Variable Frequency Drives are used in many different applications to closely control machinery, motors, generators or pumps. Drives can instantly change the torque or speed of motors.

Drives range in size from fractional horsepower (1/4 HP) up to 500 HP off the shelf. All of the top drives on the market today have hundreds (over 900 in some cases) of separate functions built in. VFD’s convert single phase or three phase AC power into DC power and then back into AC power. The output AC power is now infinitely variable.

Drives are not indicated in every situation. In instances where motors or machinery are already running at peak efficiency, drives will add nothing of value. However, in most applications, motors have varying loads or other external forces where drives can drastically improve the performance. They are ideally suited to a fluid pump environment where changes in head pressure is highly variable. This includes almost all water and waste water applications.

There are a number of advantages using drives:

Electrical Control - A drive can change the speed of a motor to maintain a constant torque on a pump. This can result in very high energy saving as well as greatly reduced mechanical stresses. A slow down in speed from 100% to 80% can actually save 50% of the energy costs. Drives can control soft starts and active breaking. PID functions provide process control.

Mechanical Savings - VFD’s can eliminate the need for dampers, throttling valves, pressure tanks and other energy wasting devices. A VFD when properly installed and programmed, will perfectly match the motor to it’s application on a second by second basis.

Single Phase Input -Increasingly, pumping stations are being located where three phase power is not available. VFD’s can take single phase AC power and convert it to three phase AC power. This allows the station to avoid the extra expense of purchasing DC motors with their higher initial cost and higher maintenance costs.

Environment Response - VFD’s can sense changes or problems in the environment. Most pump stations have a generator backup which, when activated, can create surges. VFD’s can instantly respond to change speed or shut down before serious mechanical failures can occur.

Remote Monitoring - VFD’s are frequently used as part of a remote monitoring station to help monitor and regulate unoccupied pumping stations. VFD’s are self protective and self checking to a high degree. Through the use of land lines or telemetry, VFD’s constantly monitor systems performance to help control manpower costs.

Whatever your needs, Stultz Electric technicians are experts at solving wastewater and fresh water problems. We are not only in the business of selling drives. We are in the business of building custom panels (including drives) to solve our customers’ unique needs.

No matter what your pumping station requirements, we at Stultz Electric can help you solve your unique problems. We have the experience and commitment to quality that our customers have come to expect of us for the past quarter of a century.

Enclosures: NEMA Type 1, Type 12, or Type 4 may be specified.

Bypass: Allows the motor to be switched from inverter to across the line operation. This utilizes two mechanically interlocked contactors controlled by a front panel mounted inverter/bypass selector switch.

Auto-Bypass: Same as bypass except it automatically transfers the motor to across the line operation.

Local/Remote: Allows for the selection of panel front speed control or remote station speed control. Includes a local/remote selector switch, auto/manual selector switch and terminal connection for remote speed pot and start/stop push buttons.

Isolation Transformers: For added protection of equipment and personnel, electrostatically shielded isolation transformers are available. The transformers are mounted in Type 1 enclosures and are available in most common voltages.

Climate Control: Space heater and air conditioners are used to control the internal environment of the inverter enclosure. Fans and filters can also be supplied for the industrial environments.

Single Phase Input: Units may be set up for single phase input to operate a three phase motor.

Line Reactors: Provide additional line impedance for installations where the incoming power is unstable. Recommended where a drive is powered by a very large supply transformer.

Transducers: Voltage or current devices can be supplied to interface with instrumentation systems. Level, pressure and temperature are common.

Dynamic Braking: For applications requiring fast deceleration, or applications with high inertia load, dynamic breaking resistors may be specified.

Special Meters: A number of meters can be provided for customer use. Optional meters include (digital or analog) frequency, voltmeters, ammeters, watt meters, elapsed time meters and percent load.

Remote Stations: Remote stations can be provided with many different combination of devices. Standard stations contain an analog frequency meter, a speed pot and either a run/stop selector switch or stop/start pushbuttons.

Jogging: Includes a run/jog selector switch. When in the jog position, the start pushbutton is momentary only.

Controllers: A complete line of process control equipment is available to simplify even the most complex operations.

UL: Listing is available for all built up units.

Disconnect Switch: Circuit breaker or main switch may be incorporated in a built-up panel.

Harmonic Filters: May be added to minimize harmonic current distortion that can effect electrical systems.

RFI/EMI Filters: Solve noise problems to and from equipment by reducing radio frequency emissions.

Long Lead Filters: Used where the length of cable between the drive and motor is long resulting in damaging voltages.

Communication: Many digital communication options are available for interfacing with various brand name protocols.