Automated voltage and VAR control in power transmission and distribution networks

• US 5,422,561 A
• Filed: 11/23/1992
• Issued: 06/06/1995
• Est. Priority Date: 11/23/1992
• Status: Expired due to Fees

• Current Assignee: Southern California Edison Company (Edison International)
• Original Assignee: Southern California Edison Company (Edison International)
• Inventors: Williams, Bradley R., Krause, Richard C., Eastman, Dennis A., Pham, Bryan H.
• Primary Examiner(s): Stephan, Steven L.
• Assistant Examiner(s): BERHANE, ADOLF D
• Application Number:
  US07/980,385
• Time in Patent Office: 925 Days
• Field of Search: 323/205, 323/208, 323/209, 323/210, 323/211, 323/218, 307/31, 307/33, 364/492, 364/483, 364/571.01, 364/571.07, 364/153
• US Class Current: 323/209
• CPC Class Codes: H02J 3/1821 using shunt compensators H02J3/1807, H02J3/1878 take precedence
• CPC Class Codes: Y02E 40/30 Reactive power compensation

Abstract

Controlling a customer voltage and VAR flow in a power transmission and distribution system includes measuring first voltages in a power line directed to a first location related to customers. Both the customer voltage and the VAR flow for the network is determined in relation to the number of capacitors associated with the first location which are switched in or out of the network. The measured voltages are communicated to a voltage control. Voltage deviations of the measured first voltage are determined relative to a predetermined voltage range intended to be present at the first locations. Switching the capacitor means into or out of the network is determined by the voltage control in accordance with a voltage rise table. A VAR flow controller is responsive to the voltage at the first locations, the effect of the VAR generation by the capacitors and the change of VAR generation by the capacitor. A decrease in voltage at the customers saves energy use. A decrease in the VAR generated upstream of the customer results in greater efficiency of energy generation.

Claims

1. A method for controlling voltage in a power distribution network including power lines for distributing power at a lower voltage and at a higher voltage, power being distributed at the lower voltage to multiple lower-voltage locations, the network including, at the higher voltage, capacitor means and switch means for selectively switching the capacitor means into or out of the network, the method comprising the steps of:

(a) measuring the voltage at one or more lower-voltage location,

(b) ascertaining the deviation, if any, of the measured voltage from a predetermined voltage range intended to be present at the lower-voltage location,

(c) determining whether switching the capacitor means into or out of the network changes the voltage deviation to bring the voltage at the measured lower-voltage location within the predetermined voltage range, and

(d) selectively transmitting a signal to the switch means for switching the capacitor means into or out of operation in the network to effect a change in the voltage at the measured lower-voltage location.

2. A method as claimed in claim 1 wherein the step of selectively transmitting a signal comprises transmitting the signal from a voltage controller, wherein the voltage controller is located remote from the lower-voltage locations.

3. The method of claim 1 wherein controlling the voltage at the measured lower-voltage location in step (d) results in reducing energy consumption at said lower-voltage location.

4. A method as claimed in claim 1 wherein the step of measuring comprises measuring at multiple lower-voltage locations and step (c) comprises determining the effect of switching the capacitor means on the voltage at the multiple lower-voltage locations.

5. A method as claimed in claim 4 wherein the step of selectively transmitting a signal comprises transmitting a signal to change the voltage at one or more lower-voltage locations while maintaining the voltage in the predetermined voltage range at one or more other lower-voltage locations.

6. A method as claimed in claim 1, 4, or 5 wherein the network further comprises transformer means at the higher voltage, the transformer means having a primary side and a secondary side, and wherein the capacitor means comprises multiple capacitor means located on the primary side of the transformer means, and wherein the step of measuring comprises measuring the voltage on the secondary side of the transformer means.

7. A method as claimed in claim 1, 4 or 5 wherein the network comprises multiple service locations related to each lower-voltage location, and wherein the voltage measured at the lower-voltage location is representative of the voltages at the multiple service locations.

8. A method as claimed in claim 1, 4, or 5 wherein the network comprises a distribution circuit at the higher voltage, the distribution circuit being selectively operable at a nominal voltage between about 4 kV and 33 kV, and wherein the capacitor means is switched into or out of the distribution circuit, and wherein the lower-voltage locations have a predetermined voltage range selectively between about 500 volts and 110 volts.

9. A method as claimed in claim 1, 4 or 5 wherein the step of selectively transmitting a signal comprises transmitting a signal to maintain the lower voltage at the lower-voltage locations close to a minimum level of the predetermined voltage range.

10. A method as claimed in claim 1, 4, or 5 wherein the capacitor means comprises multiple capacitor means, and step (c) comprises determining via a voltage rise table the effect of switching the capacitor means into or out of the networks, wherein the voltage rise table provides information about the effect of switching the capacitor means into or out of the network on the voltage at multiple lower-voltage locations.

64. The method of claim 1, 11, or 19 wherein the step of measuring comprises:

(i) measuring the voltage at a plurality of lower-voltage locations, and (ii) statistically converting the measured voltages to a representative voltage.

65. The method of claim 64 wherein converting the measured voltages comprises averaging the measured voltages.

11. A method for controlling reactive power flow in a power transmission and distribution network including power lines and transformer means for distributing power at a lower voltage and at a higher voltage, power being distributed at the lower voltage to multiple lower-voltage locations, the network including, at the higher voltage, capacitor means and switch means for selectively lowering or raising the higher voltage, the method comprising the steps of:

(a) measuring the voltage at one or more lower-voltage location

(b) measuring the reactive power flow at the higher voltage, and upstream of the higher voltage

(c) determining;

(1) whether a change of the measured voltage, within a predetermined voltage range, at said lower-voltage location causes the capacitor means to switch into or out of the network,

(2) the changes in reactive power flow resulting from a change of voltage, within the predetermined range, at said lower-voltage location,

(3) with the proviso that the measured voltage is maintained within the predetermined voltage range, at least one of the following;

(i) the available reactive power from available capacitor means not presently in the network, or (ii) the removable reactive power at the higher voltage by switching capacitor means presently in the network out of the network, and

(d) depending on the reactive power availability or removability, and the measured reactive power flows, selectively transmitting a signal to the switch means for lowering or raising the higher voltage to effect a change in the reactive power generated at the higher voltage with the proviso that the lower voltage remains within the predetermined voltage range.

12. A method as claimed in claim 11 wherein the network further comprises a voltage controller associated with the lower-voltage location to be measured, the voltage controller having information about (i) the voltage at the lower-voltage location, and (ii) capacitor means available to be switched into or out of the network, and wherein the step of measuring the voltage includes obtaining the voltage from the voltage controller and wherein the determining steps c(3)(i) and c(3)(ii) include obtaining information from the voltage controller about capacitor means available to be switched into or out of the network.

13. A method as claimed in claim 11 wherein the network further comprises capacitor switch means for selectively switching the capacitor means into or out of the network, and wherein the step of selectively transmitting a signal includes selectively transmitting a signal to the capacitor switch means to selectively switch the capacitor means into or out of the network to effect a change in the reactive power generated at the higher voltage.

14. A method as claimed in claim 11 wherein the network further comprises a transformer at the higher voltage, the transformer including a load tap changer, the network including transformer switch means for adjusting the load tap changer, and wherein the step of selectively transmitting a signal comprises selectively transmitting a signal to the transformer switch means to selectively adjust the load tap changer for lowering or raising the higher voltage.

15. A method as claimed in claim 11 wherein the step of measuring the voltage comprises measuring the voltage at a plurality of lower-voltage locations.

16. A method as claimed in claim 11 wherein the network further comprises capacitor means at the lower voltage, and wherein step b(3)(ii) comprises determining:

(1) the effect of decreasing the higher voltage by a predetermined amount on decreasing the voltages at the lower-voltage locations thereby permitting the capacitor means at the lower voltage to be switched into the network and (2) the reactive power flow made available by switching the capacitor means at the lower voltage into the network thereby making reactive power available from the capacitor means at the lower-voltage for distribution in the network in place of reactive power generated at the higher voltage.

17. A method as claimed in claim 11 wherein the network further comprises capacitor means at the lower-voltage locations, and wherein the method includes changing the number of capacitor means in the network at different lower-voltage locations thereby to adjust the voltages at the lower-voltage locations and the amount of reactive power generated from the lower-voltage locations.

18. The method of claim 11 wherein controlling reactive power flow in step (d) results in reducing energy losses in the network.

19. A method for controlling voltage and reactive power flow in a power transmission and distribution network including power lines and transformer means for distributing power at a lower voltage, at an intermediate voltage, and at a higher voltage, power being distributed at the lower voltage to multiple lower-voltage locations, the network including, at the intermediate voltage, capacitor means and capacitor switch means for selectively switching the capacitor means into or out of the network, the network further comprising voltage switch means for selectively lowering or raising the higher voltage, the method comprising the steps of:

(a) measuring the voltage at one or more lower-voltage location,

(b) ascertaining the deviation, if any, of the measured voltage from a predetermined voltage range intended to be present at the lower-voltage location,

(c) determining whether switching the capacitor means into or out of the network changes the voltage deviation to bring the voltage at the measured lower-voltage location within the predetermined voltage range,

(d) selectively transmitting a signal to the capacitor switch means for switching the capacitor means into or out of operation in the network to effect a change in the voltage at the measured lower-voltage location,

(e) measuring the reactive power flow at the higher voltage,

(f) determining;

(1) whether a change of the measured voltage, within the predetermined voltage range, at said lower-voltage location causes the capacitor means to switch into or out of the network,

(2) the changes in reactive power flow resulting from a change of voltage, within the predetermined range, at said lower-voltage location,

(3) with the proviso that the measured voltage is maintained within the predetermined voltage range, at least one of the following;

(i) the available reactive power from available capacitor means not presently in the network, or (ii) the removable reactive power at the intermediate voltage by switching capacitor means presently in the network out of the network, and

(g) depending on the reactive power availability or removability, and the measured reactive power flow, selectively transmitting a signal to the voltage switch means for lowering or raising the higher voltage to effect a change in the reactive power generated at the higher voltage, with the proviso that the lower voltage remains within the predetermined voltage range.

20. A method as claimed in claim 19 wherein the step of measuring the voltage comprises measuring at multiple lower-voltage locations and step (c) comprises determining the effect of switching the capacitor means into or out of-the network on the voltage at the multiple lower-voltage locations, and wherein step (d) comprises transmitting a signal to change the voltage at one or more lower-voltage locations while maintaining the voltage in the predetermined voltage range at one or more other lower-voltage locations.

21. A method as claimed in claim 19 wherein the network comprises multiple service locations related to each lower-voltage location, and wherein the voltage measured at lower-voltage location is representative of the voltages at the multiple service locations.

22. A method as claimed in claim 19 wherein the step of selectively transmitting a signal to the capacitor switch means comprises transmitting the signal from a voltage controller, and wherein the step of selectively transmitting a signal to the voltage switch means comprises transmitting the signal from a reactive power controller, wherein the voltage controller and the reactive power controller are located remote from the lower-voltage locations.

23. A method as claimed in claim 19 wherein the network further comprises a distribution circuit at the intermediate voltage, and a subtransmission circuit at the higher voltage, the distribution circuit being selectively operable at a nominal voltage between about 4 kV and 33 kV, and wherein the capacitor means is selectively switched into or out of the distribution circuit, and wherein the lower-voltage locations have a predetermined voltage range selectively between about 500 volts and 110 volts, and wherein the subtransmission circuit is at a nominal voltage of about 66 kV and 115 kV.

24. A method as claimed in claim 19, 20 or 21 wherein the capacitor means comprises multiple capacitors, and wherein step (c) comprises determining via a voltage rise table the effect of switching the capacitors into and out of the network, wherein the voltage rise table provides information about the effect of switching the capacitor means on the voltage at multiple lower-voltage locations.

25. The method of claim 19 wherein controlling the voltage at the measured lower-voltage location in step (d) results in reducing energy consumption at said lower-voltage location, and wherein controlling reactive power flow in step (g) results in reducing energy losses in the network.

26. The method of claim 19 wherein steps b-d are taken after the steps e-g.

27. A method as claimed in claim 26 wherein the step of measuring comprises measuring at multiple lower-voltage locations, and the step of determining whether switching the capacitor means in or out of operation comprises determining the effect of switching the capacitor means into or out of the network on the voltage at the multiple lower-voltage locations, and wherein the step of selectively transmitting a signal to the capacitor switch means comprises transmitting a signal to change the voltage at one or more lower-voltage locations while maintaining the voltage in the predetermined voltage range at one or more other lower-voltage locations.

28. A method as claimed in claim 26 wherein the network comprises multiple service locations related to each lower-voltage location, and wherein the voltage measured at the lower-voltage location is representative of the voltages at the multiple service locations.

29. A method as claimed in claim 26 wherein the step of selectively transmitting a signal to the capacitor switch means comprises transmitting the signal from a voltage controller, and wherein the step of selectively transmitting a signal to the voltage switch means comprises transmitting the signal from a reactive power controller, wherein the voltage controller and the reactive power controller are located remote from the lower-voltage locations.

30. A method as claimed in claim 26 wherein the network further comprises a distribution circuit at the intermediate voltage, and a subtransmission circuit at the higher voltage, the distribution circuit being selectively at a nominal voltage between about 4 kV and 33 kV, and wherein the capacitor means is selectively switched into or out of the distribution circuit, and wherein the lower-voltage locations have a predetermined voltage range selectively between about 500 volts and 110 volts, and wherein the subtransmission circuit is at a nominal voltage of about 66 kV and 115kV.

31. A method as claimed in claim 26, 27 or 28 wherein the capacitor means comprises multiple capacitors, and wherein step (c) comprises determining via a voltage rise table the effect of switching the capacitors into and out of the network, wherein the voltage rise table provides information about the effect of switching the capacitors on the voltage at multiple lower-voltage locations.

32. The system of claim 26 wherein the measuring means comprises:

(i) means for measuring the voltage at a plurality of lower-voltage locations, and (ii) means for statistically converting the measured voltages to a representative voltage.

33. The system of claim 32 wherein the conversion means averages the measured voltages.

66. A method as claimed in claim 8 or 23 wherein the network further comprises multiple distribution circuits at the higher voltage, and wherein power is distributed from the distribution circuits to multiple lower-voltage locations.

34. A system for controlling voltage in a power distribution network including power lines for distributing power at a lower voltage and at a higher voltage, power being distributed at the lower voltage to multiple lower-voltage locations, the network including, at the higher voltage, capacitor means and switch means for selectively switching the capacitor means into or out of the network, the system comprising:

(a) means for measuring the voltage at one or more lower-voltage location,

(b) means for ascertaining the deviation, if any, of the measured voltage from a predetermined voltage range intended to be present at the lower-voltage location,

(c) means for determining whether switching the capacitor means into or out of the network changes the voltage deviation to bring the voltage at the measured lower-voltage location within the predetermined voltage range, and

(d) means for selectively transmitting a signal to the switch means for switching the capacitor means into or out of operation in the network to effect a change in the voltage at the measured lower-voltage location.

35. A system as claimed in claim 34 wherein the measuring means further comprises means for measuring the voltage at multiple lower-voltage locations, and wherein the determining means comprises means for determining the effect of switching the capacitor means into or out of the network on the voltage at multiple lower-voltage locations.

36. A system as claimed in claim 34 wherein the system further comprises a voltage controller, the voltage controller comprising means for transmitting a signal to the switch means, and wherein the means for selectively transmitting a signal transmits the signal from the voltage controller, and wherein the voltage controller is located remote from the lower-voltage locations.

37. A system as claimed in claim 34 wherein controlling the voltage at the measured lower-voltage location results in reducing energy consumption at said lower-voltage location.

38. A system as claimed in claim 35 wherein the means for selectively transmitting a signal further comprises means for transmitting a signal to change the voltage at one or more lower-voltage locations while maintaining the voltage in the predetermined voltage range at one or more other lower-voltage locations.

39. A system as claimed in claim 34, 35, or 38 wherein the network comprises a distribution circuit at the higher voltage, the distribution circuit being selectively operable at a nominal voltage between about 4 kV and 33 kV, and wherein the switch means switches the capacitor means into or out of the distribution circuit, and wherein the lower-voltage locations have a predetermined voltage range selectively between about 500 volts and 110 volts.

40. A system as claimed in claim 34, 35, or 38 wherein the network further comprises transformer means at the higher voltage, the transformer means having a primary side and a secondary side, and wherein the capacitor means comprises multiple capacitor means located on the primary side of the transformer means, and wherein the measuring means further comprises means for measuring the voltage on the secondary side of the transformer means.

41. A method as claimed in claim 34, 35 or 38 wherein the network comprises multiple service locations related to each lower-voltage location, and wherein the measuring means further comprises means for measuring the voltage at the lower-voltage location, wherein the measured voltage is representative of the voltages at the multiple service locations.

42. A system as claimed in claim 34, 35, or 38 wherein the capacitor means comprises multiple capacitor:

means and wherein the system further comprises a voltage controller comprising a voltage rise table, the voltage rise table providing information about the effect of switching the capacitor means into or out of the network on the voltage at multiple lower voltage locations, and wherein the determining means further comprises means for using the voltage rise table to switch the capacitor means into or out of the network.

43. A system as claimed in claim 34, 35, or 38 wherein the means for selectively transmitting a signal further comprises means for selectively transmitting a signal to maintain the lower voltage at the lower-voltage locations close to a minimum level of the predetermined voltage range.

67. The system of claim 34, 44, or 51 wherein the measuring means comprises:

(i) means for measuring the voltage at a plurality of lower-voltage locations, and (ii) means for statistically converting the measured voltages to a representative voltage.

68. The system of claim 67 wherein the conversion means averages the measured voltages.

69. The system of claim 36 or 55 wherein the network further comprises multiple distribution circuits at the higher voltage, and wherein power is distributed from the distribution circuits to multiple lower-voltage locations.

44. A system for controlling reactive power flow in a power transmission and distribution network including power lines and transformer means for distributing power at a lower voltage and at a higher voltage, power being distributed to multiple lower-voltage locations at the lower voltage, the network including, at the higher voltage, capacitor means and switch means for selectively lowering or raising the higher voltage, the system comprising:

(a) means for measuring the voltage at one or more lower-voltage location,

(b) means for measuring the reactive power flow at the higher voltage and upstream of the higher voltage,

(c) means for determining whether a voltage change at the lower-voltage location causes the capacitor means to switch into or out of the network while maintaining the lower voltage within a predetermined voltage range,

(d) means for ascertaining, with the proviso that the measured voltage is maintained within the predetermined voltage range, at least one of the following;

(i) the available reactive power from available capacitor means not presently in the network or (ii) the removable reactive power at the higher voltage by switching the capacitor means presently in the network out of the network,

(e) means for determining the changes in reactive power resulting from the change of voltage, within the predetermined range, at said lower-voltage location, and

(f) means for selectively transmitting a signal to the switch means, depending on reactive power availability or removability, and the measured reactive power flows, for lowering or raising the higher voltage to effect a change in the reactive power generated at the higher voltage, with the proviso that the lower voltage remains within the predetermined voltage range.

45. A system as claimed in claim 44 wherein the system further comprises a voltage controller associated with the lower-voltage location to be measured, the voltage controller having information about (i) the voltage at the lower-voltage location, and (ii) capacitor means available to be switched into or out of the network, and wherein the means for measuring the voltage obtains the voltage at the lower-voltage location from the voltage controller and wherein the ascertaining means further comprises means for obtaining information from the voltage controller about capacitor means available to be switched into or out of the network.

46. A system as claimed in claim 44 wherein the network further comprises capacitor switch means for selectively switching the capacitor means into or out of the network, and wherein the means for selectively transmitting a signal comprises means for transmitting a signal to the capacitor switch means for selectively switching the capacitor means into or out of the network to effect a change in the reactive power generated at the higher voltage.

47. A system as claimed in claim 44 wherein the network further comprises a transformer at the higher voltage, the transformer including a load tap changer, the network including transformer switch means for adjusting the load tap changer, and wherein the means for selectively transmitting a signal comprises means for selectively transmitting a signal to the transformer switch means to selectively adjust the load tap changer for lowering or raising the higher voltage.

48. A system as claimed in claim 44 wherein the network further comprises capacitor means at the lower voltage, and wherein the means for selectively transmitting a signal further comprises (1) means for determining the effect of decreasing the higher voltage by a predetermined amount on decreasing the voltages at the lower-voltage locations thereby permitting the capacitor means at the lower voltage to be switched into the network and (2) means for determining the reactive power made available by switching the capacitor means at the lower voltage into the network while maintaining the voltage at the lower-voltage locations within the predetermined voltage range.

49. A system as claimed in claim 44 wherein the network further comprises capacitor means at the lower-voltage locations, and means for changing the number of capacitor means in the network at different lower-voltage locations thereby to adjust the voltages at the lower-voltage locations and the amount of reactive power generated from the lower-voltage locations.

50. A system as claimed in claim 44 wherein controlling reactive power flow results in reducing energy losses in the network.

51. A system of controlling voltage and reactive power flow in a power transmission distribution network including power lines and transformer means for distributing power at a lower voltage, a intermediate voltage, and a higher voltage, power being distributed at the lower voltage to multiple lower-voltage locations, the network including, at the intermediate voltage, capacitor means and capacitor switch means for switching the capacitor means into or out of the network, the network further comprising voltage switch means for selectively lowering or raising the higher voltage, the system comprising:

(a) means for measuring the voltage at one or more lower-voltage location,

(b) first determining means for determining deviation, if any, of the measured voltage from a predetermined voltage range intended to be present at the lower-voltage location,

(c) second determining means for determining whether switching the capacitor means into or out of the network changes the voltage deviation to bring the voltage at the measured lower-voltage location within the predetermined voltage range,

(d) first means for selectively transmitting a signal to the capacitor switch means for switching the capacitor means into or out of operation in the network to effect a change in the voltage at the measured lower-voltage location,

(e) means for measuring the reactive power flow at the higher voltage,

(f) third determining means for determining whether a voltage change, within the predetermined voltage range, at said lower-voltage location causes capacitor means to switch into or out of the network,

(g) means for ascertaining, with the proviso that the measured voltage is maintained within the predetermined voltage range, at least one of the following;

(i) the available reactive power from available capacitor means not presently in the network or (ii) the removable reactive power at the higher voltage by switching the capacitor means presently in the network out of the network,

(h) fourth determining means for determining the changes in reactive power resulting from the change of voltage, within the predetermined range, at said lower-voltage location, and

(i) second means for selectively transmitting a signal to the voltage switch means, depending on reactive power availability or removability, and the measured reactive power flow, for lowering or raising the higher voltage to effect a change in the reactive power generated at the higher voltage, with the proviso that the lower voltage remains within the predetermined voltage range.

52. A system as claimed in claim 51 wherein the voltage measuring means further comprises means for measuring the voltage at multiple lower-voltage locations and wherein the second determining means comprises means for determining the effect of switching the capacitor means in and out of the network on the voltage at multiple lower-voltage locations, and wherein the first means for selectively transmitting a signal comprises means for selectively transmitting a signal to change the voltage at one or more lower-voltage locations while maintaining the voltage in the predetermined voltage range at one or more other lower-voltage locations.

53. A system as claimed in claim 51 wherein the network further comprises multiple service locations related to each lower-voltage location, and wherein the voltage measured at the lower-voltage location is representative of the voltages at the multiple service locations.

54. A system as claimed in claim 51 wherein the system further comprises (i) a voltage controller comprising means for transmitting a signal to the capacitor switch means, wherein the first means for selectively transmitting a signal transmits the signal from the voltage controller, and (ii) a reactive power controller comprising means for transmitting a signal to the voltage switch means, wherein the second means for selectively transmitting a signal transmits the signal from the reactive power controller,

wherein the voltage controller and the reactive power controller are located remote from the lower-voltage locations.

55. A system as claimed in claim 51 wherein the network further comprises a distribution circuit at the intermediate voltage being selectively at a nominal voltage of about 4 kV to about 33 kV, and a subtransmission. circuit at the higher voltage being selectively at a nominal voltage of about 66 kV to about 115 kV, and wherein the network further comprises means for switching the capacitor means into or out of the distribution circuit, and wherein the lower-voltage locations have a predetermined voltage range selectively between about 500 volts and 110 volts.

56. A system as claimed in claim 51 wherein controlling the voltage at the measured lower-voltage location results in reducing energy consumption at said lower-voltage location, and wherein controlling reactive power flow results in reducing energy losses in the network.

57. A system as claimed in claim 51, 52, or 53 wherein the capacitor means comprises multiple capacitor means and wherein the system further comprises a voltage controller comprising a voltage rise table, the voltage rise table providing information about the effect of switching the capacitor means on the voltage at the lower voltage locations, and wherein the second determining means further comprises means for using the voltage rise table to switch the capacitor means into or out of the network.

58. A voltage controller for controlling voltage in a power distribution network including power lines for distributing power at a lower voltage and at a higher voltage, power being distributed at the lower voltage to multiple lower-voltage locations, the network including, at the higher voltage, capacitor means and switch means for selectively switching the capacitor means into or out of the network, the voltage controller comprising:

(a) means for receiving a voltage measured at one or more lower-voltage location,

(b) means for determining the deviation, if any, of the measured voltage from a predetermined voltage range intended to be present at the measured lower-voltage location,

(c) means for determining whether switching the capacitor means into or out of the network changes the voltage deviation to bring the voltage at the measured lower-voltage location within the predetermined voltage range, and

(d) means for selectively transmitting a signal to the switch means for switching the capacitor means into or out of operation in the network to effect a change in the voltage at the measured lower-voltage location.

59. A voltage controller as claimed in claim 58 further comprising means for changing the first lower voltage at one or more lower-voltage locations while maintaining the voltage in a predetermined voltage range at one or more other lower-voltage locations.

60. A voltage controller as claimed in claim 58 further comprising means for maintaining the voltage at the lower-voltage location close to a minimum level of the predetermined voltage range.

61. A voltage controller as claimed in claim 59 wherein the capacitor means comprises multiple capacitor means and wherein the voltage controller further comprises a voltage rise table, the voltage rise table providing information about the effect of switching the capacitor means into or out of the network on the voltage at the lower voltage locations, and wherein the determining means further comprises means for using the voltage rise table to switch the capacitor means into or out of the network.

62. A reactive power controller for controlling reactive power flow in a power transmission and distribution network including power lines and transformer means for distributing power at a lower voltage and at a higher voltage, power being distributed to multiple lower-voltage locations at the lower voltage, the network including capacitor means at the higher voltage and switch means for selectively switching the capacitor means into or out of the network, the system comprising:

(a) means for receiving a voltage measured at one or more lower-voltage location,

(b) means for receiving a reactive power flow measured at the higher voltage,

(c) means for determining whether a change of the measured voltage, within a predetermined voltage range, at said lower-voltage location causes the capacitor means to switch into or out of the network,

(d) means for ascertaining, with the proviso that the measured voltage is maintained within the predetermined voltage range, at least one of the following;

(i) the available reactive power from available capacitor means not presently in the network or (ii) the removable reactive power at the higher voltage by switching the capacitor means presently in the network out of the network,

(e) means for determining the changes in reactive power resulting from the change of voltage, within the predetermined range, at said lower-voltage location, and

(f) means for selectively transmitting a signal to the switch means, depending on reactive power availability or removability, and the measured reactive power flow, for lowering or raising the higher voltage to effect a change in the reactive power generated at the higher voltage with the proviso that the lower voltage remains within the predetermined voltage range.

63. An apparatus for controlling voltage and reactive power flow in a power transmission distribution network including power lines and transformer means for distributing power at a lower voltage, an intermediate voltage, and a higher voltage, power being distributed at the lower voltage to multiple lower-voltage locations, the network including capacitor means at the intermediate voltage and capacitor switch means for switching the capacitor means into or out of the network, the network further comprising voltage switch means for selectively lowering or raising the higher voltage, the apparatus comprising:

(a) means for receiving a voltage measured at one or more lower-voltage location,

(b) means for determining the deviation, if any, of the measured voltage from a predetermined voltage range intended to be present at the measured lower-voltage location,

(c) means for determining whether switching the capacitor means into or out of the network changes the voltage deviation to bring the first voltage at the measured lower-voltage location within the predetermined voltage range, and

(d) means for selectively transmitting a signal to the capacitor switch means for switching the capacitor means into or out of operation in the network to effect a change in the lower voltage at the measured lower-voltage location,

(e) means for receiving a reactive power flow measured at the higher voltage,

(f) means for determining whether a change of the measured voltage, within the predetermined voltage range, at said lower-voltage location causes the capacitor means to switch into or out of the network,

(g) means for ascertaining, with the proviso that the measured voltage is maintained within the predetermined voltage range, at least one of the following;

(i) the available reactive power from available capacitor means not presently in the network or (ii) the removable reactive power at the higher voltage by switching the capacitor means presently in the network out of the network,

(h) means for determining the changes in reactive power resulting from the change of voltage, within the predetermined range, at said lower-voltage location, and

(i) means for selectively transmitting a signal to the voltage switch means, depending on reactive power availability or removability, and the measured reactive power flow, for lowering or raising the higher voltage to effect a change in the reactive power generated at the higher voltage, with the proviso that the first lower voltage remains within the predetermined voltage range.

70. A method for controlled reactive power flow in a power transmission and distribution network including power lines and transformer means for distributing power at a lower voltage and at a higher voltage, power being distributed at the lower voltage to multiple lower-voltage locations, the network including, at the higher voltage, capacitor means and switch means for selectively switching the capacitor means into or out of the network, the method comprising the steps of:

(a) measuring the voltage at one or more lower-voltage location,

(b) measuring the reactive power flow at the higher voltage, and upstream of the higher voltage,

(c) determining;

(1) whether a change of the measured voltage, within a predetermined voltage range, at said lower-voltage location causes the capacitor means to switch into or out of the network,

(2) the change in reactive power resulting from a change of voltage, within the predetermined range, at said lower-voltage location,

(3) with the proviso that the measured voltage is maintained within the predetermined voltage range, at least one of the following;

(i) the available reactive power from available capacitor means not presently in the network, or (ii) the removable reactive power at the higher voltage by switching capacitor means presently in the network out of the network, and

(d) depending on the reactive power availability or removability, and the measured reactive power flows, selectively transmitting a signal to the switch means for switching the capacitor means in or out of the network to effect a change in the reactive power generated at the higher voltage, with the proviso that the lower voltage remains within the predetermined voltage range.

71. A method as claimed in claim 70 wherein the network further comprises a voltage controller associated with the lower-voltage location to be measured, the voltage controller having information about (i) the voltage at the lower-voltage location, and (ii) capacitor means available to be switched into or out of the network, and wherein the step of measuring the voltage includes obtaining the voltage from the voltage controller, and wherein the determining steps b(3)(i) and b(3)(ii) include obtaining information from the voltage controller about capacitor means available to be switched into or out of the network.

72. A method as claimed in claim 70 wherein the step of measuring the voltage comprises measuring the voltage at a plurality of lower-voltage locations.

73. A method as claimed in claim 70 wherein the network further comprises a transformer at the higher voltage, the transformer including a load tap changer, the network including transformer switch means for adjusting the load tap changer, and wherein the step of selectively transmitting a signal comprises selectively transmitting a signal to the transformer switch means to selectively adjust the load tap changer for lowering or raising the higher voltage.

74. A system for controlling reactive power flow in a power transmission and distribution network including power lines and transformer means for distributing power at a lower voltage and at a higher voltage, power being distributed to multiple lower-voltage locations at the lower voltage, the network including, at the higher voltage, capacitor means and switch means for selectively switching the capacitor means into or out of the network, the system comprising:

(a) means for measuring the voltage at one or more lower-voltage location,

(b) means for measuring the reactive power flow at the higher voltage, and upstream of the higher voltage,

(c) means for determining whether a voltage change at the lower-voltage location causes the capacitor means to switch into or out of the network while maintaining the measured voltage within a predetermined voltage range,

(d) ascertaining, with the proviso that the measured voltage is maintained within the predetermined voltage range, at least one of the following;

(i) the available reactive power from available capacitor means not presently in the network or (ii) the removable reactive power at the higher voltage by switching the capacitor means presently in the network out of the network,

(e) means for determining the changes in reactive power resulting from the change of voltage, within the predetermined range, at said lower-voltage location, and

(f) means for selectively transmitting a signal to the switch means, depending on reactive power availability or removability, and the measured reactive power flows, for lowering or raising the higher voltage to effect a change in the reactive power generated at the higher voltage, with the proviso that the measured voltage remains within the predetermined voltage range.

75. A system as claimed in claim 74 wherein the system further comprises a voltage controller associated with the lower-voltage location to be measured, the voltage controller having information about (i) the voltage at the lower-voltage location, and (ii) capacitor means available to be switched into or out of the network, and wherein the means for measuring the voltage obtains the voltage at the lower-voltage location from the voltage controller, and wherein the ascertaining means further comprises means for obtaining information from the voltage controller about the capacitor means.

76. A system as claimed in claim 75 wherein the network further comprises a transformer at the higher voltage, the transformer including a load tap changer, the network including transformer switch means for adjusting the load tap changer, and wherein the means for selectively transmitting a signal comprises means for selectively transmitting a signal to the transformer switch means to selectively adjust the load tap changer for lowering or raising the higher voltage.