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Voltage transformer secondary circuit short circuit fault online monitoring and preventive measures - Database & Sql Blog Articles
Voltage transformers play a crucial role in power systems, acting as essential components that connect the primary and secondary circuits in AC systems. They are used to transmit voltage information to measuring instruments, protective relays, and control devices. Like regular transformers, they operate on similar principles, consisting of a primary winding, secondary winding, and an iron core. The windings and core are insulated to ensure safe operation. Under normal conditions, the secondary voltage is proportional to the primary voltage.
It is important to note that the secondary winding of a voltage transformer must never be short-circuited or grounded. If this occurs, the secondary voltage drops to zero, causing the core to become highly saturated. This saturation leads to distorted magnetic flux, which induces large currents in the windings, increasing heat and potentially damaging the insulation. In severe cases, the fuse may blow, leading to incorrect meter readings, protection malfunctions, and even destruction of the voltage transformer. According to national standards such as DL408-91, it is strictly prohibited to short-circuit or ground the secondary circuit of an energized voltage transformer.
Common causes of secondary circuit short circuits include:
(1) Shorted connection cables within the loop.
(2) Grounding due to moisture, corrosion, or physical damage, leading to a two-phase ground fault.
(3) Internal metal defects causing a short in the secondary circuit.
(4) Moisture and rust in outdoor terminal boxes, affecting the connections.
(5) Poor wiring practices during installation.
(6) Omissions during testing and maintenance.
Regular inspections can help identify these issues through observable signs such as:
(1) Unusual noise from the voltage transformer.
(2) Excessive heat and burning smell.
(3) Abnormal meter readings or malfunctioning protection devices.
(4) Burnt secondary windings or damaged equipment.
To address these challenges, online monitoring systems have been developed. These systems continuously monitor the current in the PT secondary loops. When the current exceeds a set threshold (e.g., 8A for 20ms), the system triggers an alarm, isolates the faulty loop, and alerts maintenance personnel with visual and auditory signals. This real-time monitoring not only helps detect faults early but also reduces the risk of accidents and equipment damage.
In conclusion, both routine inspections and advanced monitoring techniques are vital in preventing secondary circuit short circuits in voltage transformers. These methods align with safety guidelines like DL408-91 and significantly enhance the reliability and safety of power systems. By implementing these strategies, potential hazards can be identified and addressed before they lead to serious consequences.