Transformers Detailed Introduction and Contrast

Differentiate according to process

Oil transformer: Oil-immersed transformer, winding insulation adopts integral oil-immersed process.

Dry transformer: Dry type transformer, winding insulation with integral epoxy resin process.

Distinguish by function

Main transformer: the main step-down transformer of the substation or the main step-up transformer station of the step-up station.

Distribution transformer: The transformer used in the power distribution system generally has a voltage of 10KV.

Box transformer: box type substation, integrating transformer, high voltage cabinet, low voltage cabinet in one box equipment.

European-style substation: It adopts the combination of high-voltage cabinet, low-voltage cabinet and three parts of the transformer body.

American-style substation: There is no high-voltage cabinet, the high-voltage chamber only has lightning arresters, the load switch is oil-immersed inside the transformer, the transformer body cancels the oil pillow, and directly exposes the transformer shell to the air (not enclosed inside the box transformer box).

China Substation: An improved structure of American substation in China, changing oil-immersed load switch to external switch (compression gas load switch or vacuum circuit breaker), this structure is called China Substation. A Chinese substation can be considered an improved or upgraded version of an American substation.

Standard calculation: Transformer of 800 KVA, it has a rated output current of: I＝800 KVA ÷(1.732*0.38 KV) ＝1215 A

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

The high-voltage side of the box transformer (10KV and 35KV) is generally connected by △, and there is no neutral point. The entire local power grid uses a grounding transformer + arc suppression coil to ground together;

Box transformer low voltage side (400V): Generally, Y connection is adopted, with a neutral point. After the neutral point is grounded, an outlet line is drawn (that is, a 220V neutral line)

Main transformer high voltage side (110 KV and above): generally Y connection, with neutral point, the neutral point is directly grounded.

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

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

Commonly used models of 110 KV transformers (KVA) 6300, 8000, 10000, 12500, 16000, 20000, 25000, 31500, 40000, 50000, 63000, 75000, 90000, 120000, 150000, 180000

Commonly used models of 220 KV transformers (KVA) 31500, 40000, 50000, 63000, 75000, 90000, 120000, 150000, 180000, 240000, 300000, 360000, 370000, 400000, 420000, 450000

Transformers Yyn0 and D y11 What do the numeric symbols mean

Yyn0: It means high-voltage Y connection, which is a star connection. Low-voltage is also a y connection. The neutral point of low-voltage is led out. The phase angle of the high and low-voltage sides is 0 on the clock.

D, yn11: It means high-voltage D connection, which is a triangular connection, and low-voltage is also a y connection. The phase angle on the high and low voltage sides is the angle at 11 o'clock above the clock, which is 30 degrees.

(That is, the phase lag of the secondary current is 330 degrees)

11 means that the phase angle of the secondary side winding coil lags the primary winding coil by 330 degrees.

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

Dry change code meaning

S: Three-phase transformer

C: Solid molding (epoxy resin pouring)

B: Foil coil

11: Performance level

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

Oil changes the meaning of the code

S-three-phase transformer

11-series No

Transformer impedance introduction, ud=6.5% means that the impedance voltage of this transformer is 6.5%. It indicates that one side of this transformer is short-circuited in three phases, and 6.5% of the rated voltage is applied from the other side, and the rated current will flow through the transformer.

Oil-immersed transformers

Advantages of Oil-immersed Transformer: Low cost, can adapt to all kinds of harsh outdoor environment.

Disadvantages of oil-immersed transformers: they have leakage and fire protection problems and cannot be installed directly in the distribution room.

Dry-type transformers

Advantages of dry transformer: no leakage and fire protection problem, can be installed directly in the distribution room.

Disadvantages of dry-type transformers: high cost and relatively poor resistance to harsh environments, in general they can only be installed indoors.

Differences between dry and oil-immersed transformers:

The cost is different, for transformers of the same capacity, the purchase price of dry-type transformers is much higher than that of oil-type transformers.

The capacity and voltage are different. Dry-type transformers are generally suitable for power distribution. Most of them have a capacity below 1600KVA and a voltage below 10KV. There are also some that achieve a voltage level of 35KV; while oil-type transformers can achieve full capacity from small to large, the voltage level also achieves all voltages; the UHV 1000KV test line under construction in my country must use oil-type transformers.

Insulation and heat dissipation are different. Dry-type transformers are generally insulated with resin and rely on natural air cooling. Large-capacity transformers rely on fans for cooling. Oil-type transformers rely on insulating oil for insulation. The insulation oil circulates inside the transformer to transfer the heat generated by the coil to the transformer. The heat sink (sheet) is used for heat dissipation.

Applicable places, dry-type transformers are mostly used in places that require "fire prevention, explosion-proof", and are generally easy to use in large buildings and high-rise buildings; while oil-type transformers may cause fires due to oil spouting or leakage after "an accident", and are mostly used outdoors, and there are places where sites are dug "accident oil pools".

The appearance packaging form is different; the dry-type transformer can see the core and coil directly, while the oil-type transformer can only see the casing of the transformer;

Different lead forms Dry type transformers mostly use silicone rubber casing, while oil type transformers mostly use porcelain casing.

The load bearing capacity is different. Generally, dry-type transformers should operate at rated capacity, while oil-type transformers have better overload capacity.

Ⅷ. Introduction to Z-type winding on the high voltage side of grounding transformer (wiring method): 1 is connected to the end of 3, 2 is connected to the end of 1, 3 is connected to the end of 2.