There are many types of transformers, such as power transformers, distribution transformers, dry-type transformers, and amorphous alloy transformers. To enhance your understanding of transformers, this article will introduce their composition and connection groups. If you are interested in transformers, feel free to continue reading with us!
I. Transformers and their components
Transformers are fundamental equipment for power transmission and distribution, widely used in industry, agriculture, transportation, and urban communities. There are approximately 17 million transformers in operation in my country, with a total capacity of about 11 billion kilovolt-amperes. Transformer losses account for about 40% of power transmission and distribution losses, indicating significant potential for energy conservation. To accelerate the promotion and application of high-efficiency energy-saving transformers, improve energy resource utilization efficiency, and promote green, low-carbon, and high-quality development, in January 2021, the Ministry of Industry and Information Technology, the State Administration for Market Regulation, and the National Energy Administration jointly formulated the "Transformer Energy Efficiency Improvement Plan (2021-2023)".
The components of a transformer include the transformer body (core, windings, insulation, leads), transformer oil, oil tank and cooling system, voltage regulating device, protection devices (dehumidifier, safety vent, gas relay, oil conservator and temperature measuring device, etc.), and outgoing bushings. Specific composition and functions:
(1) Core. The core is the main magnetic circuit part of the transformer. It is usually made of hot-rolled or cold-rolled silicon steel sheets with high silicon content, thicknesses of 0.35mm, 0.3mm, and 0.27mm respectively, and coated with insulating varnish. The core is divided into two parts: core columns and cross-sections. The core columns are fitted with windings; the cross-sections are used to close the magnetic circuit.
(2) Windings. The windings are the circuit part of the transformer, and they are made of double-insulated flat wire or enameled round wire. The basic principle of a transformer is electromagnetic induction. Taking a single-phase double-winding transformer as an example, its basic working principle is explained as follows: When a voltage U1 is applied to the primary winding, a current I1 flows through it, generating an alternating magnetic flux O1 in the iron core. This magnetic flux is called the main magnetic flux. Under its action, the two windings induce electromotive forces, which in turn drive the transformer control device.
II. What are the transformer connection groups?
In transformer design, the choice of wiring method is often overlooked. Three-phase transformers have A/B/C windings on the 1/2 side. The connection method between them has a significant impact on the operating performance of the transformer, especially the distribution transformer, and directly affects the power supply quality. Therefore, the selection of the wiring method is a very important task in transformer design.
A distribution transformer is a combination of a primary winding and a secondary winding, both in the form of a wiring diagram. The high-voltage and low-voltage windings of the same phase are wound on the same core column and connected by the same main magnetic flux. When the main magnetic flux changes, the induced electromotive forces in the high-voltage and low-voltage windings exhibit a certain polarity relationship.
At any given time, the potential at one end of the high-voltage winding is positive, and the potential at one end of the low-voltage winding is also positive. The ends of two windings with the same polarity are called the same end with the same name, denoted by "·", and vice versa. For the end of a synonym, it is denoted by "-".
A transformer connection group is a representation method that combines the primary winding and the secondary system.
The common transformer winding has two connections, namely, "delta connection" and "star connection"; the transformer coupling group "d" indicates a delta connection, "n" indicates a star connection with the neutral line, Y indicates star, and n indicates neutral band; '11' indicates that the line voltage UAB on the primary side of the transformer lags UAB by 330 degrees (30 degrees or higher).
The transformer connection group is indicated by uppercase letters for the primary side (or primary side connection method) and lowercase letters for the secondary side (or secondary side connection method).
y (or y) represents a stellar connection, and d (or d) represents a delta connection. The numbers are represented by a clock, indicating the phase relationship between the first and second lateral voltages. The lateral voltage phasor is used as the minute hand, fixed at the clock position, while the second-order line voltage phasor is used as the hour hand.
"YN, DL1", where 11 means that when the primary voltage phase is represented by a needle pointing to the 12:00 position on the clock, the secondary line voltage phasor is located at the 11:00 position on the clock. In other words, the secondary line voltage UAB lags behind the primary voltage UAB by 330 degrees (or leads by 30 degrees).
Two winding transformers are formed by combining four terminal groups: “Y,Y”, “d,Y”, “Y,d”, and “d,d”. Only “Y,Y” and “Y,d” are used. Since the strip is also connected to the neutral line Y and two non-empty sections, there is no sign from the empty section that does not increase with the letter after the letter n in the neutral line Y. n indicates the leading edge of the neutral section there. YN0 wiring group, UAB and UAB are consistent, in the reference 12 of the minute hand. The new group in the terminal of “12”, in a “0” position in the table simply means: the secondary winding of the transformer ends at the primary and three different sequences or the connection of the terminals to end on each side by the induced alternating current corresponding to its induced phase angle to the reference phase angle is different.
