Motor Starters, Soft Starters and VFD's
Motor_Starters_Soft_Starters_and_VFDs.pdf
Motor Starters
A starter is a device that allows us to safely start and stop a motor (primarily used in industrial applications). It is basically a switching device which can allow us to operate a motor from a remote location. They also give use the ability to monitor the state of the motor (run status).
They consist of several parts including:
Typically used in areas where basic motor control is needed. Where torque on the motor is not a concern and where there is no speed control needed.
Advantages
- Lower cost
- Allows for remote operation
- Allows us to monitor motor state (w/ use of Aux. Contacts)
- Safe
- Efficient
Disadvantages
- High In-rush current (6-8 more current then the FLA (full load amps) of the motor). This can cause fuse to burn up and breakers to trip if the inrush is too high.
- Will allow a full torque start of the motor (this means that when power is applied to the motor, full current is applied to the motor instantly. This causes the motor to ramp up to full speed very quickly. This creates a lot of torque; this high amount of torque can cause the motor to wear and degrade more quickly.
Soft Starters
Provide all the same functions as a traditional starter. In addition, a soft starter is a device protects AC electrical motors from being damaged by sudden spikes of power. It does this by limiting the inrush current that can be cause by AC motors upon startup. They allow us to gently ramp up the motor to full speed. They are most commonly used upon startup only, however some models allow a ramp down period during shutdown as well. By slowing increasing the voltage upon startup, we are able to produce a gradual increase in motor speed.
Common Applications of Soft Starters
- Where torque and wear and tear on the motor is a concern
- When we need to reduce the inrush current that is created upon motor startup. (Saves money, saves motor)
- In pumping systems where it is necessary to reduce the pressure surge by a fast startup of a motor or pump.
Advantages
- Less expensive than a VFD when control is needed for startup only
- Smaller than other system, so space is not as much of a concern in comparison to VFD’s
- Allow for reduced inrush current
- Saves unwanted torque to the motor upon startup, prolonging the life of the motor.
Disadvantages
- More expensive than a normal motor starter
- Don’t allow for full speed control
VFD (Variable Frequency Drive)
VFD’s can provide all of the same functions as both starters and soft starts with some additional functionality. A VFD is a motor control device that allows us to both protect the motor as well as give us almost full control over the speed of the motor (AC motors). A VFD gives us the ability to slowly ramp of and down the speed during the start and stop of the motor, but it also allows for full speed control during the entire run cycle of the motor. This allows for more efficient use of the motor allowing use to save money and reduces the stress applied to the motor due to running at speed 100% of the time.
Common applications for VFD use:
- Where full speed control is required on the motor
- When energy savings is important
Example: based of the laws the govern how much power is needed to run at certain speeds, if you can run a motor at 70% speed, you would only need about 35% of the power needed to run the motor at full speed. That offers a huge savings in electrical costs. - Where more custom control and monitoring is required
Advantages
- Full speed control (Start, Stop, and in-between)
- Typically, more custom control and monitoring
- Energy savings due to more efficient motor usage Less wear on tear on the motors they are connected to
Disadvantages
- They are the most expensive options for motor control
- They often are much larger than other options and require much more space
- They can generate large amounts of heat that may require fan units or AC units
Transcript:
[0m:4s] Hi I'm Josh Bloom, welcome to another video in the RSP Supply education series. Today we're going to be talking about the difference between starters, soft starters, and VFDs, the different types of applications we might use these in, and the types of things we want to consider when choosing one of these devices.
[0m:20s] Let's first talk about starters. Starters simply allow us to start and stop a motor. Typically they're used in industrial applications. They allow us to control the start and stop function from a remote location.
[0m:33s] Starters also commonly allow us to monitor the state of the motor whether it's on or off. This is referred to as run status. Starters consist of just a few different components. First, the contactor. The contactor operates much like a relay in that when the coil on the contractor is energized, it allows the contact island shut allowing current to pass through to our motor.
[0m:55s] They also have an overload. The overload’s purpose is to monitor the current that is passing through to our motor and make sure that we don't have too much over current that will allow our motor to overheat and burn up.
[1m:7s] Also commonly used with starters, we have some form of circuit protection. This allows us to protect the motor against any high spikes and inrush current or voltage. Starters are going to be using applications where we only need basic motor control, where torque or where on the motor is not a major concern, and where we don't need any type of speed control.
[1m:29s] Some advantages of using a starter is first off, they are going to be a much more lower cost than some of the other options.
[1m:35s] They allow us to remotely start and stop a motor.
[1m:39s] They also are very safe, they're efficient, and they give us the ability to monitor the state or the run status of the motor. Some of the disadvantages that come with using a starter is that they allow for a full torque start of our motor. What this means is when we start our motor, we get a large inrush of current. This in rush can sometimes be as much as 6 to 8 times of the full load AMP rating of our motor. So, this large inrush of current causes, the motor to ramp up much more quickly, putting much more torque and stress on the motor. This causes the motor to damage and causes more wear over time. Another disadvantage with starters is because they allow such a high end rush of current and they only run at the full load AMP rating of the motor, we have a higher operating cost due to this.
[2m:26s] Next let's talk about soft starters. Soft starters provide all the same functionality as a starter, but they allow us to protect the motor from high spikes and voltage that may cause damage to our motor. They do this by preventing that large inrush of current to our motor by limiting the voltage and current when we first start our motor. So, by limiting this voltage and current upon startup, it allows us to slowly ramp up the speed of the motor, which causes less wear and tear. Now, soft starters are commonly used only upon startup, however, depending on the model, we can see them used in the shutdown process of a motor as well.
[3m:2s] Keep in mind with a soft starter, once we actually get up to the full load amps or full speed of our motor, it operates the exact same way as a normal starter.
[3m:11s] So some common applications where we might see soft starters used is where we are concerned about the torque or the wear and tear on our motor. We also might see them in applications where we want to reduce the inrush current when we start a motor, which allows us to save cost and the longevity of our motor. Another common application we might see these used is in pumping systems where we want to reduce the pressor surge by a sudden start or stop of our motor, or any application where we are starting and stopping our motor on a frequent basis because of that heavy inrush of current and wear and tear that can cause in our motors.
[3m:45s] So some of the main advantages of using a soft start versus a starter is because we are allowing the motor to ramp up slowly, it reduces the inrush current to our motor. Because of this, it saves on operating costs. It also allows us to increase the longevity of our motor because we're not putting so much torque and wear and tear on that motor upon startup.
[4m:6s] A few of the disadvantages associated with soft starters is cost. They are a little more expensive than a starter, and also they don't give us full motor speed control if we need that operation. Lastly we're going to talk about VFDs or a variable frequency drive. A
VFD provides all of the same functionality as both a starter and a soft starter, but also gives us some added functionality.
[4m:28s] A VFD gives us the ability to ramp up and down the speed of a motor during the start and stop function. It also gives us the ability to give full speed control during the entire run cycle of the motor.
[4m:39s] Because of these efficiencies, VFDs allow us to run the motor at a much lower cost while also reducing the wear and tear and stress on the motor. Some very common applications where we see VFDs used are in scenarios where we need full speed control over our motor. Another application where we commonly see a VFD is used is where energy savings is very important. One specific example: laws that govern how much power is required to run a motor at certain speed. We can actually run a motor at about 70% speed and only need about 35% of the full power needed to run that motor. This offers us a huge savings and electrical cost. It also allows the motor to operate with much less stress and torque allowing it to last much longer. Some other applications where we commonly see VFDs used are where we need more custom control and monitoring in our motor systems. So, the advantages of using a via include everything that we get from the soft starter, as well as full speed control of our motor. That includes during the start and stop operation
[5m:42s] and also during the full run cycle of the motor. It also gives us increased protection of our motor decreasing the wear and tear and stress of our motor over time.
[5m:51s] So, because of this, it allows for the lowest operating cost of all three options that we have discussed today.
[5m:57s] It also gives us the ability to monitor and control our motors more effectively.
[6m:2s] A few of the disadvantages associated with VFDs are first, cost. They do cost more than both soft starters and starters. They also are going to be much larger in most cases, and so we need to take that into consideration when planning our motor starter scenarios. Lastly, VFDs do put off more heat than the other two options, so we need to make sure that we plan for proper cooling and ventilation of our systems. So, now let's compare the three different options. First, we have the starter which again is going to be the lowest cost option, all the way up to the VFD which is going to be the most expensive option with the soft starter falling somewhere in between. So, starters offer no speed control, which means they ramp up quickly and they stay at full speed the whole time that they're running. Soft starters give us a gradual ramp up in speed until they get to full speed and then they stay there and operate much like a starter, where a VFD gives us full motor speed control which allows us to ramp up and down the speed during the start and stop as well as the full run cycle of the motor.
[7m:1s] Next, we have very little monitoring with a starter, maybe run status. A soft starter gives us a little extra monitoring if we need it, but a VFD gives us, the ability to fully monitor our motor control. When we're talking about wear in tear of our motor a starter is going to
be the hardest on our motor because it ramps up so quickly and there's such a high inrush of current our motor becomes damaged and degrades over time much more quickly, whereas a VFD gives us very minimal motor damage and wear over time because of the control that we have, whereas a soft start fall somewhere in between because it allows us to slowly ramp up only upon startup, and in some cases upon operation shutdown. So, lastly, let's talk about the cost savings and efficiency of using each of these options. With a starter it is going to be the least efficient of the three options which gives it the highest operating cost because of the way it functions. With the soft starter, we do get a little bit more efficiency because of that slow ramp up, which gives us a little bit more operating cost. But with the VFD we get by far the highest efficiency because of the ability to fully control the motor speed, which gives us by far the lowest operating cost of the three options. For a full line of starters, soft starters and VFDs and thousands of other products, please go to our website. For more information or other educational videos, go to RSPSupply.com, the Internet's top source for industrial hardware. Also, don't forget: like and subscribe.
