FORM 2
THE PATENTS ACT 1970 (39 of 1970)
COMPLETE SPECIFICATION
(See Section 10; rule 13)
TITLE
Electronically controlled under voltage release device used with circuit breakers
APPLICANTS
LARSEN & TOUBRO LIMITED , L & T House, Ballard Estate, Mumbai 400001 ,Maharashtra, India, an Indian company
The following specification particularly describes the nature of this invention and the manner in which it is to be performed
I 5 MAR 2004

This invention relates to an electronically controlled under voltage release device for using with circuit brakers.
Circuit breakers are used with under voltage release device to protect electrical equipments such as motors transformers and generators. The under voltage release device is a device to prevent the damage to the apparatus due to drop in the system voltage below the desired level. Conventionally known under voltage release device comprises a fixed electromagnet with a wound coil and a moving electromagnet with electrical contacts which makes and breaks the supply to the circuit breaker coil. However, the difference between the pick up voltage and the drop off voltage in such under voltage release can be as much as 50% depending upon the characteristics of the hysterisis characteristics of the core used in the under voltage release device and the sensitivity of the spring holding the moving electromagnet.
The object of this invention is to provide an under voltage release device which has a narrow preset difference between the pick up voltage and drop off voltage. This is achieved by providing supply to the winding of the under voltage release device through make and break
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contacts of an electronically controlled relay. The control circuit comprises a supply voltage sensor, a comparator which compares the supply voltage against a preset reference voltage. The output from the comparator is connected through an amplifier to operate the control relay. Such an arrangement can achieve very narrow difference of less than 10 percent between the pick up voltage and release voltage and is independent of the hystensis characteristics of the core used in the electromagnets of the under voltage release device.
Thus the invention provides an electronically controlled under voltage release device for circuit breakers comprising a fixed electro¬magnet with a wound coil and a spring loaded moving electromagnet, characterized in that the said wound coil of the said voltage release device being connected to the supply voltage through a make and break contacts of a controlled relay controlled by an electronic control circuit comprising a supply voltage sensor, a comparator for comparing the supply voltage sensed with a reference voltage, the output of the comparator being connected to the controlled relay coil so that when the supply voltage hills
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below a predetermined value, under voltage release device is in the released position and when the supply voltage is above a pre set value the under voltage release device is in the closed position.
The accompanying drawing of Figure 1 shows the electronically controlled under voltage release device for circuit breakers according to the invention.
The electronically controlled presettable under voltage release device comprises a control circuit with a voltage sensor (1) for sensing the supply voltage, (Vsys) a voltage regulator (2) with a setting means (3) to set a reference voltage (Vref). The setting can be achieved by adjustment in electronic circuit and by mechanical adjustment in electro-mechanical release. The reference voltage (Vref) and the output from the supply voltage sensor are fed to a comparator (4). The output of the comparator is connected through an amplifier (5) to a relay (6). Supply voltage to the under voltage release device is connected through the make and break contacts of the control relay (6) which controls the pick up and release of the under voltage release device. The supply voltage is sensed after rectification and is compared with a preset reference voltage.
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We Claim :
i. An electronically controlled under voltage release device for circuit breakers comprising a fixed electromagnet with a wound coil and a spring loaded moving electromagnet, characterized in that the said wound coil of the said voltage release device being connected to the supply voltage through make and break contacts of a control relay controlled by an electronic control circuit comprising a supply voltage sensor, a comparator for comparing the supply voltage sensed with a reference voltage, the output of the comparator being connected to the control relay coil so that when the supply voltage fells below a predetermined value, under voltage release device is in the released position and when the supply voltage is above a pre determined value the under voltage release device is in the closed position.
2. An electronically controlled under voltage release device for circuit breakers substantially as herein described with reference to the drawings. Dated this 14th day of November 2003.