Transformer Broadband Equivalent Circuit And Transient Analysis

The outage contingencies of fault line will bring about a load transfer in power system, if the non-fault line’s over load is getting worse and the relay protection puts in disordered action once and again as a result of the load transfer, it will lead to wide spread break out, Based on this situation, many scholars have began to study on system protection, they try to change the existing protection conception and criterion radically, and strength the coordination between relay protections and emergency control. In spite this, the existing relay protection’s reliable, correct and fast action still plays an important role in improving the network transmission capability and its’ stability. So far. most relay protections are based on the detection of power frequency components.Instrument transformers are mainly used for measurement and transformation in power system. They transfer high-voltage and high-current from primary side into low breakdown voltage and low operating current on secondary side, which was used for Measuring instruments and Relay protection devices. What the relay protection basically demands is that the transformers could factually reflect high transient signal. The previous studies suggested that the transient responses of current transformer could meet the requirements quite well. However, the capacitor voltage transformer’ transient response is not ideal, distance protections use both the voltage and current*variation characteristics to value the ratio between voltage and current, the result could reflect the fault location. The different transient characteristic between CVT and CT will result in the phenomenon of transient overreach, which will be detrimental to accurate fault location.We should model wide frequency equivalent circuit of transformer before we analyze its characteristic when they transfer the voltage and current. Transformer has a quite complex structure with coupling capacitance, mutual inductance, and so on, there are lots of influencing factors for its characteristic, it’s much more difficult to model its circuit according to its physical structure. There is another feasible way to model its wide frequency equivalent circuit, which measures the wide-band transfer characteristics and scattering parameters of transformers, then has a rational approximation and network synthesis on the measurement, the wide-band characteristics for the ports of the transformers are acquired.This thesis models the wide frequency equivalent circuit using the both ways mentioned above, then, we could calculate the outputs of transformers combining numerical method for the analysis of electromagnetic transient and signal processing technology, based on all these, we could have a systematical analysis on the wide-band transfer characteristics of instrument transformers.