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I am not an eletrical engineer and have a question about demand side management in smart grids. One application is peak shaving, which means that the maxium power is reduced. Does this decrease the stress on the power lines?

Basically I would like to write the following sentence in a scientific article: "Another application for flexible electrical loads is to reduce the peak load in a local grid in order to decrease the stress on the transformers and power lines"

Is that true or would you advice me not to state something like this

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    \$\begingroup\$ What do you mean by "flexible electrical loads?" Just the ability to turn the load down a bit? Less power generally would mean less stress on the power lines but I do not see why a facility would care about that when they normally run full throttle anyways. They probably care more about higher cost of electricity at peak hours but in that case wouldn't it be better to just shut down? I imagine just reducing the throttle a bit wouldn't do much. \$\endgroup\$ – DKNguyen Mar 17 at 19:19
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    \$\begingroup\$ If you aren't an electrical engineer, why would you write a scientific article about electrical loads and grid stress? That would be like me, an engineer, writing a scientific article about the colinearity of muon particles in a vacuum system (these are random cool sounding words, but either way I'm not qualified to write about that in any kind of peer reviewed publication). \$\endgroup\$ – Ron Beyer Mar 17 at 19:21
  • \$\begingroup\$ Hi Ron Beyer. I guess you have never heard about something like smart grids, demand side management and load flexibility. I am a computer scietist that designs algorithms to utilize flexibility of residential electric loads (like electric vehicles and heat pumps). There are many applications for this. One includes peak shaving aiming at minimizing the maxium load which definitely has advantages for the grid \$\endgroup\$ – PeterBe Mar 19 at 9:57
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Stress on transformers, transmission lines and other power generation, transmission and distribution equipment is considered in in determining the capacity of the systems. However stress is concerned mostly with the life of the equipment and the maintenance and renewal or capital spending budgets.

Peak shaving is concerned with the operating budget. Peak shaving is a method of avoiding the use of generation sources that can be quickly dispatched but have a higher operating cost. The overriding objective of peak shaving from the energy supplier's point of view is to minimize the use of equipment and fuels that have a high operating cost. From the consumer's point of view, the objective of peak shaving is to avoid "penalty" charges that are imposed by utilities to help recover the cost of using higher-cost equipment and fuels.

"Flexible loads" might be considered to be those loads that can simply be "turned down" rather than shut off. However it could also be considered to be the scheduling of of equipment use so that loads that do not need to be run all the time or at a particular time are scheduled not to operate simultaneously.

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  • \$\begingroup\$ Thanks Charles Cowie for your answer. Same response as to the post before: It is basically not only about costs. Imagine a residential area with high shares of electric vehicles and heat pumps. If all electric vehicles and heat pumps start charging simulatenously with high power, there might be a problem for the grid. This is why, it well understood in the scientific literature, the peaks have to be minimized through demand side management \$\endgroup\$ – PeterBe Mar 19 at 10:04
  • \$\begingroup\$ Of course excessive peaks can be a problem for the grid, but that is not really about stress on power lines. That was the original question wasn't it? It is about capacity in general. Ultimately, everything is about cost. Capacity that is far away is more expensive because to the cost of long-distance transmission lines. Cost that is close could be more expensive because the only close place is costly to the environment or reduces the value of residential property esthetically. Storage and retrieval of energy is more costly than simple generation and use.. \$\endgroup\$ – Charles Cowie Mar 19 at 10:33
  • \$\begingroup\$ Thanks Charles Cowie for your answer. I was told that excessice peaks increase the stress on transformers. Is that correct? If I understood your answer correctly, those excessive peaks are not harmful for the power lines themselves (and thus no problem). \$\endgroup\$ – PeterBe Mar 19 at 19:15
  • \$\begingroup\$ For reliability, distribution companies try to keep a safety margin between average customer demand and the maximum rating of distribution components. The life of all components is proportional to the average current that they carry, heat-up cool-down cycles, weather and perhaps other factors. The various types of component, overhead lines, underground lines, insulators, transformers, capacitors, switching devices, metering equipment etc. are each influenced differently by duty conditions. Transformers have the highest mass/current, so they are presumably less sensitive to overloads < 1 hr. \$\endgroup\$ – Charles Cowie Mar 19 at 19:43
  • \$\begingroup\$ I believe that variations in usage that can be managed by peak shaving are those that take place from one 15 minute interval to the next, up to day vs. night. Perhaps week-day vs. week-end could be included. The main concerns are the ability voltage regulation, grid stability and the avoidance of using high cost generators. Concerns about power peaks high enough to cause concerns for equipment failure would generally be addressed by upgrading the system rather than peak shaving. I believe peak shaving is more about current cost rather than adding a few years to decades of equipment life. \$\endgroup\$ – Charles Cowie Mar 19 at 20:07
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No, don't say "in order to decrease the stress on the transformers and power lines". Much better to say something like "to lower overall costs".

Most electrical grids have a variety of power sources which are switched on or turned up and down according to the load. Some power sources take weeks to turn on and off, some take minutes, such as gas, and some are variable, such as solar and wind. So typically you have a despatch order with the slow things always on and the fast-response thing -- gas -- turned up and down to match load.

I've always heard peak shaving's main purpose as saving you turning the gas on too much because it's expensive. (Normally calculated as cost of fuel, but increasingly also CO2 or tariffs.) You might also do it to improve overall reliability, but this is often considered to be simply a cheaper way to achieve a target reliability.

Anything like load-related wear-and-tear will be "just money", and factored into the peak shaving the same as anything else. From my understanding, almost nothing counts compared to the cost of fuel and capital expenditure on building and decommissioning.

My understanding is load affects cost mostly through different efficiencies at different loads, as opposed to wear, but there must certainly be portions of the grid which do wear out. There's a chapter on efficiencies and costs in the excellent Copper for Busbars – Guidance for Design and Installation, David Chapman and Prof. Toby Norris, The Copper Alliance Pub. 22, (2014 ed., 103 pp) Download page.

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  • \$\begingroup\$ Thanks jonathanjo for your answer. It is basically not only about costs. Imagine a residential area with high shares of electric vehicles and heat pumps. If all electric vehicles and heat pumps start charging simulatenously with high power, there might be a problem for the grid. This is why, it well understood in the scientific literature, the peaks have to be minimized through demand side management. \$\endgroup\$ – PeterBe Mar 19 at 10:02
  • \$\begingroup\$ @PeterBe there are lots of reasons for demand-side management, exactly as you say, and various kinds. What you describe (too much demand) is dealt with by load limiting or generation increase. Peak shaving as I have heard it used is about shifting peaks by a small amount of time, saving on the capacity purely for the peak, normally by not turning up gas. \$\endgroup\$ – jonathanjo Mar 19 at 12:31

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