Induction Motor

SYNCHRONOUS: means "turns at a speed proportional to applied frequency independent of load".

For this to occur, the magnetic field on the rotor must be powered separately from the stator magnetic field. As Hector pointed out - the rotor field may result from permanent (e.g. rare earth) magnets, or from an electromagnet.

If the rotor field is electrically created, the current has to come from somewhere. One way to do this is to use a separate DC supply and supply power th ...

More specifically, a low voltage (LV) motor is normally <1000 V or <600 V, depending on who you ask. They are usually wound with round enamel-covered wire. This is called random-wound or mush-wound coils. Medium voltage (MV) motors, with voltages up to 13.8 kV or even higher, are wound with rectangular cross-section copper wire with enamel or mica tape insulation, depending on the voltage level. This is known as form-wound coils.

Because form-wound coils must be individually ...

During a discussion with a colleague, I came to know that for motors with antifriction bearings, you only need one accelerometer to measure the vibrations, whereas for motors with sleeve bearings two accelerometers are needed (one for measurement in X direction and other for measurement in Y direction).

ALL bearings are "anti-friction", otherwise they would not be bearings.

There are basically two types of bearing: non-contact (e.g. magnetic) and contact. The contact typ ...

Why do we need to Split the Stator of Single Phase A-synchronous (Induction Motor) unlike the 3 Phase Induction Motor?

A 3 phase induction motor has 3 different currents flowing through it... these 3 cause 3 different magnetic fields that are oscillating at 120 degrees (ideally) apart, the interaction of these 3 magnetic fields in the air gap causes a rotating magnetic field, this magnetic field rotates at a speed we call synchronous speed, which is also the maximum speed the motor ca ...

So called "sensorless control" of AC machines means having no mechanical (speed and/or position) sensors. However, usually this term only includes vector controlled drives, i.e. it does not comprise V/f open-loop control of Induction Motors (which is the simplest technique for driving an IM motor without a mechanical sensor).

For the induction mold, sensorless vector control is a mature technology, it has been around for a few decades. Almost all reputable drive manufacturers have ...

First of all, a DOL controlled motor may run in Fwd only, or in Fwd and Rev, depending upon the load and process (quad 1 or quad1 & quad 3 operation) - you simply switch it on/off via a contactor and it accelerates/decelerates between 0 and full speed, through its designed torque/slip curve. There will be no generation in these quads, the contactor is open, therefore the electrical supply to the motor windings is OFF and the motor will simply slow and stop in a load defined time (instanta ...

We were called in to replace an old imperial frame 180 kW motor on a circular saw because they needed a faster cutting speed. Shipping a motor of that size to a remote location was expensive, plus all the mounts and pulleys would have to be changed (imperial to metric and smaller frame size.). Instead we changed the VFD, the forced cooling fan and made some changes to the programmed cutting cycle.

With an older motor you often get more copper, and a lower efficiency. But you do get ...

Induction motor with squirrel cage rotor has two different speeds. The synchronous speed refers to the stator rotating magnetic field, which depends on the number of poles and frequency. The other speed is the rotor's. The rotor speed will be always slower than the stator speed, we call it slip. Without the slip, the squirrel cage induction motor doesn't have torque. Even without load the motor has slip. It increases with the load, according to the current x torque curves you can check it out ...

If we define nominal torque, it's generated at the motors peak efficiency point, that being at the apex of rated voltage and Hz. The lower the RPM, the higher the nominal torque, but the higher the current. Then, nominal torque is basically what the motor can generate continuously at the peak efficiency point without overheating. To define using nominal torque at zero speed is better defined as stall torque, and not really applied in high torque startin ...

For someone who works with machines that are for large, heavy-duty industrial processes (like steel mills), the answer will be different than if they come from a background of moderate process requirements (pumps and fans) or precision processes (servo motors, actuators, etc).

From my perspective (which is the "large industrial" side of things): I work with designs that have continuous torque ratings that start at about 4500 lb.ft (6.1 x 10^3 N.m) and go up from there. The largest ...

We are looking at an approx 90% + efficiency rating using asynchronous motors with the proper VFD's. With using regen instead of dynamic braking resistors, both in deceleration in traversal motions and in the overhauling effect of the load to the motor in lowering mode, the energy generated by the motor is channeled back to the line source, instead of being dissipated away as heat.
Crane

However, ...

The key factor in determining how much torque is available for a synchronous motor at startup is this: Is the intention to operate as an asynchronous start - or to supply power to the synch rotor field at zero speed and effectively have a synchronized start?

If the operation is for an asynchronous start, then the cage material can be adjusted to raise the available starting torque significantly (compared to a "plain" copper bar). To do this, higher-resistivity materials are chosen. ...

An induction machine isn't a constant power device and the power rating is specified at a specific voltage and frequency, decrease the voltage and you decrease the power.

It's a common misconception, from looking at
P=VI

That a given power rating will try to balance this equation and the same misconception that a 100W light bulb will always draw 100 watts, when in fact power ratings are always rated at a specific voltage and frequency. At the most b ...

The induction motor coming up to speed plays a large role and this involves rotor resistance and slip. Now remember when an induction motor is started the slip is equal to one and since the parallel combination between the magnetizing branch of the stator and the rotor circuit will be close to zero because of the extremely low impedance of the rotor circuit hence high starting current (the all so famous 6× full load current).

Now when the motor is at the full speed the slip i ...

When the induction motor starts the rotor winding is stationary and maximum voltage is induced in the rotor which will produce maximum rotor current. At starting the rotor is stationary and acts in a similar to a transformer with its secondary winding short circuited except that there is an air gap in the motor. At starting the motor current can be like 6 times of the rated current. The voltage is reduced during motor starting to decrease the current but still the current is much higher than ...

Case:
I am used a 20hp VFD in Hoist application (415v three phase). In this application there is a problem that in the time of starting main motor Drum is Roll back first. So to avoid this Roll back problem it is any possibly to increase the output torque of the VFD by changing the Rotor resistance of motor in VFD motor parameter group. What happen if I increased or decreased rotor resistance in VFD motor parameter group?
...

I do not understand how Power Factor can be affected with typical DC drives, as power factor only exist in AC system when the current wave is either leading or lagging the voltage wave. For DC drives, since phase angles do not exist, why would power factor be affected? This is also my understanding on why power factor is not affected on the line side of variable frequency drive (VFD), as AC voltage is first converted into the DC link volt ...

It is clear by now if a power factor correction capacitor (a capacitance) is connected across the terminals of an induction motor the power factor looking from the source side improves.

Let's consider an example of a 100 HP motor. The incoming KW is about 80 KW and the power factor is about 0.85 for a 4 pole motor. Slower speed motors have more iron, they are in larger frames, therefore require more magnetizing current. This ...

They were on two different subjects.
(1) Regarding unbalance in winding resistance - If the resistance that if the unbalance in phase resistance is more than 2% the motor has to be rewound.
However, this answer was given assuming the motor is wire wound. However, if it is a motor with formed coils, there exists a possibility that the motor could be partially repaired by detecting the defective coil and repairing/replacing the defective coil.

(2) The other part of the d ...

Recently tried to drive an IE3 15kW induction motor via a soft start. Although current rating is 29.5 amps for continuous running, the inrush for these high efficiency motors is much higher than that of lower efficiency motors. Motor stalled on first attempt, then tripped breaker. Ok - easy to think this was an overload as it was from a 32 amp mains breaker. Upon checking windings it could be seen that U1-U2, V1-V2 and W1 to W2 were all balanced at 0.1 ohms. Yes 0.1 ohms. Not exactly the resi ...