Simple Solutions That Work! Issue 6

In the industrial and commercial environment there are many electrical motors at work driving a myriad of devices (loads). Some of those loads are constant, requiring the same amount of horsepower the entire time that the device is running. On the other hand many of the loads are variable, using differing amounts of horsepower depending on what the machine is doing at the time. In order for this type of machine to work, the electric motor is sized to the largest & heaviest work that the machine is expected to perform. Many of these machines idle at full horsepower waiting either for the next part of the cycle to take place (perhaps a part cooling enough to take out), or even worse, waiting for the operator (who is outside the back door taking a smoke break) to load another part into the machine. In many factories a single operator will tend several machines, alternately loading & unloading them as they finish processing their respective parts. What if these machines could set themselves into a low energy consumption idle state after finishing their processing operation? What if it could turn itself off after the cycle is finished and turn back on for the next cycle? In many cases a Variable Frequency Drive (VFD) can help match the horsepower supplied by the electric motor to the demand desired by the machine process. In the following example, we are showing the difference in energy consumption between running the motor constantly and using a VFD to ramp down and shut off a machine between cycles. The power values shown are as measured. The machine in the example is a Metal Mechanics 35 ton capacity hydraulic trim press with a 15 horsepower electric motor and running a cycle two times per minute. The following graph details the energy consumption through the 30 second cycle. The upper graph line shown in red is the current drawn by the machine during the conventional cycle with the electric motor running at full speed during the entire cycle. This machine is drawing 10 amps of electricity during the idle part of the cycle. The lower graph line shown in green is the current drawn by the machine during the conventional cycle with the electric motor ramped down and shut off during the idle part of the cycle. This machine is drawing 0.1 amps of electricity during the idle part of the cycle. The area above the green line and below the red line is energy wasted, providing no benefit to the organization. The following table shows the energy savings per shift per 50 week year. This table based on 5 days per week ( if 6 days add 20% if 7days add 40%) Energy cost based on $0.10 per KWH (factor as necessary). Our example fits into the middle column of this chart where 80% of the energy is used by the machine during idle and wasted. Five machines equipped with VFD technology have the same energy footprint as one machine running in a conventional manner. TOM DAILY President JOHN KISON Engineering Manager METAL MECHANICS, INC. ARTICLE TAKEAWAYS: • How to tell if Micro Logix, Compact Logix or Control Logix is the right PLC for your organization • Machine communication & networks on the plant floor – can your machines ask for maintenance? • Delay, phase-in, or jump in with both feet, and alternative strategies for implementation SYSTEMS INTEGRATION 52 REDUCING ENERGY CONSUMPTION IN AVARIABLE LOADAPPLICATIONUSING VARIABLE FREQUENCY DRIVES