Case Study 1 33/11kV Substation
Mechanical key interlocking remains one of the most critical — yet least understood — safety systems in substations, particularly in brownfield environments where new equipment must interface safely with existing assets.
What you’ll learn
- Why interlocking is required.
- Types of interlocks.
- Interlocking Examples.
- Designing of actual 33/11kV substation mechanical key interlocking.
Course Content
- Introduction –> 1 lecture • 3min.
- Green Field Vs Brown Field Projects –> 1 lecture • 8min.
- Scope of work –> 1 lecture • 13min.
- Why interlocking is required –> 1 lecture • 13min.
- Types of Interlocking –> 1 lecture • 10min.
- Reviewing Existing SLD and New SLD –> 1 lecture • 14min.
- Key Exchange Box –> 1 lecture • 10min.
- Key Interlocking of Actual Brown Field Project –> 1 lecture • 20min.
- Interlock Warning –> 1 lecture • 2min.
- Bonus Section –> 1 lecture • 3min.
Requirements
Mechanical key interlocking remains one of the most critical — yet least understood — safety systems in substations, particularly in brownfield environments where new equipment must interface safely with existing assets.
This course is a practical, step-by-step training focused on the design of mechanical key interlocking systems for substations, with a real-world case study based on a 33/11 kV brownfield substation.
The training begins by establishing a strong foundation, clearly explaining the difference between greenfield and brownfield projects, and why brownfield substations demand a more careful, interface-driven design approach. You will then be guided through the scope of work for a typical 33/11 kV substation, including the challenges of working with existing switchgear, transformers, and live systems.
Using a realistic scenario, the course explains how new 11 kV switchgear is introduced into an existing substation and safely interfaced with existing 33 kV switchgear and transformers, including provisions for future transformer bays. Special focus is given to the design of mechanical key interlocks between new and existing equipment, ensuring correct operational sequences and preventing unsafe switching.
You will learn:
- Why interlocking is required in substations
- The differences between electrical, mechanical, key-based, and software (relay/SAS) interlocks
- How mechanical key interlocking systems work in practice
- The role of key exchange units, trapped keys, and release logic
- How to read and review Single Line Diagrams (SLDs) specifically for interlocking design
- The symbols and conventions used in mechanical interlocking schemes
The course then walks through a complete mechanical key interlocking design for:
- Three 11 kV incomers
- Two bus sections
- Interfaces with existing 33/11 kV transformers (two existing and one future transformer)
This training is not theoretical. It reflects how mechanical interlocks are actually designed and implemented in old and mixed-technology substations, covering AIS, GIS, and metal-clad switchgear, and their interfaces — a combination rarely addressed in a single course.
By the end of this course, engineers will be able to:
- Design mechanical key interlocking schemes for both greenfield and brownfield substations
- Confidently handle existing-to-new equipment interfaces
- Apply safe, industry-proven interlocking logic to real projects
This is a unique, practical, and industry-focused course, ideal for protection engineers, substation designers, commissioning engineers, and anyone involved in upgrading or extending existing substations.