Polarity (Transformer)
The instantaneous voltage relationship between primary and secondary terminals determining series/parallel connection compatibility.
Transformer polarity defines the instantaneous voltage relationship between primary and secondary terminals. Two types: additive polarity (secondary voltage adds to primary) and subtractive polarity (voltages subtract).
Standard for IEC transformers: subtractive polarity (dot convention). ANSI/IEEE uses subtractive for transformers above 200 kV.
Critical for: parallel operation (must match), CT connections for metering/protection, vector group determination. Verified during factory testing.
QDTB tests and documents polarity for every transformer. Standard IEC subtractive polarity applied unless project specifies otherwise.
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Related Terms
Vector Group
Standardized designation of transformer winding connections and phase displacement between HV and LV.
IEC 60076
The IEC standard series defining requirements for power transformers, the global reference standard.
Current Transformer
An instrument transformer producing secondary current proportional to primary current, for measurement and protection.
Turns Ratio
The ratio of primary to secondary winding turns directly determining voltage transformation ratio.
More Terms Starting with “P”
Power Transformer
A large transformer (>10 MVA) used in transmission networks for stepping voltage between system levels.
Power Factor
The ratio of real power (kW) to apparent power (kVA) indicating how effectively electrical power is utilized.
Partial Discharge (PD)
Localized electrical discharges in small insulation regions not bridging electrodes, indicating defects or aging.
Prefabricated Substation
A factory-assembled complete substation integrating transformer, switchgear, and protection for rapid installation.
More in “Electrical Fundamentals”
Apparent Power (kVA)
The total power in an AC circuit combining real (active) and reactive power, measured in kilovolt-amperes (kVA).
Eddy Current
Circulating currents induced in conductive materials by changing magnetic fields, causing energy losses in transformers.
EMF (Electromotive Force)
The voltage generated by electromagnetic induction in a transformer winding, proportional to flux change and turns.
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