What is difference between transformer and power transformer?

Answer 1

In electricity supply systems, a 'power transformer' is a category of step-up or step-down transformer used in the high-voltage transmission and primary distribution systems. Step-down Transformers used in the secondary distribution system are called 'distribution transformers'.

A power transformer is designed to handle large amounts of power (as the name implies) and usually converts voltages; they are used in power supplies and in electrical supply.

Transformers have three main functions in electronics; impedance conversion, voltage conversion and isolation. Because of these three applications, there are specialist types of transformers. For example, signal transformers are designed to match impedances - for example, between a record cartridge and an amplifier.

Answer 2

A transformer is an electromagnetic device which often consists of two separate windings around the same iron core. The two windings are called the primary and the secondary and normally they are electrically insulated from each other. Current in the primary is normally driven by the circuit to which it is connected. Current in the secondary normally drives the circuit to which it is connected. Many variations of this theme exist and most of them aren't relevant here.

A power transformer is intended to transform large amounts of power at one voltage to a very similar amount of power at a different voltage. A little power will always be lost in the transformer core and windings, and good transformer design keeps that loss very small. You will most often come across 'step-down' transformers, where the voltage on the primary is high and the voltage on the secondary is low. For example if you have a model train set with electrically driven trains, for safety reasons the voltage on the rails has to be quite low - a few volts. Unfortunately for efficiency reasons the voltage of the power delivered to your home has to be quite high - one or two hundred volts. A power transformer is used to transform the voltage from the dangerous levels delivered to your home to a few volts, which is much safer. Nobody cares very much how accurately the transformer does this, so a cheap transformer with a turns ratio of the order of a hundred (on the primary) to one (on the secondary) will do. Note that in a power transformer, the voltage ratio from primary to secondary is approximately the same as the turns ratio of primary to secondary. The primary winding will usually be placed on the core first, then the secondary winding will be wound on top of that.

A current transformer is usually a measurement device. The emphasis here is on measurement, not on power transformation, and on accuracy, not on efficiency. If you work in a power station and you want to measure a current of tens of thousands of amperes you might not have a multimeter which has a range that high. So you can use a current transformer to make the measurement. The current transformer will (usually) mirror the flow of current in its primary with a current in its secondary which is exactly proportional to the flow in the primary but very much smaller. For example a current transformer with a turns ration of one (on the primary) to ten thousand (on the secondary) will produce a current in the secondary of one ten-thousandth of the current in the primary. Then your multimeter, connected directly across the secondary of the transformer and set to measure current, will register only 100 milliamps when there is a current in the primary of a thousand amps. Do not connect a multimeter on a current range to the secondary of a power transformer!

When a power transformer is not being used, the primary winding can be left connected to the power supply and the secondary winding can simply be disconnected. The transformer itself will consume very little power. With a current transformer, if it is left in circuit when it is not being used then the secondary winding must be short-circuited; otherwise dangerous voltages will be developed in the winding which may destroy insulation. Do not short-circuit the secondary of a power transformer!

http://en.wikipedia.org/wiki/Current_transformer

-- GWH --

CURRENT TRANSFORMER:

Think firstly of ac current indication on a distribution switchboard incomer - maybe on a power condition monitoring relay or an incomer protection relay.

For a low voltage board ( 400V ) it may be several hundred amps or more.

This current cannot flow directly through the relays, due to a number of reasons of practicality.

The size of terminations & separation are not suitable for starters - consider the csa of bus bars carrying a few hundred amps....

A current transformer is an interface device which will provide a secondary winding current, proportional to that a) in its primary winding if wired or b) the conductor passing through its centre ( torroidal CT ), which can be used for metering, protection & indication purposes. CTs have standard ratios available, ie 100:5 & 2000:1 are common, & are also accuracy classed. Certain protection applications will require matched pairs of CTs to be used at higher accuracy levels.

CTs are tested to demonstrate their kneepoint, which is the point at which they saturate, electromagnetically.

A typical application of CTs would be on a large motor feeder circuit. At the MCC, the outgoing cable ends wound each pass through perhaps a 100 : 5 CT, & then all three cables would pass through a common CT for earth fault detection which maybe 2000:1 ratio.

POWER TRANSFORMER:

Changes voltage level up for distribution or down for consumption.

Range from a few VA rated, to several hundred MVA.

Can be tapped to control voltage.

May be star or delta connected on each winding, and give phase shift depending on this connection & resultant vector group. eg Dyn11

May be air or oil, forced or natural cooled - ONAN, ONAF ( with fans ), OFAF ( fans and pumps )

Are protected for over temp, over pressure, over current, gas in oil etc.

CTB.

Answer 3

Basicly a power supply is a transformer, but it has a few extras...

Lets start by looking at the what a transformer does, although the science part can get a little tricky, I'll keep it simple so you can get an understanding of the basics.

A transformer takes a voltage and either increases it, or decreases it to a safer level. In the case of computers the transformer takes the mains voltage from the wall socket in your house, and reduces it to a level the computer can deal with.

Here in lies the problem, the mains voltage in your house is what's known as alternating current, this is when the voltage as a result of the generation process keeps swapping between positive and negative voltage either 50 or 60 times a second, depending on where you live. For a lot of things this is no problem, light bulbs for example work quite happily this way, and motors are more efficient when run from this alternating current.

Most electronics devices need the voltage to be fixed to a positive value to work, and your computer would not even start if it was supplied with alternating current. So we need a power source like a battery that is fixed in its output. This is the distinction between a power supply and a transformer.

The power supply uses a transformer to reduce the voltage, then uses some electrickery to make the voltage fixed, and at the correct voltage and as a positive source. In the case of a desktop computer, the power supply has to make outputs at 12 volts, 5 volts, 3.3 volts and 0 Volts. If any of these voltages are even slightly out your computer will become unstable, and may well even stop working, so be glad your power supply's working well, even though you'll probably never even see it!

Answer 4

A power transformer is in the device, such as in your stereo, and it converts line voltage (120VAC) to the voltages needs in the stereo's power supply.

A distribution transfer is on the utility pole, underground in a vault, or in the utility power room, and it converts distribution voltage (13,200VAC) down to line voltage (120VAC).

Answer

Unfortunately, there is no standardised definitions for different types of transformer however, in the context of the electricity supply system:

• A power transformer is the name given to a step-up or step-down transformer used in electrical transmissionsystems, in the UK typically400 kV/275 kV/132 kV. They are also used in the primary distribution system -i.e. 33/11 kV.
• A distribution transformer is the name given to a step-down transformer used in electrical distributionsystems, in the UK typically operating in the 11 kV/400-230 V region.

Answer 5

Very little, other than capacity and direction.

Transmission transformers (part of the distribution system) step up generated power into high voltage. Distribution transformers step it back down to intermediate voltage. Service transformers (also part of the distribution system) then step it down to service voltage for use in the home or industry. All of these transformers are high in power, decreasing from transmission to distribution to service.

A power transformer reduces (or sometimes increases) service voltage to operating voltage for use in a particular component.

In the final analysis, however, a transformer is a transformer, and it is a magnetic-inductive device that changes one voltage to another, based on turns ratio.

Another Answer

The above answer is not altogether correct, as transmission-system transformers (termed 'power transformers' in the industry) can be either 'step up' or 'step down' transformers. They step up generated voltages at power stations, but step down voltages at load-centre substations.

Answer 6

A power supply, such as those in a computer take the power supplied by the wall outlet and split it into the various forms that your computer hardware needs to operate.

A battery has a set amount of power stored inside it which is constantly being drained (or replenished if rechargeable).

Answer 7

A transformer is something that can change.A power transformer is something from the Transformers films.

Answer

A 'power transformer' is simply a category of transformer type. It is used in transmission systems as opposed to a 'distribution transformer' which is used in distribution systems.

Answer 8

A rectifier converts AC (alternating current) to DC (direct current).

A power supply provides power at the desired voltage using a transformer, and may also has a rectifier to convert it to DC.

Answer 9

"http://wiki.answers.com/Q/What_is_difference_between_distribution_transformer_and_power_transformer"