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Krishna K.C.

Aug 2023 – Jun 2024 · Noesis Engineering Solution, Kathmandu

33/11 kV Substation & Protection Design

Single-Line Design · Transformer Sizing · Short-Circuit & Coordination

Substation and distribution design for utility and industrial projects: 33/11 kV layouts and single-line diagrams, transformer sizing, short-circuit analysis and protection coordination to IEEE and IEC standards.

Simplified 33/11 kV substation single-line diagram. A 33 kV incoming line, protected by a surge arrester and a circuit breaker, connects to the 33 kV busbar. A 33/11 kV transformer steps the voltage down to an 11 kV busbar, which supplies several protected outgoing feeders. The station is tied to an earthing grid designed to IEEE Std 80 and IEC 62305. This is an illustrative portfolio diagram, not an actual client drawing.

Illustrative diagram — not a client or employer drawing.

01Project overview

At Noesis Engineering Solution, the work covered 33/11 kV substation design and MV/LV distribution for utility and industrial projects.

Deliverables included substation layouts, single-line diagrams, cable schedules, equipment layouts and technical reports.

02Engineering problem

A substation has to step voltage down safely and reliably while protecting equipment and personnel against faults, overvoltages and lightning.

That requires coordinated sizing, protection and earthing decisions backed by standards-based calculations.

03Responsibilities

  • Designed 33/11 kV substation layouts and single-line diagrams, cable schedules, equipment layouts and technical reports.
  • Performed transformer sizing, short-circuit analysis and overcurrent-protection coordination.
  • Engineered earthing grids and lightning protection to IEEE Std 80 / IEC 62305.
  • Sized MV/LV cables against ampacity, voltage drop (< 3%) and short-circuit withstand.

04System architecture

  • An incoming 33 kV line connects through a circuit breaker to the incoming busbar.
  • A 33/11 kV transformer steps the voltage down to an 11 kV bus.
  • Protected outgoing feeders leave the 11 kV bus; the station is tied to an earthing grid with lightning protection.

05Engineering methodology

  • Transformers were sized for the served load, and short-circuit analysis established fault levels.
  • Overcurrent protection was coordinated so the device nearest a fault operates first.
  • Earthing and lightning protection were designed to IEEE Std 80 and IEC 62305; cables were sized for ampacity, voltage drop and short-circuit withstand.

06Tools & platforms

  • ETAP
  • AutoCAD
  • IEEE Std 80
  • IEC 62305

07Validation approach

  • Cable sizing was checked against ampacity, a voltage-drop limit of under 3%, and short-circuit withstand.
  • Protection settings were checked through coordination so that upstream and downstream devices operate selectively.

08Engineering considerations

  • Design balanced electrical performance, safety and equipment protection against project cost.
  • Earthing and lightning protection were treated as integral to personnel and equipment safety.

09Outcomes

  • Substation layouts, single-line diagrams, cable schedules and technical reports for utility and industrial projects.
  • Standards-based transformer sizing, short-circuit analysis and protection coordination.

10Skills demonstrated

  • Substation design
  • Single-line diagrams
  • Short-circuit analysis
  • Protection coordination
  • Cable sizing
  • Earthing & lightning protection

Confidentiality note

The single-line diagram below is a simplified portfolio illustration of a generic 33/11 kV arrangement. It is not an actual client drawing and contains no project-specific data.

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