The coupling-capacitor voltage transformer (CCVT) acceptance test is a comprehensive electrical and mechanical inspection of a newly installed or reconditioned CCVT unit before it is first connected to the transmission or distribution system. Per NETA ATS-2025 7.10.3, the test covers identification (manufacturer, model, serial number, rated primary and secondary voltages, marked ratio, basic insulation level, rated burden, and insulation class); visual and mechanical inspection for damage or loose connections; bolted-connection resistance at all accessible terminals; insulation resistance of primary and secondary circuits; polarity verification; voltage transformation ratio at each tap position; voltage-circuit burden measurements; optional dielectric withstand testing; capacitance and power factor or dissipation factor of the capacitor stack; and grounding-point configuration and connection. The test applies to CCVTs that step down transmission or subtransmission voltages to a standard 120 V secondary for relaying, metering, or monitoring equipment downstream.
A CCVT's role is to provide an isolated, step-down replica of the primary voltage to relay and metering circuits without exposing those circuits to high voltage. If the unit is installed with loose bolted connections, has internal insulation degradation, or carries a secondary load burden that exceeds the nameplate rating, the secondary voltage can become unreliable - it may dip, distort, or become unstable under load, causing relays to misoperate, meters to misread, or both. The acceptance test confirms the unit is connected correctly to the system (proper grounding and potential points), that internal insulation is sound, that the turns ratio and secondary burden do not exceed the nameplate limits, and that the transformer is safe to energize without additional remedial work.
Acceptance: performed before a new or reconditioned CCVT is first energized, as part of the standard test sequence for instrument transformer installations. The test is typically run in the field after the unit is installed on the structure but before it is connected to the primary system or the secondary control circuits. Maintenance: the test is not typically repeated on a periodic interval during the unit's in-service life, unless there is a triggering event such as a known voltage transient, physical damage to the unit, or a relay or meter failure downstream that suggests a secondary-voltage or burden problem.
With the primary system isolated and de-energized, and the secondary circuits disconnected from the CCVT secondary terminal, the technician first verifies the unit's nameplate data (manufacturer, model, serial number, voltages, ratio, BIL, burden) and checks the physical installation for proper grounding, correct polarity and connection of the capacitor stack, and absence of visible damage. Bolted-connection resistance is measured at all accessible terminal points and compared against a baseline or a manufacturer's specification. Insulation resistance is measured from primary to ground and secondary to ground using a megohmmeter, and the result is compared against the NETA minimum. Polarity is confirmed by applying a low AC or DC test signal and verifying the secondary output phase relationship. The turns ratio is measured at each tap setting and compared against the marked ratio. Secondary-circuit voltage burden is measured by connecting a calibrated burden box to the secondary terminals and logging the voltage drop and power consumption at the rated secondary voltage. Optional dielectric withstand testing applies a high voltage across the primary-to-secondary and primary-to-ground gaps if the unit is to be de-energized and tested in the field, or may be deferred to the manufacturer's factory test. Capacitance and power factor or dissipation factor of the capacitor stack are measured and compared against the NETA limits. The grounding point (usually a center tap or a designated primary conductor connection) is verified to be bonded correctly to the station ground.
Nameplate data (manufacturer, model, serial number, rated primary and secondary voltages, marked ratio, BIL, rated burden in VA at rated secondary voltage, insulation class, and equipment designation); bolted-connection resistance readings in milliohms at each accessible terminal; insulation resistance in megohms for primary-to-ground and secondary-to-ground; polarity test result (phase relationship of secondary output relative to primary input); measured turns ratio and percent deviation from marked ratio at each tap position; secondary-circuit voltage burden in VA and voltage drop as a percent of rated secondary voltage; dielectric withstand test voltage applied and duration (if performed); capacitance in picofarads or nanofarads and power factor or dissipation factor of the capacitor stack as a percent; grounding-point connection details; ambient temperature; test-instrument identification (make, model, serial, calibration due date); and comments or deficiencies noted.
NETA ATS-2025 7.10.3 calls out several go/no-go acceptance criteria. Bolted-connection resistance at each terminal should not exceed a manufacturer-specified value, typically in the range of a few milliohms, and should be symmetrical across all three phases; an outlier or a reading that cannot be achieved suggests corrosion or a loose bolt. Insulation resistance of primary and secondary circuits should exceed specified NETA minimums, which depend on insulation class; a result below the minimum signals moisture ingress or internal contamination. Polarity test confirms proper phase relationship and terminal connection. The measured turns ratio should agree with the marked ratio within one-half of one percent, and all three phases should be balanced; a ratio error calls for removal and factory rework or replacement. Secondary-circuit voltage burden measured with the rated burden connected should not cause the secondary voltage to drop more than a specified percent (typically two to three percent) from the ideal no-load secondary voltage; an oversized burden or deteriorated connections can violate this limit. Capacitance and power factor or dissipation factor of the capacitor stack should fall within the NETA band; a value outside that band may indicate moisture, contamination, or aging of the capacitor. See the purchased NETA ATS-2025 standard for the complete numeric limits and the voltage-class breakpoints that govern each criterion.
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