DESC:UNDER VOLTAGE RELEASE FOR CONTROLLING OPERATION OF CIRCUIT BREAKER

Field of the invention:

The present invention relates to a low voltage switchgear for example an air circuit breaker, used in a power distribution system, and more particularly, to an apparatus incorporating an under voltage release to monitor voltage supplied thereto and accordingly control an operation of the circuit breaker or other such devices.

Background of the invention:

An air circuit breaker is a switching apparatus that has been designed to carry current and make and break a circuit. A main contact system of the air circuit breaker consists of fixed and movable contacts. The air circuit breaker consists of a mechanism that is used to store energy and the stored energy is discharged to (join) latch the fixed and movable contacts together, thereby closing the circuit. Under normal operating conditions, the air circuit breaker remains closed. The air circuit breaker also has a tripping mechanism that opens the circuit i.e. switches off the air circuit breaker either intentionally or during any abnormal conditions like an under voltage, a short circuit, an overload, and the like.

The under voltage condition can be dangerous as downstream equipments connected to the air circuit breaker can get damaged, due to high current drawn by the load, if they are not disconnected during the under voltage condition. For this, an under voltage release as a control accessory is provided with the air circuit breaker. The under voltage release constantly monitors the voltage at its input terminals and correspondingly allows the air circuit breaker to switch on or switch off during the under voltage condition. However, due to the location of the under voltage release in the circuit breaker, it becomes difficult for the user to understand if the under voltage release is energized or not.

Accordingly, there exists a need to provide a device/apparatus that overcomes abovementioned drawbacks in the prior art for controlling operation of a circuit breaker.

Objects of the invention:

An object of the present invention is to provide an under voltage release whose coil status can be easily understood by a user.

Another object of the present invention is to monitor different voltage levels and combine signals suitably to form an input for next stage of an electronic circuit.

Summary of the invention:

Accordingly, the present invention provides an under voltage release for controlling an operation of a circuit breaker. The under voltage release comprises of a bridge rectifier, a power supply, a dual voltage sensing circuit, a signal latching circuit, a coil control circuit, an under voltage coil and a visual indication means. The bridge rectifier receives an input selected by a user from any one of an AC input and a DC input from an input supply. The input is monitored for controlling the operation of the circuit breaker. After receiving the input, the bridge rectifier gives an output in a DC form with a polarity suitable for working of the under voltage release. The power supply receives the output of the bridge rectifier as an input and converts the input into a fixed low voltage output. The dual voltage sensing circuit includes at least two operational amplifiers (hereinafter ‘the Op-Amps) arranged in a comparator mode. The Op-Amps act as voltage comparators. The Op-Amps receive outputs of the power supply and the bridge rectifier as inputs and generates two outputs, in response to the input from bridge rectifier thereto. The output from the power supply received by the Op-Amps acts as a power source and also as an internal reference voltage for continuously monitoring the input received by the Op-Amps from the bridge rectifier.

The signal latching circuit receives the two outputs from the dual voltage sensing circuit and generates a latched output. The coil control circuit receives the latched output from the signal latching circuit. The coil control circuit is also adapted to receive the power from any one of the power supply, an output of the bridge rectifier and a combination thereof. The coil control circuit activates if the latched output is high and de-activates if the latched output is low. The under voltage coil is capable of switching on and off in response to an input received from the coil control circuit. The under voltage coil includes a moving plunger being capable of switching on and off the circuit breaker in response to the switching on and off of the under voltage coil. The visual indication means is arranged to indicate the switching on and off of the under voltage coil. The circuit breaker is switched on when the input is above a predefined percentage of the rated input voltage of the under voltage release and is switched off when the input is below a predefined percentage of the rated input voltage of the under voltage release.

Brief description of the invention:

Other features as well as the advantages of the invention will be clear from the following description.

In the appended drawing:

Figure 1 shows a block diagram of an under voltage release for controlling the operation of an air circuit breaker, in accordance with the present invention.

Detailed description of the invention:

The foregoing objects of the present invention are accomplished and the problems and shortcomings associated with the prior art, techniques and approaches are overcome by the present invention as described below in the preferred embodiments.

The present invention provides an under voltage release for controlling the operation of an air circuit breaker. The under voltage release includes a dual voltage comparator in combination with a signal latching circuit. The dual voltage comparator monitors two different voltage levels at the same time, that otherwise would have been difficult with a single comparator.

The present invention is illustrated with reference to the accompanying drawings, throughout which reference numbers indicate corresponding parts in the various figures. These reference numbers are shown in bracket in the following description.

Referring to figure 1, a block diagram of an under voltage release (200) for controlling the operation of a circuit breaker (not shown) for example an air circuit breaker is shown in accordance with the present invention. The under voltage release (200) is mounted on a circuit breaker mechanism (not shown) that facilitates tripping (switching off) of the circuit breaker in an event of an under voltage condition.

An input supply (10) is connected to the under voltage release (200) to provide an input (20) thereto. The under voltage release (200) is used to monitor a healthiness of the input supply (10). In an embodiment, the input (20) provided by the input supply (10) is selected by a user from any one of an AC input and a DC input. In a specific embodiment, the input (20) can be either from the bus bars where the circuit breaker is connected or a control supply voltage (AC or DC) whose voltage is to be monitored.

The under voltage release (200) comprises a bridge rectifier (30), a power supply (70), a dual voltage sensing circuit (90), a signal latching circuit (120), a coil control circuit (140), an under voltage coil (150) and a visual indication means (160). Specifically, the bridge rectifier (30), the power supply (70), the dual voltage sensing circuit (90), the signal latching circuit (120), the coil control circuit (140), the under voltage coil (150) and the visual indication means (160) are the functional blocks of an electronic circuit that build the under voltage release (200).

The bridge rectifier (30) is connected to the input supply (10) for receiving the input (20) therefrom. The bridge rectifier (30) gives an output (not numbered) in a DC form with a polarity required for working of the under voltage release (200). In the embodiment, the polarity of the output of the bridge rectifier (30) is such that irrespective of a polarity of the input (20), the bridge rectifier (30) can always provide the output of a fixed polarity. Specifically, a positive terminal of the bridge rectifier (30) would always be positive and a negative terminal of the bridge rectifier (30) would always be negative. When the AC input is fed to the under voltage release (200), the bridge rectifier (30) converts the AC input to a pulsating DC output. When the DC input is fed to the under voltage release (200), the bridge rectifier (30) corrects the polarity of the DC input for proper working of the under voltage release (200). The output of the bridge rectifier (30) is supplied as an input (40) to the power supply (70). Simultaneously, the output of the bridge rectifier (30) is also supplied as an input (50) to the coil control circuit (140) and also as an input (60) to the dual voltage sensing circuit (90).

The power supply (70) is adapted to receive the output of the bridge rectifier (30). The power supply (70) converts the output received from the bridge rectifier (30) to a voltage level that is suitable to power up (work) internal semiconductor ICs (not shown) of the under voltage release (200). Specifically, the power supply (70) gives a fixed low voltage output for a wide range of high voltage input. The power supply (70) gives power to the dual voltage sensing circuit (90), the signal latching circuit (120) and the coil control circuit (140).

The dual voltage sensing circuit (90) is adapted to receive the outputs of the bridge rectifier (30) and the power supply (70) as the inputs (60, 80), respectively. The dual voltage sensing circuit (90) consists of at least two operational amplifiers (herein after ‘the Op-AMPs’) (not shown) arranged in a comparator mode. Specifically, the Op-AMPs act as voltage comparators. The Op-AMPs include semiconductor ICs. The inputs (60, 80) are received by the Op-AMPs of the dual voltage sensing circuit (90). The input (80) acts as a power source for the Op-Amps to work. Two different reference values are created from the input (80), internal to the dual voltage sensing circuit (90) and then the Op-AMPs continuously monitor the input (60) with the two internal reference voltages created from the input (80). The dual voltage sensing circuit (90) generates two outputs (100, 110) by comparing the inputs (60, 80).

The signal latching circuit (120) is adapted to receive the two outputs (100, 110) from the dual voltage sensing circuit (90). The two outputs (100, 110) are combined into a single signal to generate a latched output (130). In an embodiment, when the output (110) of one of the Op-AMPs which is the 75% threshold voltage sensing comparator goes high, the output of the signal latching circuit (120) also goes high and stays high till the output of one of the Op-AMPs which is the output (100) of the 60% threshold voltage sensing comparator stays high. When the input (60) drops below 60% of the rated voltage of the circuit breaker, the output (100) of one of the Op-AMPs goes low, subsequently the output of the signal latching circuit (120) also goes low. If the output of the comparator is going high, then the voltage level is equal to some positive voltage for example, 3V and if the output of the comparator is going low, then the voltage level is becoming zero.
The latched output (130) from the signal latching circuit (120) is fed to the coil control circuit (140). The coil control circuit (140) is adapted to receive the power from any one of the power supply (70), the output (50) of the bridge rectifier (30) and a combination thereof. Specifically, the coil control circuit (140) draws power directly from the bridge rectifier (30) through the output (50) thereof to provide enough power for the working of the under voltage coil (150). The coil control circuit (140) controls the under voltage coil (150) and the visual indication means (160). The coil control circuit (140) includes a controller IC (not shown) with an Activation pin (not shown). The latched output (130) activates/deactivates the controller IC via the Activation pin for controlling the operation of the under voltage coil (150). The controller IC works on pulse width modulation (PWM) technique and controls current flowing through the under voltage coil (150) to facilitate proper working of the under voltage coil (150). When the voltage at the Activation pin is made high, the controller IC starts working and the under voltage coil (150) switches on while when the voltage at the Activation pin is made low/grounded, the controller IC stops working and the under voltage coil (150) switches off. Specifically, when the latched output (130) of the signal latching circuit (120) goes high, the coil control circuit (140) is enabled and the under voltage coil (150) switches on. When the latched output (130) of the signal latching circuit (120) goes low, the coil control circuit (140) is disabled and the under voltage coil (150) switches off.

The visual indication means (160) includes a light emitting diode (LED) (not shown). Specifically, the visual indication means (160) is added for the user to know that the under voltage coil (150) has been energized and that the circuit breaker is switched on. When the latched output (130) of the signal latching circuit (120) goes high, the under voltage coil (150) is switched on, simultaneously, the visual indication means (160) is also switched on. In a specific embodiment, if the input (60) is above a predefined percentage (for example 75%) of a rated input voltage of the under voltage release (200), then the under voltage coil (150) is switched on thereby allowing the switching on of the circuit breaker and when the input (60) is below the predefined percentage (for example 60%) of the rated input voltage of the under voltage release (200), then the under voltage coil (150) is switched off thereby switching off the circuit breaker.

Further, the under voltage coil (150) consists of a mechanical assembly (not shown) that is responsible for tripping/ controlling the circuit breaker. The under voltage coil (150) includes a moving plunger (not shown). When the under voltage coil (150) is switched on, the moving plunger allows the circuit breaker to switch on. When the under voltage coil (150) is switched off, the moving plunger switches off the circuit breaker and does not allow the circuit breaker to switch on.

Advantages of the invention:

1. The under voltage release (200) allows the user to easily understand the status of the under voltage coil (150).
2. The under voltage release (200) uses simple circuit and is reliable.
3. The under voltage release (200) uses less components.
4. The under voltage release (200) has the flexibility of using any one of digital and analog coil control circuitry.
5. The under voltage release (200) provides dual voltage sensing with signal latching.

The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the present invention and its practical application, and to thereby enable others skilled in the art to best utilize the present invention and various embodiments with various modifications as are suited to the particular use contemplated. It is understood that various omissions and substitutions of equivalents are contemplated as circumstances may suggest or render expedient, but such omissions and substitutions are intended to cover the application or implementation without departing from the spirit or scope of the claims of the present invention.

,CLAIMS:We Claim:

1. An under voltage release (200) for controlling an operation of a circuit breaker, the under voltage release (200) comprising:
a bridge rectifier (30) adapted to receive an input (20) selected from any one of an AC input and a DC input received from an input supply (10) being monitored for controlling the operation of the circuit breaker and to give an output in a DC form with a polarity required for working of the under voltage release (200);
a power supply (70) adapted to receive the output of the bridge rectifier (30) as an input (40) and to convert the input (40) into a fixed low voltage output;
a dual voltage sensing circuit (90) having at least two operational amplifiers arranged in a comparator mode to receive outputs of the bridge rectifier (30) and the power supply (70) as inputs (60, 80) and to generate two outputs (100, 110) in response thereto, thereafter the at least two operational amplifiers use the input (80) as a power source to create two different internal reference voltages for continuously monitoring the input (60);
a signal latching circuit (120) adapted to receive the two outputs (100, 110) from the dual voltage sensing circuit (90) and to generate a latched output (130);
a coil control circuit (140) adapted to receive the latched output (130) from the signal latching circuit (120), the coil control circuit (140) adapted to receive the power from any one of the power supply (70), an output (50) of the bridge rectifier (30) and a combination thereof, the coil control circuit (140) being capable of activating in response to a high latched output (130) and de-activating in response to a low latched output (130);
an under voltage coil (150) being capable of switching on and off in response to an input received from the coil control circuit (140), the under voltage coil (150) having a moving plunger being capable of switching on and off the circuit breaker in response to the switching on and off of the under voltage coil (150) and;
a visual indication means (160) indicating the switching on and off of the under voltage coil (150),
wherein, the circuit breaker is switched on when the input (20) is above a predefined percentage of a rated input voltage of the under voltage release (200) and is switched off when the input (20) is below the predefined percentage of the rated input voltage of the under voltage release (200).

2. The under voltage release (200) as claimed in claim 1, wherein when the AC input is fed to the under voltage release (200), the bridge rectifier (30) converts the AC input to a pulsating DC with the polarity suitable for working of the under voltage release (200).

3. The under voltage release (200) as claimed in claim 1, wherein when the DC input is fed to the under voltage release (200), the bridge rectifier (30) corrects a polarity of the DC input for working of the under voltage release (200).

4. The under voltage release (200) as claimed in claim 1, wherein the at least two operational amplifiers act as voltage comparators.

5. The under voltage release (200) as claimed in claim 1, wherein the at least two operational amplifiers include semiconductor ICs.

6. The under voltage release (200) as claimed in claim 1, wherein the visual indication means (160) includes a light emitting diode (LED).