Schulz Group Medium Voltage Motor Repair Capabilities
An engineering manager who works at Smith Services, one of the sister brands that work with us and are a part of Timken Power Systems, answers some questions regarding medium voltage industrial motors and motor repair.
Q: Can you describe your role as engineering manager at Smith Services? What are your qualifications for the position?
A: I oversee daily electrical and mechanical engineering activities at Smith Services, and I have a dual degree in electrical and mechanical engineering.
Q: What distinguishes Smith Services from other repair companies in the industry?
A: EASA (Electrical Apparatus Service Association) is a primary resource for providing specifications and standards for electric motor repair or electrical mechanical equipment, and their website lists over 1,000 service centers in the United States. Even though there are a lot of competitive repair shops in the country, most motor repair services work locally, and most shops are small. Smith Services is highly active in the EASA community, and, as the largest electric motor repair shop in the eastern-half of the United States, our size enables us to repair a wider range of motors, and offer a wider range of repair services.
Q: What are some details regarding medium voltage motors?
A: Medium voltage motors are classified through voltage ratings. Many have a typical voltage rating of 2,300 volts, ranging between 1,000 volts and 13,800 volts. Common industrial voltages, like 240 volt or 480 volt motors, are usually used for sub-hundred horsepower applications. Unfortunately, lower voltage ratings become cost prohibitive to operate for larger horsepower equipment. With additional insulation protection, switching to higher voltage systems makes it possible to achieve exponential gains in efficiency.
Q: What applications use medium voltage motors?
A: Medium voltage motors are typically applied to industrial operations that range from 200-300 HP, up to 700 HP. Sub-600 voltage equipment is evenly distributed for low voltage equipment and equipment that runs on more than 1,000 volts. When more horsepower is needed, most motor applications employ medium voltage motors or larger. Because of their greater efficiency and long term savings in operational costs, medium voltage motors are often used for mission-critical applications.
Q: What criteria are used for selecting a motor?
A: The key criteria to use for selecting a motor are the specific application requirements, so the application type and its associated operational details will determine the choice. Pumps and fans have specialized requirements, and thermal control is a key factor in motor design for compressors, because they are usually highly stressed components. Special mechanical engineering is also required for belt drive applications because they experience a significant amount of radial loading. Specialized equipment like centrifuges also have detailed design requirements that affect the motor selection, so, the selection process requires considerable expertise.
Q: What industries typically use medium voltage motors for day-to-day operations?
A: Medium voltage applications are widely used in every major industry, including petrochemical, pulp and paper, metals manufacturing, and power generation. In the past, industries depended on their location. For example, fifty years ago, pulp and paper mills were built in areas that were centrally located near water sources, taking less consideration to the power infrastructure. Now, new plants will select a location that allows them to take optimum advantage of the power grid for medium voltage applications.
Q: Can most motor repair facilities provide services for medium voltage motors?
A: Smith Services’ ability to service medium voltage motors separates the company from about half of its competition, and since most repair services are highly localized, the number of competitive repair shops that can handle medium voltage motors falls even lower. And then there are repair companies who focus on high voltage equipment, higher than 13,800 volts. These are also much less common. Smith Services can troubleshoot breaker systems, transformers, and highly trained staff carries out all of the necessary electrical tests in the field. Repair services are available on-site or in a highly equipped, OSHA certified machine shop.
For equipment that is not cost feasible to transport, specialized onsite large motor repair can provide valuable repair services. For medium voltage equipment, a full array of large motor repair or large generator repair services can be done in-house. Although Smith Services keeps focused on electrical motor repair services, such as servicing the driver, switchgear, and repairing the transformer, through our association with the Timken Power Systems’ network, we can provide our customers access to the large motor facilities in the network, and an expanded scope of capabilities. With this network in place, Smith Services can repair medium voltage motors and equipment for nearly three-quarters of the eastern United States within eight hours.
Q: What are the details regarding Smith Services’ load testing and spin test capabilities?
A: In order to carry out validation testing for medium voltage motors, a facility needs ready access to available power sources and apply them to that particular motor. Access to properly calibrated power sources gives Smith Services a distinct advantage over their competitors. All of the medium volt classification can be tested with a dedicated 2,500 KVA test center; 13,800 volts, 7,200 volts, 4,000 volts, and 2,300 volts. Smith Services’ dynamometer capacity is 12,000 lb-ft of torque, equating to 2,500 HP at 1,200 RPM. This level of capability makes it possible to test a 5,000 HP motor with a full complement of documentation at proportional values.
Q: Please outline the terms of the warranties and describe Smith Services’ approach to maintenance.
A: Because Smith Services is highly experienced, we are confident in the level of repair services we provide for all of the motors we work on. Customers receive up to 6 months on the shelf, and a year in service for low voltage or medium voltage, and all warranties are the same, whether they have large motor or large generator ratings.
Some short term exceptions were made for manufacturers involved with random wound equipment in medium voltage, in a 2,300 volt class, because the OEMs pushed the design envelope. Some of these motors were notoriously difficult to repair. There is a proportionally increased requirement to contain the voltage anytime the voltage is increased, and additional insulation is required. Fortunately, advances in insulation material technology make it possible to offer long lasting, reliable repairs.
As for any facility cleanliness is a key part of maintenance, and this means routine inspections for all large industrial motors. If motors are dirty, then they need to be cleaned. Whether it is a simple blow down or inspection, routine electrical tests will indicate whether there is a cleanliness problem. For large motors and applications, this data can also be used as predictive maintenance, which is especially important for mission critical equipment. This way, outages can be scheduled in advance, or inspections can be made onsite before removing equipment for repairs. Good maintenance is even more important for large voltage motors because the higher the voltage rating, the lower the current rating. While there are significant gains in efficiency more insulation must be added to contain that voltage or pressure.
Q: What is the specific relationship between the footprint of the equipment, the voltage rating and horsepower rating?
A: Torque output is what drives the footprint of a motor. To provide a common example, a 100 HP large motor that is rated for 1,800 RPM will produce 300 pound-feet of torque. When the speed rating is changed to 300 RPM with the same 100 HP motor, almost 1,800 pound-feet of torque can be produced. The additional mechanical load requires more mechanical structure.
Q: Do you have any concluding remarks regarding medium motor repair?
A: Routine inspections, cleaning, vibration monitoring, and electrical testing are the best procedures to ensure to a long-lasting motor and the most effective predictive maintenance.
