Restoration of variable frequency drive that have been exposed to excessive moisture or have been in a flood pose a more difficult challenge. A typical variable speed drive contains a wide range of operating voltages and power supplies, complicated printed circuit boards and intricate control circuits. The severity of damage to the variable speed drive usually will depend on whether or not the variable speed drive was operating when the exposure occurred. The damage that occurs is most likely more severe if exposure occurs while the variable speed drive is operating. If the variable speed drive is exposed while it is not energized, the damage can be less severe but will usually be latent in nature. In either case, if any input line or internal power supply fuse is open or significant corrosion is present, contact the manufacturer for specific corrective measures.

When an application requires more current at a reduced speed, that means more heat and less cooling at the lower speeds. Most VSDs have limits to protect the VSD and consequently the motor. Too low a setting and there will be lot of trips. Too high a setting and there may be damage in high ambient temperatures.

If the pump has to operate at its max HP, the 125% may not be enough given the losses (excess current) required by the variable speed drive, especially with long feeders. In addition, noise from other high frequency devices like other variable speed drives, arc welders, etc can cause problems with the variable speed drive as well as the variable speed drive causing other problems on the electrical service. A line reactor or filter may be required there also. The lower the carrier frequency is, typically 2 KHz to 4 KHz, the noisier the motor but less losses and more efficient. The higher the carrier frequency, the quieter the motor operation but greater loses and more line current.

The variable speed drives of degree of protection IP20 are designed, as a standard, for installation in electrical cabinets. During the VSD installation, both the installation and the safety instructions as well as the variable speed drive specifications must be complied with.

• To avoid serious physical injury or considerable damage to property, only qualified staff may work on the variable speed drive.
• During assembly, make sure that no foreign particles (e.g. chips, dust, wires, screws, tools) can get inside the variable speed drive. Otherwise there is the risk of short circuits and fire.
• The variable speed drive complies with protection class IP20 only if the covers, components and terminals are mounted properly.
• Overhead Installation or installation in horizontal position is not permissible.

The typical variable speed drive operator interface provides a means for an operator to start & stop the motor & adjust the operating speed. Additional operator control functions might include reversing & switching between manual speed adjustment & automatic control from an external process control signal. The operator interface often includes an alphanumeric display and/or indication lights & meters to provide information about the operation of the variable speed drive. When mounted within another enclosure, a remote operator keypad & display may be cable-connected & mounted a short distance from the controller.

Most small variable speed drives are mounted in rack slots or on a DIN rail. The clips for mounting to the DIN rail are usually built into the fins of the heat sink to which the variable speed drive is mounted. This makes them easily installable in control cabinets. Larger variable speed drive units usually have through-hole mounting to accommodate individual fasteners. The fastening method should be adequate to support the weight of the variable speed drive & allow the free flow of air across the heat sink; airflow in some applications is aided by a cooling fan.

Mount the variable speed drive near the motor. Excessive cable length between the variable speed drive & the motor can result in extremely high voltage spikes at the motor leads. It's important to verify the maximum cable distance stated in the variable speed drive specifications, when you are installing variable speed drives onto AC induction motors. Excessive voltages can reduce the expected life of the insulation system, especially non-inverter-duty motors.

Line reactors stabilize the current waveform on the input side of a variable speed drive, reducing harmonic distortion & the burden on upstream electrical equipment. Harmonics are high-frequency voltage & current distortions within the power system normally caused by nonlinear loads that don't have a constant current draw, but rather draw current in pulses. Variable speed drives create harmonics when they convert AC to DC & DC back to AC.