electrical current. Such test are useful for checking the quality of insulation, not only of a product when is first manufactured, but over time as the product is used.

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Some Common Tests (Continued)

Earth Continuity Test: This test checks that a path exist between all exposed conductive surfaces and the power system earth. This ground circuit provides the most fundamental means of electric shock protection for a user. The maximum acceptable value is generally 0.5 ohms although certain standards may specify 0.1 ohms.

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• Earth Bond Test: An earth bond test verifies integrity of the earth path by applying a high current, low voltage source to the earth path circuit. This test is similar to the earth continuity test with the additional benefit of verifying how an equipment will perform under actual fault conditions. When a ground faults occurs, current starts to flow through the earth circuit. If the current-carrying capacity is high enough and the circuit resistance low enough, the system operates properly and the user is protected from shock.

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Leakage Current Test (Line Leakage Test): This test is to measure the undesirable leakage current that flows through or across the surface of the insulation or the dielectric of a capacitor. This test is generally carried out at 100%-110% of the rated input voltage of the product under test. The maximum acceptable limit of a leakage current is generally 210 micro amperes. In other words, this test simulates a person touching exposed metal of a product and detects whether or not the leakage current that would flow through the person’s body remains below a safe level.

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Electrical Testing and Electrical Testing and Measuring InstrumentsMeasuring Instruments

Dielectric Withstand TestDielectric Withstand Test•A dielectric withstand test is an electrical test performed on a component or product to determine the effectiveness of its insulation. The Hipot test is a test of the insulation surrounding the primary circuits. It involves the application of a high voltage from the primary circuit to the grounding (earth) circuit and to the low-voltage secondary circuits. The potential used for each test is pre-determined by the applicable safety standard. It is based on the ac input voltage, the grade of insulation used in the equipment and the accessibility of the secondary voltages.

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• A dielectric Withstand test verifies that the insulation of an equipment or component is sufficient to protect the operator from electrical shock.

• If insulation can withstand a voltage above its normal rating for a given period of time, it will function adequately at its normal voltage levels. The Hipot test (sometimes called a Dielectric Withstand test or breakdown test) stresses the insulation well beyond what it would encounter in normal use.

• The Hipot test is probably the best known, the most often performed and most important electrical production line safety test.

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• The theory behind the test is that if a deliberate over-application of test voltage does not cause the insulation to break down, the product will be safe to use under normal operating conditions—hence the name, Dielectric Withstanding Voltage test.

• In addition to over-stressing the insulation, the test can also be performed to detect material and workmanship defects, most importantly small gap spacings between current-carrying conductors and earth ground.

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• When a product is operated under normal conditions, environmental factors such as humidity, dirt, vibration, shock and contaminants can close these small gaps and allow current to flow. This condition can create a shock hazard if the defects are not corrected at the factory.

• No other test can uncover this type of defect as well as the Dielectric Withstand test.

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• Dielectric Withstand Test Procedure:Dielectric Withstand Test Procedure:• Perform a Hipot test by connecting the RTN/LOW

terminal of the tester to one side of the device and the HV terminal (or probe) to the other side. (When testing an appliance, the low side is usually connected to the ground and/or the exposed case of the product and the high side to the power line and neutral tied together.) To prevent damaging the device, the test voltage should be “ramped,” or increased gradually. The test instrument monitors the current for changes that exceed the limit for steady state, or short duration pulses (arcs), or both. The voltage level is maintained for a programmed duration, after which the voltage is shut off and the device discharged.

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• If at any time while the voltage is applied the current limit is exceeded, the high voltage is automatically turned off and a breakdown indicated. The actual voltage and current at breakdown is often indicated. If no breakdown occurs over the specified test time, the tester would indicate a PASS, signifying that the device is good.

• Only after the tester high voltage is turned off and the device allowed to discharge should the device be disconnected.

• Since a Hipot test can be destructive, perform an insulation resistance measurement on a device before and after a Hipot test.

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Earth Continuity TestingEarth Continuity Testing•It is important to ensure the earthing of structures and equipment in substations and power generation plant is continuous and of low enough resistance to meet protection and safety requirements.

How to Test Earth Continuity With a Multi-MeterHow to Test Earth Continuity With a Multi-Meter•Electricity involves the motion of electrically charged particles through metallic wires, and it has allowed mankind essential technologies such as lighting and heating. Electrical currents flow from high voltage to zero voltage, which is also called ground or earth voltage. The continuity of this voltage path is essential to the safe functioning of any electrical device. A digital multi-meter is a portable unit capable of measuring resistance, voltage and current. It can also be used to check the safe functioning of electrical appliances by measuring the appliances earth continuity.

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•InstructionsInstructions1.Switch off the appliance that needs to be checked and remove the electrical plug from the outlet socket. To be safe, wait one hour for any capacitors to discharge. Using a screwdriver, remove screws, and open back of the appliance where the power line enters.

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Instructions…..ContinuedInstructions…..Continued

2.Locate the earth wiring. This will normally be a thick green wire attached to the casing of the appliance.

3.Switch on the multi-meter, and using the dial on the front, select the resistance function. The multi-meter will have two probes with metallic pointed ends. Place the probes on either side of the earth wire. The display on the multi-meter should show a low resistance of approximately 0.5 Ohms. If the resistance is significantly higher than this, the wire is faulty and needs to be replaced.

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Note: Note: Earth resistance tests are required to Earth resistance tests are required to

confirm the installed earthing system will confirm the installed earthing system will cause circuit protective devices to operate cause circuit protective devices to operate and maintain cable integrity if there is a and maintain cable integrity if there is a

fault between live parts and exposed fault between live parts and exposed conductive parts.conductive parts.

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Earth (Ground) Bond TestEarth (Ground) Bond Test•The term “ground” is defined as a conducting connection by which a circuit or equipment is connected to the earth. The connection is used to establish and maintain, as closely as possible, the potential of the earth on the circuit or equipment connected to it. A “ground” consists of a grounding conductor, a bonding connector, its grounding electrodes, and the soil in contact with the electrode.•The Ground Bond test provides the high current levels needed in order to ensure that the earth ground conductor of a product can handle any fault current likely to be imposed on it.

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• In fact, most Ground Bond tests are specified to be performed at two times the rating of a product’s fuse or branch circuit for up to two minutes.

• Testing under these conditions not only verifies the presence of a continuous earth ground conductor, but also verifies the integrity of that conductor.

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• Grounds have several protection applications. For natural phenomena such as lighting, grounds are used to discharge the system of current before personnel can be injured or system components damaged. For foreign potentials due to faults in electric power systems with ground returns, grounds help ensure rapid protection by providing low resistance fault paths. This provides the removal of the foreign potential before personnel are injured and the power or communications system is damaged.

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Electrical Testing and Electrical Testing and Measuring Measuring

InstrumentsInstruments• Ideally, to maintain a reference potential for instrument safety, protect against static electricity, and limit the system to frame voltage for operator safety, a ground resistance should be zero ohms. In reality this value cannot be obtained.

• The ground resistance value for maintenance purposes should preferably not exceed 15 ohms when installed and should be inspected by qualified personnel once every two years in dry weather only. Results of inspections and tests shall be recorded and available upon an inspector’s request.

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• All ground rods should be 5/8 of an inch (15.875 mm) or larger in diameter, circular, solid steel rods with a copper cladding, each 10 feet (3 meters) long. Rods should be plainly and permanently marked with manufacturer’s name, rod length and nominal rod diameter. Length markings should be within the top 12 inches of the rod to permit determining length after installation. Connectors can be of the compression, impact or exothermic welded connection and made of a low resistance copper alloy containing not less than 80% copper. To prevent a tripping hazard, ground rods should be buried below ground level and covered with ground electrode boxes for easy access for inspection.

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InstrumentsInstruments• The most reliable post-installation testing procedure

involves the fall-of-potential (three-point) method. With the help of a digital ground resistance meter, two auxiliary electrodes are driven into the soil at predetermined distances - as per testing specifications - in a straight line from the ground rod under test. The meter supplies a constant current between the ground rod being tested and the most remote electrode. The Three Point Vibroground, with a range of at least 0 to 300 ohms, shall be used to perform these tests. Manufacturer’s instructions for using this instrument must be followed.

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Leakage Current Test (Line Leakage Test):Leakage Current Test (Line Leakage Test):

•In any electrical installation, some current will flow through the protective ground conductor to ground. This is usually called leakage current. Leakage current most commonly flows in the insulation surrounding conductors and in the filters protecting electronic equipment.•So what's the problem? On circuits protected by GFCIs (Ground Fault Current Interrupters), leakage current can cause unnecessary and intermittent tripping. In extreme cases, it can cause a rise in voltage on accessible conductive parts.

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InstrumentsInstrumentsThe causes of leakage current:The causes of leakage current:

•Insulation has both electrical resistance and capacitance – and it conducts current through both paths. Given the high resistance of insulation, very little current should actually leak. But -- if the insulation is old or damaged, the resistance is lower and substantial current may flow. Additionally, longer conductors have a higher capacitance, causing more leakage current. That's why GFCI breaker manufacturers recommend one-way feeder length be limited to 250 feet, maximum.

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• Electronic equipment, meanwhile, contains filters designed to protect against voltage surges and other disruptions. These filters typically have capacitors on the input, which adds to the overall capacitance of the wiring system and the overall level of leakage current.

Minimizing the effects of leakage current:Minimizing the effects of leakage current:• So, how can you eliminate or minimize the effects of

leakage current? Quantify the leakage current and then identify the source. One way of going about this is to use a leakage current clamp meter. These are very much like the clamp meters used for measuring load currents, but deliver significantly better performance when measuring currents below 5 mA. Most clamp meters simply won't register such low currents.

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InstrumentsInstruments• The clamp meter detects the magnetic field

surrounding conductors such as a single core cable, a wire armor cable, a water pipe, etc.; or the paired phase and neutral conductors of a single-phase circuit; or all live conductors (3-wire or 4-wire) of a three-phase circuit (like a GFCI or residual current device).

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• When testing the grouped live conductors of a circuit, the magnetic fields produced by the load currents cancel each other out. Any imbalance current comes from leakage from the conductors to ground or elsewhere. To measure this current, a leakage clamp meter should be able to read less than 0.1 mA.

• For example, taking a measurement on a 240 V ac circuit with all loads disconnected might result in a value of. 0.02 A (20 mA) leakage. This value represents an insulation impedance of:

240 V / (20 x 10-6) = 12 MΩ. (Ohms Law R=V/I)240 V / (20 x 10-6) = 12 MΩ. (Ohms Law R=V/I)

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InstrumentsInstruments• A clamp meter will detect and measure a wide range

of alternating or changing currents passing through a conductor under test. When telecommunications equipment is present, the value of leakage indicated by a clamp meter may be considerably more than that resulting from insulation impedance at 60 Hz. This is because telecommunications equipment typically incorporates filters that produce functional grounding currents and other equipment that produces harmonics, etc. You can only measure the characteristic leakage at 60 Hz by using a clamp meter that incorporates a narrow band-pass filter for removing currents at other frequencies.

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Measurement of Leakage Current to GroundMeasurement of Leakage Current to Ground•When the load is connected (switched on), the leakage current measured includes leakage in load equipment. If the leakage is acceptably low with the load connected, then circuit wiring leakage is even lower. If circuit wiring leakage alone is required, disconnect (switch off) the load.

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InstrumentsInstruments• Test single-phase circuits by clamping the phase

and neutral conductor. The measured value will be any current flowing to ground.

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• Test three-phase circuits by clamping around all three-phase conductors. If a neutral is present, it should be clamped along with the phase conductors. The measured value will be any current flowing to ground.

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Measuring leakage current through the ground Measuring leakage current through the ground conductorconductor

•To measure the total leakage flowing to the intended ground connection, place the clamp around the ground conductor.

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Measuring leakage current to ground via Measuring leakage current to ground via unintentional paths to ground.unintentional paths to ground.

•Clamping phase/neutral/ground together identifies imbalance current that represents leakage at an outlet or electrical panel via unintentional paths to ground (such as the panel sitting on a concrete base). If other electrical bonding connections exist (such as a connection to a water pipe), a similar imbalance may result.

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Tracing the source of leakage currentTracing the source of leakage current•This series of measurements identifies the overall leakage and the source. The first measurement can be made on the main conductor to the panel. Measurements 2, 3, 4 and 5 are made subsequently to identify circuits carrying the larger amounts of leakage current.

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InstrumentsInstruments

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Summary:Summary:•Leakage current can be an indicator of the effectiveness of insulation on conductors. High levels of leakage current may be present in circuits where electronic equipment with filters is used, and can cause voltages that disrupt normal operation of equipment. It is possible to locate the source of leakage current by using a low current leakage current clamp to take methodical measurements as described above. If necessary, this enables you to re-distribute loads around the installation in a more balanced way.

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Electrical Testing and Measuring Electrical Testing and Measuring InstrumentsInstruments

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Electrical Testing and Measuring Electrical Testing and Measuring InstrumentsInstruments

• Electrical testing and measurement devices can tell you if a circuit or wire is energized as well as tell you how much voltage or current an electrical circuit is carrying. Other types of testing devices can tell you if a network cable is connected properly or if there is continuity in that cable.

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InstrumentsInstruments• There are many different types of electrical

measuring and testing devices. Some of these test for the presence of electrical current, whether alternating current or direct current. Others test for whether or not an electrical receptacle is properly wired. Electrical measuring devices can be either analoganalog or digitaldigital. Some of these measuring devices only measure current, voltage, or resistance, while others will measure all of these circuit or device characteristics.

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Analog Vs. DigitalAnalog Vs. DigitalElectrical Measuring Devices-AnalogElectrical Measuring Devices-Analog

• Electrical measuring devices are more commonly referred to as meters. Analog meters can either measure one circuit value (current, voltage, and resistance), or they can measure all of these. An analog meter has a needle that swings one way or another to indicate the value being measured.

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Analog Vs. DigitalAnalog Vs. DigitalElectrical Measuring Devices-DigitalElectrical Measuring Devices-Digital

•Like analog meters, digital meters can test one value, or they can test a combination of values. Also, some of these only have three settings- current, voltage, and resistance- while more advanced meters have different scales for each of the three types of values.

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AmmeterAmmeter•An ammeter is a measuring instrument used to measure the electric current in a circuit. Electric currents are measured in amperes (A), hence the name. Instruments used to measure smaller currents, in the milli-ampere, are designated as milli-ammeters .

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OhmmeterOhmmeter•An ohmmeter is an electrical instrument that measures electrical resistance, the opposition to an electric current. The unit of measurement for resistance is ohms (Ω).

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WattmeterWattmeter•The wattmeter is an instrument for measuring the electric power (or the supply rate of electrical energy) in watts of any given circuit.•An electricity meter or energy meter is a device that measures the amount of electric energy consumed by a residence, business, or an electrically powered device

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VoltmeterVoltmeter•A voltmeter is an instrument used for measuring electrical potential difference between two points in an electric circuit.

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Digital Multi-MeterDigital Multi-Meter•Digital multi-meters can solve most electrical problems - at the hands of a qualified electrical test profession. In fact, With a good wiring diagram and a good meter, a trained electrical professional can find the cause of almost any problem.•They will test for voltage, current and resistance. Some advanced ones will test for watts as well

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• When you purchase a digital multi-meter, one of the most important things to look at is the meter's impedance, which is the meter's operating resistance.

• Most digital multi-meters have very high impedance. Since the meter is part of the circuit being tested, its resistance will affect the current flow through that circuit

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• The digital multi-meter is available in all sorts of styles and designs

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InstrumentsInstrumentsClamp MetersClamp Meters

•A current meter, or clamp meter allows you to measure the current without disconnecting the device or the circuit. It is designed to be attached around the conductor, enabling you to measure the current or amperage of a particular cable or wire.

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• Clamp meters are also used to measure voltage and resistance. Testing everything you touch before you touch is a big part of safety in the workplace.

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• Insulation Resistance Testing:Insulation Resistance Testing:• In a perfect world, all the electrical current sent along a

conductive wire would reach its intended destination. • However, in the real world some of it is lost along the

way for various reasons. Wires are insulated with a resistant sheathing to contain the conductivity of the typically copper or aluminum core, but even with this insulation in place, some of the current still manages to escape.

• Much like a leak in a water pipe, an imperfection in the insulation of a wire allows a steady flow of electricity to escape, which can be detrimental to electrical circuits and machinery.

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• However, testing can help you determine whether the insulation is performing at an effective and safe level. Routine testing can identify problems before they result in injury or equipment failure.

• Insulation is subject to many elements that can cause it to perform at a less-than-acceptable level. Excessive heat or cold, moisture, vibration, dirt, oil, and corrosive vapors can all contribute to deterioration. For this reason, routine insulation testing is necessary.

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Electrical Testing and Electrical Testing and Measuring instrumentsMeasuring instruments

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• Total current in insulation testing:Total current in insulation testing:• Testing the integrity of insulation requires measuring

its resistance to current flow across it. A high level of resistance means that very little current is escaping through the insulation. Conversely, a low level of resistance indicates a significant amount of current may be leaking through and along the insulation.

• By pressurizing a conductor with a given voltage, it's possible to use Ohm's Law (R=V÷I) to apply a numerical value to resistance measurements. Divide the voltage by the current that escapes through the insulation and returns to the meter.


instrumentsinstruments• This total current that flows through and along the

insulation during a test is the result of capacitive current, absorption current, and leakage current.

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instrumentsinstrumentsCapacitive current.Capacitive current.

•The initial burst of current that occurs when voltage is first applied to a conductor is called capacitive current. Like the first rush of water flowing through a hose, it typically starts out high and then drops quickly once the conductor is fully charged.

Absorption current.Absorption current.•Like capacitive current, absorption current also starts out high and then drops. However, it falls at a much slower rate. As the voltage builds up, the absorption level in the insulation decreases. This gradual change reflects the storage of potential energy in and along the insulation. Incidentally, absorption current is an important part of the time resistance method of insulation testing.

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instrumentsinstrumentsLeakage current.Leakage current.

•Also commonly referred to as conduction current, the small, steady current present both through and over the insulation is called leakage current. Any increase in leakage current over time is usually an indication of deteriorating insulation. This would be noted on the insulation test meter as a decrease in resistance.

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instrumentsinstruments• Types of insulation resistance tests.Types of insulation resistance tests.

• With an understanding of the definition of insulation resistance and why it's important to measure it, it's possible to examine when and how to test.

• When installing new electrical machinery or equipment, testing insulation resistance is important for two reasons. First, it ensures that the insulation is in adequate condition to begin operation. This type of initial test is usually referred to as a proof test. Second, it provides a baseline reading to use as a reference for future testing.

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• Due to fluctuating factors like moisture and temperature, insulation testing is mostly based on relative measurements. In other words, a reading of 1.5 mega-ohms is more or less insignificant without a previous set of measurements against which to compare it.

• Measurements taken during routine maintenance tests can give valuable information about the quality of insulation, as conditions vary.

• The proof test, short time/spot reading test, time resistance test, and step voltage test are four of the most prominent tests used today, and they encompass the steps necessary for keeping tabs on equipment from installation through day-to-day use.

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instrumentsinstruments

Electrical Testing Electrical Testing and Measuring and Measuring


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Proof TestProof Test•Proof testing is an important step in the installation of new machinery to protect against miswired and defective equipment. A proof test is often referred to as a go/no go test because it tests the system for errors or incorrect installation. •The test is accomplished by applying DC voltage through the de-energized circuit using an insulation tester. If no failures occur during the measurement, the test is a success. Proof testing voltages are much higher than those used in routine maintenance test methods.


instrumentsinstruments• The general guideline for choosing a test

voltage is based on the equipment's nameplate rating. Follow the equation below to arrive at an acceptable test voltage.

• Step 1: (2×nameplate rating)+1,000V=Factory AC Test

• Step 2: 0.8×Factory AC Test×1.6=DC Proof Test Voltage

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instrumentsinstrumentsShort time/Spot reading testShort time/Spot reading test

•In a short time/spot reading test, the tester is connected across the insulation of the motor windings. A test voltage is then applied for a fixed period of time, usually 60 seconds. The most important aspect of this test is that it remains consistent in duration from test to test. Once the time period has elapsed, an insulation resistance measurement can be recorded.•A single maintenance test can act only as a rough guide for insulation quality. A more effective use of the short time/spot reading testing method is the establishment of a series of test results over several months so long-term trends may be examined. 64


instrumentsinstruments• It's important to understand that a variety of

factors like temperature and moisture can cause fluctuations in test readings. Typically, insulation will deteriorate at an extremely gradual, but consistent pace. A significant downward trend over the course of several measurements is usually a sign of insulation breakdown.

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Time Resistance Test.Time Resistance Test.•Unlike the short time/spot reading test, the time resistance method test can provide fairly conclusive results without the luxury of past test measurements. This test method is based on taking successive readings at fixed time intervals, and then plotting the readings. This is an especially effective method when moisture and other contaminants might be present.


instrumentsinstruments• As mentioned earlier, absorption current starts out

high and gradually decreases over time as voltage is applied. In a machine with healthy insulation, this trend will continue for several minutes and show an increasing level of resistance.

• On the other hand, if the insulation is poor, the level of resistance will flatten out after an initial burst.

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instrumentsinstruments• The best way to quantify the results of a time

resistance test is through a dielectric absorption ratio. The dielectric absorption ratio consists of two time resistance readings.

• A commonly used set of intervals is a 60-second reading divided by a 30-second reading. Another frequently used set is a 10-minute reading divided by a 1-minute reading. This resulting value is referred to as the polarization index.

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instrumentsinstruments• The information summarized in the table below above

provides general guidelines for interpreting dielectric absorption ratios.

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Step Voltage Test.Step Voltage Test.•A step voltage test involves testing the insulation at two or more voltages and comparing the results. Good insulation will show a relatively consistent resistance reading regardless of the voltage applied. •On the other hand, when the resistance level drops as the voltage level increases, it's usually an indication that the insulation is aging, contaminated, or brittle. This occurs because small imperfections like pinholes and cracks reveal themselves under increased electrical stress.


instrumentsinstruments• When performing a step voltage test, it's important

that you start with the lowest test voltage and then move to a higher voltage level. Test duration is typically 60 seconds.

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Conclusion:Conclusion:

• Function and accuracy tests of measurement devices in electrical power systems are either prescribed by mandatory standards and regulations or form part of an established quality assurance concept. There’re several testing and measuring equipment used in electrical testing. This presentation only covers the most basic equipment and principles. Some tests require the expertise of professionals and consultants for conducting and interpretation.

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References:References:

• http://electrical.about.com/od/electricaltools/tp/top16electricaltools.htm

• http://electricaltechnology.org/2014/01/basic-electrical-engineering-tools.html

• http://www.fluke.com/fluke/uses/comunidad/fluke-news-plus/articlecategories/electrical/leakagebasics.htm

• http://ecmweb.com/content/monitor-ground-fault-leakage-currents

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http://electrical.about.com/od/electricaltools/tp/top16electricaltools.htm

http://electrical.about.com/od/electricaltools/tp/top16electricaltools.htm

http://electricaltechnology.org/2014/01/basic-electrical-engineering-tools.html

http://electricaltechnology.org/2014/01/basic-electrical-engineering-tools.html

http://www.fluke.com/fluke/uses/comunidad/fluke-news-plus/articlecategories/electrical/leakagebasics.htm



http://ecmweb.com/content/monitor-ground-fault-leakage-currents

http://ecmweb.com/content/monitor-ground-fault-leakage-currents

Questions???Questions???

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3.measuring and testing equipment.ppt

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