What is the reason why voltage transformers often explode?
Over - voltage and Over - current Aspects
Ferroresonant over - voltage: In a non - effectively earthed neutral system, the magnetic circuits of equipment such as transformers, voltage transformers, and arc suppression coils may saturate, potentially triggering ferroresonance. The resulting over - voltage can increase the excitation current of the voltage transformer by dozens of times. Operating under high voltage and large current for an extended period causes the temperature of the transformer to rise rapidly. The thermal vaporization of insulating materials increases the internal pressure, ultimately leading to an explosion. For example, this situation is relatively common in 6 - 35kV systems.
Switching over - voltage: The operation of switches within the system or the occurrence of an accident changes the state of the power system, causing the oscillation, exchange, and redistribution of internal electromagnetic energy, which generates switching over - voltage. Examples include the arc - grounding over - voltage in a non - solidly earthed neutral system and the switching - off over - voltage of an unloaded line or capacitive load. When switching capacitors, a relatively high over - voltage may be generated. In particular, when the switch reignites during capacitor disconnection, an over - voltage of more than three times the system voltage may occur, and the inter - phase over - voltage during two - phase reignition can even reach more than six times the system voltage. This can cause inter - turn short - circuits in the voltage transformer, triggering an over - current, and the rapid vaporization of the insulating medium, leading to an explosion.
Lightning over - voltage: If the lightning protection facilities are not perfect, the high voltage generated by lightning strikes acting on the voltage transformer may break down its insulation, and then trigger an explosion.
Long - term low - amplitude over - voltage and over - current: Due to resonance or other reasons, although the over - voltage and over - current endured by the voltage transformer have relatively small amplitudes, they last for a long time. A large amount of electrical energy is converted into heat, causing the transformer to heat up continuously. When the heat accumulates to a certain extent, the insulating paper and insulating medium vaporize. Since the internal space of a dry - type transformer is limited, when the pressure increases to a certain level, an explosion will occur.
Over - current caused by instant high - amplitude over - voltage: An over - voltage with a high enough amplitude can cause inter - turn short - circuits inside the transformer, generating a relatively large over - current, which rapidly vaporizes the insulating medium and triggers a violent explosion.
Insulation - related Issues
Insulation aging: If a voltage transformer has been in use for too long or has been operating in harsh environments such as high temperature, humidity, and pollution for a long time, the insulating materials will gradually age and deteriorate, reducing the insulation performance. It is then easily broken down, leading to internal short - circuits and triggering an explosion.
Insulation quality defects: During the manufacturing process, if there are problems such as defective insulation wrapping or improper insulation treatment, the voltage transformer will have inherent insulation weaknesses. During operation, these weaknesses may be broken down under high voltage, triggering coil short - circuits and causing an explosion.
Moisture ingress: If the voltage transformer is placed in a humid environment and water vapor enters the equipment, it will reduce the insulation performance, increasing the risk of insulation breakdown and potentially leading to an explosion.
Equipment - self and Usage Aspects
Product quality problems: For some voltage transformers, due to unreasonable design, poor material quality, or substandard winding processes, excessive heating may occur during operation. This exposes the insulation to high temperatures for a long time, accelerating insulation aging and even causing breakdown. Subsequently, inter - turn short - circuits in the primary winding may occur, resulting in a rapid increase in current and magnetic saturation, generating resonant over - voltage, and ultimately causing an explosion.
Secondary - side short - circuit: A short - circuit on the secondary side of the voltage transformer will cause a sharp increase in the secondary - side current. According to the principle of electromagnetic induction, a relatively large current will also be generated on the primary side, leading to overheating of the windings and insulation damage, thus triggering an explosion. In addition, incorrect secondary wiring, such as accidentally short - circuiting the secondary side of the voltage transformer, will also cause a sharp increase in current, resulting in damage due to overheating and an explosion.
Overload operation: When a voltage transformer operates in an overloaded state for a long time, it will damage the equipment and increase the risk of an explosion.
External impact: An accidental external impact may damage the internal structure of the voltage transformer and disrupt the insulation, triggering a fault or even an explosion.
Operation, Maintenance, and Management Aspects
Lack of maintenance and management: If regular inspections, maintenance, and overhauls of the voltage transformer are not carried out, potential hazards such as insulation aging and loose connections cannot be detected in a timely manner. The long - term accumulation of these hazards may lead to an explosion accident.
Insufficient skills of operators: If operators lack professional knowledge and operate improperly, for example, making incorrect wiring during tests (when doing the excitation characteristic test of a grounded voltage transformer, the terminal n is not grounded), it may damage the insulation of the transformer, affect its service life, and increase the possibility of an explosion.
