Relationship between insulation resistance and temperature

Measurement of insulation resistance (IR) - Part 2

relationship between insulation resistance and temperature

The temperature corrected insulation resistance is a factor of 2 below the actual insulation resistance for every 10C that winding temp is below. Trying to capture the Hot Insulation resistance reading any other way than Temperature Effects on Electrical Insulation Materials which are classed as the vibration of the atoms causes many collisions between the free. The Insulation Resistance Test consists in measuring the Insulation resistance of a device Any harsh installation environments, especially those with temperature extremes and/or . Difference Between Dielectric Strength Test and IR Test.

This is critical in determining the electrical condition of the insulation materials.

Measurement of insulation resistance (IR) - Part 2

The lower Hot reading should always increase several times as the insulation cools and then end up at a higher safe level, as called out by the IEEE Standard Polarization Index test is looking for by comparing a 10 minute reading to a 1 minute reading. The reasons why insulation materials change their electrical resistance during heating can be explained by the following: Materials used for practical insulators glass, plastic, dielectric paper, etc should only exhibit a marked drop in their resistivity at very high temperatures.

They remain good insulators over all temperatures they are likely to encounter in use. If after the insulator material cools to the normal ambient temperature, the resistance does not increase it is an indicator that the insulator material is no longer working properly and should be repaired or replaced.

relationship between insulation resistance and temperature

The reasons for these changes in resistivity can be explained by considering the flow of current through the material. The flow of current is actually the movement of electrons from one atom to another under the influence of an electric field.

Resistivity and Resistance Formula, Conductivity, Temperature Coefficient, Physics Problems

Electrons are very small negatively charged particles and will be repelled by a negative electric charge and attracted by a positive electric charge. Only some electrons are free to migrate however.

relationship between insulation resistance and temperature

Others within each atom are held so tightly to their particular atom that even an electric field will not dislodge them. The effect of heat on the atomic structure of a material is to make the atoms vibrate, and the higher the temperature the more violently the atoms vibrate.

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Temperature and relative humidity are two important parameters which influence the resistance value of an insulator. In reality, this voltage surge may be due to lightning or the induction caused by a fault on a power transmission line.

  • Learn How Insulation Resistance Test is Done
  • Insulation Resistance Evaluation

The main purpose of this test is to ensure that the construction rules concerning leakage paths and clearances have been followed. This type of measurement requires a hipot tester. The result obtained is a voltage value usually expressed in kilovolts kV. Dielectric testing may be destructive in the event of a fault, depending on the test levels and the available energy in the instrument. For this reason, it is reserved for type tests on new or reconditioned equipment. Insulation resistance measurement, however, is non-destructive under normal test conditions.

This resistance indicates the quality of the insulation between two conductors.

relationship between insulation resistance and temperature

Because it is non-destructive, it is particularly useful for monitoring insulation aging during the operating life of electrical equipment or installations. This measurement is performed using an insulation tester, also called a megohmmeter Factors affecting values of insulation resistance: Current that starts out high and drops after the insulation has been charged to full voltage much like water flow in a garden hose when you first turn on the spigot.

Also an initially high current which then drops for reasons discussed under the section Time-Resistance Method. Conduction or Leakage Current A small essentially steady current both through and over the insulation.

relationship between insulation resistance and temperature

Equipment should be discharged shunted or shorted out for at least as long as the test voltage was applied in order to be absolutely safe for the person conducting the test. Never use Megger in an explosive atmosphere. Make sure all switches are blocked out and cable ends marked properly for safety. Make sure when testing for earth, that the far end of the conductor is not touching, otherwise the test will show faulty insulation when such is not actually the case.

Make sure that all connections in the test circuit are tight.

relationship between insulation resistance and temperature

Cable ends to be isolated shall be disconnected from the supply and protected from contact to supply, or ground, or accidental contact. Erection of safety barriers with warning signs, and an open communication channel between testing personnel. A megohmmeter usually is equipped with three terminals. A multimeter is able measure different magnitudes, including electrical resistance, whose unit is given in ohms.

Its operation, particularly to measure resistance, is given by the action of an internal battery low voltage that circulates a small current through the resistance being measured or, failing that, the conductor or winding.

The value in ohm obtained belongs to the electrical resistance, which causes the current to pass through the conductor and is incremented according to its longitude and section. On the other hand, a megohmeter, also known as Megger, is often used to measure the insulation resistance of an insulated body.

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The results obtained in the ohm test are related to the insulation resistance, which has an insulated element relating to an active element or a conductor.

Bear in mind also that temperature and humidity, as well as condition of your insulation affect your reading. If the apparatus you are testing has very small capacitance, such as a short run of house wiring, the spot reading test is all that is necessary.

For many years, maintenance professionals have used the one-megohm rule to establish the allowable lower limit for insulation resistance.