The following sequence is suitable for developing a detailed installation schedule, method statement and project ITP. The duration ranges are preliminary estimates for each activity, assuming a single transformer and no major defects.
This post is also a part of Extra High Voltage EHV Substation Design & 380kV Substation Design. If you are new on our website and want to learn 380kV Level, it is recommended to read first the below Posts
- 380kV Gantries & Gantry Equipment
- Inside a 380kV BSP: Overall Layout Drawing Explained
- 380kV Gas-Insulated Switchgear (GIS)
- Power Transformers
- Auxiliary Transformer Sizing for a 380kV BSP
- Vector Group of Transformers
- Autotransformers
We will complete Power Transformer Installation Plan in 4 to 5 posts and two parts given below
- PART 1 – WORK BREAKDOWN (ACTIVITY SEQUENCE)
- PART 2 -COMPONENT-BY-COMPONENT INSTALLATION ANALYSIS
Site readiness and civil acceptance
Purpose: Confirm that the site can safely receive and support the transformer, lifting equipment and installation operations.
Predecessor: Civil construction substantially complete. Successor: Delivery and receiving inspection.
Execution sequence
- Verify approved foundation drawings, dimensions, elevation, concrete strength and curing acceptance.
- Check rails or skid beams, wheel stops, jacking points, anchor bolts, seismic restraints and final positioning tolerances.
- Inspect the oil soak pit, drainage, oil-water separation or containment arrangement, and fire walls against approved civil and fire-protection drawings.
- Verify the availability of the main earthing grid and transformer earth connections.
- Confirm access-road bearing capacity, transport turning radius, crane working platform, laydown area and delivery route.
- Provide suitable temporary power, lighting, weather protection and emergency arrangements.
- Close outstanding civil punch-list items before releasing the delivery and lifting operation.
Hold/witness points
- Civil and structural acceptance by the responsible site engineer.
- Foundation and rail dimensional survey.
- Earthing continuity and approved inspection records.
- Release of the lifting platform and access route.
- SEC/client inspection or approval where required by the project ITP.
Critical/high-risk: High. Foundation defects, inadequate crane-platform bearing capacity or incomplete oil containment can stop delivery or lifting. Do not accept concrete strength or anchor-bolt positions by visual inspection alone.
Delivery and receiving inspection
Purpose: Establish that the transformer arrived in an acceptable condition and that transport preservation has been maintained.
Predecessor: Site access and receiving area released. Successor: Unloading and positioning.
Execution sequence
- Review shipping documents, packing list, serial numbers, shipping drawings and manufacturer’s preservation instructions.
- Download and review impact-recorder data, including event history and permitted limits, with the manufacturer.
- Record tank pressure, gas type, pressure trend and dew point using calibrated instruments and the manufacturer’s acceptance criteria.
- Inspect the tank, radiators, flanges, valves, welded areas, lifting lugs, transport restraints and accessories for damage or leakage.
- Verify that separately shipped bushings, CTs, radiators, conservator, OLTC components, fans and fittings are present and protected.
- Perform receiving insulation-resistance measurements only where specified, with results interpreted against factory records, temperature and manufacturer’s criteria. Do not treat an initial field reading as proof of internal integrity.
- Photograph the delivery condition and issue a discrepancy report for missing parts, pressure loss or impact events outside the permitted limits.
Hold/witness points
- Manufacturer review of abnormal impact-recorder results.
- Acceptance of preservation gas pressure and dew point against OEM limits.
- Joint inspection and signed receiving report.
- Quarantine or written disposition of damage and discrepancies before proceeding.
Critical/high-risk: High. Loss of dry gas, excessive moisture or an abnormal impact event may require further investigation, drying or manufacturer’s authorization.
Unloading, jacking, skidding and final positioning
Purpose: Transfer the main tank and accessories safely from the transport vehicle to the approved final position.
Predecessor: Receiving inspection accepted and lift plan approved. Successor: Preparation for internal work and assembly.
Execution sequence
- Verify the actual shipping mass, centre of gravity, lifting points, jack capacities and approved rigging arrangement.
- Conduct a toolbox talk, establish exclusion zones and inspect crane certificates, lifting accessories and ground conditions.
- Unload the tank using the OEM-approved lifting or jacking method. Use skidding systems or hydraulic jacks only where approved.
- Position the transformer on its rails, skid beams or foundation supports; maintain the required orientation and clearances.
- Check alignment, level, wheel stops, anchor bolts and seismic restraints against the approved drawings.
- Install temporary and permanent tank earthing as required by the approved method statement.
- Secure the transformer and remove transport restraints only when authorized.
Hold/witness points
- Approved lift plan and crane setup inspection.
- Verification of lifting points and shipping mass.
- Position, level and alignment survey.
- Acceptance of anchoring and restraint arrangements.
Critical/high-risk: High. This is a high-consequence lifting operation. Crane capacity must be selected from the actual lift study, including radius, configuration, rigging weight, ground bearing pressure and applicable safety factors—not from MVA rating alone.
Preparation for internal work
Purpose: Establish a controlled, dry and clean environment for opening the tank, making internal connections or carrying out any approved internal inspection.
Predecessor: Tank positioned and secured. Successor: Internal work and component assembly.
Execution sequence
- Review the manufacturer’s maximum permitted exposure time and whether internal entry is necessary.
- Establish dry-air supply, dew-point monitoring, clean temporary covers and a protected work area.
- Confirm the required dry-air quality, gas displacement and atmospheric conditions before opening the tank.
- Apply the approved confined-space permit, isolation, ventilation, gas monitoring, attendant and rescue arrangements whenever personnel entry is required.
- Record ambient temperature, relative humidity, tank temperature and the start of any exposure-time clock.
- Keep openings protected from dust, sand, moisture and foreign objects; stop work if the permitted conditions are exceeded.
- Close the tank or restore the prescribed dry atmosphere promptly after the authorized work.
Hold/witness points
- Approved method statement, risk assessment and confined-space permit where applicable.
- Dry-air quality and dew-point acceptance.
- Manufacturer’s authorization for internal inspection, if required.
- Exposure-time log and cleanliness inspection.
Critical/high-risk: Very high. Open-tank exposure limits are manufacturer-specific. No universal maximum exposure time should be assumed for a 380 kV transformer. Nitrogen is an asphyxiant; entry must not occur in an oxygen-deficient atmosphere.
Assembly of transformer components
Purpose: Install and seal the bushings, cooling equipment, conservator, OLTC accessories, protection devices, piping and other loose-shipped components.
Predecessor: Positioning accepted; work environment ready. Successor: Cabling, oil-system preparation and vacuum treatment.
Execution sequence
- Confirm each component against the approved general arrangement and packing list.
- Inspect mating surfaces, sealing grooves, gaskets and O-rings; clean them using OEM-approved methods.
- Assemble HV, IV, neutral and tertiary bushings, including turrets and bushing CT connections, in the specified sequence.
- Install radiators, headers, valves, fan assemblies and any specified oil pumps.
- Assemble the conservator, air cell or diaphragm, breather and connecting pipework.
- Install OLTC components, drive mechanism, shafts, bevel gears, oil compartment accessories and associated conservator where applicable.
- Install Buchholz relay, pressure-relief devices, temperature instruments and other protection accessories.
- Tighten connections to OEM torque values, record completed assemblies and verify valve positions.
Hold/witness points
- Manufacturer inspection of bushing installation and internal lead connections where required.
- Inspection of sealing surfaces, gasket installation and flange torque records.
- Radiator and pipework leak checks before oil filling.
- OLTC mechanical assembly and drive alignment checks.
- Confirmation that vacuum-incompatible accessories are isolated as required.
Critical/high-risk: High. Incorrect bushing handling, contaminated sealing surfaces, trapped air or incorrect OLTC drive alignment may cause leaks or prevent energization. The scope depends heavily on how much is factory-assembled.
Cabling, marshalling kiosk, cooling control and SCADA/protection interface
Purpose: Establish the electrical and control interfaces required for transformer protection, staged cooling and remote supervision.
Predecessor: Component assembly sufficiently complete for cable routing. Successor: Final filling completion and integrated pre-commissioning checks; work may overlap with oil processing.
Execution sequence
- Mount the marshalling kiosk and cooling-control cabinet, if supplied separately.
- Install cable trays, supports, glands, ferrules, terminal blocks and control wiring.
- Terminate fan motors and control circuits for ONAN/ONAF1/ONAF2 operation.
- Connect OTI, WTI, RTDs, bushing CTs, OLTC drive signals and alarm/trip contacts.
- Connect Buchholz, pressure-relief, sudden-pressure and other protection circuits.
- Complete interfaces with the station protection panels, SCADA, interposing relays and fire-protection system.
- Carry out point-to-point, continuity, insulation and functional checks under approved test procedures.
Hold/witness points
- Cable and termination inspection.
- Wiring and interconnection checks against approved schematics.
- Verification of fan staging, alarms, trips and remote signals.
- Protection and SCADA interface acceptance by the relevant parties.
Critical/high-risk: Medium to high. Missing interface wiring, incorrect CT polarity or incomplete trip circuits can delay energization even when mechanical installation is complete.
Oil receipt, storage and treatment preparation
Purpose: Ensure the correct insulating oil is available in adequate quantity and can be processed without moisture, air or particulate contamination.
Predecessor: Oil-handling equipment and filling connections prepared; assembly sufficiently complete. Successor: Vacuum treatment and filling.
Execution sequence
- Verify the approved oil type, supply certificates, batch details and compliance with IEC 60296 and project requirements.
- Inspect storage tanks, hoses, filter elements, seals and transfer connections for cleanliness and compatibility.
- Obtain representative incoming-oil samples and arrange the required laboratory tests.
- Set up the vacuum oil-treatment plant, storage tanks, hoses, calibrated instruments and spill containment.
- Filter, dehydrate and degas the oil until the required acceptance criteria are achieved.
- Maintain clean, sealed storage and traceability between oil batches, treatment records and final filling records.
Hold/witness points
- Oil certificates and incoming-oil laboratory results accepted.
- Treatment equipment and storage system inspection.
- Treated-oil sample accepted before filling.
- Verification of available oil quantity and approved filling connections.
Critical/high-risk: High. Oil shortages, inadequate treatment capacity, contaminated storage tanks or delayed laboratory results can hold the critical path. Oil preparation may overlap with component assembly.
Vacuum treatment, oil filling, circulation and settling
Purpose: Remove moisture and air as required, fill the transformer under the approved conditions and allow insulation and oil systems to stabilize before commissioning.
Predecessor: Required assembly complete, oil accepted and tank configuration approved for vacuum. Successor: Final checks and pre-commissioning inspections.
Execution sequence
- Confirm that the tank, bushings, cable boxes, conservator and OLTC compartment are configured according to the OEM’s vacuum procedure.
- Verify that all vacuum connections, gauges, valves, isolation points and seals are suitable and leak-tight.
- Apply vacuum to the specified pressure and maintain it for the manufacturer’s required period.
- Record vacuum level, duration, temperature and any pressure-rise or leakage checks.
- Fill with treated oil under vacuum at the permitted rate and temperature, maintaining the required vacuum conditions.
- Complete filling of the main tank, conservator, OLTC compartment and other oil-filled compartments using the relevant OEM procedure.
- Carry out hot-oil circulation only if specified or approved by the manufacturer.
- Release the vacuum using the approved method, vent designated high points, inspect for leakage and restore normal oil levels.
- Allow the specified settling period, take oil samples and complete the required post-treatment laboratory checks.
Hold/witness points
- OEM authorization to apply vacuum.
- Vacuum level, duration and leak/pressure-rise acceptance.
- Oil-filling log, oil temperature and treated-oil quality records.
- Post-filling settling period and oil-level checks.
- Required oil laboratory results accepted before release for testing.
Critical/high-risk: Very high; normally a critical-path activity. The transformer may require a prolonged vacuum cycle and settling period. For EHV equipment, manufacturer-specific vacuum limits and waiting times take precedence over generic estimates. Published manufacturer guidance for 245–550 kV equipment includes reference evacuation periods of 48 hours or more in certain procedures; this is not a universal SEC requirement.
Final checks, painting touch-up, nameplate and labelling
Purpose: Close mechanical installation, confirm configuration and complete identification and finishing work.
Predecessor: Major assembly and oil filling substantially complete. Successor: Pre-commissioning inspections; may overlap with approved cable checks.
Execution sequence
- Check oil levels in the main tank, conservator and OLTC compartment.
- Verify valve positions, breather condition, piping, fan guards, terminal connections and earthing.
- Inspect for oil leakage at flanges, radiators, bushings, valves and pipework.
- Complete paint touch-up using the approved coating system and colour.
- Verify nameplate, rating plate, serial numbers, warning labels, valve tags and phase identification.
- Close installation punch-list items and compile as-built installation records.
Hold/witness points
- Mechanical completion inspection.
- Leak inspection and oil-level acceptance.
- Nameplate and rating data verification.
- Closure of installation punch-list items.
Critical/high-risk: Medium. Incorrect phase identification, incomplete earthing, leaking joints or omitted valve-position checks can prevent release for commissioning.
Pre-commissioning tests and SEC inspections
Purpose: Demonstrate that installation is complete and the transformer is ready for energization, without repeating the factory test programme.
Predecessor: Mechanical completion, filling and settling accepted. Successor: Energization authorization and support.
Execution sequence
- Review approved factory test records, installation records and manufacturer’s outstanding-item list.
- Complete the specified transformer electrical checks, such as insulation-related measurements, winding resistance, ratio/vector-group checks and other tests required by the approved commissioning procedure.
- Verify bushing CT ratios/polarity, OLTC operation, interlocks and drive indication as applicable.
- Check cooling-stage operation, motor currents, alarms, trips and temperature instrumentation.
- Verify protection schemes, trip circuits, SCADA indications, intertripping and fire-protection interfaces.
- Complete oil sampling and laboratory acceptance, where required by the approved procedure.
- Close SEC/client witness points and obtain written release for energization.
Hold/witness points
- OEM and SEC/client witnessing as required by the project ITP.
- Acceptance of electrical test results against approved criteria and factory baselines.
- Protection, interlock, trip-circuit and SCADA acceptance.
- Closure of critical punch-list items and signed energization-readiness release.
Critical/high-risk: Very high. Any unresolved protection, oil-quality, insulation or mechanical issue can prevent energization. The exact test list and acceptance limits must be verified against the project’s approved commissioning procedure and SEC requirements.
Energization support, post-energization checks and handover
Purpose: Support controlled energization, monitor initial operation and hand over complete installation records.
Predecessor: All required approvals and energization permits issued. Successor: Operational handover.
Execution sequence
- Attend the pre-energization meeting and confirm the approved switching programme, clearances and responsible switching authority.
- Verify that temporary earths and work permits are managed under the approved switching and safety procedure.
- Confirm transformer protection, trip circuits, cooling controls, OLTC position and required operational settings.
- Support the authorized energization and monitor abnormal noise, leakage, indications, alarms and other specified parameters.
- Check oil levels, temperatures, cooling operation and gas/pressure indications after energization in accordance with the OEM’s instructions.
- Record the initial operating condition and arrange follow-up inspections at the intervals required by the manufacturer and SEC.
- Submit the final installation dossier, test records, oil reports, inspection reports, as-built documents and outstanding-item closure evidence.
Hold/witness points
- Written energization authorization.
- Approved switching programme and protection readiness.
- Initial operating checks and recorded observations.
- Handover dossier acceptance.
Critical/high-risk: High. Actual energization timing is controlled by SEC/the authorized system operator and system conditions; these estimates do not include utility scheduling delays.
Power Transformer Installation Plan part 1, 2, 3