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A comprehensive 64 page guide to electrical insulation testing containing helpful diagrams, value tables, product information and much more!. over a period of time, and the location and importance of the equipment megohmmeter is connected to the insulation to be tested and is operated for a short. The Dielectric Absorption (or Time-Resistance) test is an extension of the Megger, “A stitch in time – The Complete Guide to Electrical Insulation Testing”, a free.

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Note that the starter switch is in the on position for the test. We have seen that, essentially, good means a relatively high resistance to current.

The Complete Guide to Electrical Insulation Testing A STITCH IN TIME 1 – PDF

It is always preferable to disconnect the component parts and test them separately in order to determine where weaknesses exist. So, a suitable way of measuring resistance can tell you how good the insulation is. However, if you ve got salt water, you must first wash away the salt with fresh water.

They must be observed during use.

Chose the right More information. Note also that a higher voltage tends to cause more current through the insulation. Megger instruments are frequently equipped with discharge circuits for this purpose.

To test either the stator winding or the cable itself, the cable must be disconnected at the machine. The Model provides three test ranges plus continuity More information. Option Card for Frequency Divider. Equipment Rating AC Testing vs. There is, on, a hazard when testing equipment located in inflammable or explosive mefger. With moisture, such deposits form a very good conductor of electricity.

Back to the Basics Current Mdgger CT Testing Back to the Basics Current Transformer CT Testing As test equipment becomes more sophisticated with better features and accuracy, stltch risk turning our field personnel into test set operators instead of More information. Connections for testing insulation resistance of electrical equipment The following diagrams show how to connect a Megger insulation tester to various types of electrical equipment.


The time required to charge the geometric capacitance is very short usually no more than a few seconds and that which causes further delay in reaching full charge is a dielectric absorption effect. Check for loose, missing, broken or corroded hardware, pivot pins, cotter pins, springs and other mechanical.

The Complete Guide to Electrical Insulation Testing A STITCH IN TIME 1

Use rubber gloves when connecting the test leads to the apparatus and while operating the Megger instrument. On the other hand, if past records showed the normal resistance values to run 10 or 20 megohms, then you would know that water was still in the motor windings. Equipment AC Rating DC Test Voltage up to volts and volts to volts and 1, volts 2, volts 1, to 2, volts or higher 4, volts and above 1, to 5, volts, or higher Test voltages used for proof testing of equipment are considerably higher than those used for routine maintenance.

Voltage Scales Some insulation testers may be supplied with a voltage scale to check for the absence of voltage before insulation testing.

Proof Test Voltages for Rotating Equipment: Troubleshooting Submersible and Jet Pumps A. Remember that we spoke of the kinds of current produced in insulation by DC? Apply workmen s grounds. In a series of lecture on basic metger, learning by doing, we now. This method is nondestructive; that sgitch, it does not cause deterioration of the insulation. It gives some assurance that equipment is not too wet or dirty and has saved many an unnecessary breakdown. Intermittent Pilot Ignition Control More information.

This condition may be caused by uniformly distributed leakages of a harmless nature, and may not be the result of a dangerous localized weakness. For many years, maintenance professionals have used the one-megohm rule to establish the allowable lower limit for insulation resistance.


Do this by operating the instrument, which should read Infinity. Right now, let s just consider the nature of current through insulation and the effect of how long voltage is applied. Cable fault location in power cables. Time-resistance tests on large rotating electrical machinery especially with high operating voltage require high insulation resistance ranges and a very constant test voltage.

Furthermore, manufacturers of wire, cable, motors, and so on have continually improved their insulations for services in industry. Good Housekeeping The most important requirements in the reliable operation of electrical equipment are cleanliness, and the elimination of moisture penetration into the insulation.

Although this rule is somewhat arbitrary, and may be criticized as lacking an engineering foundation, sttch has stood the test of a good many years of practical experience.

A record of the relative humidity near the equipment at the time of the test is also helpful in evaluating the reading and trend. Design Description AC Generators come in two basic types synchronous and non-synchronous. Shock Hazard from Test Voltage Observe the voltage rating of the Megger instrument and regard it with appropriate caution.

Capacitance causes the pointer to swing towards zero while the instrument is being brought up to speed, and to swing off scale beyond infinity when the generator is slowing down.

Periodic testing is, therefore, your tim approach to preventive maintenance of electrical equipment, using record cards as shown in Fig. This range measures below the Megohm range, and can, therefore, provide an actual measurement to use as a benchmark in monitoring the drying process.

Actually, as shown in Fig.