Feature Drives & controls
Energy efficiency and beyond - the benefits of variable speed drives
Variable speed drives have been around for many years, but they are still breaking new ground and finding new uses throughout all sectors of industry. Matt Handley, Mitsubishi Electric’s product manager for Drives and Low Voltage, considers the current hot buttons for drives
T
oday, the three most important topics for drives are energy, energy and energy. After that you can list developing standalone drives systems, networking drives and servos, and integrating safety into drives as almost as significant. Several years ago governments finally woke up to the fact that carbon emissions were getting critical and set about encouraging energy users to look for ways to cut their power demands. The tool they are using for this is basi- cally tax. Details vary from country to country, but organisations that reduce their consumption stand to save signif- icant amounts of money.
Drives are brilliant at saving energy. If you reduce the speed of a motor, it is possible in the majority of pump and fan applications to save energy propor- tional to either the square or cube (depending on the application) of the reduction. It may be that in a particu- lar application you never need full speed and power, so a drive can trim output to a lower optimum level. In other applications you may need full speed, but not all of the time. Sometimes half speed is appropriate, while at other times quarter speed is adequate. You can set a drive up to provide this sort of variable output, either on a timer or as a response to real-time sensor inputs.
And of course in some applications there may be the possibility of stop- ping the motor altogether for signifi- cant periods of time. Savings like that soon add up.
Another way of energy saving that is gaining in popularity is using a drive to regenerate power that would other- wise be wasted. Most applications have deceleration stages in their duty cycle – that is to say kinetic energy is removed from the moving load. Traditionally this is simply lost, per- haps through braking resistors or a mechanical brake. However a drive can capture this energy and feed it
Automation JUNE 2012
back into the mains, often leading to significant net energy savings. Regeneration is also possible if a conveyor runs downhill, if an air or water flow is reduced, or if a load is lowered.
It is estimated that something like 66 per cent of all industrial electricity generated is used to run motors which equates to about 25 per cent of total UK consumption. A large percentage of these motors where speed or load could be varied are yet to be fitted with variable speed drives. So the potential for drives to make a signifi- cant contribution to carbon reduction is enormous.
But we also need to look at the oper- ating efficiency of the motors. On the face of it motors are very efficient, but dig a little deeper and several issues come to light. Many motors are over- sized for the job they are doing; swap- ping them for a smaller one will provide constant energy savings – and a drive can be used to ‘beef up’ output for those parts of the duty cycle where extra power is needed. Induction motors are the workhorses of industry, but in many cases switching to perma- nent magnet motors will pay hand- some energy dividends, and again a drive will optimise energy usage.
Networking & precision motion Discrete parts manufacturing, process control, building management… Nearly every technical system you can name is becoming more intelligent. Various parts of the system communi- cate with one another to optimise overall performance.
This requires that individual devices, such as drives, PLCs, HMIs, and sensors can send and receive data – and act intelligently on it. For instance, modern drives can receive a temperature signal and adjust the speed of a ventilation fan or water pump accordingly utilising built in PID controllers. Other drives may
Reduced energy bills can be cele- brated with drives
Dust and splash proof drives can be used in demanding environments
work with counters or timers to con- trol parts production. A motion detec- tor in a building’s security system could work with a drive to close a shutter, turn down the air condition- ing, open a car park gate, etc. Modern drives are offering ever greater levels of motor shaft control and this is especially important when they are used in motion control appli- cations. A good example of this is when they are networked together with servo drives over specialist high speed fibre optic networks such as SSCNet. The servos will control the high preci- sion axes in the system, and they will be communicating with the inverter drives on the general axes to improve overall system performance. It is worth noting that a top-of-the-range drive can enhance an industrial motor’s dynamic performance to near servo capability, so is suitable for axes where some extra precision is required.
Standalone drive systems A very interesting trend in drives engi- neering is the rise of standalone sys-
23
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56