Monthly Archives: April 2015

Tutorial: Key Players in the Energy Markets

I will be making a conference to investors later this year and I will also be training some people internally at my employer. The topics will touch on the electricity industry structure and I am preparing some material for it.

The industry can be quite complex in some jurisdictions. I boiled the complexity down to just this:

New Picture

Traditional large-scale generator own and maintain coal, natural gas, nuclear, hydro, wind and solar plants connected to transmission lines. Those are large plants – typically hundreds of megawatts.

Transmitters own and maintain transmission lines – the large steel towers seen going from large generators to cities. Those typically run at 120,000 volts and more, up to over 1,000,000 volts in some cases.

Distributors own and maintain the local infrastructure of poles and conduits going to customer sites. Those typically run at 1,200 to 70,000 volts, usually stepped down to 600 volts. 480 volts, 240 volts or 120 volts for connection to customers.

Most customers are connected to distributors, although some large industrial facilities (such as aluminum smelters) are directly connected to transmission lines.

While customers are connected to distributors, they purchase electricity from an independent retailer or from the retail arm of a distributor.

With customer installing distributed generation on their premises, they sell back power to the market, often through aggregators.

Retailers buy electricity from generators in an energy market – like a stock exchange, but for electricity.

By definition, the energy produced at any instant must be equal to the energy taken by customers, accounting for a small percentage of losses in transmission and distribution. (We are starting to see large-scale storage operators, which may act as both consumer and generator, depending they are charging or releasing electricity in the network.) This critical balance is maintained by the system operator that direct generators to produce more ore less to match load; in some case, the system operator will also direct distributors to shed load (customers) if generation or transmission is insufficient to meet the demand.

The next post will deal with energy and money flows in the market.

Covered Conductors Vs. Single-Phase Reclosers

A utility client told me that they were trying out covered conductors on a feeder in a forested area. This was the first time that this large utility tried covered conductors. The objective is to reduce the impact of tree contacts and falling branches that blow fuses and therefore result in permanent outages for customers. In this context, the great length of feeders and the high system voltage (25 kV) make coordinating reclosers and fuses difficult.

Covered conductors have a thin insulation covering – not rated for the full phase voltage, but sufficient to reduce the risks of flashovers and fire when a tree branch falls between phases, when a tree makes momentary contact with a conductor, or when an animal jumps to it. Covered conductors also allow utilities to use tighter spacing between conductors.

While covered conductors help with tree contacts, they also have a number of operational disadvantages:

  • High impedance faults with a downed conductor are more likely, leading to public safety issues, especially since the conductor may not show arcing and may not look as if it is energized.
  • Covered conductors are more susceptible to burndowns caused by fault arcing. Covering prevents the arc from motoring with magnetic forces along the wire, concentrating heat damage. Repair time and cost increase significantly.
  • Covered wires have a larger diameter and are heavier, increasing loading, especially with freezing ice and high wind, which can likeliness of mechanical damages (including broken poles and cross arms), leading again to high repair time and costs.
  • Covered conductors have somewhat lower ampacity at high temperature (worsened by the black color that absorb more heat from the sun), with more limited short-circuit capability. High temperature also degrades the insulation. This results in more design and planning constraints that may increase construction costs.
  • Water can accumulate between insulation and wire at the low point between of a span, causing premature corrosion and weaken the conductor and can lead to failure.
  • Covered conductors must be installed differently than bare ones. For instance, using conducting insulator tie can lead to partial discharges and radio interference.
  • Finally, cost is an obvious issue – replacing conductors on existing lines is extremely expensive, possibly as much as $100k per km.

These issues got me thinking on how I could provide a better alternative. Replacing fuses with single-phase reclosers appears to be an interesting (if unlikely) alternative to covered conductors. Cutout-mounted single-phase reclosers can easily be installed in existing cutouts to protect lateral circuits. Those circuits are then protected against tree contacts without the disadvantage of covered conductors. Coordination with upstream mainline reclosers is eased by making the single-phase recloser faster than the mainline recloser. Cost is clearly lower than re-conductoring.

Full disclosure: I am employed by S&C, and S&C makes a cutout-mounted recloser.