System

MBSE review session for {{entity:Emergency Diesel Generator for a UK Nuclear Licensed Site}} (project se-edg-uk-nuclear). The project holds 116 requirements across 6 documents. Prior to this session the diagram library contained 7 entries, but one was a zero-block duplicate and five of the nine subsystems had no internal component diagram at all — the model did not reflect the full decomposition held in Substrate.

Diagrams

EDG System Context

flowchart TB
  n0["system - Emergency Diesel Generator"]
  n1["actor - National Grid"]
  n2["actor - Emergency AC Bus"]
  n3["actor - Plant Protection System"]
  n4["actor - Main Control Room"]
  n5["actor - Ultimate Heat Sink"]
  n6["actor - Fuel Supply"]
  n7["actor - DC Battery System"]
  n1 -->|LOOP signal| n0
  n0 -->|6.6kV AC power| n2
  n3 -->|Start/stop commands| n0
  n0 -->|Status signals| n3
  n0 -->|HMI data| n4
  n4 -->|Manual controls| n0
  n5 -->|Cooling water| n0
  n6 -->|Diesel fuel| n0
  n7 -->|Control/start power| n0

Emergency Diesel Generator — Decomposition

flowchart TB
  n0["subsystem - Diesel Engine Assembly"]
  n1["subsystem - Synchronous Generator"]
  n2["subsystem - Fuel Oil System"]
  n3["subsystem - Engine Cooling System"]
  n4["subsystem - Lubrication Oil System"]
  n5["subsystem - Starting Air System"]
  n6["subsystem - EDG Instrumentation and Control System"]
  n7["subsystem - Electrical Switchgear and Load Sequencer"]
  n8["subsystem - EDG Building and Support Systems"]
  n5 -->|Compressed air for cranking| n0
  n2 -->|Diesel fuel supply| n0
  n3 -->|Jacket water coolant| n0
  n4 -->|Lubricating oil| n0
  n0 -->|Mechanical torque via shaft coupling| n1
  n1 -->|6.6kV 3-phase AC output| n7
  n0 -->|Speed, temp, pressure signals| n6
  n6 -->|Auto-start initiation| n5
  n6 -->|Governor control / trip| n0
  n6 -->|Breaker control commands| n7

Electrical Switchgear and Load Sequencer — Internal Components

flowchart TB
  n0["component - Generator Circuit Breaker"]
  n1["component - Bus Undervoltage Sensing Relay"]
  n2["component - Load Sequencer Logic Controller"]
  n3["component - Generator Electrical Protection Relay Package"]
  n4["component - Synchronising Check Relay"]
  n5["component - Class 1E Switchgear Control Power Supply"]
  n1 -->|LOOP trip signal| n0
  n4 -->|close permissive| n0
  n3 -->|protection trip| n0
  n5 -->|125VDC control power| n0
  n5 -->|125VDC control power| n2
  n2 -->|load pickup command| n0

Synchronous Generator — Internal Components

flowchart TB
  n0["component - Stator and Stator Winding Assembly"]
  n1["component - Rotor and Field Winding"]
  n2["component - Automatic Voltage Regulator"]
  n3["component - Generator Neutral Earthing Unit"]
  n4["component - Generator Cooling Fan"]
  n2 -->|excitation current| n1
  n1 -->|rotating magnetic field| n0
  n0 -->|neutral connection| n3
  n4 -->|cooling airflow| n0
  n0 -->|terminal voltage feedback| n2

Fuel Oil System — Internal Components

flowchart TB
  n0["component - Bulk Storage Tank"]
  n1["component - Day Tank"]
  n2["component - Fuel Transfer Pump"]
  n3["component - Fuel Oil Strainer and Filter Assembly"]
  n4["component - Day Tank Level Control and Alarm"]
  n0 -->|bulk fuel supply| n2
  n2 -->|filtered fuel| n3
  n3 -->|clean fuel to day tank| n1
  n4 -->|start/stop signal| n2
  n2 -->|fuel delivery| n1

Engine Cooling System — Internal Components

flowchart TB
  n0["component - Engine Jacket Water Circuit"]
  n1["component - Radiator/Heat Exchanger"]
  n2["component - Coolant Circulation Pump"]
  n3["component - Thermostatic Control Valve"]
  n4["component - Engine Pre-heat System"]
  n2 -->|coolant flow| n0
  n0 -->|hot coolant return| n3
  n3 -->|coolant to cooler| n1
  n1 -->|cooled coolant| n2
  n4 -->|standby heat| n0

Lubrication Oil System — Internal Components

flowchart TB
  n0["component - Engine Lube Oil Sump"]
  n1["component - Engine-Driven Lube Oil Pump"]
  n2["component - Pre-Lube and Post-Lube Pump"]
  n3["component - Lube Oil Cooler"]
  n4["component - Lube Oil Filter and Strainer"]
  n0 -->|oil draw| n1
  n1 -->|pressurised oil| n3
  n3 -->|cooled oil| n4
  n2 -->|pre/post-lube flow| n0

EDG Building and Support Systems — Internal Components

flowchart TB
  n0["component - Ventilation and Combustion Air System"]
  n1["component - Exhaust Silencer and Discharge Stack"]
  n2["component - Fire Detection and Suppression System"]
  n3["component - Category 1 Building Structure"]
  n4["component - Drain and Spill Containment System"]
  n3 -->|air intake penetrations| n0
  n3 -->|exhaust penetration| n1
  n2 -->|fire/shutdown signal| n0
  n3 -->|floor drain collection| n4

Findings

• Duplicate diagram deleted: diagram-1774508659986 was a zero-block duplicate of the {{entity:Electrical Switchgear and Load Sequencer}} internal diagram. The spec tree correctly referenced the newer ID (diagram-1774508666044) but that diagram was also empty — a race condition from the prior creation session. Both entries had 0 blocks and 0 connectors.
• Electrical Switchgear diagram populated: Added all 6 components ({{entity:Generator Circuit Breaker}}, {{entity:Bus Undervoltage Sensing Relay}}, {{entity:Load Sequencer Logic Controller}}, {{entity:Generator Electrical Protection Relay Package}}, {{entity:Synchronising Check Relay}}, {{entity:Class 1E Switchgear Control Power Supply}}) with 6 connectors representing the 125VDC control power distribution and protection trip paths.
• Five internal diagrams created from scratch: {{entity:Synchronous Generator}}, {{entity:Fuel Oil System}}, {{entity:Engine Cooling System}}, {{entity:Lubrication Oil System}}, and {{entity:EDG Building and Support Systems}} had no diagrams despite having subsystem requirements. Each was created with 5 components and 4–5 connectors.
• 25 PART_OF facts stored via bulk to Substrate namespace SE:edg-uk-nuclear, recording component ownership for all newly diagrammed subsystems.
• Spec tree updated for all 5 new subsystems with diagram IDs and status in-progress.
• System Context diagram validated: All 7 {{trait:System-integrated}} external interfaces from INTERFACES_WITH facts (National Grid, Emergency AC Bus, Plant Protection System, Main Control Room, Ultimate Heat Sink, Fuel Supply, DC Battery System) are represented as actor blocks with labelled connectors — no gaps found.

Statistics

• Diagrams before: 7, after: 11 (net; duplicate deleted, 5 created)
• Blocks added: 31 (6 switchgear + 25 new subsystem components)
• Connectors added: 30 (6 switchgear + 24 across 5 new diagrams)
• Subsystems with complete diagrams: 4/9 (Diesel Engine Assembly, I&C System, Starting Air System, Electrical Switchgear)
• Subsystems with diagrams now started: 9/9 (all subsystems have at least an in-progress diagram)

Next

The five newly created diagrams are structurally correct but their connectors are sparse — particularly {{entity:Lubrication Oil System}} (no return path to sump) and {{entity:EDG Building and Support Systems}} (no connector between Fire Detection and Building Structure). Subsystem requirements for Synchronous Generator and Lubrication Oil System remain at SIL 0 with no SUB requirements written; these are the next priority for the reqs-engineer flow. The {{entity:Fuel Oil System}} (SIL 2) and {{entity:Engine Cooling System}} (SIL 2) both need interface requirements covering their connections to the Diesel Engine Assembly — the IFC document currently has no entries for coolant or fuel supply interfaces.