Transformer

The real reason behind the choice of 11, 22, 33, 66 and 132kV levels is not clear from the responses to date and it may have passes into history unknown. Most likely, it was a decision arising from a standards committee and it may be an optimum transformation ratio chosen to minimize total losses. Someone still alive may yet know the reason. Then again, it may have a legacy resembling that of the standard rail gauge.

These numbers were chosen arbitrarily in the past and have actual ...

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 ...

You can run the 50Hz transformer on a 60Hz supply. Now since the frequency has changed the only variable thing in the existing transformer that can change (assuming simple one input and one output) is the flux density. In its simple form we are operating the transformer (60Hz/50Hz = 1.2) at 20% lower flux density.

If the things were reversed the flux density would be 20% higher and may saturate depending on design. You can even run the transformer at 400Hz providing that the volta ...

Many people think that UPS is a magic box that solves all the electrical problems. UPS systems have capacities varying from few hundreds of VAs to massive kVAs. The only thing that is worth noting in a UPS system is that, it can be viewed as a source as well as a load. Depending upon the configuration, the grounding needs to be planned. If the UPS system is transformer based, and operating only in inverter mode (Frequency converter mode), then it is called as separately derived source and out ...

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 ...

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 ...

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 ...

The best use of a transformer's internal impedance is for calculating available short circuit current on the secondary winding. This allows you to select an appropriate downstream OCPD. You not only need to know the KVA and % impedance but the open circuit output voltage as well. For example a 1500 KVA 3 phase transformer at 480 volts secondary has a nominal available current of 1804 amps at full output. With a 6.41% internal impedance it has an available short circuit current of 28,148 amps. ...

In this area of Canada, three winding transformers are used for several reasons. They are used to supply two secondary voltage levels [such as 13.8kV and 27.6kV]. They are also used to reduce fault levels at the secondary bus level by effectively doubling the transformer per unit impedance on large station transformers up to 75/125 MVA ratings.

Another reason for using a three winding transformer is to feed two redundant busses on the secondary side. This has been a common practice ...

Required or not, ground ring provides a better (lower impedance) grounding system. It really depends on what the specifications of the project call for. Here, ground rings are typically only used for sensitive electrical equipment installations - such as computer/data/network server rooms. For industrial/motor control/general light and power applications, a properly sized equipment grounding conductor (green wire), sized in relationship to the overcurrent protective device, is installed in th ...