Tuesday, 14 February 2012

3 Phase Power Converted to Single Phase for Households

Usually a household AC supply of electricity is single phase achieved by using the energy supplier’s 3 phase transformers that are in underground and overhead lines from the power company's power station.
Most power companies normally supply a certain area of households and housing estates with 3-phase power and then divide it and dispense it as individual single phase supplies per street or group of streets, giving each house in each street single phase power.

3 Phase Transformer

 Most power companies can provide 3-phase power to households or establishments if needed. This is very advantageous for businesses such as vehicle repair garage, factories, engineering workshops etc that need to power heavy machinery and equipment, such as power tools where motors are installed in the machinery.

The deliverance of the type of power supplied to a building (single phase or three phase) from the street depends on the building’s usage requirements: an industrial site or factory which uses powerful machinery and large power tools, etc., will usually require electricity delivered as 3-phase power. Small offices and domestic buildings usually only power single-phase appliances and lighting, so only require a single-phase power supply from the street.

Typically the electrical power is produced at the power station in three individual phases. The live wires (L1, L2 and L3) of each of the phases are timed to delay each other in wave and cycle periods as follows: the first phase live wire (L1) is produced at Zero degrees, which is equal to 360o, the 2nd phase’s live wire (L2) is timed to lag the first phase’s live wire (L1) by 120o and the live wire (L3) of the third phase is timed to lag the first phase’s (L1) by 240o. Typically, in most European countries the colours of the live wires are brown for L1, black for L2 and grey for L3 and blue for the neutral wires.

The reason why energy supply companies use 3 phase transformers to transmit their energy is due to the efficiency and low running cost of the transformers. 3 phase transformers provide a constant supply of energy and because of the way they operate, 3 phase transformers are low maintenance and make little noise. Typically large power generators provide electric currents at up to 30KV and at the power stations; this is increased for the suitability of the transmission process.

Tuesday, 27 September 2011

3 Phase Motors

The electric motor is the most important part of a three phase load for many reasons.
The 3 Phase Motors that are fully enclosed in casing can handle extremely heavy thrust loads, the ball bearings are greased to resist the chance of oxidisation and moisture entering making them last 10 years or so continuous use under temperatures reaching up to 108 degrees Fahrenheit.

The simple design of 3 Phase Motors offers high efficiency and high starting torque. The motor is smaller than a single phase motor and has the ability to generate more power.
It vibrates a lot less than single phase motors which is another reason why it lasts so much longer under the same conditions.

3 Phase Motors Power UsesThe high power levels and high voltage distribution of 3 Phase Motors means that systems that may not even require the revolving magnetic field characteristic of the 3 Phase Motor still use them as a power source. 
These include heating resistance loads such as electric boilers and self contained heating systems. Establishments that use florescent lighting units also use the motors to eradicate any flickering that may occur when being powered by Single Phase Motors. This is due to the continuous feed of energy that the 3 Phase Motors transmit.

Three Phase Motors also have the benefit of being able to transmit power over long distances through smaller conductor feeds. A good example of this is the common Pylon that is seen dotted through the countryside holding cables that carry energy transmitted by the 3 Phase Motors attached to each one.

Although 3 Phase Motors are usually very large, they are 75 percent smaller than Single Phase Motors and there are the exceptions to the usual large 3 Phase Motors. Tiny versions of 3 Phase Motors are used in electrical appliances that require a cooling mechanism such as PCs and laptops which contain an internal cooling fan. 

Friday, 12 August 2011

3 Phase Transformers and Their Uses

3 Phase Transformers are extremely successful in transmitting electricity at a more efficient rate than the single phase transformers. This is due to their clever design consisting of an internal iron leg wrapped in three sets of primary and secondary windings and secured into an enclosure filled with dielectric oil (a non-conductor). The dielectric oil prevents moisture, acts as a cooler for the coils and stops the current reaching the enclosure. This unique design allows more power to be transmitted at a constant, balanced and linear rate. Because of this clever design, 3 phase transformers are manufactured using less materials and can be made to a smaller, lighter design, they can also vary on how much power they transmit.

3 phase transformers are popular in many industries. They are popular in the building trade where machinery is constantly used throughout the day. For example, in a carpenters workshop with a diverse array of machinery demanding different levels of power to operate (such as five horsepower drills and ten horsepower saws),  3 phase transformers are very useful. This is because they power this machinery with a balanced supply of energy which prevents the machinery motors overheating and burning out! 3 phase transformers are also popular in the building trade for on-site operations. This is due to the portability of the transformer to use on the sites for the required power. Figure 1 shows a good example of an on-site 3 phase transformer
Figure 1

3 phase transformers can supply anything, they are used for powering air-conditioning systems. Large air-con machines with heavy duty use in big buildings would be subject to overheating if they were not equip with 3 phase transformers supplying energy. 3 phase transformers are used in hospitals to supply medical equipment and many more industries.

Tuesday, 15 March 2011

More About Three Phase Power Transformers

Three phase electricity is used so often for power distribution systems, hence the need for 3 Phase Transformers to be able to step voltages up or down. Regular single-phase transformers can also be ganged together to transform power between two three-phase systems in a variety of configurations, eliminating the requirement for a special 3 phase transformer. However, special three phase transformers are able to perform with less material requirement, less size, and less weight than their modular counterparts.

Three Phase Power Transformers are composed of three single phase transformers winded around a single core. These transformers are put into a case which is then filled with an insulating (dielectric) oil. This oil provides electrical insulation between the windings and the enclosure. It is also used to to prevent the formation of moisture, which can deteriorate the winding insulation and help provide cooling functions. Three single phase transformers can be connected to form a three phase bank if a 3 Phase Transformer is needed and a Three Phase Power Transformer of the proper size and turns ratio is not available. When three single phase transformers are used to make a three phase transformer bank, their primary and secondary windings are conected in a wye or delta conection.

Three phase power is a standard method of electric power transmission. It is a variety of polyphase system primarily used to power motors as well as many other devices. The main advantage of a 3 phase power system is that it uses less conductor material to transmit electric power than equivalent single-phase, two-phase, or direct-current systems at the same voltage. In a three phase power system, three circuit conductors transport three alternating currents (with the same frequency). These reach their instantaneous peak
values at different times. Taking one conductor as the reference, the other two currents are delayed in time by one-third and two-thirds of one cycle of the electrical current. It is this delay between "phases" that gives the effect of continuous power transfer over each cycle of the current. This also makes it possible to produce a rotating magnetic field in an electric motor.

Three phase transformers are used throughout industry to change values of three phase voltage and current and is the most common way in which power is produced, transmitted, and used. An understanding of how three phase transformer connections are made is therefore essential.

Friday, 3 December 2010

Three-phase loads in 3 phase power

3 phase motor (source Wikimedia)
In a 3 phase power system, large power generators provide an electric current which can potentially be a few hundred volts to about 30 kV. At the power station, 3 phase transformers step this voltage up to one which is suitable for transmission. After numerous further conversions in the transmission and distribution network, the power is finally transformed using 3 phase transformers to the standard utilization voltage for lighting and equipment. Single-phase loads are connected from one phase to neutral or between two phases. Three phase loads such as motors must be connected to all three phases of the supply.

The most important class of three-phase load is the electric motor. A three-phase induction motor has a simple design, intrinsically high starting torque and excellent efficiency. These motors are applied in industry for blowers, fans, pumps, conveyor drives, compressors, electric vehicles etc. A 3 phase motor is more compact and less costly than a single-phase motor of the same voltage class and rating. Three-phase motors also vibrate less and hence last longer than single-phase motors of the same power used under the same conditions.

Occasionally the advantages of 3 phase power motors make it worthwhile to convert single-phase power to three-phase. Small customers, such as residential or farm properties, may not have access to a three-phase supply or may not want to pay for the extra cost of a three-phase service but may still wish to use 3 phase equipment. Such converters may also allow the frequency to be varied allowing speed control.

One-phase loads may be connected to a three-phase system in two different ways.  This can be done either by connecting across two live conductors (phase-to-phase connection), or by connecting between a 3 phase conductor and the system neutral, which is either connected to the center of the Y (star) secondary winding of the supply 3 phase transformer, or is connected to the center winding of a delta transformer (High Leg Delta system). Single-phase loads should be distributed evenly between the phases of the 3 phase system
for efficient use of the supply conductors and supply 3 phase transformer.

We hope you enjoyed our latest post on understanding the advantages of 3 phase power and 3 phase transformers. We look forward to your comments.

Tuesday, 5 October 2010

The Advantages of 3 Phase Power and 3 Phase Transformers

Three phase electric power is used by electric power grids worldwide to distribute power, and is the most common used method for doing so. There are various reasons for this, mainly due to the many advantages of 3 phase power.

Firstly, a 3 phase distribution system is generally more economical because it uses less conductor material to transmit power than single-phase systems at the same voltage. This also makes a 3 phase transformer more compact, using less material and weighing less. The smaller conductor size also allows three phase power to be transmitted over long distances.

Secondly, a three phase transformer uses three conductors carrying the same current giving a more balanced load and hence can provide much more power than a single phase system.

Increasing Reliablily and Efficiency

Three phase systems are much more reliable and allow heavy duty industrial equipment to operate more smoothly and efficiently. This makes it desirable to manufacturing and industrial companies who need to power large industrial equipment such as electric boilers, refrigeration and air conditioning, whether generating thier own electricity, or making it more efficient.

That concludes our second post on understanding the advantages of 3 phase power and 3 phase transformers. We hope you enjoyed it and look forward to your comments.

Friday, 3 September 2010

Understanding 3 Phase Power Generated by a 3 Phase Transformer

So what is meant by 3 phase power?

The easiest way to grasp the nature of 3 phase power is to put it into context, so, for example; consider the large power companies such as Eon, Npower & British Energy

Three phase power flow begins in a power station. Their generators produce electricity by rotating 3 coils or windings through a magnetic field within the generator. Electrical power generators convert mechanical power to alternating electric currents.

At this point, the power could have already been split into single phase or into three phase. With three phase power, the output of the transformer is generally star connected with the mains voltage, 120 volts in North America and 230 volts in Europe.

These coils or windings are commonly positioned 120 degrees apart.

Whilst rotating through the magnetic field they generate power which can then be sent out along three lines, hence three phase power. See 3 phase flow diagram by Wikipedia.

The coils or windings connected in a 3 phase transformer must be in the right sequence to match the incoming power and subsequently transform the power company voltage to the level of voltage we need and maintain the proper polarity (phasing). So after many conversions in the transmission and distribution network, the power is transformed into the standard mains voltage.

So that concludes our first entry on understanding 3 phase power generated by a 3 phase transformer. We hope you enjoyed it and look forward to your comments.