A solid ground requires rewinding or replacing the motor. Water is the most common cause of a grounded winding. The problem is usually found in a slot, where the slot insulation has broken down. When a motor is “ grounded“, the winding is shorted either to the laminated core or to the motor’s frame. They become charred quickly from the high circulating current that is transformed into them (Figure 2). Shorted turns in any AC winding are usually visible. Please note that the rotor should be turned during this test to eliminate its effect. Without the ampere demand of the circulating current, the difference lessens between the amperes of the faulty phase and those of the normal phases.Ī very small difference in resistance is all that is needed to identify the faulty phase. Only the resistance of the wire (turns) within the closed loop is now eliminated from the phase winding.
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