Data processing: generic control systems or specific application – Specific application – apparatus or process – Electrical power generation or distribution system
Reexamination Certificate
2001-08-15
2003-12-30
Picard, Leo (Department: 2125)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Electrical power generation or distribution system
Reexamination Certificate
active
06671586
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to controlling power demand in an electric power distribution system and, in particular, to a system and method for ordering power demand reductions at customer premises through an integrated wireless communication network.
2. Related Art
Electric utilities and other organizations are responsible for supplying an economic, reliable and safe source of electricity to customers. The electric utility or other responsible organization, through its energy delivery system, provides to its customers electricity at a suitable voltage and frequency. This electricity is provided on an instantaneous basis. That is, when the customer turns on the light switch to light a room, the electric utility or other responsible organization provides the electricity to the customer's light bulb the instant that the customer flips the light switch on.
One of the well known difficulties in providing electricity to customers is precisely matching the aggregate amount of electricity consumed by all of the customers on an instantaneous basis with the amount of electricity generated and/or purchased by the providing electric utility or other responsible organization. That is, at any instant in time, the electric utility or other responsible organization must provide exactly the amount of electricity used by all of the customers (plus the associated transmission system losses). The total amount of electricity used by all of the customers at any given instant in time is commonly referred to as demand. Demand typically is measured in units of watts, kilo-watts (kW), mega-watts (MW) or the like. For example, a conventional light bulb may have a demand of 60 watts. One thousand of these light bulbs has a demand of 6 kW. If all one thousand of these light bulbs are all turned on at the same instant in time, the electric utility or other responsible organization must instantly provide an additional 6 kW of electricity (in addition to any associated increases in transmission system losses) by increasing generation or purchases.
Failure by the electric utility or other responsible organization to exactly match the electric demand of their customers with the supply (generation and purchases), during every instant in time, may have very undesirable consequences should the mismatch become significant. When significant mismatches between demand and supply occur, distortions in the electric system frequency occurs. Although the electric system components are designed to operate when the electric frequency is slightly distorted, protective devices coupled to selected components in the electric system are designed to operate to automatically reduce or eliminate significant mismatches between demand and supply. Furthermore, other electricity characteristics may be undesirably distorted, such as voltage, such that other types of protective relays begin to operate.
For example, if the electric utility or other responsible organization loses a generator in an unplanned manner, the electric system demand will exceed supply (because the supply decreases when the generator shuts down). If the mismatch is sufficiently large, the electric frequency will decrease from its nominal value of 60 hertz (Hz). If the frequency drops to below 59.8 Hz, relays sense the frequency decay and operate to selectively disconnect predefined groups of customers from the energy delivery system. That is, power is shut off to some customers. Thus, demand is reduced, hopefully to the point where demand again approximately equals supply such that the frequency recovers back to its nominal 60 Hz value. Disconnecting customer loads to arrest frequency decay is known as load shedding.
Although the action of the frequency sensitive relays effectively arrests the undesirable frequency decay, thereby saving the energy delivery system from a more severe decay in frequency and other undesirable associated problems, those customers that were disconnected are impacted in an undesirable manner. That is, the customers who were selected to participate in the load shedding scheme had their power shut off. The affected customers are inconvenienced when they are disconnected from the energy delivery system, and the affected customers did not volunteer to be selected as participants in the load shedding scheme. Furthermore, the electric utility or other responsible organization loses the associated sales to the affected customers, thereby negatively impacting the electric utility's or other responsible organization's revenue stream.
Electric utilities and the other responsible organizations have implemented a variety of techniques to decrease the frequency of occurrence of these undesirable mismatches between energy demand and supply. One well known technique is to couple selected energy consuming appliances to radio frequency (RF) controlled receivers. Then, when a mismatch in demand and supply occurs, or when the electric utility or other responsible organization anticipates that a mismatch occurrence is eminent, the electric utility or other responsible organization orders the shut off of the selected energy consuming appliances by transmitting a shut-off signal via a RF signal to the RF receivers. Typically, a group of appliances are coordinated to respond to a single RF frequency or a single command delivered to the RF receivers. Such a group of aggregated appliances is commonly referred to as a load block. Thus, by issuing a single shut-off command, appliances in the entire load block can be shut off such that a meaningful decrease in demand occurs.
Participation in such a load block is typically voluntary. Often, customers are offered incentives to participate. For example, a customer can be given a decrease in rate and/or a rebate to voluntarily allow the utility or other responsible organization to couple an RF receiver to their appliance.
For example, a load block can be formed by coupling each one of the above described one thousand light bulbs to RF receivers such that a 6 kW demand reduction is realized (assuming that all of the light bulbs were on prior to sending the shut-off command). However, this is not a very effective technique for reducing demand. The 6 kW decrease in demand does not provide a meaningful demand reduction because the demand decrease is too small to be of practical help in matching demand of the entire system with supply. Also, the cost of the RF receivers is not likely justifiable for so little of a demand reduction.
On the other hand, forming a load block by connecting one hundred air conditioning units may provide a meaningful technique of reducing demand in a controlled manner. For example, if each air conditioning unit, when on, consumes approximately 10 kW, the electric utility or other responsible organization can reduce demand by as much as 1.0 MW. A 1.0 MW demand reduction is sufficiently large to make a meaningful reduction in system demand. Even if only a portion of the air conditioning units were on at the time the shut-off command was transmitted to the RF receivers, the demand reduction may still be sufficiently large to be meaningful.
Typically, electric utilities or other responsible organizations having such RF controlled energy demand reduction schemes will have a plurality of load blocks that can be selectively shut off depending upon the particular needs at hand. For example, a load block may be designed to provide an expected demand reduction of 5 MW. The system may have eight such blocks. At some point in time, the electric utility or other responsible organization may determine that a 5 MW demand reduction is needed for a two hour period. The eight load blocks would be sequentially shut off for fifteen minute intervals over the two hour period. Such an approach is desirable in that the negative impact to the customers will be minimized since the temperature of the customers' premises is not likely to become noticeably uncomfortable during the 15 minute period that their air conditioners are shut off.
Davis James
Petite Thomas D.
Kosowski Alexander
Picard Leo
StatSignal Systems, Inc.
Thomas Kayden Horstemeyer & Risley LLP
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