All electrical installations and equipment comply with insulation resistance specifications so they can operate safely. Whether it involves the connection cables. IR Testing for Low voltage. Circuit voltage, Test voltage, IR Value(Min). Extra Low Voltage, V DC, MΩ. Up to V except for above. These minimum IR testing voltages must always be adhered to in order to accurately measure the Insulation Resistance in all electrical equipment. Any test .

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Continued from first part: Measurement of insulation resistance IR — Part 1.

IR Value ir.testing Transformer 3. IR Value for Tap Changer 4. IR Value for Electric motor 5. IR Value for Electrical cable and wiring 6. IR Value for Panel Bus 8. IR Value for Substation Equipment 9. At a pressure of V applied between each live conductor and earth for a period of one minute the insulation resistance of HV installations shall be at least 1 Mega ohm or as i.r.testinf by the Bureau of Indian Standards.

Medium and Low Voltage Installations- At a pressure of V applied between each live conductor and earth for a period of one minute, the insulation resistance of medium and low i.r.testiny installations shall be at least 1 Mega ohm or as specified by the Bureau of Indian Standards] from time to time.

Insulation resistance tests are made to determine insulation resistance from individual windings to ground or between individual windings. Insulation resistance tests are commonly measured directly in megohms or may be calculated from measurements of applied voltage and leakage current.

Measurement of insulation resistance (IR) – Part 2

The recommended practice in measuring insulation resistance is to always ground the tank and the core. Short circuit each winding of the transformer at the bushing terminals. Resistance measurements are then made between each winding and all other windings grounded. Transformer windings i.r.testinng never left floating for insulation resistance measurements. Solidly grounded winding must have the ground removed i.r.testinh order to measure the insulation resistance of the winding grounded. If the ground cannot be removed, as in the case of some windings with solidly grounded neutrals, the insulation resistance of the winding cannot be measured.

Treat it as part of the grounded section of the circuit. We need to test winding k.r.testing winding and winding to ground E. Three winding transformer 1. Auto transformer two windings 1. Auto Transformer three winding 1. For any installation, the insulation resistance measured shall not be less than: For electric motorwe used a insulation tester to measure the resistance of motor winding with earthing E.

Benefits of Permanently Installed Automatic Insulation Resistance (IR) Testing: Part 3 of 3

For insulation testing, we need to disconnect from panel or equipment and keep them isolated from power supply. The wiring and cables need to test for each other phase to phase with a ground E cable.

A low resistance between phase and neutral conductors, or from live conductors to earth, will result in a leakage current. This cause deterioration of the insulation, as well as involving a waste of energy which would increase the running costs of the installation. The resistance between Phase-Phase-Neutral-Earth must never be less than 0. In addition to the leakage current due to insulation resistance, there is a further current leakage in the i.r.testung of the insulation, because it acts as the dielectric of a capacitor.


This current dissipates no energy and is not harmful, but we wish to measure the resistance of the insulation, so DC Voltage is used to prevent reactance from being included in the measurement.

Where two-way switching is wired, only one of the two stripper wires will be tested. To test the other, both two-way switches should be operated and the system retested. If desired, the installation can be tested as a whole, when a value of at least 0. In the case of a very large installation where there are many earth paths in parallel, the reading would be expected to be lower. If this happens, the installation should be subdivided and retested, when each part must meet the minimum requirement.

The IR tests must be carried out between Phase-Phase-Neutral-Earth with a minimum acceptable value for each test of 0. Electronic equipment like electronic fluorescent starter switches, touch switches, dimmer switches, power controllers, delay timers could be damaged by the application of the high test voltage should be disconnected.

Capacitors and indicator or pilot lamps must be disconnected or an inaccurate test reading will result. Where any equipment is disconnected for testing purposes, it must be subjected to its own insulation test, using a voltage which is not likely to result in damage.

The result must conform with that specified in the British Standard concerned, or be at least 0. I need to know the HV and Megger test voltage value and routine tests to be performed for medium voltage 6. Dear Sir Thanks for all this good work that you have done. I just have doubt that one of the examples of insulation temperature correction factors is given with a probable mistake from the point I looked to the insulator.

The example you stated mention some thing in contrary See Below.

For the 22 KV cable 3 cores x sq. To whomever this may concern, whilst the information contained on this website is useful, it is no substitute for the application of competent electrical engineering by experienced practitioners. Electrical engineering practitioners should always u.r.testing and understand the appropriate guidance, incorrect information is misleading.

The primary source of information is described within IEEE, IEC or national standards which must be reviewed before embarking upon electrical engineering works or projects. I wish to thank the author for making this information available to the general public who could be harmed as ir.testing consequence. A little knowledge is dangerous. Sir,one 40MVA Transformer which was in service for 3 years. Value below which Insulation is not acceptable etc. Thank you for this very useful article. Is there any IR lower-limit for turn-to-turn insulation in random wound low voltage electric motors?

An electrician performed Insulation Resistance test on Low Voltage cable between a Generator and switchboard. Due to site constraints the cable could not be disconnected at both ends of the installation, however the circuit breakers were switched off at both ends leaving the neutral and earth connected.


Sir, it has been observed that during oil replacement procedure of a power transformer in one of our Substations IR values were taken after draining of oil and after filling with oil. It was found that the reading was less with oil than without oil. What is the reason?

Thanks for your i.r.testong. I sent your link to one of overhead crane supplier which was located in some part in Europe, because we were requesting for the IR but they say they do not know such IR. Luckily after searching in the web your i.r.testibg showed up. Its urgent, Plz help. Please can you help me to know the maximium fire resistance temperture for the follow fire cable with following specifiction: Megger Value of HV 6.

Definitely there will be a temperature rise of 10 degree Celsius from cold to No-load running. Very useful articleI appreciate your efferots to collect all these indexes and values in one paper Thank you….

Measurement of insulation resistance IR — 2. Fluke insulation resistance tester up to 10kV Continued from first part: Steps for measuring the IR of Transformer: Shut down the transformer and disconnect the jumpers and lightning arrestors. Discharge the winding capacitance. Thoroughly clean all bushings Short circuit the windings. Guard the terminals to eliminate surface leakage over terminal bushings.

Benefits of Permanently Installed Automatic Insulation Resistance (IR) Testing: Part 1 of 3

Connect the test leads avoid joints. Apply the test voltage and note the reading. Value at 60 seconds after application of the test voltage is referred to as the Insulation Resistance of the transformer at the test temperature.

The transformer Neutral bushing is to be disconnected from earth during the test. All LV surge diverter earth connections are to be disconnected during the test. Due to the inductive characteristics i.r.texting transformers, the insulation resistance reading shall not be taken until — test current stabilizes. Avoid meggering when the transformer is under vacuum. Premium Membership Premium membership gives you an access to specialized technical articles and extra premium content electrical guides and software.

Jignesh Parmar Jignesh Parmar has completed M.

Tech Power System Control ,B. He is Presently associate with one of the leading business group as a Deputy Manager at Ahmedabad,India. Krishnaiah Oct 24, Jeevan Ranadive Sep 29, Dear Sir, I need to know i.r.teeting HV and Megger test voltage value and routine tests to be performed for medium voltage 6. Please email me to my email. Usha Aug 31, Abdulhameed Jul 01, Bilel Alibi Jun 07, Prageeth Mar 05, Arabinda Feb 08, Sagar Vaghasiya Feb 03, Excellent i.r.tssting on single paper.

Vincenzo Dec 30,