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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 ...

We know that the entire grid is at the exact same frequency (50Hz or 60Hz). This is because the grid is made up of synchronous machines. The difference is that of the phase angles. If you go back to the fundamentals of synchronous machines, you will see how important the frequency is to its operation. In fact, power transfer between two nodes depends largely on the angular difference between the nodes.

Load is inversely proportional to frequency. When load increases, that is curren ...

Most of the variable frequency drives (VFD) below 600 HP or so are IGBT with Diodes to supply the DC. If only six pulse the harmonics can become a concern if a number of VFDs are used on the same bus. One of the jobs I'm currently trouble shooting has 6x600 HP VFDs all connected to the same power source. This means that my harmonics are added together as there are no filters or phase shifting transformers. I expect the power factor at full load to be aro ...

Simple power factor correction calculation:
Motor input = P = 5 kW
Original P.F = Cosθ1 = 0.75
Final P.F = Cosθ2 = 0.90
θ1 = Cos-1 = (0.75) = 41°.41; Tan θ1 = Tan (41°.41) = 0.8819
θ2 = Cos-1 = (0.90) = 25°.84; Tan θ2 = Tan (25°.50) = 0.4843
Required Capacitor kVAR to improve P.F from 0.75 to 0.90
Required Capacitor kVAR = P (Tan θ1 &nd ...

In circuit theory, current through two series resistors is the same even if the resistors are of different resistances. It's the voltage across the resistors that is different. Look at reactors/capacitors, and it's the same thing. Now, current through parallel resistors is different through each resistor, as the current divides among the parallel resistors. So, put the meters in series on the secondary of a current transformer.

Now, whether one CAN put two of them in series, versus ...

Most DC drives do not have capacitors to generate reactive current, they draw current from the AC lines only. When the motor is moving slowly with high torque, the drive has to produce full current even though little work is being done. This current has to come directly from the line side. So, even though there is no power factor on the DC side (just high current and low voltage), a demand for reactive power is created on the ...

If you have an electrical circuit consisting of a capacitor (capacitance C) and an inductive coil (inductance L) and you load the capacitor, you will observe a sin-wave oscillation in this circuit as soon as you remove the supply. Caused by the losses, the amplitude of the oscillation will decrease with every cycle. The frequency of the oscillation is the natural frequency of this circuit and is given by 2*π*f=1/sqrt(L*C).

If you connect a frequency variable supply (exciter) in ...

When I at Siemens (my former employer) began building gvpi stators in the 100 mw to 300 mw size, we experienced serious vibration troubles on the end turns both locally in the series connectors and globally in the winding. This was evident in both the 50 Hz and 60 Hz fleets but was more serious in the 50 Hz fleet. This problem led to several forced outages and a few total losses. The problem was that the win ...

During the transient condition associated with acceleration of an AC machine started as an inductive load, current is drawn from the source that can be several times the full-load rating of the machine winding. To handle this current, the protective device (e.g. circuit breaker) located at the juncture of the distribution bus and the feeder to the rotating load should have an instantaneous setting and short time setting that will adequately protect the downstream equipment but will also avoid ...

Vibration is produced by the electromagnetic forces between the current-carrying conductors that make up the end-winding. The forces are proportional to the square of the current, with currents in the same direction causing attraction, and current in opposite directions causing repulsion.

The vibration can be reduced by improved support and bracing the end-winding, and particularly ensuring that the end-winding does not have natural / resonant vibration frequencies at or close to s ...

The application of capacitors generally falls in one of two categories - correction of power factor and correction of low voltage. The power factor correction aspect has been addressed above. The impact of the capacitors on voltage level is directly proportional to its kVar rating and the inductive reactance of the circuit. This is related by the following formula:

Percentage voltage rise = (kvar)(X)(l)÷((10)(kV)²)

where kvar = 3Ø kilovars
X = re ...

If the generation side of the point-of-common-coupling (PCC) is essentially an islanded setup consisting of a few specific generators, then the amount of harmonics resulting from the generation "source" can be readily identified in a mathematical fashion from the relative impedance on the generation side of the PCC compared to the combined impedance on the load side of the PCC. (The source of such harmonics is related to both the rotor geometry and the stator winding geometry of the rotating ...

Q:
I'm looking for ways to estimate the supply current to variable frequency drive (VFD) when an asynchronous motor is running under different torque and speed outputs.

Motor manufacturers usually provide the rated torque, rated current and rated speed of the motor, but when the motor is not running at the rated conditions, how can one estimate the supply current to the VFD from the actual speed and torque output of the motor?

A: ...

That's a reasonable, practical way to measure the approximate inductance. A couple of things to keep in mind:

(1) You're actually measuring the impedance magnitude, which will include both the resistive and inductive components of the impedance (but the resistive component is probably small compared with the inductive component);

(2) Assuming you're using true-RMS meters to measure both the current and the voltage, your estimate of the impedance will be affected by the h ...

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?