Dynamic Equivalence. Lu In The Grid After Power Balance Analysis

Now the power system is rapidly developing towards the direction of high-capacity, long-distance and extra-high voltage. However the increasingly expanding scale of power system makes it more difficult to carry out transient stability analysis and power calculation. The calculation time, accuracy and complexity are faced with great challenges.When taking on calculation of transient stability of modern power system, the amount of memory is large and costs long time. We need all information of system, thus the power system is simplified by dynamic equivalent to reduce the scale of power system.Generally speaking, analyzing large scale power system, we are usually interested in some part which called studied system and not interested in some part which called outside system. An idea of simplifying outside system was bring up. We call above process dynamic equivalence. The essence of dynamic equivalence is using a simplified model to replace original system's influence on studied system.This paper adopts dynamic equivalence based-on identification of coherent generator. Equivalent system's model is real power system's model. So we can use these models in transient stability directly. This equivalent method is adapted to non-linear and big disturb. It's conveniently to control the precision of dynamic equivalence.Transient stability calculation is composed of four parts: identification of coherent generator, dynamic equivalence, power flow calculation, transient stability calculation.In this paper, the dynamic equivalent can be divided into two major parts: e-coherent identification of generators and the equivalent simplification of power system. The equivalent simplification of network has two steps: simplifying the buses of coherent generators and combining the load buses of external system. The dynamic equivalent method discussed in this paper avoids complicated calculation, thus time is saved to a large extent. This method is extremely efficient when multi-faults are analyzed at the same time.This paper uses the 639-bus Shandong power system as an example to verify the dynamic equivalent method. The scale of Shandong 639-bus power system is largely reduced after dynamic equivalence. This paper focuses on the zibo-system, after the power flow caculation convergence. It can be easily known through this example that desired results have been achieved without any distortion occurring to the simplified system.