📚 Transformers in Electricity Transmission | 电力传输中的变压器
Transformers play a central role in the efficient distribution of electrical energy across the UK's National Grid and similar networks worldwide. This article covers the structure, working principle and key equations of transformers, with a focus on how step-up and step-down devices reduce energy losses during high-voltage transmission. Aligned with Edexcel IGCSE Science (specification point 6.25P), the following sections offer clear explanations, useful comparisons and essential exam tips.
变压器在英国家电网和世界各地类似电网的高效电力分配中起着核心作用。本文介绍变压器的结构、工作原理和关键方程，重点解释升压和降压装置如何在高电压传输过程中减少能量损耗。内容紧扣艾德思 IGCSE 科学（考点 6.25P），各小节提供了清晰的解释、实用的对比和关键的考试提示。
1. Introduction to Transformers | 变压器简介
A transformer is an electrical device that changes the voltage of an alternating current (AC) supply without changing the frequency. Transformers are essential because electricity must be sent over long distances at very high voltage to minimise energy wasted as heat, but end users need a much lower, safer voltage. By using electromagnetic induction, a transformer can step voltage up or down with high efficiency, typically better than 95%.
变压器是一种能够改变交流电源电压而不改变其频率的电气装置。变压器之所以不可或缺，是因为电能必须以很高的电压进行远距离输送以减少热损耗，而最终用户需要的电压则要低得多、安全得多。利用电磁感应原理，变压器可以高效地升高或降低电压，效率通常超过 95%。
2. The Structure of a Transformer | 变压器的结构
A basic transformer consists of two coils of insulated wire wound around a common soft iron core. The coil connected to the input AC supply is called the primary coil, and the coil delivering the transformed output is the secondary coil. The soft iron core is laminated – made of thin sheets with insulating layers – to reduce eddy currents that would otherwise heat the core and waste energy.
一个基本的变压器由两卷绝缘导线构成，它们绕在一个共同的软铁芯上。连接交流输入电源的线圈称为初级线圈，输出变压后电能的线圈称为次级线圈。软铁芯是叠片式的——由涂有绝缘层的薄片制成——目的是减少涡流，否则涡流会使铁芯发热并浪费能量。
3. How a Transformer Works | 变压器的工作原理
When an alternating current flows through the primary coil, it produces a changing magnetic field in the iron core. Because the core provides a continuous magnetic path, this alternating flux passes through the secondary coil. The continuously changing flux induces an alternating voltage across the secondary coil by electromagnetic induction. No electrical connection exists between the two coils; energy is transferred magnetically.
当交流电通过初级线圈时，它会在铁芯中产生变化的磁场。由于铁芯提供了连续的磁路，这一交变磁通会穿过次级线圈。不断变化的磁通通过电磁感应在次级线圈两端感应出交流电压。两个线圈之间没有电连接；能量是通过磁路传递的。
4. The Turns Ratio Equation | 线圈匝数比方程
The relationship between the voltages and the numbers of turns on the two coils is given by the transformer equation:
V₂ / V₁ = N₂ / N₁
where V₁ and V₂ are the primary and secondary voltages, and N₁ and N₂ are the numbers of turns on the primary and secondary coils respectively. This equation assumes an ideal transformer with no flux leakage and no energy loss. If N₂ is greater than N₁, V₂ will be greater than V₁ – a step-up transformer. If N₂ is smaller, the transformer steps the voltage down.
初级和次级线圈的电压与匝数之间的关系由变压器方程给出：
V₂ / V₁ = N₂ / N₁
其中 V₁ 和 V₂ 分别是初级和次级电压，N₁ 和 N₂ 分别是初级和次级线圈的匝数。该方程假设变压器是理想的，没有漏磁且无能量损失。若 N₂ 大于 N₁，则 V₂ 大于 V₁——这是升压变压器。若 N₂ 较小，则变压器的输出电压降低。
5. Power and Current in Transformers | 变压器中的功率与电流
For an ideal transformer with 100% he secondary coil: P = V₁ × I₁ = V₂ × I₂. Real transformers have efficiencies close to 100% the current must decrease in proportion to keep the power nearly constant, and vice versa.
对于理想变压器（效率为 100%），输入初级线圈的功率等于次级线圈输出的功率：P = V₁ × I₁ = V₂ × I₂。实际变压器的效率接近 100%，因此该方程是一个很好的近似。如果电压被升高，电流就必须成比例地减小，以保持功率基本不变；反之亦然。
6. Step-Up Transformers: Boosting Voltage | 升压变压器：提高电压
A step-up transformer has more turns on the secondary coil than on the primary, so N₂ > N₁. It increases voltage from the primary side to a higher secondary voltage. In electricity generation, step-up transformers are placed at power stations to raise the generated voltage (typically around 25 kV) to transmission voltages of 132 kV, 275 kV or even 400 kV. The reduced current during transmission cuts down I²R losses in the cables dramatically.
升压变压器的次级线圈匝数多于初级线圈，即 N₂ > N₁。它将初级侧的电压升高到更高的次级电压。在发电环节，升压变压器安装在发电厂，将发电机发出的电压（通常约为 25 kV）提升至 132 kV、275 kV 甚至 400 kV 的输电电压。输电过程中电流减小，大幅降低了电缆中的 I²R 损耗。
7. Step-Down Transformers: Reducing Voltage | 降压变压器：降低电压
A step-down transformer has fewer turns on the secondary coil (N₂ < N₁), so the output voltage is lower than the input voltage. Before electricity reaches homes, schools and factories, step-down transformers reduce the grid voltage to safer, usable levels – typically 230 V in the UK. Local substations house these transformers, ensuring the final voltage is stable and appropriate for domestic appliances.
降压变压器的次级线圈匝数较少（N₂ < N₁），因此输出电压低于输入电压。电力进入家庭、学校和工厂之前，降压变压器将电网电压降至安全可用的水平——英国通常为 230 V。当地的变电站内装有这些变压器，确保最终的电压稳定并适用于家用电器。
8. Electricity Transmission and the National Grid | 电力传输与国家电网
The National Grid is a network of cables and transformers that carries electricity from power stations to consumers. High-voltage overhead lines or underground cables transport bulk power across Britain. Step-up transformers feed electricity into the grid, and step-down transformers extract it at suitable voltages. This system allows centralised generation, reduces overall energy waste and permits load balancing across regions.
国家电网是由电缆和变压器组成的网络，将电力从发电厂输送给用户。高压架空线或地下电缆在英国各地输送大量电能。升压变压器将电力送入电网，降压变压器则以合适的电压将其取出。这一系统实现了集中发电，减少了总的能量浪费，并允许各地区之间进行负荷平衡。
9. Why High Voltage Reduces Energy Loss | 为何高电压能减少能量损耗
The power lost as heat in a transmission cable is given by Ploss aising the transmission voltage V causes the current I to fall. Since the loss depends on I², even a modest increase in voltage produces a large reduction in wasted heat. That is why the grid uses extremely high voltages for long-distance links.
传输电缆中以热能形式损耗的功率由 Ploss = I² × R 给出，其中 R 是电缆电阻。对于固定的输电功率（P = V × I），提高输电电压 V 会导致电流 I 下降。由于损耗正比于 I²，即便电压只是适度增加，也能大幅减少热损耗。这就是电网在远距离传输中使用超高电压的原因。
10. Practical Considerations and Safety | 实际考虑与安全
Although high voltage reduces resistive losses, it demands thicker insulation, taller pylons and careful safety management. Transformers operate with alternating current; a direct current supply cannot induce a changing magnetic flux and would damage the device. Modern transformers are oil-cooled or air-cooled to dissipate heat, and they include protective measures such as fuses and circuit breakers to isolate faults quickly.
尽管高电压能减少电阻损耗，但它需要更厚的绝缘、更高的输电塔以及细致的安全管理。变压器必须使用交流电工作；直流电源无法产生变化的磁通，会损坏设备。现代变压器利用油冷或风冷来散热，并配有熔断器和断路器之类的保护装置，以便快速隔离故障。
11. Summary of Key Points | 重点总结
- Transformers change AC voltages via electromagnetic induction.
- Key equation: V₂ / V₁ = N₂ / N₁; ideal power: V₁ I₁ = V₂ I₂.
- Step-up: N₂ > N₁, raises voltage, lowers current.
- Step-down: N₂ < N₁, lowers voltage for consumer use.
- High transmission voltage minimises I²R losses over distance.
- Laminated soft iron core reduces eddy currents and improves efficiency.
- Only works with alternating current; safety systems are essential.
- 变压器通过电磁感应来改变交流电压。
- 关键方程：V₂ / V₁ = N₂ / N₁；理想功率：V₁ I₁ = V₂ I₂。
- 升压：N₂ > N₁，提高电压，降低电流。
- 降压：N₂ < N₁，为消费者降低电压。
- 高输电电压可最大程度降低远距离 I²R 损耗。
- 叠片式软铁芯减少涡流，提高效率。
- 仅适用于交流电；安全系统必不可少。
12. Exam Tips and Common Mistakes | 考试提示与常见错误
ns ratio; a larger N₂ gives a larger V₂. Do not apply P = V² / R to the transformer itself – g the National Grid, be explicit that step-up transformers are used before transmission and step-down near consumers.
许多学生对匝数比的方向感到困惑。请记住：电压比等于匝数比；N₂ 越大，V₂ 越大。不要把 P = V² / R 用到变压器本身——这是电缆损耗的公式。一定要说明变压器需要交流电才能产生变化的磁场。在描述国家电网时，要明确指出升压变压器在输电前使用，降压变压器则在靠近用户处使用。
Published by TutorHao | IGCSE Science Revision Series | aleveler.com
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