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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 ...

This is one of my favorite topics and have been involved for many years. The point to remember is that in Beemans, it says that while harmonic currents are theoretically possible, there is no reason to be concerned about them. That book was written sometime around 1950 or earlier. I am not sure. However, the point made is important. A harmonic problem doesn't exist until you have one. At that time we didn't have many power electronic devices.

What this means, is that harmonic curr ...

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 ...

There is a widely spread error that it was introduced by Nicola Tesla. Nicola Tesla was mostly interested in 2-phase system that is usually referred as "poly-phase" system in the USA. He also created 2 phase induction motor. You can find a picture of that design from Internet. (I should mention, the first induction motor was invented and built by Ferraries from Italy, it was single-phase one and had slipping of 0,5!!! As result, efficiency was very low).

The 3-phase system was deve ...

For large mills requiring variable speed, the wound rotor motor and SER drive are economical for a total rating of approximately 2MW to 16MW. Above 16MW, the gearless drive (cyclo-converter) is typically used because gearboxes and pinion gears reach their present limit in size. Around 2MW and below, the squirrel cage/VVVF drive is simple and cost effective.

Advantages of the wound rotor/SER drive are:

1. If the SER converter drive fa ...

We have 220 DC (UPS) distributions board supplying 220v/110v converters and 220/24v converters, only in the 110 dc board we get a frequent earth fault alarms in DCS (every 30 min not a permanent ) the problem that we can not localize which feeders are making the fault due to the big number (more than 100 solenoids valve are supplied ) and when we make the voltage monitoring all of them are indicating an unbalance value between + and ...

Transformers are essentially 2 coils of different number of turns linking a common time varying flux, so that different voltages can be connected on the two sides. Three applications arise: 1. Using transformer to drive a load with voltage rating different from that available at the source. This is power transformer action. 2. Using it for instrumentation, i.e., measuring currents of hundreds/ thousands of amperes with a low range ampere meter. No 'power' is expected to be drawn through it by ...

The calculations are no different than those for determining how to start a large synchronous motor, it all depends upon the type of generator and how big it is relative to the system that you are connecting it to. Take a look at the SLD (Single Line Diagram) and get the GSU (Generator Step Up) transformer rating and impedance, transmission line impedance to the grid, as well as any information that you have on the generator. Then you can determine how much the voltage will dip if the generat ...

For the Logic Power supply I want to convert AC 120/240V to 24/15/5/3.3 VDC. I am wondering what is the best topology to do this. Currently I am using a power transformer to convert down to 24vac rectify and tap off of that. Is there a way to reduce/remove the power transformer? Should I change to a flyback style of converter? I need about 5-10 Watts DC power total.

If you do not care about power factor (means no need of power factor correction), then indeed a possible solution is ...

Most of the users installed variable frequency drive (VFD) near the MCC because it's easy to maintain the system but there are some issue's which may happen due to placing the VFD near the MCC like there is a kind voltage reflection issue if the length of the cable is more than the critical length which may damage the motor.

In this case we need to follow instructions given in the user's manual supplied with the variable frequency drive. Generally following are recommended by manuf ...

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 ...

Three major issues in designing a power electronic system are Losses, EMI (Electromagnetic interference) and Harmonics. These issues affect system cost, size, efficiency and quality and it is a trade-off between these factors when we design a power converter. In power electronics, high voltages and high currents are processed by fast switching to reduce losses which are significant sources of electromagnetic noise and it cause additional costs.

Magnetic interference in power system ...

Generally, provision of effective earthing system depends on aim and goal involved, and the environment where the earthing or grounding as the case may be, is actually required. For instance in Power Engineering, providing adequate Earthing in a substation is an important essential safety measure. The aim and goal is to provide under and around the substation, a surface of uniform potential, at near or absolute zero earth potential.

In some cases, earthing or Grounding terminology ...

Understanding the motor load is critical to specify a VFD. There are three basic types of load; constant torque, variable torque, and constant horsepower and you only need to know which you have. The machine defines it; the VFD difference is the amount of overload they allow. There are also options available for overhauling/regenerative loads.

PWM VFDs are still the predominate type and are simple t ...

It is possible. However, UPS, VFD etc. manufacturer's follow the IEEE519 recommendations for the allowable I & V limits. Generally, the user must specify for the requirements of IEEE519. But, there will be other Non-Linear loads are not only Electronic Converters but also Ferromagnetic Devices e.g. Mag. Ballasts, Trafo's, Mag. Circuits etc. and Arcing Devices e.g. Arc Furnace, Fluo. Lights etc. These Non-Linear Loads produce Harmonics which are classified as Excursion and flow where there ...

Many installation sites need electric power for construction activities. When the site not large all construction equipments are powered with single phase supply. Such single phase DG sets may be available. Site gets single phase supply from utilities for construction. A new construction equipment requires a three phase supply. We have three DG sets of small capacities say 10 KVA etc. With this single phase DG sets can we provide supply to a three phase construction gadget?

Yes, ho ...

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 ...

Under the conditions of a stuttering arcing ground fault (intermittent arc condition), the voltage to ground of the phase voltages can increase to many times the magnitude of the line-to-line voltage. I would not want to attempt to mitigate that with a surge arrester. You can have the same advantages of an ungrounded system (such as continuity of service), and control the transient overvoltage by applying a high-resistance grounded system. Hence my comment to convert the ungrounded system to ...

The rectifier switches (SCRs or IGBTs) are likely the only components that will be similar between AC drives and DC drives. There will be many differences some of which are the design of the energy storage and filtering components (inductors, capacitors), the control of the DC section and the inverter control and switching in the AC drive, the design range of the DC bus voltage (for the DC drive it needs to go to zero; for the AC drive it does not).

An AC drive does contain an int ...

A power adaptor is a devise or means by which any utility can be used / accessed without any changes to the property of the utility, only used to match the devise. While in the power converter some of the metrological properties will be changed either type or quantity.

I would simply make out the difference as
Adapter - change of AC to DC power with required voltage level but specification like voltage and currents are fixed for example SMPS which is commonly ...