2

Considering a mostly meshed distribution network (with some radial spurs) connecting zone substations (loads) to grid exit points (GXPs or sources).

I am attempting to find the proportion of the network each loads utilises i.e. what proportion of the total power flow in a particular constituent part of the network does each load contribute?

I would also like to then do a similar analysis on embedded generation, for example, a small hydro or wind plant connected to one of the zone substations, how much of the total capacity in the constituent parts of the network would this generator utilise?

There are three main constituent parts that make up a network, these are sources (both embedded generation and GXP), zone substations (and their loads), and lines. There are also shared assets, for instance, ripple injection plants, backup lines (lines normally out of service), but these can be ignored.

Before embedded generation needed to be considered this problem was normally solved by a "superposition", where all but one substation/load was turned off and the power flow in each branch/part of the network was measured using a load flow program. This was repeated for every substation on the network (sharing the same GXP) and the load flow results for every branch were then aggregated together to give a total. The proportion asset utilisation was worked out by then dividing the load flow results for a particular zone substation (load) by the aggregated total for that particular constituent part of the network.

This method does however have a problem in that there is squared relationship between current and power losses, so for large loads the aggregated sum is less than the results recorded in the loadflow under normal operating conditions (it seems to work okay for the smaller loads). One of the problems with extending this "superposition" concept to multiple sources is that depending on the load which is turned on a small embedded source may or may not have enough capacity to fully supply the zone substation (load) in question.

Meshed network configurations

ocrdu
  • 8,705
  • 21
  • 30
  • 42
Mr. Anderson
  • 71
  • 4
  • I don't think I can help with this but you didn't really ask a question at the end of your post. What exactly do you want to know? – Transistor Jun 09 '16 at 23:19
  • I want to know a valid method for determining the proportion of the network each loads (and source) utilises. So basically how much power flow (as a proportion of the total power flow) in any given part of the network is due to a particular load or source. – Mr. Anderson Jun 09 '16 at 23:29
  • Transmission lines for power and substations use phase-shifting to correct for voltage peaks and sags during daily usage. How can we possibly help you with a network that is self-correcting (in a limited way) and fused? What is your question? –  Jun 09 '16 at 23:29
  • This is a steady state situation - no transient events. A embedded source is either generating at its rating or it's not generating at all. Substations are constant power loads and the GXP is the only swing source. The embedded generators would be fixed-value PV synchronous machines (P is specified as a parameter (kW), V is specified by the bus voltage). – Mr. Anderson Jun 10 '16 at 00:06
  • And why can you not use import / export power meters (using CTs and VTs) at each network node or branch to give you the information? By the way, add any missing information to the question so that anyone answering has all the information in one place. – Transistor Jun 10 '16 at 02:53
  • I can get those values simulated, but that doesn't help me find out what portion of that power is delivered/consumed by what source or generator. If you consider the ring network (bottom picture) with a embedded source on the second substation, how much of that power flows to the first substation, is absorbed by the load at the second substation, flows to the third substation? It depends on the impedance of the lines and transformers and what the other sources are doing. – Mr. Anderson Jun 10 '16 at 04:14

1 Answers1

1

So, I've found a method that seems like it will work - it's called Power Flow Tracing. Basically, it's an application of KCL that works on the idea that the proportion of power flowing into a node from a particular generator is equal to the proportion of power leaving the node on all other circuits/branches.

I've found two papers that help explain it:

  1. Broad overview: Power flow tracing in NZ
  2. Technical paper: Tracing the flow of electricity or here

I'd still be interested to hear of any more practical use cases of this method either in the context of a simulation type study or something more real world, or any software that already implements power flow tracing as part of its load flow.

Glorfindel
  • 1,245
  • 3
  • 15
  • 20
Mr. Anderson
  • 71
  • 4