The easiest way to choose the right frequency inverter for food processes

Choosing the right variable frequency drive for food processes that meets production demand and lowers energy consumption can be a daunting task, as there are many variables with each application and system. However, there are some helpful hints and tips for selecting the right unit.

Before explaining which measures to consider in order to make a sound decision on the frequency inverter best suited to the needs of the installation, it is essential to obtain basic information about the motor and the required system in order to make comparisons with other units.

This information can be found on the engine nameplate, on which the engine nameplate stands out:

• Kilo Watt Power.
• Full Load Amps (FLA).
• Voltage.
• RPM.
• Service factor.
• It is also useful to know whether the motor has the rated capacity of the inverter.

Other information will be specific to the needs of the system and application, such as:

• Type of load (constant torque or variable torque).
• Speed range and control method.
• Special enclosure requirements.
• The length and construction of the cable is also a factor, as it determines whether additional filtering is necessary.
• All standard applications can be catered for, but need to be specified.

This data is of vital importance to establish and compare drive ranges according to operating requirements. The easy way to choose the most suitable food process inverter is to recognise the most suitable drives. factors to consider when incorporating variable frequency drives for industrial processesThe organisation's management can avoid unnecessary and counterproductive costs.

7 considerations when choosing the right variable frequency drive for food processes

1. Knowing the kilowatt of the load is an excellent way to find units that suit the required application.
2. Check the full load amps (FLA), as they are the correct way to size a variable frequency drive. This is especially important if you have a constant torque load or a load that is difficult to start. While it may initially cost a little more to buy a unit with a higher amp rating, it will likely pay for itself over time in reliability and functionality.
3. The voltage of the variable frequency drive should be matched to the motor voltage available at the site. For medium voltage or other applications, it would be a good idea to have an application specialist or engineer help you establish your needs.

On a three-phase input the choice may be easier, however, when the input is single phase there are a few more things to consider. The rule of thumb for sizing the single phase input on a three phase drive is to use a VFD rated for 2 times the FLA of the motor. 

For example, if your motor is a 10 HP motor with an FLA of 28 amps, then you should select a VFD with an amperage of 56 amps which ends up being approximately 20 HP. In addition, if continuous operation is a necessity, the following should be specified:

• +/- 10% voltage fluctuation.
• +/- 3% of frequency variation.

4. Establishing the type of load required on the motors before choosing the most suitable variable frequency drive for food processes is important because if the equipment being driven is centrifugal, such as a fan or pump, then a variable torque drive will be more appropriate. 

Energy savings is often the primary motivation for installing variable frequency drives in centrifugal applications, and variable torque drives offer the greatest energy savings. Variable torque operation allows the motor to apply only the required torque resulting in reduced energy consumption, which is one of the many benefits of VSD.

5. Ensure speed range. It is recommended that an engine should not run at less than 20% of its maximum permissible specified speed. If it is run at a speed lower than this without auxiliary engine cooling, the engine will overheat.
6. In food process factories, the 3-wire control method is used, in which two switches are used to run the drive where multiple stations can start/stop the VFD, but a single safety circuit must be made to allow this operation to be initiated.
7. An important aspect of the configuration and commissioning of frequency inverters and choosing variable frequency drives for food processes is the environment surrounding the drive. There are a few types of certifications into which drives are classified, including ingress protection (IP), NEMA and UL enclosures. It is important to match the needs of the installation. 

This can be done by finding a stand-alone unit with the proper cabinet rating, or you can place the VFD inside another cabinet. There are applications and loads that may require special sizing and consideration. When you are sizing or specifying a VFD for any application, it pays to be conservative and leave some buffer space in the FLA and overload ratings. This is especially true if the load is difficult to start or if a heavy load is seen during operation. 

Understanding how to selecting frequency inverters to improve motor control and efficiency is a competitive advantage for the food sector, because it helps to reduce energy consumption and contributes to improving production demand, which is ultimately the goal. For more information subscribe to the Technology for Industry Newsletter.