Subsynchronous resonance is a condition that can exist on a power system where the network has natural frequencies that fall below the fundamental frequency of the generated voltages. Transient currents flowing in the ac network have two components; one component at the frequency of the driving voltages and another component at a frequency that depends entirely on the elements of the network. For a network with only series resistance and inductance, an isolated transient, such as switching a load, will consist of a fundamental component and a de component that decays with a time constant that depends on the LIR ratio of the equivalent impedance between source and load.
Since loads are frequently switched on and off, the transient currents usually appear as random noise, superimposed on the fundamental frequency currents. The addition of shunt capacitors to the network result in new natural frequencies of oscillation that are always greater than the fundamental frequency. In networks containing series capacitors, the currents will include oscillatory components with frequencies that depend on the relative magnitude of the transmission line Land C elements, but have frequencies that are below the system fundamental frequency.
Breaker Schemes in Substations — Types, Design, Advantages, Disadvantages, and Comparison Author: Engr. Aneel Kumar Figure 1: Infographic overview of breaker schemes commonly used in substations. Introduction The breaker scheme or busbar arrangement in a substation defines how incoming feeders, outgoing feeders, and power transformers are connected to the bus. The choice of scheme has a direct impact on system reliability, maintainability, safety, and cost . A simple bus scheme is economical but vulnerable to outages, while advanced schemes such as breaker-and-a-half or double-bus/double-breaker provide very high reliability but at much higher cost and design complexity. Engineers select breaker schemes considering fault tolerance, maintenance needs, space requirements, expansion possibilities, protection coordination, and capital investment . Below, we explain eac...
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