Relay protection engineering · RelaNex Energy

Understand the fault. Engineer the response.

Vendor-independent protection studies, relay logic and modernization support for industrial electrical systems — from investigating unexpected trips to developing documented engineering solutions.

Explore your challenge Discuss your system
  1. 01Understand the protection challenge.
  2. 02Define the engineering work.
  3. 03Develop a documented solution.

Start from what your system is doing

Choose a challenge to see which parts of an illustrative system may need attention, what is typically investigated, and what engineering work could follow.

Illustrative system Not connected to any installation · no measurements shown
Illustrative single-line diagram of an industrial switchboard Illustrative system, not a real installation. An incoming supply feeds breaker Q0 and transformer T1, then main breaker Q1 and a busbar with two outgoing feeders, each with its own breaker (Q2, Q3). Relay R1 protects the transformer, R2 the incomer, R3 and R4 the feeders. A voltage transformer on the busbar and a station control link to R2 are also shown. Incoming supply upstream network Q0 T1 transformer Q1 main busbar VT M Q2 Feeder 1 process load Q3 Feeder 2 distribution G New generation illustrative change illustrated fault R1 87T · 50/51 R2 51 · 51N Station control R3 50/51 R4 50/51
Highlighted for review Illustrated fault or attention Illustrative addition Actual protection behaviour depends on system data, settings, equipment and fault conditions.

01 Challenge

Unexpected or non-selective trips

An illustrated fault on Feeder 1. Relay R3 is expected to clear it by opening breaker Q2. Relay R2 on the incomer acts as upstream backup — whether the two are correctly graded depends on their settings and the actual fault level.

In the diagram

  1. Illustrated fault location on Feeder 1
  2. R3 feeder relay — expected to operate first and open Q2
  3. R2 incomer relay — upstream backup; its timing against R3 is a common point of investigation
  4. Q1 main breaker — if Q1 opened instead of Q2, the whole busbar lost supply

What may need investigation

  • Disturbance and event records from the relays involved, where they exist.
  • Time–current coordination between the feeder, incomer and upstream devices at the relevant fault levels.
  • Settings as found compared with the settings intended — including setting groups and enabled functions.

Typical information required

  • Single-line diagram, as-built where available
  • Relay settings files or printouts
  • Disturbance and event records with timestamps
  • A description of the event and the operating conditions

Potential deliverables

The actual scope depends on the installation and the information available.

Discuss an unexpected trip More on this challenge

02 Challenge

Changes to the electrical network

An illustrative change: on-site generation connected downstream of Feeder 2. Fault current can now flow from more than one source, so fault levels and coordination may need reassessment.

In the diagram

  1. Illustrative change — new on-site generation (dashed)
  2. R4 feeder relay — may now see fault current in either direction
  3. Busbar fault level may increase with the added source
  4. R2 incomer relay — grading with downstream devices may need rechecking

What may need investigation

  • Updated short-circuit levels at the relevant points, for maximum and minimum conditions.
  • Whether existing pickup settings remain sensitive enough for minimum fault conditions.
  • Grading margins between devices after the change.

Typical information required

  • Updated single-line diagram showing the change
  • Data for new equipment: transformer impedance, generator or inverter data, motor data
  • Utility fault level information
  • Existing relay settings

Potential deliverables

The actual scope depends on the installation and the information available.

Discuss a network change More on this challenge

03 Challenge

Aging relays and protection systems

R2, the incomer relay, is shown as an existing relay under review. A replacement has to work with every interface around it — measurement inputs, trip circuits, logic and communications.

In the diagram

  1. R2 existing relay under review
  2. CT inputs — ratio, accuracy class and wiring
  3. VT input — voltage-based functions and supervision
  4. Trip circuit to Q1 — including interlocks and supervision
  5. Communications to station control or SCADA

What may need investigation

  • Inventory and condition of existing relays and associated equipment, based on available records.
  • Which protection functions the existing scheme provides — and which the replacement should provide.
  • CT and VT inputs, trip and close circuits, DC supply and interlocks the new relay must interface with.

Typical information required

  • Relay schedules and nameplate data
  • Schematic and wiring drawings
  • Existing settings, as found if available
  • Maintenance and test records

Potential deliverables

The actual scope depends on the installation and the information available.

Discuss aging protection More on this challenge

04 Challenge

New protection designs

Protection zones around the transformer, busbar and feeders. Each zone needs defined functions, settings and verification, and zones overlap at circuit breakers so that no section is left unprotected.

In the diagram

  1. Transformer zone — for example differential protection with overcurrent backup
  2. Busbar zone
  3. Feeder zones
  4. Zones overlap at circuit breakers

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.

Typical information required

  • Single-line diagram and equipment data
  • Owner or utility protection requirements
  • Selected or candidate relay platforms
  • Project schedule and interfaces with other packages

Potential deliverables

The actual scope depends on the installation and the information available.

Discuss a new design More on this challenge

Engineering deliverables

What you may receive.

Each project has its own scope, but the outputs are documents your team can review, question and keep. The previews below show the kind of structure to expect — they are examples, not client work.

Protection study and coordination report

Fault levels, the coordination between protective devices and the reasoning behind each recommended setting — with the data and assumptions stated.

Typically contains

  • System data, sources and assumptions
  • Short-circuit results for the agreed operating cases
  • Time–current plots for each protection path
  • Grading margins checked against the agreed criteria
  • Issues found and recommended changes

What it is not. A study documents calculations and recommendations. It is not field commissioning and does not confirm how installed relays are actually set.

Illustrative deliverable — not a client project.
Study report Example document · layout only

4.2 · Coordination: Feeder 1 → Incomer

CheckCriterionStatus
Margin at max. faultAgreed CTISee §4.3
Margin at min. faultAgreed CTISee §4.4

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.

Illustrative deliverable — not a client project.
Settings schedule Example document · layout only

3 · Settings schedule — Feeder 1 and incomer

RelayFunctionParameterValueBasis
R351I>400 ACalc. 3.1
R351Curve · TMSIEC SI · 0.10Calc. 3.2
R350I>>OffNote 2
R251I>800 ACalc. 3.4
R251Curve · TMSIEC SI · 0.25Calc. 3.5
R251NIN>120 ACalc. 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.

Illustrative deliverable — not a client project.
Logic diagram Example document · layout only

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.

Illustrative deliverable — not a client project.
I/O matrix Example document · layout only

6 · Trip and signal matrix

SignalQ0Q1Q2Q3SCADA
R1 87T trip●●●
R2 51 trip●●
R3 50/51 trip●●
R4 50/51 trip●●
50BF Q2 backtrip●●
Relay fail alarm●

Modernization assessment

A structured view of the existing protection — what is installed, how it interfaces, where the risks are — and options for replacing it.

Typically contains

  • Inventory of relays and associated equipment
  • Observations from records and drawings
  • Interfaces the replacement must respect
  • Replacement options and possible phasing
  • Further information or surveys required

What it is not. An assessment is based on the records and drawings available. Findings may need to be confirmed by a site survey before detailed design.

Illustrative deliverable — not a client project.
Assessment Example document · layout only

2 · Existing protection — observations

ItemObservationPriorityNext step
R2 incomerElectromechanical; no event recordsHighReplacement option A/B
CT1Ratio known; class not documentedMediumConfirm by survey
Trip circuit Q1Single coil; no supervisionMediumReview in design
DC supplyNot shown on drawingsUnknownInformation request

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.

Illustrative deliverable — not a client project.
Test plan Example document · layout only

7 · Test steps — Feeder 1 relay R3

  1. T-01 Pickup of 51 element — expected: start at set value within relay toleranceResult: ______
  2. T-02 Operate time at 2×, 5× and 10× I> — expected: per calculated curveResult: ______
  3. T-03 Trip output to Q2 — expected: Q2 trip coil energizedResult: ______
  4. T-04 Breaker-failure initiation and backtrip pathResult: ______

Results are recorded by the test team. A blank plan is not a test record.

Technical findings and recommendations

A concise record of what was reviewed, what was observed, what it may mean, and what we recommend — including where the evidence is incomplete.

Typically contains

  • Scope of the review and information used
  • Observations with supporting evidence
  • Likely implications, with their confidence
  • Recommendations and suggested next steps

What it is not. Findings reflect the data reviewed. Where records are incomplete, the report says so rather than presenting a single definitive cause.

Illustrative deliverable — not a client project.
Findings Example document · layout only

Finding F1 · Feeder 1 and incomer grading

Observation
From the settings provided, the R2/R3 margin is below the agreed criterion at the higher fault levels.
Implication
Q1 may trip before Q2 for close-in faults on Feeder 1.
Recommendation
Revise R2 time multiplier; confirm CT data before implementation.
Confidence
Medium — disturbance record incomplete.

How collaboration works

Four stages, agreed with you.

Most of the engineering is carried out remotely, with review points agreed with your team. Activities on site are planned only where the scope requires them.

Can be done remotely

  • Short-circuit and coordination calculations
  • Settings development and review
  • Logic diagrams, I/O and signal matrices
  • Review of disturbance and event records you provide
  • Test specifications and review of test results
  • Technical reports and recommendations

Requires site arrangements

  • Switching and isolation
  • Secondary injection and other physical testing
  • Commissioning and energization
  • Operational acceptance

Carried out by appropriately authorised personnel under agreed site arrangements. Not every project includes site attendance or commissioning.

  1. 01

    Define the problem and available information

    A first conversation about what the system is doing, what has changed and what you need. Together we identify which drawings, settings and records exist — and what is missing.

    Where Remote

  2. 02

    Assess the system and agree the scope

    We review the information provided and propose a defined scope: the questions to answer, the deliverables, the assumptions and what is excluded.

    Where Remote

  3. 03

    Develop and review the engineering deliverables

    Calculations, settings, logic and documentation are developed and issued for review at agreed points, so your engineers can question the basis of each decision.

    Where Remote

  4. 04

    Support agreed implementation and verification activities

    Where agreed, we support settings implementation, test planning and review of test results. Switching, physical testing, commissioning and operational acceptance are carried out by appropriately authorised personnel under your site's arrangements.

    Where Remote support · site activities only where agreed

Tools & insights

Background reading and educational tools.

All insights
Tool · A Overcurrent time-margin check Compare two inverse-time relays (IEC 60255-151 and IEEE curves) at a fault current you choose. Tool · B Breaker-failure timing Step through a simplified 50BF scheme: healthy breaker, failed trip coil, stuck breaker. Tool · C Feeder fault sequence Watch the order of events when a feeder relay clears a fault and an auto-reclose follows.

Educational illustrations only — not a substitute for a protection study.

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.

Start from a challenge

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