变压器的主要技术参数都有哪些？这些技术参数的定义是怎样的？

变压器的主要技术指标较多，常有变压比、额定功率、效率、额定电压、空载电流及绝缘电阻等。

1、变压比

变压比是变压器初级电压（或阻抗）与次级电压（或阻抗）的比值。通常变压比直接标出电压变换值，如220V/10V；变阻比则以比值表示，如3：1表示初次级阻抗比为3：1。

2、额定功率

额定功率是变压器在指定频率和电压下能长期连续工作，而不超过规定温升时次级输出的功率，用伏安表示，习惯称瓦或千瓦。电子产品中变压器功率一般都在数百瓦以下。

3、效率

效率是输出功率与输入功率之比。一般变压器的效率与设计参数、材料、制造工艺及功率有关。通常20W以下的变压器效率约为70％～80％，而100W以上变压器可达95％以上。

4、额定电压

额定电压是指在变压器的初级线圈上所允许施加的电压，正常工作时变压器初级绕组上施加的电压不得大于规定值。

5、空载电流

变压器在工作电压下次级空载或开路时，初级线圈流过的电流称为空载电流。一般不超过额定电流的10％，设计、制作良好的变压器空载电流可小于5％。空载电流大的变压器损耗大、效率低。

6、绝缘电阻

表示变压器各线圈之间、各线圈与铁芯之间的绝缘性能。绝缘电阻的高低与所使用的绝缘材料的性能、温度高低和潮湿程度有关。

There are many main technical indexes of transformer, such as transformation ratio, rated power, efficiency, rated voltage, no-load current and insulation resistance.

1. Transformation ratio

Transformation ratio is the ratio of primary voltage (or impedance) to secondary voltage (or impedance) of transformer. Usually, the transformation ratio is directly marked with the voltage transformation value, such as 220V / 10V; For example, 3:1 means that the impedance ratio of primary stage is 3:1.

2. Rated power

Rated power refers to the power that the transformer can work continuously for a long time under the specified frequency and voltage without exceeding the secondary output power at the specified temperature rise. It is expressed in volt ampere and is used to be called watt or kilowatt. In electronic products, the power of transformer is generally below several hundred watts.

3. Efficiency

Efficiency is the ratio of output power to input power. The efficiency of general transformer is related to design parameters, materials, manufacturing process and power. Generally, the efficiency of transformer below 20W is about 70% ～ 80%, while that of transformer above 100W is more than 95%.

4. Rated voltage

The rated voltage refers to the voltage allowed to be applied on the primary winding of the transformer. During normal operation, the voltage applied on the primary winding of the transformer shall not be greater than the specified value.

5. No load current

When the secondary of transformer is no-load or open circuit under working voltage, the current flowing through the primary coil is called no-load current. Generally, it is not more than 10% of the rated current, and the no-load current of well designed and manufactured transformer can be less than 5%. The transformer with large no-load current has large loss and low efficiency.

6. Insulation resistance

It refers to the insulation performance between the coils of the transformer and between the coils and the iron core. The insulation resistance is related to the performance, temperature and humidity of the insulating materials used.