Harmonics

Depending on your local electrical code, if you need a grounded (earthed) system, you can use a 400V-Delta to 208/120V WYE transformer to feed a variable frequency drive (VFD), and then set it a 60Hz to supply 208V 60Hz to the motor. Although I do not normally recommend it, if it is appropriate for you to run the system ungrounded (unearthed), then you can feed the VFD with through a 400V-Delta to 230V-Delta transformer and then supply the motor with 230V 60Hz power from the VFD. (As with mos ...

Harmonic waves are commonly generated by any equipment that utilizes capacitors, think VFD and a multitude of single phase equipment. You will probably have to install power factor correction to get the best from your generators and these capacitors also generate harmonics. Unlike faults, the harmonics generated are not likely to trip the equipment circuit breakers and thus affect the power supply system. It causes ripples in the voltage sinus wave, one effect this produces in practical terms ...

We know that harmonics are generally due to the non linear loads connected at the load end. But whether harmonic distortion is increased or decreased by changing the X/R ratio of the source, feeder, transformer etc. And whether injecting power factor correction equipment into the grid will have an influence on harmonics.

Are harmonics produced only due to the non linear loads or also due to various other aspects in the trans ...

The 3rd harmonic currents are not in phase with each other, they are just at 150 Hz but still 120 degrees apart relative to their period now being 6.67 ms instead of 20 ms - i.e. the zero crossings on each phase now occur every 3.33 ms instead of every 10 ms and are spread apart as a normal 3-phase set of waveforms.

But that does not mean that the A phase @ 150 Hz is in phase with the B phase and in phase with the C phase.

Remember what a delta is doing - we generally re ...

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 dat ...

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 arou ...

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 ...

Anything that changes the voltage (or current) waveform from a pure single-frequency sinusoid (in the case of AC) or a pure "flat line" (in the case of DC) is considered to be harmonic distortion.

In actual fact, there are transient conditions - events measured in the 0.001 to 0.05 second range - which cause such distortions very frequently (typically on the order of several times a second), even around the home. Such instances can be caused by switching (physically closing or open ...

According to standard BS 7821 part 4: A distribution x-former supplying non-sinusoidal load would end up with few percent of overloading with respect to same amount of sinusoidal load which is usually reflected in X-former sizing procedure by a k-factor, I suppose. However, taking up to 20% of spare capacity in distribution x-former sizing, this will hardly result in over temperature trip out unless in case of very marginal sizing design or poorly filtered non-sinusoidal loads e.g. variable f ...

Harmonics cause overvoltage, through resonance and amplification. Zero sequence harmonics are commonly known as triplens and add in the neutral of a 4-wire 3-phase system causing neutral overload and heating. Negative sequence harmonics cause additional losses and heating in motors by producing a magnetic field that rotates in the opposite direction to those driving the motor (positive sequence).

Harmonics is a frequency domain interpretation of a time domain reality, distortions i ...

Simple answer is any current carrying cable can cause EMI in an adjacent cable. The "noisier" the source cable is, the greater the EMI. Too provide a quantitative answer, many factors need to be defined. Say on a 22 kV cable, you would need a lot of harmonics to cause EMI.

First, I would assume this is a 3-phase industrial/utility/marine installation, where you may have cables running in trays, racks, or conduit banks; and the conduit is not ferrous. Threaded rigid steel conduit w ...

Passive filters consisting of a bank of tuned filters and/or a high-pass filter have been broadly used to suppress harmonics because of low initial costs and high efficiency. However, passive filters have the following drawbacks:
1) Filtering characteristics are strongly affected by the source impedance
2) Amplification of currents on the source side at specific frequencies can appear due to the parallel resonance between the source and the passive filter
3) Excessive harmon ...

Power Factor is defined as the ratio of the active power to total power. When the load has linear behavior (motor for instance) the current is sinusoidal and power factor equals the cosine of the angle between current and voltage. Voltage (or current depending on the circuit) injection is used in nonlinear circuits in order to increase Power Factor.

In case of nonlinear loads, generally associated with power supplies and rectifiers used to feed computers and battery chargers, the i ...

It's been nearly 30 years since my first encounter with harmonics due to switching mode power supplies. A 75 KVA transformer with almost no measurable load using a conventional clamp on ammeter was so hot I couldn't touch it for more than a couple of seconds without getting burned. Thermoscanning showed up cherry red. Switching the transformer to a 112.5 KVA known to be reliable helped some. The source of much of the harmonics was a large photocopy machine. Ever science it has become increasi ...

For Metro DC traction power systems, the commonly adopted nominal voltages are 750V DC and 1500V DC. The DC substations are normally fed from a High Voltage (HV) 11 kV or 33 kV 3-phase AC network in the UK. To convert the 3-phase AC voltage to DC voltage, a modern DC substation employs a 3-winding transformer (delta-delta-star) to feed a 12-pulse rectifier (consisting of 2 x 6-pulse diode bridges, the outputs of which are connected in either parallel or series to form a 12-pulse rectifier). N ...

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 ...

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 ...

A VFD is shortened for variable frequency drive it's a sort of AC drive which control the speed of the ac motors depending on frequency change. VFD is very useful in industry today, but much thought to the application must be taken. For example, if you are controlling motor speeds at or below 50% to 75% (and maintaining them in this range), you may want to consider changing motors to a different RPM. VFD produces harmonics that can ...

Any non-linear load (such as a computer, a microwave oven, some refrigerators and electric stoves, or a variable frequency drive) will generate harmonics to some extent. Motors and generators themselves - because of inherent dissymmetries in the manufacture - can create some as well. The variable frequency drives that are referred to as "active front end" topologies are probably the worst, since their whole approach is to introduce ...

In variable speed drive (VSD) systems, both AC and DC, the first stage of power conversion is from AC to DC. In a DC drive, it's the only stage - from fixed AC to variable DC. In an AC drive there are two additional stages: filtration and inversion back to AC.

The simplest converter is a full-wave diode bridge, which converts the incoming AC to a fixed DC voltage. This isn't useful in a DC drive, but works fine for AC variable frequency drive (VFD). Standard industrial drives - bot ...