Abstract: An automatic voltage regulator senses and controls the terminal voltage of a separately excited generator by controlling the field current applied to the field winding. In order to improve the response time of the circuit, the circuitry relies on the phasor relationships between the generator phase voltages to obviate the need for a rectification and filtering circuit, used in known AVR's. More specifically, each of the sinusoidal phase voltages is sampled and squared. The squared phase voltages are then summed together. The square root of the sum is used to provide a DC voltage signal, proportional to the terminal phase voltages V.sub.A, V.sub.B and V.sub.C. The DC voltage signal may then be compared with a reference signal to generate an error signal for use in regulating the generator terminal voltage by controlling the field current applied to the generator field winding.

Abstract: A synchronous machine is protected from closely spaced instances of excessive field current and an excessive volts/hertz ratio by a control system which models rotor and stator cooling to provide memory of recent periods of excessive heating. Maximum excitation limiting and volts/hertz ratio limiting modules in a microprocessor based automatic voltage regulator for the machine generate time delayed limit signals which override voltage feedback control when the respective parameters exceed threshold values. The limiters each increment a count when the associated threshold value is exceeded and generate the associated limit signal when a predetermined count is reached. The predetermined counts and the counting rates are selected such that the delay intervals are inversely proportional to the amount by which the threshold values are exceeded. The counts are decremented at a rate which models rotor and stator cooling when the respective parameters return below the threshold values.

Abstract: Apparatus for protecting a synchronous generator from under-excitation, includes a limiter implemented as part of a microprocessor based voltage regulator. The limiter selectively characterizes one or more limiting parameters, such as, system stability, machine capability and loss of field protection, as straight line segments in the real/reactive power plane to provide versatile, easily modified limits on excitation.

Abstract: Apparatus for determining when two periodic signals are within preselected limits of being in phase, includes square wave generators which convert the periodic signals to pulse trains, and an AND gate which combines the pulse trains to generate a rectangular wave signal having a logic one value when the two pulse trains overlap. A monostable one-shot multivibrator generates clock pulses in response to the leading edge of the rectangular wave signal. A flip-flop latches its output to the logic level of the rectangular wave signal on the trailing edge of the clock pulses. The clock pulses are of a duration representative of the selected phase angle limit, so that the output of the flip-flop is a phase angle acceptance window having a logic 1 value when the difference in phase between the periodic signals is within the selected limits.