Check the motor winding resistance or ohms reading using a multimeter or ohmmeter for phase to phase terminal ( U to V,V to W ,W to U ). The ohms reading for each winding must be the same (or nearly the same). Remember that the three phases have identical windings or nearly so!
The rule may be stated: Insulation resistance should be approximately one megohm for each 1,000 volts of operating voltage, with a minimum value of one megohm. For example, a motor rated at 2,400 volts should have a minimum insulation resistance of 2.4 megohms.
The rule may be stated: Insulation resistance should be approximately one megohm for each 1,000 volts of operating voltage, with a minimum value of one megohm. In practice, megohm readings normally are considerably above this minimum value in new equipment or when insulation is in good condition.
If the megger reads a resistance under 1 (1,000 ohms) on your meter after the initial 60-second interval, the cable has failed and the cable should be removed. If the megger reads a resistance between 1-1.25 on your meter, then the cable passes. Any reading above 1.25 is considered excellent.
The measurement of insulation resistance is carried out by means of a
megohmmeter – high resistance range ohmmeter.
A general rule-of-thumb is 10 Megohm or more.
| Insulation resistance value | Insulation level |
|---|
| 2 Megohm or less | Bad |
| 2-5 Megohm | Critical |
| 5-10 Megohm | Abnormal |
| 10-50 Megohm | Good |
Perform the insulation resistance test between conductors at a reduced test voltage of 250 V DC. However, where this option is used, the minimum acceptable insulation resistance remains 1 MΩ.
Action to improve insulation resistance (or to improve BDV), is accordingly taken on following lines: Clean the insulation surface physically of any dirt. Dry the surface by hot air / air blast to dry moisture traces on surface. Sometimes even letting the equipment or component dry in air alone solves the problem.
Anything reading between 2 megohms and 1000 megohms is usually considered a good reading, unless other problems have been noted. Anything less than 2 megohms indicates an insulation problem.
IR Value Measurement (Conductor to Earth Insulation)
- Connect conductor under test to the Line terminal of the megger.
- Connect earth terminal of the megger to the earth.
- Rotate the handle of megger or press push button of megger. The reading of meter will show the insulation resistance of the conductors.
DC resistance between pair of terminals with DC field winding open is measured. The volmeter reading divided by the ammeter gives the value of resistance of two phases connected in series.So resistance of each phase will be equal to the half the resistance measured.
How to Test Your Spindle Motor for Open or Short in Windings
- Set your multimeter to Ohms.
- Test T1 to T2, T2 to T3, and T1 to T3.
- If your spindle motor fails the test, you may want to make sure the problem is not with the connector, which may have coolant on it that's interfering with your results.
- Check your inserts.
For many years, maintenance professionals have used the one-megohm rule to establish the allowable lower limit for insulation resistance. The rule may be stated: Insulation resistance should be approximately one megohm for each 1,000 volts of operating voltage, with a minimum value of one megohm.
Anything reading between 2 megohms and 1000 megohms is usually considered a good reading, unless other problems have been noted.
The insulation resistance is the resistance in ohms of wires, cables and electrical equipment. It is important to guard against electric shocks and avoid equipment damage from accidental discharges. The method of measuring the insulation resistance is to test and assess the state of the isolation (head and body.)
Dead testing is, as it sounds, performed on the circuits when they are de-energized, and form the initial testing of the circuits. These tests will outline the insulation resistance of the new circuits, and the continuity of the ring circuits.
At the last socket, use the multimeter to measure the resistance between live and neutral on a low resistance range. On a non-faulty circuit the resistance will be typically be less than one ohm.
Factors that affect insulation resistance measurements include such things as temperature, humidity, previous conditioning, test voltage, charging current and duration of the test voltage (electrification time).
Voltage Measurement between Neutral to Ground: A rule-of-thumb used by many in the industry is that Neutral to ground voltage of 2V or less at the receptacle is okay, while a few volts or more indicates overloading; 5V is seen as the upper limit.
A megohmmeter (also called insulation resistance tester, teraohmmeter) is then used to measure the ohmic value of an insulator under a direct voltage of great stability. To measure a high value resistance, techniques for measuring a low value current are used.
Testing for Open or short in windings
Put meter on ohms: T1 to T2 T2 to T3 T1 to T3 The range usually expected is . 3 to 2.0 ohms, though most are about . 8ohms. If you read zero, a short between phases exists.For good insulation, the resistance usually reads in the megohm range. The Megger insulation tester is essentially a high-range resistance meter (ohmmeter) with a built-in direct-current generator. This method is nondestructive; that is, it does not cause deterioration of the insulation.
The resistance between a winding and the core/ground is called the insulation resistance. At the other end of the spectrum, winding resistance is the electrical resistance for the wire in a given winding. This is usually measured using a low-voltage ohmmeter and is typically ohms or tens of ohms.
