As the air demand within a plant can often vary, it is not uncommon to occasionally start/stop the air compressor and the associated drive motor. Normal starting and stopping of your compressor occurs pending the demand necessary for the job location. What is important to remember is to avoid unnecessary starts and stops that could lead to internal damage, as this damage may not be evident until it's too late.
Following NEMA Recommendations
The National Electrical Manufacturers Association (NEMA) provides recommended standards for starting motors. One standard has been highlighted below:
- "… the life of the motor is affected by the number of starts."
Depending on the type of motor starter, the motor can draw anywhere from 500 to 700% of the full load amperage during acceleration. The motor windings experience a temperature rise due to this high in-rush amperage during starting. And keep in mind that the motor windings are subjected to this temperature rise during each motor start; therefore, an excessive number of motor starts can result in premature failure of the motor windings. While motors are designed to handle a high number of starts, NEMA still recommends limiting unnecessary starts and stops.
NEMA also notes that the number of starts within a period of time should be limited. To assist our compressor operators, FS-Elliott control systems provide protection from frequent starting of the motor. Our software allocates two starts within a 60-minute timeframe for the user to perform. If the compressor would need to be started for a third time within the 60-minute time frame, then a bypass would be required to override the safety feature. But doing so should be avoided as much as possible since these additional starts can wear on the machine over time.
Consider Your Starter & Motor
Both starters and motors are heavily impacted by frequent starts and stops, so paying extra attention to these areas is important. At FS-Elliott, we work to provide the best-in-class motors and starters with each of our Polaris® and PAP Plus® machines. However, if you select your own starter and motor, many factors should be considered.
When sizing a starter for a compressor, it's important to consult an electrical engineer to check the location's power supply and understand the KWs needed to start the compressor. At FS-Elliott, we offer motors that are two-pole and typically run at 3600rpm, so they require slightly more power to start versus a slower four-pole, 1850rpm motor.
Smart starters contain internal protection for how many times you can start your compressor per hour. This setting needs to be programmed in during the commissioning of your FS-Elliott compressor and is supplied in our technical manual under the motors and starters section. General starter types are listed below:
- Full Voltage Across the Line
- Reduced Voltage Solid State
Numerous variations of motors can be installed within your air compressor. Every start initiated will heat up the windings, stators, and rotor inside the motor, regardless of your brand. Programming the time between the hot motor starts and stops per hour will allow the motor to cool down and reliably start again. Bypassing this option can lead to overheating of the parts within the motor, thus causing damage. This information is also included in our technical manual and should be checked during your compressor's commissioning and servicing.
Short Cycling Risk - Associated with Frequent Starts & Stops
Short cycling is a risk that operators take when turning an air compressor motor on and off too frequently. When a motor short cycles, it increases the energy consumption and draws more current in during the startup of the motor compared to the current used during normal operation. Heat builds up, and turning the motor off and on doesn't allow the motor to dissipate this heat buildup. This increases the motor's temperature even further, reducing lifespan. FS-Elliott control panels offer hot motor protection to prevent operators from dangerous frequent starts and stops.
Although there are times when you may need to start and stop your compressor within a short period of time, it is critical to minimize the start and stops. Ensuring that you have a quality motor and starter and taking advantage of programmable start/stops will play a pivotal role in keeping your compressor in good shape.
If you have any questions, please do not hesitate to contact your local FS-Elliott authorized channel partner
to discuss your motor settings or any additional items on your FS-Elliott compressor.