Distributed frequency relay

• US 6,314,378 B1
• Filed: 10/01/1998
• Issued: 11/06/2001
• Est. Priority Date: 04/01/1996
• Status: Expired due to Term

• Current Assignee: Aclara Technologies LLC (Hubbell, Inc.)
• Original Assignee: CLC Global LLC
• Inventors: Hodge, James Graham, Sutton, Roger Anthony
• Primary Examiner(s): ASSOUAD, PATRICK J
• Application Number:
  US09/164,804
• Time in Patent Office: 1,132 Days
• Field of Search: 307/73, 307/129, 702/57, 702/58, 702/60, 324/76.39, 361/62, 700/286, 700/292, 700/293, 700/294, 700/295, 700/296
• US Class Current: 702/57
• CPC Class Codes: H02J 2310/60 Limiting power consumption in the network or in one section of the network, e.g. load shedding or peak shaving
• CPC Class Codes: H02J 3/144 Demand-response operation of the power transmission or distribution network
• CPC Class Codes: Y02B 70/3225 Demand response systems, e.g. load shedding, peak shaving
• CPC Class Codes: Y04S 20/222 Demand response systems, e.g. load shedding, peak shaving

Abstract

A method of increasing the system stability of an electricity supply network including the steps of locating programmable frequency sensitive relays at load shedding points within the network. Each relay controls one or more loads and contains programmable disconnect and reconnect conditions. One or more of the loads are disconnected from the network upon a relay detecting the programmable disconnect conditions. Each relay reconnects the load to the network when it detects the programmable reconnect conditions. Each relay includes a device for detecting the network frequency, a micro-processor including memory and software and a switching mechanism to disconnect and reconnect one or more of the loads. Each relay is programmed from a centralized network stability manager which can designate programmable conditions for each relay. The communications between each relay and the stability manager can be via broadcast or sequential point-to-point communications.

Claims

1. A method of increasing the system stability of an electricity supply network, said method including locating programmable frequency sensitive relays at load shedding points within said network, characterized in that each of said relays controls one or more loads connected to said network and contains programmable disconnect and reconnect conditions such that one or more said loads are disconnected from said network upon said relay detecting said programmable disconnect conditions on said network, and such that one or more said loads are reconnected to said network upon said relay detecting said programmable reconnect conditions on said network;

programming each said relay by a centralized network stability manager with respective programmable conditions transmitted by a broadcast or sequential point to point communications link,

wherein said programmable disconnect conditions include a low frequency disconnect level and a rate of decrease in frequency disconnect level, and said programmable reconnect conditions include a high frequency reconnect level and a rate of increase in frequency reconnect level.

2. A method as claimed in claim 1, wherein each said relay contains said programmable conditions for more than one load or group of loads controlled by said relay.

3. A method as claimed in claim 1, wherein each said relay implements a delay after detecting said disconnect conditions or a minimum duration of said conditions before disconnecting said loads.

4. A method as claimed in claim 1, wherein each said relay implements a delay after detecting said reconnect conditions or a minimum duration of said conditions before reconnecting said loads.

5. A method as claimed in claim 1 characterized in that said load shedding points are selected from the following:

substations;

factories;

office buildings;

households;

individual appliances;

plant;

a combination of any one of the preceding load shedding points.

6. A method as claimed in claim 1, wherein said load shedding points are selected from the following:

substations;

factories;

office buildings;

households;

individual appliances;

plant;

a combination of any one of the preceeding load shedding points.

7. A programmable frequency sensitive relay for location in an electricity supply network, said relay including:

means for detecting a network frequency and a rate of change of network frequency;

micro-processor means including memory means and software;

means for disconnecting and reconnecting one or more loads to said network;

characterized in that said micro-processor means stores and compares programmable disconnect and reconnect conditions with said detected network frequency and rate of change of network frequency such that one or more said loads are disconnected from said network upon said micro-processor means detecting said programmable disconnect conditions and such that one or more said loads are reconnected to said network upon said micro-processor means detecting said programmable reconnect conditions,

wherein said programmable disconnect conditions include a low frequency disconnect level and a rate of decrease in frequency disconnect level; and

said programmable reconnect conditions include a high frequency reconnect level and a rate of increase in frequency reconnect level.

8. A programmable frequency sensitive relay as claimed in claim 7, wherein said relay is reprogrammed by a centralised network stability manager.

9. A programmable sensitive relay as claimed in claim 7, wherein said frequency detection means includes a signal squarer.

10. A programmable frequency sensitive relay as claimed in claim 7 wherein said frequency detection means includes a software algorithm run by said micro-processor means which implements phase to frequency clock generation, phase comparison and low pass filtering functions.

11. A programmable frequency sensitive relay as claimed in claim 7, wherein said frequency detection means includes a software algorithm run by said micro-processor means which implements a first digital fourier transform algorithm with an output proportional to said network frequency.

12. A programmable frequency sensitive relay as claimed in claim 11, wherein said software algorithm further implements a second digital fourier transform algorithm operating at a different sampling rate from said first digital fourier transform algorithm, the ratio of the first and second digital fourier transform outputs being proportional to said network frequency.

13. A programmable frequency sensitive relay as claimed in claim 7 wherein the frequency detection means further includes a network frequency band pass filter.

14. A programmable frequency sensitive relay as claimed in claim 12 wherein the frequency detection means further includes a network frequency band pass filter.