This Bachelor thesis is about the basics of Power Transformers, . If 1 is the input power for a three-phase transformer and 2 its output. PDF | Transformers may be classified according to dielectric insulation material as follows: • Oil-filled transformers• Dry type transformers. Library of Congress Cataloging-in-Publication Data Electric power transformer engineering / edited by James H. Harlow. p. cm. — (The Electric Power.
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BPA has hundreds of power transformers installed throughout the system, and few power Transformers (>1 MVA) be tested with TTR test set. VRT Power Ltd. We Enable Energy. VRT is a modern manufacturer for high- performance oil-immersed power transformers up to MVA kV. Customized. of oil-filled power transformers ( kilovoltamperes [kVA] and larger), owned and operated by Reclamation, although routine maintenance of other transformer .
An air-core transformer eliminates loss due to hysteresis in the core material. Air-core transformers are unsuitable for use in power distribution,  but are frequently employed in radio-frequency applications. Windings are usually arranged concentrically to minimize flux leakage.
Cut view through transformer windings. Legend: White: Air, liquid or other insulating medium Black: Primary winding Red: Secondary winding The electrical conductor used for the windings depends upon the application, but in all cases the individual turns must be electrically insulated from each other to ensure that the current travels throughout every turn. For small transformers, in which currents are low and the potential difference between adjacent turns is small, the coils are often wound from enamelled magnet wire.
Larger power transformers may be wound with copper rectangular strip conductors insulated by oil-impregnated paper and blocks of pressboard. The transposition equalizes the current flowing in each strand of the conductor, and reduces eddy current losses in the winding itself.
The stranded conductor is also more flexible than a solid conductor of similar size, aiding manufacture. Coils are split into sections, and those sections interleaved between the sections of the other winding. Power-frequency transformers may have taps at intermediate points on the winding, usually on the higher voltage winding side, for voltage adjustment. Taps may be manually reconnected, or a manual or automatic switch may be provided for changing taps.
Automatic on-load tap changers are used in electric power transmission or distribution, on equipment such as arc furnace transformers, or for automatic voltage regulators for sensitive loads. Audio-frequency transformers, used for the distribution of audio to public address loudspeakers, have taps to allow adjustment of impedance to each speaker.
A center-tapped transformer is often used in the output stage of an audio power amplifier in a push-pull circuit. Modulation transformers in AM transmitters are very similar. Cooling[ edit ] Cutaway view of liquid-immersed transformer. The conservator reservoir at top provides liquid-to-atmosphere isolation as coolant level and temperature changes.
The walls and fins provide required heat dissipation. As power ratings increase, transformers are often cooled by forced-air cooling, forced-oil cooling, water-cooling, or combinations of these. The mineral oil and paper insulation system has been extensively studied and used for more than years. Bridge transformers connect 2-wire and 4-wire communication circuits. Being magnetic devices, audio transformers are susceptible to external magnetic fields such as those generated by AC current-carrying conductors.
Audio transformers were originally designed to connect different telephone systems to one another while keeping their respective power supplies isolated, and are still commonly used to interconnect professional audio systems or system components, to eliminate buzz and hum. Such transformers typically have a ratio between the primary and the secondary.
These can also be used for splitting signals, balancing unbalanced signals , or feeding a balanced signal to unbalanced equipment. Transformers are also used in DI boxes to convert high-impedance instrument signals e.
A particularly critical component is the output transformer of a valve amplifier. Valve circuits for quality reproduction have long been produced with no other inter-stage audio transformers, but an output transformer is needed to couple the relatively high impedance up to a few hundred ohms depending upon configuration of the output valve s to the low impedance of a loudspeaker. The valves can deliver a low current at a high voltage; the speakers require high current at low voltage.
Most solid-state power amplifiers need no output transformer at all. Audio transformers affect the sound quality because they are non-linear. They add harmonic distortion to the original signal, especially odd-order harmonics, with an emphasis on third-order harmonics. When the incoming signal amplitude is very low there is not enough level to energize the magnetic core see coercivity and magnetic hysteresis.
When the incoming signal amplitude is very high the transformer saturates and adds harmonics from soft clipping. For good low-frequency response a relatively large magnetic core is required; high power handling increases the required core size. Good high-frequency response requires carefully designed and implemented windings without excessive leakage inductance or stray capacitance.
All this makes for an expensive component. Early transistor audio power amplifiers often had output transformers, but they were eliminated as advances in semiconductors allowed the design of amplifiers with sufficiently low output impedance to drive a loudspeaker directly.
Loudspeaker transformer[ edit ] Loudspeaker transformer in old radio In the same way that transformers create high voltage power transmission circuits that minimize transmission losses, loudspeaker transformers can power many individual loudspeakers from a single audio circuit operated at higher than normal loudspeaker voltages. This application is common in public address applications. Such circuits are commonly referred to as constant-voltage speaker systems.
Such systems are also known by the nominal voltage of the loudspeaker line, such as , and volt speaker systems the voltage corresponding to the power rating of a speaker or amplifier.
A transformer steps up the output of the system's amplifier to the distribution voltage. At the distant loudspeaker locations, a step-down transformer matches the speaker to the rated voltage of the line, so the speaker produces rated nominal output when the line is at nominal voltage.
Loudspeaker transformers commonly have multiple primary taps to adjust the volume at each speaker in steps. Output transformer[ edit ] Valve tube amplifiers almost always use an output transformer to match the high load impedance requirement of the valves several kilohms to a low impedance speaker Small-signal transformer[ edit ] Moving coil phonograph cartridges produce a very small voltage.
For this to be amplified with a reasonable signal-noise ratio usually requires a transformer to convert the voltage to the range of the more common moving-magnet cartridges. Microphones may also be matched to their load with a small transformer, which is mumetal shielded to minimise noise pickup. These transformers are less widely used today, as transistorized buffers are now cheaper.
Interstage and coupling transformer[ edit ] In a push—pull amplifier , an inverted signal is required and can be obtained from a transformer with a center-tapped winding, used to drive two active devices in opposite phase. These phase splitting transformers are not much used today. This section does not cite any sources. Please help improve this section by adding citations to reliable sources.
Unsourced material may be challenged and removed. January Transactor[ edit ] A transactor is a combination of a transformer and a reactor. A transactor has an iron core with an air-gap, which limits the coupling between windings. They are homemade audio interstage coupling transformers. Enameled copper wire is wound round the central half of the length of a bundle of insulated iron wire e.
The ends of the iron wires are then bent around the electrical winding to complete the magnetic circuit, and the whole is wrapped with tape or string to hold it together. Variometer and variocoupler[ edit ] Variometer used in s radio receiver A variometer is a type of continuously variable air-core RF inductor with two windings. The two coils are connected in series. When the two coils are collinear, with their magnetic fields pointed in the same direction, the two magnetic fields add, and the inductance is maximum.
If the inner coil is rotated so its axis is at an angle to the outer coil, the magnetic fields do not add and the inductance is less.
If the inner coil is rotated so it is collinear with the outer coil but their magnetic fields point in opposite directions, the fields cancel each other out and the inductance is very small or zero. The advantage of the variometer is that inductance can be adjusted continuously, over a wide range. Variometers were widely used in s radio receivers. One of their main uses today is as antenna matching coils to match longwave radio transmitters to their antennas.
The vario-coupler was a device with similar construction, but the two coils were not connected but attached to separate circuits. So it functioned as an air-core RF transformer with variable coupling. The pancake coil variometer was another common construction used in both s receivers and transmitters.
The flat spiral design served to reduce parasitic capacitance and losses at radio frequencies. Pancake or "honeycomb" coil vario-couplers were used in the s in the common Armstrong or "tickler" regenerative radio receivers. Pressure changes are balanced by a flow of atmospheric air in and out of the conservator, which is how moisture can enter the system. If the insulating oil encounters moisture, it can affect the paper insulation or may even lead to internal faults.
Therefore, it is necessary that the air entering the tank is moisture-free.
The transformer's breather is a cylindrical container that is filled with silica gel. When the atmospheric air passes through the silica gel of the breather, the air's moisture is absorbed by the silica crystals. The breather acts like an air filter for the transformer and controls the moisture level inside a transformer.
It is connected to the end of breather pipe. Tap Changer Tap Changer The output voltage of transformers vary according to its input voltage and the load. During loaded conditions, the voltage on the output terminal decreases, whereas during off-load conditions the output voltage increases.
In order to balance the voltage variations, tap changers are used.
Tap changers can be either on-load tap changers or off-load tap changers. In an on-load tap changer, the tapping can be changed without isolating the transformer from the supply. In an off-load tap changer, it is done after disconnecting the transformer.
Automatic tap changers are also available. Cooling Tubes Cooling tubes are used to cool the transformer oil. The transformer oil is circulated through the cooling tubes. The circulation of the oil may either be natural or forced. In natural circulation, when the temperature of the oil rises the hot oil naturally rises to the top and the cold oil sinks downward.
Thus the oil naturally circulates through the tubes. In forced circulation, an external pump is used to circulate the oil. Buchholz Relay The Buchholz Relay is a protective device container housed over the connecting pipe from the main tank to the conservator tank. It is used to sense the faults occurring inside the transformer.