Categories

# Induction Motor

#### Motor Running Speed

##### Friday, January 30, 2015

I have changed the existing winding with a different winding scheme. I have also changed the shaft of the rotor and bearing. Original shaft has been replaced with a new longer shaft and accordingly supported by a different bearing at the end of the shaft. Two touchdown bearing has also been used near the end plate to protect the winding. The question is that I know natural frequency of the rotor and if we bypass that frequency quickly then we can achieve higher speed. So what are the constrai ...

#### How fast can a motor go?

##### Tuesday, January 27, 2015

The rotating speed of the stand was nowhere near enough, so we made an emergency plan with a Variable Speed Drive on the original (4 pole) motor - up to about 200 Hz. This was still not fast enough (we reached the constant power flux limit) so we procured a new 2 pole (22 kW) motor.

I must emphasize that this was an absolutely standard off-the-shelf (Chinese manufacture actually) motor from our sister company who supplies these motors. There was absolutely nothing special about it ...

#### Induction motor over speed limitation

##### Saturday, January 24, 2015

Reputable manufacturers are required to design the mechanical system of an induction motor (or generator) to be mechanically safe at a minimum of 25 percent above listed nameplate maximum speed. In some specific instances, a user may have defined something even higher, but the chance of this is vanishingly small.

What "mechanically safe" means is that the rotating components of the machine will not "break" under the higher centrifugal / centripetal loading resulting from the highe ...

#### Star/Delta motor connection 380V/220V

##### Thursday, January 22, 2015

If the motor is designed to run in star a 380V 3-phase power supply, then it cannot be connected in delta on the 'same' supply. That would be the equivalent of applying 380 volt to 220v windings so clearly the motor would fail.

Note that in star, each winding gets root3 of the applied voltage (or 380/1.732) connecting in delta means that each winding get the phase-phase voltage EG 380V.

If the motor is rated at 380V - 'delta connected' then it could be connected in sta ...

#### Should I oversize induction motor for the loads?

##### Wednesday, January 21, 2015

If your load requires a motor, say 50HP, then you should use a 50HP motor. The motor is designed to provide the HP required by the load. If you use a higher HP motor you may lose efficiency and power factor (PF).

In general, all the trick is to use smallest motor that is capable to drive the load at 100% duty so its temperature doesn't g ...

#### Under loaded electro motor power consumption

##### Tuesday, January 20, 2015

Just a basic analysis if your motor is rated for 30 kW then the rated HP is 40 and actual load on the motor will be 29.5 HP. If the source system is considered stiff then supply frequency doesn't change. Torque varies with the motor terminal voltage squared so the torque being at 75% of motor rating means voltage can be decreased to 87% to have run adequately (assuming slip stays constant).

Reality is that the supply voltage (again system is stiff) will not drop so to compensate sl ...

#### Generator Power Factor

##### Monday, January 19, 2015

The Power Factor used to declare power ratings on three phase generators is 0.8 (so 100kVA = 80kWs etc.). Unfortunately the difficulty for installers is understanding the effect of power factors within an electrical installation is a changeable situation dependent on equipment within a load. This is something that the installation engineer needs to understand when specifying a generator for a load and in my experience the best method of evaluating what happens in a load is to test it for a le ...

#### Improve Mechanical Efficiency by a Variable Frequency Drive

##### Saturday, January 17, 2015

For the only reason that actually we have on the industrial market enough technology and tools to comply with all process using rotating machine, so actually just having a look to technology is not enough anymore.

And more than this if we build high efficiency product and we talk a lot all around the world of energy saving is not only for fun, but to push people working in technical business like ours to go a bit more deeper than just make something moving and more and more take c ...

#### How capacitors improve induction motor efficiency?

##### Friday, January 16, 2015

A single phase motor is nothing but an AC electro magnet. In order to spin the rotor we need a rotating electric field. By adding two more coils and a capacitor to cause phase change we get two magnets and a time delay between their cycles - like magic we have a rotating field.

Many parameters of inductance, resistance and capacitance need to be optimized for high efficiency. Once the motor is up close to synchronous speed some designs switch out the second set of coils with a cen ...

#### Can I drive a 40hp load by a 100hp motor?

##### Thursday, January 15, 2015

If you know your load is exactly 40 Hp, never higher, then it's best to use a motor that's rated for 40 Hp. The nameplate rating of a motor means that is where it was designed to run most efficiently. If you use a higher Hp motor than you need, you will just be running somewhere in the lower part of it's speed-torque curve. Your efficiency will not improve if you use a 100 Hp motor but only load it to 40 Hp.

Also, many motors have a service factor of 1.1 or 1.25. If it does, then ...

#### How induction generator works?

##### Thursday, January 8, 2015

In its simplest form an induction generator is simply an induction motor that is rotated above synchronous speed. Unlike a synchronous generator, the field in the rotor is created by drawing large amounts of reactive current from the line.

Synchronization is automatic because line frequency is applied to the stator once the prime mover has accelerated the rotor to near synchronous speed. Remember, unlike a synchronous generator, there is no rotating field on the rotor until it is ...

#### What is a Gearbox and What does it do?

##### Wednesday, January 7, 2015

Gears are used for transmitting power from one part of a machine to another. In a bicycle, for example, it's gears that take power from the pedals to the back wheel. Similarly, in a car, gears transmit power from the crankshaft (the rotating axle that takes power from the engine) to the drive shaft running under the car that ultimately powers the wheels. You can have any number of gears connected together and they can be in different shapes and sizes. Each time you pass power from one gear wh ...

#### The purpose of capacitor on single phase motor

##### Monday, January 5, 2015

In single phase motors capacitor is used to convert motor to two phase. Otherwise the single phase motor will not have starting torque. Capacitor is connected in series with the starting winding of the motor. The value of the capacitor depends on the starting torque required. Phase advancement in the starting winding with respect to running winding is the key. There is nothing called as 3 phase capacitor or single phase capacitor. Capacitors are individual components and have only two termina ...

#### Induction Motor Working Principle

##### Thursday, December 25, 2014

Induction motors operate on the principle of current induction in the rotor which must rotate at a speed less than synchronous speed for induction to occur. This is referred to as slip speed and should not be confused with pole slipping.

Why induction motors have no pole slipping and why other motors have pole slipping? I will attempt to answer this for you but first let's define poles and synchronous speed in regards to electric motor operation.

Poles in an electric m ...

#### Why using dynamic braking resistor in motor speed controls?

##### Monday, December 22, 2014

The power developed by Induction motor during idling time if wasted in power resistor used for braking is called dynamic braking resistor. Dynamic braking resistors are used to dissipate the power generated by the motors during dynamic braking. Typically, the variable frequency drive (VFD) will rectify the power back to a DC source and the resistors are cut into the dc link via a heavy-duty contactor. The power is then converted to heat in the braking resistor grids. These resistors must be a ...

#### Distance between VFD and motor

##### Sunday, December 21, 2014

The value of critical distance depends on the propagation voltage and output rise time so as much the value of propagation voltage the critical distance will be increases. Mostly variable frequency drives (VFDs have same critical length and it already mentioned in VFD manuals so there is no need to measure the critical distance as you can get information from your distributor or manufacturer of the VFD.

Some manufacturers of large variable frequency drives integrate output circuit ...

#### Can an electric motor run as a generator?

##### Tuesday, December 16, 2014

YES, but it can only be done long term with an electric motor that is designed to also run as a generator and if the generator will be paralleled with other generation the motor will need to be a synchronous motor.

I served in the US Navy on a submarine as an electrician nuclear qualified. My electrical plant includes 2 - 500 KW motor generators. When the AC end was operating as an AC motor the DC end was a DC generator that supplied power to the sub's battery, reverse current and ...

#### How to design an induction motor for wide voltage fluctuation?

##### Saturday, December 13, 2014

In villages sometimes we have to face this problem of voltage fluctuations...normally we design induction motor (single phase) for 230 volts rated. So it can work satisfactorily for 200 volts to 240 volts range but due to some reasons our supply may give us 150-160 volts so in that case induction motor draws more current which causes i^2 R LOSSES, consequently heating so we want to get rid of this problem by doing any modification in motor (stator winding).

The voltage variation fr ...

#### Variable Frequency Drive makes induction motor smart

##### Sunday, December 7, 2014

Variable frequency drive (VFD) is a whole science and even a very broad deliberation here will not give you any good picture. I was teaching VFD course for one of the manufacturers and for an introductory session I talked for 8 hours, full course - 5 days and this is still just facts. Surely, you can buy 1HP VFD hook to 1HP motor and it is going to work regulating the speed by a pot on it. However, if you buy 4MW (that is 4 mega watts) VFD to run pil ...

#### Cautions of VFD on existing motor

##### Friday, December 5, 2014

Just a note of caution if you are going to use a variable frequency drive (VFD) on an existing motor it should be manufactured with at least Class F insulation and be rated for inverter power source. Because of the PWM (Pulse Width Modulated) waveform there is residual heating and most motors will go to 1.0 SF from 1.15 SF. There can also be issues relating to lead lengths in excess of 100 feet or more, output filtering may be required, ie. ...