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Helping the Customer

When helping a customer select an adjustable frequency drive for an application, there are a large number of factors that you must take into consideration. Let’s look at each one briefly.

Factors to Consider

  • Consider the application itself
    High-torque, large inertia, quick ramp-up applications are not recommended for use with an AF drive.

  • Load type, power and torque
    How large is the load? How much torque is required to get it moving? Is it a constant torque or variable torque application?

  • Motor type, full load amps and horsepower
    What type of motor is it? What is the motor’s full load amps and horsepower? Get the brand and model number of the motor so you know exactly what you are dealing with.

  • Speed range needed
    What range of motor speeds does the customer want available to him?

  • Speed regulation needed
    How precise does the speed setting need to be?

  • Control response
    How quickly should the control respond to changes in the load, or changes in operational settings?

  • Efficiency
    Higher efficiency means lower energy costs.

  • Overload capacity
    What class (10, 20) of overload protection is required for the application?

  • Reliability
    We can assume the customer would like the unit to fail as little as possible, of course. How critical is it to avoid nuisance tripping? How important is it to be able to adjust the trip settings?

  • Physical size of the unit
    How much physical space is available at the application site for a motor speed control unit?

  • Audible noise
    Does the customer have any concerns related to audible noise produced by the motor or speed control unit?

  • Harmonics
    Does the customer have any concerns regarding harmonics on the line? Take into consideration the entire system of which the drive is a part.

  • Enclosure type
    Does the customer have any special needs relating to the application’s environment? Choose a NEMA enclosure type to match.

  • Location
    Is the distance between the motor and the AF drive a problem? Check in the product catalog. An output filter may be necessary.

  • Cost
    Customers want the least expensive product that will meet all the application’s requirements. As you explain the cost of a particular unit, be sure to put it in terms of the total cost to the customer. What may seem like a high initial cost may in fact save the customer a lot of money over the life of the unit. Energy cost savings, reduced downtime because of on-board diagnostics, and the like can be presented as returns on the investment in the device.

Application Checklist

Here is a good checklist to use when helping a customer decide which type of AF Drive is best for the application.

MOTOR

New ____ Existing ___ Hp ____ Base Speed _____ Voltage _____
FLA ____ LRA ___ NEMA Design ____ Gearbox/Pulley Ratio _____
Hz _____ Service Factor _____

LOAD

Application: ________________________________________________________

Load Type: Constant Torque _____ Variable Torque ____Constant HP _____

Load inertia reflected to motor: _____________ lb.ft2

Required breakaway torque from motor: ___________ ft.-lb.

Running load on motor: ___________ ft.-lb.

Peak torque (above 100% running): __________ ft.-lb.

Shortest/Longest accel time: ____ / ____ sec. up to ____ Hz from stop

Shortest/Longest decel time: ____ / ____ sec. down to ____ Hz from max. speed

Operating speed range: ______ Hz to _____ Hz

Time for motor/load to coast to stop: _____ seconds.

AF DRIVE

Source of start/stop commands: I/O terminals ____ Keypad ____ Other ______

Source of speed adjustment: ________________________________

Other operating requirements: _______________________________

Will the motor ever be spinning when the AF Drive is started? Yes___ No ____

How far apart are the motor and the AF Drive? _________ feet

Is the load considered high-inertia? Yes___ No ____

Is the load considered hard to start? Yes___ No ____

Options desired: Multiple operators ______ Output Signals ______
Power Options _________________________________
Other ________________________________________

Other requirements or conditions: ________________________

POWER SUPPLY

Supply transformer: _____ KVA, or short circuit current at drive input _____ amps

Total Horsepower of all drives connected to supply transformer/feeder ______ Hp

Is a drive transformer or line reactor desired? (May be required) ________

Any harmonic requirements? Y/N % Voltage THD ____% Current THD ____

Total non-drive load connected to the drive’s feeder: ________ amps

SERVICE

Start-Up Assistance: ____________ Customer Training:__________

Preventive Maintenance: _________ Spare Parts: ________

ADDITIONAL ISSUES – Answer Yes or No

____ Will the AF Drive operate multiple motors?

____ Will the power supply source ever be switched with the AF Drive running?

____ Is starting or stopping time critical?

____ Are there any peak torques or impact loads?

____ Will user-supplied contactors be used on the input or output of the AF Drive?

Recommending a Product to the Customer

Using all the information gathered here, consult your product catalogs to make a recommendation to the customer.

It is possible that you may have to suggest more than one product, as you may not find a perfect match for all the application’s requirements.

The centrifugal pump on a chilled water system, shown here, is an ideal candidate for use with an adjustable frequency drive.

As the pump turns faster, it moves more water, and it requires more torque.

This application also requires water flow through the pump to be regulated.

You will need to work with the customer to select an adjustable frequency drive for an application such as this, taking into consideration the factors mentioned above.

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