Electronic trip unit capable of analog and digital setting of circuit breaker setpoints

#Electronic trip units (trip units) for actuating the separable contacts in a circuit breaker are well known. An electronic trip unit typically comprises current sensors and may include voltage sensors that provide analog signals indicative of the power line signals. The analog signals are converted by an A/D (analog/digital) converter to digital signals that are processed by a microcontroller. The trip unit further includes RAM (random access memory), ROM (read only memory) and EEPROM (electronic erasable programmable read only memory) all of which interface with the microcontroller. The ROM includes trip unit application code, e.g., main functionality trip setting values, including initializing parameters, boot code, and operational parameters (e.g., trip setting instructions). Operational parameters for the application code are also stored in the EEPROM. An output of the electronic trip unit actuates a trip module, such as a solenoid that trips a mechanical operating mechanism. The mechanical operating mechanism, in turn, separates a pair of main contacts within the circuit breaker. When the contacts open, circuit current is prevented from flowing from one contact to the other, and electrical current is prevented from flowing to a load that is connected to the breaker. The electronic trip unit initiates a trip for instantaneous, short time, long time, ground fault and manual conditions.

#Circuit Breakers having electronic trip units are described in U.S. Pat. No. 4,672,501 entitled “Circuit Breaker and Protective Relay Unit”. Such trip units often include a keypad along with a display for accessing the processor and for entering and changing the trip unit settings. One such circuit breaker having a keypad and display is described within U.S. Pat. No. 4,870,531 entitled “Circuit Breaker With Removable Display & Keypad”.

#Remote setting of a circuit breaker is desirable to customers who would like to be able to adjust set points of multiple breakers from a single workstation. One such circuit breaker having a local keypad and display with remote setting capability is described within U.S. Pat. No. 5,019,956 entitled “Power Control Apparatus.” However, the circuit breaker described in U.S. Pat. No. 5,019,956 does not display the settings if there is no power to the trip unit.

#Referring to the exemplary drawings wherein like elements are numbered alike in the several FIGURES:

#FIG. 1 is a front plan view of a circuit breaker trip unit;

#FIG. 2 is a schematic block diagram of an exemplary embodiment of an electronic trip unit; and

#A circuit breaker electronic trip unit 10 similar to that used within the circuit breaker described within the aforementioned U.S. Pat. No. 4,672,501 is depicted in FIG. 1 and includes a cover 11 that is attached to a case 12 by means of screws 13. A plug-in indicator unit 14 is employed to display the condition of the contacts within an associated circuit breaker (not shown). Indicating diodes 15 as well as target indicators 16 provide such visual indication to an operator in lieu of the display arrangement described in the aforementioned U.S. Pat. No. 4,870,531. A first set of knobs 17 are used to enter the long time and short time overcurrent protection settings within the trip unit printed circuit board (not shown) while a second knob 21 is used to set the trip unit short circuit ratings. Knobs 17 and 21 are collectively referred to as analog dials shown generally at 23 in FIG. 2. A plug-in type rating plug 24 such as described in U.S. Pat. No. 4,649,455 entitled “Rating Plug for Molded Case Circuit Breaker” and U.S. Pat. No. 5,027,091 entitled “Molded Case Circuit Interrupter Rating Plug Keying and Interlock Arrangement” is used to set the circuit breaker trip unit ampere rating. Switches 26 are used to actuate the trip unit for ground fault determination in the manner described within U.S. patent application Ser. No. 08/767,748 entitled “Ground Fault Rating Plug for Molded Case Circuit Breakers.” Trip unit 10 further comprises a keypad unit that is generally shown at 27 having a keypad 28 that includes 4 keys for setting the trip unit settings aforementioned and a display 34.

#Referring to FIG. 2, a general schematic of an electronic trip unit of the present invention is generally shown at 10. Power passes along power lines 35 to load 36. Circuit breaker contacts 37, shown in the open position are normally in the closed position so that power can pass to load 36. Voltage sensor 38 and current sensor 39 sense voltage and current in power lines 35 and provide analog signals indicative of voltage and current measurements on signal lines 40 and 41, respectively. The present disclosure is not limited to requiring that both voltage and current sensors be present, but instead contemplates that either type of sensor, or any other sensor capable of sensing a fault condition of load 36 may be employed.

#The analog signals on lines 40 and 41 are presented to a signal converter, such as an A/D (analog/digital) converter 42, which converts these analog signals to digital signals. The digital signals are transferred over datapath 43 to a microcontroller (microprocessor or signal microprocessor) 44, such being commercially available from the Hitachi Electronics Components Group (Hitachi's H8/300 family of microcontrollers). Trip unit 10 further includes RAM (random access memory) 46, ROM (read only memory) 48 and EEPROM (electronic erasable programmable read only memory) or flash memory (including sector erasable flash memory) 50 all of which communicate with the microcontroller 44 over a control bus 52. It will be appreciated that A/D converter 42, ROM 48, RAM 46, or any combination thereof may be internal to microcontroller 44, as is well known. EEPROM 50 is non-volatile so that system information and programming will not be lost during a power interruption or outage. Data, typically status of the circuit breaker, is displayed by the display 34 in response to display signals received from microcontroller 44 over control bus 52. The display 34 is also capable of displaying a trip setting value selected and indicate from which input source/storage device the trip setting value is obtained. An input source/storage device is selected via switch 54 giving a switching instruction, switch 54 operably instructs microcontroller 44 from which source (i.e., input source or an associated storage device for an input source) to read a trip setting value from. Associated storage devices may include for example, but not limited to, different registers within non-volatile memory. An output control device 56, in response to control signals received from microcontroller 44 over control bus 52, controls a trip module 58 with a trip signal via a line 60.