![]() ![]() These days, sometimes the load is a generator, and the transmission line towards the generator is a load, and you can't ring up all those houses to control the generation. There was a known voltage drop across the substation. ![]() In the "good old days", you knew where your generators were, and you knew where your load was, and you could control the load by controlling the generators. The power Engineer's Lament What annoys electricity operators about solar cells is that it obsoletes all their network diagrams. A Single Line Diagram is like a dashboard for the substation. In a substation, it helps experienced operators to see at a glance: - how to set voltage ratios on transformers - Whether you need to turn on power factor correction, and how much - how to share power between different transmission lines, so they don't get overloaded - whether part of the substation is shut down for maintenance - if some part of the network is drawing unusually high power - when some fault has occurred: - where the fault is located - what has shut down because of the fault - whether some equipment is now overloaded because something else shut down - how to route power around the fault - etc etc. See: Ī single-line diagram is a useful overview of a substation or a whole network. It focusses on power generated and power consumed (which must always be equal), and ignores: - The fact that there are three phases in an AC system - Voltage and Current in each phase - An earth wire may or may not be present (star or delta, respectively) - Often a tower will carry two independent three-phase circuits (6 wires), to assist maintenance - Geography Instead, it focuses on: - the product of Volts and Amps when they are in-phase: VA (or Millions of Volts x Amps = MVA), which could be considered a measure of AC power - the product of Volts and Amps when they are at 90° Phase: VAR (or Millions of Volts x Amps Reactive = MVAR), which could be considered a measure of wasted AC power (it must be carried, causes load on the network, but it delivers no real energy) - The generators of this power - The consumers of this power - The boxes in-between that let you control this power (circuit breakers, power factor correction devices, etc). ![]() A single line diagram is a high-level overview of a three-phase electrical network. ![]()
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