MXPA98001627A - Solid state control device for an anti-bom circuit - Google Patents

Abstract

A solid-state control system for controlling the activation of the electromechanical closing coils of a circuit breaker is disclosed. The system employs a novel configuration of a silicon-controlled rectifier (SCR) and other electronic components, such as an FET, to provide "anti-pumping". The system blocks the continuous closing signals after the closing signal has been removed, and then reaplies

Description

Standards C37.09-1979 and C37.1 1-1979 of the American National Standards Institute (ANSI) specify that a circuit breaker must close only once in response to any closing signal. A circuit breaker that meets this specification is said to have anti-pumping. According to these standards of ANS I, if a closing signal is applied to a circuit breaker and subsequently maintained or sustained, the circuit breaker must not close once more until the closing signal is first removed and a new signal is applied closing. This rule holds even if the circuit breaker opens while maintaining the initial closing signal. In this case, the closing signal must be removed before allowing the switch to close again. The prior art circuit breaker applications attempted to meet ANSI standards by designing the electromechanical "Y" coil to "block" redundant closing signals that are received prior to the release of a prior closing signal. However, electromechanical coils, including those used as "Y" coils, are subject to rebound and vibration. The rebound in the "Y" coil is problematic in particular with respect to anti-pumping standards in that it can cause an activation signal to be transmitted inadvertently to the closing coil. For example, due to the inherent rebound in all electromechanical coils, which is amplified by the close-force impact of the switch itself, a "Y" coil can transmit an activation signal to the closing coil when the closing coil it must be electrically blocked. Such inaccuracy in the operation of the "Y" coil violates the anti-pumping standards of the ANSI. In addition, this deficiency in the electromechanical "Y" coil can cause the switch to close again during the interruption, which can lead to failure of the circuit breaker. Therefore, a circuit breaker control system is needed that provides accurate and reliable anti-pumping control.

BRIEF DESCRIPTION OF THE INVENTION The present invention meets this need by providing a solid-state control device for controlling the closing and opening signals for a circuit breaker. The solid state control device operates to inhibit the circuit breaker from closing more than once in response to any closing signal without the use of a "Y" coil. The solid state control device includes an electronic switch, such as a field effect transistor, connected in series with the closing coil. The electronic switch is controlled by a gate, so that the closing coil is activated when a signal is applied to the gate of the electronic switch. Additionally, a silicon control rectifier (SCR) which also has a gate is electrically coupled to the gate of the electronic switch, so that a signal is supplied to the gate of the electronic switch when the SCR is not driving. A closing spring sensor switch is connected to the SCR gate, so that the SCR drives when the closing spring sensor switch is closed. Other features of the present invention are described below.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be better understood, and its numerous objects and advantages will be apparent by reference to the following detailed description of the invention taken in conjunction with the following drawings, wherein: Figure 1 is a schematic and block diagram showing an arrangement of circuit for a system in accordance with the present invention; Figure 2 is a time diagram of the anti-pumping circuit of the present invention during a normal closing operation; and, Figure 3 is a time diagram of the anti-pumping circuit of the present invention during blocking.

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a system for providing anti-pumping capabilities to a circuit breaker closing circuit. In the preferred embodiment of the invention, a field effect transistor (FET) and a silicon control rectifier (SCR) are employed. However, other components can be replaced by these components to provide a similar function. For example, a transistor switch may be used instead of the FET and a thyristor may be used instead of the SC R. Further, although the invention is described throughout the description with reference to an electromechanical closing coil, as it progresses The state of the art The invention can be used with other circuit breaker closing mechanisms. The present invention overcomes the problems associated with the inaccurate and unreliable electromechanical "Y" coil by eliminating the "Y" coil and placing the functionality to block closure signals in a solid state control device (SSCD). As explained in detail below, the anti-pumping function is provided by a Silicon Controlled Rectifier (SCR), a field effect transistor (FET) and support circuit. When a closing signal is applied to the SCR gate, the SCR turns on. Consequently, the FET is turned off as the SCR drives removing current from the FET gate. As is generally the case with SCR's, after the SCR turns on the gate it loses the ability to control the SCR until the voltage is removed from the anode and cathode. In this way, the SCR closes the closing signal of the SSCD. As distinguished from the electromechanical "Y" coils of the prior art, SCR Q 1"reliably and accurately" locks additional closing signals to prevent the circuit breaker from closing more than once in response to any closing signal . Figure 1 is a schematic and block diagram of the SSCD of the invention. As shown in Figure 1, upon receipt of a closing signal, either in AC or DC form, from an external signal source 2 such as the power company, the SSCD rectifies and filters the closing signal when using a diode bridge D 1 and filter capacitor in bypass C 1. Two transient voltage suppressors Z 1, Z 2 are placed in series along the positive 4 and negative 6 terminals in order to fix the level of the transient voltage spikes. A series / parallel combination of resistors R1, R2, R3, R4, R5, R6 connected between points 4 and 8 reduces the current of the rectified and filtered closing signal. A Zener diode Z3 coupled along points 8 and 10 regulates the closing signal at approximately 20 V DC. A resistor R9 connected between points 8 and 12 limits the current supplied to SCR Q 1 and Zener Z5. The resistor R 1 1 prevents the short circuit of the zener Z5 when the SCR Q 1 is turned on. The zener Z5 regulates the closing voltage at approximately 1 5 VDC at point 14. Upon receiving a closing signal at point 14, the FET Q2 receives a signal at its gate terminal sufficient to activate and allow the current to flow to through the device from point 20 to point 22. A capacitor C3 together with the resistor R 10 comprises a rejection circuit for the SCR Q 1. The activation of FET Q2 closes the electric path between points 20 and 22. As a result, a circuit is complete and the current can flow. Specifically, the current flows through the bridge rectifier D2, outside the SSCD to the normally closed contact (b) of the circuit breaker, through the closing coil 30, back to the SSC D, and through the FET Q2. When the circuit breaker closes physically in response to the closing coil, the contact (b) disconnects and interrupts the circuit current. As noted above, the ANSI standards require that a circuit breaker close only once in response to any closing signal. Thus, if the closing signal is maintained and the switch is opened, the switch will not close anymore until the closing signal is first eliminated and a new closing signal is applied. In addition, the closing coil may not activate while the switch is in the closed position. As shown, the SCR Q 1 is arranged in parallel to the resistor R 1 1 and zener Z 5. When the SCR Q 1 is diverted to conduct, the electric current, which would otherwise flow through the R 1 1 to the gate of the FET Q2, flows through the SCR Q 1. This reduces the gate voltage of FET Q2 to approximately 0.7 VDC and subsequently shuts off the FET Q2.

For a high-power circuit breaker to work, its contacts must be kept together with a specific minimum force. Here, necessary force is supplied by means of closing springs. These springs can be compressed (ie, "loaded") by a motor or a manual load lever, for example. In addition, a load motor switch is used to shut off the charging motor once the springs are loaded. A closing spring sensor switch S 1 is connected to two SSCD inputs. When the circuit breaker closes, the closing springs discharge, which closes the switch S 1. After the closing spring sensor switch S 1 has closed, the SCR Q 1 is activated by current flowing through a resistor R7 to the activation gate 38. As a consequence of the parallel arrangement between the SCR Q 1 and R1 1 and Z5, once the SCR Q 1 has been activated, little or no current reaches the FET gate Q2. A resistor R8, zener Z4 and capacitor C2 are connected parallel to each other and in series with the first resistor R7 in order to provide sufficient impedance to keep SCR Q 1 off until it closes the closing spring sensor switch S 1. Zener Z4 is used to set the gate voltage level of SCR Q1 to less than about 3.5 VDC. A resistor R 1 0 and capacitor C3 form a rejection circuit to protect SCR Q 1 from an overcurrent condition. In this way, SCR Q 1 and the surrounding circuit ensure that after the circuit breaker closes, the circuit breaker will not close again until the initial closing signal is first removed. SCR Q 1 will continue to drive, blocking additional closing current to reach FET Q2 for as long as the closing signal is present. SCR Q 1 is reconnected when the closing signal is removed. The elimination of the closing signal carries the SCR current to zero and deactivates the SCR Q 1. With SCR Q 1 deactivated, a new closing signal can reach the FET gate Q2 and restart the sequence described above. The SSCD also provides signal control to the opening coil 40 of the circuit breaker. As shown, the signals of the opening coil pass through a rectifier D3 and are supplied to the opening coil 40 of the circuit breaker. Two transient voltage suppressors Z8, Z9 connected in series along rectifier D3, between points 24 and 26, protect against voltage spikes. Figures 2 and 3 provide SSCD time diagrams for a normal closing operation (Figure 2) and a fault closing operation (Figure 3). The curve 52 shows the closing signal provided to the SSC D. The curve 54 provides the state of the spring load switch S 1. Curve 56 shows the state of FET Q2. Curve 58 shows the state of SC R Q 1. And curve 60 shows the state of contact "b". As shown in Figure 2, at the start of the switch closing sequence, spring load switch S 1 is in the closed position, SCR Q 1 is not driving and contact "b" is closed. In addition, FET Q2 is off and no closing signal is present. After the switch springs are fully loaded, the spring load switch S 1 opens. An external closing signal will then reach the gate of FET Q2. Shortly thereafter, the FET Q2 drives a closing coil 30. When the coil drives, the closing springs are discharged by closing the load switch S 1. This creates a voltage in the gate of SCR Q 1 causing SCR Q 1 to drive. As the SCR Q 1 conducts, the gate voltage of the FET Q2 is eliminated. Consequently, FET Q2 is blocked (ie, the circuit between point 20 and 22 is opened until voltage is applied to the FET gate Q2). The switch then closes causing contact "b" to open. After, when the closing signal is removed, the SCR goes off. Figure 3 presents the time diagram where the switch trips in a fault condition before eliminating the closing signal. The first seven time steps are the same as in Figure 2. However, in this diagram, the switch subsequently triggers a fault before eliminating the closing signal. The switch can not close again since SCR Q 1 is still driving and blocking FET Q2. The present invention can be used in other specific forms without departing from the spirit of the essential attributes thereof. For example, any number of combinations of resistors connected in series and parallel may be used instead of the present combination of resistors R 1, R 2, R 3, R 4, R 5 and R 6. In addition, several combinations of resistors and capacitors can be used to control the flow of current to the SCR gate. Although the invention has been described and illustrated with reference to specific embodiments, those skilled in the art will realize that modifications and variations can be made without departing from the principles of the invention as described above and set forth in the following claims. In addition, any zener diode voltage can be used with the resistor networks to control the gate of the SCR.

CLAIMS 1. - A solid state control device for a circuit breaker, said circuit breaker having a closing coil that closes said circuit breaker when activated, the control device comprising: circuit means operatively coupled to the coil of Close to inhibit the circuit breaker from closing more than once in response to any closing signal without the use of a "Y" coil. 2. - The solid state control device according to claim 1, wherein said circuit means for inhibiting the circuit breaker from closing more than once in response to any closing signal comprises: an electronic switch connected in series with the closing coil, said electronic switch being controlled by a gate, so that the closing coil is activated when a signal is applied to the gate of said electronic switch; a silicon control rectifier (SC) having a gate, said SCR being electrically coupled to the gate of said electronic switch, so that a signal is supplied to the gate of the electronic switch when said SCR is driving; and, a closing spring sensor connected to the gate of said SCR, so that said SCR conduace when said closing spring sensor switch is closed. 3. - The solid state control device according to claim 2, wherein said electronic switch is a field effect transistor. 4. - A solid state control system, comprising: a closing coil circuit having a closing coil and an electronic switch coupled together in a series configuration, said electronic switch having a door, said circuit closing coil being closed when an electrical signal is applied to the gate of the electronic switch and said closing coil circuit being open when it is iminaed by said electrical signal from the gate of the electronic switch; a silicon controlled rectifier coupled to the gate of the electronic switch, so that the electrical signal is removed from the gate of the electronic switch when the SCR is activated.

. - The solid state control system according to claim 4, further comprising a sensor switch coupled to a gate of the SCR, so that the SCR is able to activate when said sensor switch is closed. 6. - The solid state control system according to claim 4, wherein said electronic switch comprises a field effect transistor. 7. - The solid state control system according to claim 5, wherein said sensor switch comprises a closing spring sensor switch.