Considering the long history of electric motors powering the industrial world, it is no surprise when the need arises to replace a large induction motor. This article details what should be considered when attempting to replace an outdated or failed machine with a new induction motor. Many factors could lead to the replacement of a motor, including defects, a desire to operate at higher efficiencies or a demand to achieve higher power factors. Every case is different and specific to each operation. However, there are universal considerations that should be accounted for when upgrading a large induction motor. Frames within the National Electrical Manufacturers Association (NEMA) range of small to medium industrial motors are not complicated to replace due to the universal dimension standards. However, medium- or high-voltage motors do not have dimensional standardization. Additionally, unlike motors with power less than 500 horsepower (hp), large motors are not required to maintain comparable torque or current levels from manufacturer to manufacturer.
Understand accessories, sizing, electrical performance and color.
TMEIC
06/04/2019
Image 1 (left to right). Motor side. Image 2. Motor end view. Image 3. Shaft details (Images courtesy of TMEIC)
Unless the end user intends to rebuild the foundation, these high-power ratings and frame dimensions require detailed attention to verify the mechanical interchangeability of an upgraded motor, in addition to an accurate evaluation of the electrical performance.
The following are critical mechanical and electrical considerations required to ensure a successful transition when replacing large motors.
Table 1. Explaining relevance for “drop-in replacement motors”
It is the end user’s responsibility to ensure the new motor does not interfere with equipment surrounding the motor, pipes and other utility and architectural structures. If provided the opportunity for a site walkthrough, the manufacturer’s application engineer can assist in observing space limitations.
The end user could request the relocation of terminal boxes and water and oil connections to be closer to the existing terminal boxes and connections. It is possible to accommodate the request by locating all terminal boxes on the same side of the motor, but an exact match is unlikely.
Shift toward the drive end or the nondrive end and locate the power cables entry point to the same side as the existing terminal box. This reduces pipe bending. Using flexible conductors yields easier assembly.
Table 2. Checklist for motor owners before sending in quote request to application engineer
When applicable, water and oil inlet and outlets should be on the side of the motor with existing connections, but adjustments to incoming pipes may be required. It is important for the end user to understand this possibility ahead of time, no later than the proposal stage.
During the initial process, the project’s engineer will use the existing motor outline drawing to evaluate and quote a frame with matching dimensions. If no drawing exists, the motor OEM cannot guarantee interchangeability of the equipment.
Image 4. Belt and sheave data requirements