||||l|||||l|l|IllIllll||l|||l|||lllll||||||l|||lllllIllllllllllllllllllllll
`IJS005311392IX
`,
`5,311,392
`[11] Patent Number:
`[19]
`Umted States Patent
`Kinney et a1.
`[45] Date of Patent: May 10, 1994
`
`
`[54] DUAL PROCESSOR ELECTRIC POWER
`TRIP UNIT
`
`[75]
`
`Inventors: Michael A. Kinney; Stephen F.
`Gillette, both of Raleigh, N.C.
`
`4,710,845 12/1987 Demeyer ............................... 361/96
`..
`4,811,154 3/1989 Trenkler et a1.
`361/93
`
`324/142
`9/1989 Milkovic ...........
`4,870,351
`
`. 364/483
`4,996,646
`2/1991 Fartington
`7/1991 Hartman ............................... 371/29
`5,031,178
`
`[73] Assignee:
`
`Siemens Energy & Automation, Inc.,
`'Alpharetta, Ga.
`
`Primary Examiner—A. D- Pellinen
`Assistant Examiner—S. Jackson
`
`[21] Appl. No.: 753,286
`
`[22] Filed:
`
`Aug. 30, 1991
`
`Int. CLS ............................................... HOZH 3/08
`[51]
`[52] US. Cl. ........................................ 361/93; 361/96;
`_
`361/87
`[58] Field of Search ....................... 361/21, 23, 25, 31,
`3151/42, 47, 50, 76, 87, 88, 96, 62, 67, 93
`References Cited
`
`[56]
`
`U-S- PATENT DOCUMENTS
`4,470,092 9/1984 Lombardi .............................. 361/23
`4,689,712
`8/1987 Demeyer ............................ 361/96
`
`[57]
`
`ABSTRACI‘
`
`A low voltage electric power monitoring and circuit
`breaker system includes two processors. The first pro-
`CCSSOl' activates the circuit breaker when an OVCICUI-
`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 the first processor to activate
`the breaker. If a current of this magnitude is detected,
`the second processor activates the circuit breaker as a
`backup protection for the first circuit breaker.
`
`18 Claims, 14 Drawing Sheets
`
`113
`
`"" 202 r """"""""""""""""""""""""""" 1
`--
`POTTER
`FRONT PANEL
`HATEHIDB
`l
`SUPPLY
`SWITCHES
`CIRCUIT
`I
`
`i
`
`:
`FRONT PANEL
`351me
`|
`TRIP
`ACTUATOR
`
`
`230
`
`
`1|
`UMP
`
`
`
`I
`
`""""
`
`OVER CURRENT
`HICHOCOMPUTER
`
`210
`
`250
`
`COMMUNICATIONS 1‘ HONITUTING
`_______ MICROCOMPUTEH
`MEMORY
`:
`
`253
`
`262
`
`COWTCH
`
`ISOLATED
`
`ISOLATED
`
`ADC
`
`251
`255
`
`ISOLATED
`PORT
`SUPPLY
`;
`259
`CLOSE
`L """"""""""""""""""""""""""" J
`,
`15V DC
`SUPPLY m 11
`TRIP LNIT115
`
`25°
`
`7
`
`
`
`ISOLATED
`INPUT
`
`1133111”
`CLOSE
`
`ISOLATED
`“BOATS
`
`'
`
`:
`
`;
`
`
`NEW“
`25“
`,0 ms,
`COMPUTER 140
`
`BREAKER
`POSITION
`
`270
`
`INTERPOSING
`RELAY
`
`271
`
`TO
`BREAKER
`19111101?
`
`m
`BREAKER
`CONTROL
`HIRING
`
`APPLE 1027
`
`1
`
`APPLE 1027
`
`

`

`US. Patent
`
`May 10, 1994
`
`Sheet 1 of 14
`
`5,311,392
`
`125
`
`124
`
`1 F
`
`IG.
`
`N:91
`.—
`
`110
`
`2
`
`

`

`US. Patent
`
`May 10, 1994
`
`Sheet 2 of 14
`
`5,311,392
`
`«2
`
`m.“.mHl
`
`3
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`3
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`

`

`US. Patent
`
`May 10, 1994
`
`Sheet 3 of 14
`
`5,311,392
`
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`

`US. Patent
`
`May 10, 1994
`
`Sheet 4 of 14
`
`5,311,392
`
`FIG. Ea
`
`220D
`
`SHORT
`CIRCUIT
`
`LONG TIME PICKUP
`
`SHORT TIME
`GROUND PICKUP
`
`INSTANTANEDUS
`
`SETTING
`
`DELAY
`
`PICKUP
`
`SHORT TIME
`
`BRDUND FAULT
`
`;;246
`
`PICKUP
`
`DELAY
`
`PICKUP
`
`DELAY
`
`CDMM HATCH
`
`5
`
`

`

`U.S. Patent
`
`May 10, 1994
`
`Sheet 5 of 14
`
`5,311,392
`
`
`
`LL]
`z—u
`._..
`
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`6
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`

`

`US. Patent
`
`May 10, 1994
`
`Sheet 6 of 14
`
`5,311,392
`
`FIG. 4a
`
`INIT HARDWARE
`+
`
`VARIABLES
`
`41°
`
`412
`
`LOG A START
`UP EVENT
`
`414
`
`CHECK FOR SEABUS
`COMMUNICATION.
`PROCESS ANY PACKETS
`
`~ 0
`
`415
`
`
`
`
` SUM OF
`SOUARES FOR
`
`CURRENT
`READY?
`
`418
`
`
`YES
`
`BLOCK ACCESS TO
`NON-VOLATILE
`MEMORY
`
`420
`
`
`CALCULATE CURRENT
`RMS FOR PHASES
`A. B. C. CALCULATE I
`GROUND NEUTRAL + AVG.
`
`
`
`
`422
`
`
`IS THIS A
`PROTECTIVE FUNCTION
`OR EMULATION
`SYSTEM?
`
`‘24
`
`PROCESS CURRENT
`
`PROTECTION
`UNBALANCE
`
`o
`
`7
`
`

`

`US. Patent
`
`May 10, 1994
`
`Sheet 7 of 14
`
`5,311,392
`
`a
`
`FIG. 4b
`
`426
`
`
`IS THIS
`
`
`
`SYSTEM IN
`EMULATTON?
`
`
`NI
`
`RRUCESS CURRENT
`SETPUINTS
`
`430
`
`
` DUES BREAKER
`
`COUNTER NEED
`NON-VOLATILE
`
`UPDATE?
`
`
`YES
`
`UPDATE
`NUN-VULATILE
`MENURY COPY
`
`428
`
`432
`
`434
`
`435
`
`438
`
`RELEASE ACCESS
`TU NUN-voLATTLE
`NENURv
`
`CLEAR CURRENT
`SUN SUUARE FLAG
`FOR ANUTHER SAMPLE
`
`PROCESS DIGITAL
`
`SRAUUN
`
`RRUTECTTUN
`
`440
`
`READY
`
`
`
`
`EUR RUNER
`
`
`METERING?
`
`
`YES
`
`”0 a
`
`442
`
`BLOCK ACCESS TU
`NON-VDLATILE
`MEMORY
`
`444
`
`~
`
`PROCESS POHER
`METERING
`
`8
`
`

`

`US. Patent
`
`May 10, 1994
`
`. Sheet 3 of 14
`
`5,311,392
`
`FIG. 40
`
`445
`
`448
`
`45°
`
`
`
`IS THIS
`
`SYSTEM IN
`EMULATION?
`
`
`
`
`RELEASE ACCESS
`TO NON-VOLATILE
`MEMORY
`
`
` CLEAR POHER
`
`
`METERING FLAG
`FOR ANOTHER SAMPLE
`
`CHECK FDR SEABUS
`
`
`COMMUNICATION.
`PROCESS ANY PACKETS
`
`
`
`BLOCK ACCESS TO
`
`
`NON-VOLATILE
`MEMORY
`
`
` IS THIS A
`
`PROTECTIVE ANO
`POHER METERING
`
`SYSTEM?
`
`454
`
`456
`
`458
`
`PROCESS POMER
`PROTECTION
`
`9
`
`

`

`US. Patent
`
`May 10, 1994
`
`Sheet 9 of 14
`
`5,311,392
`
`FIG. 4d
`
`460
`
` IS THIS A
`POWER METERING
`
`SYSTEM?
`
`NU
`
`
`
`PROCESS POHER
`SETPUINTS
`
`RELEASE ACCESS
`TO NON-NOLATTLE
`MEMORY
`
`452
`
`454
`
`455
`
`CHECK FDR
`SEABUS COMMUNICATION.
`PROCESS ANY PACKETS
`
`‘53
`
`'
`
`UPOATE MINIMAX
`CURRENT, VOLTAOE.
`KVFR, KHATT VALUES
`
`472
`
`ADJUST AM
`HOURS. AN OEMANO
`
`+ KVAR HOURS
`
`YES
`
`
`TIME T0
`
`
`00 KT! HRS?
`
`
`(45)
`
`
`
`470
`
`N0
`
`e
`
`NO
`
`0
`
`474
`
`
`TlflE
`
`TO STORE
`
`ANN, KVAL IN
`
`
`NON-VOLATTLE?
`
`
`
`
`_
`
`YES
`
`BLOCK ACCESS TO
`NON-VDLATILE
`
`MEMORY
`
`.
`476
`
`a
`
`10
`
`10
`
`

`

`US. Patent
`
`May 10, 1994
`
`Sheet 10 of 14
`
`5,311,392
`
`FIG. 49
`
`478
`
`48°
`
`482
`
`UPDATE NON-VOLATILE
`MEMORY KHH,
`KHH REV, KVARH
`
`RELEASE ACCESS
`TO NON-VOLATILE
`MEMORY
`
`CLEAR THE
`STORE KHH, KM
`DEMAND + KVARH FLAG
`
`CHECK FOR SEABUS
`
`COMMUNICATIONS.
`PROCESS ANY PACKETS
`
`484
`
`0
`
`
`490
`
`
`
`IS SUM
`IS SUM
`IS SUM
`
`
`
`
`
`
`SQUARE FOR
`SQUARE FOR
`SQUARE FOR
`
`
`
`
`
`TRIP HMS
`SHORT TIME
`LONG IIME
`
`
`PICKUP
`PICKUP
`
`
`READY?
`
`
`READY?
`READY?
`
`
`
`
`486
`
`492
`
`494
`
`BLOCK ACCESS TO
`NDN-VOLATILE
`MEMORY
`
`PROCESS RMS
`CALCULATIONS FOR
`PICKUP + TRIP
`
`11
`
`11
`
`

`

`US. Patent
`
`May 10, 1994
`
`Sheet 11 of 14
`
`5,311,392
`
`a
`
`FIG. 41‘
`
`. 495
`
`RELEASE ACCESS
`TO NON-VOLATILE
`MEMORY
`
`498
`
`500
`
`LOG BACKGROUND
`EVENTS
`ITPU. STPU + INACTIVE
`
`CHECK FOR SEABUS
`COMMUNICATION.
`PROCESS ANY PACKETS
`
`504
`
`506
`
`503
`
`51°
`
`513
`
`514
`
`12
`
`502
`
`
` CURRENT
`
`
`CALIBRATION
`REOUESTEO?
`
`
`
`YES
`
`me
`
`SET NUMBER OF
`CALIBRATIONS TO
`PERFORM
`
`MATT FOR CURRENT
`+ POWER SUM
`OF SQUARES
`
`BLOCK ACCESS TO
`NON-VOLATILE
`MEMORY
`
`CALIBRATE
`SYSTEM + REDUCE
`NUMBER TO PERFORM
`
`RELEASE ACCESS
`TO NON-VOLATILE
`MEMORY
`
`CLEAR CURRENT +
`
`SUM SRUARE FLAG 0
`
`FOR ANOTHER SAMPLE
`
`12
`
`

`

`US. Patent
`
`May 10, 1994
`
`Sheet 12 of 14
`
`5,311,392
`
`FIG. 49
`
`
` MORE CURRENT
`CALIBRATION TO
`
`PERFORM?
`
` 516
`
`
`518
`520
`
`TIME
`
`
`BLOCK ACCESS TO
`
`TO CHECKSUM
`
`
`NON-VOLATILE
`
`NON-VOLATILE
`
`MEMORY
`
`
`MEMORY?
`
`
`
`
`
`
`
`
`522
`
`CHECKSUM SETPOINT
`CALIBRATION +
`CONFIGURATION TABLE
`IN NON-VOLATILE
`
`524
`
`
`IS THIS
`
`
`A PROTECTIVE
`
`FUNCTION
`
`SYSTEM?
`
`
`
`526
`CHECKSUM RELAY
`
`PROTECTION TABLE
`IN NON-VOLATILE
`
`
`
`
`
`
`
`528
`
`RELEASE ACCESS
`
`
`TO NON-VOLATILE
`
`
`MEMORY
`
`
`
`13
`
`13
`
`

`

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

`US. Patent
`
`blay 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
`reserves all copyright rights whatsoever.
`BACKGROUND OF THE INVENTION
`
`The present invention is directed to apparatus for
`monitoring an'electric power distribution system and in
`particular to a multiprocessor unit which provides two
`levels of circuit protection.
`In a typical factory power distribution 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.
`Power distribution systems of this type are typically
`divided into branches, where each branch supplies
`power to a portion of the factory. The entire power
`distribution system is protected by installing 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 power distrib-
`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
`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 of this type, however, may respond too slowly
`to provide effective protection against high-current
`short circuit conditions.
`Another type 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-
`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
`time frame, the breaker is 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
`harmonic frequencies. When the microcontroller,
`which assumes a sinusoidal current waveform, detects
`these peaks, it may trip the breaker even though the
`
`10
`
`15
`
`20
`
`25
`
`3O
`
`35
`
`45
`
`50
`
`55
`
`65
`
`16
`
`2
`heating effect of the distorted waveform may not re-
`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 purpose line
`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 knowledge of the 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 may be more difficult to locate. Many circuit
`breakers provide no information on the conditions pres
`cut at the time the breaker was tripped. Thus, the tech-
`nician may need to 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 should fail 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 include a fuse, in
`series with the branch line, which blows at a short-cir-
`cuit current slightly higher than the short-circuit cur-
`rent of the breaker. If the microcontroller or any of its
`associated circuitry fails, a lower-level overcurrent
`condition may damage the distribution system and/or
`the equipment being protected before the backup fuse is
`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 one of a 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-
`cludes a trip unit containing an embodiment of the pres-
`ent invention.
`FIG. la 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 of a trip unit suitable for use in the system
`shown in FIGS. 1 and la.
`FIG. 2a is an elevation drawing of the front panel of
`one of the trip units shown in FIGS. 1 and 1a.
`FIGS. 3:: and 3b are graphs of current versus time
`which are useful for describing the operation of the trip
`unit shown in FIG. 2.
`FIGS. 4a through 4g 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 used, by 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 shown in greater detail
`in FIGS. 2 and 2a, 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 200a, 2001) and 200C to detect overcurrent condi-
`tions and to trip the circuit breaker 202 immediately if a
`large overcurrent is detected or if, after a programma-
`ble delay time, a relatively small overcurrent is de-
`tected.
`The microcontroller 250 monitors the potential de—
`veloped across the power lines 200a, 2001) and 200:: in
`addition to monitoring the current flowing through the
`power lines 200a, 20% 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 maxima for 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. la, is
`coupled to multiple trip units to provide, at one loca-
`tion, the continuing status of the electric power distribu-
`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 power signal, are electrically isolated from
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`the outside circuitry to prevent damage to 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 power lines are three-phase lines even
`though only one line is shown.
`As shown in FIG. 1, a high voltage source 110, which
`may be a power company substation, 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 power distribution system of, for example, a factory.
`The low voltage power is 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 power distribution 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 power distribution system while the trip unit 114
`protects the transformer 112 from faults not handled by
`one or more of the other trip units and from faults on
`the main distribution bus 113.
`FIG. 1a is a block diagram which illustrates 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. la. It is contemplated, however, that all 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 ACCESS TM 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 power distribution system at the main bus and at
`each branch bus. In addition, the host computer 140 can
`issue commands to the various trip 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 may be used
`to monitor the status and history of the power distribu-
`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 which isolates its
`branch line from the main bus 113 as shown in FIG. 1.
`The trip 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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`5
`tions functions and provides auxiliary circuit protection
`functions.
`The exemplary overcurrent microcomputer 210 in-
`cludes an 80049 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, 20% and 2000 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 200a, 20015 and 200a 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 addition to the current sensors on the three phase
`lines 200a, 20017 and 200e,
`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
`power signal to generate direct current,(DC) opera-
`tional power for the overcurrent microcomputer 210.
`The power supply 214 is also coupled to provide opera-
`tional power to the ADC 212, watchdog circuitry 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 pickup level is 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. Even if it is successful in restarting
`the microcomputer 210, the watchdog circuit 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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`6
`interval, the microcontroller 210 activates the trip actu-
`ator 230, causing the breaker 202 to break the connec-
`tion between the branch lines 200a, 20% and 2000 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 the trip. 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” are displayed. If
`the event was a large overcurrent, causing a short time
`or instantaneous trip, 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 LEDs is
`lighted when a long-time pickup event occurs and the
`other is 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. 2a 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 since it
`primarily relates to the overcurrent microcomputer
`210.
`The front panel display 220 includes an LCD array
`2200 the long-time pickup LED 22017 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-
`neous trip of the breaker 202. This current is specified a
`multiple of the rated current of the current sensors 204.
`In the exemplary embodiment of the invention, this may
`be set to between twice and fifteen times the rated cur-
`rent of the sensor. Switches 21617 and 2150 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 216a 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 and 216g. 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 which is
`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 68HC] lFl 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 which is inter-
`nal to the microcontroller. In this embodiment of the
`invention, the PROM 253 is 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 power is applied to the microcomputer
`250 and to the circuitry to which it is coupled from an
`external 15 volt direct current instrument supply 260.
`The operational power for the microcomputer 250 is
`further shielded by an isolating power supply 258 inter-
`posed between the microcomputer 250 and the instru-
`ment power supply 260. This isolating power supply
`258 may be include, 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 or tripped. 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 2000,
`20017 and 200C 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
`ground and neutral currents from sensors coupled to the
`branch lines 200. In an exemplary system, these sensors
`may include 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 252 is 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 ADC is controlled by the microcomputer
`250 to determine which sample to provide at any given
`time.
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`The communications microcomputer 250 is coupled
`to the COMM WATCH LED 256 on the front panel of 60
`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 of these links is a dedicated com-
`munications port 262 which is coupled to the BDU 117.
`The other communications link is an RS485 port 266
`through which the communications microprocessor is
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`coupled to the host computer 140. Both of the ports 262
`and 266 include conventional opto-isolators to prevent
`any electrical 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 signal line,
`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
`' t