Power factor correction using hierarchical context of a power monitoring system

• US 8,076,910 B2
• Filed: 08/11/2008
• Issued: 12/13/2011
• Est. Priority Date: 08/11/2008
• Status: Active Grant

• Current Assignee: Schneider Electric USA, Inc. (Schneider Electric SE)
• Original Assignee: Schneider Electric USA, Inc. (Schneider Electric SE)
• Inventors: Bickel, Jon A.
• Primary Examiner(s): Berhane, Adolf
• Assistant Examiner(s): Tran, Nguyen
• Application Number:
  US12/228,209
• Publication Number:
  US 20100037189A1
• Time in Patent Office: 1,219 Days
• Field of Search: 323/205, 323/206, 323/207, 323/208, 323/209, 323/210, 363/16, 363/17, 363/20, 363/21.01, 363/21.12, 363/21.13, 363/95, 363/96, 363/97, 363/98
• US Class Current: 323/205
• CPC Class Codes: G05F 1/70 Regulating power factor; Regulating reactive current or power
• CPC Class Codes: G06F 30/367 Design verification, e.g. using simulation, simulation program with integrated circuit emphasis [SPICE], direct methods or relaxation methods
• CPC Class Codes: H02J 3/1871 Methods for planning installation of shunt reactive power compensators

Abstract

Automated power factor correction analysis methods based on an automatically determined hierarchy representing how IEDs and transformers are linked together in an electrical system for reducing a utility bill, releasing capacity to the electrical system, reducing losses, and/or improving voltages. The automatically determined hierarchy places the system elements in spatial context and is exploited by the power factor correction analysis methods to identify power factor correction opportunities. Recommendations are made as to sizing and location of capacitors within the hierarchy where power factor improvements can be achieved. Harmonic distortion levels can be checked first to determine whether safe levels exist for capacitor banks. Recommendations are also checked to avoid leading power factors anywhere in the system due to the addition of capacitor banks. Capacitor bank location is tailored to the end-user'"'"'s goal for power factor correction. Cost savings and payback periods associated with any ameliorative power factor correction activities are also determined.

Claims

1. An automatic power factor correction analysis method, comprising:

automatically determining a hierarchy of an electrical system, the hierarchy indicating how a number of intelligent electronic devices (IEDs) are linked to one another in the electrical system, each of the IEDs monitoring electrical characteristics;

automatically storing a data representation of the hierarchy;

automatically identifying from the automatically determined hierarchy a main IED that is monitoring a main power supply in the hierarchy;

receiving maximum power data from corresponding current and voltage signals monitored by the main IED and an associated power factor that is coincident with the maximum power data;

determining a reactive power value coincident with the maximum power data by receiving the reactive power value from the main IED or by deriving the reactive power value from the maximum power data or from data representing the current and voltage signals and the power factor coincident with the maximum power data; and

calculating, based on the coincident power factor, an amount of positive or negative reactive power to supply to improve the coincident power factor toward a unity value, and, responsive thereto, storing a recommendation indicating at least a location and a size of one or more capacitors to be added in the automatically determined hierarchy for producing at least the amount of the reactive power such that the reactive power value is offset by the amount of the reactive power.

2. The method of claim 1, further comprising:

receiving minimum power data from the corresponding current and voltage signals monitored by the main IED and an associated second power factor;

determining a second reactive power value coincident with the minimum power data by receiving the second reactive power value from the main IED or by deriving the second reactive power value from the minimum power data or from data representing the current and voltage signals and the second power factor coincident with the minimum power data; and

verifying whether producing the amount of the reactive power automatically determined based on the coincident power factor would result in a leading power factor based on the second reactive power value.

3. The method of claim 2, further comprising, if the verifying would result in the leading power factor, reducing the size of the one or more capacitors such that the amount of reactive power produced by the one or more capacitors is reduced so as to cause a corresponding power factor to not be leading.

4. The method of claim 2, further comprising, if the verifying would result in the leading power factor, determining a periodicity to cycle at least one of the one or more capacitors on and off so as to cause a corresponding power factor to not be leading.

5. The method of claim 1, further comprising calculating a cost savings realized by the addition of the one or more capacitors.

6. The method of claim 5, further comprising calculating a payback period indicating how long it would take for a cost of adding the one or more capacitors to be offset by the cost savings realized by adding the one or more capacitors.

7. The method of claim 1, further comprising receiving an indication of a desired power factor between the coincident power factor and the unity value, wherein the calculating the amount of reactive power is based on the desired power factor.

8. The method of claim 1, further comprising, prior to the storing the recommendation:

automatically determining whether an elevated level of harmonic frequencies exist in current or voltage signals being monitored by the main IED in the hierarchy; and

if the level of the harmonic frequencies exceeds a threshold, storing with the recommendation an indication that the harmonic frequencies are present.

9. The method of claim 8, wherein the automatically determining whether the elevated level of harmonic frequencies exist is carried out by comparing a true power factor with a displacement power factor.

10. The method of claim 8, wherein the automatically determining whether the elevated level of harmonic frequencies exist is carried out by measuring, at the main IED, reactive currents at non-fundamental frequencies, and determining whether the reactive currents exceed at least one criterion.

11. The method of claim 1, further comprising:

identifying a transformer in the hierarchy;

identifying from the automatically determined hierarchy a first IED that is upstream of the transformer;

determining a first power factor from power data monitored by the first IED;

calculating, based on the first power factor, a corrected power factor that would release an amount of volt-amps capacity of the transformer to cause the transformer to be loaded at a reduced volt-amps capacity; and

calculating, based on the amount of volt-amps capacity, a corresponding corrective reactive power value to be supplied by a capacitor bank, wherein the recommendation includes an indication of a size and a location of the capacitor bank, wherein the size is related to the corrective reactive power value and the location is downstream of the transformer in the automatically determined hierarchy.

12. The method of claim 1, further comprising:

receiving a selection of a first of the IEDs;

receiving from the first IED power data measured by the first IED;

calculating a loss reduction factor as a function of a power factor based on the power data and a desired power factor;

calculating a loss reduction improvement value representing an improvement in loss reduction of the electrical system and storing the loss reduction improvement value; and

calculating a size of a second set of one or more capacitors that will correct the power factor to the desired power factor, wherein the recommendation includes an indication of the size of the second set of the one or more capacitors.

13. An automatic power factor correction analysis method, comprising:

automatically determining a hierarchy of an electrical system, the hierarchy indicating how a number of intelligent electronic devices (IEDs) are linked to one another in the electrical system, each of the IEDs monitoring electrical characteristics;

automatically storing a data representation of the hierarchy;

identifying a transformer in the hierarchy;

identifying from the automatically determined hierarchy a first IED that is upstream of the transformer;

determining a coincident power factor from power data monitored by the first IED;

calculating, based on the coincident power factor, a corrected power factor that would release an amount of volt-amps capacity of the transformer to cause the transformer to be loaded at a reduced volt-amps capacity;

calculating, based on the amount of volt-amps capacity, a corresponding corrective reactive power value to be supplied by a capacitor bank; and

storing a recommendation indicating a size and a location of the capacitor bank, wherein the size is related to the corrective reactive power value and the location is downstream of the transformer in the automatically determined hierarchy.

14. The method of claim 13, further comprising:

automatically identifying at least one IED in the automatically determined hierarchy that is upstream of the first IED;

receiving respective power data from the first IED and the at least one IED pseudo-synchronously;

based on the corrective reactive power value, calculating an amount of released volt-amps capacity at the at least one IED; and

storing the amount of released volt-amps capacity at the at least one IED.

15. An automatic power factor correction analysis method, comprising:

automatically determining a hierarchy of an electrical system, the hierarchy indicating how a number of intelligent electronic devices (IEDs) are linked to one another in the electrical system, each of the IEDs monitoring electrical characteristics;

automatically storing a data representation of the hierarchy;

receiving a selection of a first of the IEDs;

receiving from the first IED power data measured by the first IED;

calculating a loss reduction factor as a function of a power factor based on the power data and a desired power factor;

calculating a loss reduction improvement value representing an improvement in loss reduction of the electrical system and storing the loss reduction improvement value;

calculating a size of one or more capacitors that will correct the power factor to the desired power factor; and

storing a recommendation indicating the size of the one or more capacitors.

16. The method of claim 15, further comprising calculating a cost savings realized by the addition of the one or more capacitors.

17. The method of claim 15, further comprising calculating a payback period indicating how long it would take for a cost of adding the one or more capacitors to be offset by the cost savings realized by adding the one or more capacitors.

18. The method of claim 15, further comprising calculating how much the voltage drop between the first IED and another of the IEDs would improve by the addition of the one or more capacitors, wherein the recommendation includes an indication of the voltage drop improvement.