Distribution transformer, referred to as "distribution transformer", refers to a static electrical apparatus in which alternating current energy is transmitted by changing AC voltage and current according to the law of electromagnetic induction. Some areas call power transformers with voltage levels of less than 35 kV (mostly 10kV and below), which are referred to as "Distribution Transformers" or "Distribution Transformers". The place and place where the "distribution transformer" is installed is not only a substation. The distribution transformer should be installed on the column or on the ground in the open air.
Distribution transformer classification
According to the different insulation medium, distribution transformer is divided into oil immersed transformer and dry type transformer; according to the different voltage regulation mode, it can be divided into non excitation voltage regulating transformer and on load voltage regulating transformer.
1. Oil immersed transformer is divided into the following types according to the shell type:
1) Non enclosed oil immersed transformer: it mainly has series products such as S8, S9 and S10, which is widely used in industrial and mining enterprises, agriculture and civil buildings.
2) Closed type oil immersed transformer: it mainly includes S9, S9-M, s10-m and other products, and is mainly used in places with many oil and chemical substances in the petroleum and chemical industries.
3) Sealed oil immersed transformer: mainly bs9, s9-, s10-, s11-mr, SH, sh12-m and other products, can be used for distribution in various places such as industrial and mining enterprises, agriculture, civil buildings, etc.
2. Dry type transformer is divided into three parts according to insulation medium:
1) Sealed coil dry type transformer: mainly includes series products such as scb8, SC (b) 9, SC (b) 10, scr-10, etc., which are suitable for high-rise buildings, commercial centers, airports, stations, subway, hospitals, factories and other places.
2) Non enveloped coil dry type transformer: mainly SG10 series products, suitable for high-rise buildings, commercial centers, airports, stations, subway, petrochemical and other places.
1. Model
The model of transformer is shown as follows:
Classification, specification and model of distribution transformer
For example: sfz-10000 / 110 represents three-phase natural circulation air cooling on load voltage regulation, rated capacity of 10000kva, rated voltage of high voltage winding lOkV power transformer.
S9-160/10 means three-phase oil immersed self cooling type, two winding excitation free voltage regulation, rated capacity of 160KVA, rated voltage of high voltage side winding is 10kV power transformer.
Sc8-315 / 10 represents three-phase dry cast insulation, two winding excitation free voltage regulation, rated capacity of 315KVA, and rated voltage of high voltage side winding is lOkV power transformer.
S11-M (R) -100/10 means three-phase oil immersed self-cooled type, two winding excitation free voltage regulation, winding type core (circular section), sealed type, rated capacity of 100kVA, rated voltage of high voltage side winding is 10kV power transformer.
Sh11-m-50 / 10 represents three-phase oil immersed self cooling type, two winding excitation free voltage regulation, amorphous alloy core, sealed type, rated capacity of 50KVA, rated voltage of high voltage side winding is 10kV power transformer.
Power transformer can be classified according to winding coupling mode, phase number, cooling mode, winding number, winding wire material and voltage regulating mode. However, this classification is not enough to express all the characteristics of the transformer, so in the transformer model, in addition to the classification characteristics, it is necessary to mark its rated capacity and rated voltage level of high voltage winding.
Some new special structure distribution transformers, such as amorphous alloy core, winding core and sealed transformer, are respectively expressed by H, R and m.
2. phase number
Transformers are divided into two types: single phase and three-phase, which are generally made into three-phase transformers to meet the requirements of transmission and distribution directly. Small transformers are made of single phase. After the super large transformer is made into single phase, it is composed of three-phase transformer group to meet the requirements of transportation.
3. rated frequency
The rated frequency of transformer is the designed operating frequency, and 50Hz in China.
4. rated voltage
Rated voltage refers to the voltage of transformer line (effective value), which shall conform to the voltage of the transmission and transformation line connected. The voltage level of transmission and transformation lines in China (i.e. line terminal voltage) is 0.38, 3, 6, 10, 35, 63, 110, 220, 330, 500kV, so the rated voltage of the primary side of the transformer connected to the line terminal (called step-down transformer) is the same as the above values.
Considering the voltage drop of the line, the voltage at the beginning (power supply side) of the line will be higher than the grade voltage, and the voltage below 35KV shall be 5%, and the height of 35kV and above shall be 10%, that is, the starting voltage of the line is 0.4, 3.15, 6.3, 10.5, 38.5, 69, 121, 242, 363, 550kV. Therefore, the rated voltage of the secondary side is the same as the value listed above for the transformer connected to the beginning of the line (i.e. step-up transformer).
The transformer product series is divided into high voltage grades, including 10kV and below, 20kV, 35kV, 66kV, 110kV series and 220kV series.
5. rated capacity
Rated capacity refers to the output capacity (kVA) of the secondary side of the transformer under the rated state specified on the transformer nameplate. For three-phase transformers, the rated capacity is the sum of the three-phase capacity.
The rated capacity of transformer is different from that of winding: the rated capacity of double winding transformer is the rated capacity of winding; the rated capacity of each winding shall be specified for multi winding transformer, and its rated capacity is the maximum rated capacity of winding; when the transformer capacity is changed by cooling mode, rated capacity refers to the maximum capacity.
The rated capacity of transformer is also closely related to voltage level. When the voltage is low and the capacity is large, the current is large and the loss increases; the high voltage and the capacity are small, the insulation ratio is too large, and the transformer size is relatively increased. Therefore, the capacity of low voltage will be small and the capacity with high voltage will be large.
6. rated current
The rated current of the transformer is the current passing through the winding line end, namely, the line current (effective value). Its size is equal to the rated capacity of the winding divided by the rated voltage of the winding and the corresponding phase coefficient (1 for single phase and 3 for three phases).
Rated current of single-phase transformer is
Classification and specification and model of distribution transformer (7-7)
Where jn is rated current at primary side and secondary side;
Sn rated capacity of transformer;
Un- rated voltage at primary and secondary sides.
Rated current of three-phase transformer is
Classification and specification and model of distribution transformer (7-8)
When the winding of three-phase transformer is Y-connected, the line current is winding current; when △ is connected, the line current = √ 3 groups of current.
7. winding connection group label
The same side winding of transformer is connected in a certain form.
Three phase transformers or single-phase transformers which form three-phase transformer group can be connected into star, triangle, etc. Star connection is that one end of each phase coil is connected to a common point (neutral point), and its terminal is connected to the corresponding wire end; triangle connection is that three phase loops are connected in series to form a closed circuit, and connected to corresponding wire end from series.
For star, triangle and zigzag connection, the symbols y, D and Z are used for high voltage winding respectively; for medium voltage and low voltage winding, the symbols y, D and Z are respectively used. When the neutral point is out, the symbols YN, Zn, yn and Zn are used respectively.
The combination of transformers in the order of high voltage, medium voltage and low voltage winding connection is the connection group of winding. For example, if the transformer is connected by D at high voltage and yn at low voltage, then the winding connection group is dyn (Dyn11).
8. pressure regulating range
When the transformer is connected to the power grid, the voltage at the secondary side of the transformer will change due to various reasons, which will affect the normal operation of the power equipment, so the transformer shall have certain voltage regulating capacity. According to the working principle of transformer, when the turn ratio of high and low voltage winding changes, the voltage at the secondary side of transformer also changes. The purpose of voltage regulation can be achieved by changing the turn to turn ratio of transformer. The voltage regulation of transformer is usually divided into two ways: excitation free voltage regulation and on load voltage regulation. The voltage regulation of the secondary side without load and the primary side disconnected from the power grid is excitation free voltage regulation, and the voltage regulation under the load on the secondary side is on load regulation.
9. no load current
When the secondary winding of the transformer is open and the rated voltage of rated frequency is applied to the primary winding, the current flowing through the primary winding is called no-load current, and there is a large impact current when the transformer is closed without load.
10. impedance voltage and short circuit loss
When the secondary side of the transformer is short circuited, the voltage applied on the primary side makes its current reach the rated value. At this time, the voltage applied is called impedance voltage UZ. The power absorbed by the transformer from the power supply is the short circuit loss, expressed as the percentage of the impedance voltage in proportion to the rated voltage UN, that is, the resistance voltage is expressed as a percentage of the rated voltage UN, that is, the voltage applied is called the impedance voltage UZ
Classification and specification and model of distribution transformer (7-9)
11. voltage adjustment rate
When the transformer is running under load, the secondary voltage will change with the change of load current and load power factor due to the impedance voltage drop in the transformer. The voltage adjustment rate means that the change of secondary voltage of transformer is not large. In order to measure the power supply quality of transformer, it is defined as: the ratio between the difference between the secondary no-load voltage and the secondary load voltage and the secondary rated voltage under the given load power factor (generally taken as 0.8), namely
5（7-10）
Where 2n is the secondary rated voltage, i.e. secondary no-load voltage;
U2 secondary load voltage.
Voltage adjustment rate is a data to measure the quality of transformer power supply.
12. efficiency
The efficiency of transformer is the percentage of the ratio of the output active power to the input active power. Generally, the efficiency of small and medium-sized transformers is about 95%.
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