When to Use Medium voltage electric motor？

What is a Medium Voltage Electric Motor?

Medium Voltage Electric Motors typically refer to an electric motor designed to operate at voltages of 1,000 volts and above, although the exact range may vary according to different standards and applications. These motors are commonly used in various industrial and commercial applications that require higher power output than what low-voltage motors can provide.
GAMAK Medium voltage motors are used in all industries where heavy loads are moved or work connected with particularly complex applications is carried out. These motors are used in a wide range of applications in all industries, including oil and gas, power generation, marine, pulp and paper, cement, mining, metal, and water processing. GAMAK medium voltage asynchronous motors are superior to their counterparts in terms of performance and durability.
What makes GAMAK different from its competitors in this field is our custom-made design, customization, reliability, and flexibility capabilities. Our medium voltage motor and generator solutions are developed using advanced analytical tools to identify the best design for the specific customer application and to determine the performance-cost optimization.
GAMAK Medium Voltage Motors include motors manufactured for general use in industry in the range of 150– kW with a structure size of 315 – 630.

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Understanding the Basic Principles of Medium Voltage Electric Motors

Cage Rotor / Cast Iron Frame
Full Closed (TEFC) - (TEFV) - (TEAAC)

Voltage Range: - V
Power Range: 150 - kW
Structure Size: 315 - 630 (IEC)
Mounting Type: IMB3-IMV1-IMV3
Operating Type : S1 Standard, S1-8 Optional
Protection Class: IP 55
Insulation Class: F (155 ° C)
Temperature Rise Class: Class B (80K)
Number of poles: 2-12
Cooling Type: IC411-IC416-IC611
PT100 in Bearing and Winding    
Thermistor    
Lubricating nipples    
Co-Bearing

Starting Method: DOL, VFD, Soft Starter
Cable Box: 180-degree changeable (left-right)
Painting: Standart RAL , other colors optional
Protection: Up to IP56
Bearing: Standart Bearing, Reinforced design for radial forces optional Bearings
Rotation: Both Side Rotation
Frequency: 50-60Hz

What are the Different Types of Medium Voltage Electric Motors?

Synchronous Motors

Medium Voltage Synchronous Motors are a specialized type of electric motor renowned for their remarkable ability to maintain precise speed control. Unlike other types of motors, synchronous motors operate at a fixed speed, determined by the frequency of the power supply. This synchronous speed is directly related to the number of poles in the motor and the frequency of the electrical power.

The inherent characteristic of precise speed control makes synchronous motors ideal for applications that necessitate synchronization with other machinery or processes. One prominent field of application is power generation. In power plants, synchronous motors are commonly employed to drive power generators. The constant speed of synchronous motors ensures that the generated electricity remains synchronized with the frequency of the power grid, which is essential for maintaining the stability and reliability of the power supply.

 Induction Motors

Medium Voltage Induction Motors operate based on the fundamental principle of electromagnetic induction. These motors are highly prevalent in numerous industries due to their versatility and wide range of general-purpose applications. One of their primary advantages is their ability to efficiently convert electrical energy into mechanical energy through the interaction of magnetic fields.

These motors find extensive use in various industrial settings, particularly in driving pumps, compressors, conveyors, and fans. Their robust and reliable design makes them suitable for heavy-duty tasks, allowing them to handle substantial loads and provide consistent performance over extended periods.

How are Medium Voltage Electric Motors Used?

Our medium voltage motor and generator solutions are developed using advanced analytical tools to identify the best design for the specific customer application and to determine the performance-cost optimization.

How to Install and Maintain Medium Voltage Electric Motors

Step-by-Step Installation Guide for Medium Voltage Electric Motors

• Preparation: Before installing the motor, review the manufacturer's guidelines and ensure that you have all the necessary tools and equipment. Prepare the installation site, ensuring it is clean, dry, and free from debris.
• Electrical Connections: Hire a licensed electrician to make the electrical connections. Ensure that the motor is properly grounded and that the electrical wiring is appropriately sized and connected according to the motor's specifications and local electrical codes.
• Alignment: Accurate alignment between the motor and the driven equipment is crucial for smooth operation and longevity. Use precision tools to align the motor shaft with the driven shaft within the allowable tolerances.
• Cooling System: For motors with cooling systems, such as air or liquid cooling, ensure that the cooling system is correctly set up and functioning optimally. Proper cooling is essential for preventing overheating and prolonging the motor's life.
• Bearing Lubrication: If the motor has grease or oil-lubricated bearings, follow the manufacturer's instructions for proper lubrication. Over- or under-lubrication can lead to premature bearing failure.
• Testing: Once the installation is complete, conduct initial tests to ensure the motor operates smoothly and without any abnormal vibrations or noises.

Tips for Maintaining and Troubleshooting Medium Voltage Electric Motors

• Regular inspections: Schedule regular inspections of the motor to detect any signs of wear, damage, or other issues. Check for loose connections, insulation degradation, or any abnormal operating conditions.
• Lubrication: Follow the manufacturer's recommended lubrication schedule for the motor's bearings. Ensure the correct type and amount of lubricant are used.
• Cleaning: Keep the motor and its surroundings clean. Regularly remove dirt, dust, and debris from the motor and its cooling system to prevent overheating and ensure optimal performance.
• Vibration Analysis: Periodically conduct vibration analysis to detect any imbalances or misalignments in the motor. Address any issues promptly to avoid further damage.
• Temperature Monitoring: Monitor the motor's temperature during operation. Overheating can be a sign of problems, and early detection can prevent major failures.
• Infrared Thermography: Use infrared thermography to identify hot spots or abnormal heat patterns in the motor, which may indicate potential issues with windings or connections.
• Operating Conditions: Ensure that the motor operates within its design specifications. Avoid overloading the motor and ensure it is operated under appropriate environmental conditions.
• Training: Train maintenance personnel on proper motor maintenance and troubleshooting techniques.

How Energy Efficient are Medium Voltage Electric Motors?

Medium Voltage Electric Motors are generally more energy-efficient compared to low-voltage motors, especially in higher power ranges. Their efficiency is a critical factor in reducing energy consumption and operating costs in various industrial and commercial applications. The energy efficiency of medium voltage motors can be attributed to several factors: size and design, improved materials and manufacturing, higher voltage operation, lower currents, advanced motor design, Premium Efficiency Standards, and improved cooling systems. 

It's essential to consider that the efficiency of a medium-voltage motor may vary based on its design, load conditions, and operating environment. Choosing a motor with higher efficiency, adhering to best practices in installation and maintenance, and considering motor load requirements can further enhance the energy efficiency of medium-voltage electric motors, leading to significant energy savings and reduced environmental impact. 

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.

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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.

Cabling

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.

Size

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.

Windings

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.

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