Method and circuit for measuring a current
AssigneeSiemens Aktiengesellschaft
InventorsUlrich Baumgaertl, Wolfgang Röhl, Holger Hochgraef
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Abstract
A method and circuit arrangement for measuring a current are described, which can be used in electrical engineering to precisely trigger electronic tripping devices in circuit breakers. The current is measured according to magnitude and phase in such a way that only the fundamental wave of the current between precisely determined current zero crossings is sampled at a low sampling rate, and the root mean square is calculated on the basis of the measured phase angle and amplitude. The exact phase angle is measured using a conventional PLL circuit with a downstream zero switch.
Claims8
A method for measuring a current to generate a tripping signal for a circuit breaker, comprising:
- sampling only a fundamental wave of the current between current zero crossings;
- converting the samples to digital values;
- determining a magnitude and phase angle as a function of the digital values;
- determining a root mean square as a function of the determined magnitude and phase angle;
- and
- generating the tripping signal for the circuit breaker as a function of the root mean square.
A circuit for measuring a current to generate a current to generate a tripping signal for a circuit breaker, comprising:
- an electronic tripping device including a switching contact arranged in a main conducting path, a latching mechanism, a tripping magnet, a Rogowski coil, a normalized amplifier and a microprocessor with an A/D converter;
- and
- a PLL circuit including a downstream zero switch coupled in parallel to an input of the A/D converter and to a port input of the microprocessor, wherein the microprocessor samples a fundamental wave of a current and forms precise value pairs each composed of a magnitude and a phase, the microprocessor determining a root mean square as a function of the value pairs and generating a tripping signal as a function of the root mean square.
A circuit for measuring a current to generate a current to generate a tripping signal for a circuit breaker, comprising:
- an electronic tripping device including a switching contact arranged in a main conducting path, a latching mechanism, a tripping magnet, a Rogowski coil, a normalized amplifier and a microprocessor with an A/D converter;
- and
- a PLL circuit including a downstream zero switch coupled in parallel to an input of the A/D converter and to a port input of the microprocessor;
- wherein the PLL circuit includes a controlled oscillator that is frequency-limited so that the controlled oscillator responds only to a fundamental wave of the current, and
- wherein the zero switch emits a signal for an edge change precisely at a zero crossing of the fundamental wave.
A method for measuring a current to generate a tripping signal for a circuit breaker, comprising:
- emitting a signal for an edge change precisely at a zero crossing of a fundamental wave;
- sampling only the fundamental wave of the current between current zero crossings of the fundamental wave as a function of the emitted signal;
- converting the samples to digital values;
- determining a magnitude and phase angle as a function of the digital values;
- determining a root mean square as a function of the determined magnitude and phase angle;
- and
- generating the tripping signal for the circuit breaker as a function of the root mean square.
Dependencies are inferred from the claim text.