High Voltage
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High Voltage
High Voltage vs. Low Voltage Transformers
Category: Transformers
If your company is planning to invest in a power transformer, it is best to get as well acquainted with these devices as possible, before you ask for quotes and go about buying one. A transformer is a complex and vital component of power transmission and once installed, its life could span anywhere from two to three decades. It is therefore important to make a wise and knowledge-based choice.
There are a few basic things about transformers that you must know. The first is the voltage aspect. There are broadly three voltage ratings in which transformers are available, high voltage, medium voltage, and low voltage. Below is a brief that should help you understand each of them better.
High voltage transformers
The high voltage transformer deals with voltages that cannot be used directly by the consumer, but are used in power transmission applications. High voltage transformers usually handle electrical energy in the range of 230,000 to 35,000 volts. Due to the particular demands of transmitting these voltages across long distances, a highvoltage transformer has considerably different core geometry, winding methods, and insulation methods than low voltage transformers.
High voltage transformers that have the capacity to increase the primary voltage to transmission-level high voltage are called step-up transformers. Conversely, highvoltage transformers can also be used to step-down voltages, depending on where they are in the transmission chain. Some of the applications of high voltage transformers are in electrical isolation, instrumentation and power distribution and control. This type of transformer can also be easily configured from single phase to three phase.
Medium voltage transformers
Transformers in this range are typically deployed in the local distribution sector of the power delivery system. They range from 35,000 volts to 2,400 volts and are used to deliver power from local distribution circuits to end users. Where residential customers are the end user, the output voltage can be as low as 120 volts, or for industrial customers, it can be 5,000 volts. This transformer can be viewed as a link from the end user to the utility provider.
These transformers are most often seen mounted on utility poles or as green boxes with tamperproof enclosures for connections located in shopping malls, residential subdivisions, schools and mobile home parks, in newer residential developments they can even be seen along sitting curb-side in front of the users home. These are usually liquid filled and are by far the most numerous of the three sizes.
Low voltage transformers
A lowvoltage transformer, also sometimes called a magnetic lowvoltage transformer, is typically used at the consumer end of the energy grid. A lowvoltage transformer is a distribution transformer with both the primary and secondary windings designed to operate at system voltages in the low voltage classes. Typically, electronic lowvoltage transformers convert 120 volts into 12 volts or 24 volts. A DC low voltage transformer uses a rectifier to convert its output to direct current (DC) and to lessen radio frequency interference (RFI). Lowvoltage transformers offer a variety of mounting configurations and are often small in size.
So unless your company is a huge steel plant, has a huge furnace, or runs machinery for the mining or petrochemical industry, in all probability your company will have to invest in a medium or low voltage transformer. The exact rating (expressed in terms of kVA), of course, will depend on your energy requirement.
Whatever your eventual requirement, it is important that you consider vendors that can provide customized, environmentally friendly units that conform strictly to DOE standards.
To know more about Transformers check out Pacific Crest Transformers website.
http://www.pacificcresttrans.com/home.html
About the Author
Mike Dickinson is Contributing author for Pacific Crest Transformer
When someone accidentally touches a high voltage generator while not on ground?
What would happen if someone touches a high voltage generator while his foot or any part of his body is not touching the ground? Please explain why, because I don't quite understand it when my professor said that if in the same scenario but your foot would be on the ground and that would be a short circuit. Then, he said that if any part of your body wouldn't be touching the ground, that would be safe.
Depends what you mean by high voltage. The simple explanation is that the output of a generator has one side connected to ground in almost all situations for various reasons. The circuit can only be completed through the ground or by touching two wires with voltage between them. Touching just one side of the circuit that is active above ground does not complete the circuit if you are not connected to the ground (because the floor, shoes etc are insulated). The circuit is not completed, and no current flows. I would be very cautious of trying it though.
In a practical situation, generator voltages in a power station are high enough to break down such insulation. The typical generator voltage is 6-18KV, so that it is likely that current will flow at a hazardous level through the insulation, or over its surface due to minor contamination. It would be risky or foolhardy, considering there is no certainty of the insulation. There are additional risks of discharges through the ionised air. See the link below if you doubt this. The picture shows only 1700V with a grounded hot dog drawing this flash over. This was probably done by touching the wire and drawing it away.
An additional cause of current flow with AC is the capacitance of your body to ground. This is despite your body being insulated from the ground to DC flow. There may be something like 100-300pF depending on the situation. For this capacitance the reactance at 60Hz is ~11 meg-ohms, but with 11KV the current is 1mA, enough to give a shock. I wouldn't take that risk.
With a low voltage generator (120/240V) the idea of touching an active line while the body is well insulated from ground is more likely to be reasonable. In electrical regulations voltages under 600V are considered 'low voltage'. This is because the result is more likely to be predictable. It is still risky, it is just too easy to make a mistake along the lines of 'I didn't know the gun was loaded'. Where I live the electrical regulations require all electrical work to be done with the power isolated.
Electric Six - "Danger! High Voltage" (Hi Res)