How to calculate the voltage regulation rate of transformer

In power system, transformer is an important equipment for power transmission, and its performance directly affects the quality of power supply and the stability of the system. Among them, the voltage regulation rate is a key parameter to measure the output voltage stability of transformer when the load changes.

---

First, the basic concept of voltage regulation rate

Voltage Regulation of transformer refers to the ratio of the change of secondary side voltage to full load voltage when the secondary side load changes from no load to full load under the condition that the primary side voltage remains unchanged. Usually expressed as a percentage:

$$
ext{ voltage regulation rate} = frac{V_{2( ext{ no load })}-V_{2( ext{ full load})} {v _ {2 ( text {full load})}} Times 100 %
$$

Among them:
-$V_{2( ext{ no load})} $: no load voltage of secondary side;
-$V_{2( ext{ full load})} $: full load voltage of secondary side;

The smaller the voltage regulation rate, the smaller the voltage fluctuation when the transformer is loaded, and the higher the power supply quality.

---

Second, the theoretical derivation of voltage regulation rate

In order to facilitate calculation, the equivalent circuit of transformer and short-circuit test data are usually used to estimate the voltage regulation rate in engineering.

For an actual transformer, it can be equivalent to an ideal transformer plus the impedance of primary and secondary sides. In the simplified analysis, the parameters of the secondary side are usually reduced to the primary side to form a simplified equivalent circuit model.

When the excitation branch is ignored, the voltage change is mainly determined by the voltage drop caused by the equivalent impedance. The voltage regulation rate can be expressed as:

$$
Delta U% = left( frac{R_{eq} cdot I_2 cosvarphi + X_{eq} cdot I_2 sinvarphi}{V_{2n}}
ight) imes 100%
$$

Or:

$$
Delta U% approx beta left( R% cosvarphi + X% sinvarphi
ight)
$$

Among them:
-$R_{eq}$: equivalent resistance;
-$X_{eq}$: equivalent reactance;
-$I_2$: secondary side current;
-$cosvarphi$: load power factor;
-$V_{2n}$: secondary rated voltage;
-$beta$: load ratio (ratio of load current to rated current);
-$R%$, $X%$: the percentage value of transformer resistance and reactance (usually measured by short-circuit experiment).

---

Third, the factors affecting the voltage regulation rate

1. Load power factor:
Inductive load will increase the voltage regulation rate, while capacitive load may increase the secondary voltage, and the voltage regulation rate is negative.

2. Transformer short-circuit impedance:
The greater the impedance, the greater the voltage drop and the higher the voltage regulation rate.

3. Load size:
The greater the load, the greater the current, resulting in an increase in voltage drop and voltage regulation rate.

4. Transformer design structure:
Transformers with different structures (such as dry-type and oil-immersed transformers) will also have an impact on the voltage regulation rate because of their different impedance characteristics.

---

Fourth, the practical application of voltage regulation rate

In the design and operation of power system, voltage regulation rate is one of the important bases for selecting transformers. For example:

-For occasions requiring high voltage quality (such as hospitals and data centers), transformers with low voltage regulation rate should be selected.
-In long-distance power transmission, transformer and voltage regulator should be considered to ensure the stability of terminal voltage.

In addition, when transformers run in parallel, the inconsistent voltage regulation rate may lead to uneven load distribution and affect the operation safety.

---

V. Conclusion

To sum up, the voltage regulation rate of transformer is an important index to measure its output voltage stability and power supply quality. By reasonably designing transformer parameters, selecting appropriate load matching and adopting voltage regulation means, the voltage regulation rate can be effectively improved, and the stability and reliability of power system can be improved. In practical work, engineers and technicians should scientifically calculate and optimize the voltage regulation rate of transformers according to system requirements to ensure the quality and safety of power supply.