Load management

Load management, also known as demand-side management (DSM), is the process of balancing the supply of electricity on the network with the electrical load by adjusting or controlling the load rather than the power station output. This can be achieved by direct intervention of the utility in real time, by the use of frequency sensitive relays triggering the circuit breakers (ripple control), by time clocks, or by using special tariffs to influence consumer behavior. Load management allows utilities to reduce demand for electricity during peak usage times (peak shaving), which can, in turn, reduce costs by eliminating the need for peaking power plants. In addition, some peaking power plants can take more than an hour to bring on-line which makes load management even more critical should a plant go off-line unexpectedly for example. Load management can also help reduce harmful emissions, since peaking plants or backup generators are often dirtier and less efficient than base load power plants. New load-management technologies are constantly under development — both by private industry and public entities.

Modern utility load management began about 1938, using ripple control. By 1948 ripple control was a practical system in wide use.

The Czechs first used ripple control in the 1950s. Early transmitters were low power, compared to modern systems, only 50 kilovolt-amps. They were rotating generators that fed a 1050 Hz signal into transformers attached to power distribution networks. Early receivers were electromechanical relays. Later, in the 1970s, transmitters with high-power semiconductors were used. These are more reliable because they have no moving parts. Modern Czech systems send a digital "telegram". Each telegram takes about thirty seconds to send. It has pulses about one second long. There are several formats, used in different districts.

In 1972, Theodore George "Ted" Paraskevakos, while working for Boeing in Huntsville, Alabama, developed a sensor monitoring system which used digital transmission for security, fire, and medical alarm systems as well as meter-reading capabilities for all utilities. This technology was a spin-off of his patented automatic telephone line identification system, now known as caller ID. In, 1974, Paraskevakos was awarded a U.S. patent for this technology.

At the request of the Alabama Power Company, Paraskevakos developed a load-management system along with automatic meter-reading technology. In doing so, he utilized the ability of the system to monitor the speed of the watt power meter disc and, consequently, power consumption. This information, along with the time of day, gave the power company the ability to instruct individual meters to manage water heater and air conditioning consumption in order to prevent peaks in usage during the high consumption portions of the day. For this approach, Paraskevakos was awarded multiple patents.

Since electrical energy is a form of energy that cannot be effectively stored in bulk, it must be generated, distributed, and consumed immediately. When the load on a system approaches the maximum generating capacity, network operators must either find additional supplies of energy or find ways to curtail the load, hence load management. If they are unsuccessful, the system will become unstable and blackouts can occur.

Long-term load management planning may begin by building sophisticated models to describe the physical properties of the distribution network (i.e. topology, capacity, and other characteristics of the lines), as well as the load behavior. The analysis may include scenarios that account for weather forecasts, the predicted impact of proposed load-shed commands, estimated time-to-repair for off-line equipment, and other factors.

The utilization of load management can help a power plant achieve a higher capacity factor, a measure of average capacity utilization. Capacity factor is a measure of the output of a power plant compared to the maximum output it could produce. Capacity factor is often defined as the ratio of average load to capacity or the ratio of average load to peak load in a period of time. A higher load factor is advantageous because a power plant may be less efficient at low load factors, a high load factor means fixed costs are spread over more kWh of output (resulting in a lower price per unit of electricity), and a higher load factor means greater total output. If the power load factor is affected by non-availability of fuel, maintenance shut-down, unplanned breakdown, or reduced demand (as consumption pattern fluctuate throughout the day), the generation has to be adjusted, since grid energy storage is often prohibitively expensive.