Motor control fundamentals

Mastering motor control secrets
Motor control fundamentals
Not only that, but the excess power draw from the grid can cause voltage drops on weak power systems.
Reduced voltage starters evolve to help manage inrush currents and are required by some utilities to mitigate large voltage drops during startup.
The early forms of reduced voltage starters include reduced voltage autotransformers and reduced voltage primary reactors.
These starters utilize the tap setting of a transformer to start the motor at a reduced voltage of either 50%, 65% or 80% of full voltage for a preset time.
Once the motor ramps to full speed, the motor is connected to full line voltage through the opening and closing of contactors.
solid-state Soft Starters or RVSS.
emerged as a more refined approach to mitigate mechanical stress and voltage drops associated with motor starts.
An RVSS provides a controlled startup of a motor by gradually increasing the voltage output.
This is achieved through SCRS that allows small amounts of current throughout a time, creating a soft start.
RVSS provides a greater degree of control for reduced voltage starting, which prevents motor coupling and shaft damage, rotor and winding failure, and stops drive belt squeal and breakage.
Additionally, with electronic control, an RVSS offers a wide range of current limit settings, providing greater control flexibility as compared to the discrete steps of a reduced voltage auto transformer starter.
For pumping processes in particular, soft starters can ramp down the voltage when a stop command is given.
This avoids water hammer in pipes by allowing for a soft stop, reducing that line pressure so valves can close gently and prevent a surge wave.
Let's see an RVSS in action.
Hear that smooth ramp up.
The inrush current was significantly reduced compared to an across-the-line starter, which in turn improves the lifespan and uptime of your motor system.
It's worth noting that an RVSS only ramps speed and torque during motor startup and shutdown as the motor approaches full speed.
The bypass contactor closes, which applies full line voltage, similar to what we saw in that auto transformer.
So what if we wanted even
more sophisticated control than an RV?
That's where something like a variable frequency drive, or VFD, comes in.
Let's go back to that light switch analogy.
If an across-the-line starter is like a light switch, then a VFD is more like a dimmer switch.
A dimmer switch allows you to fine-tune how much power is applied to the bulb, therefore giving you full control
of the lighting in a room.
And if you were to leave that light bulb at, say, 30% power, you would see energy savings on your bill compared to if that light was fully lit the entire time.
A VFD is like a dimmer switch for your motor, allowing complete speed and torque control throughout the motor's start, stop, and run cycle.
If you have a process with variable demand, then a VFD can be a much more efficient solution with significant energy savings compared to traditional starting methods.
This is great for applications such as a pump that requires different flow rates or a fan that operates at different speeds depending on ambient temperature with motor control.
Motors can operate safely and efficiently without the need for manual intervention.
Now that we know some of the different types of motor control solutions, let's talk a little bit more about applications.
Motor starters, just like motors, come in all shapes and sizes.
Part of that depends on system voltage.
Motor starters are available for low voltage applications from 230 volt to 460 volt AC.
such as these NEMA size 00-9 starters.
Starters are often seen in applications such as rotary turntables, conveyors for material movement, and small industrial fans and blowers.
Medium voltage motors are most often used when industrial processes require high horsepower loads.
Switching from low voltage to medium voltage significantly reduces the current required for those high horsepower motors.
For example, a 500 horsepower for 180 volt motor will typically require about 550 amps at full load.
That same 500 horsepower load will only require 64 amps at 4,160 volts.