Low-voltage motors are often a preferred choice due to familiarity with products and available services, as well as the typically lower cost of individual components. However, as horsepower (hp) increases, there can be advantages to moving to a medium-voltage motor. Low-voltage motors typically go up to 1,000 hp while medium-voltage motors can cover 250 hp and higher.
Furthermore, in special variable frequency drive (VFD) applications, low-voltage motors can go up to or even over 5,000 hp. This high rating is preferably above the National Electrical Manufacturers Association (NEMA) low-voltage limit of 600 volts but still under International Electrotechnical Commission (IEC) low-voltage limit of 1,000 volts.
Knowing when to select the right motor for an application can save users time, space and money. Here are some areas to consider when choosing between low- and medium-voltage electric motors.
In low-voltage motors, as the hp range increases, the size of cabling increases to handle the increase in amps. With conductors being a copper component, this increase in wire gauge can add cost, especially on longer cabling runs across a large facility or over a long distance to a remote pumping station. This increase in diameter also makes turn radii larger, which increases the difficulty in making connections within the terminal boxes. This can be time-consuming and introduce additional risk to the maintenance crew during initial setup of the motor.
A lower current in medium voltage motors allows for smaller cables (leads) even at higher hp. The use of smaller gauge leads reduces the cost per foot for those long-distance connections to remote pumping stations. Also, during the motor connection procedures, the small gauge wires are easier to work with and connect within the motor terminal box. This can reduce the maintenance crew&#;s time in making the connections and reduce the risk of damage to the cables.
The cost of copper as a commodity and the difference in thickness of leads sized for low-voltage machines versus medium-voltage machines can be so large that this can be the primary determining factor in what voltage service is specified. The higher cost of medium-voltage equipment can easily be offset in applications with long cable runs from distribution.
When space is a consideration, more than motor size should be reviewed as the choice between a low- or medium-voltage motor that has an impact on the components in the entire system.
Low-voltage drives are smaller than medium-voltage drives when variable speed applications play a role in the motor selection. However, above 1,000 hp this ratio starts to flip, and drive size may be comparable or even smaller. Due to lower amps, medium-voltage motors also enable the use of smaller supply side switch gear, supply transformer and controls.
To prevent short circuits and preserve the longevity of medium-voltage windings, they are commonly produced using a form wound insulation system. The insulation system is sealed using a vacuum pressure impregnated (VPI) system, which fills the voids in the coils to protect from contamination. The coils are organized outside of the stator core to ensure the ideal spacing of turns, which allows for air flow around the coils to improve heat transfer. It is a more labor-intensive process but is well suited to the rigors of the voltage impulses of a medium-voltage system. Additionally, due to the smaller conductors used in the windings, there is the possibility of having more turns, so there is greater flexibility in the electrical design, making it possible to achieve specific performance characteristics.
In low-voltage motor windings with larger diameter conductors, there are more limitations to the electrical design but less need for the precisely ordered coils required to withstand medium voltage. Because of this, low-voltage machines can use a more cost-effective random or mush wound design with a thorough dip-and-bake in varnish that is often coupled with a vacuum impregnation of the winding to ensure that the insulating material fills all voids. The result is a low-voltage insulation system that is capable of exceeding industry standards for longevity while achieving the performance characteristics necessary for a broad range of applications.
Like all good questions, whether to pick a low- or medium-voltage motor for a pump system does not have an easy answer. There are several factors to weigh, including site and installation specifics that will impact what voltage service is best for a given project. When selecting a motor for an application, evaluating these three factors should provide the best all-around motor for the facility.
Wayne Paschall is a product market specialist with ABB Inc., in the large machine and generator division. For more information, visit abb.com.
What are the differences between high voltage motors and low voltage motors? Let China Leading Electric Motor Supplier tell you:
High-voltage motors and low-voltage motors differ in several aspects, including the following:
1. Operating Voltage
High-Voltage Motors: The operating voltage is typically above volts (V), with common voltage levels including 3kV, 6kV, and 10kV.
Low-Voltage Motors: The operating voltage is usually below volts (V), with common voltage levels including 220V, 380V, and 690V.
2. Application Fields
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High-Voltage Motors: Widely used in heavy industries such as power generation, petrochemicals, steel, cement, and mining, as well as in high-power applications like wind turbines, pumps, and compressors.
Low-Voltage Motors: Mainly used in manufacturing, construction, and consumer equipment, suitable for low-power equipment and machinery such as fans, pumps, machine tools, and elevators.
3. Structure and Design
High-Voltage Motors: Typically use materials with high insulation grades, have more complex insulation systems, more rigorous designs, and sturdier mechanical structures to meet the demands of high voltage and high power.
Low-Voltage Motors: Comparatively simple structures with lower insulation requirements and lighter designs, suitable for lower power applications.
4. Control and Protection
High-Voltage Motors: Require more complex control and protection systems, such as high-voltage switchgear, high-voltage circuit breakers, and protection relays, to ensure safe operation.
Low-Voltage Motors: Relatively simple control and protection systems, including low-voltage circuit breakers, contactors, and thermal relays.
5. Cost and Maintenance
High-Voltage Motors: Higher manufacturing and maintenance costs, with stringent maintenance requirements, necessitating regular inspections and upkeep.
Low-Voltage Motors: Lower manufacturing and maintenance costs, relatively simple maintenance, and only basic checks and maintenance needed in daily use.
6. Size and Weight
High-Voltage Motors: Generally larger and heavier due to high power and insulation requirements.
Low-Voltage Motors: Smaller and lighter, suitable for lower power applications.
7. Efficiency and Losses
High-Voltage Motors: Usually have higher efficiency and lower losses due to their design and high-power characteristics, suitable for long-term continuous operation.
Low-Voltage Motors: Relatively lower efficiency, suitable for short-term or intermittent operation.
In summary, high-voltage motors and low-voltage motors differ significantly in terms of operating voltage, application fields, structure and design, control and protection, cost and maintenance, size and weight, and efficiency and losses. The choice between the two depends primarily on the specific application requirements and usage environment.
For more information, please visit low voltage motors supplier.