1. Changing the GIS Bus Potential Transformer (PT)
A Potential Transformer (PT) , also known as a Voltage Transformer (VT), is used in substations to step down high voltages to lower levels for metering and protection purposes. Replacing a PT involves several steps:
Preparation:
1. Safety Precautions:
- Obtain Work Permits: Ensure all necessary work permits and authorizations are obtained before starting.
- Personal Protective Equipment (PPE): Wear appropriate PPE, including insulated gloves, safety goggles, and flame-resistant clothing.
- Isolation of the Bus Section: De-energize the bus section where the PT is to be replaced. This involves opening the relevant circuit breakers and disconnect switches to ensure no live parts are present.
- Earth the Busbar: Apply proper grounding to discharge any stored energy and prevent accidental energization.
PT Replacement:
1. Removal of Old PT:
- Disconnect Wiring: Carefully disconnect all wiring and connections from the old PT, including secondary wiring used for protection and metering.
- Remove Fixings: Loosen and remove any bolts or clamps securing the PT in place.
- Lift Out PT: Use appropriate lifting equipment (such as a crane or hoist) to safely remove the old PT from its position.
2. Installation of New PT:
- Position New PT: Carefully place the new PT into position using lifting equipment, ensuring it is correctly aligned with the mounting points.
- Secure PT: Fasten the PT using bolts or clamps, ensuring it is securely fixed in place.
- Reconnect Wiring: Reconnect all wiring and ensure all connections are tight and correctly installed as per the schematic diagrams.
3. Testing and Commissioning:
- Perform Electrical Tests: Conduct electrical tests such as insulation resistance, ratio, polarity, and burden tests to verify the correct operation of the new PT.
- Check Secondary Circuits: Verify the correct operation of secondary circuits for protection and metering by simulating signals and checking relay responses.
SF₆ Gas Filling Procedure
SF₆ gas is used in GIS for insulation and arc quenching. Proper filling of SF₆ gas is crucial for maintaining the dielectric properties of the GIS.
Preparation for SF₆ Gas Filling:
1. Safety Measures:
- Work Permits: Ensure all necessary permits and safety checks are in place.
- PPE: Use appropriate PPE, including respirators, gloves, and eye protection, since SF₆ gas is an asphyxiant.
- Leak Check: Check all fittings and connections for potential leaks using SF₆ leak detectors.
2. Gas Handling Equipment:
- Gas Filling Cart: Use an SF₆ gas filling cart that includes a gas cylinder, pressure regulator, and connecting hoses designed for SF₆ gas handling.
- Vacuum Pump: A vacuum pump is used to evacuate air and moisture from the compartment before filling with SF₆ gas.
SF₆ Gas Filling Steps:
1. Evacuate the Compartment:
- Connect the Vacuum Pump: Connect the vacuum pump to the gas filling valve of the GIS compartment.
- Evacuate Air and Moisture: Start the vacuum pump and evacuate air and moisture from the compartment until the desired vacuum level is achieved (typically 1 to 5 millibars).
2. Filling with SF₆ Gas:
- Connect Gas Filling Cart: Connect the SF₆ gas filling cart to the gas filling valve.
- Slow Gas Filling: Slowly fill SF₆ gas into the compartment to avoid pressure surges. Monitor the pressure gauge closely to ensure a controlled filling process.
- Achieve Required Pressure: Continue filling until the gas pressure reaches the required operating level, as specified by the manufacturer (typically 5 to 7 bar gauge for 400 kV GIS).
3. Leak Testing:
- Conduct Leak Tests: Use an SF₆ leak detector to check all flanges, joints, and valves for any gas leaks. Tighten any leaking connections as necessary.
- Gas Quality Check: Use a gas analyzer to check the purity and moisture content of the SF₆ gas to ensure it meets specifications.
4. Final Checks:
- Pressure Monitoring: Monitor the gas pressure for a short period to ensure stability and no further leaks.
- Record Pressure Readings: Document the final pressure readings and gas quality parameters for future reference.
Post-Replacement and Gas Filling:
1. Re-energize the Busbar:
- After ensuring all tests are successful and no leaks are present, the bus section can be re-energized by closing the disconnect switches and circuit breakers in the correct sequence.
2. System Monitoring:
- Continuous Monitoring: Continuously monitor the GIS and PT parameters (like voltage, current, gas pressure, and temperature) to ensure they are within normal operating limits.
3. Maintenance Logs:
- Update Records: Update maintenance logs and records with details of the PT replacement and SF₆ gas filling procedures, including the results of all tests and checks performed.
20 сен 2024
