What is overvoltage ?

Overvoltage refers to the voltage value in the power system exceeding the allowable range of its rated voltage. Overvoltage can have a serious negative impact on power equipment, system stability and power users, and may even cause accidents such as equipment damage and power outages. Therefore, it is crucial to understand the classification of overvoltage, its impact on the power system and effective preventive measures.

1. Classification of overvoltage

Overvoltage is usually divided into the following types according to its cause and duration:

1. External overvoltage:

- Definition: Overvoltage caused by external factors, usually caused by natural factors such as lightning.

- Characteristics: The amplitude of external overvoltage is very high, usually short-term (milliseconds or microseconds), and transient overvoltage often occurs during lightning strikes.

- Source:

- Lightning overvoltage: When lightning directly or indirectly hits power equipment or lines, the resulting current fluctuations cause a sudden increase in voltage.

- Induced overvoltage: When lightning strikes the ground or other conductors at a distance, it induces high voltage on the power line.

2. Internal overvoltage:

- Definition: Overvoltage caused by operation or failure within the power system.

- Characteristics: The amplitude of internal overvoltage is usually low, but the duration is long.

- Source:

- Operation overvoltage: Voltage fluctuation caused by switch operation or power system switching, such as closing and opening operation of circuit breakers or disconnectors.

- Arc grounding overvoltage: When the neutral point of the power system is not grounded or high-resistance grounded, a single-phase grounding fault will cause a high-amplitude voltage fluctuation.

- Resonance overvoltage: Electromagnetic resonance occurs in the inductive and capacitive components (such as reactors and capacitors) in the system, resulting in voltage increase.

3. Transient overvoltage:

- Definition: Temporary voltage increase, usually for a short time (microseconds to milliseconds).

- Source: Transient overvoltage generated by lightning strikes, power equipment operation, fault clearing, etc.

4. Long-term overvoltage:

- Definition: System voltage continues to be higher than the rated voltage for a long period of time (seconds to hours).

- Source: Failure of voltage regulator, improper grid operation parameters, etc.

2. Impact of overvoltage on power system

Overvoltage will have a series of adverse effects on power system and its equipment, including:

1. Damage to electrical equipment:

- Overvoltage may cause insulation breakdown of electrical equipment, such as insulation system of transformers, circuit breakers, cables and other equipment, leading to short circuit or damage of equipment.

2. Overheating and aging of equipment:

- Overvoltage will cause excessive current to flow through power equipment, causing equipment overheating, accelerating aging of insulation materials and shortening equipment service life.

3. Malfunction of protection equipment:

- Overvoltage may cause malfunction of protection equipment (such as relay protection device), leading to system tripping or frequent power outages, affecting the continuity and reliability of power supply.

4. Power quality issues:

- Overvoltage will cause voltage fluctuations and affect the normal operation of user equipment. Sensitive equipment such as computers, automatic control systems, etc. may fail due to overvoltage.

5. Arcing and fire:

- Overvoltage may cause arc discharge between high-voltage lines or equipment, and even cause fire in severe cases.

3. Measures to prevent overvoltage

To prevent and alleviate the impact of overvoltage on the power system, common measures include the following aspects:

1. Lightning arrester (lightning rod, lightning conductor):

- Function: used to protect against external lightning overvoltage. Lightning arrester can lead lightning to the ground, reduce the direct entry of lightning current into the power system, and thus prevent overvoltage caused by lightning.

- Application scenario: widely used in high-voltage substations, power plants and transmission lines.

2. Arc suppression coil:

- Function: Arc suppression coil is used to limit arc grounding overvoltage. When a single-phase grounding fault occurs in the power system, the arc suppression coil can compensate for the inductive current in the system and avoid the reignition of the arc.

- Application scenario: suitable for power systems with ungrounded neutral points or grounded through arc suppression coils.

3. Overvoltage protector:

- Function: Installing an overvoltage protector can quickly divert excessive voltage fluctuations when overvoltage occurs in the system, protecting the equipment from overvoltage.

- Application scenario: suitable for various power equipment, such as transformers, generators, etc.

4. Optimization of power system operation:

- Measures: Avoid frequent operation of power equipment, especially unplanned switching operation. Minimize the frequent operation of the switching circuit to prevent the generation of operational overvoltage.

5. Install parallel capacitors:

- Function: By installing parallel capacitors, the power factor can be improved, the voltage level can be adjusted, and the occurrence of overvoltage can be avoided. At the same time, the reactive power transmission in the power system can be reduced, thereby reducing the resonance overvoltage.

6. Resonance inhibitor:

- Function: When resonance may occur in the system, the resonance inhibitor can eliminate or weaken the resonance phenomenon and avoid the generation of resonance overvoltage.

7. Adjust system operating parameters:

- Measures: Ensure that the system's voltage regulator and automatic voltage control device work properly, reasonably adjust the excitation current of the generator and transformer, and keep the system voltage within the rated range.

IV. Summary

Overvoltage is a common and destructive phenomenon in power systems, which may be caused by lightning strikes, operating errors or system failures. Overvoltage can cause problems such as damage to electrical equipment and system instability. By installing lightning arresters, arc suppression coils, overvoltage protectors and other equipment and taking reasonable operating measures, the impact of overvoltage on the power system can be effectively prevented.