Fun facts about transformers!

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Hi, I’m the Industrial Control Assistant. Every day, I share a little piece of knowledge related to industrial control. In the previous installment, we discussed the working principle of mass flow meters. Today, we’ll give a brief introduction to transformers. In power distribution and transformation processes, transformers are essential, and it’s very important to have a basic understanding of them. Let’s take a look together. 1. What is a transformer? In AC circuits, a device that is used to increase or decrease voltage is called a transformer. A transformer can convert voltage of any value into the desired voltage level with the same frequency, in order to meet the requirements for the transmission, distribution, and use of electrical energy. For example, the electricity generated by power plants has a low voltage level, and it must be stepped up in voltage before it can be transmitted to distant areas where it is needed. In those areas, the voltage must then be reduced to an appropriate level so that it can be used by power equipment and everyday electrical devices. 2. How does a transformer change voltage? Transformers are made based on electromagnetic induction. It consists of an iron core made up of stacked silicon steel sheets, and two sets of coils wound around the core; the core and the coils are insulated from each other, with no electrical connection between them. The coil connected to the transformer and the power supply is called the primary coil (or primary side), while the coil connected to the electrical equipment is called the secondary coil (or secondary side). When the primary coil of the transformer is connected to an AC power source, changing magnetic flux lines are generated in the core. Since the secondary coil is wound around the same core, the magnetic flux lines cut through the secondary coil, which inevitably generates an induced electromotive force and results in a voltage across the ends of the coil. Since the magnetic flux lines are alternating, the voltage in the secondary coil is also alternating. Moreover, the frequency is exactly the same as the power supply frequency. Theoretically, it has been proven that the voltage ratio between the primary and secondary coils of a transformer is related to the ratio of the number of turns in these coils, and this can be expressed by the following formula: Primary coil voltage/Secondary coil voltage = Number of turns in primary coil/Number of turns in secondary coil. This shows that the greater the number of turns, the higher the voltage. Thus, it can be seen that the secondary coil is fewer in number than the primary coil, which is a step-down transformer. Otherwise, it is a step-up transformer. 3. What are the types of transformer design? Classified by the number of phases, there are single-phase and three-phase transformers. Classified by purpose, they include power transformers, special-purpose power transformers, voltage-regulating transformers, measurement transformers (voltage transformers, current transformers), small power transformers (used for low-power devices), and safety transformers. Classified by structure, they are divided into core-type and shell-type. Coils can be double-wound and multi-wound, as in autotransformers. Based on the cooling method, they are divided into oil-immersed and air-cooled types. 4. What are the components of a transformer? Transformer components mainly consist of a core and windings, in addition to things such as an oil tank, oil conservator, insulating bushings, and tap changers. 5. What is the use of transformer oil? (1) Insulation function, (2) Heat dissipation function, (3) Arc extinguishing function. 6. What is an autotransformer? An autotransformer has only one set of coils, with the secondary coil being derived from taps on the primary coil. Its power transfer occurs not only through electromagnetic induction but also through direct electrical conduction. This type of transformer uses fewer silicon steel sheets and copper wires compared to ordinary transformers, and it is commonly used for voltage regulation. 7. How does a voltage regulator adjust the voltage? The structure of the voltage regulator is the same as that of an autotransformer; the only difference is that the core is made in the form of a ring, around which the windings are placed. The secondary coil taps are equipped with slidable brush contacts that slide circumferentially along the surface of the coil, thereby enabling smooth voltage regulation. 8. What is the current relationship between the primary coil and the secondary coil of a transformer? When the transformer is operating under load, changes in the current in the secondary coil cause corresponding changes in the current in the primary coil. Based on the principle of magnetic potential balance, it can be derived that the current in the primary and secondary coils is inversely proportional to the number of turns in those coils; the side with more turns has a lower current, while the side with fewer turns has a higher current. It can be expressed by the following formula: primary coil current/secondary coil current = number of turns in the secondary coil/number of turns in the primary coil. 9. What is the voltage change rate of a transformer? The voltage change rate of a voltage regulator is one of the key performance indicators of a transformer. When a transformer supplies power to a load, the voltage at the load side of the transformer inevitably drops. By comparing this reduced voltage value with the rated voltage value and expressing it as a percentage, the voltage change rate is obtained, which can be represented by a formula ； Voltage change rate = [((Secondary rated voltage – Voltage at the load side) / Secondary rated voltage)] × 100%. In a typical power transformer, when connected to its rated load, the voltage variation rate is 4–6%. 10. How to ensure that the transformer delivers a rated voltage output? Too high or too low voltage can affect the proper operation and service life of the transformer, so voltage regulation is necessary. The method of voltage regulation involves providing several taps on the primary coil, which are connected to tap changers; the tap changers alter the number of turns in the coil by rotating contacts. By adjusting the position of the tap switch, the desired rated voltage value can be obtained. It should be noted that voltage regulation should generally be performed after disconnecting the load connected to the transformer. 11. What do commonly used small transformers look like? In what situations is it applied? Small transformers refer to single-phase transformers with a capacity of less than 1 kVA, which are mostly used as power transformers for controlling electrical equipment, as power transformers for electronic devices, and as power transformers for safety lighting. Well, that’s all for today’s content. If there’s anything you’d like to know or discuss, feel free to leave a message anytime. New updates will be posted regularly, so please stay tuned.