The dangerous points of transformer operation include the potential for operating overvoltage when adapting to a no-load transformer, which can damage the insulation. Another risk is the rise in no-load voltage, which may also harm the transformer's insulation.
To address the issue of operating overvoltage caused by no-load transformers, it's crucial to ensure proper grounding of the transformer’s neutral point. Grounding the neutral point helps prevent overvoltage conditions that can arise during switching operations or asymmetric faults. In high-voltage systems (110 kV and above), some transformers have their neutral points ungrounded to limit short-circuit currents. However, this requires careful planning to maintain system stability, ensure reliable relay protection, and avoid insulation failures.
Transformer neutral grounding should follow specific principles:
1. When multiple transformers are connected to different busbars, at least one transformer on each busbar must have its neutral point directly grounded. This prevents the busbar from becoming ungrounded after a fault occurs.
2. If power is present on the low-voltage side of the transformer, the neutral point must be grounded to avoid the transformer becoming an insulated system if the high-voltage switch trips.
3. When several transformers operate in parallel, only one should be directly grounded under normal conditions. Before de-energizing a transformer, the neutral point of another must be closed first. Similarly, before energizing a transformer, the neutral point of the previously grounded one should be opened to maintain grounding continuity.
4. Before energizing or de-energizing a transformer, the neutral point must be grounded to prevent inductive effects due to non-synchronous or incomplete phase switching. The grounding method should be adjusted based on the operational mode of the transformer.
In addition to managing overvoltage, attention must also be given to the risk of no-load voltage rise. To minimize this, dispatchers should avoid operations that could cause such a rise, such as energizing reactors or using inductive loads. Adjusting the tap changer or lowering the receiving voltage can also help. If the power source is a plant feeding a substation, the plant’s voltage can be reduced according to equipment requirements. If the plant has other loads, part of the power supply can be isolated to adjust the voltage as needed.
By following these guidelines, operators can significantly reduce the risks associated with transformer operation and ensure safer, more stable power system performance.
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