System

MBSE review session for {{entity:Emergency Diesel Generator for a UK Nuclear Licensed Site}}, session 594. Audited 7 existing diagrams against PART_OF facts and INTERFACES_WITH facts in the SE namespace. Prior sessions had populated all 7 subsystem internal diagrams but had never created a system context diagram. Two subsystem diagrams also had gaps against their PART_OF fact inventory.

Diagrams

System context — showing the EDG against all seven external interfaces:

flowchart TB
  n0["system - Emergency Diesel Generator for a UK Nuclear Licensed Site"]
  n1["actor - DC Battery System"]
  n2["actor - Emergency AC Bus"]
  n3["actor - Plant Protection System"]
  n4["actor - Main Control Room"]
  n5["actor - National Grid"]
  n6["actor - Ultimate Heat Sink"]
  n7["actor - Fuel Supply"]
  n3 -->|Start/stop command| n0
  n1 -->|110V DC control power| n0
  n0 -->|6.6kV Class 1E power| n2
  n0 -->|Status and alarms| n4
  n5 -->|LOOP detection signal| n0
  n7 -->|Diesel fuel| n0
  n6 -->|Cooling water| n0

Starting and Control Subsystem — SIL 3, 4 components

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 Subsystem — SIL 3

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 Subsystem — SIL 2

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 — SIL 2 (updated — bearing assembly added)

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"]
  n6["component - Generator Bearing and Mechanical Support Assembly"]
  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
  n4 -->|shaft coupling| n6
  n6 -->|rotor shaft| n0

Fuel Oil System — SIL 2 (updated — pipework and bulk storage added)

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"]
  n6["component - Fuel Supply Pipework and Valve Assembly"]
  n7["component - Bulk Fuel 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
  n7 -->|bulk fuel supply| n1
  n1 -->|pressurised fuel| n6
  n6 -->|metered fill| n0

Cooling System — SIL 2

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
  n0 -->|coolant flow| n4
  n4 -->|hot coolant| n1
  n2 -->|bypass| n0

Monitoring and Instrumentation Subsystem — SIL 2

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"]
  n6["component - Engine Parameter Sensor Array"]
  n7["component - Protective Trip Logic Unit"]
  n8["component - Local Alarm and Indication Panel"]
  n9["component - Remote Monitoring Gateway"]
  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
  n6 -->|4-20mA dual-channel| n7
  n7 -->|hardwired trip| n5
  n7 -->|alarm signals| n8
  n7 -->|status discretes| n9

Findings

• Missing system context diagram: No block-level context diagram existed showing the EDG against its seven external systems. Created Emergency Diesel Generator — System Context (view: block) with 8 blocks and 7 interface connectors derived from INTERFACES_WITH facts.
• Alternator Subsystem diagram gap: {{entity:Generator Bearing and Mechanical Support Assembly}} was present in PART_OF facts but absent from the diagram. Added as a component block with shaft-coupling and rotor-shaft connectors to the diesel engine external block.
• Fuel Oil System diagram gap: {{entity:Fuel Supply Pipework and Valve Assembly}} was in PART_OF but missing from the diagram. Added with connectors from the transfer pump through to the day tank. {{entity:Bulk Fuel Storage Tank}} was in PART_OF but only represented as a legacy external block “Bulk Storage Tank” — added as a proper internal component block.
• Alternator name drift: “Stator and Armature Winding” in the diagram vs “Generator Stator Winding and Thermal Protection” in PART_OF, and “Brushless Exciter” vs “{{entity:Brushless Excitation System}}”. The diagram names are more concise but omit thermal protection scope — flagged for requirements alignment.
• Spec tree updated: Added system-level entry for the new context diagram; refreshed Alternator and Fuel Oil entries.

Statistics

• Diagrams before: 7, after: 8
• Blocks added: 4 (context diagram: 8 net new; Alternator: 1; Fuel Oil: 2)
• Connectors added: 12 (context: 7; Alternator: 2; Fuel Oil: 3)
• Subsystems with complete diagrams: 7/7 (plus 1 system context)

Next

Two naming mismatches in the Alternator diagram should be resolved in the next QC pass: the “Stator and Armature Winding” block name should align with the PART_OF entity “Generator Stator Winding and Thermal Protection” to ensure thermal protection requirements are traceable to the diagram element. The Fuel Oil diagram now has a legacy “Bulk Storage Tank” (external) block that duplicates the new “Bulk Fuel Storage Tank” (internal) component — the external block should be removed and its connector re-pointed to the internal block.