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# Induction Motor

#### Difference between star and delta connected motor

##### Thursday, December 4, 2014

Star connected motors have a central connected point, called a short circuit point or star point and each winding receives phase voltages (230volts), star connected motor only run at one third of the motor rated torque and power, whereas delta connected motors have no connected point and each winding receives line voltages (415volts) and operates at full torque and power.
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#### Can I run 2 parallel VFDs on one motor?

##### Wednesday, December 3, 2014

I believe you are more concerned with why a single motor should be running using 2 variable frequency drives (VFD):
The primary requirement will be catering critical application where the shutting down of the motor is not feasible just in the VFD fails so we go for redundancy concept which is possible in certain makes of VFDs.

Load sharing is also a requirement in order to avoid loading of a single VFD and reducing its life, where 2 VFDs of motor FLC is selected but ran on 5 ...

#### What's the minimum frequency (speed) can a VFD run?

##### Wednesday, December 3, 2014

What really happens with a variable frequency drive (VFD) / variable speed drive (VSD) and the actual frequency that is imposed on the electric motor terminals? For induction motors, it is never 0 Hz. For synchronous motors - it can be DC / 0 Hz - but this is only in the case of Permanent Magnet Synchronous machines, and motors with Wound Fields that have the ability to supply significant Current into the wound fields at standstill.

I am not going to discuss synchronous motors fur ...

#### Induction generator synchronization with grid

##### Wednesday, November 26, 2014

You can find a simple explanation of what an induction generator can do. It is totally self-synchronizing with the grid it is feeding power into. It stays in sync and delivers energy as long as it is driven at an rpm higher than its synchronous speed. If it is feeding a 50 Hz power supply it must be driven 2% to 5% above ts sync speed. Sync speed is 120 X frequency / number of poles thus a 4 pole machine ...

#### How you define a Heavy Duty Motor?

##### Saturday, November 22, 2014

Most modern motors are built to standards and frame sizes, efficiencies, power factor are very close from manufacturer to manufacturer. The definition depends on what you mean by "Heavy Duty". Examples would be "Punch Press" or a "Rock Crusher", anything with a high inertia or heavy intermittent load. If the load is a high inertia load the first thing to look as is the design letter of the motor. The standard motor is Design "B" and a motor for a high inertial load should be Design "C". A mot ...

#### What is Motor Stalling?

##### Thursday, November 20, 2014

In a simple definition, motor stalling means that the electric motor has more load on it than it is designed for and it can no longer supply enough torque to keep it spinning. In general this could happen at all types of motors. The main thing is when the load torque has increased more and more (which is above the characteristic of the main torque of the motor) so called "overload region" where the motor develops its maximum torque. At this point if the load torque is further increased the sp ...

#### Using soft starter to build an intelligent motor control center

##### Thursday, November 20, 2014

Once a time one of our customers ask to install three numbers of 150HP capacity soft starters (with auxiliary I/O's) to build an intelligent motor control center. Their main goal is to limit the high starting current of the chillers compressors. They do not need an expensive variable frequency drive (VFD) as the system is designed to operate at full capacity most of the times. They need a AC motor soft starter with Modbus RTU communications ...

#### What's the way to wind an 8-pole induction motor?

##### Wednesday, November 19, 2014

First of all think of a DC Motor. If it is an 8-pole motor is will have 8 field coils evenly spaced all the way around it. Now, in an AC Motor with 3-phases you will have the 8-poles 3 times. That means you would have 24-groups of coils. If the motor has 48 slots and 48 coils you would wind the stator with 24 groups of 2 coils. If you were to go round the 24 groups of coils and number them 1, 2, 3 repeat all the way around you would have 8 number 1's, 8 number 2's and 8 number 3's. All the nu ...

#### How to determine the pole number of an induction motor?

##### Saturday, November 15, 2014

There are many much more interesting questions related to the pole number of induction motors, e.g.:
1. Does the induction motor supplied by the main grid (say, 50 Hz) increases its torque capability in "p" times with growing pole number "p" since its speed decreases in "p" time (like in a gearbox)?
2. Let's we have an induction motor with p=2 and feed it from 50 Hz grid. Then we re-connect the winding coils to arrange p=4 and feed if grow 100 Hz grid. Are performances of these tw ...

#### Efficiency of a 2 pole motor running at high frequency

##### Saturday, November 15, 2014

While modeling a 2 pole motor for 250Hz, we found out that at frequencies above 80Hz there is little to no difference in efficiency between a magnetizable or non-magnetizable shaft. We found this odd, because the field lines go through the shaft in either configuration. So we put a motor with and without a magnetizable shaft on the test bench and tested it between 0 and 135Hz. The results were compliant with the model, but not able to explain the phenomenon.

There is a relationship ...

#### Why does a PM AC motor need a VFD?

##### Tuesday, November 4, 2014

The brief observations that follow will assume that you have a 3 phase permanent magnet (PM) AC motor. In a PM AC motor, max continuous torque is achieved when the stator MMF (or current) vector is 90deg displaced from the rotor's flux vector. Recall the Torque = Rotor_Flux x Stator_MMF ... i.e. the torque is the vector cross product of the vector Rotor_Flux with the vector Stator_MMF, or Torque = |Rotor_Flux| * |Stator_MMF| * sin(theta), where theta is the angle between the two vectors. Torq ...

#### What is vector control of induction motor?

##### Monday, November 3, 2014

The stator voltage and current to an induction motor produces a magnetizing flux to transfer the stator energy to the rotor. In Scalar or V/Hz control, this control does not provide very accurate speed regulation typically in the 2-4% range. This accuracy is good enough for controlling fans and pumps, since the control parameter is not speed accuracy, but temperature or pressure control over an average time period. Also using scalar or V/Hz control, you cannot control zero speed, ie no holdin ...