FEATURE CABLING & CABLE MANAGEMENT


HOW TO STOP YOUR cable costs from spiralling


Steve Hughes, managing director of REO UK, explores how OEMs can find cost effective solutions to rising cabling costs


T


he need for lengthy shielded cable to tackle attenuation and


electromagnetic compatibility (EMC) issues has resulted in an increase in the cost of cables in manufacturing. This in turn has been compounded by increasing commodity prices, leading many original equipment manufacturers (OEMs) to look for cost effective solutions. The humble cable is a necessity in


modern society. The cable may be modern, but the word is certainly not. Originating in the age of sail, the term ‘cable length’ was given to the length of a ships anchor, which in time standardised to become the generally accepted length of a nautical mile.


THE NEED FOR CABLING Wireless connectivity such as Wi-Fi and induction charging have yet to replace the need for physical cabling in manufacturing industries throughout the world, and the demand for cable lengths in industrial environments can be high. Variable speed drives (VSDs) and long cable runs, over 50m between the VSD and the motor, are common, but can conspire to create further electrical interference. Three-phase induction motor control


has been greatly enhanced in recent years by the use of VSDs. The rotary speed of the induction motor can be easily manipulated by altering the frequency of the supply current. The result is a fixed voltage, variable frequency output. Although the benefit of the VSD is to lower cost by increasing efficiency, the process has some drawbacks. Pulse width modulation (PWM), the process used to switch the VSD inverter (typically between 8-16kHz), produces a series of output pulses that average to a


34 APRIL 2014 | ELECTRICAL ENGINEERING


sine wave. The power conversion process creates unwanted frequency components such as harmonic currents which, in substantive quantities, can lead to electromagnetic interference (EMI). The degradation caused by EMI can be


significant and varied, wearing down the ability of components to operate at optimal performance and potentially even lead to machine failure. The damage ranges from overheating transformers, windings and capacitors, to interference affecting telecommunication equipment and metering apparatus. As well as this, excessive currents in the neutral cable of a 3-phase system and high voltage fluctuations, known as electrical flicker, can affect the supply for domestic users on public low voltage networks or OEMs on industrial networks. Continuous and problematic levels of EMI


can constitute electromagnetic compatibility (EMC) issues, rendering some equipment unsafe to use. Standards set at European level, dictate the minimum requirements for safe usage of VSDs in power drive systems (PDS). IEC/EN 61800- 3 directives apply to manufacturers, panel builders and systems integrators. The purpose of these directives is to


minimise harmonics, demand the assessment of all connected equipment prior to use, and provide sufficient technical documentation for all users. Further practical requirements aim to


improve conduction and reduce radiation- based emissions - as well as reduce the high voltage differences (dv/dt) generated from the high frequency switching of insulated gate bipolar transistors (IGBT). Consequently, minimum requirements have been set for cabinet grounding and terminal quality using shielded cable.


BEST PRACTICE Many manufacturers have gone one step further and sought to replace entirely or upgrade a significant portion of their cabling to shielded cable. It is no coincidence then that this higher demand for copper has raised the commodity pricing in international markets which, until six months ago, was falling. To provide a robust, but cost effective


Above: Steve Hughes, managing director of REO UK


solution, REO has developed a special filter to overcome interference problems, which are inevitably exacerbated by the use of long cable runs. The 400V three line CNW933 sinusoidal filter range is available in units rated from 2-1200A. The CNW933 eliminates the need for


shielded cable by suppressing unwanted frequencies. This is achieved by an efficient use of various inductance and capacitance solutions, which eradicate harmonic currents, smoothing the peak waveform created by PWM and producing a near sine wave supply. Motor life is increased whilst noise, mechanical stress and thermal conduction are alleviated. The cost savings of using standard


cable can be considerable. In a typical drive installation using a 4kW drive at a distance of 200m from the motor, cable savings alone can be around £100. This means that almost three times as many installations could be cabled using standard cable, as opposed to shielded. In a world becoming increasingly


intangible, it seems that cabling is yet to be swayed. Despite the regulatory complexity and financial pressure under which manufacturers operate, it is evident that there are still cost effective measures that can yield longer term return on investment.


REO UK www.reo.co.uk T: 01588 673 411


Enter 221 / ELECTRICALENGINEERING


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