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Motors and drives, purchase cost versus lifetime cost by Steve Brambley of GAMBICA

Imagine that you are scouting the market for a shiny new car. You would probably look at getting good value for money, the newest fuel technology and an attractive design. By comparison, when purchasing an industrial motor, it seems to be completely the opposite situation. Steve Brambley, deputy director at GAMBICA draws the parallel.

The car manufacturing industry has shifted most of it efforts towards producing energy efficient vehicles, be they electric, hybrid or fossil fuel powered. The biggest investment for the lifetime of the average car is the purchasing cost. After that, the fuel consumption would be relatively small, amounting to roughly 79% of the purchasing cost over a decade.

By contrast, industrial motors might only set you back a few hundred pounds to purchase, but their greatest expenditure comes from running costs. A motor which only cost £600 to buy will eat up over £20,000 in energy bills over a ten year period – that’s a whopping 2700% of its acquisition price!

So if fuel consumption is one of the main concerns for our cars, why do we not apply the same logic when it comes to running motors? Many industrial manufacturers settle for paying eye-watering electricity bills, unaware that they have other options.

The first thing to consider when looking for a motor system for your industrial application is low energy consumption. Having a holistic view of your system and the load it is supposed to drive enables accurate specification. Finding the correct size of motor and then looking for the most energy efficient model in its category is essential pre-purchasing research.

It is also important to keep in mind that the price tag for industrial motors is not the most important part in your decision. Choosing a cheaper one and jubilating over a £200 saving is a false economy. What you save by not investing in energy efficient systems is lost several times over in subsequent energy costs.

Option 1: Installing a variable speed drive
With 21% of all UK electricity consumption attributed to running industrial motors, manufacturers need to act fast and make wiser decisions. But what is to be done if a company has inherited a system running an electricity-hungry motor?

In such situations, one of the best ways to make an application more energy efficient is by controlling the motor speed. Where applicable, installing a variable speed drive (VSD) is considered to be the best form of controlling energy consumption, often resulting in efficiency improvements of 30% or more.

To further educate users about the energy saving solutions available, GAMBICA has published a guide on the ‘Selection of Efficient Motors & Controls’, available as a free download from the GAMBICA Website.

This guide assists in the selection of the best motor and control technology, addressing the differences between motor efficiency ratings, the considerations and benefits of different control methods, and the issues that affect the decision-making process for fixed or variable speed controls. The free paper is aimed at senior managers and decision makers looking to reduce energy costs in an organisation. As such it is a concise, non-technical publication with a focus on the life-cycle costs of a motor driven system.

Option 2: Using fixed speed control
Another option available where speed control is not applicable is fixed speed control, such as a softstart or contactor. Here the energy saving comes from switching the motor off when it is not required, using automation to ensure maximum system efficiency. Relying on manual control usually results in the motor being left on too often, where using sensors and logic controllers for example can switch the motor off every opportunity available.

A softstart is used mainly with AC electric motors to temporarily reduce the load and torque in the powertrain and electrical current surge of the motor during startup. This reduces the mechanical stress on the motor and shaft, as well as the electrodynamic stresses on the attached power cables and electrical distribution network, thereby extending the lifespan of the system.

Electrical soft starters can use solid state devices to control the current flow and therefore the voltage applied to the motor. They can be set up to the requirements of the individual application.

In pump applications, a softstart can avoid pressure surges. Conveyor belt systems can be smoothly started, avoiding jerk and stress on drive components. Fans or other systems with belt drives can be started slowly to avoid belt slippage. In all systems, a softstart limits the inrush current and improves stability of the power supply and reduces transient voltage drops that may affect other loads.

In its simplest form, a contactor is an electrically controlled switch for switching a power circuit, similar to a relay but with a higher current rating.

Contactors come in many forms with varying capacities and features. Unlike a circuit breaker, a contactor is not intended to interrupt a short circuit current. Contactors are used to control electric motors, lighting, heating, capacitor banks, thermal evaporators, and other electrical loads.

Furthermore, an ‘economizer’ circuit can also be installed to reduce the power required to keep a contactor closed; an auxiliary contact reduces coil current after the contactor closes.

A somewhat greater amount of power is initially required to close a contactor than that required to keep it closed. Such a circuit can save a substantial amount of power and allow the energised coil to run cooler. Economizer circuits are nearly always applied on direct-current contactor coils and on large alternating current contactor coils.

Most motor control contactors that operate at low voltage up to 600V are air break contactors; air at atmospheric pressure surrounds the contacts and extinguishes the arc when interrupting the circuit.

Modern medium-voltage motor controllers use vacuum contactors. High voltage contactors above 1kV may use vacuum or an inert gas around the contacts.

The lesson to take home here is that if buying a car is about the purchase cost, buying a motor should be about how much energy it uses throughout its life. But unlike a car which cannot easily be made more efficient after you buy it, electric motors can be retrofitted and their consumption can be controlled with a VSD, softstart or contactor.

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