Technical guide
Detailed information about Secondary Tests and Relay Tests
secondary and relay tests — this guide covers the scope, application method, quality criteria and reporting process for your needs.
The complete protection chain in secondary testing
Secondary and relay tests carry a scope broader than verifying the measured values on the protection relay's display. Starting from the current and voltage transformer secondaries, the entire chain is evaluated up to the wiring, test blocks, relay inputs and outputs, auxiliary relays, interlocks, circuit breaker trip coil, signals, and SCADA points. A fault in any link of the chain can cause a correctly set relay to fail to clear the fault or to trip unnecessarily.
Plan-Test begins by reviewing the protection philosophy, single-line diagram, relay setting files, trip matrix, and secondary designs. CT/VT ratios, polarities, grounding points, and relay software versions are verified. Test scenarios are prepared according to the fault types expected in the system. In each scenario, the applied current-voltage, the relay's operating time, the output contact, the circuit breaker trip, and the relevant alarm are recorded. In this way, the test result becomes repeatable and auditable.
Protection relay testing and function verification
Protection relay testing can cover functions such as overcurrent, earth fault, directional protection, distance, differential, under-overvoltage, under-overfrequency, busbar, and circuit breaker failure. The scope to be applied is determined according to the relay's duty and the facility's protection philosophy. Threshold values, time curves, directional characteristic, zone reaches, and blocking logics are tested by secondary injection. The results are compared with the approved setting file and the IEC 60255 approach.
In numerical relays, logic equations, communication messages, time synchronization, event records, and fault oscillographies are also important. It is checked that the setting file is loaded into the correct device with the correct version. As much as a function's independent operation, its priority and blocking relationship with other functions is tested on a scenario basis. Because a wrong signal name or inverted contact logic can lead to serious interpretation errors in operation, the HMI and SCADA displays are matched with the actual behavior of the field equipment.
Differential, distance, and busbar protection tests
In transformer differential protection, CT ratio and connection group compensation, the slope characteristic, harmonic blocking, and the instantaneous trip zones are verified. A simple current test performed without considering phase shift and zero-sequence behavior does not represent real operating conditions. In distance protection, line impedance, zone reaches, fault resistance, direction, load zone, and tripping times are tested at different fault points. Voltage and current phase angles are applied to suit the scenario.
Because busbar differential and circuit breaker failure protections interact with many feeders, the test plan is prepared in more detail. CT circuits, disconnector position information, busbar selection, control zones, and trip distribution are verified. In the circuit breaker failure function, the initiation criterion, current supervision, time delay, and the tripping signals sent to upstream breakers are monitored. End-to-end tests show that the system operates correctly not only within the relay but together with the field connections.
Trip circuit, interlock, and SCADA tests
Trip circuit testing verifies continuity and the actual function from the relay output to the circuit breaker trip coil. When the operation permits it, the breaker's tripping is observed; when it does not, safe simulation points are used. Trip circuit supervision, coil supply, auxiliary contact feedback, and open-close interlocks are checked. The electrical-mechanical interlocks depending on disconnector and grounding switch positions are tested with normal and erroneous switching scenarios.
It is important that alarm, status, and measurement points reach SCADA with the correct name, value, and timestamp. Local-remote selection, control authority, connection loss, communication redundancy, and time synchronization can be checked. Every event created during the test is compared with the expected HMI screen and event list. Proceeding through a function matrix, Plan-Test records which point was tested, the expected result, and the actual result, and tracks open items together with their owners.
Relay coordination and short-circuit calculation
Relay coordination aims for the protection element closest to the fault to operate with sufficient speed and selectivity. The network topology, minimum-maximum short-circuit currents, transformer impedances, motor contributions, cable thermal withstands, and distribution stages are entered into the calculation model. Under different operating scenarios, the relays' detection sensitivity and backup protection times are checked. The current-time curves are evaluated together with circuit breaker tripping times and equipment withstand.
Preparing a setting proposal is not sufficient on its own; its consistency with the on-site CT ratio, relay model, software version, and existing logic must be verified. The approved settings are loaded in a controlled manner, a change record is kept, and the actual operating values are measured with an injection test. The coordination report explains the assumptions and the network conditions used. In this way, when short-circuit power, generation capacity, or grid connection changes in the future, it is understood which settings need to be re-examined.
Secondary test report and commissioning records
The secondary test report contains the relay identity, hardware-software version, setting file reference, test device, applied scenarios, and measured operating times. Settings and test modes changed temporarily are reverted at the end of the work; the relay target and event records are checked. Trip links, test blocks, fuses, and switches are restored to the operating position, and an independent closing check is performed.
Plan-Test combines the test scenarios, the setting verification sheet, the function matrix, and the open items list into a single commissioning file. Critical nonconformities are closed before energization. The test results serve as a reference in the analysis of failures that may occur later. Systematic recording turns the statement 'the relay was tested' into measurable evidence; it is demonstrated, specific to the facility, that the protection system operates correctly, selectively, and within the expected time.
Plan-Test’s quality, safety and reporting approach
Plan-Test does not treat the service scope merely as a list of operations to be performed on site. The facility's operating objective, outage availability, existing documentation, equipment history, and risk level are evaluated together. Before the work begins, responsibilities, access conditions, de-energization and re-energization steps, and reporting expectations are clarified. This is intended to keep teams working from the same plan, prevent critical checks from being skipped, and make efficient use of site time. Because each project is planned according to its own technical conditions, the method, devices, team size, and delivery documents to be used are clearly defined at the proposal stage.
Our quality approach is based on explaining what the result means rather than presenting the measurement result on its own. The calibration status of the test devices used, the ambient and load conditions, the connection arrangement, the applied standard, manufacturer criteria, and any previous measurements are linked together in the report. Nonconformities are classified by severity; findings requiring immediate intervention, issues that can be addressed in planned maintenance, and trends that should be monitored are separated from one another. This method helps the investor, the operations manager, and the site team turn the same technical data into a decision-ready output.
Occupational health and safety is an inseparable part of all services. The site-specific risk assessment, personal protective equipment, lockout-tagout steps, absence-of-voltage verification, and grounding and bonding rules are reviewed before the field work begins. Inspections carried out in an energized facility are based on safe approach distances and operating instructions. Plan-Test's goal is to combine technical verification with a safe working discipline in the same process and deliver sustainable, traceable, and auditable engineering services in 1–380 kV energy facilities.
At the proposal and mobilization stage, clearly defining the scope matters for both the employer and the site team. Plan-Test determines the required activities by reviewing the existing drawings, the equipment list, the facility's operating regime, previous reports, and the employer's expectations. Out-of-scope items, necessary preparatory work, the need for de-energization, operational accompaniment, and third-party responsibilities are put in writing. When a new condition arises on site, no uncontrolled scope change is made before its impact is evaluated in terms of technical, schedule, and resource aspects. In this way, all parties understand throughout the project which activity is being performed and why, which data is expected, and against which criterion acceptance will be made. This clarity reduces repeat visits and misplaced expectations while making the delivered engineering service comparable.
The quality of field work depends on the team's experience and cross-disciplinary communication as much as on the equipment used. Plan-Test assigns tasks according to the test or maintenance steps and opens points requiring primary, secondary, project, and operational knowledge to joint evaluation. Measurement devices are used with accessories suited to the application, their calibration validity is checked, and raw data is stored securely. When a critical result is observed, the connection, device settings, environmental conditions, and the equipment's operating history are reviewed again instead of jumping to a hasty interpretation. Verification with a different method is proposed when necessary. This culture of technical scrutiny helps prevent incidental or erroneous measurements from steering the decision process and helps define the real risk on site more accurately.
Completion of the service does not end with the delivery of the report; the actions in the report must be implementable and traceable. Plan-Test links its recommendations to priority, the responsible discipline, the recommended due date, and the verification method. If the employer wishes, a scope for a technical meeting, post-correction check, or repeat measurement can be established for critical items. When new results are compared with historical data under the same equipment code, the facility's condition trend becomes visible. These records support the preparation of the future maintenance budget, spare parts plan, modernization decisions, and outage calendar. The goal is not to document a single project moment, but to build a corporate technical memory that contributes to safe operation and high availability targets throughout the energy facility's entire life cycle.
In every engagement, the relevant national legislation, the grid operator's requirements, IEC and IEEE standards, and the equipment manufacturer's instructions are considered together. While the general provisions of the standards are adapted to the facility's actual conditions, the contract and approved project requirements are also preserved. Where several criteria give different limits, the acceptance approach used is explained in the report; uncertain points are recorded with the employer as a technical decision. Using unique site codes instead of equipment names in documents strengthens traceability among drawings, test results, photographs, and actions. With this documentation discipline, Plan-Test aims to ensure that the technical evidence needed during an audit, provisional acceptance, warranty discussion, or a future failure investigation can be found quickly and reliably.
For the site program you need, it is sufficient to share the facility type, voltage level, equipment count, location, and target date. After the preliminary review, the technical team clarifies the appropriate scope, preparations, and delivery plan.