Low-Voltage Controls Contribute to Optimum Operations

Improve performance in machines and plants.

Written by:
Brian Libby, Siemens Industry, Inc.
August 29, 2013

The setting ranges in the company’s motor starter protectors overlap and there is, therefore, a simple tip for saving energy. If users require a circuit breaker for a 15-amp motor, for example, they can use a version with a setting range of either 11 to 16 amps or 14 to 20 amps. Using the larger version and the low overload protection setting that comes with it could reduce intrinsic energy losses by up to an additional 40 percent.

Although fuseless motor starters are becoming more widely used, good reasons still exist to choose overload relays, including:

  • Differentiation of the signals for overload and short circuit
  • In combination with fuses, extremely high short circuit breaking capacity in high-rated operating voltage ranges

Additional benefits of choosing electronic overload relays instead of their widely used thermal counterparts include:

  • Wide setting range for the rated operational current of up to 1:10
  • Adjustable trip classes—also suitable for heavy starting
  • Remote reset following an overload trip

Regarding energy efficiency, these devices offer exceptional power loss reductions of up to 98 percent. The reason for this improved performance is that the overload relay does not include a bimetallic trip. With compact structures, reduction in intrinsic heat buildup allows for a much simpler air conditioning setup in the control cabinet.

This specific compact starter represents a new class of energy-efficient motor control. It is a compact combination of a circuit breaker, contactor and solid-state overload relay in a single enclosure. By combining these benefits in a single device, intrinsic power loss savings of up to 80 percent can be achieved compared to conventional motor starters.

Consistent use of energy-efficient motor controls switchgear allows significant reductions in the intrinsic losses of the devices and means that fewer heat dissipation measures are required in the control cabinet. This benefits both energy costs and plant availability.

A drive will offer a high level of integrated safety, energy savings and network connectivity.

Optimum Drive Solution

Three-phase, asynchronous motors are the brawn of a machine and can be operated in different ways. While VFDs are best suited for closed-loop speed control, soft starters specialize in regulating current and torque during startup and runout. In combination with contactor-based motor starters and load feeders, soft starters are cost-optimized for long operating periods at the rated speed of the motors.

In these applications, it is also a good idea to use NEMA Premium Efficiency motors that offer a particularly low level of current consumption during operation and, therefore, bring additional benefits in terms of the energy balance. In this configuration, the products are compliant with the second stage of the European Directive relating to ecodesign (EuP/ErP Lot 11), due to come into force in 2015.

Because more functions mean more power losses in devices, selecting a drive solution with the simplest possible design can lead to savings. This involves optimum sizing for the motor power to prevent the introduction of high losses caused by oversized motors. Adapting an oversized motor to lower requirements retrospectively by using a VFD may not be the right approach.

It also involves choosing simple methods of regulation—the golden rule that the motor that consumes the least amount of energy is one that is not running. With pumps, fans or compressors, combining a cascade VFD and controls (a process often referred to as staging) is a good way to exploit additional potential for savings. While a VFD satisfies the requirements of the variable element of the application, the motor control covers the plant’s basic load requirements. This allows for the best operation of both drive systems—that is, an exceptionally user-friendly control concept on one hand and low intrinsic energy losses with the same high level of efficiency on the other.


Cahaba Media Group

See also:

Upstream Pumping

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