When it comes to procurement of High Voltage (HV) motors, few end users ever think about the bigger picture – total cost of ownership. In fact, many still don’t understand what it costs to operate this type of equipment. While the spotlight is largely cast on the upfront capital cost, the fact of the matter is that purchase price is a very small factor in the overall cost of HV motor ownership. By Munesu Shoko.
In a world where the sticker price is a key influencer in many procurement decisions, David Spohr, business development executive at Zest WEG Group, reasons that it is completely a different scenario when it comes to HV motors. According to Spohr, total cost of ownership (TCO) should be the principal consideration, and two key factors – efficiency and maintenance costs – are crucial parameters in the TCO equation.
To help operators of HV motors in Africa run efficiently and profitably, Zest WEG Group has established a dedicated HV equipment division which specifically looks after its HV motors, medium voltage variable speed drives (VSDs) and power transformers. The division has been operational for the past four months and is led by Spohr, who has a wealth of experience in this market sector.
In Africa, HV in motors is considered to be 3,3 kV; 6,6 kV and 11 kV. Globally, they get to a maximum of 13,8 kV, which is uncommon in Africa. WEG’s HV motors are typically purpose-engineered motors that are used in manufacturing facilities, beneficiation plants, mines and quarries. “Very few of the end users of this equipment think about TCO and probably even fewer actually understand what it costs to operate HV motors,” reasons Spohr.
Efficiency matters
According to Spohr, efficiency is a big factor in achieving lower TCO in motors. Firstly, it is important to understand what efficiency is. Motor efficiency is the ratio between power output, which is mechanical, and power input, which is electrical. You will never find a motor that operates at 100% efficiency because losses exist in all motors due to friction, heat generation and materials, to name a few factors.
When it comes to the efficiency benchmark, Spohr says there is no specific benchmark in large HV motors because they fall out of SABS standards – they are usually purpose-built, application-engineered motors. However, WEG’s machines are designed to the highest efficiency standards, which range from 90-96%.
Spohr says HV motors are capital intensive pieces of equipment. They may cost anywhere between R2-million and R25-million. Because of the high capital cost, some operators of this gear tend to run their motors well beyond their design lifetime. Meanwhile, when it is replacement time, there is always a big focus on the capital cost at the expense of efficiency, which is a key factor in overall cost of ownership.
When it comes to running old technology motors, Spohr reasons that it is always important to remember that every motor is designed with a specific economical lifetime. He reasons that today’s engineering is a lot more precise and motors are designed for 25-30 year operation with guaranteed efficiency within that period of time. “Due to the perceived large capital cost of these machines, some end users tend to run their HV motors for a much longer period than what they were designed for. Some of them even exceed by an additional 10-15 years,” he says.
According to Spohr, if one looks at a five to 10-year running cycle of a low voltage motor, for example, the capital cost of the machine equates to only 2% of the total cost of ownership during that time. This is because of the high energy consumption costs; motors by their very nature consume a lot of electricity, and for that reason, efficiency is a key priority.
“For example, in low voltage motors, within a five-week period, the actual running cost – what the end user has paid in electricity consumption to run the motor – will come close or exceed the initial capital cost of a new motor,” says Spohr, adding that this may be slightly different when it comes to high voltage motors because the capital cost is significantly higher.
“For instance, the capital cost of a 110 kW motor is about R66 000, and within five weeks, the motor would have consumed R71 000 worth of electricity. Over a five-year period, the end user would have paid about R4,1-million in electricity consumption costs. That scenario best explains why efficiency matters when it comes to motors,” says Spohr.
When it is procurement time, Spohr reiterates that the upfront capital cost of a motor should be no big factor. “It’s the cost of running the motor that really matters. The most common problem in Africa is that many people tasked with procurement duties do not understand this concept. They will buy a motor that is 2% cheaper, but not considering the efficiency, which has a direct impact on the total cost of ownership, which in turn is the difference between profitability and stagnation,” adds Spohr.
Spohr’s views are corroborated by a paper entitled Policy Guidelines for Electric Motor Systems, which shows that only 2% of the total lifecycle cost of an electric motor is attributable to the initial purchase price, and some 97% represents the energy costs used to power the machine. Therefore, the efficiency of the motor, its reliability and its correct sizing for the application, are all critical factors in achieving maximum efficiency and minimising the costs of operation.
Maintenance costs
Another important factor when it comes to the operation of HV motors is maintenance costs. Spohr reasons that the operation of motors beyond their design lifetime means that end users keep on repairing their old machines at a much higher cost. Customers tend to keep repairing the old gear, finding comfort in the belief that maintenance is an operational expense. However, if one looks at the cost of repairing the motor repeatedly, say over three years, it may amount to the cost of buying a new, efficient motor.
Spohr says the cost of a major HV motor overhaul or repair, for example, is generally about 60% of the replacement value. “Customers tend to do continuous repairs on their old motors, but never consider the value of their maintenance and repair costs. There is also need to be aware of the replacement value of the motor, versus the cost of repairs,” says Spohr.
If a motor is burning out on a regular basis, it is a trigger point to make a replacement decision. “One needs to consider the actual amount of money they have already spent on repairs, which is normally quite substantial, as well as the money they have lost through downtime. When you get to a point where you constantly repair a motor, there is need to consider replacing it with a new motor, which effectively reduces risk and maintenance costs, while increasing efficiency.”
Modern way
Commenting on old generation motors, Spohr says many old pump and fan application motors are started in a very old-fashioned manner because technology wasn’t available or considered expensive at the time of installation. The required flow of air and liquid was controlled via mechanical ways – an old and inefficient way of doing it.
With the establishment of its HV equipment division, Zest WEG Group now offers WEG motor-VSD combinations. “We can walk into a factory and do an audit on a specific existing application. We can offer a new motor which fits on an old footprint, but we can also recommend that the customer considers the modern way of doing things – the motor-VSD combination. This is for applications where you need to control the speed of the motor or the flow of air or liquid required,” explains Spohr.
He reasons that there are tangible cost savings to be made with a matched WEG motor and VSD combination. Long-term reliability and efficiency of energy use are the result of a truly compatible motor and VSD combination. VSDs are said to be probably the best method for controlling motor speed in response to varying process demands.
VSDs take the fixed-frequency AC supply and convert it to a variable-frequency AC supply. This controls the power use and mechanical power output so that the motor can run at the most efficient speed for the process. The control of the motor speed can be based on feedback from the process, for example, flow rate, temperature or pressure, so that process control is improved.
As a result, small decreases in the speed of pumps and fans can lead to large decreases in energy consumption. According to ScienceDirect’s research paper, Energy Management Principles, using a VSD to reduce the speed of an AC motor by 20% could reduce the energy consumption by around 50%.
“The WEG motor-VSD combination significantly reduces annual running costs. When it is replacement time, don’t just replace the motor, but consider replacing it with an upgraded version of what is available on the market right now. At Zest WEG Group, we have new technologies available that can help end users save on their energy costs, and ultimately reduce their TCO,” concludes Spohr.
