Motor Control

For induction motors if you run the motor at a high flux level the winding flux magnetizing current has a significant third harmonic content that can flow around the Delta winding without appearing in the lines to the VFD.

This is good for the flux waveform but it is not seen by the VFD internal current sensors so you can over-flux and get high motor winding currents giving motor overheating with no indication in the VFD. So with Delta I recommend winding current sensors but this i ...

The torque speed curves are completely different between an induction motor and slip ring motor. You need to understand the differences. If you have selected your slip ring motor to limit starting currents you can short out the slip rings and run your motor but the starting torque is reduced unless you use some features on the VFD to boost starting torque.

If you are using it as torque control on a crane then y ...

The Dahlander motor refers to a specific set of optional connections to the main stator winding. These are done OUTSIDE the motor frame (or at least within the main terminal box).

This gives a single pole count for the motor, and the VFD can effectively control the machine as if it were not capable of multiple connections.

The VFD - by itself - cannot "switch" the lead connections to achieve a different pole count. However, it can modify both the applied voltage and freq ...

The main difference between slip ring and cage types is that the slip ring rotor generally has a much lower slip at full speed than the cage rotor if it is properly shorted directly at the rings. We need to check that the variable frequency drive (VFD) slip setting can go low enough. Otherwise only general things need to be considered......mainly the insulation quality of the stator since its likely you are dealing with an older motor.

The slip-ring motor has slightly different imp ...

The only requirement for open loop control is to maintain proper voltage current and frequency to the motor. Motor is run in closed loop where you need controlling. For example in a 3d printer you need continuous control of motor rotation, so you need to provide feedback to know the motor position.

A pressure transducer driving a VFD driving a motor driving a pump to provide a set pressure would be a closed control loop. The motor itself is operated open loop, as part of a closed p ...

Variable frequency drive (VFD) will capable of varying the output speed of a motor without the need for mechanical pulleys, thus reducing the number of mechanical components and overall maintenance. But the biggest advantage that a VFD has is the ability to save the user money through its inherit nature to save energy by consuming only the power that's needed.

A VFD will convert its incoming power, fixed voltage and frequency to variable volta ...

The current drawn at starting (starting current, also called "locked rotor" or "inrush") is directly proportional to the voltage applied at the terminals. This is why soft starters (also called "reduced voltage" starters) are used in the first place.

A reasonable assumption for "standard" squirrel cage induction machines is to assume that the motor will draw somewhere between 7X and 10X the rated line current if started direct-on-line at full rated voltage. As the machine speeds up ...

All driven loads have some relationship between power and speed. As a general statement - more power is consumed at higher speeds.

Most motors are designed to operate at a constant speed and provide a constant output; however, modern technology requires different speeds in many applications where electric motors are used. A variable frequency drive (VFD) is a device that regulates the speed and rotational force, or output torque of mechanical equipment. Effects of applying VFDs are ...

The soft starter is actually quite a simple device and in many applications, you must use some form of reduced voltage starter to reduce the starting current of the induction motor. If you are compelled to use a reduced voltage starter to reduce electrical disturbances, or to reduce torque transients, then that is a good reason to use a soft starter which complies with these requirements and is stepless and ea ...

Friction losses in motors (AC or DC) are pretty simple when you get right down to it. Basically, any book on the relevant bearing type (sleeve or rolling element) will cover almost everything you need to know.

Induction motors (both squirrel cage and wound rotor) are pretty easy, as they're essentially cylindrical. This means the "friction" developed from moving the rotor through a medium (typically air) is minimal. As the rotor geometry deviates from a true cylinder toward a "fan" ...

Is there any problem in conducting dynamic balancing of rotor with lower rpm than the rated rpm of the machine? For e.g. for a 3000 rpm motor rotor if we are doing the dynamic balancing @ 750 rpm will it create any vibrational problems. If it is so what is the acceptable speed limit for doing the dynamic balance of 3000 rpm rated motor rotor.

As a minimum, the equipment really should be balanced at operating speed. The "acceptable" capability limit of the facility performing dynami ...

There is more than three protections methods for this case.
1-You can use overload with phase failure detection function this device monitor the current at the three phases if there is no current at one phase the device stop the motor.
2-You can use a sensitive phase failure relay with unbalance detection function and adjust the action time to 0.1 second and the rate of unbalance to less than 5% when one phase loss a high current pass through the other two phases that make drop down ...

We have done several years of research on recycling rotating electric machines. We have tried to identify new guidance on this matter. We conclude:
1. There are cases where a rewound motor is better than a new one. We have the opportunity to design the winding tuned to the application. The result in this case might be an upgraded motor.
2. The biggest problem we identify in our research has been mentioned by several discussions. The magnetic core might suffer degradation during repa ...

How can I control through the VFD Torque for a motor as I have a pump motor of 110 KW of rated current 200A controlled by Soft Starter and during the actual operation it consumed only 65 KW with 98A so I want to change this motor with another one lower in KW with VFD to control at the new motor Torque, so how to do that?
If the new motor is large enough to provide the load requirements then reducing the motor size will not affect performance. It is the load that dictates torque required ...

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 ...

A very common problem affecting submersible motors is over-temperature. Causes for over-temperature include pumping hot water, overloading of the motor by the pump, loss of cooling flow past the motor, ochre or scale buildup and frequent motor starts and stops.

Submersible motors somehow must cool themselves. This is accomplished almost universally by transferring the motor's internally generated heat to the water that is flowing past the motor and into the pump. Most standard wate ...

Q: I heard that if we have a 3 phase induction motor constantly operating under 40% of rated power, we can reduce its losses using a Wye connection. But I can't find any reference of recommendation about that. So is it a practical solution to maintain energy efficiency? And is there any practical intelligent Wye-Delta switch?

The voltage across each winding drops by sqrt(3). So the torque-speed curve is reduced (by a factor of 3). The equilibrium speed is only slightly changed, but ...

Question: I have a motor of 100HP with FLC of 123A. It's load is Centrifugal Fan. We are currently using a Star Delta Starter. It's current in star mode various from 276A to 220A for 35secs. Is it safe? While changeover in delta it takes a peak of 376A and then comes normal 60A phase current. In this operation we are using a microprocessor based relay which is bypassed initially for 25 seconds. I want to know how safe is this operation and life of motor in long run. Or should ...