Classifications

• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
  • H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
  • H02H3/46—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to frequency deviations
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
  • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
  • H02J3/12—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load
  • H02J3/14—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load by switching loads on to, or off from, network, e.g. progressively balanced loading
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
  • H02J2310/00—The network for supplying or distributing electric power characterised by its spatial reach or by the load
  • H02J2310/10—The network having a local or delimited stationary reach
  • H02J2310/12—The local stationary network supplying a household or a building
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
  • Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
  • Y02B70/30—Systems integrating technologies related to power network operation and communication or information technologies for improving the carbon footprint of the management of residential or tertiary loads, i.e. smart grids as climate change mitigation technology in the buildings sector, including also the last stages of power distribution and the control, monitoring or operating management systems at local level
  • Y02B70/3225—Demand response systems, e.g. load shedding, peak shaving
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y04—INFORMATION OR COMMUNICATION TECHNOLOGIES HAVING AN IMPACT ON OTHER TECHNOLOGY AREAS
  • Y04S—SYSTEMS INTEGRATING TECHNOLOGIES RELATED TO POWER NETWORK OPERATION, COMMUNICATION OR INFORMATION TECHNOLOGIES FOR IMPROVING THE ELECTRICAL POWER GENERATION, TRANSMISSION, DISTRIBUTION, MANAGEMENT OR USAGE, i.e. SMART GRIDS
  • Y04S20/00—Management or operation of end-user stationary applications or the last stages of power distribution; Controlling, monitoring or operating thereof
  • Y04S20/20—End-user application control systems
  • Y04S20/222—Demand response systems, e.g. load shedding, peak shaving

Definitions

• This invention relates to emergency load shedding means for AC elec ⁇ tricity power supply systems supplying power to a plurality of consumers.
• a command signal is transmitted from the power utility's control centre to a remotely operated switch at the consumers premises, turning off non-essential loads such as large ca ⁇ pacity hot water heaters, swimming pool filters etc.
• a major problem with such a method is the amount of time taken to transmit the command signal to the consumers premises which may take up to several minutes and require a relatively complex communication link.
• emergency conditions such as the loss of a generator
• the power begins to drop immediately, possibly leading to a collapse of the system before commands can be issued to turn off the non-essential loads.
• One known system devised to solve this problem utilizes the drop in supply frequency, hereinafter referred to as an under-frequency, which occurs when a generator becomes overloaded.
• an under-frequency the drop in supply frequency
• SUBSTITUTE SHEET ror signal which is used to control switching means to shed at least part of the load at the consumer's premises.
• a disadvantage of the last mentioned known system is that the lock range of the phase lock loop is determined by analogue components whose tolerances do not permit the accurate setting of the threshold frequency in a reproducable way. Moreover, the threshold frequency must be set during manufacture and cannot be easily altered.
• a still further object of the present invention is to provide a method and device for controlling the load of an AC electricity supply system which may employ a simple telephone line as a link to the utility command centre.
• a method of controlling the load of an alternating-current electricity supply system supplying power to a plurality of consumers comprising the steps of, for each of the plurality of consumers, measuring the fre ⁇ quency of the alternating-current supply, comparing the measured frequency to at least one threshold value stored in storage means which corresponds to a predetermined frequency below the normal frequency of the supplied voltage, and upon the measured frequency falling below said threshold value causing, after a predetermined delay, at least part of the consumers lead to be disconnected from the said supply system, said load being re ⁇ connected to the said supply system when the measured frequency has risen above said threshold value.
• an apparatus for use by a consumer using power for a load from an alternating- current electricity supply system supplying power to a plurality of consum ⁇ ers comprising frequency measuring means arranged to measure the frequency of the alternating-current supply and provide a frequency output signal in ⁇ dicative of the measured frequency, comparison means to which said fre ⁇ quency output signal is applied and which compares said frequency output signal to at least one threshold value, said threshold value corresponding to a first predetermined frequency which is below the normal frequency of said alternating current supply, wherein when said frequency output signal indicates that the measured frequency has fallen below said one threshold value, a switch control signal is provided by said comparison means after a first predetermined disconnect delay provided by disconnect delay means, said switch control signal being extended to a load switch means which is rendered non-conducting thereby to disconnect at least part of said consum ⁇ er's load from the said supply means, said load switch means being rendered conducting upon said measured frequency rising above said threshold value, thereby re-connecting said at least part of said
• the present invention ensures, that if an under-frequency condition occurs, electrical loads are shed before load-shedding commands could be issued over conventional load-control systems.
• Load-shedding is achieved with the present invention on a priority basis, by dropping first non- essential loads, and then more important loads for successively more severe failures, reducing network load before indiscriminate (suburb-wide) blackouts occur.
• a load 1 is connected to an AC mains 2 via a load switch 3. Across mains 2 is coupled a zero-crossing detector 4 whose output is coupled to an input of a counter means 5 associated with a crys ⁇ tal oscillator 6. Outputs of counter means 5 are respectively connected to inputs of comparator means 7 and 8 each of which is associated with respec ⁇ tive limit register means 9 and 10. Respective outputs of comparator means 7 and 8 are connected to inputs a and b of processor means (CPU) 11.
• CPU processor means
• a memory 12 associated with processor 11 includes four delay registers 13, 14, 15 and 16 and two memory registers 17 and 18 respectively associ ⁇ ated with delay registers 13 and 14.
• processor 11 An output of processor 11 is coupled to load switch 3. A phone line
• SCADA System Control and Data Aquisition
• the load control arrangement of the present invention can be programmed to operate independently of com ⁇ mands for SCADA in which case interface 20 and phone line 19 would not be needed.
• the frequency of the power supply on mains 2 is monitored by zero crossing detector 4, which produces a pulse every time the power supply waveform passes through zero, producing nominally 100 or 120 pulses per second for 40Hz or 60Hz respectively.
• the zero-crossing detector is filtered in hardware (not shown) to reduce the incidence of
• a counter 5 is continually incremented by crystal oscillator 6 at a rate which will preferably count at least 1000 counts per AC cycle, giving a resolution of better than 0.01 ms. This provides a fine control over the order of shedding different types of load.
• Counter 5 is reset by a pulse from zero-crossing detector 4 twice for every AC cycle.
• the value of the output of counter 5 is continually compared in comparator means 7 and 8 to threshold values programmed into two limit registers 9 and 10 respectively associated therewith.
• a threshold value corresponding to a severe under- frequency is contained in limit register 10 and a threshold value corre ⁇ sponding to a less severe under-frequency is contained in limit register 9.
• an interrupt signal is provided at the output of the comparator means 7. This signal is extended to input a of the processor means 11 which prepares to operate load switch 3 and shed load 1.
• the processor means includes filter means in the form of software.
• Two delay registers 13 and 14 are provided in a memory 12 associated with the processor means.
• the delay register is decreased at regular intervals, for example, by 1 every 40 ms.
• the processor means waits until the count exceeds the preset maximum value stored in memory register 15 as ⁇ sociated with delay register 13. Typically, this maximum value is 1750 which causes a delay of about 25 seconds at 50 Hz. This method imposes no interrupt load on the processor means software until an under-frequency condition occurs. After 25 seconds, the processor means operates load switch 3 and sheds load 1.
• SUBSTITUTE SHEET Similarly, when the threshold value programmed in limit register 10 As.. exceeded, due to a severe under-frequency, an interrupt signal is provided at the output of comparator means 8. This signal is extended to input b of: the processor means which prepares to operate the load switch 3 and shed load 1. The processor means waits until the count in the delay register 14 exceeds the preset maximum value stored in memory register 18 associated with the delay register 14. Typically, the maximum value is 10 resulting in a delay of about 150 ms at 50 Hz. After 150 ms the processor means op ⁇ erates the load switch 3 and sheds load 1.
• Delay registers 15 and 16 provide a maximum and minimum delay time limit and processor 11 selects a delay within those limits. Typically the minimum delay is 5 min ⁇ utes and the maximum delay is 10 minutes. This allows the highest priority loads to be switched to the supply quickly, and the lowest priority loads remain shed for a longer period. This delay may be selected randomly to prevent all loads being restored simultaneously. The delay also allows sufficient time for the SCADA system to transmit overriding commands over telephone line 17 if required. The load may be restored or restoration in ⁇ hibited by these commands.
• the power utility's SCADA system coupled to phone line 17 is pro ⁇ grammed with the characteristics of all non-essential loads controlled by the load shedding arrangement of the present invention.
• the under- requency limit values are programmed into each limit register 9 and 10 and delay registers 13 and 14 for the type of load controlled by these regis ⁇ ters which allows gradual load shedding as the power is lost.
• the regis ⁇ ters may be programmed remotely via phone line 17, or via the supply line 2 or manually during manufacture, or later on site.
• BSTITUTE SHEET Processor means 11 may form part of an energy management terminal such as, for example, the one described in Australian Patent Application No. 65,908/86.
• limit registers may be included to provide further frequency/delay profiles for a single load, or provide respective under-frequency thresh ⁇ olds for a plurality of loads.
• the threshold values programmed in the limit registers may be :
• the less severe under-frequency condition might occur, say, during a cold snap when many consumers switch on electrical heating apparatus.
• the load increases gradually and the frequency of the power supply correspond ⁇ ingly falls. If it reaches 49.0 Hz and remains there for at least 25 sec ⁇ onds load shedding commences.

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• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Supply And Distribution Of Alternating Current (AREA)
• Remote Monitoring And Control Of Power-Distribution Networks (AREA)

Applications Claiming Priority (2)

Publications (2)

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Citations (1)

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• 1989
  • 1989-01-06 WO PCT/AU1989/000006 patent/WO1989008342A1/en not_active Application Discontinuation
  • 1989-01-06 KR KR1019890701945A patent/KR900701072A/ko not_active Application Discontinuation
  • 1989-01-06 EP EP19890901251 patent/EP0402362A4/en not_active Withdrawn
  • 1989-01-06 JP JP1501007A patent/JPH03503833A/ja active Pending
• 1990
  • 1990-08-22 DK DK201290A patent/DK201290D0/da not_active Application Discontinuation

Patent Citations (1)

Non-Patent Citations (1)

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