When a three-phase motor suffers burned windings, it is vital to always identify the real cause behind this problem before replacing it. The appearance of the windings will be different depending on the failure situation, be it a single-phase burnout, voltage spike, unbalanced voltage, or overload, which helps quickly identify the root cause. Below are some of the most common winding problems encountered in three-phase motors that will require a replacement or motor repair in Singapore.
1. Shorted turns
Short-circuited turns are one of the common reasons for windings to break down and will require a motor rewind or complete replacement. A short occurs when the insulation between wires becomes degraded, causing one or several coil turns to get bypassed. Many factors can cause shorted turns, including aged insulation, high-voltage spikes, nickel coil wire, overheated winding, conductive contaminants, and loosened, vibrating coil wires.
Whenever an electric motor gets “grounded”, it usually means that the winding is short-circuited into either the motor’s frame or its laminated core. Water exposure causes grounded winding in most cases, and if it is solid ground, the motor will need to be rewound or replaced.
The issue typically develops in slots where the insulation has worn out, and these breakdowns are often a result of overheating, age, conducting contaminants, excessive coil movement, the pressure of a tight coil fit, hotspots due to lamination damage, and, in rare cases, lightning.
3. Open winding
Undersized lead lugs are the most common cause of open winding problems in motors, and the charred connections in its connection or terminal box are a dead giveaway of this problem. However, open windings can also occur due to shorted turns, ground-to-frame shorts, phase-to-phase shorts, severe overloads, damaged internal coil-to-coil connections, and physically damaged coils. Depending on the motor’s internal connection, open winding problems may show several different symptoms.
4. Phase-to-phase short circuit
Phase-to-phase shorts happen when the insulation at the end of the coils or the slots break down. The voltage between phases tends to be incredibly high, so a large part of the winding gets bypassed whenever a short develops. This results in the phase windings melting open in most cases, making it easy to detect the problem. The usual factors that cause interphase breakdown include mechanical damage, age, and tight fit (in the slot) and contamination.
5. Submerged motor
If a three-phase motor gets submerged in water, it may not need to be rewound or replaced, provided it was not energised. Cleaning and baking the windings will suffice to get it operational again, and it is recommended to do this and disassemble the motor as soon as possible.
If the motor uses ball bearings, they must be replaced immediately. However, if it uses sleeve bearings, replace the oil-wicking material immediately to prevent it from pitting or rusting the shaft area near the bearing window. If the motor comes with an oil reservoir and oil ring, they must also be cleaned thoroughly.
Apart from the problems discussed above, other common rotor problems can lead to winding issues, such as open rotor bars, misaligned rotor/stator iron, and a loose rotor on a shaft. Once identified, it is important to document these problems so that each plant motor can have a detailed history that allows for uncovering problem areas that need to be improved or eliminated. When it comes to three-phase motor rewinding, it is important to also take note of the three steps to restore performance.
Moreover, all these issues likely stem from in-plant faults and require immediate attention. Otherwise, even the replacement motor will encounter the same failure, leading to more downtime. Getting help from companies that provide mechanical and electrical engineering services is recommended to address both your motor issues and any in-plant faults you may find.