Claims:We Claim:

1. A method for determining degradation of one or more capacitors configured in an electrical power system, said method comprising the step of:
measuring, for said one or more capacitors, using a current sensor, respective capacitor line current values;
measuring, for said one or more capacitors, phase angles between said capacitor line currents;
comparing, using zero crossing detectors operational Amplifiers and a controller operatively coupled with said electrical power system, said measured capacitor line current values and said measured phone angles with respective threshold values and generating comparison outputs; and
determining, using said controller, degradation of said one or more capacitors based on said generated comparison outputs.

2. The method of claim 1, wherein said one or more capacitors are configured in a capacitor bank, said capacitor bank being operatively coupled to or forming part of an automatic power factor control (APFC) panel.

3. The method of claim 1, wherein said one or more capacitors are configured in a delta connected capacitor bank.

4. The method of claim 1, wherein said method further comprises the step of measuring, using a voltage sensor, voltage at terminal(s) of said one or more capacitors, and wherein the step of determining degradation of said one or more capacitors is performed based on said measured voltage.

5. The method of claim 4, wherein said voltage sensor is a shunt resistor.

6. The method of claim 1, wherein at least one of said one or more capacitors are determined to be degraded when its respective line current value is below a first threshold value and/or when its respective phase angle is below a second threshold.

7. The method of claim 1, wherein said current sensor is a current transformer (CT).

8. A controller operatively coupled with an electrical power system and configured to:
receive, for one or more capacitors configured in a capacitor bank, respective capacitor line current values and phase angles between said capacitor line currents;
compare said received capacitor line current values and said phone angles with respective threshold values;
generate comparison outputs based on said comparison; and
determine degradation of said one or more capacitors based on said generated comparison outputs.

9. The controller of claim 8, wherein said controller further receives measured voltage value at terminal(s) of said one or more capacitors, and determines degradation of said one or more capacitors based on said measured voltage value.

10. The controller of claim 8, wherein at least one of said one or more capacitors are determined to be degraded when its respective line current value is below a first threshold value, and/or when its respective phase angle is below a second threshold.
, Description:TECHNICAL FIELD
[0001] This present disclosure pertains to a system/controller and method for determining capacitor degradation.

BACKGROUND
[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[0003] Automatic Power Factor Control (APFC) Panels are mainly used for Power Factor (PF) correction, wherein capacitor degradation in such a scenario may lead to voltage imbalance, inefficient system operation, which may cause power outage. To prevent such course of action, there exists a need for timely and efficient detection of capacitor degradation.
[0004] United States Patent 8466689 discloses a method of capacitor degradation detection based on dissipation factor and high frequency spectral signature measurement. In this reference, measured dissipation factor is compared with expected dissipation factor value to estimate the health of a capacitor. In another approach described in this reference, spectral signature is determined from monitored high frequency signal, wherein said spectral signature is then compared with one or more known spectral signature to estimate the health of the capacitor.
[0005] United States Patent 9318944 discloses an apparatus and method to detect degradation of delta and star connected capacitor banks in an active front end power converter. For delta connected capacitor, leg currents are calculated from measured branch currents. The filter capacitor impedances are calculated from leg current, measured line to line voltage and corresponding phase angle. These impedances values are then compared with one or more threshold values to selectively detect degradation of filter capacitors.
[0006] United States Patent 9653984 discloses methods of capacitor degradation detection based on capacitor currents or instantaneous power values. Sum of squares of filter capacitor currents and instantaneous power values are compared with one or more threshold values. In one method, current flowing to the filter capacitor is passed through low pass filter with a cut off frequency between 2nd and 3rd harmonics. In another method, both active and reactive power is calculated from measured current and voltage values and instantaneous power is compared with threshold values.
[0007] All these above-methods either require manual intervention or have accuracy issues, thereby resulting in incorrect or untimely determination of capacitor degradation. Also, existing manual systems for distinguishing faulty capacitors from a capacitor bank normally include disconnecting the capacitors and testing them separately to figure out the broken or degraded capacitors. Such systems are expensive, and in the long run, enable untimely shutdown of the capacitor bank along with power loss.
[0008] There is therefore a need in the art for an improved and more efficient method of detecting capacitor degradation.
[0009] All publications herein are incorporated by reference to the same extent as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.
[0010] In some embodiments, the numbers expressing quantities of ingredients, properties such as concentration, reaction conditions, and so forth, used to describe and claim certain embodiments of the invention are to be understood as being modified in some instances by the term “about.” Accordingly, in some embodiments, the numerical parameters set forth in the written description and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable. The numerical values presented in some embodiments of the invention may contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements.
[0011] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
[0012] The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g. “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.
[0013] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all groups used in the appended claims.

OBJECTS OF THE INVENTION
[0014] An object of the present disclosure is to provide a method that enables determination of capacitor degradation.
[0015] Another object of the present disclosure is to enable identification of degraded capacitor connected in delta connected capacitor bank to avoid adverse effect of lower Power Factor (PF).
[0016] An object of the present disclosure is to provide efficient, faster, and easier processing and determination of capacitor degradation.
[0017] An object of the present disclosure is to provide a method that is capable of detecting capacitor degradation precisely even with unbalanced load.
[0018] An object of the present disclosure is to provide a method that raises an alarm in case of fault by measuring the line to line voltages at capacitor bank terminal.

SUMMARY
[0019] This present disclosure pertains to a system/controller and method for determining capacitor degradation.
[0020] In an aspect, the present disclosure relates to a method for determining degradation of one or more capacitors configured in an electrical power system, the method include the steps of: measuring, for the one or more capacitors, using a current sensor, respective capacitor line current values; measuring, for said one or more capacitors, phase angles between the capacitor line currents using analog ZCDs; comparing, using a controller operatively coupled with the electrical power system, the measured capacitor line current values and the measured phone angles with respective threshold values and generating comparison outputs; and determining, using the controller, degradation of the one or more capacitors based on the generated comparison outputs.
[0021] In an aspect, the one or more capacitors can be configured in a capacitor bank, said capacitor bank being operatively coupled to or forming part of an automatic power factor control (APFC) panel. In another aspect, the one or more capacitors can be configured in a delta connected capacitor bank.
[0022] In an aspect, the proposed method can further include the step of measuring, using a voltage sensor, voltage at terminal(s) of said one or more capacitors, and wherein the step of determining degradation of said one or more capacitors is performed based on said measured voltage. In an exemplary aspect, the voltage sensor can be a shunt resistor.
[0023] In another aspect, at least one of said one or more capacitors can be determined to be degraded when its respective line current value is below a first threshold value and/or when its respective phase angle is below a second threshold.
[0024] In an aspect, the current sensor can be a current transformer (CT).
[0025] In an aspect, the present disclosure further relates to a controller that is operatively coupled with an electrical power system and configured to: receive, for one or more capacitors configured in a capacitor bank, respective capacitor line current values and phase angles between said capacitor line currents calculated from analog operational amplifiers (ZCDs); compare said received capacitor line current values and said phone angles with respective threshold values; generate comparison outputs based on said comparison; and determine degradation of said one or more capacitors based on said generated comparison outputs.
[0026] In an aspect, the controller can further be configured to receive measured voltage value at terminal(s) of the one or more capacitors, and determine degradation of the one or more capacitors based on the measured voltage value. In an aspect, at least one of the one or more capacitors can be determined to be degraded when its respective line current value is below a first threshold value, and/or when its respective phase angle is below a second threshold.
[0027] Various objects, features, aspects and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components

BRIEF DESCRIPTION OF THE DRAWINGS
[0028] The accompanying drawings are included to provide a further understanding of the present disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure.
[0029] FIG. 1 is an exemplary representation of a capacitor monitoring system in accordance with an embodiment of the present disclosure.
[0030] FIG. 2 is an exemplary phasor diagram illustrating phase relationship between currents of a healthy capacitor in accordance with an embodiment of the present disclosure.
[0031] FIG. 3 illustrates an exemplary phasor diagram of a degraded capacitor bank.
[0032] FIGs. 4A and 4B illustrate exemplary flow diagrams showing working of the proposed method in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION
[0033] The following is a detailed description of embodiments of the disclosure depicted in the accompanying drawings. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[0034] Each of the appended claims defines a separate invention, which for infringement purposes is recognized as including equivalents to the various elements or limitations specified in the claims. Depending on the context, all references below to the "invention" may in some cases refer to certain specific embodiments only. In other cases it will be recognized that references to the "invention" will refer to subject matter recited in one or more, but not necessarily all, of the claims.
[0035] Various terms as used herein are shown below. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing.
[0036] This present disclosure pertains to a system/controller and method for determining capacitor degradation.
[0037] In an aspect, the present disclosure relates to a method for determining degradation of one or more capacitors configured in an electrical power system, the method include the steps of: measuring, for the one or more capacitors, using a current sensor, respective capacitor line current values; measuring, for said one or more capacitors, phase angles between the capacitor line currents by ZCDs; comparing, using a controller operatively coupled with the electrical power system, the measured capacitor line current values and the measured phone angles with respective threshold values and generating comparison outputs; and determining, using the controller, degradation of the one or more capacitors based on the generated comparison outputs.
[0038] In an aspect, the one or more capacitors can be configured in a capacitor bank, said capacitor bank being operatively coupled to or forming part of an automatic power factor control (APFC) panel. In another aspect, the one or more capacitors can be configured in a delta connected capacitor bank.
[0039] In an aspect, the proposed method can further include the step of measuring, using a voltage sensor, voltage at terminal(s) of said one or more capacitors, and wherein the step of determining degradation of said one or more capacitors is performed based on said measured voltage. In an exemplary aspect, the voltage sensor can be a shunt resistor.
[0040] In another aspect, at least one of said one or more capacitors can be determined to be degraded when its respective line current value is below a first threshold value and/or when its respective phase angle is below a second threshold.
[0041] In an aspect, the current sensor can be a current transformer (CT).
[0042] In an aspect, the present disclosure further relates to a controller that is operatively coupled with an electrical power system and configured to: receive, for one or more capacitors configured in a capacitor bank, respective capacitor line current values and phase angles between said capacitor line currents using analog operation amplifiers; compare said received capacitor line current values and said phone angles with respective threshold values; generate comparison outputs based on said comparison; and determine degradation of said one or more capacitors based on said generated comparison outputs.
[0043] In an aspect, the controller can further be configured to receive measured voltage value at terminal(s) of the one or more capacitors, and determine degradation of the one or more capacitors based on the measured voltage value. In an aspect, at least one of the one or more capacitors can be determined to be degraded when its respective line current value is below a first threshold value, and/or when its respective phase angle is below a second threshold.
[0044] Aspects of the present disclosure relate to a novel technique of capacitor degradation detection for capacitor banks used in electrical power systems generally for power factor improvement. In the proposed disclosure, capacitor line currents are measured and angles between such capacitor line currents are calculated, and then compared with their respective threshold values so as to determine status of degradation of capacitor(s) involved.
[0045] The present disclosure relates to a method for capacitor degradation detection that, in an exemplary implementation, measures line currents in a delta connected capacitor bank that is configured in an electrical power transmission and distribution system. The present disclosure enables measurement of health of one or more capacitors by monitoring line currents of each phase, and then calculating angle between them. For healthy capacitor banks, line currents will be in balanced condition and 120-degree phase angle apart, however, if one or more capacitors are degraded, current magnitude and the angle between line currents changes according to degradation rate.
[0046] The present disclosure aims at identification of degraded capacitor connected in delta connected capacitor bank to avoid adverse effect of lower PF. Lower PF attracts operational losses and a penalty from electricity board, responsible for electricity supply. The present method comprises line current magnitude (also interchangeably referred to as capacitor line current value hereinafter) and phase angle measurement between them to provide information of capacitor degradation.
[0047] In an aspect, the proposed method involves detection of degraded capacitor connected in between two phases with the knowledge of current phasor rotation and amplitude. Detection of particular faulty capacitor eliminates the need of separate capacitor testing and eventually the time to restart the system. In another aspect, the present disclosure involves filter capacitor line current measurement (capacitor line current value), along with knowledge of phasor position when the capacitor bank is connected in delta network in electrical power systems so as to determine capacitor degradation. It is to be appreciated that capacitor degradation affects phase angle between line currents and magnitudes in both balanced and unbalanced load conditions. Capacitor line current also changes under faulty load condition such as overload and short circuit. To discriminate such condition with degradation, voltage at capacitor terminal is also measured.
[0048] With reference to FIG. 1, an exemplary block diagram representation of the proposed architecture/power system is shown in accordance with an aspect of the present invention. As shown, a three-phase load 110 can be connected to a three phase Y network source 120 through line impedance 130. A delta connected capacitor bank 140 can be connected for power factor correction in the system. Line current in the capacitor bank 140 and voltage at its terminal can be sensed through current and voltage sensors and given to controller 150 for further analysis.
[0049] In an aspect, the controller 150 can be configured to check for phase angle distribution (FRY, FYB, FBR) and the capacitor line current magnitudes (IR, IY, IB) are calculated by performing RMS calculation on current samples. Line to line voltage (VRY) is used as a reference signal for the calculation of all current phase angles. Angle between delta connected capacitor bank line currents and the reference voltage is calculated by passing both the signals through ZCD’s which detect the zero crossing and pass the information to the controller. Wherein healthy capacitor line current and phase angle can be used as a reference or threshold for detection of degradation in any capacitor of capacitor bank. Also, measurement of terminal voltage VRY, VYB, VBR can give information of system health for reliable capacitor degradation detection. According to an aspect of the present disclosure (as also shown in FIG. 3), degradation in capacitor connected in line R-Y results in lower current magnitude in lines R & Y, i.e. IR, IY and lower phase angle FRY.
[0050] FIG. 2 is an exemplary phasor diagram illustrating ideal phase relationship between currents of a healthy capacitor in accordance with an embodiment of the present invention. In a healthy capacitor bank utilization, currents are 120º phase apart and the magnitude of currents are same in all three phases under balanced/unbalanced load condition. As the capacitor ages, conductance G of capacitor caused by imperfections in the dielectric material, plate material, and in terminal leads, gradually increase over time, while the capacitance diminishes. FIG. 3 shows phasor diagram of degraded capacitor bank. Degraded capacitor brings down current magnitude and phase angles in same phases.
[0051] Therefore, as mentioned above, in a healthy capacitor bank:
IR = IY = IB
FRY = FYB = FBR = 120º

Whereas, in a degraded capacitor CRY
IR = IY < IB
FYB = FBR > FRY
[0052] Voltage dip at capacitor bank terminal due to any fault condition in the system may cause a false alarm for capacitor degradation detection unit 160. Thus, for trustworthy detection under healthy electrical power system, voltage can be sensed and fed to the controller 150, which is used as reference to generate an alert signal in case of capacitor degradation.
[0053] FIGs. 4A and 4B illustrate exemplary flow diagrams showing working of the proposed method in accordance with an embodiment of the present disclosure. With reference to FIG. 4A, at step 402, the method can include the step of measuring, for said one or more capacitors, using a current sensor, respective capacitor line current values; at step 404, measuring, for said one or more capacitors, phase angles between said capacitor line currents by using zero crossing detectors taking terminal voltage as reference for calculation; at step 406 measuring, for said one or more capacitors, respective capacitor line current values, , by using a current sensor; and at step 408, measuring, for one or more capacitors, respective capacitor line current values, by using a current sensor. With reference to FIG. 4B, at step 452, current in capacitor bank branch is sensed through CT, and terminal voltage is sensed through voltage sensors. In an exemplary implementation, shunt resistors can be utilized for voltage measurement. At step 454, sensed signals can be digitized by an Analog to Digital (A/D) converter and directly fed to the controller for further processing. At step 456, capacitor current RMS and phase angle between the line current is calculated in order to estimate capacitor degradation. At step 458, current magnitude in all three lines IMag are compared with respective thresholds, wherein change in magnitude ?IMag is an indication of the degradation in capacitor. Comparison of the current magnitude in all the three lines IMag with the threshold criteria TH1 defines the further course of action, wherein as shown at step 460, if (?IMag > TH1), then second check for phase angle deviation takes place. At step 462, it is determined that if there is no change in phase angles between line current, there is an equal capacitor degradation in all 3 capacitors connected in capacitor bank. On the other hand, if ?Fcap also breaches the threshold TH2 (?Fcap > TH2), at step 464, voltage at capacitor terminal is checked by comparing the VLL with rated terminal voltage. In case of fault, at step 466, fall in line to line voltage takes place due to excessive current flow in the lines which affects the capacitor line current and phase angles. On the other hand, if there is no dip in voltage while the above two criteria (?IMag > TH1) & (?Fcap > TH2) are satisfied, it is determined at step 468 that one or more of the capacitors are degraded, and at step 470, an alarm for capacitor degradation is raised along with identification of the faulty capacitor. Further, identification of phase where degraded capacitor is connected is done by identifying the change in current magnitude and phase angle in a particular phase. Only one faulty capacitor connected in RY phase causes lower IR & IY and FRY. This same phenomenon is applicable when one capacitor connected to any phase degraded, while two equally degraded capacitors connected in RY and YB phases causes maximum drop in common line current IY. Equally Degraded capacitor CRY and CYB have: IY< IB= IR & ?IMag > TH1 and ?Fcap > TH2.
[0054] In an aspect, differently degraded capacitor connected in RY and YB has different phenomena. Degraded capacitor CRY and CYB where degradation in CRY is 50% while CYB is degraded up to 80%, in which case:
IY < IB < IR & ?IMag > TH1
IB is lower than IR as the capacitor connected in YB phase is largely degraded than CRY.
[0055] In an aspect, the present disclosure enables efficient, faster, and easier processing and calculation as it processes only filter capacitor current magnitude and their phasor vectors. The proposed method is also capable of detecting capacitor degradation precisely even with unbalanced load. The proposed method also raises an alarm in case of fault by measuring the line to line voltages at capacitor bank terminal.
[0056] In an aspect, the present invention detects capacitor degradation by measuring line currents of each phase, and calculating phase angle between them. Any change in capacitance or series resistance values can be clearly identified by measuring line currents and angle between them. In the proposed method therefore, line to line voltage is measured to detect the system health for reliable detection.
[0057] While the foregoing describes various embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. The scope of the invention is determined by the claims that follow. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.

ADVANTAGES OF THE INVENTION
[0058] The present disclosure provides a method that enables determination of capacitor degradation.
[0059] The present disclosure enables identification of degraded capacitor connected in delta connected capacitor bank to avoid adverse effect of lower Power Factor (PF).
[0060] The present disclosure provides efficient, faster, and easier processing and determination of capacitor degradation.
[0061] The present disclosure provides a method that is capable of detecting capacitor degradation precisely even with unbalanced load.
[0062] The present disclosure provides a method that raises an alarm in case of fault by measuring the line to line voltages at capacitor bank terminal.