Harmonic impedance measurement using a thyristor-controlled short circuit

An effective and easy-to-implement method for measuring power system harmonic impedances is presented. The method uses a thyristor to create a controlled short circuit at the measurement point. The short circuit produces a pulse current and a voltage distortion, which are then used to estimate the system impedance. The strength of the current pulse is controlled through the thyristor firing angle so that enough signal energy is available for precise measurement and yet the disturbance is small enough not to cause power quality problems. The method can be implemented into a portable impedance measurement device. Computer simulations and lab tests were used to verify the effectiveness of the method. A criterion for determining the frequency range of reliable measurements using the proposed device is also established.