Electrical Drive keeps blowing fuses/tripping breakers

Electrical drives troubleshooting consist of the complete understanding of maintenance. This is one of the area most engineers are not compatible with. While a bad service is certainly a possibility. Electrical drives troubleshooting topic will let you understand this easily. There are several things you can do to insure you’re looking in the right place for the root cause of the problem.

Drive keeps blowing fuses/tripping breakers

A defective drive can definitely cause fuses or breakers to trip. Since the drive conducts the same amount of current as the motor, it’s one of the most stressed components of a drive system. In most cases, drives don’t simply go bad but rather are stressed to the point of failure. Locating the source of the stress is the key to correcting the problem.

• Grounded motor: Check to make sure the motor hasn’t become grounded by checking the resistance from each terminal of the motor to earth ground. If using an ohmmeter, the resistance to ground should be millions of ohms or essentially an open. A motor’s internals can either permanently or momentarily short to the case. A grounded motor will almost instantly cause permanent drive damage, giving the false impression that the drive is the source of the problem.

• Line Power: Make sure that the line power is clean. Certain drives are more susceptible to problems caused by “dirty” line voltage as they may use certain portions of the 60Hz line as a clock. Line power can be distorted by the cycling of large machines, motors, pumps or welding operations. AC line filters can help maintain a clean AC waveform.

• Wiring: If using a field or shunt wound motor, connecting the armature winding of the motor to the field output of the drive will permanently damage the drive and give the false impression that the drive is the problem. Even if the motor is disconnected, a damaged drive will continue to blow fuses or trip breakers.

• Speed command signal: If using an external command signal to control motor speed, make sure the signal is isolated or make sure the drive has input isolation. Connecting two non-isolated devices together will cause damage to the drive and the device providing the signal.

• Overloading: Exceeding the drive’s current rating or ambient operating temperature can stress the drive to the point of failure. Monitor motor current to make sure it’s within the level expected and doesn’t exceed the rating of the drive. If the drive is in an enclosure, adding forced air will help insure the drive is operating within the ambient rating.

• Noise issues: For instance, running a wire from the potentiometer to the drive. A wire will act as an antenna, picking up ambient noise in the form of electromagnetic interference (EMI) and radio frequency (RF) signals that can impact the drive signals. Shielded wires can help protect the potentiometer from noise. Whenever possible, keep logic level wires separate from power and motor wires.

The importance of signal isolation

In motor drive applications it’s sometimes necessary to send an analog speed command signal to a drive. In those cases it’s important to make sure that either the output of the device sending the signal, or the input of the device receiving the signal, is isolated.

Having input or output isolation is an added feature and is typically noted on the data sheet of the respective device. Connecting two non-isolated devices together will cause catastrophic damage to both devices. If neither device has isolation, a stand-alone isolation module can be used…

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