System

MBSE review session for the {{entity:Emergency Diesel Generator System for UK Nuclear Licensed Site}}. The project holds 68 requirements across seven subsystems. Three internal block diagrams had been created in prior sessions but all were showing as empty in the diagram list — the diag list API was misreporting block counts, while diag get confirmed the blocks existed. Four subsystems ({{entity:Alternator Subsystem}}, {{entity:Fuel Oil System}}, {{entity:Cooling System}}, and {{entity:Monitoring and Instrumentation Subsystem}}) had no diagrams at all. The session target was full diagram coverage for all seven subsystems.

Diagrams

Starting and Control — Internal Block (existing, verified)

flowchart TB
  n0["component - Automatic Load Controller"]
  n1["component - Engine Control Panel"]
  n2["component - Compressed Air Starting System"]
  n3["component - Isochronous Governor System"]
  n4["external - Class 1E Safety Bus"]
  n5["external - Diesel Engine"]
  n4 -->|LOOP detection voltage/freq| n0
  n0 -->|Start demand hardwired 24VDC| n1
  n1 -->|Air start valve open signal| n2
  n2 -->|30 bar cranking air| n5
  n5 -->|Speed feedback dual MPU| n3
  n3 -->|Fuel rack position| n5
  n1 -->|Speed setpoint / trip| n3

Electrical Protection and Switchgear — Internal Block (existing, verified)

flowchart TB
  n0["component - Generator Protection Relay"]
  n1["component - Main Generator Circuit Breaker"]
  n2["component - Safety Bus Transfer Contactor"]
  n3["component - Voltage Sensing and Monitoring Unit"]
  n4["external - Automatic Load Controller"]
  n5["external - Class 1E Safety Bus"]
  n3 -->|4-20mA voltage signals| n0
  n0 -->|110VDC trip signal| n1
  n4 -->|24VDC bus transfer cmd| n2
  n2 -->|safety bus supply| n5
  n1 -.->|anti-paralleling interlock| n2

Diesel Engine — Internal Block (existing, verified)

flowchart TB
  n0["component - Engine Block and Rotating Assembly"]
  n1["component - Fuel Injection System"]
  n2["component - Lubrication and Bearing System"]
  n3["component - Turbocharger and Charge Air System"]
  n4["component - Engine Exhaust and Silencing System"]
  n5["external - Fuel Oil System"]
  n6["external - Alternator Subsystem"]
  n7["external - Cooling System"]
  n8["external - Isochronous Governor System"]
  n5 -->|diesel fuel 3-6 bar| n1
  n1 -->|metered fuel spray| n0
  n8 -->|fuel rack demand| n1
  n0 -->|shaft torque 1500 RPM| n6
  n0 -->|exhaust gases| n3
  n3 -->|charge air below 45C| n0
  n7 -->|jacket water 70-85C| n0
  n2 -->|oil 3.5-5 bar| n0
  n0 -->|exhaust to atmosphere| n4

Alternator Subsystem — Internal Components (new)

flowchart TB
  n0["component - Rotor and Field Winding"]
  n1["component - Stator and Armature Winding"]
  n2["component - Automatic Voltage Regulator"]
  n3["component - Brushless Exciter"]
  n4["external - Diesel Engine"]
  n5["external - Generator Protection Relay"]
  n4 -->|shaft torque 1500 RPM| n0
  n0 -->|field rotation| n3
  n3 -->|DC excitation current| n0
  n2 -->|excitation demand signal| n3
  n1 -->|11kV terminal voltage| n2
  n1 -->|11kV 3-phase output| n5

Fuel Oil System — Internal Components (new)

flowchart TB
  n0["component - Day Tank"]
  n1["component - Fuel Transfer Pump"]
  n2["component - Duplex Fuel Filter"]
  n3["component - Fuel Level and Alarm Unit"]
  n4["external - Fuel Injection System"]
  n5["external - Bulk Storage Tank"]
  n5 -->|bulk fuel supply| n1
  n1 -->|diesel fill| n0
  n0 -->|gravity feed 0.3 bar| n2
  n2 -->|filtered fuel 3-6 bar| n4
  n3 -->|level alarm / pump start| n1

Cooling System — Internal Components (new)

flowchart TB
  n0["component - Jacket Water Pump"]
  n1["component - Radiator and Fan Assembly"]
  n2["component - Thermostat Valve"]
  n3["component - Coolant Header Tank"]
  n4["external - Engine Block"]
  n5["component - Intercooler"]
  n0 -->|hot coolant| n2
  n2 -->|coolant above 71C| n1
  n1 -->|cooled water return| n0
  n2 -->|bypass/through coolant| n4
  n4 -->|warm jacket water| n0
  n5 -->|charge air below 45C| n4
  n3 -->|system pressure / top-up| n0

Monitoring and Instrumentation — Internal Components (new)

flowchart TB
  n0["component - Engine Monitoring Unit"]
  n1["component - Temperature Sensor Array"]
  n2["component - Pressure Sensor Array"]
  n3["component - Speed and Frequency Monitor"]
  n4["component - Local Alarm Annunciator"]
  n5["external - Engine Control Panel"]
  n1 -->|temperature signals 4-20mA| n0
  n2 -->|pressure signals 4-20mA| n0
  n3 -->|speed/freq pulse signals| n0
  n0 -->|alarm discrete outputs| n4
  n0 -->|trip and shutdown signals| n5
  n3 -->|overspeed trip hardwired| n5

Findings

• airgen diag list was reporting 0 blocks and 0 connectors for all diagrams — confirmed as a display count bug; diag get shows correct data. Three existing diagrams (Starting and Control, Electrical Protection, Diesel Engine) are fully populated from prior sessions.
• Four subsystems had no diagrams at all: Alternator, Fuel Oil System, Cooling System, Monitoring and Instrumentation. All four created this session.
• Duplicate diagram creation occurred due to em-dash (—) in names causing jq parse errors while commands executed silently. Three duplicates deleted before population.
• PART_OF facts added to SE namespace for 18 new components across the four new subsystems.
• All four spec tree entries updated from status:pending to status:complete.

Statistics

• Diagrams before: 3, after: 7
• Blocks added: 24 (across four new diagrams)
• Connectors added: 24 (Alternator: 6, Fuel Oil: 5, Cooling: 7, M&I: 6)
• PART_OF facts added: 18
• Subsystems with complete diagrams: 7/7

Next

All seven subsystems now have internal block diagrams with populated blocks and connectors. The next priority is subsystem-level requirements for the two highest-risk subsystems: {{entity:Starting and Control Subsystem}} (SIL 3, start-within-10-seconds constraint) and {{entity:Electrical Protection and Switchgear Subsystem}} (SIL 3, anti-paralleling and bus transfer logic). Interface requirements between the Alternator and Electrical Protection subsystems — specifically the voltage sensing path from {{entity:Voltage Sensing and Monitoring Unit}} through the {{entity:Automatic Voltage Regulator}} to the {{entity:Generator Protection Relay}} — should be formalised next.