Turnkey substation construction for industrial plants

Construction / installation / new-build substation (EPC newbuild)

New substation construction begins with an on-site survey and a connection dossier with the distribution utility (EVN); these are mandatory before foundation design and the installation of connection lines. During the plant survey, identify the medium-voltage connection point, safety corridors, geotechnical conditions, groundwater level and routing for cables/overhead lines. ^[0][0]

Foundation and structural design must use transformer data (weight, lifting points, anti-vibration criteria) as input, and comply with appropriate substation standards. On-site, check electrical clearance distances and the planned location of the medium-voltage switchgear before pouring foundations to avoid major rework during construction.

Selection of transformers and medium-voltage equipment includes determining rated capacity, transformer ratio, earthing type, insulating medium (oil/solid insulation) and short-circuit impedance; RMU/switchgear assemblies must match the nominal voltage range and switching type. During commissioning/run tests, testing should include insulation resistance, leakage current checks, no-load/load run tests and verification of the earthing system.

Regulatory and coordination requirements for connection: a connection application and an approval/consent record from EVN must be in place before building lines or performing outages. During construction, propose a coordinated outage plan and a joint energization acceptance with EVN to ensure N-1 conditions and safe operation.

Occupational safety and fire protection require safety corridor plans, signage, electrical outage procedures for works, lightning protection and fire protection measures for the transformer room/switchgear room. Operational warning: do not start connection works or energize without EVN connection approval or if geotechnical surveys have not confirmed foundation stability.

Next steps: after completing construction dossiers and technical acceptance before energization, prepare the joint energization acceptance minutes with EVN and handover operation documentation. If any required input documents (connection approval, geotechnical report, equipment data) are missing, suspend the related construction activity until the documentation is complete.

Transformer & substation repair – maintenance – servicing

Transformer and substation repair and maintenance require visual inspections, electrical measurements and pre/post-repair testing to ensure insulation integrity and safe operation. ^[4][0]

On site, start by assessing the condition: inspect for oil leaks, oil level, signs of overheating and abnormal noise; then take oil samples for moisture, acid number and dissolved gas analysis before deciding on filtration or oil replacement. During maintenance, measure insulation resistance, tan delta (Tgδ), capacitance and winding resistance; these results form the basis for post-repair acceptance.

Common fault handling steps include: identifying the leak source (gasket, bushing, cracked tank), isolating the transformer from the network if needed, collecting oil samples, performing temporary sealing measures (gasket replacement or welding/patching) and assessing environmental impact. For thermal management, inspect fans, radiators and measure winding/oil temperatures to differentiate overload, blocked oil flow or cooler failure.

• Periodic check list: visual inspection; oil level and moisture; Tgδ; winding resistance; transformation ratio; post-repair dielectric tests.
• Oil replacement: based on sample analysis (moisture, acid number, sludge); if quantitative data is missing, sample testing and operational history must be reviewed before deciding.
• Noise/vibration: classify source (mechanical, electromagnetic), inspect magnetic clamp and structure, mitigate by tightening fasteners or installing vibration pads when surveyed on site.

Minimum acceptance tests after repair must include: winding resistance, insulation resistance and tan delta, dielectric withstand test and technical acceptance report; this report is legal evidence required before re-energizing the station. When applying condition-based maintenance (CBM), use PD monitoring, thermal imaging and online oil analysis to prioritize interventions based on condition.

Operational warning: on-site, if there is no inspection certificate or clear operational history, legal and safety risks increase; arrange for an accredited inspection before re-energizing. Also, all live work must follow lockout/tagout and temporary earthing procedures per occupational safety regulations.

Capacity upgrade – modernization – refurbishment of substations

When increasing capacity or replacing a transformer, conduct a load condition survey, protection compatibility checks and analyze options such as rewinding, replacing or adding a transformer to decide the optimal solution. ^[0][0]

On-site, collect the substation technical dossier and perform checks including: connection diagram, transformer documentation, bay capacity, foundation condition, earthing and protection/control systems. Transformer technical data should include: rated capacity (MVA), rated voltages, vector group and tap ratio, short-circuit current and impedance, overload capability, cooling requirements, dimensions and weight, foundation dimensions and earthing requirements.

At minimum compare three specific options before deciding:

1. Upgrade the existing transformer (e.g., rewind or improve cooling) — advantage: minimal infrastructure changes; disadvantage: sometimes technically infeasible or limited by foundation constraints.
2. Replace the transformer with a larger unit — advantage: direct capacity increase; disadvantage: requires foundation, earthing and switchgear adjustments and typically a longer outage.
3. Add a second transformer / additional bay — advantage: increased redundancy, easier to meet N-1; disadvantage: requires space, extra bay and may need a new connection agreement with the grid operator.

On site, prepare temporary outage and load transfer plans for maintenance, heavy lifting/transformer handling procedures and measures to control oil spill risks and fire protection. Before changing capacity or connection configuration, verify connection approval/requirements with the grid operator (EVN/distribution/transmission unit) — a new connection agreement may be required under power development planning.

Construction and acceptance risks must be managed: plan post-installation testing (insulation tests, ratio tests, leak checks), complete transformer technical documentation and perform energization acceptance per EVN and legal requirements. Site survey results and technical dossiers are mandatory inputs for detailed design, solution proposals and subsequent connection procedures.

Relocation / moving a substation

Conduct a pre-move survey, prepare dismantling and transport plans before breaking ground; all steps must be confirmed with EVN and relevant authorities. ^[11][0]

On site, check: insulating oil condition, sealing systems, as-built drawings, foundation condition and earthing capability; the new location must be evaluated for connection direction and construction conditions.

Typical pre-move checks include:

• Oil inspection (level, leaks, suspected PCB) and logging handling actions;
• Identify isolation points, label cables, seal and photograph as-built conditions;
• Assess lifting equipment, limit vibration and survey transport routes.

The dismantling plan must list equipment items, procedures for de-energization and oil draining, hazardous goods packaging and measures to prevent coil damage during transport.

For temporary power supply planning, assess auxiliary loads, maximum allowable outage duration and choose between temporary transformer, generator or temporary tie-in to another network; all temporary schemes require coordinated outage scheduling with EVN.

Safety and legal requirements must be strictly followed: handle suspect PCB oil and package hazardous goods per regulations, and collect inspection, transport and final acceptance records for legal documentation.

Post-installation tests must include insulation tests, ratio measurements, no-load tests, protection and control checks before energization; acceptance minutes and completion dossiers are mandatory for handover to EVN.

Practical warning: lack of transport route survey or missing EVN connection information can change scope and schedule; prepare risk management and mitigation plans before relocation.

Undergrounding / lowering medium-voltage network related to substations

It is feasible to underground medium-voltage lines related to a substation but only when the connection approval dossier and complete on-site surveys are available. ^[12][0]

On site, survey the route, identify soil cover, groundwater level and underground infrastructure maps (telecom ducts, water pipes, sewers). These determine burial depth, need for protection conduits or cable pits and cable thermal dissipation solutions; during maintenance, verify geotechnical survey results before excavation permits. Measure soil resistivity/ground resistance at cable locations to assess earthing and thermal impact when loaded.

Cable route design must specify voltage level, cable type (insulation, cores, shielding), safe distances to other infrastructure and mechanical protection measures. On site at a plant, check mechanical load capacity where cables will be located and construction access to decide between ducts or direct burial. Construction dossiers should include underground cable installation drawings and detailed construction method statements to coordinate with local power utility.

Legally, have a connection agreement and a safety supervision contract with the power utility before infringing on the underground network. When the route crosses public roads, obtain excavation permits, commit to road reinstatement and secure approvals from local authorities; do not excavate without permits. In practice at a plant, construction procedures must include contingency power plans if undergrounding may cause outages.

Acceptance criteria include insulation checks (insulation resistance measurements), continuity of shielding/earthing and as-built drawings verification. If applicable, perform loop impedance measurements and record electrical acceptance minutes before energization; acceptance testing results must match the as-built documentation.

Decisions should be based on the compiled survey dossiers and connection approval documents; if any are missing, suspend works and complete the documentation before excavation. Providing complete as-built drawings and test results speeds up acceptance and energization with the grid operator.

Regulatory documents and reference sources (current requirements)

Regulatory documents, technical standards and EVN/PC connection approvals must be listed, validated for currency and stored in the project dossier before signing off design, construction or energization. ^[0][0]

From a compliance perspective, classify sources into two groups: current (in force, mandatory) and background/superseded (for reference only). On site, check document items such as issuance date, effective date, amendments and issuing authority. If applying international standards (IEC/ISO/IEEE), note the code and edition and compare to any adopted Vietnamese standards (TCVN) where applicable.

Minimum mandatory approval documents and certificates before operation include: connection approval decision, official letters / connection acceptance minutes, connection contract and competence certificates of consultants/contractors. EVN/PC connection approval is mandatory before energization.

During maintenance or before commissioning tests, directly compare the documents above with the technical dossier on site. Operational warning: do not accept or energize when EVN/PC connection approval is missing or when the applicable standards have not been confirmed current.

Conclusion: after verifying legal sources and standards, complete the technical acceptance dossier and archive certified copies of approval documents, acceptance minutes and contractor certificates in the project file for future audits.