As variable frequency becomes a larger requirement in systems, variable frequency drives (VFD) are becoming very common in the industrial control market. On smaller systems and lower power range systems, the VFD may be too powerful for the application. A complex high feature drive can cause long installation processes and cumbersome commissioning, as these drives typically have a broad number of parameters. Many applications are basic—simple fans, small motors, conveyors, or pumps. Fortunately, you can reduce drive complexity for simple applications that do not require advanced parameter settings and achieve basic and simple installation and commissioning.
When considering motor control, there are many options on how to control a motor, fan, pump, etc. Contactors start and stop motors. Starters start and stop motors with overload protection. Soft starters add a smooth ramp up and ramp down during starting and stopping. Drives do all of this with adjustable frequency and advanced motor and device protections. Drives have the highest growth in the market due to the pressure for energy efficiency. They are used more and more in many applications.
There are three aspects to consider when building a panel around a variable frequency drive: application, wiring, and commissioning.
VFDs are used in many diverse applications, from fan walls to warehouse conveyors to booster pumps. Applications can have very basic motor control.
- In the HVAC market segment, thousands of fans only follow an input that changes the speed of the fan dependent on the environment and temperature. These applications only use an analog input or a fixed frequency value to control the fan.
- Conveyor motors follow references from sensors tracking when to turn on or off. Drives are used to handle the additional torque the motors experiences when starting up a loaded conveyor more smoothly and safely.
These examples are basic applications that require adjustable frequency, but are also typically burdened with long installation and commissioning due to the use of a complex VFD.
Using products with default control terminal operation that matches the basic application requirements, like the Siemens V20 series drive, can reduce the installation and commissioning time. Selecting the proper drive can save time and money when paying attention to the application.
Applications with multiple motors in a control cabinet require a motor control component and upstream circuit protection for each motor. An example system is a fan wall with 10 fans. This requires 10 motors, 10 drives, and 10 circuit breakers or fuses and results in a larger control panel to accommodate the additional components, wiring, and heat dissipation. Considering a drive that has been UL tested for group motor installation can accommodate those three factors.
Group motoring allows for up to five drives controlling five motors to be protected by one upstream short-circuit device. Drives that are rated for group motoring typically have common accessories that link the main wiring of each drive properly. There are significant savings in material cost, installation time, and complexity. In the example of 10 fans on a fan wall, the user will see these benefits:
- Reducing the number of circuit protection devices from 10 to two
- Reducing the time and complexity of wiring the system—point-to-point wiring from each circuit protection device to each drive
- Reducing the panel size as the number of components and wiring is reduced
- Promoting a clean, simplistic panel design
The VFD’s physical layout can lead to a wiring consideration. There are two different layouts for the line and load wires: (1) line, load, and control wiring through the bottom of the drives and (2) contactor-like wiring where the line-side wiring is located at the top of the drive, the load-side wiring is at the bottom of the drive, and the control wiring is on the face of the drive. Drives with contactor-like wiring have easier wiring and a less complex wiring diagram.
Reversing contactors and starters are used in many applications in which adjustable frequency is not required but changing the direction of the motor or fan is required. These control components typically necessitate additional wiring to meet the electrical reversing requirements, mechanical interlocking to eliminate both reversing and non-reversing signals to the motor, and additional space as the products are mounted side by side. Products like the variable speed starter and other drives can eliminate the additional wiring and mechanical interlock while reducing the panel space required.
Setting the parameters of a drive adds additional time for commissioning and installation. Copy/paste tools are the easiest and most efficient way to set up the parameters of the drive. These tools have many beneficial functions:
- They can copy the parameter set from one drive to the next if a system like a fan wall has identical fans and configurations.
- They can store parameters to maintain the parameter set for a different application configuration. For example, if an HVAC system has a cooling fan and compressor, the copy/paste modules can store the parameters for the individual fan and compressor application with labels for the application name.
- They can be used to easily replace down or failed drives. The user can pull the parameters from the failed drive and then easily and quickly install the new drive for reduced downtime. Just the same, the OEM or panel builder can send out a copy/paste module to a customer’s site for inexpensive and quick troubleshooting.
These tools can easily decrease the complexity of installing, commissioning, and troubleshooting systems.
For basic applications, there are a few parameters that may need to be changed from defaults, such as the ramp time, motor rated current, motor frequency, fixed frequency, or the control terminal configuration. The user can easily change these parameters by going through the keypad parameter menu or using the PC tools.
There are many considerations when building a control panel around a variable frequency drive. By considering the application before selecting the drive, you can reduce wiring time, commissioning time, and material cost such as with group motor applications. Wiring consideration is another piece of the puzzle, but selecting products that improve the wiring diagram and wire complexity will help create a more effective panel. Using tools to quicken the commissioning time will alleviate the stressful burden of repetitive setup and installation. With the continued advancement of technology and products, more tools will become available to help reduce the complexity that surrounds adjustable frequency requirements.