This month we’re taking a more technical look at what parts make the wheels turn in an irrigation system. More specifically we’ll be looking at Variable Speed Drives (VSD), why this component can play a key role in the irrigation system and what you need to know when selecting one for your farm’s irrigation.
What are Variable Speed Drives?
A variable speed drive (VSD), can be a valuable tool for managing energy in a mechanical system. Typically the VSD system consists of a three-phase AC induction motor and a variable frequency power supply. A VSD is connected to a pump or fan applications to vary the pump or fan speed according to demand. The result can be large energy savings1 if a hydraulic design is done.
Because the electric motors that drive pumps in irrigation systems are energy-intensive, VSDs can be used to lower the energy consumption by regulating electric motor speeds to match the energy demand with the system load. The electricity used during irrigation on farms can often be one of the most costly expenses. A VSD we can lower the energy output and optimise your irrigation system if there are multiple service points.
Variable Speed Drives adjust the speed of electric motors to match the actual demand of the application, thereby reducing motor energy consumption typically by 20 to 50%.2
VSDs are available in varying sizes, encased in a box and are usually stand-alone devices connected to the electric motor of your system.
How do VSDs optimise your irrigation system?
In the case of an irrigation system where various sizes of land are irrigated using the same pump, a VSD can be used to adapt the speed according to the respective water and pressure requirements of the various sizes of land, instead of having the motor running at full speed and all the excess energy being dissipated by the pump’s pressure regulator or throttle valve.
However, it’s important to note that a VSD does not guarantee an energy saving. When using this application it’s important to design hydraulic system that supports the advantages of a VSD in order for the necessary energy savings to be made.
How do you know if you need a VSD?
In the instance of a movable pipe system and micro- and drip-irrigation, a VSD can optimise your irrigation system, in the following instances:
- When the distance between the blocks of land and pump stations are different, causing a variation in friction loss and power requirements.
- Irrigation blocks are different sizes and a different number of sprayers or drippers are required.
- If the irrigation blocks are on sloped topographies that require different pressure and power.
- Pumps and motors are designed to deliver water to the irrigation block that requires the most pressure.
Additional benefits of having a VSD?
- A VSD protects the faults in electric motors and cables, thereby increasing the life span of your complete irrigation system.
- It reduces mechanical stress and damage.
- Emergency set points and trips protect equipment and motors.
- It has exact process control.
- The VSD improves the management of the systems’ electricity use outside peak hours.
- It’s simple to install, configure and use.
What else do I need to consider when installing a VSD?
A VSD might not be necessary and in some instances a soft starter may be a better option for your system. A VSD is a costly but effective, when applied correctly, application. Never feel pressured to purchase a part if you do not fully understand how it works and the alternative available. Please consult with one of our irrigation specialist to find out what solution will best fit your irrigation system and your farm.
Bekmar can assist with a proper feasibility study before investing in a VSD to ensure that it’s the best and most appropriate solution to optimise your irrigation system.
We know how costly equipment is but as we often say in Afrikaans, goedkoop koop is duur koop, meaning that in this instance we recommend spending a bit more on a quality VSD, especially if the rest of your equipment is high-tech. Mixing low quality with high tech is never recommended.
VSDs must be installed by qualified installers such as our technicians at Bekmar who will be able to assist you from start to finish. Once the VSD is installed, it must be correctly programmed according to the parameters prescribed by our irrigation consultant, incorrect settings will result in poor control and energy wastage.
Bekmar Irrigation supplies a wide range of VSDs for agricultural irrigation. Talk to us today about optimising your farm’s irrigation and if you would like to save energy and money.
- Management of Process Energy by Craig B. Smith, Kelly E. Parmenter, in Energy Management Principles (Second Edition), 2016