No Jolt Starter Extends Motor Life

No Jolt Starter Extends Motor Life


Image courtesy of SiriusSoft starters are steadily growing in popularity because they reduce maintenance, conserve energy, avoid peak penalties and play a significant part in improving plant performance and operating costs. Today, soft starting is increasingly common in many control applications from water treatment plants to food and beverage factories.
A gentle approach is often the best. With electric motors, using a SIRIUS soft starter from Siemens can prevent unpleasant side-effects such as mechanical impacts inside the machine or voltage dips in the power supply system.
Conveyor belts, ventilators, milling machines, pumps and stone crushers all have one thing in common. Starting these machines suddenly causes wear and tear on motors and their associated drive systems. Their mechanical systems benefit from a smooth start rather than being jolted into operation. This leads to costly maintenance and inefficient energy use. Soft starters prevent pressure surges in rotary or piston pumps, they allow for the smooth starting of a conveyor system and they can reduce a saw’s start-up current.
When a three-phase induction motor is started up, the current it draws is several times more than its rated operating current. This can vary from 3 to 15 times the motor’s full load amp (FLA) rating, depending on the characteristics of the motor.
Other torque surge problems can occur when a motor is started directly across the line (ATL).
With ATL contactor starting, the motor and the supplying utility network are abruptly loaded with the full motor start-up current. This strongly strains the current network, which shows as a flickering of the lights. As the current increases abruptly, the torque applied to the load by the motor also rises to a multiple value of the nominal motor torque at the start up.

Image courtesy of Sirius

This torque surge can, for example, cause transported goods on a conveyor belt to fall or fans drive belts to spin. In general, ATL starting requires more frequent maintenance than controlled smooth motor start-up. It also leads to higher maintenance costs for the overall system.
Wye-delta starters offer some improvement. The technique, so called because the motor windings are switched from a wye connection to a delta connection, reduces both start-up current and torque by about two thirds. However, at the switching point, there is still a current surge that can cause an electrical and mechanical shock to the system.
Using a soft starter can prevent current surges altogether.
Soft starter devices provide step-less motor control, which allows you to adjust both the start-up torque and the current in small increments. Not only can you control these parameters; soft starters will also allow you to vary the time taken to run the motor up to its normal operating speed. The devices operate by gradually increasing the voltage to the motor during the starting period, using phased control of the input AC voltage.
Doing this will accelerate the mechanical equipment but decrease stress levels. This will have a positive effect on the operating characteristics of the equipment. The machine’s lifetime will also be extended.
When deciding on what soft starter to buy, the key consideration should be the space available in the load feeder.
Some starters have integrated protective functions, making it unnecessary to purchase and install stand alone devices, such as overload relays. This saves space within the control cabinet and wiring labor costs within the feeder.
The newest starters on the market have motor protection with adjustable overload tripping time. The overload tripping classes can be variably set. You can use either a 4-step rotary potentiometer or an integrated graphic display, depending on the model of soft starter you are using. Because this integrated motor overload protection is in accordance with IEC 60 947 4 2, you do not require an additional overload relay. Internal device protection is another valuable built-in feature available today. This prevents both a thermal overload of the thyristors and subsequent damage to the power components.
Start-up current of motors with extremely high capacities can overstress the local electrical network in the start-up phase. This can happen even with motors operated by soft starters.
Simply due to cost, most soft starters are two-phase controlled starters. When you remove one phase, the starter remains smaller and more compact. It is also more economical.
With two-phase controlled soft starters, the current resulting from the overlapping of the two controlled phases flows in the uncontrolled phases. This leads to a physically caused asymmetric distribution of the three phase currents during the motor’s start-up process.
The more demanding motor starting and stopping applications need torque control. This can allow a starter to start and stop motors up to a power rating of 950HP/480V in a standard configuration.
For almost every starting and stopping application, soft starters offer the soft alternative to ensure that motors start smoothly. Control and monitoring technology are now available as part of a standard soft starter package, as are communication capabilities.
Soft starting offers significant cost and reliability advantages over conventional electro-mechanical solutions. Thus, an end user can have much more control and feedback over a specific process or application.
To learn more about how SIRIUS soft starters from Siemens can extend motor life at your operation, contact IBT.  


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