Common method for finding grounding points - Solutions - Huaqiang

SMD Aluminum Electrolytic Capacitor

AVX TPSE226M035R0125 Low Impedance Tantalum Capacitor, 22µF

Adjustable Capacitor from Murata - Genuine and Original

STM32L151CCU6 Single-Chip Microcontroller

Current/Voltage Probe with 420x4450 Head, 5.0mm Diameter

1) Shake Table Method: For a 6kV motor, if the insulation resistance between the winding and ground is below 6MΩ, it indicates that the winding is wet or the insulation has deteriorated. If the resistance is zero, it means there is a grounding fault. 2) Light Bulb Test: Remove the end cover, take out the rotor, and disassemble the phase windings. Connect a 60W, 220V bulb in series between the end of the measured winding and the motor casing. Apply 220V AC to both ends of the winding. If the bulb glows brightly, it indicates poor insulation, commonly referred to as a "virtual connection." If the bulb shines very brightly, it suggests a grounding fault, often called a "real connection." In the case of a "real connection," the insulation at the grounding point may show cracks or blackened marks. You can visually inspect the slot for these signs. For a "virtual connection," you can apply a high voltage to break down the weak spot, and determine the grounding point by observing sparks or smoke marks. 3) Current Orientation Method: Apply DC voltage to the first end of the faulty phase in parallel. Use a 6–12V battery with a variable resistor in series, keeping the current under 5A. Move a small magnetic needle across the slots. The direction change of the needle indicates the grounding point. Then move the needle axially along the slot; when the needle changes direction, that's the fault location. If conditions allow, you can also use current burn-through or voltage drop techniques to locate the grounding point more precisely. Based on past experience, most winding grounding faults occur at the slot or the end of the winding. Grounding within the slot is rare because the end is a weaker point of insulation. As the motor capacity increases, the electromagnetic forces acting on the stator winding ends become stronger. If the natural frequency of the winding end is close to 100 Hz, resonance may occur during operation, causing large amplitude vibrations. This can lead to severe mechanical stress and damage. In recent years, some large motors have experienced failures due to resonance in the stator winding ends, or other issues like loose binding wires, unsecured brackets, or worn insulation on the wire rods.