Liquid-Filled Reactor Acceptance Test

What it is

A liquid-filled reactor acceptance test is a field protocol that verifies a shunt or current-limiting reactor, its bushings, its cooling and protection accessories, and its insulating liquid are all fit for service before energization. It records the identification (manufacturer, model and catalog number, serial number, reactor type, kVAR rating, rated voltage and current, impedance, phase configuration, insulating liquid type, liquid volume, temperature rise, insulation class, and equipment designation) with the as-found and as-left tap positions. The inspection covers nameplate data against the drawings, condition, the impact recorder read before unloading, removal of shipping bracing after final placement, anchorage, alignment and grounding, cleanliness, the temperature devices, the cooling fans and pumps with their motor overcurrent protection, the alarm, control and trip circuits, bolted-connection tightness, liquid level in all tanks and bushings, positive pressure on a nitrogen-blanketed unit, the manufacturer's recommended inspections, tap connections, and a thermographic survey. The electrical work covers bolted-connection resistance, winding-to-ground insulation resistance with polarization index, winding power factor, bushing power factor and capacitance or hot collar, winding resistance against the factory values, oxygen content in the nitrogen blanket, a full insulating-liquid screen, and dissolved gas analysis. NETA ATS-2025 section 7.20.3.2 lists this as the standard acceptance sequence.

Why it is performed

Putting a reactor in oil changes what the acceptance test is for. The winding questions are the same as on a dry unit, and winding resistance against the factory value is still the sharpest evidence of a shorted turn, but the liquid now carries the condition of the whole insulation system and has to be characterized in its own right: breakdown voltage for present dielectric strength, neutralization number and interfacial tension for oxidation, water content for the moisture the paper insulation shares with the oil, power factor for contamination, and color and visual condition as the quick screen. Dissolved gas analysis adds the only view of what is happening inside the tank while it is closed, which is why it is part of acceptance and not just maintenance: a gas pattern present on a brand-new unit means it left the factory or arrived with a defect. The accessory checks matter for the same reason as on a transformer, since a reactor that loses its cooling or its temperature protection overheats quietly.

When it is performed

Acceptance: after installation and before the reactor is energized, as part of the standard acceptance sequence, with the impact recorder read before the unit is unloaded and the liquid samples drawn early enough for the laboratory results to arrive with the record. The same form carries a maintenance service type, and the liquid tests and dissolved gas analysis are the measurements that drive the maintenance interval, since both trend rather than pass or fail once. Insulation resistance and the polarization index are taken with the top liquid temperature recorded, because both move with temperature, and tap positions are recorded as found and as left.

How it is typically performed

With the reactor de-energized, isolated, and grounded per site safety procedures, the identification data, the as-found tap position, and the impact recorder are read and the inspection is worked through: shipping bracing removal, anchorage, alignment and grounding, cleanliness, every temperature device's setting and operation, the cooling fans and pumps with their motor overcurrent protection, the alarm, control and trip circuits, liquid levels in all tanks and bushings, positive pressure on a nitrogen-blanketed unit, and bolted connections verified by torque wrench or resistance measurement. Bolted-connection resistance is measured phase by phase. Winding-to-ground insulation resistance is measured on each winding at the test voltage the standard's table assigns, corrected to a common temperature, and carried long enough to calculate a polarization index. Winding power factor is measured at the stated test voltage, and each bushing is tested at its power-factor and capacitance tap or by hot collar where no tap exists. Winding resistance is measured per phase and set against the factory values. On a nitrogen-blanketed unit the oxygen content of the blanket is measured. A liquid sample is drawn by the standard sampling practice and tested for dielectric breakdown at the specified electrode gap, neutralization number, specific gravity, interfacial tension, color, visual condition, water content, and liquid power factor, and a second sample goes to the laboratory for dissolved gas analysis reporting the individual gases and total dissolved combustible gas. The as-left tap position, ambient temperature, relative humidity, top liquid temperature, and the test equipment with its calibration due date are recorded with the results.

What gets recorded

The identification (manufacturer, model and catalog number, serial number, reactor type, kVAR rating, rated voltage and current, impedance, phase, liquid type, liquid volume, temperature rise, insulation class, and equipment designation); the as-found and as-left tap positions; the result of each visual and mechanical item, including the impact recorder, the temperature devices, the cooling equipment, the alarm, control and trip circuits, liquid levels, blanket pressure, and thermography; bolted-connection resistance per phase; the insulation-resistance test voltage, the winding-to-ground readings as measured and corrected, and the polarization index per winding; the winding power-factor test voltage and per-phase values; bushing power factor and capacitance against the nameplate values, or the hot-collar results; the measured and factory winding resistance per phase; the oxygen content of the nitrogen blanket; the insulating-liquid results for each property with the electrode gap used; the dissolved gas analysis results including total dissolved combustible gas; and the ambient temperature, relative humidity, top liquid temperature, test equipment with calibration due date, comments, and deficiencies.

How results are evaluated

Bolted-connection resistance readings are compared with similar connections and a reading well above the lowest is investigated. Winding-to-ground insulation resistance must meet the manufacturer's published data or, in its absence, the minimum in the standard's insulation-resistance table, with lower values investigated, and the polarization index must exceed the published floor. Winding power factor is judged against the manufacturer's published maximum or, failing that, against the test equipment manufacturer's data, with the standard's power-factor table giving representative maxima by liquid type at the reference temperature. Bushing power factor and capacitance are expected within a published percentage of the nameplate rating, and hot-collar results are compared on milliampere and milliwatt loss against similar bushings. Winding resistance calls for consulting the manufacturer if it varies beyond the published percentage from the factory values or between adjacent phases. Any oxygen in the nitrogen blanket is investigated. Insulating-liquid results are judged against the standard's liquid table for the liquid type and voltage class, which sets a minimum breakdown voltage at each electrode gap, a minimum interfacial tension, maximum neutralization number, water content, power factor, and color, and a bright and clear visual requirement, with specific gravity carried as information rather than a limit. Dissolved gas analysis is evaluated against the transformer gas-in-oil guide. Temperature devices, cooling equipment, liquid levels, and blanket pressure are judged against the system requirements and the manufacturer's tolerances. See the purchased NETA standard for every table value.