Controlling

Controlling hot air mixtures
Regler für Siemens S7-300 und Vipa 300 V/S

PDPI-Algorithm for induction heating systems
Regelmodul R355 für VIPA und Siemens

Precision control in chemical reactors
Siemens Regler S7-300

Reliably packaged temperature control

Tablet packaging safety

Power quality

Dirty power - Oberschwingungen durch nichtlineare Verbraucher (german)

More publications
Power Quality by Dranetz BMI

Power engineering

Energizing Magnetized Transformers
Problems can be created when the core of a transformer becomes magnetized prior to being energized for use. Damage to the insulation and deformation of the windings are two of the most common side effects.
Generally, Transformer cores, during operation, are magnetized, demagnetized and then magnetized and demagnetized in the opposite direction for each sine wave cycle. It is not easy to determine the magnitude the core is magnetized at the moment the Alternating Current source is switched off. The magnitude of magnetization depends upon the moment the transformer is switched off, the Core material (the larger the hysteresis of the iron, the greater the magnetization level), and the applied voltage level during the power on state. The highest magnetization in this scenario occurs when a transformer is switched off right at the moment the voltage source sine wave crosses the zero-line.
Transformer cores are also magnetized after having a Direct Current source flow in a winding. For example, the application of Direct Current when performing a winding resistance test. After measuring the Winding Resistance the core is magnetized to it's maximum Hysteresis.
Both of these scenarios can leave the core in an unpredictable state which can cause damage when energized. These problems can be eliminated if the transformer is demagnetized prior to being energized for use.
Conclusion
- A transformer is magnetized when power is switched off. Even if a transformer is completely deenergized, it can still be in a magnetized state!
- After performing DC tests on a transformer winding, the core is magnetized.

Consequences of Energizing a Magnetized Transformer
When a magnetized transformer is switched back on line, it is quite possible, depending upon the position of the sine wave and other variables, that inrush current can exceed 8 times the nominal current flow. This hazardous situation may cause tripping of over-current relays, damage the insulation medium and deformation of the transformer windings.

Procedure for eliminating the magnetized state of a Transformer
One option that can be taken to safely switch a transformer back on line and avoid a dangerous and damaging situation is to apply a reduced source voltage and increase to operating levels. Under controlled conditions this may be possible. However, this undertaking may not be theoretically possible when energizing a transformer on site. Such equipment required to fully demagnetize a transformer is large and expensive. Or a better solution is the new Raytech Winding Resistance Meter, WR50-Series.
These easy to use systems are recognized throughout the World for Precision Winding Resistance measurements. A unique and new feature built into the WR50 series is the ability to Automatically Demagnetize a Transformer core on site. Avoid unnecessary damage and unsafe conditions when energizing a transformer; use one of the Raytech WR50 series instruments and be sure.

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Specialized publications by Camille-Bauer

Dranetz' Power Quality Quick Tipps

The right tool for the job
Many power quality problems will require the use of some type of measuring or monitoring equipment, and some will be nearly impossible to solve without. Having the right tool at your disposal can shorten the time to uncovering the source, and getting the process running smoothly again. But the tools of observation and common sense should be the first that are brought out. A key observation skill is determining what has changed. When systems run fine for months on end and then suddenly start to fail regularly, determining what has changed is usually the first step. Use all of your senses except your touch (and "taste" as someone at a seminar recently pointed out). Looking for wiring problems and code violations, such as neutral-to-ground bonds at distribution panels that are not from separately derived sources. These bonds are in violation of the National Electric Code, and can pose a safety problem as well as a power quality problem.

Flickering Lights
Some changes or modulations of the voltage that aren't large enough to be consider sags may not seem to effect equipment operation. However, these anomalies can result in quality variations in extrusion and textile processes and in flickering lights that can cause human discomfort. In the case of flicker, the frequency of the modulation is critical as to whether it will be noticeable to the particular susceptibilities of the human eye and brain. For example, it would only take about 0.3 volts of modulation at 9Hz on a 120V system for most people to notice the flicker in a 60W light bulb. However, at 1 Hz, it would take nearly 10 times the modulation to be noticeable.

Electromagnetic phenomena
The most common type of electromagnetic phenomena that cause power quality related problems are changes in the basic waveshape of the voltage - the sine wave. One mathematical number used to represent this complex shape with a single number is RMS --- root mean squared. It takes each of the sample points (typically 128) in one cycle of the waveform, multiplies the value by itself (squares it), adds them all up and takes the average (mean), and then takes the square root of that number. This is different than the peak value, which is the largest sample value in a cycle. For different waveshapes, there are different relationships between the peak and RMS. For sine waves, the peak is 1.414 times larger than the RMS value, or the RMS value is 0.707 times smaller than the peak. This relationship doesn't hold with distorted waveforms, such as when harmonics are present, which is why you should use a "true RMS" meter, not one that multiplies the peak value times 0.707 to determine RMS.

Harmonic Magnitutdes
Harmonics are often displayed as a harmonic spectrum, which is either a list or bar graph showing the magnitude of each harmonic, for voltage and current. The magnitudes are a good clue as the source of the harmonics. If the current harmonics have a significant 3rd harmonic, slightly smaller 5th, even smaller 7th and so on, this is often caused by single phase, rectified-input, switching power supplies, such as in computers, printers, and other information technology equipment found in office environments. If the dominant harmonics are the 5th and 7th, then the 11th and 13th, then the 17th and 19th, then the source is often a 6 pulse or pole converter, also know as a 3 phase, full wave rectifier, which is found in adjustable speed drivers and other larger "electronic" loads.

Harmonic Pollution
It is usually the harmonic currents that are of concern, as they can cause "harmonic pollution" to spread to other equipment. Just like Current * Impedance = Voltage for fundamental frequency, Ohm's Law also applies to harmonic current, impedance and voltage. Loads that draw current in a non-linear manner will cause harmonic-rich current to react with harmonic impedances and generate harmonic voltages that other loads will see. Harmonic impedances can change values with frequency or the harmonic number, often increasing significantly with the higher harmonics. This means that it will take less harmonic current to produce a significant harmonic voltage.

RMS Sags
Variations in the RMS value are often used to trigger capturing of PQ data. The most common type of RMS variation is the sag, (or dip in European lingo). Some studies show over 60% of the PQ disturbances are sags, which is when the RMS value goes below 90% of the nominal value. On a typical office or residential outlet, that would be dropping from 120Vrms to 108Vrms. If the voltage goes down below 10% of nominal, we call that an interruption. Conversely, if it increases above 110% of nominal, that is a swell.

Causes of Sags
Sags are often caused by sudden, large increases in current, which causes a proportional voltage drop in the wiring, leaving less voltage remaining for the loads. If it is a fault on the electric distribution system, such as a phase-to-ground short circuit caused by lightning, animals, tree branches, or accidents, then the direction of the sag is called upstream or source side, or towards the generating source. If a load starts up, such as a large HP motor, then the direction of the sag is said to be downstream or load side. If the remaining voltage during the sag is too low for the equipment to operate properly, the process can be interrupted or corrupted. Though equipment is usually not damaged during such, the product being produced often has to be scrapped, and there may be a significant restart time to get the operation running smooth again.

Causes of Transients
Transients are very short duration disturbances, less than ¼ cycle of power frequency and more often, measured in microseconds. They used to be referred to as impulses, surges, spikes or glitches. But those terms can have ambiguous meanings, so the term "transient" was adopted by the IEEE and other standards groups. Common causes of voltage transients are power factor capacitor banks being switched on or off, lightning striking a conductor or adjacent to a conductor, arcing from a phase conductor coming in contact with some sort of ground potential (such as a tree), and the notches resulting from the commutation period of the SCRs on rectified input 3 phase power supplies (such as in ASDs).

Loose connections
If you have taken a distribution panel off for whatever reason, it is a good time to use one of the most important power quality tools, the screwdriver. Be sure to wear the proper safety equipment and to follow all necessary safety precautions. In most facilities, the current flows during only part of the day. Today, this current is often contains heat-generating harmonic currents. The heating/cooling/heating/cooling cycle and resulting expansion and contraction of the wires can cause the connections to loosen over time. This loosening increases the impedance of the connection, which further increases the heating effects. Tightening loose connections with the screwdriver can help reduce voltage drops and minimize the fire potential.

Harmonic Differnces
Harmonics are typically grouped by their harmonic number, either odd or even. Odd are the 3, 5, 7, 9, etc and even being the 2,4,6,8...and so on. There is another grouping used, called the triplens, which are the 3, 6, 9, 12, etc. The triplens are so grouped because triplen harmonic currents will add in the neutral of a three-phase, four wire wye circuit, as opposed to canceling out. This has resulted in the need to make the neutral conductor equal to or up to 1.73 times as large in current-carrying-capability as the phase conductors. Even harmonics are grouped together as they typically aren't found in systems with properly functioning equipment, unless there are half-wave rectifiers present as loads. If half of the input rectifiers aren't functioning properly in a full wave rectifier, then the load will draw current as if it is a half wave rectifier, and the current waveform will be rich in even harmonics. This is a clue that something maybe broken. Even harmonics are recognizable in a waveform as they cause a loss in symmetry within the halves of the waveform.

Common Harmonics
Harmonics are typically defined as "frequencies that are integer multiples of the fundamental frequency". For 60Hz power systems, these means that the 2nd harmonic is 120Hz, the third harmonic is 180Hz, the fourth is 240 Hz..., the nth harmonic is n*60. Frequencies are found that are actually in between these harmonic frequencies are called interharmonics (such as 185Hz), but are generally much less common than harmonic frequencies themselves. Frequencies below the fundamental frequencies are called subharmonics (such as 9Hz), and often contribute to the phenomena of light flicker.

High Even Harmonics
The presence of a high percentage of even harmonics usually indicates that there is a significantly large half-wave rectifier on the circuit, or that a full-wave rectifier is damaged and is acting like a half-wave rectifier. Odd harmonics are usually make up the majority of the spectrum on most electrical circuits. Even harmonics in significant proportions are usually not found, except where current is being drawn on only half the cycle. The Fourier expansion of a half-wave rectified signal is composed entirely of even harmonics, whereas the typical electronic loads, such as PCs, laser printers, or ASDs, have predominately odd harmonic spectrums. Even harmonics are often detectable by the lack of quarter-wave symmetry of the waveform. This means that the part of the waveform up to the first peak of the sine wave doesnt look like the mirror image of the 2nd part of the waveform, as it goes from the peak back to the zero axis. The same dis-symmetry will show up between the 3rd and the 4th parts in the negative half cycle of the waveform.

Power Factors
Power factor is another parameter that is affected by power quality phenomena, particularly distortion and imbalance. This creates even more confusion about the term "true power factor". Power factor is a measure of how efficiently a load uses the electricity, or, how much energy is consumed by the load versus how much the electricity provider must deliver. This has been defined as real power divided by apparent power, watts / volt-amperes, or W / VA. Until the onslaught of rectified input type loads (also called switching power supplies, or electronic or non-linear loads), most electrical loads were resistive and/or inductive loads, such as heaters, incandescent lights, and electrical motors. Whereas the voltage and current may not have been exactly in phase, both were nearly sinusoidal in their waveshapes, having only fundamental frequency components present. Hence, real power being equal to Vrms * Irms * cos (angle between V & I called theta) and apparent power being Vrms * I rms reduced down to Power Factor equal to Cos (angle theta). People then assumed that this was the "real" formula for PF, and revenue meters used such for billing purposes. As the rectified input loads began to become the norm, the current waveshape in particular lost its sinusoidal shape, becoming rich in other harmonic frequency components. SCR-gated loads conducted current only during part of the voltage waveform. Even if the fundamental frequency components were in-phase, the real power was no longer just the Vrms * I rms * cos (theta), since each of the harmonic voltages and currents could have a different value for theta. Not surprising, watts become a lower value, since the purpose of the rectified input switching power supplies and SCR-gated loads was to reduce the real power being consumed. But the apparent power, Vrms * Irms, was still the same. So, surprising as it may be to some people, the power factor become smaller. In one example, a utility person replaced an old electromechanical meter with a new one that called PF with the traditional W/VA method and now the customer owed for a PF penalty (which the customer refused to pay since they hadn't changed their loads).

Causes of swells
Swells are increases in the voltage, typically above 110% of the nominal. Though must less common than sags, swells can cause catastrophic failures in equipment if the voltage exceeds the safe input level of the equipment for too long. Swells can be caused when a large load is suddenly turned off (opposite of the cause of sags). The voltage will increase for 30-60 cycles, until the automatic tap changers can bring the voltage back into normal regulation limits.

The sum of THD
A common statistical number used is called THD, or total harmonic distortion. This is a mathematical process where: the magnitude of the harmonics for voltage or current are squared; summed; the square root is taken on the sum; and the result is the divided by either the fundamental RMS or the total RMS value; and lastly, multiplied by 100%. This number can different significantly based on the divisor. (Typically, Fundamental is used in North America, and Total in Europe) Using THD for current can be very misleading and should generally be avoided. The actual magnitudes of the harmonic current are more meaningful. If there is very little magnitude of harmonic current, as in the neutral of a wye circuit, then the THD can be very large and it still wouldn't be a problem. For example, 0.5A of current in the neutral of a 30A circuit could be made of 0.25 A fundamental, and 0.25 A of 3rd harmonic. This would yield a 100% THD, which sounds bad, but is really insignificant on a 30A circuit.