Variable Speed Drives: Reducing energy costs in dairy parlours

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1 Variable Speed Drives: Reducing energy costs in dairy parlours Factsheet

2 Variable Speed Drives: Reducing energy costs in dairy parlours Vacuum pumps account for about 80% of the energy used by equipment in dairy parlours - farmers can dramatically cut their energy costs by installing Variable Speed Drives (VSDs) to optimise their milking systems. By matching the speed of vacuum pumps with the actual air flow requirements, VSDs reduce the pump s kilowatt demand and the amount of energy consumed they automatically vary pumps speed to maintain an accurate and even vacuum level, which can reduce energy costs by up to 60%, whilst extending the life span of equipment and reducing noise levels in the parlour. What is a VSD? A VSD, also known as a variable frequency drive or adjustable speed drive, is a device that can adjust electricity supply and regulates and adapts motor speed to match the actual demand required by the system or application it is driving, resulting in a reduction in energy consumption. Variable speed drives offer a high degree of motor control. It can accurately vary motor speeds, ranging from zero revolutions per minute to over 100% of the motor s rated speed, whilst adjusting torque accordingly all within the specifications of a particular manufacturer. VSDs come in many different sizes and are typically encased in boxes that can be as small as a milk carton or as big as a cupboard. Sizes range from 0.18kW through to several MW. They are available as stand-alone devices connected to the electricity supply of the motor. On some smaller motor designs - usually under 15kW - VSDs may be built onto motors and are available as integrated motor-drives. A basic VSD can be used for simple applications - such as to control a pump or a fan - where variable loads are required. It can also be interfaced with a transducer, such as a pressure or flow rate sensor, and programmed to maintain a particular setting. More advanced VSDs can be used for precise speed and torque control in complex applications like materials forming and can be interfaced with a computing system to provide real-time operating data on the status and performance of a motor.

3 How can VSDs save electricity in your dairy parlour? Vacuum pumps are designed to produce sufficient air flow to operate milk harvesting equipment and guarantee a minimum reserve requirement. This is to ensure that the pump is able to cope with a maximum demand that rarely or never occurs. As a result, they often use more electricity than needed because they typically operate at a constant speed regardless of the demand for air flow.this wastes electricity and increases energy costs unnecessarily. Vacuum pumps are variable-torque applications that offer the highest potential to save power with the use of VSDs - reducing the speed of the pump by a small amount will result in a massive reduction in the amount of electricity used because pumps are governed by the Affinity Law of Power α (Speed)3. VSDs can be attached to new or existing vacuum pumps to vary motor speed according to the exact needs of the milking system. A VSD will only produce the minimum reserve requirement when there is extra demand for airflow over and above what is required to operate the milking equipment. Lowering motor speed affords greater control of the vacuum level from the pump - maintaining a constant vacuum level and only producing the necessary amount of airflow can achieve significant energy savings of between 50 and 60%. VSDs reduce motor speed and cut energy use based on the number of cows being milked - as cows finish milking, the motor will slow down accordingly. Accurate vacuum control can also improve udder health and milking quality. VSD could be beneficial for milk pumping from the receiver to the refrigerated tank, if the milking period is long enough. VSDs can help to extend the life of vacuum pumps and motors by quickly and smoothly responding to fluctuations. Some VSDs are powerful enough to run more than one pump. Note: When linked by remote control, a VSD can be used to switch off motors or to lower the speed of pump motors to decrease the flow rate during Eskom s peak hours.

4 Energy savings are greater and the payback period shorter for blower vacuum pumps compared to oil vane vacuum pumps. What are the other benefits of VSDs? They: Lessen wear and tear on equipment. Reduce noise levels. Improve milking comfort for cows. Help to improve power factor (some makes of VSDs). Are easy to install and use. VSDs with a built-in Programmable Logic Controller (PLC) can do sequence starting and sequence stopping and, therefore, replace a number of devices. Consider these things before installing a VSD in your milking parlour: The age of your equipment - the working condition of existing pumps can influence potential energy savings, particularly older pumps. Your pump running times - the size of the dairy relative to the number of cows being milked can impact potential energy savings; the greatest gains can be made on longer pump running times. Your pump size - match it with the size of your parlour; if it does not match consider upgrading the pump. Correct installation and machine testing full energy saving gains will be achieved when filter protections and components are properly installed and tested. Dairy parlour power supply type single phase power may require a larger drive or inverter and increase energy use; three-phase power may be a better option. Your existing pump s motor speed or revolutions per minute (RPM) - greater energy savings are possible where the pump can operate at a lower RPM (e.g. half capacity); for example, a RPM motor that can be geared down to 700 RPM will benefit from a VSD. Pumps are some of the best applications for VSDs because they have variable-torque loads whose outputs have been regulated in some way.

5 How to put VSDs to work in your dairy parlour? Conduct a proper feasibility study before investing in a VSD to ensure that it is the most appropriate solution for optimising your milking system. VSDs can increase harmonics in the electricity supply, which disturb the sine curve of the alternating current and cause motors to run warmer than they are designed for, reducing their life expectancy. Where automatic electronic measurements are, for instance, used to determine milk production per cow, harmonics can be responsible for incorrect readings. Harmonics can also decrease the life expectancy of computers and negatively infl uence the operation and accuracy of electronic measuring devices. The appropriate harmonic fi lters and chokes must, therefore, be installed along with the VSD to fi lter out the harmonics and protect your equipment. Spend a bit more on quality - VSDs are high tech; mixing low quality with high tech is not recommended. Full energy saving gains will be achieved when harmonic fi lter protections and components are properly installed and tested Since VSDs are dust sensitive, an appropriate dust fi lter needs to be installed when operating in dusty conditions they also need to operate within specifi ed temperature and humidity parameters. VSDs must be installed by qualifi ed installers that can back up their product. Once installed, the VSD must be correctly programmed as setting incorrect parameters will result in poor control and energy wastage. Regular maintenance on VSDs and associated motors is essential to maintain energy savings; preventive maintenance is always less expensive than correcting faults and having unanticipated breakdowns. Opt for a maintenance contract with your supplier to ensure the VSD is kept in an optimal condition. Important note: If you have a power factor correction capacitor installed, remove it before installing a VSD.

6 Some equipment is not designed to operate at reduced speeds. Check with suppliers to ensure your equipment is compatible with variable speed operation. Eskom s Energy Advisors are on standby to assist you: Eskom s national Advisory Service offers information on manufacturers and suppliers of VSDs. The team can also advise businesses on: Reducing energy usage Doing walk-through energy assessments to identify energy usage patterns, energy needs, areas of energy wastage and energy saving opportunities Improving the energy effi ciency of operations and electrical systems and processes Prioritising maintenance as an important contributor to reducing energy usage Finding SANAS approved energy savings Measurement & Verifi cation Authorities. Advisors also provide information on funding opportunities for energy effi ciency projects. Call , leave your name and number and an Eskom Energy Advisor will contact you, alternatively, ask for a specifi c advisor to contact you. Visit for more information. Credits: Fanie Steyn, technical paper - Energy savings on motor-driven systems (Johannesburg, South Africa, 2012) Issued by Eskom Integrated Demand Management November 2015 Eskom Holdings SOC Ltd Reg No 2002/015527/30