PMU 500/275 kV Sedenak West GIS

Scope of works

Establishment of the 500/275 kV Sedenak West gas-insulated main intake substation, 3 × 1,050 MVA.

At 500/275 kV, a main intake substation is transmission infrastructure: the establishment of PMU Sedenak West comprised gas-insulated switchgear and 3 × 1,050 MVA of transformation. GIS is the deciding choice at this rating where land is constrained — it compresses what would otherwise be a very large air-insulated switchyard into a building, at the cost of specialised maintenance access and unforgiving installation tolerances.

Work at this voltage is governed by the utility's standards end to end: protection philosophy, interlocking, earthing design and commissioning are all proven against TNB requirements before energisation, and the civil works must anticipate transformer delivery and replacement for the life of the asset.

Technical particulars

Voltage

500 / 275 kV

Transformers

3 × 1,050 MVA

Switchgear type

Gas-insulated switchgear (GIS)

Function

Main intake substation (PMU)

What this kind of commission involves

High voltage supply work is where the programme risk sits in a large development. The engineering is well understood and largely codified; what consumes the schedule is land, access, wayleave and utility approval. A supply arrangement settled early shapes the building. One settled late means redesigning around a substation that has nowhere to go.

Disciplines engaged

• Maximum demand assessment and diversified load schedules
• Supply strategy — voltage level, firm supply, number of incomers
• Intake and distribution substations (PMU/PPU) and consumer substation (SSU) layout and civil requirements
• Transformer sizing, vector group, tap range and loss evaluation
• Switchgear specification — air-insulated or gas-insulated, ratings and interlocking
• Protection philosophy, relay grading and utility interface coordination
• Earthing, lightning protection and step/touch potential assessment
• HV cable routing, sizing, wayleave and joint/termination specification
• Standby generation, essential services and changeover schemes
• Utility application, technical submission and energisation witnessing

What we watch for

The failures that recur on this building type, and where we look for them.

• Substation position agreed after the architecture is frozen
• Wayleave for the incoming cable route started too late
• Declared maximum demand that no longer matches the built development
• Protection grading assumed rather than agreed with the utility and proven on site

The following describes the standard engineering scope for this sector. The specific scope of any individual commission is set by its brief and contract.

Project location