There are quite different methods
for starting an electric motor such as “Direct On Line (DOL)”, “Star-Delta”,
“Auto Transformer”, “Primary Resistor” or using solid-state power electronic
devices such as “VFD” or “Soft Starter”. Every single method has its own
specific applications and benefits. In this lesson, we are going to
discuss the “Soft Starter” method amongst all and we will cover the
rest of methods in future videos. before we get started on today's video if you love our videos, be sure to click the like button below. then make sure to click subscribe and the little bell to receive
notifications of new RealPars videos. This way you never miss another one! Since Electric Motors often require large amounts of
electricity during their accelerating to the nominal speed, a Soft Starter can be used to limit the surge of current
known as “inrush current” and torque of the electric motors, resulting in a safer, smoother and gradual start-up. Soft starters will protect your
electric motor from possible damage and at the same time extend the lifespan of
your electric motor and the whole system by declining the heating caused by frequent start/stops,
reducing the mechanical stress on the motor, its shaft and reducing the electrodynamic
stresses on the power cables. Large inrush current also places a high demand on the
electrical supply system, which results in extra cost. Soft Starters are commonly used
in industrial applications that have a high inertia load that
requires a large inrush of current. One example of this is an Air Scrubber or Dust
Collector,These will have large fans inside. In this application, it will take
some time to get the fan moving but once the fan is moving the current
and torque load on the motor is reduced. In the system the fan will pull air into filters
where dust particles are collected. Then the clean air is pushed back to the factory. Water supply applications are another
great use for soft starters. When using pumps in a process you
have to bring them up slowly. If not you will cause pressure surges in the water
system that could lead to dangerous conditions. Conveyor systems that move heavy loads can be
maximized by using a soft starter as well. A soft starter will be located inside the control panel
and will be supplied with 3 phase power on the top. Then on the bottom, the soft starter will
supply 3 phase power out to the motor. The soft starter can be controlled either by a direct
start/stop wiring or, it can be controlled over ethernet. Both control methods have their
advantages and disadvantages. Direct start/stop signals would
not require a PLC, They would be less expensive, Using
ethernet control, a PLC is required. This will allow there to be feedback, which will
give adjustable control and monitoring capabilities. Now that we have talked about some applications
and how the soft starter is wired into a system, let's dive into the internal
workings of the soft starter. The main component of a soft starter is a Triac which
is designed to limit the applied voltage to the motor. Triac consists of two
back-to-back Thyristors or SCRs. When an internal pulse is applied to its gate it allows
current to flow which then sends current out to our motor. The pulses are sent based on ramp time so the
current will be slowly applied to the motor. This will allow our motor to start slowly
reducing torque and inrush current. When the motor reaches full speed the
soft starter and DOL work the same. The difference is how they act
while getting to full speed. When comparing the voltage between a
DOL starter versus a Soft Starter, we can see that there is a direct
in rush of voltage on the DOL where the Soft Starter takes more
time to get up to full voltage. The current is more regulated
using a soft starter. With a DOL there will be larger spikes
in current as the motor starts. With a soft starter, the time the motor gets
us to speed is slower and more controlled. While a DOL gets the motor up
to speed almost instantly. This can have undesirable effects
that we will talk about next. The torque applied to the motor as speed
increases is greater when using a DOL opposed to a gradual torque
increase using a Soft Starter. Now that we know what a soft
starter is and how it works let's go back to our industrial
applications and apply what we know on why a soft starter can prevent undesirable
mechanical and electrical effects. When a DOL is used in these applications, there will be a sudden impact
at startup on the load along with a rapid acceleration
which causes excessive wear. Our Air Scrubber fan will be driven
by a motor using belts and pulleys. Using a DOL can cause the
belts to slip and wear. With our water supply example, the DOL will
cause pressure surges on the water lines. This can cause excessive wear
which could lead to line breaks. And our last application is the conveyor system. DOL’s will cause strain on the components that drive
the conveyors along with the couplings and bearings. These undesirable mechanical effects
can lead to continuous maintenance, unscheduled shutdowns, and shorter component life. There are also electrical effects that we
want to avoid by using a soft starter. The heavy current surgers that a DOL can
cause, can burn out contacts and motors. In conclusion, when an industrial application has a high
inertia load that will require a large inrush of current, a soft starter is an ideal option
for controlling the system. Also, we talked about the wiring and control of the
soft starter as well as the internal components, and how Triacs control voltage
to the motor based on ramp time. We concluded with undesirable mechanical and electrical
effects that can be prevented by using a Soft Starter. Want to learn PLC programming
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