ELECTRICAL DEMAND LIMITING SYSTEM

• US 3,862,430 A
• Filed: 07/31/1973
• Issued: 01/21/1975
• Est. Priority Date: 07/31/1973
• Status: Expired due to Term

• Current Assignee: James Herbert Fuller Lenhart, Purushottam Manilal Patel
• Original Assignee: James Herbert Fuller Lenhart, Purushottam Manilal Patel
• Inventors: Lenhart, James Herbert Fuller, Patel, Purushottam Manilal
• Primary Examiner(s): Schaefer, Robert K.
• Assistant Examiner(s): Ginsburg, M.
• Application Number:
  US05/384,169
• Time in Patent Office: 539 Days
• Field of Search: 307/35,125,34,38,39,62
• US Class Current: 307/35
• CPC Class Codes: H02J 2310/54 according to a pre-established time schedule
• 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

An electrical demand limiting system is disclosed in which a DC signal proportional to the total power demand averaged for a given interval of time is compared with a plurality of preselected demand limits. Each demand limit is a percentage of the total permissible power demand. A plurality of loads are sequentially switched from each of the demand set points over a predetermined time period.

Claims

1. An electrical demand limiting system for limiting the load demand of multiple loads during a demand period, the demand period being a period of time over which power demand is measured for billing purposes, comprising:

means, responsive to the power consumption of the loads for producing an output signal proportional to an integrated power demand of the loads during the demand period;

means, responsive to said output signal, for disconecting said loads from the power system when the power demand exceeds predetermined adjustable percentages of the permissible demand limit, said means including means for presetting a plurality of predetermined adjustable percentage set points; and

means coupling the loads to the predetermined adjustable percentage set points for sequentially switching, over a predetermined time period, each of the loads to each of the predetermined adjustable percentage set points.

2. An electrical demand limiting system as in claim 1 wherein the meaNs for producing an output signal proportional to the integrated electrical power demand comprises means for continuously measuring the instantaneous power demand over a predetermined time period;

and means, responsive to the measured power demand, for producing an output signal proportional to the integrated power demand over the predetermined time period.

3. An electrical demand limiting system as in claim 2 wherein the means for disconnecting said loads comprises a plurality of adjustable comparison means responsive to the output signal proportional to the integrated power demand, each of said comparison means comparing integrated power demand with the adjustable percentage of the power demand limit, each comparison means producing an output signal when the integrated power demand exceeds its associated adjustable percentage of the power demand;

and means responsive to the output of each comparison means for disconnecting at least one load when the integrated power demand exceeds its associated predetermined adjustable set point.

4. An electrical demand limiting system as in claim 3 wherein the output signal proportional to the integrated power demand comprises an electrical signal whose magnitude is proportional to the integrated power demand, the signal being compared in each of the comparison means to individual adjustable signals each proportional to a percentage of the integrated power demand and each of the loads being connected to the output of one of the comparison means through a disconnect means responsive to the output of its associated comparison means to disconnect a load when the integrated power demand exceeds its adjustable signal.

5. An electrical demand limiting system as in claim 4 wherein the means for sequentially switching the loads comprises means for periodically producing an output signal after a predetermined time interval;

and switching means, responsive to the periodic signal, for sequentially switching each multiple load to a different comparison means in response to the periodic signal.

6. An electrical demand limiting system as in claim 5 wherein said switching means comprises:

means providing a plurality of sequential outputs such that only one is present at one time in response to said periodic signal; and

means having as inputs the outputs of said comparison means and responsive to said plurality of sequential outputs to connect its inputs to different outputs in response to each of said sequential outputs.

7. An electrical demand limiting system as in claim 6 wherein said means providing a plurality of sequential outpus comprises a stepper switch.

8. The invention according to claim 6 wherein said means for providing a plurality of outputs comprises a stepper switch and said means having as inputs the output of said comparison means comprise a plurality of semi-conductor switches.

9. An electrical demand limiting system for limiting the load demand of multiple loads during a demand period comprising:

a power transducer, responsive to the power consumption of the loads, for producing a continuous signal proportional to the instantaneous power demand of the loads;

means, responsive to the continuous signal, to periodically produce a pulse output signal having a time duration proportional to an integrated power demand of the loads during a predetermined time interval;

means, responsive to the pulse output signal, for periodically producing a voltage signal proportional to the integrated power demand of the loads during the predetermined time interval;

means producing a plurality of output signals, each of said signals proportional to a predetermined variable percentage of the permissible power demand;

a plurality of means for comparing the voltage signal proportional to the integrated power demand with the plurality of signals proportional to a predetermined variable percentage of the permissible power demand, each of said comparing means producing an output sIgnal when the integrated power demand exceeds its associated predetermined percentage of the power demand;

a plurality of means, responsive to the output signals of said comparing means, for disconnecting the loads; and

means, coupling the comparing means to the disconnecting means, for sequentially connecting over a predetermined time period the outputs of each of the comparing means to the input of each of the disconnecting means so that each load over a given time period is progressively connected to each of the comparing means.

10. An electrical demand limiting system as in claim 9 wherein the means to produce a pulse output signal comprises:

an integrator for integrating the signal proportional to the instantaneous power demand over a predetermined time period;

means for generating periodic timing signals;

means, responsive to the timing signals, for periodically sampling and holding the integral of the instantaneous power demand; and

means, having as an input the output of the sample and hold means and responsive to the timing signals, for generating the pulse output signal, the duration of which is proportional to the magnitude of the integrated power demand occurring from the beginning of the predetermined time period up to the time of the sampling.

11. An electrical demand limiting system as in claim 9 wherein the means for producing a voltage signal proportional to the integrated power demand, comprises:

an integration means, responsive to the pulse output signal, having its operating period controlled by the duration of said pulse output signal;

a sample and hold means coupled to the output of the integration means, for sampling and holding the output of the integration means, said sample and hold means providing an output proportional to the output of said integration means at the time of sampling; and

means, responsive to the termination of said pulse output signal for causing said sample and hold means to sample said intergration means to produce the voltage signal proportional to the integrated power demand of the loads during the predetermined time interval.

12. An electrical demand limiting system for limiting the load demand of multiple loads during a demand period comprising:

means, responsive to the power consumption of the loads, for producing an output signal proportional to the averaged electrical power demand of the loads from the beginning of the demand period;

means providing predetermined adjustable percentage set points of the demand;

means, responsive to the averaged electrical power demand signal, for disconnecting loads when the power demand exceeds the predetermined adjustable percentage set points; and

means, coupling the loads to the predetermined adjustable percentage set points, for sequentially switching, over a predetermined time period, each of the loads to each of the predetermined adjustable percentage set points.

13. An electrical demand limiting system as in claim 12 and furthr including means for reconnecting said loads when the averaged electrical power demand drops below said predetermined adjustable percentage set points.

14. An electrical demand limiting system as in claim 12 wherein the means for producing an output signal proportional to the averaged electrical power demand comprises:

means for measuring the integral of the instantaneous power demand from the beginning of the demand period and for providing an output proportional thereto;

means for developing a signal proportional to the time from the beginning of the demand period; and

means for dividing said output proportional to the integral of the instantaneous power demand by said signal proportional to the time to obtain an output signal proportional to said averaged power demand.

15. An electrical demand limiting system as in claim 14 wherein said means for providing an output proportional to said integral of the instantaneous power demand comprises:

a power Transducer for producing a continuous DC signal proportional to the instantaneous power demand of the loads; and

a first integrator having said DC signal as an input and providing an output which is the integral of the instantaneous power demand; and

wherein said means for developing a signal proportional to time comprises a second integrator having a constant DC voltage as its input and providing an output voltage.

16. An electrical demand limiting system as in claim 15 wherein said means to divide comprises:

a third integrator;

means to convert the output of said second integrator to a timed pulse of a length inversely proportional to the output voltage of said second integrator; and

means responsive to said timed pulse to couple the output of said first integrator to the input of said third integrator for the duration of said pulse.

17. An electrical demand limiting system as in claim 16 wherein said means to convert said second integrator output comprises:

a voltage controlled oscillator having the output of said second integrator as an input and providing as an output a frequency proportional to its input voltage;

a digital counter of predetermined modulus having the output of said oscillator as a count input;

a bistable device having complementary Q and Q outputs and having at least a set and a reset input with its Q output coupled to hold said counter reset when said bistable device is reset and the reset input of the device coupled to the output of said counter with the Q output of said device providing said timed pulse; and

means coupled to the set input of said bistable device to initiate a division by setting said device.

18. An electrical demand limiting system as in claim 17 wherein said first integrator, has its output coupled through a first sample and hold circuit adapted to sample and hold the output of said first integrator in response to the setting of said bistable device and wherein a second sample and hold circuit is coupled to the output of said third integrator, said second sample and hold circuit adapted to sample and hold the output present at said third integrator at the end of said timed pulse and further including means to reset said third integrator at the end of said timed pulse.

19. Apparatus for providing a pulse duration siganl proportional to an integrated power demand of a load comprising:

a. means responsive to the power consumption of the load for continuously measuring the power demand over a time period;

b. means responsive to the measured power demand for producing an output signal the magnitude of which is proportional to integrated power demand over the time period; and

c. means converting said output signal to a pulse output signal having a time duration proportional to the integrated power demand over the time period.

20. The invention according to claim 19 in combination with means to transmit said pulse output signal to a remote location.

21. The invention according to claim 20 in combination with means for receiving said pulse output signal and converting said signal to a voltage proportional to said integrated power demand.

22. The invention according to claim 21 wherein said means for receiving said pulse output signal and converting said signal to a voltage proportional to said integrated power demand is comprised of:

an integration means, responsive to the pulse output signal, having its operating period controlled by the duration of said pulse output signal;

a sample and hold means coupled to the output of the integration means, for sampling and holding the output of the integration means, said sample and hold means providing an output proportional to the output of said integration means at the time of sampling; and

means, responsive to the termination of said pulse output signal for causing said sample and hold means to sample said integrating means to produce the voltage signal proportional to the integrated poweR demand of the loads during the predetermined time interval.

23. The invention according to claim 19 wherein the means for producing an output signal the magnitdue of which is proportional to the integrated power demand over the time period and converting said output signal to a pulse signal comprises:

an integrator for integrating the measured power demand, the integrator being controlled to integrate the measured power demand during a predetermined time period;

means, for generating periodic timing signals;

means, responsive to the timing signals, for periodically sampling and holding the integral of the measured power demand; and

means, having as an input the output of the sample and hold means and responsive to the timing signals, for generating a pulse signal, the duration of which is proportional to the magnitude of the integrated power demand occurring from the beginning of the predetermined time period up to the time of the sampling.

24. Means for developing an output signal which is proportional to the average electrical power demand of a load comprising:

a. a power transducer responsive to power consumption of the load for producing a continuous signal proportional to the instantaneous power demand of the load;

b. means for computing the integral of the instantaneous power demand from the beginning of a demand period and providing an output signal proportional thereto;

c. means developing a signal proportional to the time from the beginning of the demand period; and

d. means dividing said signal proportional to the integral of the instantaneous power demand by said signal proportional to the time to obtain an output signal proportional to said average power demand.

25. The invention according to claim 24 and further including means for converting said signal proportional to the average power demand to a pulse duration signal.

26. The invention according to claim 25 in combination with means to transmit said pulse duration signal to a remote location.

27. The invention according to claim 25 further comprising:

means providing predetermined adjustable set points;

a plurality of loads;

means, responsive to said pulse duration signal, for disconnecting a load when the power demand exceeds said predetermined adjustable set points, said set points representing predetermined adjustable percentages of the demand.

28. The invention according to claim 27 and further including means for sequentially switching over a predetermined time period each of the loads to each of the predetermined adjustable set points.

29. The invention according to claim 23 in combination with means to receive said pulse duration signal and convert said signal to a voltage.