Jan 11 2018

# Power Transformers Encyclopedia

Summary

The power transformer is a static electrical device, which is used to transform a numerical value of alternating voltage (current) into another frequency or the same number of different voltage (current) devices. When a primary winding is connected to alternating current, it produces alternating magnetic flux. Alternating magnetic flux induces the AC electromotive force in the two winding through magnetic core conduction. This paper will mainly introduces about power transformer,such as the working principle,function of power transformer; the main power transformers or differences between power and distribution transformer.

 Article core Basic knowledge of Power Transformers Funtion transform a numerical value of alternating voltage into another frequency and etc. English name Power Transformers Category Power

Catalogs

 Catalogs I.What is power transformer 1.Original & auxiliary side coil of the ordinary transformer II.Power transformer Illustrations 2.The main power transformers III.Working of Power Transformer VI.Distribution transformer IV.Function of power transformer VII.Differences between power and distribution transformer V.Parts of Power Transformer and its function

Introduction

I.What is power transformer

The power transformer is a static electrical device, which is used to transform a numerical value of alternating voltage (current) into another frequency or the same number of different voltage (current) devices. When a primary winding is connected to alternating current, it produces alternating magnetic flux. Alternating magnetic flux induces the AC electromotive force in the two winding through magnetic core conduction. The height of the two induction electromotive force is related to the number of turns of the one or two winding, that is, the size of the voltage is proportional to the number of turns. The main function is to transmit electric energy, so the rated capacity is its main parameter. Rated capacity is a manifestation of the value of conventional power, it is a characterization of the power transmission size, using kVA or MVA to express, when the rated voltage is applied to the transformer, according to it to determine under specified conditions does not exceed the rated current value of temperature rise. The most energy saving power transformer is the amorphous alloy iron core distribution transformer, its greatest advantage is that the value of the no-load loss is very low. It is the core problem to be considered in the whole process of the whole design. When the product structure is arranged, the amorphous alloy core itself is not affected by external force. Meanwhile, the characteristic parameters of amorphous alloy must be selected accurately and reasonably when calculating.

II.Power transformer Illustrations

The picture: shape diagram of three phase oil immersed power transformer

In the above picture: The number corresponding to the name is as following:

1- nameplate; 2- signal thermometer; 3- humidifier; 4- oil mark; 5- oil storage cabinet; 6- safe airway; 7- gas relay; 8- high pressure casing; 9- low voltage casing; 10- tap changer; 11- oil tank; 12- oil discharge valve; 13- body; 14- floor; 15- car
In the above picture: The number corresponding to the name is as following:

Power supply and distribution mode: 10KV high voltage power grid adopts three phase three line neutral point ungrounded system operation mode. The user transformer power supply mostly chooses the neutral point direct grounding system operation mode of Y/Yno junction mode, which can realize three phase four wire system or five wire system power supply, such as TN-S system.

III.Working of Power Transformer

Do you know how does a power transormer work? Let's see a vedio firstly:

This video gives a detailed animated illustration on the working of electrical Transformers. The basic working principle and

construction of transformer, step-up transformer, step-down transformer, transformer winding and core construction are well illustrated.

The high voltage windings used in domestic transformers are usually connected to Y connection, and the connection between the middle voltage windings and the low voltage windings depends on the system conditions. The system condition refers to the relationship between the voltage phase of the high voltage transmission system and the voltage phase of the medium voltage or low voltage transmission system. If the low voltage system distribution system, it can be determined according to the standard. High voltage winding connection method is often Liancheng Y due to the phase voltage line voltage can be equal to 57.7%, each turn voltage can be lower.

• (1).The voltage phasors of 500, 330, 220 and 110kV transmission systems are all the same phase in China.

Therefore, the three phase three winding or three phase autotransformer with the following voltage ratio should be connected by star connection. When the iron core structure of three-phase column, low voltage winding can also adopt star connection or angle connection, it depends on the voltage of low voltage power transmission system is phase voltage and high voltage transmission system voltage phasor for the same phase or lag 30 degrees electric angle.

• 500/220/LVkV - YN, yn0, yn0 or YN, yn0, D11

• 220/110/LVkV - YN, yn0, yn0 or YN, yn0, D11

• 330/220/LVkV - YN, yn0, yn0 or YN, yn0, D11

• 330/110/LVkV - YN, yn0, yn0 or YN, yn0, D11

• (2). There are two different phase angles in the transmission system voltage of 60 and 35kV in China.

For example, 220/60kV transformer adopts YNd11 connection, and 220/69/10kV transformer is connected with YN, yn0, D11, and the two 60kV transmission systems have a difference of 30 degrees of electrical angle.

When 220/110/35kV transformer adopts YN, yn0 and D11 connection, 110/35/10kV transformer adopts YN, yn0 and D11 connection. The voltage phase of the above two 35kV transmission systems is also 30 degrees electric angle.

Therefore, it is prudent to determine the connection between the 60 and the 35kV winding, and the connection method must meet the requirements of the voltage phasor of the transmission system. The connection between the 60 and the 35kV stage windings is determined according to the relative relation of the voltage phase quantity. Otherwise, even if the capacity is right, the voltage ratio is also right, the transformer can not be used, the connection is wrong, the transformer can not be connected with the transmission system.

• (3). There are also two phases of the domestic 10, 6, 3 and 0.4kV transmission and distribution systems.

In the Shanghai area, there is a 10kV and 110kV transmission system voltage phase difference of 60 degrees electric angle, can use 110/35/10kV at the voltage ratio with YN, yn0, Y10 connection of the three-phase three winding power transformer, but limit the use of three-phase three limb core heart.

• (4). But note: single-phase transformers connected in three-phase connection method, cannot use the YNy0 connection of the three-phase group. YNy0 connection can not be used in three phase shell transformer.

Three-phase five pole transformer must be used in YN, yn0, yn0 connection, in the transformer to be connected into a corner fourth winding connection, it leads to the top (the structure to do electrical test leads out not in this case).

• (5). When the transformer is in parallel operation in different joint groups, the general regulation is that the connection number must be the same.

• (6). Distribution transformer is used for lightning intensified area, can use the Yzn11 connection, when using Z method, impedance voltage algorithm and Yyn0 method, and Z method of winding copper consumption to more. The lightning protection performance of Yzn11 distribution transformer is better.

• (7). The YNy0 connection can not be used when the three-phase transformer uses four coiled core frames.

• (8). All of the above are used for the connection of domestic transformers. When the export is exported, a suitable connection and joint group label should be supplied as required.

• (9). In general, the joint and the split switch are connected in the high voltage windings. Therefore, when the selection switch (including load tap changer and no excitation voltage regulating tap switch), must pay attention to the connection with the transformer tap switch connected with (including grounding method, test voltage, rated current, each voltage level, voltage range etc.). The YN connection of the load tap for on load tap changer in transformer, but also pay attention to the midpoint must be able to lead.

IV.Function of power transformer

Power transformers are one of the main equipment for power plants and substations. The functions of transformers are manifold. They can not only increase the voltage, but also reduce the voltage to voltage at all levels, so as to meet the need of electricity. In a word, both the boost and the depressurization must be done by the transformer. In the process of power transmission, there will be two parts of voltage and power loss. When transporting the same power, the voltage loss is inversely proportional to the voltage, and the power loss is inversely proportional to the square of the voltage. The voltage is raised by using the transformer, and the loss of power supply is reduced.

The transformer is composed of two or more than two winding coils that are wound around the same core. The winding is connected by alternating magnetic field, and works according to the electromagnetic induction principle. The installation position of the transformer should be considered for easy operation, maintenance and transportation, and the safe and reliable place should be selected. The rated capacity of the transformer must be reasonably selected when the transformer is used. When the transformer is running in no-load, it needs greater reactive power. The reactive power is supplied by the power supply system. If the capacity of the transformer is too large, it will not only increase the initial investment, but also make the transformer run at no load or light load for a long time. It will increase the proportion of no load loss, reduce the power factor and increase the network loss. So the operation is neither economical nor unreasonable. The transformer capacity is too small, which will make the transformer overload for a long time and easily damage the equipment. Therefore, the rated capacity of the transformer should be selected according to the needs of the electric load, so it should not be too large or too small. More detailed please look at Part Five.

Detail

V.Parts of Power Transformer and its function

1.Original & auxiliary side coil of the ordinary transformer

The side coil is concentrically placed on a core column with a low voltage winding and a high voltage winding. The original and secondary coils of the welder transformer are respectively mounted on two iron core columns. When the transformer is running on load, when the secondary side current increases, the transformer must maintain the main flux in the core, and the primary side current must also increase correspondingly to achieve the balance of the secondary side current. The two active power of the transformer is generally equal to the rated capacity of the transformer (KVA) * 0.8 (transformer power factor) = KW.

2.The main power transformers

• A, breathers (silica gel tube): inside the silicone oil storage cabinet (oil pillow) insulating oil within the breather is communicated with air through the desiccant to absorb moisture in the air and impurities, in order to maintain good insulation performance of transformer winding; silicone discoloration, metamorphic easily lead to clogging.

• B, the oil level gauge: reflect the transformer oil level state, in general about +20O, high oil, gas is too low; the winter temperature is low, when the load is light level changes little, or level slightly decreased; the summer temperature rises when the load is heavy, the oil level also increased slightly; two of them are normal.

• C, oil pillow: adjust the oil volume of the tank to prevent the overspeed oxidation of the transformer oil, and the upper gas hole.

• D, explosion-proof pipe: prevent sudden accident against oil.The increase of pressure in the box causes the danger of explosion.

• E, signal thermometer: monitor transformer operating temperature and send out signal. It indicates the oil temperature in the upper layer of the transformer, and the temperature of the transformer coil is 10 degrees centigrade higher than the upper oil temperature. The national standard provides that the limit working temperature of the transformer winding is 105OC, that is, when the ambient temperature is 40OC, the upper layer temperature should not exceed 95OC, usually the monitoring temperature (the upper oil temperature) is set at 85OC or below.

• F, split switch: by changing the head of the high voltage winding, increasing or reducing the number of winding turns to change the voltage ratio.

because：U1/U2＝W1/W2，U1W2＝U2W1

result：U2＝U1W2/W1

All transformers are no load voltage regulation. They need power outage. They are often divided into +5%, 0% and -5% three, II and III, the first one is 10.5KV, 10KV and 0.95KV are 380V, 400V and 420V two times. G, gas signal relay: (gas relay) light gas, heavy gas signal protection. On the contact point for the light gas signal is generally applied to signal to the alarm, said transformer abnormal operation; under the contact point for the heavy gas signal, at the same time after the action signal to trip the circuit breaker and drop alarm; general gas relay filled with oil description without gas tank, gas will enter the gas relay within reach to some extent, crowding out the gas oil contact action; open the gas relay cover, the top two adjusting rod, unscrew one cap can be released within the gas relay; the other is the adjusting rod protection test button; charged operating gloves and safety must be emphasized.

VI.Distribution transformer

When it comes to power transformer, people think of a distribution transformer.Let’s also understand something about distribution transformer.

The distribution power transformer is a static electrical equipment, which is used to transform a numerical value of alternating voltage (flow) into another frequency or the same number of different voltage (current) devices. When a primary winding is connected to alternating current, it produces alternating magnetic flux. Alternating magnetic flux induces the AC electromotive force in the two winding through magnetic core conduction. The height of the two induction electromotive force is related to the number of turns of the one or two winding, that is, the size of the voltage is proportional to the number of turns. The main function is to transmit electric energy, so the rated capacity is its main parameter. Rated capacity is a manifestation of the value of conventional power, it is a characterization of the power transmission size, with kVA or MVA, when the rated voltage is applied to the transformer, according to it to determine under specified conditions does not exceed the rated current value of temperature rise. The most energy saving power transformer is the amorphous alloy iron core distribution transformer, its greatest advantage is that the value of the no-load loss is very low. It is the core problem to be considered in the whole process of the whole design. When the product structure is arranged, the amorphous alloy core itself is not affected by external force. Meanwhile, the characteristic parameters of amorphous alloy must be selected accurately and reasonably when calculating.

Analysis

VII.Differences between power and distribution transformer

All the transformers used in the power network are called power transformers, which are all levels of transformer used before distribution, and the general low voltage is 3kV and above. The transformer that reduces the voltage to the working voltage of the electrical equipment is called the distribution transformer, which is used for daily lighting and factory power, and the general low voltage is 0.4kV or less. The distribution power transformer is a static electrical equipment, which is used to transform a numerical value of alternating voltage (current) into another frequency or the same number of different voltage (current) devices. When a primary winding is connected to alternating current, it produces alternating magnetic flux. Alternating magnetic flux induces the AC electromotive force in the two winding through magnetic core conduction. The height of the two induction electromotive force is related to the number of turns of the one or two winding, that is, the size of the voltage is proportional to the number of turns. The main function is to transmit electric energy, so the rated capacity is its main parameter. Rated capacity is a manifestation of the value of conventional power, it is a characterization of the power transmission size, with kVA or MVA, when the rated voltage is applied to the transformer, according to it to determine under specified conditions does not exceed the rated current value of temperature rise. Now the more energy saving power transformer is the amorphous alloy iron core distribution transformer, its biggest advantage is that the value of the no-load loss is very low. It is the core problem to be considered in the whole process of the whole design. When the product structure is arranged, the amorphous alloy core itself is not affected by external force. Meanwhile, the characteristic parameters of amorphous alloy must be selected accurately and reasonably when calculating.

Book Recommendation

• Power Transformers: Principles and Applications (Power Engineering (Willis))

Complete with equations, illustrations, and tables, this book covers the basic theory of electric power transformers, its application to transformer designs, and their application in utility and industrial power systems. The author presents the principles of the two-winding transformer and its connection to polyphase systems, the origins of transformer losses, autotransformers, and three-winding transformers and compares different types of transformer coil and coil construction. He describes the effects of short circuits on transformers, the design and maintenance of ancillary equipment, and preventative and predictive maintenance practices for extending transformer life.

--John Winders (Author)

• Modern power transformer practice 1st Edition Edition

--R. Feinberg (Other Contributor)

• Electric Power Transformer Engineering, Third Edition (The Electric Power Engineering Handbook)

Electric Power Transformer Engineering, Third Edition expounds the latest information and developments to engineers who are familiar with basic principles and applications, perhaps including a hands-on working knowledge of power transformers. Targeting all from the merely curious to seasoned professionals and acknowledged experts, its content is structured to enable readers to easily access essential material in order to appreciate the many facets of an electric power transformer.

--James H. Harlow (Editor)

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