1, we see a graphic representation of a single-phase transformer with primary and secondary windings. Note that the primary terminations are designated "H1" . EMF across primary and secondary coil of transformer are related as follows: ( number of It sparks investors and market watchers on a path to acquire stock in . than one secondary winding, each related to the primary by the relationship given if the current through the secondary winding is limited by the load impedance? At this point, the designer should determine what market the power supply.
Three-phase transformers consist of three primary and three secondary windings, wound either in a star or delta configuration. This type of transformer operates on the same basic principle as single-phase transformers. Step-Up Transformers A step-up transformer is used to increase the transmission voltage to reduce line losses. By increasing voltage, line current proportionally decreases, and power loss from cable resistance is reduced.
The smaller current also allows for the downsizing of conductors to smaller diameters. Typically, electricity is generated at 11 kV and transmitted at 22 kV, or 44 kV and higher voltage levels. Step-up transformers are employed at this stage to increase the transmission voltage to those levels. Because of the relatively high value of primary current, these transformers have primary windings constructed of thick, insulated copper.
In addition to the number of primary and secondary turns, the secondary voltage of a three-phase circuit also depends on the type of winding configuration used. This factor must be considered when calculating the required turns ratio of a three-phase transformer to achieve the desired value of step-up voltage. Step-Down Transformers At the end of a transmission line, the high transmission voltage must be reduced to lower values as power distribution and ultimately, power consumption, occurs at much lower voltages.
Three-phase step-down transformers are employed in such cases. Using the same principles as a step-up transformer, these devices transform the high-voltage, low-current power in the primary to high-current, low-voltage power in the secondary.
Typical secondary voltages are of the order of a few hundred volts, and these transformers are equipped with thick copper windings in the secondary coils to accommodate the higher secondary currents resulting from the stepped down voltage.
Conversely, if voltage is halved in the secondary, current is doubled in the secondary. In this manner, all the power delivered to the primary by the source is also delivered to the load by the secondary minus whatever power is consumed by the transformer in the form of losses. Refer again to the transformer illustrated in figure The turns ratio is If the input to the primary is 0.
If the transformer has no losses, 30 watts is delivered to the secondary. The secondary steps down the voltage to 15 volts and steps up the current to 2 amperes. The reason for this is that when the number of turns in the secondary is decreased, the opposition to the flow of the current is also decreased. Hence, more current will flow in the secondary. If the turns ratio of the transformer is increased to 1: This means the opposition to current is doubled.
Thus, voltage is doubled, but current is halved due to the increased opposition to current in the secondary. The important thing to remember is that with the exception of the power consumed within the transformer, all power delivered to the primary by the source will be delivered to the load.
The form of the power may change, but the power in the secondary almost equals the power in the primary. Small power transformers used in electrical equipment have an 80 to 90 percent efficiency range, while large, commercial power line transformers may have efficiencies exceeding 98 percent. The total power loss in a transformer is a combination of three types of losses.
One loss is due to the dc resistance in the primary and secondary windings. Copper loss, eddy-current loss, and Hysteresis loss result in undesirable conversion of electrical energy into heat energy.
Step-Up Vs. Step-Down Three-Phase Transformers
Copper Loss Whenever current flows in a conductor, power is dissipated in the resistance of the conductor in the form of heat. The amount of power dissipated by the conductor is directly proportional to the resistance of the wire, and to the square of the current through it.
The greater the value of either resistance or current, the greater is the power dissipated.
The primary and secondary windings of a transformer are usually made of low-resistance copper wire. The resistance of a given winding is a function of the diameter of the wire and its length.
Copper loss can be minimized by using the proper diameter wire. Large diameter wire is required for high-current windings, whereas small diameter wire can be used for low-current windings.
How Does a Transformer Work? | Owlcation
Eddy-Current Loss The core of a transformer is usually constructed of some type of ferromagnetic material because it is a good conductor of magnetic lines of flux. Whenever the primary of an iron-core transformer is energized by an alternating-current source, a fluctuating magnetic field is produced.
This magnetic field cuts the conducting core material and induces a voltage into it. The induced voltage causes random currents to flow through the core which dissipates power in the form of heat.
RELATIONSHIP BETWEEN PRIMARY AND SECONDARY WINDINGS
Since the thin, insulated laminations do not provide an easy path for current, eddy-current losses are greatly reduced. Hysteresis Loss When a magnetic field is passed through a core, the core material becomes magnetized.
To become magnetized, the domains within the core must align themselves with the external field. If the direction of the field is reversed, the domains must turn so that their poles are aligned with the new direction of the external field.
Power transformers normally operate from either 50 Hz, or Hz alternating current. Each tiny domain must realign itself twice during each cycle, or a total of times a second when 50 Hz alternating current is used. The energy used to turn each domain is dissipated as heat within the iron core.
Hysteresis loss can be held to a small value by proper choice of core materials. The input power is equal to the product of the voltage applied to the primary and the current in the primary.
The output power is equal to the product of the voltage across the secondary and the current in the secondary. The difference between the input power and the output power represents a power loss. You can calculate the percentage of efficiency of a transformer by using the standard efficiency formula shown below: If the input power to a transformer is watts and the output power is watts, what is the efficiency? Hence, the efficiency is approximately The voltage, current, and power-handling capabilities of the primary and secondary windings must also be considered.
The maximum voltage that can safely be applied to any winding is determined by the type and thickness of the insulation used.
When a better and thicker insulation is used between the windings, a higher maximum voltage can be applied to the windings. The maximum current that can be carried by a transformer winding is determined by the diameter of the wire used for the winding.