Improve performance in machines and plants.
by Brian Libby, Siemens Industry, Inc.

Certain topics continue to surface during recent expert discussions on energy efficiency in machines and plants. The topics include variable frequency drives (VFDs) for optimum drive solutions and increasing efficiency in low-voltage induction motors. However, low-voltage controls rarely enter the debate—which is an injustice. Low-voltage controls can increase energy efficiency in three primary ways:

  • Enabling the acquisition of measured energy values
  • Helping reduce intrinsic power losses
  • Providing an optimum drive solution

For machine manufacturers or operators, each of these provides considerable improvement in energy performance figures and leads to the commercial benefits associated with a positive energy balance and better eco credentials.

Acquiring Measured Energy Values

The first of the key steps toward increasing energy efficiency involves acquiring values relating to power flows. Energy management systems cannot perform satisfactorily unless the machines and plants associated with them are analyzed in detail. However, installing additional measuring instruments is not necessary if, during the planning stage, a simple automation system with an integrated current measuring facility and communication interface—such as motor starters with distributed peripheral systems—is incorporated. This simple automation system can transfer the most recent current value to the higher level controller via the communication bus system or an Ethernet automation system.

With a high quality motor protection and control device or a soft starter, it is also possible to acquire and transfer additional measured values—such as voltage and power values. Like the high-feature motor starter, the motor starter with a degree of protection IP65 provides current values in the standard format of the energy profile. This makes integration into energy management systems even simpler.

Soft starters are a cost-effective alternative to using direct or wye-delta starters for starting three-phase motors, and a soft start in control cabinets can be implemented in almost any application.

The measured values of the actuators—which also serve as sensors in this case—can be dragged and dropped into the visualization system for the energy data. The option of evaluating and analyzing measured current values allows energy management systems to assess the situation and shut down individual loads or load groups, if necessary. End users can easily monitor the quarter-hour values that are often used by power supply companies for billing purposes, which can enable them to keep costs as low as possible.

Reducing Power Losses

Each device installed in a control cabinet produces power losses to a greater or lesser extent. For example, devices with integrated power electronics (soft starters) are burdened with higher power losses than power contactors because of their system configuration. Power losses for VFDs are even more significant.

Heat is a sign of these losses. In some applications, installing high-maintenance fans is required. Others use air conditioning equipment that consumes additional energy. The aim should be to create a drive solution that is straightforward.

If a soft starter solution is the answer, however, then using a modern series will make it considerably more economical, because these feature bypass contacts which jumper the power semi-conductors after the run-up stage and keep the resulting heat losses to a minimum. These soft starters can reduce power loss by 90 percent.

Many think that if contactors are used in an application, they can do nothing else to produce savings. Contactors demonstrate exceptionally low power losses compared to soft starters or even VFDs because the heat losses generated by the electromechanical contacts are low.

However, the potential for savings can still be found with the control circuit. In fact, it may be possible to reduce the pull-in current and holding current in conventional AC and DC coils by up to 92 percent by using control electronics, which also offer other benefits:

To start and protect a motor and other loads, a motor starter can handle both drive and automation tasks without a cabinet.
  • Smaller power supply units needed in the control circuit because of significantly reduced pull-in currents and holding currents
  • The option of control with DC voltage or AC voltage
  • Wide voltage ranges, enabling less stock keeping
  • Control using cost-effective 0.5-amp outputs of the controller
  • Integrated protective circuit for preventing overvoltage damage in control electronics

An automation technology company introduced a dedicated range of contactors featuring universal current (UC) coils. These supplement conventional contactors and can be used with the lower power range of up to 25 horsepower.

Since the breakthrough of IEC-compliant fuseless motor starters, most applications in this area include circuit breakers or motor circuit breakers designed for the protection of plants, lines and motors. High pricing pressure on the market restricts these systems to using conventional electromechanical structures. These involve bimetal strips that provide protection against overload but have the drawback of heat losses.