Secondary Engineering Document Architecture for MV Switchgear Projects

Secondary engineering fails when the same fact is copied into many drawings with no declared source of truth. A professional document architecture gives every device, wire, terminal, signal, function, setting and network object one persistent identity, then generates or cross-links the views needed for design, manufacture, FAT, commissioning, operation and modification.

This guide defines the information model, document families, identifiers, revision workflow, traceability and handover structure for conventional and IEC 61850 MV switchgear projects.

Executive rules

Separate requirements, design intent, implementation/configuration, verification and as-built evidence.
Use an object/reference-designation system consistently across drawings, labels, BOM, I/O, relay files, SCL and tests.
Use IEC 81355-1:2024 for current information classification; it replaced IEC 61355-1:2008.
Apply IEC 61082-1 rules to diagram/drawing/table presentation; symbols and project conventions must be controlled.
Declare an authoritative source for every data class and generate secondary views where practical.
Model connectivity at terminal/pin/conductor level, not only graphical lines.
Trace every protection/control signal end-to-end through primary source, terminals, IED logic, communication and destination.
Keep IEC 61850 SCL/configuration, firmware/settings and drawings under one coordinated baseline.
Never overwrite approved evidence; revisions/status/effective configuration must remain reproducible.
Handover machine-readable native data plus human-readable controlled documents and verified as-built records.

1. Standards and information layers

Reference	Role
IEC 61082-1:2014	Rules/guidance for presenting information in electrotechnical diagrams, drawings and tables
IEC 81346-1:2022	System structuring and unambiguous reference designations
ISO 81346-10:2022	Supplementary structuring/classes for power-supply systems
IEC 81355-1:2024	Classification/designation of information containers across lifecycle; replaces IEC 61355-1
IEC 61850-6:2009+AMD1:2018+AMD2:2024	SCL exchange of IED capability/configuration, communication, function structure and relations
IEC 60255-27	Product safety requirements affecting protection equipment/circuits
IEC 62271-200	Switchgear assembly/auxiliary-control interface and project evidence context

These horizontal/product standards complement the contract, utility conventions, drawing templates and cybersecurity/configuration rules. Freeze exact editions and define precedence. Do not continue using the withdrawn IEC 61355-1 merely because a legacy project code exists; map it deliberately to the current IEC 81355-1 architecture when the project adopts the new standard.

2. Five information layers

Layer	Question answered	Examples
Requirement	What must the system do/withstand?	Functional specification, signal list, standards, cybersecurity and availability requirements
Design intent	How will functions/architecture satisfy it?	Single line, protection philosophy, logic narratives, network and DC architecture
Implementation	Exactly what is built/configured?	Schematics, terminal/wiring, BOM, settings, PLC/IED/SCL files
Verification	How was each requirement proven?	Design reviews, FAT/SAT procedures/results, test certificates and issue logs
As-built/lifecycle	What is actually in service now?	As-built drawings/files, firmware, settings checksum, modifications and maintenance records

Never let a FAT mark-up become the only as-built definition. Convert approved field changes into the implementation source, regenerate affected views, verify, approve and archive the superseded baseline.

3. Structure objects before numbering documents

site/substation, voltage system and switchgear lineup;
bus section, functional unit/bay and compartment;
primary function: incomer, feeder, coupler, VT, earth, auxiliary;
protection/control function and logical node group;
physical product: breaker, relay, terminal block, sensor, switch;
location: panel, door, LV compartment, marshalling kiosk;
connection: terminal, pin, core, cable, fibre, Ethernet port and GOOSE/SV dataset.

IEC 81346-1 supports aspect-oriented designations so function, product and location views can coexist. Document the project-specific application and separators; never invent informal abbreviations that collide. The label on a component should retrieve the same object across BOM, schematic, wiring, I/O, settings and test records.

4. Document and information-container identification

project/plant/system scope;
information kind/classification code per adopted IEC 81355-1 scheme;
object/functional-unit association;
sequential/variant/language identifier;
revision, lifecycle status and suitability/purpose of issue;
security classification/access and retention class;
native format/version, PDF/render and machine-readable export;
author/checker/approver and approval timestamps;
effective product/configuration serial range.

Keep document ID distinct from revision and sheet number. A sheet may move within a multi-sheet document without becoming a new technical object. Avoid file names as the only metadata; store fields in the document-management system and title block.

5. Core secondary document families

Family	Minimum content
Design basis/philosophy	Functions, architecture, redundancy, fail states, conventions and assumptions
Single-line/protection zone	Primary topology, CT/VT locations/polarity, trip devices and isolation boundaries
Functional/block logic	Inputs, algorithms/permissives, timers, outputs, fail-safe states and reset
Elementary schematic	Complete current path by function: DC, trip/close, CT/VT, alarms, interlocks
Wiring/interconnection	Device pin/terminal, conductor, cable/core, destination and shield/earth
Terminal plan	Terminal type/number, links/shorting, side, wire, spare and test function
Cable schedule	From/to, cores/pairs, area/type, shield/armour, route, gland and test status
I/O/signal list	Source/destination, semantics, normal/fail state, class, time and SCADA mapping
BOM/device schedule	Object ID, manufacturer/type, rating, firmware, terminal/accessory and spare
Settings/configuration	Relay/IED settings, logic, firmware, SCL/network and checksums
Test/commissioning	Traceable cases, methods, expected/actual results and accepted deviations

6. Define authoritative sources

Create a data-ownership matrix. Example:

device/product/type/rating: approved component database/BOM;
terminal/pin connectivity: ECAD connectivity model;
cable from/to/cores: cable database generated from connectivity;
protection setting: approved relay-setting database/file;
IEC 61850 communication/data model: controlled SCL baseline;
SCADA point naming/scaling: approved signal database;
test result: test-management record tied to requirement/configuration.

If a value must be reproduced in another view, generate it or validate it automatically. Manual copy/paste creates silent divergence. State reconciliation rules for external vendor formats that cannot be integrated.

7. Schematic architecture

one function/current path per readable sheet group;
source and return shown, including fuse/MCB, isolation and earth;
cross-references that resolve uniquely both directions;
contact state/position convention defined and consistent;
wire/terminal/device IDs at every discontinuity;
off-page and external interfaces with destination document/terminal;
CT shorting, VT isolation/backfeed and trip-circuit safety visibly explicit;
spares and unused contacts shown as intentional, not omitted ambiguity;
functional notes/timers only when the authoritative logic source is clear.

IEC 61082 presentation improves consistency, but a neat diagram can still be logically wrong. Validate connectivity and functional requirements, not appearance alone.

8. CT and VT circuits are safety-critical documents

core/winding ID, ratio/tap, polarity and protection zone;
terminal shorting-before-opening sequence and physical link state;
secondary earth location and prevention/detection of unwanted multiple earths;
burden/lead resistance, wire area and terminal rating;
test-switch normal/test configuration and injection boundary;
VT fuse/MCB/disconnect, neutral earth and backfeed prevention;
residual/open-delta and ferroresonance damping connections;
warning/label links to approved test procedure.

A terminal plan that omits the removable/shorting-link state can create lethal CT voltage or disable protection. Represent physical terminal-block functionality, not an ideal wire connection.

9. Trip/close DC architecture

battery/charger/distribution source and selectivity;
dual coils/supplies and independence/common-mode points;
trip-circuit supervision path in breaker open/closed/test positions;
anti-pumping, close permissives, lockout and manual/emergency paths;
coil voltage-drop/current and contact interrupting capability;
isolation links/fuses/MCBs and safe testing;
earth-fault monitoring and DC polarity convention;
fail-safe/alarm state on supply, wire or IED failure;
breaker auxiliary-contact timing and position correspondence.

10. Signal semantics: more than an I/O address

unique signal ID and human description;
source object/terminal/logical node/data object and destination;
binary/analogue/command, engineering unit/range/scaling;
normal, alarm, de-energised and invalid/questionable states;
single/double point and intermediate/bad-state handling;
latched/momentary, pulse duration and reset authority;
time stamp source/resolution/quality and sequence-of-events class;
priority, alarm grouping, deadband and suppression;
test/simulation/substitution method and cybersecurity authority.

Use a single signal dictionary to generate I/O lists, HMI/SCADA mappings, relay points and test cases. Never let identical wording hide opposite contact semantics.

11. IEC 61850 configuration architecture

requirements/function model and substation structure;
vendor ICD/IID capability files and approved versions;
system configuration SCD as controlled integrated baseline;
IED-specific CID/instantiated files actually loaded;
logical nodes/data objects, datasets, reports, GOOSE and Sampled Values;
communication addressing, VLAN/priority, redundancy and time synchronisation;
GOOSE/SV publisher–subscriber matrix and supervision;
SCL validation/tool/version and unresolved warnings;
mapping to drawings, signal list, relay logic and FAT/SAT tests;
signed/checksummed backup plus restore/rollback procedure.

IEC 61850-6 edition 2.2 (2009+A1:2018+A2:2024 consolidated) specifies SCL exchange. A PDF dataflow drawing is a readable view, not the authoritative configured dataset. Conversely, SCL alone does not explain operational intent; maintain both with traceable generation/cross-reference.

12. Requirements-to-test traceability

Assign every requirement a unique ID and acceptance method.
Link it to design function, schematic/logic/network implementation and configuration baseline.
Generate positive, negative, fail-state and boundary test cases.
Record test equipment/calibration, inputs, expected/actual output, timing and evidence.
Link defects/deviations to resolution, retest and affected documents/files.
Close only after independent review against the same released configuration.

A test that “trip works” is insufficient. Identify which protection element, stage/setting, logical conditions, output contact/GOOSE, lockout, breaker coil, indication and event record were verified.

13. Revision, status and baseline workflow

WIP → internal check → interdisciplinary/vendor/client review → approved for manufacture/configuration/test → as-built;
purpose/status clearly separate from revision identifier;
change description names affected objects/functions, not “general update”;
automated impact list for derived documents, settings, SCL and tests;
redline/comment resolution retained with decisions;
electronic approval/permissions and audit log;
baseline package immutable and reproducible;
emergency field change process with retrospective engineering deadline;
superseded documents withdrawn at workshop/site but archived.

14. Cross-document consistency checks

every BOM device appears in location/layout and connectivity where required;
every schematic terminal exists with compatible terminal type/link/accessory;
wire/cable cores have unique ends, size/colour and no orphan/duplicate IDs;
CT/VT ratios/polarity match single line, relay settings and tests;
breaker/earth-switch contacts and interlock semantics match mechanism;
I/O point count/address/type matches IED/PLC and SCADA;
GOOSE/SV publisher/subscriber and SCL match logic/dataflow drawings;
settings/firmware/device type match loaded/configured asset;
FAT/SAT cases cover every requirement and change;
labels/nameplates match as-built reference designations.

15. Handover package

approved as-built PDF and editable native ECAD/database exports;
single lines, schematics, wiring, terminals, cables, I/O, BOM and layouts;
relay/PLC/HMI firmware and source/configuration, settings and checksums;
complete SCL/ICD/IID/SCD/CID and communication/network files;
calculation/functional design and protection logic narratives;
FAT/SAT/commissioning reports, issue/retest logs and calibration;
device manuals/certificates, spares and test/shorting procedures;
cybersecurity accounts/keys/certificates transferred through approved secure process—not drawings;
document index, metadata, dependency map and restore instructions;
training and future modification/configuration-control procedure.

16. Common architecture failures

Failure	Engineering correction
Terminal/cable data typed separately	Generate both from one connectivity model
Device tags differ by document	Adopt IEC 81346-based persistent object IDs
PDF called “source”	Retain governed native/model data and rendered controlled view
Relay settings emailed as latest	Approved repository, version/checksum, loaded-file verification
SCL disconnected from drawings	Cross-map objects/signals and automate consistency checks
FAT redlines never consolidated	Update sources, regenerate/retest and issue as-built baseline
Old IEC 61355 used unknowingly	Adopt/map current IEC 81355-1:2024 deliberately
Normal contact state undefined	Publish convention and state by equipment/energy condition

17. Practical implementation sequence

Approve system/object structure, reference-designation and information-classification rules.
Define document register, metadata, roles/status/revision and authoritative-source matrix.
Create component, terminal, cable and signal data dictionaries with validation rules.
Model requirements/functions and primary/protection-zone architecture.
Develop connectivity, logic, I/O/network and SCL in controlled tools.
Generate/check human-readable schematics, terminal/cable/BOM/signal views.
Run automated consistency and independent engineering reviews.
Baseline the exact manufacture/FAT configuration and test traceability.
Capture site changes in controlled source, regenerate and retest.
Issue secure, reproducible as-built/lifecycle package and train the owner.

18. Migrating a legacy drawing set

Do not bulk-renumber a live plant without an identity/mapping strategy. Build a cross-reference from every legacy tag, wire, cable, terminal, drawing and relay point to the new object model; preserve old identifiers as searchable aliases during the agreed transition.

scan/OCR only as an aid—verify against panels and native files;
resolve duplicate/orphan tags before automated import;
validate safety-critical CT/VT/trip circuits by physical walkdown and functional test;
pilot one representative bay and measure error/rework;
issue a controlled coexistence/label-change plan so operators never face ambiguous designations;
retain superseded baselines and migration decisions for incident investigation.

References

Safety note: Documentation errors can disable protection, open CT circuits, backfeed VT primaries or misoperate breakers. Field changes require approved isolation/testing and configuration control; never treat mark-ups or unverified files as safe operating instructions.