The microprocessor-based protective relay acceptance test is a pre-energization inspection and functional verification governed by NETA ATS-2025 section 7.9.2. It begins with identification (manufacturer, model, style number, rated control voltage, firmware and software revisions checked against approved engineering documentation) and a visual and mechanical inspection confirming that indicator LEDs, displays, and targets illuminate, that the relay is clean and undamaged, that settings and logic agree with the current engineered setting files, and that the relay's internal clock shows the correct date and time. The electrical portion measures insulation resistance from each circuit to the grounded relay frame, verifies analog voltage and current metering inputs against known reference values, and - where SCADA metering is provided - checks those readings as well. The core of the test is functional: each protection element the relay implements (the full set of device types the relay is configured for) is exercised, typically by secondary injection, to confirm it operates within the manufacturer's published tolerance; control-verification inputs, outputs, and protection schemes are checked against the design; any arc-energy-reduction elements are exercised; and trip and close coil monitoring, setting-change alarms, and communication links (including SCADA communications and indications, and pilot-scheme links to remote terminals or other relays) are verified.
A protective relay that has been shipped, stored, or handled between the factory and the switchyard may have settings drift, a firmware mismatch, a metering input wired to the wrong current transformer, or a protection element that responds at the wrong pickup or time delay. Because the relay is the device that must recognize a fault and issue a trip command within a defined time, verifying its identity and settings is not enough - each protection function it is configured to provide has to be exercised and shown to operate within tolerance, just as a full electromechanical relay test would be performed on an older-technology relay. Metering-input, arc-energy-reduction, and communications checks confirm that the relay is reading the correct quantities, that any incident-energy-reducing functions will engage as intended, and that pilot or SCADA links needed for a protection scheme to work are alive, before the relay is placed into service where a hidden defect would only surface during an actual fault.
Acceptance: performed on every new or reconditioned microprocessor-based protective relay before it is energized and placed into service, prior to synchronization with the power system, as part of the standard electrical inspection sequence. Maintenance: not typically repeated at regular intervals unless the relay's firmware, software, or settings are updated in the field, in which case the affected portions of the test are repeated to confirm the update was applied correctly and the protection elements still operate within tolerance.
With the relay de-energized on the test bench (or powered from its control-voltage source), the technician records the manufacturer, model, style number, and rated control voltage from the nameplate, and reads the firmware and software revisions from the relay's display, web interface, or service port to confirm they match the approved engineering documentation. A visual and mechanical inspection confirms LEDs, displays, and targets illuminate, the unit is clean, settings and logic match the current setting files, and the date and time are correct. Insulation resistance is measured from each circuit to the grounded frame. Analog metering inputs are checked by applying known reference voltages and currents and comparing the relay's displayed or reported values; SCADA metering points are checked the same way if present. Each protection element is then exercised - ordinarily with secondary current and voltage injection matched to the relay's configured device types - confirming pickup, timing, and any directional or restraint behavior against the manufacturer's published tolerance. Control-verification points (inputs, outputs, and the logic tying them into protection schemes), arc-energy-reduction elements, and trip/close coil monitoring circuits are exercised the same way. Setting-change alarms are triggered to confirm they annunciate correctly, and communication links - SCADA and any pilot-protection channel to a remote terminal or relay - are tested for correct indication and, where applicable, a timely round-trip acknowledgment.
Identification data (manufacturer, model, style number, control voltage, firmware and software revisions, serial number); visual and mechanical inspection results; insulation-resistance values by circuit; analog and SCADA metering comparison results; for each protection element exercised, the pickup value, time delay, and any directional or restraint result against tolerance; control-verification, arc-energy-reduction, and trip/close-coil-monitoring results; setting-change-alarm response; communication-link and pilot-scheme test results including which remote terminal or relay was contacted and whether the exchange was successful; ambient conditions, test date, and technician identity.
NETA ATS-2025 7.9.2 requires that identification, firmware, and software revisions match the project's approved documentation, with any mismatch flagged for reconciliation before the relay is placed into service. LEDs, displays, and targets must illuminate; the relay must be clean and operational; settings and logic must agree with the current engineered setting files; and the relay's date and time must be correct. Insulation resistance and analog or SCADA metering readings must meet the manufacturer's published data, with any reading outside tolerance investigated. Each protection element must be operational and within the manufacturer's recommended tolerance; control-verification points and protection schemes must operate as designed; arc-energy-reduction elements must operate in accordance with manufacturer's published data. Communication links, including pilot-scheme channels, must deliver a timely, correctly acknowledged exchange; a failure to elicit a timely acknowledgment is treated as a fault in the communications link that must be resolved before the relay is energized. See the purchased NETA ATS-2025 standard for the complete device-type list, tolerance tables, and protocol-specific communication test procedures.
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