First, transformer classification introduction

(1) Differentiation according to technology

Oil change: oil immersed transformer, winding insulation using integral oil immersed process.

Dry change: dry transformer, winding insulation using integral epoxy resin process.

(2) Differentiation according to function

Main transformer: the total buck transformer of the substation or the total boost transformer of the boost station.

Distribution transformer: The transformer used in the distribution system, the general voltage is 10KV more.

Box transformer: Box-type substation, the transformer, high voltage cabinet, low voltage cabinet integrated in a box equipment.

 

Second, box change style distinction and current calculation method

1, European change: European box change using high pressure cabinet, low pressure cabinet, transformer body three-part combination, 70 years from Europe to introduce the domestic structure.

2, the United States change: there is no high pressure cabinet, the high pressure chamber only lightning arrester, the load switch uses the oil-immersed transformer inside, the transformer body cancels the oil cushion, and the transformer shell is directly exposed to the air (not closed in the box change box inside). The structure was imported from the United States in the 1990s.

3, China change: China type box change is a kind of improved structure of the United States change, the oil-immersed load switch to external switch (pressure type load switch or vacuum circuit breaker), this structure is called China change. Hua change can be regarded as a modified or upgraded version of Mei Change.

4, the low voltage side current calculation method (800KVA as an example)

4.1 Standard calculation method: 800 KVA transformer, its rated output current is: I = 800 KVA ÷ (1.732*0.38 KV) = 1215 A

4.2 Simple estimation method: transformer rated current = (approximately equal to) √2* transformer capacity, that is, I = √2*800KVA=1131 A

 

Third, transformer winding wiring

1, the high voltage side of the box (10KV and 35KV) is generally connected with △, there is no neutral point, and the entire local power grid is grounded with ground change + arc suppression coil;

2, the low-voltage side of the box (400V) : generally take Y connection, there is a neutral point, the neutral point is grounded after leading the line (that is, the 220V neutral line)

3, the main transformer high voltage side (110KV and above) : generally adopt Y connection, neutral point, neutral point directly grounded.

 

Fourth, transformer voltage and capacity

(1) 10KV transformer commonly used models (KVA) 30, 50, 63, 80, 100, 125, 160, 200, 250, 315, 400, 500, 630, 800, 1000, 1250, 1600

(2) Common models of 35KV transformer (KVA) 630, 800, 1000, 1250, 1600, 2000, 2500, 3150, 4000, 5000, 6300, 8000, 10000, 12500, 16000, 20000, 25000, 31500

(3) 110KV transformer commonly used models (KVA) 6300, 8000, 10000, 12500, 16000, 20000, 25000, 31500, 40000, 50000, 63000, 75,000, 90000, 120000, 150000, 180000

(4) 220KV transformer commonly used models (KVA) 31500, 40000, 50000, 63000, 75,000, 90,000, 120,000, 150000, 180000, 240000, 300000, 360,000, 370000, 400000, 420000, 4 50000

 

Five, transformer symbol code meaning

(1) What does the transformer Yyn0 and Dy11 number symbol mean

Yyn0: means high pressure Y connection, that is, star connection, low pressure is also y connection, low pressure neutral point leads out, high and low pressure side phase Angle is 0 time above the clock.

D, yn11: means high voltage D connection, that is, triangle connection, low pressure is y connection, high and low side phase Angle is the 11 o ‘clock Angle above the clock, that is, 30 degrees.

(i.e. secondary current phase lag 330 degrees)

11 indicates that the phase Angle of the secondary side winding coil lags the primary winding coil by 330 degrees.

Since there are two types of Y connection with neutral line and without neutral line, no symbol is added without neutral line, and the letter n is added after the letter Y

(2) Dry change code meaning

S: Three-phase transformer

C: Solid molding (epoxy casting)

B: Foil coil

11: Performance level

10 and 11 are code names for transformer performance levels. The Type 11’s no-load loss is 10% lower than the Type 10’s.

(3) Oil code meaning

S – Three-phase transformer

11 – Series number

(4)Transformer impedance introduction, ud=6.5% means that the transformer impedance voltage is 6.5%. It means that one side of the transformer three-phase short circuit, from the other side to apply 6.5% rated voltage, the transformer will flow through the rated current.

 

Six, oil change and dry change comparison

1. Oil-immersed transformer

Advantages of oil-immersed transformers: low cost, can adapt to a variety of outdoor harsh environment.

The disadvantages of the oil-immersed transformer: there are leakage and fire protection problems, and it can not be installed directly in the distribution room.

2, dry transformer

Advantages of dry transformers: no leakage and fire problems, can be installed directly in the distribution room.

The disadvantages of dry transformers: high cost, poor ability to withstand harsh environments, generally can only be installed indoors.

3, the difference between dry transformer and oil-immersed transformer:

(1) The cost is not the same, for the same capacity transformer, the purchase price of dry transformer is much higher than the price of oil-type transformer.

(2) The capacity and voltage are different, dry transformers are generally suitable for distribution, the capacity is mostly below 1600KVA, the voltage is below 10KV, and there are individual 35KV voltage levels; However, the oil transformer can achieve all capacity from small to large, and the voltage level can also achieve all voltages; The UHV 1000KV test line under construction in our country must be oil-type transformer.

(3) Insulation and heat dissipation are not the same, dry transformers are generally insulated by resin, cooled by natural air, and cooled by large capacity fans, while oil-type transformers are insulated by insulating oil, and the coil generated by the circulation of insulating oil in the transformer will dissipate heat on the radiator (sheet) of the transformer.

(4) Application places, dry transformers are mostly used in places that require “fire prevention and explosion-proof”, and are generally easy to use in large buildings and high-rise buildings; The oil-type transformer may have oil ejection or leakage after an “accident”, causing a fire, which is mostly used outdoors, and there is a place where the “accident oil pool” is dug.

(5) The appearance of the packaging form is different, dry transformer can directly see the iron core and coil, and oil transformer can only see the shell of the transformer;

(6) Different lead forms dry transformers mostly use silicone rubber bushings, while oil transformers mostly use porcelain bushings.

(7) The load bearing capacity is different. The general dry transformer should run under the rated capacity, and the oil-type transformer overload capacity is better.