A portable liquid power factor instrument

An instrument has been developed which provides a direct reading of the power factor of new and used insulating liquids with accuracy comparable to laboratory types. A unique bridge circuit is employed at fixed high voltage excitation at power line frequency which permits guarded cell measurements to be made, both in the instrument chamber itself or remotely at the end of a guarded shielded cable. The instrument is portable and double shielded to minimize electrostatic interference experienced in power distribution on-site measurements. Dielectric constants can also be determined. Problems involved in maintaining accuracy at high ambient relative humidities are also discussed.