Posted on 20th Oct 2022

A revolving magnetic field produced by the stator windings intersects the windings on the rotor of an AC induction motor.

The rotor rotates just a little bit slower than the motor's synchronous speed when the load is at maximum speed.

This is because if the rotor rotated at the same speed as the magnetic field, there would be no relative motion between the rotor and the magnetic field and no torque would be produced. Instead, the magnetic field causes currents to flow in the rotor windings, producing a torque that turns the rotor.

The motor slip is the difference in speed between the rotating magnetic field and the rotor.

The motor produces more torque the higher the slip.

The quantity of poles or coils arranged around the stator and the frequency of the supply current determine how quickly the magnetic field rotates.

The term "synchronous speed" refers to this.

Understanding how VFD drives affect the motor and electrical distribution system is necessary for their effective installation and upkeep. Check out Darwin Motion VFD complete process.

Induction motors can experience impacts when VFDs are applied; these effects must be taken into account for successful functioning.

Examples comprise:

• As a motor is slowed down, its capacity to effectively cool itself decreases.

With prolonged operation at low speeds and large loads, the motor may need to be oversized or driven externally.

• The operation of driven equipment at various speeds can result in mechanical resonances.

The motor's functioning range should be defined, and these speeds should be programmed outside of it.

• Harmonic voltages and currents produced by VFDs have the potential to occasionally have negative impacts on the electrical distribution system and interfere with the operation of equipment.

A qualified individual should inspect the electrical system if a power quality issue is detected.

To reduce these effects, isolation transformers, line reactors, or filtering equipment may occasionally be needed.

When purchasing VFDs, filtration devices should be taken into account in order to reduce electrical system power quality problems.

To analyse and ascertain this requirement, a practitioner skilled in this field should be used.

The skilled specialists at General Tech Services can develop and choose the best Darwin Motion VFD drive base for your systems.

We can design and provide panels as well as install them on schedule.

The most dependable VFD supply and service provider in the UAE is General Tech Services.

Electricity for Drives

An appropriate electrical supply is necessary for the safe, effective, and dependable operation of AC drives.

Standard voltages for single phase drives are 120 and 240 volts.

Standard voltages for three-phase motors are 200, 230, 460, and 575 volts.

To account for voltage losses from the distribution transformer to the point of consumption, the distribution system's nominal supply voltage is typically higher than the drive nameplate voltage.

How should I pick a VFD?

The temptation might be to size a variable frequency drive (VFD) only on the basis of horsepower.

Did you know that choosing the right AC drive for your application requires taking into account six more factors?

Learn more about the six things you need to take into account when picking a VFD by reading the information below.

Amperage at Maximum Load

Making sure the drive can manage the motor's current needs is the first step in this process. Find a drive that is rated for at least that much current by checking the motor nameplate for the Full Load Current requirement. Use the drive ratings for single-phase if you are feeding the drive with single-phase electricity. For single-phase operation, variable frequency drives are severely derated.


Verify that the drive can withstand any overload situations, such as those that may arise during starting or from sporadic additional stress.

Until you locate one that can manage it, you might need to increase the drive's size.

Due to beginning needs or impact loading, many programmes occasionally suffer overload circumstances.

The majority of AC drives are made to run for 60 seconds at 150% overload.

The AC drive needs to be expanded if the application calls for an overload of more than 150% for more than 60 seconds.

Type of Application

Variable torque (VT) and constant torque (CT) are the two application kinds, and there are different ratings for each.

For fans and pumps, use VT ratings, while for conveyors and general machine control, use CT ratings.

Understanding the application type is crucial because it determines how the drive specs are arranged.

It is advised to use CT if you are unsure which one to use.


The cooling of your VFD is also influenced by the altitude at which it is being used.

The air becomes less dense as one rises in altitude.

This drop in air density lowers the air's capacity to cool things down.

Most VFDs are made to work at full capacity up to 1000 metres above sea level.

The drive needs to be larger to make up for the decreased cooling at higher altitudes.


The inside temperature of an enclosure may rise over the drive's recommended operating temperature due to the substantial amount of heat that AC drives produce.

There can be a need for cooling or ventilation in the enclosure.

Calculate or measure the highest anticipated ambient temperature.

Vehicle Frequency

In general, you should search for the lowest carrier frequency that your motor is capable of handling.

The default carrier frequency will typically be adequate, but if you need to lower the audible noise, heat dissipation, or power consumption, ensure sure you can change the drive's carrier frequency.