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The source of power is an ideal voltage source having zero internal impedance with a series impedance that can have both real (resistive) and imaginary (reactive) components. This impedance is for example the transformer impedance plus the impedance of the feeder to the bus. This is called the Thevenin's equivalent circuit. This is the bus voltage. When you connect a load to the bus you are completing the circuit with another impedance. So you have a circuit with a voltage source and two impe ...

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. ...

Few days ago, GoHz made a 24V 2000W power inverter in home, sharing some design schematics and circuit diagrams.


Power inverter testing. The picture was taken in short-circuited.

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Failure to balance the V/Hz ratio with 400V/50Hz motors in the US, to accommodate for the widely varying voltage levels in all of the sectional grids across the country results in significant starting torque and HP losses. Variable Frequency Drives (VFDs) capable of full motor voltage/Hz/RPM/FLA levels are the very best option for use of these motor types.

The overall power grid across the US was created over 100 years ago, and though it has of course been expanded across the enti ...

For a hoist application
1) You can make a sensorless VFD (variable frequency drive) work on a Hoist however... If an encoder is not used and the VFD doesn't properly sense that there is a problem (it might be a rare occurrence but I've seen it), you could potentially drop the load. It only takes once to seriously damage equipment, hurt someone or worse.


2) With an encoder, and proper br ...

The application of a filter to a power system requires that, first, you know how much capacitive vars are necessary to accomplish the power factor correction you seek. Then, the process involves measurement of system loads at the secondary of each transformer. The measurement must provide the harmonic content of the current. This is determined by harmonic magnitude and phase angel for each harmonic at each location. Armed with this da ...

Due to the form factor=1.11, so output voltage must be multiply of form factor, so we get 11,22,33. First let us define form factor before we go into the question:

The form factor of an alternating current waveform (signal) is the ratio of the RMS (Root Mean Square) value to the average value (mathematical mean of absolute values of all points on the waveform). In case of a sinusoidal wave, the form factor is approximately 1.11.

The reason is something historical. In old ...

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 ...

If the induction motor was really hot and you had a premature insulation failure, probably you had an overheating problem. The main reasons for this situation are:

* The voltage waveform created by the variable frequency drive (VFD) has high frequency harmonics that will cause an increase of temperature inside the motor. If your VFD-PWM has no filter outputs and the cable connection VFD-Motor is long, you can easily get a premature insulation ...

One of the advantages of using a DC test voltage is that the leakage current trip can be set to a much lower value than that of an AC test voltage. This would allow a manufacturer to filter those products that have marginal insulation, which would have been passed by an AC tester.

When using a dc hipot tester, the capacitors in the circuit could be highly charged and, therefore, a safe-discharge device or setup is needed. However, it is a good practice to always ensure that a prod ...

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 ...

There are three ways to explain Percentage Impedance:
1) It is the % voltage drop in secondary no load voltage when a rated full load zero power factor lagging current is taken from secondary. It is the price one has to pay for transferring the current from primary to secondary side. Higher the % impedance, higher the secondary voltage drop during loading. This drop (or rise with leading loads) depends on the X/R ratio of transformer and PF of the load. % voltage drop= % ...

I find that due to the fact that the variable frequency drive (VFD) rectifies the AC to a DC bus, the power factor drawn from the supply is near unity but has harmonics. Harmonic kill the power factor correction capacitors. You need to install harmonic filters to take out these unwanted inputs. GTOs used to power the electronics generally fail open circuit. If your VFD has a ramp down to stop you need to program in a fast stop. All safety devices like E- ...

Motor duty UPS is capable of delivering the high starting current demand of the induction motor. Bypass power supply is synchronized with the UPS output (via static bypass switch) to provide the additional current during motor starting. In most of the cases, motor is started only when the main supply is available. This helps in optimizing the UPS rating. Battery backup is used to keep the motor running in the event of power failure until the alternate power supply comes online. Hence in my op ...

It depends on where the switching is taking place. The key is to keep the live system always grounded and avoid grounding neutral at more than one point.

If you are looking at an application less than 600VAC, and you have multiple sources (such as utility and generator) and you have 4-wire loads, I usually recommend switched neutral as it allows complete isolation of the sources from one another, which refers to switching neutral of a transfer switch, where neutral switching would ...

An LCI drive is an old and different topology to a VSI AFE drive. The LCI drive has a long history and its advantages and limitations are well understood. It is simple and reliable, but requires careful attention to ac power system issues related to harmonic currents and reactive power. It also demands specially designed motors with low reactance, and must work with harmonic heating and air gap torque harmonics.

LCI drives have low input power factor, 0.5-0.92, especially at lower ...

The % impedance is formally referred to as impedance voltage. It is the supply voltage, expressed as a % of rated voltage, that is required to circulate rated current through the transformer.

It is measured in the factory by a short circuit test at rated frequency. With the low-voltage winding shorted, the supply voltage to the high-voltage winding is increased until rated current flows in the transformer. ...

What the system sees with a "standard" squirrel cage induction motor connected directly to the line is the inductive loading caused by the nature of the magnetic circuits within the machine design. This can result in a reactive power demand that is anywhere from 10 to 30 percent of the real power rating of the machine (e.g. power factor lies between 0.900 and 0.700). It also gets worse (i.e. farther from unity power factor) as the machin ...

In long distance driving, it's helpless when our phones or laptops run out of batteries while there is only ordinary charger on hand. Most cars don't equip with AC 110v/220v power supply. In such case, a power inverter works with the car will absolutely keep such awkwardness away from you, a car power inverter will convert 12v DC to ordinary 110v (or 120v, 220v, 230v, 240v) AC to feed regular power source to small household appliances. But, there are lots of things we need to pay attention wh ...

A variable frequency drive (VFD) will improve the system power factor to which it is connected, primarily because the motor reactive current is supplied by the DC bus, rather than the supply system. This will only improve the displacement power factor. Modern VFDs with AFE draw almost sinusoidal current from the supply, so power factor on the source side can be controlled up to unity and the generated harmonics are ...