Part 3 of a 3 part series on Motor Life Expectancy
Many motors fail prematurely due to misapplication and this series will discuss ways to avoid these and optimize motor life. This avoids costly downtime and the expense of repair or replacement.
In Part 3 we will examine how adverse operating conditions such as heat, moisture and harsh environments affect motor life and how to best address these conditions.
Heat is the #1 cause of reduced insulation life – for every 10 degree Celsius above rated insulation temperature, insulation life is reduced by 50% as illustrated. Note the significant increase in life by utilizing a higher class of insulation.
Bearing life is also affected in much the same way – every 10 degrees Celsius rise in operation temperature results in a significant reduction in lubricant life.
Causes of high motor operating temperatures:
- Overloaded motor – operating at a higher current draw under steady state load than motor full load amp rating.
- Too many starts per hour – Current draw is approximately 6x motor full amp rating while operating on an across the line motor starter.
- Operating at low speeds under heavy loading on a VFD -airflow of cooling fans is significantly reduced.
- High ambient temperatures in motor area or restricted ventilation.
Solutions:
- Properly size the motor to the load
- Utilize VFDs or soft starts on motors that have numerous starts/hour
- Select the proper type motor for operation on a VFD – especially if application involves operating at low speeds and/or heavy loading.
- Select motor with higher class motor insulation and ensure adequate ventilation.
- Use a bearing lubricant with a higher temperature rating.
- Utilize winding and bearing temperature sensing devices, such as PT100 (RTDs) or thermisters to protect the winding and bearing from overheating.
Moisture
High moisture conditions are very detrimental to motor insulation as well as bearing lubricant life. Motor winding insulation resistance is significantly reduced when exposed to moisture leading to burn outs. As little as 100 parts per million water can cause a 32-48% decrease in bearing life.
Causes of High Moistures:
- Condensation during non operational periods. Motor insulation, unless it is encapsulated, will readily absorb moisture from condensation as the motor pull in cooler outside air.
- Washdown environments such as food processing or pharmaceutical processing routinely subjects the motor to high pressure steams of water.
Solutions:
- Utilize space heaters installed within the motor. Wired properly through the motor starter, these are turned on during non-operating periods to maintain motor temperature five to ten degrees above surrounding air to eliminate condensation.
- Specify washdown motors with epoxy coating, or stainless steel. These will include shaft seals as well as encapsulated motor windings.
- Utilize weep holes on motor, positioned at the lowest point of end bells to facilitate draining of moisture which may accumulate.
Harsh Environments
Harsh environments subject motors to a wide variety of conditions that can reduce motor life. These include harsh chemicals, dust, severed shock loading as well as heat and moisture.
Typical harsh environments include steel processing such as rollout tables, galvanizing lines and rolling mills, chemical processing, mining, foundries, pulp and paper processing, aggregate plants and refineries.
Solutions:
- Specify severe duty motors that incorporate features such as cast iron frames, higher grade insulation and various shaft seals.
- For the harshest environments specify motors that meet IEEE-841 standards. These motors incorporate corrosion resistance on both the exterior as well as motor internals, special balancing, larger conduit boxes, and Class B temperature rise.
The In-House Technical Specialists at Flolo Corporation have extensive knowledge of motor failures common across a broad range of industries and solutions that will maximize life expectancy in these demanding applications. Additional information on how to best optimize motor life are covered in extensive detail in classes available thru Flolo Tech. Please contact your sales representative for additional details.