URACA
`{11] Patent Number:
`5,311,392
`United States Patent
`[45] Date of Patent: May 10, 1994
`Kinney et al.
`
`
`e
`
`[19]
`
`US005311392A
`
`[54] DUAL PROCESSOR ELECTRIC POWER
`TRIP UNIT
`
`[75]
`
`[73] Assignee:
`
`Inventors: Michael A. Kinney; Stephen F.
`Gillette, both of Raleigh, N.C.
`Siemens Energy & Automation, Inc.,
`‘Alpharetta, Ga.
`[21] Appl. No.: 753,286
`[22] Filed:
`Aug, 30, 1991
`[51]
`Int, CLS uo.eccssssstsesncocceeenseceesesseresees H02H 3/08
`[52] WLS. C1. occesccsescecsesscssssesseteeseseaes 361/93; 361/96;
`361/87
`[58] Field of Search .......-..-seessne 361/21, 23, 25, 31,
`361/42, 47, 50, 76, 87, 88, 96, 62, 67, 93
`References Cited
`U.S. PATENT DOCUMENTS
`4,470,092 9/1984 Lombardi 0.0...sssscssseseeneone 361/23
`4,689,712
`8/1987 Demeyer ..........ccssescssnesscneees 361/96
`
`[56]
`
`
`
`4,710,845 12/1987 Demeyer...........scscssscsesesseee 361/96
`4,811,154 3/1989 Trenkleret al. ..
`“
`4,870,351
`9/1989 Milkovic...........
`.
`4,996,646
`2/1991 Farrington ....
`$,031,178
`7/1991 Hartman «0...esscesseaees 371/29
`Primary Examiner—A.D.Pellinen
`Assistant Examiner—S. Jackson
`[57]
`ABSTRACT
`A low voltage electric power monitoring and circuit
`breaker system includes two processors. Thefirst pro-
`cessor activates the circuit breaker when an overcur-
`rent condition is detected and the second processor
`monitors the current sensed by the first processor and
`activates the circuit breaker for overcurrent conditions
`which should have caused thefirst processor to activate
`the breaker. If a current of this magnitude is detected,
`the second processor activates the circuit breaker as a
`backup protection forthe first circuit breaker.
`
`18 Claims, 14 Drawing Sheets
`
`4113
`'t
`AEP er
`eyee ee ee a ew ee ee 7
`POWER||FRONT PANEL[||WATCHDOG
`SUPPLY
`SWITCHES
`CIRCUIT
`4t
`
`246
`OVER CURRENT
`__HICROCONPUTER
`
`as
`
`| |
`
`15V OC
`
`BREAKER
`CONTROL
`WIRING
`
`2m
`
`TRIPUNIT116
`
`1
`
`APPLE 1027
`
`DSIPLAY
`
`COMMUNICATIONS+MONITORING LP
`sens
`CLOSE
`
`ISOLATED
`| eS wst
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`COPUTER 140
`Feats
`ISOLATED
`1stATED
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`INTERPOSING
`Sar
`say
`RELAY
`‘eeCOSLd 4
`260—"|_
`SUPPLY
`[anu
`}-
`
`230
`
`TRIP
`ACTUATOR
`
`BREAKER
`POSITION
`
`INEgPOSING
`
`''
`
`FRONT PANEL
`
`ISOLATED
`INPUT
`
`ISOLATED
`ALARM/
`
`266
`
`DMP
`250
`
`210
`
`MICROCOMPUTER
`
`wane ees
`
`MEMORY
`
`|
`
`oe,
`
`1
`
`APPLE 1027
`
`

`

`U.S. Patent
`
`May 10, 1994
`
`Sheet 1 of 14
`
`5,311,392
`
`126
`
`124
`
`1 F
`
`IG.
`
`2
`
`

`

`U.S. Patent
`
`May 10, 1994
`
`Sheet 2 of 14
`
`5,311,392
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`U.S. Patent
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`May 10, 1994
`
`Sheet 3 of 14
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`U.S. Patent
`
`May 10, 1994
`
`Sheet 4 of 14
`
`5,311,392
`
`FIG. 2a
`
`SHORT
`
`2206
`
`LONG TIME now©
`GROUND PICKUP Q
`
`SHORT TIME
`
`CIRCUIT
`
`e20c
`
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`
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`
`PICKUP
`
`GROUND FAULT
`
`PICKUP
`
`DELAY
`
`PICKUP
`
`DELAY
`
`COMM WATCH CY256
`
`5
`
`

`

`U.S. Patent
`
`May10, 1994
`
`Sheet 5 of 14
`
`5,311,392
`
`3b
`
`FIG.
`FIG.
`
`3a
`
`TIME
`
`bd
`=—
`—
`
`CURRENT
`
`CURRENT
`
`6
`
`

`

`U.S. Patent
`
`May10, 1994
`
`Sheet 6 of 14
`
`5,311,392
`
`FIG. 4a
`INIT HARDWARE|42°
`
`t
`VARIABLES
`
`M12
`
`LOG A START
`UP EVENT
`
`4i4
`
`ne
`
`CHECK FOR SEABUS
`COMMUNICATION.
`PROCESS ANY PACKETS
`
`416 SUM OF
`
`SQUARES FOR
`CURRENT
`
`READY?
`
`YES
`BLOCK ACCESS 10
`NON- VOLATILE
`MEMORY
`
`<—©
`
`420
`
`
`
`
`CALCULATE CURRENT
`RMS FOR PHASES
`A, B, C. CALCULATE I
`GROUND NEUTRAL + AVG.
`
`
`
`422
`
`424.
`
`PROCESS CURRENT
`NBALANCE
`PROTECTION
`
`S
`
`
`
`I$ THIS A
`PROTECTIVE FUNCTION
`OR EMULATION
`
`
`
`
`7
`
`

`

`U.S. Patent
`
`May10, 1994
`
`Sheet 7 of 14
`
`5,311,392
`
`(2)
`
`FIG. 4b
`
`426
`1S THIS
`
`
`OYSTEM IN
`EMULATION?
`
`
`NO
`
`PROCESS CURRENT
`SETPOINTS
`
`42
`
`430
`
`
`
` DOES BREAKER
`432
`UPDATE
`YESeelNON-VOLATILE
`COUNTER NEED
`NON-VOLATILE
`
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`UPDATE?
`
`
`434
`
`436
`
`RELEASE ACCESS
`10 NON-VOLATILE
`MEMORY
`
`CLEAR CURRENT
`SUM SQUARE FLAG
`FOR ANOTHER SAMPLE
`
`PROTECTION
`
`438Fprocess DISITAL
`SHADOW
`
`44¢~
`
`444
`
`YES
`TaLock ACCESS 10
`NON- VOLATILE
`MEMORY
`
`PROCESS POWER
`METERING
`
`8
`
`

`

`U.S. Patent
`
`May10, 1994
`
`_ Sheet 8 of 14
`
`5,311,392
`
`FIG. 4c
`
`446
`
`448
`
`450
`
`
`RELEASE ACCESS
`TQ NON-VOLATILE
`
`MEMORY
`
`
`
`
`
`CLEAR POWER
`METERING FLAG
`FOR ANOTHER SAMPLE
`
`CHECK FOR SEABUS
`COMMUNICATION.
`PROCESS ANY PACKETS
`
`
`1S THIS
`
`SYSTEM IN
`EMULATION?
`
`
`
`
`
`
`
`
`
`
`
`404~TFacock ACCESS T0
`NON-VOLATILE
`MEMORY
`
`456
`
`IS THIS A
`PROTECTIVE AND
`POWER METERING
`SYSTEM?
`
`
`
`458
`
`PROCESS POWER
`PROTECTION
`
`9
`
`

`

`U.S. Patent
`
`May 10, 1994
`
`Sheet 9 of 14
`
`5,311,392
`
`FIG. 4d
`
`15 THIS A
`POWER METERING
`SYSTEM?
`
`460
`
`
`PROCESS POWER
`SETPOINTS
`
`RELEASE ACCESS
`TO NON-VDLATILE
`MEMORY
`
`CHECK FOR
`SEABUS COMMUNICATION.
`PROCESS ANY PACKETS
`
`UPDATE MIN/MAX
`CURRENT, VOLTAGE,
`KVFR, KWATT VALUES
`
`462
`
`464
`
`466
`
`468
`
`ATe
`
`ADJUST KW
`HOURS, KW DEMAND
`+ KVAR HOURS
`
`=<ES
`
`
`
`TIME 10
`
`
`00 KW HRS?
`(45)
`
`
`
`470
`
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`
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`
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`
`476
`|
`TIME
`10 STORE
`ves_|BLOCK ACCESS TO
`O-
`NON-VOLATILE
`(5)
`KWN, KVAL IN
`NON-VOLATILE?
`
`474
`
`
`
`
`
`MEMORY
`
`10
`
`

`

`U.S. Patent
`
`May10, 1994
`
`Sheet 10 of 14
`
`5,311,392
`
`FIG. 4e
`
`UPDATE NON-VOLATILE|478
`VEWORY KWH.
`KH REV, KVARH
`
`RELEASE ACCESS
`TO NON-VOLATILE
`MEMORY
`
`CLEAR THE
`STORE KWH, KW
`DEMAND + KVARH FLAG
`
`480
`
`482
`
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`
`COMMUNICATIONS.
`PROCESS ANY PACKETS
`
`484
`
`(F)
`
`
`
`
`IS SUN
`1S SUM
`I$ SUM
`
`
`
`SQUARE FOR
`SQUARE FOR
`
`
`SQUARE FOR
`
`SHORT TIME
`LONG TIME
`
`TRIP RMS
`PICKUP
`PICKUP
`
`
`READY?
`
`
`READY?
`READY?
`
`
`
`
`490
`
`
`486
`
`48¢~.
`
`494
`
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`NON-VOLATILE
`MEMORY
`
`PROCESS RMS
`CALCULATIONS FOR
`PICKUP + TRIP
`
`11
`
`

`

`U.S, Patent
`
`May10, 1994
`
`Sheet 11 of 14
`
`5,311,392
`
`(6)
`
`FIG. 4f
`
`502
`
`© CURRENT
`
`CALIBRATION
`REQUESTED?
`
`YEg
`SET NUMBER OF
`CALIBRATIONS 10
`PERFORM
`
`AGN
`
`RELEASE ACCESS
`TO NON-VOLATILE
`MEMORY
`
`498
`.
`
`300
`
`LOG BACKGROUND
`EVENTS
`ITPU, STPU + INACTIVE
`
`CHECK FOR SEABUS
`COMMUNICATION.
`PROCESS ANY PACKETS
`
`a0
`
`506
`
`308~\
`
`310
`
`WAIT FOR CURRENT
`+ POWER SUM
`OF SQUARES
`
`[BLOCK ACCESS TO
`NON-VOLATILE
`MEMORY
`
`CALIBRATE
`SYSTEM + REDUCE
`NUMBER TO PERFORM
`
`12|RELEASE ACCESS
`TO NON-VOLATILE
`MEMORY
`
`314
`
`CLEAR CURRENT +
`SUM SQUARE FLAG
`
`FOR ANOTHER SAMPLE
`
`(7)
`
`12
`
`

`

`U.S. Patent
`
`May 10, 1994
`
`Sheet 12 of 14
`
`5,311,392
`
`FIG. 49
`
`
`MORE CURRENT
`
`CALIBRATION 10
`PERFORM?
`
` 516
`
` TIME
`
`520TBLock ACCESS TO
`
`TO CHECKSUM
`NON-VOLATILE
`
`NON-VOLATILE
`MEMORY
`MEMORY?
`
` 3¢e~
`CHECKSUM SETPOINT
`CALIBRATION +
`IN NON-VOLATILE
`CONFIGURATION TABLE
`
` I$ THIS
`
`926
`
` CHECKSUM RELAY
`
`IN NON-VOLATILE
`PROTECTION TABLE
` | oe
`
` 328~RELEASE ACCESS
`
`524
`
`
`A PROTECTIVE
`
`FUNCTION
`
`SYSTEM?
`
`TO NON-VOLATILE
`MEMORY
`
`13
`
`

`

`U.S. Patent
`
`May 10, 1994
`
`Sheet 13 of 14
`
`5,311,392
`
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`U.S. Patent
`
`May 10, 1994
`
`Sheet 14 of 14
`
`5,311,392
`
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`

`1
`
`5,311,392
`
`DUAL PROCESSOR ELECTRIC POWER TRIP
`UNIT
`
`A portion of the disclosure of this patent document
`contains material which is subject to copyright protec-
`tion. The copyright owner has no objection to the fac-
`simile reproduction by anyone of the patent document
`or the patent disclosure as it appears in the Patent and
`Trademark Office patent file or records, but otherwise 10
`reserves all copyright rights whatsoever.
`BACKGROUNDOF THE INVENTION
`
`5
`
`The present invention is directed to apparatus for
`monitoring an electric powerdistribution system and in 15
`particular to a multiprocessor unit which provides two
`levels of circuit protection.
`In a typical factory powerdistribution system, high-
`voltage (i.e. greater than 1,000 volts) power provided
`by the power company generation station is stepped
`down to low voltage power using a transformer. The
`low voltage power is then distributed around the fac-
`tory to power equipment such as, motors, welding ma-
`chinery and large computers.
`Powerdistribution systems of this type are typically 25
`divided into branches, where each branch supplies
`power to a portion of the factory. The entire power
`distribution system is protected byinstalling low volt-
`age fuses or circuit breakers in each branch so that a
`fault such as a short circuit in a piece of equipment
`supplied by one branch will not affect the powerdistrib-
`uted to equipment coupled to the remaining branches.
`Typically, these low voltage circuit breakers detect
`more than just large overcurrent conditions caused by
`short circuit faults. In addition, they detect lower level 35
`long-time overcurrent conditions and excessive ground
`current. The simplest form of circuit breaker is ther-
`mally tripped as a result of heating caused by an over-
`current condition. This type of breaker is best for de-
`tecting relatively low level overcurrent conditions since
`it measures the cumulative heating effect of the low-
`level overcurrent condition over a period of time. A
`breaker ofthis type, however, may respond too slowly
`to provide effective protection against high-current
`short circuit conditions.
`Anothertype of breaker monitors the level of current
`being passed through the branch circuit and trips the
`breaker when the current exceeds a predefined maxi-
`mum value. Breakers of this type typically include a
`microcontroller coupled to one or more current sen- 50
`sors. The microcontroller continually monitors the digi-
`tized current values using a curve which defines permis-
`sible time frames in which both low-level and high-level
`overcurrent conditions may exist. If an overcurrent
`condition is maintained for longer than its permissible 55
`time frame, the breakeris tripped.
`Although this type of breaker provides good protec-
`tion against both long-time and short-time overcurrent
`conditions,if it does not calculate RMS current values,
`it may erroneously trip the circuit when a nonlinear
`load, such as a welding machine,
`is coupled to the
`branch that it is protecting. Non-linear loads tend to
`produce harmonics in the current waveform. These
`harmonics tend to distort the current waveform, caus-
`ing it to exhibit peak values which are augmented at the 65
`harmonic frequencies. When the microcontroller,
`which assumes a sinusoidal current waveform, detects
`these peaks, it may trip the breaker even though the
`
`40
`
`45
`
`60
`
`16
`
`2
`heating effect of the distorted waveform may notre-
`quire that the circuit be broken.
`Since circuit breakers of the type described above
`only monitor overcurrent conditions, other types of
`faults such as over or under voltage conditions and
`phase imbalances may be missed unless or until they
`result in an overcurrent fault. Typically, circuit protec-
`tion for faults of this type requires special purposeline
`monitoring and relaying equipment, separate from the
`overcurrent breakers.
`Another problem with many existing circuit breakers
`involves the time required to restore the branch to oper-
`ation once the breaker has been tripped. For purely
`transient faults, such as a power surge during an electri-
`cal storm, a technician must go onto the factory floor,
`locate the tripped breakers and reset them. Depending
`on the experience and knowledgeofthe technician, this
`may take a few minutes or a few hours. In this instance,
`however,
`the delay may be minimized by using a
`breaker with an automatic recloser.
`Faults caused by the equipment that is powered by
`the branch maybe moredifficult to locate. Many circuit
`breakers provide no information on the conditions pres-
`ent at the time the breaker was tripped. Thus, the tech-
`nician may needto install power monitors on each piece
`of equipment to determine the magnitude and duration
`of the current that caused the fault. Due to the limited
`information provided by currently available breakers,
`faults of this type may take several days to locate and
`correct.
`A final problem with existing low-voltage circuit
`breaker systems concerns the lack of effective backup
`protection if the breaker shouldfail to trip. This prob-
`lem is more of a concern with microcontroller based
`trip units than with the older thermal trip units. In gen-
`eral, effective backup protection may includea fuse,in
`series with the branchline, which blowsat a short-cir-
`cuit current slightly higher than the short-circuit cur-
`rent of the breaker. If the microcontroller or any ofits
`associated circuitry fails, a lower-level overcurrent
`condition may damage the distribution system and/or
`the equipment being protected before the backup fuseis
`blown.
`
`SUMMARY OF THE INVENTION
`
`The present invention is embodied in a low-voltage
`electronic circuit breaker system which includes two
`controller circuits. The first controller circuit monitors
`the level of current flowing through the branch line
`being protected and trips the breaker when oneofa set
`of overcurrent conditions, defined by their magnitude
`and duration, is detected. The second controller moni-
`tors,
`in parallel with the first controller, the current
`through the branch and detects overcurrent conditions
`having magnitudes and durations greater than those
`detected by the first controller and trips the breaker to
`provide backup protection for the first controller.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a schematic diagram, partly in block dia-
`gram form of a power distribution system which in-
`cludesa trip unit containing an embodimentofthe pres-
`ent invention.
`FIG.1a is a block diagram which illustrates the data
`communications interconnections of selected ones of
`the trip units shown in FIG. 1.
`
`16
`
`

`

`3
`FIG.2 is a block diagram, partly in schematic dia-
`gram form ofa trip unit suitable for use in the system
`shown in FIGS.1 and 1a.
`FIG.2a is an elevation drawing of the front panel of
`one of the trip units shown in FIGS. 1 and 1a.
`FIGS. 3a and 3 are graphs of current versus time
`which are useful for describing the operation of the trip
`unit shown in FIG.2.
`FIGS.42 through 4¢ are flow-chart diagrams which
`are useful for describing the operation of the trip unit
`shown in FIG.2.
`FIGS.5a through 5c are timing diagrams which are
`useful for describing the current and voltage sampling
`scheme usedby the trip unit shown in FIG. 2.
`FIG. 6 is a flow-chart diagram which is useful for
`describing the operation of the trip unit shown in FIG.
`2.
`
`DETAILED DESCRIPTION
`Overview
`
`The present invention is embodied in a dual processor
`low-voltage circuit breaker and power line monitoring
`system. In this system, which is shownin greater detail
`in FIGS.2 and 2, the two processors are implemented
`using respective microcontroller circuits 210 and 250.
`Referring to FIG. 2, the microcontroller 210 moni-
`tors the current flowing through the three-phase power
`lines 2002, 2005 and 200c to detect overcurrent condi-
`tions and to trip the circuit breaker 202 immediately if a
`large overcurrent is detected orif, after a programma-
`ble delay time, a relatively small overcurrent is de-
`tected.
`The microcontroller 250 monitors the potential de-
`veloped across the powerlines 2002, 2005 and 200c in
`addition to monitoring the current flowing through the
`powerlines 2002, 200 and 200c. From these values, the
`controller 250 calculates the power flowing through the
`lines and the frequency of the power signal. Based on
`these monitored parameters, the microcontroller 250
`can trip the breaker or change the state of an alarm
`output signal. The alarm signal may be used to actuate
`an alarm device, such as a light and/or a buzzer, or it
`may be used, through an interposing relay to open the
`circuit breaker 202. The microcontroller 250 can also
`reclose the breaker after receiving a specific command
`from the host computer 140.
`In addition to its protection functions, the microcon-
`troller 250 logs minima and maximafor various ones of
`the monitored variables and logs the occurrence of
`events such as the detection of overcurrent conditions,
`also known as pickup events, and trip events.
`The logged items may be monitored by a remote host
`computer 140. The computer 140, shown in FIG.1a, is
`coupled to multiple trip units to provide, at one loca-
`tion, the continuingstatusof the electric powerdistribu-
`tion system. In addition, many of these logged items
`may be monitored using a local breaker display unit 117.
`The host computer 140 can also be used to control the
`operation of the processor 250.
`The microcontroller 250 provides backup overcur-
`rent protection by tripping the breaker 202 at overcur-
`rent levels greater than those used by the microcon-
`troller 210. In addition, the microcontroller 250 uses a
`power supply which is separate and distinct from that
`used by the microcontroller 210. All input and output
`signals used by the microcontroller 250, including the
`operational powersignal, are electrically isolated from
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`the outside circuitry to prevent damageto the trip unit
`circuitry.
`DETAILED DESCRIPTION OF THE
`EXEMPLARY EMBODIMENT OF THE
`INVENTION
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`FIG.1 is a diagram of an exemplary electrical power
`distribution system. The system has been simplified to
`facilitate the explanation of the invention. In the FIG-
`URE,all of the powerlines are three-phase lines even
`though only oneline is shown.
`As shownin FIG.1, a high voltage source 110, which
`may be a power companysubstation, provides a high
`voltage electrical power signal to the primary winding
`of a transformer 112. The secondary winding of the
`transformer provides three-phase low voltage power to
`the powerdistribution system of, for example, a factory.
`The low voltage poweris distributed around the fac-
`tory floor through respective step-down transformers
`124, 126, 128 and 130 to provide power to equipment
`represented as respective loads 125, 127, 129 and 131.
`The powerdistribution system is protected by multi-
`ple trip units 114, 116, 118, 120 and 122. In this configu-
`ration, the trip units 116, 118, 120 and 122 each protect
`the system from faults occurring on a respective branch
`of the powerdistribution system while the trip unit 114
`protects the transformer 112 from faults not handled by
`one or more ofthe other trip units and from faults on
`the main distribution bus 113.
`FIG.1a is a block diagram whichillustrates how the
`trip units are connected to the host computer 140 to
`allow the power distribution system to be monitored
`from a central location. To simplify the drawing, only
`three of the trip units 114, 116 and 118 are shown in
`FIG.1a, It is contemplated, however,thatall of the trip
`units may be connected to the host computer 140, In
`this embodiment of the invention, the host computer
`140 may be an ACCESSTM electrical distribution
`communication system, available from Siemens Energy
`and Automation, Inc.
`The host computer 140 is coupled to a display device
`142 and a keyboard 144. As set forth below, the host
`computer 140 may periodically poll each of the trip
`units, via a multi-drop line 141, to monitor the status of
`the powerdistribution system at the main bus and at
`each branch bus.In addition, the host computer 140 can
`issue commandsto the varioustrip units causing them to
`open or close their respective breakers or to change the
`levels at which pickup and trip events occur for certain
`ones of the monitored parameters.
`Furthermore, as shown in FIG. 1a, each of the trip
`units 114, 116 and 118 may be coupled to a respective
`breaker display unit (BDU) 115, 117 and 119 by a sepa-
`rate data communications port. The BDU maybe used
`to monitor the status and history of the powerdistribu-
`tion system, at the trip unit. This monitoring function is
`implemented to be substantially independent of the
`monitoring functions of the main computer 140.
`FIG.2 is a block diagram, partly in schematic dia-
`gram form of an exemplary trip unit which controls a
`breaker 202. For the purpose of this explanation, the
`trip unit is assumed to be the unit 116 whichisolatesits
`branch line from the main bus 113 as shown in FIG.1.
`Thetrip unit includes an overcurrent microcomputer
`210 which implements the basic overcurrent protection
`functions of the trip unit and a communications mi-
`crocomputer 250 which implements data communica-
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`tions functions and provides auxiliary circuit protection
`functions.
`The exemplary overcurrent microcomputer 210 in-
`cludes an 80C49 microcontroller, available from Intel
`Corp, which includes an internal memory 211. The
`memory 211 includes read only memory (ROM) for
`program and fixed-value data storage as well as a small
`scratchpad random access memory (RAM).
`Electrical current flowing through the three-phase
`lines 200a, 200b and 200c is sensed by three current
`transformers 204. In the exemplary embodiment of the
`invention,
`the current
`transformers 204 are imple-
`mented as respective secondary windings wrapped
`around each of the bus bars 200g, 2006 and 200c. Cur-
`rent induced in the secondary winding is stepped down
`by three respective current transformers (not shown)
`internal to the trip unit 116. These stepped-down cur-
`rents are converted to voltage by three resistors (not
`shown) which are also internal to the trip unit. These
`voltages are applied to a multiplexed analog to digital
`converter (ADC) 212. The ADC 212, under control of
`the microcomputer 210, sequentially digitizes the volt-
`ages generated by the three stepped-down currents.
`These digitized values are supplied to the overcurrent
`microcomputer 210 as data values.
`In additionto the current sensors on the three phase
`lines 200c, 2005 and 200c,
`the trip unit may also be
`configured to accept ground current and neutral cur-
`rent at separate current sensor input terminals. As set
`forth below,the neutral current input signal is used only
`by the communications microcomputer 250. The
`ground and neutral current lines are not shown in FIG.
`2 to avoid unnecessary complexity in the drawing.
`Operational power for the overcurrent microcom-
`puter 210 is supplied from the current transformers 204.
`As shown in FIG. 2, the secondary windings of the
`transformers 204 are coupled to power supply circuitry
`214 which rectifies the provided alternating current
`powersignal to generate direct current (DC) opera-
`tional power for the overcurrent microcomputer 210.
`The powersupply 214is also coupled to provide opera-
`tional power to the ADC 212, watchdogcircuitry 218
`and front panel display 220.
`The front panel switches 216 are used to set the
`pickup and trip levels used for primary overcurrent
`protection. As set forth above, a pickuplevelis an over-
`current condition which may cause the unit to trip the
`circuit breaker, either after a delay dependent on the
`level of the detected current, or instantaneously, for
`large overcurrent conditions. The configuration of the
`front panel switches 216 is described below with refer-
`ence to FIG.2a.
`The watchdog circuit 218 continually monitors the
`status of the microcomputer 210. The exemplary circuit
`218 expects to receive a pulse signal from the mi-
`crocomputer 210 at regular intervals. If it fails to re-
`ceive a pulse within an interval centered about an ex-
`pected time, it causes a liquid crystal device (LCD)
`array on the front panel display to display the message
`“DISABLE” and attempts to reset the overcurrent
`microcomputer 210. Evenifit is successful in restarting
`the microcomputer 210, the watchdogcircuit continues
`to display the DISABLE message once a failure has
`been detected.
`If, during its current monitoring, the microcontroller
`210 detects a large overcurrent condition indicative of a
`short circuit condition, or a smaller overcurrent condi-
`tion which persists for longer than a predefined time
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`interval, the microcontroller 210 activates the trip actu-
`ator 230, causing the breaker 202 to break the connec-
`tion between the branchlines 2004, 2005 and 200c and
`the main bus 113.
`In addition to tripping the breaker, the microcom-
`puter 210 indicates on the front panel display 220 the
`type of event which caused thetrip. If the event was a
`long-time overcurrent condition, the word “OVER-
`LOAD”is displayed on the front panel display 220. If
`the event was a ground overcurrent, sensed from the
`ground current input terminal (not shown) to the ADC
`212, the words “GROUND FAULT”aredisplayed. If
`the event was a large overcurrent, causing a short time
`or instantaneoustrip, the words “SHORT CIRCUIT”
`are displayed. In addition to these event displays, the
`microcomputer 210 can activate two light emitting
`diodes (LEDs) on the front panel. One of these LEDsis
`lighted when a long-time pickup event occurs and the
`otheris activated when a short-time pickup or a ground
`fault pickup event has occurred.
`In addition to displaying these events, the overcur-
`rent microcomputer 210 provides signals via a digital
`message path (DMP)for events which have occurred to
`the communications microcomputer 250. These signals
`include all of the signals that activate the front panel
`display and, in addition, signals that indicate when a
`short-time or long-time pickup event has occurred or a
`trip event has occurred.
`FIG.2 is an elevation drawing of an exemplary front
`panel which may be used with this embodiment of the
`invention. The front panel is described now sinceit
`primarily relates to the overcurrent microcomputer
`210.
`The front panel display 220 includes an LCD array
`2202 the long-time pickup LED 220 and the short-
`time/ground fault pickup LED 220c,
`The front panel switches include a switch 216a for
`setting the current level which will cause an instanta-
`neoustrip of the breaker 202. This currentis specified a
`multiple of the rated current of the current sensors 204.
`In the exemplary embodimentof the invention, this may
`be set to between twice and fifteen times the rated cur-
`rent of the sensor. Switches 216 and 216¢ set the
`pickup level and time delay for a long-time trip. The
`exemplary pickup level may be set to between one-half
`of the rated current and the rated current. The delay
`may be set to between 3.5 seconds and 30 seconds.
`Switches 216d and 216¢ determine the short-time trip
`settings. A short-time pickup may be set to occur for
`sensed currents between twice and twelve times the
`long-time pickup setting while the delay from pickup to
`trip may be set to between 0.08 and 0.4 seconds.
`The parameters used for a ground-fault trip are con-
`trolled by the front panel switches 216f and216g. The
`ground-fault pickup may be set to between 20% and
`60% of the rated current for the ground current sensor
`and the delay can be set to between 0.1 seconds and 0.4
`seconds.
`In addition to the display 220 and control switches
`216, the front panel includes a connector 264 whichis
`used by the communications microcomputer 250 to
`implement data communications with the breaker dis-
`play unit (BDU) 117. A rear connector (not shown)
`couples the microcomputer 250 with the host computer
`140.
`Referring again to FIG. 2, the communications mi-
`crocomputer includes a 68HCIIF1 microcontroller
`available from Motorola, Inc. and a memory. This
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`memory includes an external programmable read-only
`memory (PROM) 253, which is used to hold the pro-
`gram instructions and an a memory 251 whichis inter-
`nal to the microcontroller. In this embodiment of the
`invention, the PROM 253is a 27C256 integrated circuit
`available from Intel Corp. The program stored in the ©
`PROM 253 is included as a software appendix to the
`present application.
`The internal memory includes a non-volatile random
`access memory (NVRAM)portion, which is used to
`hold certain log entries that may be provided to either
`the host computer 140 or the BDU 117 and a RAM
`portion which is used to hold log entries which may
`change frequently as well as flags and partial values of
`calculations. °
`Operational poweris applied to the microcomputer
`250 and to the circuitry to whichit is coupled from an
`external 15 volt direct current instrument supply 260.
`The operational power for the microcomputer 250 is
`further shielded byan isolating power supply 258inter-
`posed between the microcomputer 250 and the instru-
`ment power supply 260. This isolating power supply
`258 may beinclude, for example, a conventional DC to
`DC converter.
`.
`The supply 260 is desirably isolated from the branch
`lines 200 so that the communications microcomputer
`250 can continue to operate even when the breaker 202
`is open ortripped. In addition, this alternate operational
`power source shields the communications processor
`from power problems which may disable the overcur-
`rent microcomputer 210.
`In this embodiment of the invention, the communica-
`tions microcomputer 250 performs both communica-
`tions and monitoring functions. In addition to monitor-
`ing the current flowing through the lines,
`the mi-
`crocomputer 250 monitors the voltage between the
`respective three phase lines and, using this voltage and
`current data, monitors power, energy and imbalances
`among the three phases in either voltage or current.
`Data on the current flowing through the lines 200a,
`2006 and 200¢ is collected by an ADC 252 which is
`coupled, in parallel with the ADC 212, to the current
`sensors 204. In addition, the ADC 252 is coupled to a
`potential
`transformer module 254 which provides a
`measure of the voltage between each of the three pha-
`ses. The ADC 252 may also be coupled to receive
`groundand neutral currents from sensors coupled to the
`branch lines 200. In an exemplary system, these sensors
`mayinclude a circuit (not shown) which derives ground
`current as the vector sum of the three phase currents
`and a conventional current transformer coupled to the
`neutral line (not shown) of the branch lines 200.
`The ADC 252is a multiplexed ADC which provides
`instantaneous samples of one of three current signals
`(five if ground and neutral are used) and three voltage
`signals. The ADCis controlled by the microcomputer
`250 to determine which sample to provide at any given
`time.
`The communications microcomputer 250 is coupled
`to the COMM WATCHLED 256onthe front panel of
`the trip unit. The function and operation of this LED is
`described in detail below with reference to FIG.6.
`As set forth above, the communications microcom-
`puter 250 provides two substantially independent com-
`munications links. One ofthese links is a dedicated com-
`munications port 262 which is coupled to the BDU 117.
`The other communications link is an RS-485 port 266
`through which the communications microprocessoris
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`coupled to the host computer 140. Both ofthe ports 262
`and 266 include conventional opto-isolators to prevent
`anyelectrical connection between the communications
`microcomputer 250 and the BDU 117 or the host com-
`puter 140.
`The communications microcomputer 250 is also con-
`figured with an opto-isolated alarm signal output line
`268, an opto-isolated breaker position input signalline,
`an output line to the trip actuator 230 and an opto-
`isolated breaker-close signal output
`line 269. These
`signal lines allow the communications microcomputer
`250 to trip, open or close the breaker 202 and, in addi-
`tion, allow it to log the state of the breaker 202. The
`alarm line 268 may be coupled to an alarm device so
`that conditions detected by the communications mi-
`crocomputer 250 which activate the alarm signal acti-
`vate the alarm device.
`Alternatively, as shown in FIG.2, the alarm line 268
`may be coupled to an interposing relay 270 which is
`coupled to control circuitry (not shown)in the breaker
`202. In this configuration, when the alarm signal is acti-
`vated, the interposing relay closes, causing the breaker
`‘to open. The breaker may be closed by activating the
`breaker-close output line 269.
`The input signal line 272 is coupled to the breaker
`control circuitry to determine if the breaker is open or
`closed. If the breaker 202 has been opened using the
`interposing relay 270 or tripped using the trip actuator
`230,this signal indicates that the breaker is open.
`The communications microcomputer 250 has three
`functionsin the trip unit. First, it directly monitors line
`current and interline voltage for each of the three or
`four wires of the branch line 200 through the ADC 252
`and, from these values calculates other values which
`indicate the status of the line 200. Second, it controls
`communication between the trip unit 116 and the host
`comp