Apparatus for detecting the presence of subsynchronous current components in an electrical generating or transmission system is disclosed. Input signals, representative respectively of line voltage and current, are conditioned and initially filtered to suppress high frequency noise. The input voltage signal is further limited and filtered to produce a constant amplitude, sinusoid reference. The input signals are then multiplied to yield the subsynchronous current signal components, if any, which undergo further filtration by a bandpass filter circuit. In addition, the detection apparatus is provided with circuit means for insuring protection against overvoltage and current surge conditions.

A two-way electronic kWh meter is disclosed for metering electrial power and energy consumption in a single phase or polyphase electrical system wherein power and energy may be imported to the system or exported from the system to another system. Pairs of analog signals representing current and voltage variables are derived. Each pair of analog signals is multiplied together to derive partial instantaneous power signals. These signals are summed and integrated to thereby provide a signal which is proportional to the total energy being imported or exported with respect to the electrical system. The output of the integrator is converted to a pulse train having each pulse proportional to the energy being imported or exported with respect to the system. The partial instantaneous power signals are also summed and averaged, with the polarity of the resulting signal being detected by a polarity detector. Depending upon the polarity of the signal being detected, an import or export record and display arrangement is connected to receive the pulse train to record the quantity of energy being imported or exported with respect to the system. An error correction system is also provided, wherein the phasing of the voltage variable signals and the phasing of the polarity detector is switched each time an output pulse is generated.

A calibration signal source for instruments to measure power and negative sequence current of a multi-phase electric power generator. Separate signals are provided to represent load current for each phase of the generator ultimately to be tested, and to represent the instantaneous differences in voltage between each phase and a reference phase. The calibration signals are derived from a single sine wave by providing a plurality of phase shift and voltage difference networks. Means are provided for amplitude control and elimination of harmonic distortion of the single sine wave, and therefore the output calibration signals share these characteristics.

The invention set forth herein is a three phase current sensor for providing a signal indicative to the three phase current and phase imbalance. The sensor comprises an electrically insulated current carrying conductor for each phase with one end of the conductor forming a line side connection and the other end of the conductor forming a load side connection. Each conductor is substantially U-shaped in configuration having leg portions and a bight portion. The conductors are positioned proximate one another and have their bight portions overlapping forming a cylinder-like cup. The cup has a bottom portion and a wall portion, the bottom portion formed by the bight portions of the conductors and the wall portion formed by the leg portions of the conductors. The leg portions of each conductor is substantially parallel to the longitudinal axis of the cup and radially positioned approximately 60 from the leg portions of the other conductors forming the cup. A signal generator is positioned within the interior of the cup and includes a pair of magnetic sensors. These sensors are positioned substantially coaxial to the longitudinal axis of the cup and substantially orthogonal with respect to one another. The sensors are used for sensing the rotating magnetic field produced by the current flow in the conductors of the cup. The output of the sensors of the signal generator when summed and squared have a dc term indicative of the sum of the squares of the current flowing in the conductors and an ac term indicative of the phase imbalance.

Disclosed is an apparatus and method for sensing power in a variable frequency machine. The power is sensed in each phase of the three phase machine by utilizing Hall generators for multiplying the phase current flowing through each phase by a current proportional to a phase voltage for each phase. The products are then summed to obtain a reading of the instantaneous power drawn by the three phase machine. The AC component is filtered out of the summed signal using a multi-stage filter which allows for maintaining of a fast response time with low ripple. In a preferred embodiment, a four stage filter utilizing R.C. filters is employed for this purpose.