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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.
What else can I help you with?
What is the difference between power transformer and instrument transformer?
A power transformer is used to provide power (to your home, for example), an instrument transformer is used to measure voltage or current (for metering, for example).
Difference between power and furnace transformer?
Power transformer is used step up or down the voltage for the electricity transmission while furnace transformer is used to melt the metals and ores in the electric furnace.
What is the basic difference between transistor as an amplifier and a step up transformer?
The output power of an amplifier is greater than its input power, whereas the output power of a transformer is almost the same as its input power. In other words, an amplifier increases acts to increase power, whereas a transformer only increases voltage.
What is difference between interposing voltage transformer and potential transformer?
potential transformer is to maser and protection purpose the ivt is used for synchronicing purpose
What is the difference between inverter and Transformer?
An inverter changes DC power (like isgenerated from a solar panel) to AC to match the same type of power we get from the power company. A transformer reduces the power from a more powerful ACsource like a transmission lineto a lower AC source like the power to be used to be used in homes.
What is the difference between power transformer and instrument transformer?
A power transformer is used to provide power (to your home, for example), an instrument transformer is used to measure voltage or current (for metering, for example).
Difference between power and furnace transformer?
Power transformer is used step up or down the voltage for the electricity transmission while furnace transformer is used to melt the metals and ores in the electric furnace.
What is the difference between a balanced transformer and an unbalanced transformer?
there is nothing like a balanced and unbalanced transformer.
What is the basic difference between transistor as an amplifier and a step up transformer?
The output power of an amplifier is greater than its input power, whereas the output power of a transformer is almost the same as its input power. In other words, an amplifier increases acts to increase power, whereas a transformer only increases voltage.
Is there a basic difference between a three phase power transformer and a three phase distribution transformer?
The basic difference is the secondary voltages. On a distribution transformer the secondary voltage is very high. This is to overcome line loss for transmission of electricity over long distances. A three phase power transformer is used at the consumers three phase services end to manipulate voltages that consumers need to operate their equipment. The transformer that feeds your house is considered to be a single phase power transformer.
What difference's between potential transformer and voltage transformer?
Both are same. This is an instrument transformer used for metering & protections.
What is the difference between a 1.5KVA and a 3KVA transformer?
The 3 kVA transformer will weigh double the 1.5 kVA transformer.
What is the difference between isolation transformer and ferromagnetic transformer?
An isolation transformer is usually a ferromagnetic transformer. The question needs to be framed more usefully.
What is the difference between a transformer and a rectifier Which are found in a PC power supply?
A transformer is a device that changes the level of an a.c. voltage, while a rectifier is a device that converts alternating current to direct current.
What is difference between ICT and Transformers in power system?
A CT is a measuring device but does not step up or step down voltage like a transformer will.
Difference between potential transformer and current trasnformer?
The difference between current transformer and potential transformer is that the secondary of a current transformer can not be open circuited while under service whereas that of the potential transformer an be open circuited without any damage to the transformer.
4 What is the difference between a transformer and a rectifier Which are found in a PC power supply?
A rectifier is a device that converts alternating current to direct current. A transformer is a device that changes the ratio fo current to voltage. A rectifier is found in a PC power supply.
