In principle, the value of the insulation resistance is very high but not infinite, so by. The standard megger testing equipment is used, the line terminal of which is connected to the winding or core bolt under test. What is the insulation resistance of a transformer. Insulation resistance testing is a nondestructive test procedure. If the transformer is new, the resistance test also serves as a verification of the manufacturers work.
A regular program of testing insulation resistance is strongly recommended to prevent electrical shocks, assure safety of personnel and to reduce or eliminate down time. Understanding insulation resistance testing pdf 0206 rev. A read is counted each time someone views a publication summary such as the title, abstract, and list of authors, clicks on a figure, or views or downloads the fulltext. The insulation resistance test is the second test required by the electrical safety testing. All transformers are subjected to the following routine tests. The megger insulation tester is a small, portable instrument that gives you a direct reading of insulation resistance in ohms or megohms. Installation measurements should be filed for future reference 2. Find here insulation testing and continuity, power protection, power transformer testing, power cable infrastructure, cable fault location, general electrical test. Insulation resistance testing test equipment depot. The test measurement values are affected by variables such as temperature, humidity, test voltage, and size of the transformer. Test conducted at other temperature should be corrected 20c with the use of temperature correcting factor. Upon completion of this project, the neta technical committee began work on a maintenance document, and maintenance testing specifications for electrical power equipment and systems was published in 1975. Disconnect the electrical current from the transformer and grounding it. Hence, it is recommended that the dc resistance be measured on all onload and offload taps prior to energizing.
Because of that, insulation resistance can also be referred as 1 minute insulation resistance or 10 minute insulation resistance depending upon the duration of the test. Megger test is a spot insulation test which uses an applied dc voltage typically 250vdc, 500vdc. We recieve feedback from many of our customers who use power quality pq meters including utilities, industrial and service providers. Free power how to convert an old washing machine into a water powered. Ip test is conducted especially to determine the dryness and cleanliness of the insulation. Hipot test is typically used for acceptance testing or after transformer repair testing. Transformer testing insulation resistance test of transformer ir duration. Nevertheless, the hipot test for routine maintenance is typically not applied to transformers because of the possibility of damage to the winding insulation. Field testing of fluidfilled power transformers, regulators, and reactors. Record the insulation resistance, temperature, humidity, and equipment designation. Insulation resistance test is the second test required by the electrical safety testing standards.
Power transformers csa standard cancsac88m90 csa standard for power transformers and reactors 6 routine design other remark oil quality tests x quality resistance measurement x quality winding insulation resistance x quality coreclamp insulation resistance x quality ratio test x quality and performance. Pdf measurement of winding resistance and insulation. For good insulation, the resistance usually reads in the megohm range. All bushings should be power factored before they are inserted into the transformer. Recommended test voltages for routine maintenance insulation resistance tests of equipment rated to 4,160v and above. The test method is determined by the type of equipment being tested and the reason for testing. What is the megger test procedure for transformers. Ansineta mts2015, standard for maintenance testing specifications for. This test is performed at or above rated voltage to determine if there are low resistance paths to ground or. When performing insulation resistance testing, you must maintain consistency. Before conducting a transformer winding resistance test, it is important to observe all safety warnings and take proper precautions.
Insulation resistance test and oil test of distribution transformer. With a little recordkeeping and common sense, however, you can get a good picture of the insulation condition from values that are only relative. Transformer testing winding resistance test as per. Monitor the insulation resistance during the test to ensure that reading is not linear and does not increase exponentially as the test voltage increases. The megger technical library provides access to a range of additional content and resources such as technical guides, application notes and more. It helps to detect deterioration of insulation in order to schedule repair work such as.
The voltage, we apply for measurement of insulation resistance, is direct voltage. Standard for acceptance testing specifications for. Learn how insulation resistance test is done developed early in the 20th century, the insulation resistance ir test is the oldest and most widely used test for assessing the quality of insulation. Meggering transformer wiring is emphasized because of the numerous small terminal boxes mounted on large power transformers. The insulation resistance test consists in measuring the insulation resistance of a device under test, while phase and neutral are short circuited together. Minimum insulation resistance values of transformer insulation should be in accordance with manufacturers published data. Guide to transformer winding resistance measurements measuring a transformers dc resistance from one external terminal to another can reveal a great deal of information about the transformer. Routine tests are carried out on every unit manufactured. Insulation resistance tests are commonly measured directly in megohms or may be calculated from measurements of applied voltage and leakage current. Ensure that no leakage paths between phases or transformer body.
The insulation resistance ir test also commonly known as a. Time resistance testing method this method is fairly independent of temperature and often. The first neta acceptance testing specifications for electrical power equipment and systems was produced in 1972. Insulation resistance testing aemc when measurement is made, the ir value slightly increases after each measurement cycle. Whereas individual insulation resistance measurements may. Pdf this paper consist the specification of transformer and its procedure of measurement of.
Insulation resistance test of transformer is performed on the transformer to. A transformer is an electrical device that transfers electrical energy between two or more circuits through electromagnetic induction. Connect insulation resistance test equipment as required by the instrument manufacturers manual. Power transformer testing swp check this is the latest process zone version before use. Understanding the value of electrical testing for power. Whether we choose the spotreading, step voltage, or time resistance tests depends on the reason for testing and the validity of the data obtained. The complete guide to electrical insulation testing. Insulation resistance ir test of transformer reveals the condition of insulation i.
For three phase transformers, we need to test winding l1,l2,l3 with substitute earthing for delta transformer or winding l1,l2,l3 with. All wiring on transformers should be meggered at 250 or 500 vdc. How insulation resistance test practical with megger meter. Dos and donts when measuring insulation resistance of a transformer. Verify insulation integrity due to the moisture and impurity contents of insulation. The test equipment is calibrated to read in megohm and commonly know as a hv megger. Second, the range of a megohmmeter is in megohms, as its name implies, instead of ohms as in a multimeter. Meggering insulation resistance testing of drytype. The insulation resistance test should be performed at a transformer temperature as close as possible or at 20 c. In the absence of manufacturers published data, use table 100. The insulation resistance test is an electrical test which uses a certain type and level of voltage 500v d. Insulation resistance measurement has been recommended and used for more than half a century to evaluate the condition of electrical insulation. Power transformer factory test using ieee standards. Power factor testing of power and distribution transformers the transformer is probably one of the most useful electrical devices ever invented.
A test voltage is applied for a fixed period of time, usually 60 seconds and a reading is taken. Only the current through the insulation is measured, since any. The test measures the insulation resistance between the phases andor between phase and ground. Megger guide to electrical insulation testing pdf instrumart. For this test, the megohmmeter is connected across the insulation of the windings of the machine being tested. This is due to residual polarization of the previous application of voltage due to all the above factors, ir measurement becomes both difficult and complicated. Understanding insulation resistance testing pdf 0712. Understanding insulation resistance testing aemc instruments.
To test the insulation resistance in generators, transformers, motors, and wiring installations, we can employ any of the previously mentioned predictive maintenance tests. Measurement of winding resistance and insulation resistance of 3 phase 11 kv 433 v, 16kva oil cooled type transformer conference paper pdf available. Ensure that all equipment to be tested is properly grounded and treat all highvoltage power equipment as energized until proven otherwise by using the proper lockouttagout procedures. Because electrical insulation will exhibit dynamic behavior during the course of your test. A routine test of transformer is mainly for confirming operational performance of individual unit in a production lot. Polarization index test pi value test along with insulation resistance test ir value test is conducted on hv electrical machine to determine service condition of the insulation. Insulation resistance testing guide chauvin arnoux. Connections for testing insulation resistance of a transformer high voltage winding and bushings, and.
Insulation resistance measurement is based on ohms law. Insulation resistance testing introduction insulation resistance testers can be used to determine the integrity of windings or cables in motors, transformers, switchgear, and electrical installations. This introduction is not part of ieee std 432000, ieee recommended practice for testing insulation resistance of rotating machinery. A catalogue, for quick reference, of the range of megger test instruments for the maintenance of electrical power systems. To evaluate a number of test results on the same piece of equipment, you have to conduct the test the same way and under the. By injecting a known dc voltage lower than the voltage for dielectric testing and then measuring the current flowing, it is very simple to determine the value of the resistance. Ir value for transformer insulation resistance tests are made to determine insulation resistance from individual windings to ground or between individual windings. They have told us that one of the most important features of a pq meter is the ability to control the unit and and view data remotely. This test is performed at or above the rated voltage to determine if there are low resistance paths to the ground or between winding to winding as a result of winding insulation deterioration.
This guide explains the many types of transformer and the power factor test procedures for each one. Insulation resistance tests megger test are carried out on all windings, core and core clamping bolts. Every electrical wire, whether its in an f16 cockpit panel, uh60 circuit breaker, or v22 wiring harness, is carefully protected with some type of electrical insulation. Either condition could indicate insulation failure, poor insulation, andor improper test connections. The ac hv test value should not surpass 75% of the factory test value.
Test each winding in turn keeping clear of live test leads. Portable measurement equipment in a wide variety of fields. See the site fixed equipment for measurement and testing of electrical networks, energy management and optimization systems. The measured resistance indicates the condition of the insulation between two conductive parts. The standard duration of voltage application are 1 minute or 10 minutes.
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