Transformer Group-Jinn sorting

Determine the labeling of the connected group based on the phase difference between the High and Low Voltage Winding wires.

Source: Baidu Encyclopedia ":

YY connected three-phase transformer, which has six connection groups: yy0, yy4, yy8, yy6, yy10, and yy2. The number is an even number.

 

YD connected three-phase transformer, which has six connection groups: yd1, yd5, yd9, yd7, yd11, and yd3, with an odd number

 

In order to avoid confusion in manufacturing and use, the national standards stipulate that only one type of single-phase dual-winding power transformer can be connected to one group of I 0. Only yyn0, yd11, ynd11, yny0, and yy0 are required for three-phase dual-winding power transformers.

 

Standard group applications

 

The three-phase power transformer in the yyn0 group is used in the three-phase four-wire power distribution system to provide power and lighting hybrid loads;

 

The three-phase power transformer in yd11 group is used in a line with a low voltage higher than 0.4kv;

 

The three-phase power transformer in the ynd11 group is used in high-voltage lines whose neutral points must be grounded above 110kv;

 

The three-phase power transformer in yny0 group is used in the system where the source edge needs to be grounded;

 

The three-phase power transformer in the yy0 group is used to power the three-phase power load line.

 

In the connection Group of the transformer, "YN" indicates that the first side is a line with a star Neutral Line, y indicates a star, N indicates a neutral line, and "D" indicates that the second side is a triangle line. "11" indicates that the UAB voltage of the second side of the transformer lags behind the uab330 degrees (or 30 degrees ahead) of the second side of the transformer ).

 

The expression of the transformer connection group is as follows: upper-case letters indicate the wiring mode of one side (or the original side), and lower-case letters indicate the wiring mode of the secondary side (or secondary side. Y (or Y) is a star connection, and D (or D) is a triangle connection. The number uses the clock representation to represent the phase relationship between the voltage of the first and second sides. The phase of the voltage of the first side is used as the sub-needle and fixed at the 12-point of the clock, the second side of the line voltage volume as the hour hand.

 

"YN, D11", 11 indicates that when a side line voltage volume is used as a sub-needle to point at 12 o'clock, the line voltage of the secondary side is at 11 o'clock. That is, the second-side line voltage UAB lags behind a single side line voltage uab330 degrees (or 30 degrees ahead of schedule ).

 

There are four basic connection modes for transformer wiring: "Y, Y", "d, Y", "Y, D", and "D, D ". China only uses "Y, Y" and "y, D ". Because y is connected with a neutral line and without a neutral line, no sign is added without a neutral line, and a neutral line is followed by a letter N after Y.

 

In the power system and trigger circuit of Three-phase Controllable Rectification, the three-phase transformer will encounter the polarity of the transformer and the wiring problem of the connected group. The connection Group of the transformer winding is divided by the phase relationship between the original and secondary sides of the transformer and the corresponding line voltage. Generally, wire voltage vector diagrams are used to connect and identify various connected groups of three-phase transformers, which is difficult for beginners and field operators to master. The phase voltage vector diagram is used to connect and identify various connected groups of the three-phase transformer. This method is easy to learn and understand, easy to remember, and simple and reliable in practice, especially for the Y/△and △/ y join groups, it shows its superiority. The following example describes how to use the phase voltage vector diagram to identify the connection group of the three-phase transformer.

TransformerConnection Group Introduction

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Three-phase transformer windings are connected by star connections, triangular connections, and twists and turns. In the winding connection, uppercase letters A, B, and C are usually used to represent the first end of the high voltage winding, and X, Y, and Z are used to represent the end of the high voltage winding. lowercase letters A, B, and C are used to represent the first end of the low voltage winding, x, Y, and Z indicate the end, and O indicates the neutral point.

The new standard pairs are star, triangle, and tortuous connections. The symbols y, D, and Z are used for high voltage winding, and Y, D, and Z are used for medium voltage and low voltage winding, respectively. When there is a neutral point, it is not represented by YN, Zn, YN, and Zn. The self-coupling transformer has one of the lower rated voltages in the common two windings, which is indicated by symbol. Transformer is connected by high voltage, medium voltage, and low voltage winding. For example, if the high voltage is Y and the low voltage is YN, the winding connection group is yyn. The addition of the clock method indicates that the correlation between the high and low voltage sides is the connected group.

The three commonly used join groups have different features:

1y connection: the winding current is equal to the line current, and the winding voltage is equal to the line voltage 1/√ 3, and can be made into hierarchical insulation. In addition, the neutral point leads to the ground, and can also be used to realize four-wire power supply. The main drawback of this coupling is that there is no cycle loop of the Third Harmonic Current.

2d join: the features of d join are the opposite of those of Y join.

3z join: The Z join has the advantage of Y join, and the number of turns is 15.5% more than that of Y join. High cost.

According to the GB/T6451-1999 "Three-Phase Oil Immersed Power Transformer technical parameters and requirements" and GB/T10228-1997 "Dry Type Power Transformer technical parameters and requirements", distribution transformer can be connected by dyn11. China's new national code Code Civil Building electrical design code, industrial and civil power supply and distribution system design specifications, 10 kV and below substation design specifications, etc. are recommended to use dyn11 connection transformer distribution Transformer. Currently, distribution transformers in most countries use dyn11 connections, mainly because dyn11 connections have advantages over yyn0 connections:

3.1d bonding has a great impact on the suppression of higher harmonic waves.

3.1.1 The Third Harmonic circulation in the D-junction winding can generate the Third Harmonic Magnetic Potential in the transformer, which is balanced against the third harmonic magnetic potential of the Low Voltage Winding;

3.1.2 The Third Harmonic Potential of the high-voltage phase winding is in the central flow of the D-junction loop. The third harmonic current can form a circulation in the first winding of the D-junction so that it will not be injected into the public high-voltage grid.

The zero-sequence impedance of the 3.2dyn11 junction transformer is much smaller than that of the yyn0 junction transformer, which is conducive to the removal of Low-Voltage Single-phase grounding short-circuit faults.

3.3dyn11 connection transformer allows the Neutral Line Current to reach more than 75% of the phase current. Therefore, its load balancing capability is far greater than that of the yyn0 connected transformer.

3.4 When a melting wire on the high voltage side is broken, the load of the second phase of the dyn11 connecting transformer can still run, but the load of yyn0 cannot.

Therefore, it is necessary to select the dyn11 connection transformer in the selection of transformer connection groups. Because the insulation strength of the high voltage winding of the yyn0 junction transformer is slightly lower than that of the dyn11 junction transformer, it is not recommended to change the yyn0 junction transformer to the dyn11 junction.

"YN, D11", 11 indicates that when a side line voltage volume is used as a sub-needle to point at 12 o'clock, the line voltage of the secondary side is at 11 o'clock. That is, the second-side line voltage UAB lags behind a single side line voltage uab330 degrees (or 30 degrees ahead of schedule ).

Benefits of using dyn11 connections

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First, it is helpful to suppress high harmonic current. For a three-phase transformer with a yyn0 line, the original side is star connected without a midline, so the third harmonic current cannot flow. When the waveform of the original side excitation current is a sine wave, the core is flat-top, and the secondary side induction potential waveform contains a large amount of higher harmonic; the higher harmonic current, which is dominated by three harmonic waves, can form circulation at the original side when the original side is connected to a triangle. Compared with the star formed at the original side, this helps to suppress the higher harmonic current. The current waveform will be distorted when the power electronic components and gas discharge lights in the current power grid are increasingly widely used and their power is getting bigger and bigger. Even if the three-phase load balancing, the neutral line also flows through the higher harmonic current dominated by three harmonic waves. The source side of the Distribution Transformer (usually 10 kV side) uses a triangle line to suppress this type of harmonic current, so as to ensure the quality of the power supply waveform. Second, it is conducive to the removal of single-phase short-circuit grounding faults: the original side (high voltage) is connected to a triangle (d), and the winding can be generated through the zero-sequence cyclic current (induction ), therefore, it can be balanced and demagnetized with the zero-sequence current of the Low-Voltage Winding. Therefore, the zero-sequence impedance of the secondary side (low-voltage side) is very small. If the original side (high-voltage side) is connected to the Star (y side ), the winding cannot flow through zero-sequence current. When the low-voltage side is magnetized, the zero-sequence current will generate zero-sequence magnetic flux in the Transformer Core. However, the magnetic circuit cannot be closed in the core, and the air outside the core should be taken, the resistance is very high, and the zero-sequence impedance of the transformer is large. If a single-phase short circuit occurs, the short-circuit current value will be relatively reduced, resulting in many cases, the single-phase short-circuit Grounding Current can hardly make the low-voltage circuit breaker quick action or the fuse quick circuit breaking. Generally, under the same conditions, the single-phase short-circuit current of the power distribution system of the dyn11 transformer is more than three times that of yyn0. Therefore, the dyn11 line is conducive to the removal of single-phase short-circuit grounding fault. Third, the ability to make full use of transformer equipment: for distribution transformer, lighting, air conditioning, electric cooking, electric heating and other kitchen appliances, 220 V single-phase load often accounts for a large proportion. Although the single-phase load should be evenly distributed in three phases during engineering design and installation, due to the ever-changing operation conditions, there may be serious imbalance between the three phases. If the three-phase load is unbalanced or the power factor of each phase is quite different, and the transformer is in asymmetric operation, the secondary edge Neutral Line will have current passing through. Article 6.0.8 of the above Code clearly stipulates that: "In a low-voltage power grid of the TN and TT system grounding type, when a three-phase transformer of the yyn0 cabling group is selected, the Neutral Line Current caused by single-phase unbalanced load shall not exceed 25% of the rated current of the low voltage winding, and the current of the first phase shall not exceed the rated current value at full load." This regulation clearly limits the capacity of the single-phase load used when the yyn0 line is finished, thus limiting the use of the yyn0 Power Distribution Transformer-at this time, the power of the transformer equipment cannot be fully utilized. However, the dyn11 transformer has no limit on the Neutral Line Current and can reach the low-voltage side of the transformer, so as to make full use of the transformer capacity and exert its equipment capabilities, it is particularly suitable for Distribution Transformer with unbalanced three-phase due to single-phase load. Therefore, the dyn11 connection group should be preferred for the new generation of distribution transformers.

Both transformers are directly grounded at the center. Because the high-voltage winding of the transformers in dyn11 wiring group is triangular, when the user generates three harmonic and three harmonic multiples, the circulation can be formed in the Triangle Winding, this will generate magnetic flux to eliminate the power grid pollution caused by such harmonic waves.

The yyn0 transformer does not have Triangle Winding and does not have this function. If it is only a small-capacity Transformer with independent power supply, yyn0 transformer can be used. Such transformer is available everywhere for good production. If it is possible to supply power in parallel with other transformer, or as a backup power transformer for other power supplies, you should select the same wiring group as other transformer. If it is a large-capacity industrial transformer, it is recommended to select the dyn11 transformer to reduce the pollution of the power grid by the third or third harmonic.

 

Q: Will the transformer connection group change the three-phase sequence?

   Answer: The transformer coupling group only changes the electrical angle between the first and second voltage, and does not change the three-phase sequence.

   DiscriminationA Simple Method for connecting three-phase transformer groups: the transformer winding is divided into different combinations based on the phase relationship between transformer and sub-winding force. In order to distinguish different joining groups, the long needle of the clock is represented as the line EMR at the high voltage side,
The short needle of the clock is represented as the line EMR at the low voltage side.

 

 

Transformer connection group --- changed

Tianjin tongdexing Electric Technology Co., Ltd. Huang Jixi

Original address: http://hjxbk.blog.sohu.com/108461676.html

For three-phase connections, there are usually three access methods: Y, D, and Z. Yy12, yd11, and dy11 are commonly used.

The identification of the transformer connection group label usually adopts the internationally defined clock notation, that is, the EAB vector of the original Winding Line is defined as the pointer of the clock and fixed to the "12" position, the e-AB vector of the auxiliary winding is the number that points to the clock at the hour. This number is the number of the connected group of the three-phase transformer. The following uses yy0 as an example to describe how to determine the join group label. Draw the wiring diagram of the original winding and secondary winding respectively (see figure 1 ()). Note that the winding of the same core column is aligned up and down when drawing, and find the same polarity end of the winding induction potential on the same core column.

 

Figure 1 yy0 connection Group

Draw the potential vector diagram of the original edge winding according to the original edge wiring. Draw a potential vector map that regards A and A (see Figure 1 (B) as equipotential points based on the secondary edge wiring.

In the original and vice-winding EMFs vector plot, find the corresponding line-to-line EMF phase difference. That is to say, the EAB is fixed at the "12" position as the sub-needle of the clock, and the number indicated by the EAB as the hour hand is the connection group label of the transformer (in Figure 1, EAB refers to "12 ", it is usually expressed as "0 ).

Join group composition: original edge wiring and secondary edge wiring group number. As a result, the join group in Figure 1 is yy0.

By using this method, each connected Group should draw a potential vector diagram corresponding to the original and secondary edge connections. The steps are cumbersome and error-prone, which makes it difficult to master, this is especially true for employees engaged in substation operations. The author makes a comprehensive analysis on all the connected groups and finds out the relationships and change rules between them, and sums up a simple method to determine the join group label without drawing a vector chart.

2 phase variation law of each EMF vector in Transformer

The connection Group of Three-phase transformer is determined using the method prescribed internationally. The key step is to draw a vector map of the source and secondary winding EMR to find the phase difference between the source and secondary winding. Due to the characteristics of the three-phase transformer structure, the phase variation and phase difference of the original and auxiliary winding of the three-phase transformer also have certain rules to follow.

The same side (original side or secondary side) of the three-phase transformer, each of which has a phase mutual potential of 120 °.

On the same iron core column, the source and secondary winding are either in the same phase, and the phase difference is 0 ° or in reverse phase. The phase difference is + 180 ° (1 yy0 ).

Regardless of the join method, the triangle composed of potential vectors is an equilateral triangle. The phase difference between the high-voltage bypass potential EAB and the corresponding low-voltage bypass potential EAB is always an integer multiple of 30 °.

3 transformer connection Group Variation Rules

The basic wiring of the three-phase transformer is a star connection (the original side is represented by the symbol "Y", and the secondary side is represented by the symbol "Y") and a triangle connection (the original side is represented by the symbol "D, the secondary edge is represented by the symbol "D ). The original and secondary edge wiring combinations include YY, YD, Dy, and DD. Each combination has six group numbers and a total of 24 join groups. The change rules are as follows.

First, when the original and secondary winding connection modes are the same, the connection group number is an even number (as shown in 1). When the original secondary winding connection modes are different, the connection line number is an odd number (as shown in Figure 2 ).

Figure 2 yd11 connection Group

Second, when the source and secondary sides have the same wiring, the same marking, and the polarity are the same, the relative potential phase difference of the source and secondary winding is 0. The Join group is labeled as "0", for example, yy0. When the source and secondary sides have the same wiring, labeling the same, and polarity is opposite, the potential phase difference of the source and secondary winding is 180 °, and the label of the connection group should be "6" (yy6 ).

Third, when the original edge wiring, labeling, and polarity are fixed, the marking of the three-phase outlet of the secondary edge winding is shifted once in sequence, which is equivalent to a clockwise rotation of 120 °, the Join group adds "4" to the original label. For example, when "0 + 4" is used, the label is "4". After a secondary edge is displaced, the potential force of the secondary edge is converted to 120 °, it is equivalent to "4 + 4" and marked as "8" (yy8 ).

Fourth, when the wiring on one side is a triangle, if the mark remains unchanged, the polarity remains unchanged, but the wiring is changed from the sequence triangle to the reverse triangle, and the corresponding phase potential changes by 60 °. When the triangle is connected to the secondary side, it is equivalent to 60 ° clockwise for the clock, and the group number is reduced by "2". If yd1 is changed to yd11, when the triangle is connected to the original side, it is equivalent to 60 ° clockwise for the hour, and the group number is added with "2", for example, dy11 is changed to dy1.

 

 

1. Clock representation of transformer connection groups

The phase difference between the primary voltage and the secondary voltage of Various connection groups is 0 °, and the phase difference is a multiple of 30 °. On the clock surface, every two adjacent numbers have a 30 ° angle difference. Therefore, the clock representation is the most suitable among all the connection group labels.

The line voltage vector AB at the first side of the transformer acts as the long needle of the clock, it points to the clock number 12, and the second side voltage vector AB acts as the short needle of the clock. If the short needle also points to 12, it indicates that the vector AB and AB are in the same phase, reading by the clock is 12 o'clock, this connection is recorded as 12.

For example, the yy12 yy6 yd11 yy5 yy8 connection is as follows:

 

2. Various transformer connection groups