# US 10,122,162 B2 · Detection of capacitor bank fuse/switch failure

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- Number: US 10,122,162 B2
- Document ID: US10122162B2
- Status: Granted
- Kind: B2
- Application number: 14/584,911
- Filed: 2014-12-29
- Published: 2015-07-02
- Granted: 2018-11-06
- Earliest claimed: 2013-12-27
- Assignees: Beckwith Electric Co., Inc.
- Applicants: Murty Yalla
- Inventors: Murty Yalla
- Web page: https://patentgrep.com/patent/US10122162B2

## CPC

- H02H 3/382: {involving phase comparison between current and voltage or between values derived from current and voltage}
- H02H 7/16: for capacitors (for synchronous capacitors H02H7/06)
- H02H: EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS (indicating or signalling undesired working conditions G01R, e.g. G01R31/00, G08B; locating faults along lines G01R31/08; emergency protective devices H01H)

## Abstract

A method for detecting the operating condition of each phase of a three-phase capacitor bank in a power distribution system, including the steps of, if the RMS neutral current is above the bank status closed setting, comparing the phase angle of neutral current (IN) with respect to voltage on one of the phases (VA, VB or VC) and sending an alarm signal when the comparison of the phase angle of neutral current with respect to the phase voltage differs appreciably from the expected phase angles.

## Claims

### Claim 1

A method for detection of the operating condition of each phase of a three-phase capacitor bank in a power distribution system, comprising the steps of:
measuring one of the phase voltages (VA, VB or VC) and the neutral current in the capacitor bank;
comparing a RMS neutral current with all open (bank status open) and all closed (bank status closed) settings to determine if all the three phases of the capacitor bank are open or closed;
if the RMS neutral current is above the bank status closed setting, comparing the phase angle of neutral current (IN) with respect to voltage on phase A (VA), or phase B (VB) or phase C (VC);
sending an alarm signal when the comparison of the phase angle of neutral current (IN) with respect to the phase voltage (if VA is used add 0° , if VB is used add 120° or for VC add) 240° differs appreciably from the phase angles indicated in the following chart:
Phase angle of IN with respect
to VA (If VB is used add
OPEN/CLOSE state of each Phase
120° or for VC add 240° to
A
B
C
the angles shown below)
OPEN
OPEN
OPEN
N/A
CLOSE
OPEN
OPEN
90°
OPEN
CLOSE
OPEN
−30°
OPEN
OPEN
CLOSE
210°
CLOSE
CLOSE
OPEN
30°
OPEN
CLOSE
CLOSE
270°
CLOSE
OPEN
CLOSE
150°
CLOSE
CLOSE
CLOSE
N/A.

### Claim 2 (depends on 1)

The method as set forth in claim 1, wherein the appreciable difference compared between the phase angle of neutral (IN) with respect to the phase voltage comprises approximately the phase angle indicated in the chart ±10°.

### Claim 3 (depends on 1)

A method as set forth in claim 1, wherein measuring one of the three phase voltages in phases (VA), (VB), (VC) and calculating neutral current comprises as follows:
neutral current (INE) =magnitude of (IA_cap*a +IB_cap*b+IC_cap*c)
Where
a=1 if phase A is closed else a=0
b=1 if phase B is closed else b=0
c=1 if phase C is closed else c=0
IA_cap=(1000*QCAP)/(3*VA)
IB_Cap=(1000*QCAP)/(3*VB)
IC_cap=(1000*QCAP)/(3*VC)
QCAP=“3 Phase Capacitor Bank Size” in KVArs
VA, VB and VC are phase to ground voltage phasors and IA cap, IB cap and IC cap are calculated Capacitor Bank current phasors.

### Claim 4 (depends on 3)

The method as in claim 3, further including the step of detecting a high resistance contact of a switch wherein the neutral current is less than an undercurrent pickup setting.

### Claim 5 (depends on 3)

The method as in claim 3, further including the step of detecting capacitor bank short circuit wherein the neutral current is greater than a neutral overcurrent setting.

### Claim 6

An apparatus for detection of the operating condition of each phase of a three-phase capacitor bank in a power distribution system, comprising in combination:
a voltage meter for measuring one of the phase voltages (VA, VB or VC) and a current meter for measuring the neutral current in the capacitor bank;
a controller for comparing a RMS neutral current with all open (bank status open) and all closed (bank status closed) settings to determine if all the three phases of the capacitor bank are open or closed and if the RMS neutral current is above the bank status closed setting, then opening or closing each phases when required while comparing the phase angle of neutral current (IN) with respect to voltage on phase A (VA), or phase B (VB) or phase C (VC) and when the comparison of the phase angle of neutral current (IN) with respect to the phase voltage (if VA is used add 0°, if VB is used add 120° or if VC is used add 240°) differs appreciably from the phase angles indicated in the following chart:
Phase angle of IN with respect
to VA (If VB is used add
OPEN/CLOSE state of each Phase
120° or for VC add 240° to
A
B
C
the angles shown below)
OPEN
OPEN
OPEN
N/A
CLOSE
OPEN
OPEN
90°
OPEN
CLOSE
OPEN
−30°
OPEN
OPEN
CLOSE
210°
CLOSE
CLOSE
OPEN
30°
OPEN
CLOSE
CLOSE
270°
CLOSE
OPEN
CLOSE
150°
CLOSE
CLOSE
CLOSE
N/A.