IC-SUM24-PG36_Layout 1 06/06/2024 09:47 Page 36
POWER & GENERATORS
here are a couple of common questions that arise when debating the benefits of voltage optimisation (VO) for a facility that operates multiple motors. The first question is whether installing a voltage optimiser will make the motors run slower. The straightforward answer to this question is no. Three phase induction motors deliver a constant speed over a wide voltage range. The speed of the motor is dictated by the supply frequency and the winding configuration. Voltage optimisation only alters the supply voltage, not the frequency. As we are not altering the frequency, the speed of the motor is unaffected.
T
The next commonly asked question, and perhaps the question most frequently asked by electrical engineers, is whether reducing the voltage increases the current. There is a common misconception that power (W) remains constant with a change in voltage. In
fact, it is resistance, measured in Ohms (Ω), and dictated by the physical construction of electrical equipment, that remains constant. Power results from the voltage applied to the resistance of the electrical equipment. To understand how voltage optimisation can deliver energy savings by making three phase induction motors more efficient, we need to begin by understanding the crucial importance of loading requirements.
THE EFFICIENCY LOSSES OF LIGHTLY LOADED MOTORS
Three phase induction motors are very efficient, but only when loaded close to their rated capacity. The problem is, we know that most motors are oversized and therefore not loaded close to their capacity. For example, data from the EU shows that the average load factor of three-phased, squirrel-cage induction motors (SCIMS) is slightly lower than 60 per cent. In some industrial sectors, a large part of the SCIMS operates with a load factor as low as 25 per cent. This means that if you are an electrical engineer reading this, it is more than likely that that the motors in your facility are not operating at their optimal level of efficiency. To draw electricity from the supply and convert it into mechanical work, a motor will use some energy in this conversion process. To save energy, we need to make sure this process is as efficient as possible. This is generally achieved when we are running the motor at close to its loaded capacity. A 10 kW motor that is asked to deliver only a 5 Kw load might only be 65 per cent efficient, meaning that 35 per cent of the electrical energy is lost in the process of conversion to mechanical energy in the form of heat and vibration. The efficiency of a motor begins to drop exponentially when the load drops below 70 per cent of the rated load.
Many factors contribute to an abundance of oversized, lightly loaded motors. You always need to design the machine with a motor that is larger than the mechanical load, which makes
VOLTAGE OPTIMISATION AND MOTOR EFFICIENCY
For the non-technical person, voltage optimisation is straightforward to understand. Lowering your supply voltage means lower energy bills and financial savings. Engineers, however, need a more in- depth explanation of how the technology works before assessing its benefits for a specific use case. Here, Ged Hebdige, technical director at Powerdown220 explains how voltage optimisation can improve the efficiency of three-phase motors.
ensuring the motor is highly loaded automatically problematic in applications where the load will vary, like a mechanical press for example. As motors come in standard sizes, you will also generally have to pick a motor that is slightly larger than what is optimal. When designing equipment, mechanical engineers will usually work on worse-case scenario assumptions when specifying the required mechanical load. In addition to this calculation, they will generally be required to add a safety margin on top. The result of this standard process is that equipment is inevitably designed in a way that will result in larger motors being specified.
After an electrical engineer has designed a control system for the mechanical equipment, there are other factors that influence the decision-making process. Financial factors might shape the choice of motor, for example if a certain size of motor is already in stock, or a large quantity of motors are being purchased and a discount is available. Again, this further contributes to scenarios where motors are chosen without regard to the losses in efficiency.
THE COST OF OVER-VOLTING
International Electrotechnical Commission (IEC) standards for motor manufacturers stipulate that motors must deliver 100 per cent of the rated torque at the lowest voltage specified on the name plate. For most motors, that will be 380-400 volts. For historical reasons, the average UK supply is higher than on continental Europe, where most of our motors are designed and manufactured. As a result of this, your motor is likely receiving 420 volts, rather than the 380 specified on the name plate. Running higher voltage through the motor is equivalent to making the motor bigger, leading to a decrease in efficiency.
Installing a voltage optimiser will reduce the voltage supplied to the motor to 380 volts, in accordance with what is listed on the nameplate. The motor still runs at the same speed and delivers the same rated torque, but this simple reduction in voltage provides an efficiency gain. VO effectively means you have made the motor the size it ought to be for the mechanical load. The cost savings of this simple technology can be significant, particularly in a climate of rising energy costs.
36 SUMMER 2024 | INDUSTRIAL COMPLIANCE PROS AND CONS
Deciding whether voltage optimisation is right for your business requires taking individual circumstances into consideration. For example, pump or fan applications where a large motor is continually highly loaded might be less suitable. In contrast, for a cyclic process like a mechanical press in a metalworking application, the motor is only highly loaded during one part of the process, leaving an opportunity to save energy during the period where it is idling and therefore lightly loaded.
The opportunities for efficiency savings vary depending on the application and use case. If coupling a voltage optimiser with a variable speed drive (VSD), the commercial case requires more careful consideration. VO will still work with a VSD, but the efficiency gain will generally be much smaller.
The potential gain in equipment lifespan is another factor to consider. Although this is generally more difficult to calculate than for efficiency savings, it is well-established that running excess voltage through your equipment will shorten its lifespan significantly. The UK is certainly paying a high price for over-volting.
As an example, a CNC machine that operates with multiple motors, each of them receiving high voltage, will likely have excessive maintenance costs. Replacing the expensive drive cards on a regular basis is something you want to avoid, yet overvolting these machines will often lead to this outcome. In a scenario like this, voltage optimisation might deliver a significant return on investment, even without a significant efficiency saving.
In instances where supply voltage is higher and motors are loaded significantly below their rated capacity, the efficiency gains and therefore financial savings are potentially enormous. However, working out whether VO is right for you and your equipment depends on a range of factors. Arriving at the answer requires a careful and methodical process of deliberation involving the production engineers and the VO specialists working in tandem.
Powerdown220
powerdown220.co.uk
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
