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Motor_Qual_brochure 1/5/02 4:43 pm Page 1 Motor Quality Guide your questions answered Motor_Qual_brochure 1/5/02 4:44 pm Page 2 Introduction ● Reliability is by far the most important aspect of a motor The only time the motor is really noticed is when it fails. Unplanned downtime can cost as much as a new motor every five minutes, rapidly adding to the life cycle cost. ● The support and know-how of the manufacturer can be as important as the product quality For a healthy bottom line, it is important to select quality motors that won’t let you down, from a manufacturer with an adequate support infrastructure. ● Purchase price is insignificant when compared to the overall life cycle cost The AC motor is the workhorse of industry. It is a fit-and-forget item, expected to last for many years. Its life cycle cost is mainly made up by the electricity it consumes - for every £1 you spend buying the motor, you will typically spend £100 running it over a 10-year life cycle. There is more to motors than meets the eye 2 Motor_Qual_brochure 1/5/02 4:44 pm Page 3 What do you need from a manufacturer? There are three major aspects to quality - materials, systems and people information when you need it. After sales support and service systems should also be available 24/365 for a fast and efficient service. Quality materials The life expectancy of a motor can exceed 20 years, which is why the use of quality materials is of paramount importance. The motor is the prime mover and the reliability of the plant will depend on the quality of the motor. However there is more to motors than meets the eye. For this reason, care should be taken when selecting a motor supplier. A quality motor, correctly selected and dimensioned, will provide many years of trouble free performance. Making the right choice How you can recognise a quality motor is something we aim to explain over the next 10 pages, enabling you to make an informed choice. Making the wrong choice can result in lower motor life expectancy, higher running costs and increased downtime. Remember that quality normally comes at a price. While making the right choice may result in a one-off cost increase when purchasing, making the wrong choice could result in ongoing operational cost increases for the life of the motor. Quality people Motors are utilised in hundreds of applications under a variety of conditions and appropriate advice is essential to select the right motor for the job. A good manufacturer will have wide industry experience and will be able to give adequate advice for the particular conditions and demands of your industry sector. You should also expect knowledgeable advice on issues such as starting methods, variable speed drive considerations such as bearing currents and harmonics, as well as the wider issues affecting the correct selection of motors. The manufacturer you use needs to have a full range of motors to cover all your applications Quality systems Fast and efficient access to information and support is essential for any business. Online documentation, ordering and delivery tracking systems should be available 24 hours a day, 365 days a year, to provide 3 Motor_Qual_brochure 1/5/02 4:45 pm Page 4 Quality means reliability Motors should never fail. Unfortunately, they do, some more than others A motor is only as good as its constituent parts. Here, it really is a case of getting what you pay for. About 55% of the price of a motor goes towards materials, while 15% is used for labour and another 30% for other costs, e.g. R&D, logistics and general overheads. This chapter outlines what makes a good motor, and what to look out for when buying motors. Reliability - why should I care? If you need a motor for a water pump that runs once a year on a non-critical application, reliability will not be a big issue. Providing the motor is right for the application, the running hours will never mount up and the materials will almost certainly last regardless of quality. But if you are responsible for the 24/365 operation of a paper machine, or a processing plant, with a downtime cost of £10,000 per hour, you will appreciate the importance of reliability. And if you are selecting motors as an OEM, you will be putting your company’s reputation at risk Of the motor’s key components, the bearings and the winding are the ones most exposed to wear by selecting a low quality motor. It will be your company that gets the blame, not the motor manufacturer, when the product fails. As much as 55% of the motor’s price goes towards materials, while 15% goes to direct labour and 30% towards R&D, logistics and general overheads. For this reason it is difficult to cut costs substantially without affecting performance 4 Motor_Qual_brochure 1/5/02 4:45 pm Page 5 Product quality First of all, the quality of the product is secondary to the quality of the advice you receive when selecting your motors. The world’s finest materials will not help if the motor is wrong for the job. Make sure that your motor manufacturer has experienced engineers who are available to help you with selection. Bearings Check: Regardless of the type of bearing, it needs to be adequately greased. The quality, frequency and amount are all critical factors; excessive greasing reduces bearing life just as insufficient greasing does What is the quality of the bearing? Do you know the bearing manufacturer? Is bearing life defined to L1 or L10? Does the motor have a grease outlet? with the original grease. Special grease is available for operation in hot or cold ambient temperatures. Your motor manufacturer should be able to provide specific advice on lubrication. Over-greasing can have just as disastrous consequences as insufficient greasing, particularly in fast running applications. When too much grease is added, the bearing elements do not have enough room for heat expansion, which causes friction and overheating. Some motors have a grease relief valve to avoid this happening. Bearings should come from a reputable manufacturer. ABB uses bearings from, for example, SKF, NTN, and NSK. Along with a small number of other companies, these are among the world’s premier bearing manufacturers. L1 and L10 are the most common measures for bearing life (reliability) used by bearing manufacturers. L10 means that 90% of bearings achieve or exceed the calculated bearing lifetime; L1 means that 99% of bearings achieve or exceed the calculated bearing lifetime. The improved reliability is achieved by more frequent re-greasing intervals. Actions: Ask your motor supplier to recommend: Bearings dimensioned for the appropriate load Internal bearing clearance suitable for the temperature Grease suitable for the temperature Choose re-greasable or sealed-for-life bearings as appropriate The most common cause of motor failure is bearing problems. The life of the bearing depends on many different factors, the main one being the quality of the bearing. It also depends on selecting the right type of bearing for the application and load in question, and correct greasing for the application. Bearings can be either re-greasable or sealed for life. The re-greasable bearing will give a longer service life, providing that the end-user has a suitable maintenance infrastructure. If not, sealedfor-life bearings are preferable. These are also required in for instance dusty environments. The bearings should only be re-lubricated with grease compatible 5 Motor_Qual_brochure 1/5/02 4:46 pm Page 6 Product quality (continued) Winding Check: Winding insulation - Class F is better than Class B Withstand voltage above 1400 V is beneficial for variable speed drive operation Good slot fill Poor slot fill A good slot fill is one of the characteristics of a good winding Actions: Deg. C Choose high efficiency for a lower winding temperature; this gives long winding life as well as low running costs 155 130 The second most common cause of failure is the winding. At the end of a long service life, the insulation system, including varnish, that insulates the copper wire in the windings will start to break down and a short circuit may occur. If this happens, a high quality motor can in many cases be rewound without too great a reduction in efficiency. The materials and constructions used will allow the removal of the old winding and rewinding and impregnation of the motor. A low quality motor can also be rewound but typically with much greater losses in efficiency, due to lower quality electrical steel used in the stator laminations. Years Winding lifetime A lower internal temperature extends the life of the motor The windings can be insulated to different standards; Class F (155°) and Class B (130°) are the most common. Most motors are manufactured with Class F insulation material but designed to run no hotter than with Class B temperature rise. The cooler the motor runs, the longer the insulation system will last and the longer the motor will operate. Efficiency - the other side of temperature rise A low running temperature means the motor requires less cooling, enabling the use of a smaller fan. This results in low heat losses and high efficiency. High efficiency means lower energy costs, giving lower operational costs. Low temperature rise comes from using high quality materials and production methods and comes at a price. However, the additional cost for using a high efficiency motor is often repaid in reduced energy costs in less than a year. Take the following example: Purchase cost, 90kW high efficiency motor (95%) £5,532 Purchase cost, 90kW average efficiency motor (92%) £4,273 Difference in purchase price £1,259 Daily running cost, 95% efficiency £131 Daily running cost, 92% efficiency £138 Saving, per day £7 Payback time 6 months 6 Motor_Qual_brochure 1/5/02 4:46 pm Page 7 Product quality (continued) • Random winding pattern • High quality slot insulation, impregnation systems and phase insulation systems The integrity of the winding is measured in withstand voltage and is usually in the region of 1200 V. Motors with withstand voltage of 1400 V and above are available and offer increased reliability. This is especially important to help withstand the voltage spikes produced by some variable speed drives. The normal running temperature in high quality motors running at full load can be as low as 60-80° C, while lower quality motors can run in excess of 90° C. Although this still meets the criteria of Class B temperature rise, it could run considerably hotter than a quality motor of the same size. Theoretically, a reduction of 10-15° should double the life of the winding, as well as the re-greasing intervals. The life of the winding also depends to a large extent on the production techniques used in the manufacturing process. A compact winding with a good slot fill, i.e. high density of copper, gives the best performance. Automated winding equipment, as used on smaller size motors, gives a higher density slot fill than hand winding and gives a repeatable quality time after time. The characteristics of a good winding are: • Small overhang • High quality grade of copper wire • Good slot fill ratio. The more copper wire in the slot, the better the metalto-metal transfer of heat, and the cooler the running temperature of the motor. Stator electrical steel The stator is made up of laminations, thin slices of low loss steel with an insulated coating. These should be uniform and as thin as possible to maximize the strength of the magnetic fields in the stator. They must be perfectly aligned to give straight channels for the slot fills. The stack of laminations should be rotated periodically to compensate for the effect the grain in the metal has on the magnetic field. C 180 15 155 130 10 Hotspot temperature margin 10 Permissible temperature rise 80 105 125 Maximum ambient temperature 40 40 40 B 130 F 155 H 180 120 40 Insulation class Maximum winding temperature The stator is made up by laminations of low loss steel with an insulated coating A higher insulation class gives better protection against high temperatures and extends motor life 7 Motor_Qual_brochure 1/5/02 4:46 pm Page 8 Product quality (continued) normal operation, as this can cause moisture to build up inside the motor and affect reliability. Your motor supplier should be able to advise on whether IP65 is appropriate. Frame Check: Examine casting for blowholes and imperfections upon delivery, reject if unsatisfactory. Cast iron motors should be made of suitable standard cast iron, e.g. ENGJL-200/GG 20/GRS 200 Aluminium motors should be made of low copper content aluminium (max 0.3%) Noise - an invisible pollutant Most responsible employers aim to reduce the noise in their workshops. For example, the recommendations issued by the UK’s Health and Safety Executive set a maximum value of 85dbA 1 metre from the motor. Limits are continually moving downward and your supplier should be able to advice on the most recent regulations. The noise levels should be printed in motor catalogues. It is worth noting that an increase in the noise by 3db is perceived as a doubling of the noise. A difference in noise levels between two motors of, say, 3db is therefore significant. Actions: Ask your supplier for advise on the correct frame material for your application Noise level db(A) The casting should be smooth and free from blowholes. Apart from being unsightly, blowholes trap air, which hinders the transfer of heat. They can also reduce the strength of the material, leading to weak points and potential fracture. 100 Total noise Fan noise Bearing noise 90 Magnetic noise 80 70 60 50 40 0.2 0.5 1 2 5 10 20 50 100 200 500 1000 2000 Power, kW Enclosure The standard enclosure for motors is IP54. This protects against water splashing. Some motor manufacturers use IP 55 as standard. This additionally protects against water jets. Many users specify IP65 motors. This means the enclosure is dust tight. While this is appropriate in some applications, it is unnecessarily air tight for Components that raise noise level Low noise motors can make a significant impact on overall noise levels Aluminium motors should use low copper content aluminium to minimise corrosion. Modern alloys contain as little as 0.2-0.3% copper; a lesser quality alloy can contain as much as 2.5%, typically corroding at ten times the rate. Cast iron motors should be made of high-grade cast iron. Painting Actions: Ask your supplier for a paint specification appropriate for your application The motor needs to be painted according to appropriate specifications. Process industry and offshore, for instance, needs The casting should be smooth and free from blowholes 8 Motor_Qual_brochure 1/5/02 4:46 pm Page 9 Product quality (continued) a higher specification paint. A suitable cover for aluminium motors in general industrial application would be a twopack polyurethane acrylic varnish, while for cast iron motors, a two-pack epoxy primer followed by two-pack epoxy topcoat is recommended. Terminal box Check: Ensure that the terminal box is large enough to enable rapid installation with the type a cable used in your application If you have ever fitted a motor under time pressure, for instance while standstill costs were mounting up, then you will appreciate the importance of the design of the terminal box. The terminal box should be large enough to accommodate the bends of heavy gauge cables and have cable entry from two or four sides. Shaft Check: Can your supplier offer a range of shaft materials for different applications? The shaft material is selected according to application. Normally, the shaft is a hot rolled steel bar turned to the correct dimensions. Stainless steel shafts are available for use offshore or in chemical plants. If strong radial forces are expected, high tensile shaft material is available. Your selected manufacturer should be able to give advice on permissible loadings on the shaft and suitable shaft materials. Fan Check: A generously sized terminal box helps installation and is particularly useful when time is at a premium. Are original fans available as spare parts? Can the fan be re-fitted once removed? Some motors also come with a gland plate which can be easily moved from one motor to another, making re-glanding of cables a thing of the past. In addition, a spacious terminal box offers better protection against short circuit. The fan must be large enough to produce adequate cooling, but too large a fan reduces efficiency and increases noise. To achieve the optimum balance, ABB varies the blade size and pitch between models. For this reason, a broken fan cannot be replaced with any standard fan. The appropriate fan for the model should be obtained; using a standard fan can increase fan losses by as much as 20%. Check how the fan is fitted - it will need to come off when the bearings are replaced. A fan fitted to the shaft using a keyway and grub screw can be removed and re-fitted many times. Accessories Check: Availability of accessories and ease of fitting Some motors are easier to modify than others. You may want to add for example monitoring or protection devices, check how easily this can be achieved. 9 Motor_Qual_brochure 1/5/02 4:47 pm Page 10 Support and backup Having quality support and backup is as important as having a quality product. The help of an engineer can be invaluable when specifying the motor, as this can prevent problems later on. The engineer is part of a team and should be supported by other engineers in-house, who in turn should be supported by the R&D department at the factory. Only this way can you be sure you have the backup you need for all eventualities. Ensure that your supplier has backup of manpower as well as products in stock Issues affecting motor selection Check: up to 400 kW are stocked at ABB’s central stock locations in Europe and can be delivered within 24 hours. Does your motor supplier know about the wider issues affecting your industry? Your supplier should be able to advise you on all the wider issues that affect motor selection, such as the Climate Change Levy and Enhanced Capital Allowances; health and safety issues, such as noise; the ATEX directive for explosion proof motors; ISO 14001, the standard for environmental management systems; the WEEE directive, relating to the recycling of waste electrical products; WIMES, the water industry’s mechanical and electrical specification; and for exporting OEMs, EPCA, the motor efficiency norms in North America. Production lead times Check: Are modifications and custom builds available? It is not always that stock motors are appropriate for the application. Sometimes, modifications or custom builds may be necessary. It is important that your chosen manufacturer can deliver these within a reasonable time frame. Some examples of ABB’s lead times: • Fitting heaters or thermistors - four days delivered • Custom builds - normally six to eight weeks delivered Stock availability Check: Is a wide range of motors available with short delivery times? On-line services Your chosen supplier should have a wide range of motors, available in quantity at short notice. All of ABB’s national distributors stock motors up to 37 kW for local availability. Some of them stock sizes as large as 132 kW; these can be delivered nationwide overnight. Motors 10 Check: Is your supplier e-commerce enabled? Some manufacturers enable you to deal with them online, helping you reduce administrative costs. If you do business online, make sure your motor supplier does, too. Motor_Qual_brochure 1/5/02 4:47 pm Page 11 Support and backup • Data sheets • Type tests • Certificate of conformity • CE certification • Machine certificate • Speed/torque curves • Flameproof certificate • Noise curves • Drawings, general arrangement • Type test The supplier should also be able to handle your custom documentation and produce dedicated speed/torque curves for your application. Your supplier shouldn’t just ship motors; he should also be a reliable source of information for all your application needs After sales services Warranty Check: Check: Does your supplier have a reasonable structure for after sales support? Does your supplier have a clear structure for handling claims? After sales service may seem a long way away while the motor has yet to be specified, however sooner or later the need will arise, and you should make sure your chosen supplier has an adequate support infrastructure. Complicated warranty procedures are not unheard of in the motor industry. Ensure that your supplier has knowledgeable field staff that can help with your warranty claims, as well as a clear internal structure for handling warranty claims professionally. ABB’s warranty claim procedure is outlined on the internet at www.abbmsp.com Documentation Check: Is the right documentation available? If a service agent is used, it is the manufacturer’s responsibility to ensure that standards are maintained. Your supplier should be able to provide documentation within a reasonable timeframe, such as: To handle all aspects of customer service, your supplier needs a team structure, which can look something like this: Technical support Logistics After sales Application knowledge Order handling Warranty cases Dimensioning Progress reporting 24/7 support Comments on specifications Documentation packages Repair/modification Design capability Proof of delivery Service Local representation Stock profile 11 ABB Automation Ltd 9 The Towers Wilmslow Road Didsbury Manchester M20 2AB United Kingdom Tel: +44 (0) 161 445 5555 Fax: +44 (0) 161 448 1016 www.abb.co.uk MOTBRO-03/2002 Motor_Qual_brochure 1/5/02 4:43 pm Page 12