Pre-Operation Requirements for New Equipment

(1) Before startup, all equipment to be commissioned should be placed in cold standby mode. Line reactors should be connected, while the status of line PTs and bus PTs is not specifically required.

(2) If the busbar needs to be cleared, it should remain in normal operation until specific operational steps require disconnection to minimize the busbar downtime.

(3) Secondary equipment within the scope of commissioning must have all control, protection, and fault recording devices in normal operational mode. Relevant temporary relay protection measures should be executed. Any protections that are not activated under normal operation but are required temporarily (e.g., cancellation of auto-reclosing online protection) must also be listed.

Technical Principles During Commissioning Operation of New Equipment

(1) Charging Attempts: A maximum of three attempts for lines and five for transformers are permitted. There are no strict requirements for switches or busbars.

(2) Charging Switches: Use switches equipped with charging protection.

(3) Disconnector Operations: Charging a device for the first time using a disconnector is generally not allowed. It can only be done after on-site verification and direct closure of the disconnector.

(4) Charging Side Selection: Preferably, charge from the side with line reactors at the remote end of the system, from substations far from converter stations, and use switches located away from critical transformers and important lines.

(5) Relay Protection Requirements: During startup, minimize the time the busbar is de-energized and the duration multiple switches on the busbar have their charging protection enabled.

Reasons for Performing Impulse Testing Before the Commissioning of New or Overhauled Transformers, and the Required Number of Tests

Purpose of Impulse Testing

(1) When disconnecting a no-load transformer, operational overvoltages may occur. In systems with neutral points ungrounded or grounded through arc suppression coils, overvoltage amplitudes can reach 4 to 4.5 times the phase voltage. In systems with directly grounded neutral points, overvoltages can reach three times the phase voltage. Impulse testing is conducted to verify whether the transformer's insulation strength can withstand full voltage and operational overvoltages.

(2) When energizing a no-load transformer, inrush currents may occur, reaching 6 to 8 times the rated current. The inrush current decays rapidly at first, usually reducing to 0.25 to 0.5 times the rated current within 0.5 to 1 second, though complete decay can take longer, especially for large-capacity transformers (up to tens of seconds). Impulse testing evaluates the mechanical strength of the transformer against large electromagnetic forces and assesses whether the initial inrush current decay could cause relay protection malfunctions.

Number of Impulse Tests

For new transformers: 5 times.

For overhauled transformers: 3 times.