Simply words, a frequency inverter is a power conversion device. The frequency inverter converts a basic fixed-frequency, fixed voltage sine-wave power (line power) to a variable-frequency, variable-voltage output used to control speed of induction motors.
Primary function of a frequency inverter in aquatic applications is to provide energy savings. By controlling speed of a pump rather than controlling flow through use of throttling valves, energy savings can be substantial. By way of example, a speed reduction of 20% can yield energy savings of 50%. The following describes speed reduction and corresponding energy savings. In addition to energy savings, impeller, bearing and seal life is greatly improved.
Available in many different types, frequency inverters offer optimum method for matching pump and fan flow rates to system requirements. Frequency inverter is most commonly used. It converts standard plant power (220V or 380 V, 50 Hz) to adjustable voltage and frequency to power AC motor. The frequency applied to AC motor determines motor speed. The AC motors are usually same standard motors that can be connected across AC power line. By incorporating bypass starters, operation can be maintained even if inverter should fail.
Frequency inverters also offer an additional benefit - increased bearing and pump seal life. By maintaining only pressure needed in pump to satisfy system requirements, pump is not subjected to any higher pressures than necessary. Therefore, the components last longer.
The same benefits - but to a lesser extent - also apply to fans operated by frequency inverters.
To obtain optimum efficiencies and reliability, many specifiers obtain detailed information from manufacturers on frequency inverter efficiency, required maintenance, diagnostic capabilities within frequency inverter, and general operational features. Then, they make detailed analysis to determine which system will give the best return on investment.
In addition to energy savings and better process control, frequency inverters can provide other benefits:
A frequency inverter may be used for control of process temperature, pressure or flow without use of a separate controller. Suitable sensors and electronics are used to interface driven equipment with frequency inverter.
Maintenance costs can be lowered, since lower operating speeds result in longer life for bearings and motors.
Eliminating throttling valves and dampers also does away with maintaining these devices and all associated controls.
A soft starter for motor is no longer required.
Controlled ramp-up speed in a liquid system can eliminate water hammer problems.
Ability of a frequency inverter to limit torque to a user-selected level can protect driven equipment that cannot tolerate excessive torque.
Analyze System as a Whole
Since process of converting incoming power from one frequency to another will result in some losses, energy savings must always come from optimizing performance of the complete system. First step in determining energy savings potential of a system is to thoroughly analyze operation of entire system. Detailed knowledge of equipment operation and process requirements are required in order to ensure energy savings. In addition, type of frequency inverter, features offered, and overall suitability for application should be considered.
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