Abstract
Application of the frequency scan method for the determination of resonant conditions in a transmission power grid requires great effort since the harmonic power system simulation model needs to be developed. This process is rather complicated since the original model used for fundamental frequency load-flow analysis is built with respect to certain assumptions and, thus, intolerable errors are introduced when frequency-domain properties of the power system are investigated. To strike a balance between inputs needed for the development of such model (time, data amounts) and accuracy of the results, it is proposed to employ a method which makes it possible to represent dead-end, double-ended and tapped 110-220 kV substations as a single frequency-dependent equivalent so that the harmonic power system model is reduced. Such an element essentially is a series R-L or R-L-C shunt, parameters of which vary with frequency. The algorithm for the evaluation of its parameters is proposed and the test case for a real 110 kV grid area is discussed. Results of the method application show that it can be used in practice.
Highlights
Frequency scan (FS) is regarded as one of the most widely used methods for the investigation of harmonic voltage level variation trends, which consists in the estimation of the frequency response of power system positive sequence impedance as seen from the nodes of an electrical grid and subsequent identification of resonant frequencies [1,2,3,4]
It is due to the fact that 110-220 kV grid areas, which do not have a significant impact on a power system fundamental frequency load-flow, are usually modelled as equivalent power take-offs, while valid frequency response can only be obtained if such areas are fully incorporated into a power system model [1, 4]
110-220 kV substations can be represented as equivalent loads referred to HV side unless generation units are connected to MV or LV buses either directly or via dead-end grid fragments
Summary
Frequency scan (FS) is regarded as one of the most widely used methods for the investigation of harmonic voltage level variation trends, which consists in the estimation of the frequency response of power system positive (negative) sequence impedance as seen from the nodes of an electrical grid and subsequent identification of resonant frequencies [1,2,3,4]. It is due to the fact that 110-220 kV grid areas, which do not have a significant impact on a power system fundamental frequency load-flow, are usually modelled as equivalent power take-offs, while valid frequency response can only be obtained if such areas are fully incorporated into a power system model [1, 4] For this reason, considerable enhancement of the original fundamental frequency power system model is required in order to perform FS, resulting in drastic increase in its size defined by the number of nodes and branches. Since over-limit voltage harmonic distortion is a topical issue for Russian grid utilities [6], a method of power system simulation model reduction is proposed in this article The method makes it possible to represent dead-end, double-ended and tapped 110-220 kV substations as frequency-dependent equivalents (FDEs) when FS is performed at the 110 kV and above buses of the transmission grid substations
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