Overvoltage in Transformers
Overvoltage refers to a long-term voltage variation phenomenon where the RMS value of the AC voltage at power frequency exceeds 10% of the rated value and lasts for more than 1 minute.
Overvoltage usually occurs instantly during load switching, such as when inductive or capacitive loads are connected or disconnected under normal operating conditions. During transformer operation, overvoltage causes the highest probability of damage, so it is essential to pay close attention to this issue.
There are various causes of overvoltage, which can be divided into two main categories: external overvoltage and internal overvoltage.
External Overvoltage
External overvoltage, also known as lightning overvoltage or atmospheric overvoltage, includes direct lightning strike overvoltage and induced lightning overvoltage.
Direct lightning strike overvoltage occurs when lightning directly strikes the conductive part of electrical equipment. The amplitude of direct lightning overvoltage can reach millions of volts, which can damage the insulation of electrical facilities and cause short-circuit or grounding faults.
Induced lightning overvoltage occurs when lightning strikes the ground near electrical equipment. During the discharge process, rapid changes in the surrounding electromagnetic field induce overvoltage in electrical equipment that is not directly struck.
Both types of overvoltage require protection measures such as lightning arresters and grounding devices.
Internal Overvoltage
Internal overvoltage refers to overvoltage caused by changes in the power system's operating conditions. It includes resonant overvoltage, transient overvoltage, and switching overvoltage.
- Resonant overvoltage occurs when a fault in electrical equipment or frequent operations in the power system cause inductance and capacitance to match, forming a resonant circuit. Under certain conditions, this can lead to overvoltage due to the conversion of electrical and magnetic energy.
- Transient overvoltage is caused by circuit breaker operations or short-circuit faults, such as single-phase grounding faults or resonance. It mainly occurs during the switching or reclosing of unloaded lines or transformers.
- Switching overvoltage is a rapidly decaying, short-duration overvoltage caused by circuit breaker operations or sudden short-circuits.
To ensure the safety of transformers in power grid operation and prevent the occurrence and hazards of overvoltage, in addition to selecting high-quality transformers, it is essential to implement reasonable and effective overvoltage protection measures. It is recommended to communicate with professional transformer manufacturers when designing circuits and selecting transformers.
Shenzhen Shentebian Electric Equipment Co., Ltd. is a wholly-owned subsidiary of Jishengchang Group. Founded in 2004, the company has its own industrial park and is a technologically advanced and well-established professional transformer manufacturer. It is one of the earliest enterprises in Shenzhen to enter the power transformer manufacturing field. STB is the transformer brand under Shenzhen Shentebian Electric Equipment Co., Ltd.
