Side Impedance Research Articles

AC/DC harmonic interactions in the presence of GIC for the Quebec-New England Phase II HVDC transmission

During the spring of 1991, several severe geomagnetic disturbances were recorded in North America, and particularly in Northern Quebec, where Hydro-Quebec's La Grande generation complex and transmission system are located. As a result of these disturbances, the Quebec-New England Phase II HVDC system was affected by transformer saturation and harmonic voltage distortion due to geomagnetic induced current (GIC). This paper presents an analysis of the phenomenon observed at Radisson, the northernmost terminal in the system. A central issue which is discussed in the paper is the reflection of the DC side impedance to the AC side for operating converters, and the effect of this reflection on the harmonic impedance as viewed from the AC side.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Overvoltage phenomena caused by disconnecting motor‐loads on power line with open‐phase

AbstractThis paper describes overvoltage caused by disconnecting a lot of motor‐loads on a power distribution line with power‐factor‐correcting capacitors during a transmission line open‐phase. The overvoltage phenomena are studied by a field test, a steady‐state analysis and a transient analysis. Experimental results show that the line‐to‐line voltage on a 6.6 kV distribution line with an open‐phase 22 kV transmission line amounts to 1.7 per unit. The overvoltages are caused by two types of resonance. One is the linear circuit resonance between the power‐factor‐correcting capacitors and the secondary side impedance of motors. The difference between positive components and negative ones of the impedance produces the resonance. The other is the nonlinear circuit resonance between the power‐factor‐correcting capacitors and the saturated reactances of a transformer.

Calculation of Uncharacteristic Harmonics Generated by Three-Phase Diode-Bridge Rectifier with DC Filter Capacitor.

Three-phase diode-bridge rectifiers are used to convert the AC input into DC voltage. A large capacitor is connected as a filter on the DC side, since in most applications, a low ripple in the DC output voltage is desirable. Unbalance in the supply conditions of a three-phase diode-bridge rectifier with a DC filter capacitor gives rise to uncharacteristic harmonics on both the AC and DC sides.This paper proposes a simplified method for calculating the uncharacteristic harmonic currents generated by the three-phase diode-bridge rectifier under unbalance, taking into account the effects of both the AC and DC side impedances. Analytical expressions for the harmonic currents are derived using the switching functions with overlap period the AC circuit theory. Therefore, the proposed method can be executed only with algebraic computation and its accuracy is quite high. The validity of the proposed method is demonstrated by comparison with the results of time simulation.

Harmonic analysis of a single‐phase rectifier with a DC filter capacitor

AbstractA single‐phase diode bridge rectifier with a filter capacitor on the dc side is often employed to convert ac input into a dc voltage. The input current of the rectifier contains harmonic currents which cause undesirable power line effects. Recently, a method using the time domain analysis has been proposed to calculate the harmonic currents of rectifier considering noninfinite capacitance, i.e., non‐zero dc side impedance. This method is very accurate, but it requires a long computing time and a complicated algorithm.This paper proposes a new method that makes it possible to easily calculate the harmonic currents taking into account the effects of the ac and dc side impedances of rectifier. The proposed method, which is based on the frequency domain method, can be executed only with the algebraic computation, and its accuracy is quite high. The validity of the proposed method is also demonstrated by comparison with the results of time simulation.

Calculation of harmonics and interharmonics in HVDC schemes with low DC side impedance

When HVDC schemes are used to join AC systems of different frequencies, frequencies other than the well known characteristic harmonics are produced in the AC systems, and these are often called interharmonics. This paper examines these interharmonics and shows that, for HVDC schemes with low DC side reactance, another set of interharmonics will exist only on the DC side. These are a function of the impedance of the convertor seen from the DC side. It is shown that this impedance is time varying and, by modulation theory, will produce DC side harmonic frequencies some of which may be at low frequency. It is also shown that the amplitudes of characteristic harmonics and interharmonics will be changed by this effect. The method based upon modulation theory is compared to the results of a time domain computer simulation. The results shown will also be applicable to variable frequency motor drives.

A Harmonic Analysis of Single-Phase Rectifier with a DC Filter Capacitor.

A single-phase diode bridge rectifier with a filter capacitor on the DC side is often employed to convert AC input into a DC voltage. The input current of the rectifier contains harmonic currents which cause undesirable power line effects. Recently, a method using the time domain analysis has been proposed to calculate the harmonic currents of rectifier considering noninfinite capacitance, i.e. non-zero DC side impedance. This method is very accurate, but it requires a long computing time and a complicated algorithm.This paper proposes a new method that makes it possible to easily calculate the harmonic currents taking into account the effects of the AC and DC side impedances of rectifier. The proposed method, which is based on the frequency domain method, can be executed only with the algebraic computation, and its accuracy is quite high. The validity of the proposed method is also demonstrated by comparison with the results of time simulation.

High frequency scattering from polygonal impedance cylinders and strips

An analysis is presented for the high-frequency diffraction by convex polygonal cylinders with arbitrary side impedances. The authors extend their solution for the multiply diffracted fields associated with a double wedge (see ibid., vol.36, no.5, p.664-678, 1988). The analysis thus utilizes the extended spectral ray method (ESRM) that is applicable to nonray optical regions. Diffraction coefficients yielding a uniform total field are given for up to and including all fourth-order mechanisms. An important aspect of this analysis is the rigorous and uniform incorporation of the surface-wave effects in the resulting diffraction coefficients. A general polygon computer code was written that includes up to a third-order mechanisms. Based on this code, backscatter and bistatic patterns are given for impedance cylinders with triangular and square cross sections. The results are found to be in remarkable agreement with corresponding moment method data. As a matter of completeness, uniform diffraction coefficients are presented for a strip (which is a special case of a cylinder) that can have unequal face impedances.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A Ladder Network Theorem

The theorem of this paper gives four-terminal representation of ladder networks satisfying a prescribed condition on the side impedances, in terms of the three parameters specifying the network connected as a transducer, the driving-point impedance between short-circuited transducer terminal pairs, and an impedance ratio involving the side impedances only. This mode of representation has a special advantage in applications to electric railway networks in that the transducer parameters which alone involve the ladder shunt impedances (under the stated conditions) may be calculated in a relatively simple fashion, and extensive networks reduced to manageable form. The theorem is stated and proved, and its applications are sketched in some detail.