1. Field of the Invention
The present invention relates to a withdrawable device of a vacuum circuit breaker for inserting and withdrawing a vacuum circuit breaker in order to connect and disconnect power terminals.
2. Description of the Related Art
In general, a vacuum circuit breaker is an electric device for switching a normal current and blocking a fault current as occurred by a signal such as a relay.
The vacuum circuit breaker extinguishes an arc generated when the vacuum circuit breaker breaks, in a vacuum container to quickly separate a circuit, thus protecting the circuit and device.
The vacuum circuit breaker is generally installed in a circuit breaker chamber of a distributing board. Usually, in the vacuum circuit breaker, electricity flows from a main line (i.e., to which electric is incoming) to a load side (i.e., from which electricity is outgoing), and when the vacuum circuit breaker or the distributing board is inspected or when the vacuum circuit breaker or the distributing board needs repairing, contact points of the vacuum circuit breaker are separated, the vacuum circuit breaker is withdrawn to a location at which it is sufficiently insulated from a power source of the main line, and then the circuit breaker is inspected or repaired.
A withdrawable device of the related art vacuum circuit breaker will now be described with reference to the accompanying drawings.
FIG. 1 is a perspective view showing the configuration of the related art vacuum circuit breaker. FIGS. 2 and 3 are perspective views of the withdrawable device of the related art vacuum circuit breaker. FIG. 4 is a sectional view showing the configuration of the withdrawable device of the related art vacuum circuit breaker. FIG. 5 illustrates a braking unit in a safe state according to the related art. FIG. 6 illustrates the braking unit in an operational state according to the related art.
First, with reference to FIG. 1, a withdrawable device 500 of the related art vacuum circuit breaker includes a carriage 100, on which a circuit breaker main body 140 having a main circuit 141 which is coupled to or separated from a mounting frame 130 installed at a rear side of a cradle 120 is loaded such that it can be transferred (or conveyed), a carriage moving unit 200 for moving the carriage 100 in a forward/backward direction, a braking unit for limiting a transfer distance of the carriage 100 being transferred by the carriage moving unit 200, and a girder assembly 300 supporting the carriage moving unit 200.
The carriage 100 includes a box body 101 having an upper portion opened and including a wall body 101a formed with a certain height on an outer circumferential surface, and two pairs of wheels 102 form on both sides of the box body 101 such that the are inserted or withdrawn along a guide rail (not shown) installed at an inner side of both side walls of the cradle 120.
With reference to FIGS. 2 and 4, the carriage moving unit 200 includes a lead screw 201 inserted in a forward/backward direction of a through hole 101b formed on the front wall body 101a of the box body 101, a transfer nut 202 installed at an inner side of the front wall body 101a of the box body in a state of being threaded with the lead screw 201, a channel-shaped bracket 203 for fixing the transfer nut 202 to the box body 101, and a handle 213 detachably installed at a front end portion of the lead screw 201 in order to rotate the lead screw 201 forward and backward.
The transfer nut 202 includes a female screw unit threaded with an outer circumferential surface of the lead screw 201. Two guide recesses 202b having both end portions whose depths are different are formed on front and rear surfaces of the transfer nut 202. A guide groove 202c is formed on an outer circumferential surface of the transfer nut 202.
A girder 209 fixed to a rear end portion of the lead screw 201 may be movable in a forward and backward direction without wobbling on a pair of travel rails 212 and 212′ installed in a lengthwise direction on an inner side of the box body 101 of the carriage 100.
The girder assembly 300 includes a support structure 303 having a space part formed at an inner side thereof and having a bearing 214 supporting to transfer rotary power to the front end portion of the lead screw 201 that passes through a fixing hole formed at the center thereof, left and right sliding plates (not shown) installed to be movable in a left and right direction at both inner sides of the support structure 303, left and right handles 305 and 305′ fixed to the left and right sliding plates and installed to be protruded outwardly from the support structure 303, and a spring (not shown) for moving the left and right sliding plates to insert an end portion 304a into the both side walls of the cradle 120.
A braking unit 204 is installed near the transfer nut 202 and selectively constraining a rotation of the transfer nut 202 by interworking with guide recesses 202b and 202c formed on the transfer nut 202.
The position of the circuit breaker main body 140 loaded on the carriage 100 is fixed by means of the braking unit 204.
The operation of fixing the position of the circuit breaker main body 140 by means of the braking unit 204 will now be described with reference to FIGS. 5 and 6.
As shown in FIGS. 5 and 6, as for the braking unit 204, forward and backward rotation preventing pins 205 and 205′ are installed in a diagonal direction of the bracket 203 such that they can be inserted into the guide recesses 202b formed on the front and rear surfaces of the transfer nut 202. The forward and backward rotation preventing pins 205 and 205′ are connected with left and right driving pins 207 and 207′ by means of connection plates 206 and 206′. The left and right driving pins 207 and 207′ are elastically supported by springs 208 and 208′. The left and right driving pins 207 and 207′ are pressed by the girder 209 and the girder assembly 300 installed at the end portions of the lead screw 2201 when the carriage 100 moves forward and backward. A pair of support plates 211 and 211′ are installed at a certain interval in a vertical direction of the bracket 203 so that a guide pin 210 for positioning the transfer nut 202 can be inserted into the guide recess 202c of the transfer nut 202 when the forward rotation preventing pin 205 or the backward rotation preventing pin 205′ is released from the guide recess 202b of the transfer nut 202 by the left and right driving pins 207 and 207′.
The rotation of the transfer nut 202 moving in the forward and backward direction of the lead screw 201 is restrained by the braking unit 204. In this case, when the carriage 100 has moved forward completely (so as to be at a testing position), the transfer nut 202 completely moves backward along the lead screw 201, so the right driving pin 207′ is brought into contact with one side of the girder assembly 300, the backward rotation preventing pin 205′ is released from the guide recess 202b of the transfer nut 202, and the transfer nut 202 is idly rotated, thus preventing the carriage 100 from moving any further.
When the carriage 100 has completely moved backward (so as to be at an operation position), the transfer nut 202 moves completely to the rear side along the lead screw 201, the left driving pin 207 is brought into contact with the side of the girder 209 installed at the rear end portion of the lead screw 201, the forward rotation preventing pin 205 is released from the guide recess 202b of the transfer nut 202, and the transfer nut 202 is idly rotated, thus preventing the carriage 100 from moving any further.
However, the withdrawable device of the vacuum circuit breaker has the following problem. That is, when the carriage 100 is at the testing position, the carriage 100 is simply prevented from moving forward by means of the braking unit 204 and the backward rotation preventing pin 205′ interworking with the braking unit 204, while the carriage 100 cannot be prevented from changing in its position to the front side when an external force (vibration, an impact, etc.) is applied to the lead screw 201.
Based on the same principle, when the carriage 100 is at the operation position, the carriage 100 is simply prevented from moving backward by means of the braking unit 204 and the forward rotation preventing pin 205 interworking with the braking unit 204, while the carriage 100 cannot be prevented from changing in its position to the rear side when an external force (vibration, an impact, etc.) is applied to the lead screw 201.
In case of the operation position, the change in the position of the carriage 100 is likely to cause a short-circuit incident, and in the occurrence of the short-circuit incident, it makes the contact state of an electrical contact portion unstable to possibly bring about an additional incident.
Also, in case of the testing position, the contact point of the vacuum circuit breaker cannot be separated up to a position at which the vacuum circuit breaker is sufficiently insulated from the power surface of the main line, having a dangerousness of causing a safety accident.