Challenge 04
New protection designs
A new substation, switchboard or plant extension needs a protection concept that is defined, documented and verifiable from the start.
Discuss a new design- Transformer zone — for example differential protection with overcurrent backup
- Busbar zone
- Feeder zones
- Zones overlap at circuit breakers
Actual protection behaviour depends on system data, settings, equipment and fault conditions.
A new installation is the best time to get protection right on paper: which zones exist, which functions protect each item of plant, how main and backup protection overlap, how the logic trips and interlocks, and how the whole scheme will be verified. Settling these early gives equipment suppliers, panel builders and test teams a common reference.
Typical signs
- A new installation or major extension is being designed.
- A project package needs protection philosophy and settings support.
- A panel builder needs logic and I/O definitions before manufacture.
- An owner wants an independent review of a contractor's protection design.
What may need investigation
- Protection philosophy: zones, main and backup functions, and how they overlap.
- Functions required for each item of plant.
- The settings basis and coordination criteria.
- Logic for tripping, interlocking, breaker failure and alarms.
- Verification requirements: what will be tested, how and by whom.
Which of these apply depends on the installation and on what the available records show.
Information that helps
- Single-line diagram and equipment data
- Owner or utility protection requirements
- Selected or candidate relay platforms
- Project schedule and interfaces with other packages
You do not need all of this to start a conversation. We will agree how to share drawings and records after first contact.
Possible deliverables
What the engineering work could produce
Relay settings schedule
Function-by-function settings for each relay, each traced to a documented calculation or criterion.
Typically contains
- Enabled functions and setting values per relay
- Reference to the calculation or criterion behind each value
- Setting groups and conditions for their use
- Notes for implementation and checking
What it is not. A settings schedule is not necessarily a manufacturer-native configuration file. Native files can be prepared only where the relay platform, software tools and information available allow, and when they are in scope.
3 · Settings schedule — Feeder 1 and incomer
| Relay | Function | Parameter | Value | Basis |
|---|---|---|---|---|
| R3 | 51 | I> | 400 A | Calc. 3.1 |
| R3 | 51 | Curve · TMS | IEC SI · 0.10 | Calc. 3.2 |
| R3 | 50 | I>> | Off | Note 2 |
| R2 | 51 | I> | 800 A | Calc. 3.4 |
| R2 | 51 | Curve · TMS | IEC SI · 0.25 | Calc. 3.5 |
| R2 | 51N | IN> | 120 A | Calc. 3.7 |
Values in primary amperes. Conversion to relay-native settings files depends on the platform and is a separate step.
Protection logic diagram
Vendor-neutral diagrams of tripping, interlocking, breaker-failure and alarm logic that can be reviewed before anything is configured.
Typically contains
- Inputs, gates, timers and outputs for each scheme
- Timer values with their basis
- Signal names cross-referenced to the I/O matrix
- Assumptions about relay capabilities
What it is not. A logic diagram defines the intended behaviour. It is not a validated relay implementation until it has been configured and tested in the selected device.
5.1 · Breaker-failure logic — Q2
I/O and signal matrix
Which signal goes where: binary inputs, outputs, trip assignments and communications signals for each relay.
Typically contains
- Binary inputs and outputs per relay
- Trip and lockout assignments to breakers
- Alarms and indications to station control or SCADA
- Communication signals, where applicable
What it is not. A signal matrix must be reconciled with the final schematics and the relay configuration. It does not replace wiring checks.
6 · Trip and signal matrix
| Signal | Q0 | Q1 | Q2 | Q3 | SCADA |
|---|---|---|---|---|---|
| R1 87T trip | ● | ● | ● | ||
| R2 51 trip | ● | ● | |||
| R3 50/51 trip | ● | ● | |||
| R4 50/51 trip | ● | ● | |||
| 50BF Q2 backtrip | ● | ● | |||
| Relay fail alarm | ● |
Test specification or verification plan
What should be tested to verify settings and logic, the expected result of each test and the conditions for it.
Typically contains
- Test objectives and prerequisites
- Test steps with injected quantities or simulated signals
- Expected results and acceptance criteria
- Sheets for recording results
What it is not. A test plan describes what should be tested. It is not evidence that testing has been carried out — that comes from completed test records.
7 · Test steps — Feeder 1 relay R3
- T-01 Pickup of 51 element — expected: start at set value within relay toleranceResult: ______
- T-02 Operate time at 2×, 5× and 10× I> — expected: per calculated curveResult: ______
- T-03 Trip output to Q2 — expected: Q2 trip coil energizedResult: ______
- T-04 Breaker-failure initiation and backtrip pathResult: ______
Results are recorded by the test team. A blank plan is not a test record.
Scope and boundaries
- A logic diagram is not a validated relay implementation — configuration and testing in the selected relay remain separate steps.
- Design review does not establish operational acceptance.
Start a conversation
Tell us what your system is doing — and what you need it to do.
A few lines are enough to start. We will ask for drawings, settings or records later, through a channel agreed with you — there is no need to send them with your first message.