1. Field of the Invention
The present invention relates to an improved terminal apparatus for a horizontal type case drawer relay having an improved contact mechanism for preventing a secondary side of a current transformer (hereinafter referred to as "CT") from opening, and also relates to an improved batch inserting type test plug used for the measuring and testing of internal elements of such a relay.
2. Description of the Prior Art
In general, a drawer type relay case can be either a vertical type case which is long in a vertical direction, or a horizontal type case which is long in a horizontal direction.
The horizontal type case drawer relay has been developed only recently and uses print cards so that the relay becomes stationary. In order to improve heat radiation and enable arrangement of many pieces, a plurality of print cards which extend in a vertical direction are arranged side by side and enclosed within the case. The case is long in the horizontal direction and is attached to a switchboard as a horizontal type case.
The vertical type case drawer type relay is a relay box which contains mainly mechanical elements, and a terminal apparatus is arranged on a lower or an upper portion of the relay. The case is long in the vertical direction and is attached to the switchboard vertically as an embedding type.
Relay elements in the horizontal type case can be made compact in comparison with those in a vertical type case. A plurality of relay elements, which are arranged side by side, can be enclosed in one case; therefore, the horizontal type case has advantages in that the occupied area in the switchboard can be significantly reduced. Accordingly, the horizontal type case is conveniently used in large-scale protective relay apparatuses.
A terminal apparatus with a batch inserting type test plug, which is installed in a vertical type case, allows for easy measuring and testing. However, when the test plug is required to accommodate multiple poles, the terminal apparatus becomes excessively large. It is also difficult to enclose such a test plug in a horizontal type case relay which has a compact configuration; therefore, such a test plug is not used for testing and measuring in a horizontal type case relay. In place of such a test plug, a rear connector is installed to perform the required measuring and testing.
The rear connector is fixedly attached to a rear surface of the switchboard. The terminals of the rear connector are connected so that a power source in an input side is connected to the switchboard by a relay side. A protective relay inserted from the front surface of the switchboard is connected to the rear connector through fittings between male and female connecting pieces and fixed to the switchboard side in a locked state. Testing of the protective relay only can be performed by drawing out the relay from the switchboard. Since the rear connector is connected as described above, measurement of relay operation speed, voltage, current and synthetic testing are performed inevitably when the rear connector is disposed at the rear surface of the switchboard.
The rear surface of the switchboard is often crowded with connecting wires, and only a narrow space remains open. In addition, a hot-line portion may be exposed in the narrow space at the rear of the switchboard. Many measuring instruments cannot be used in testing the drawer type plug since care must be taken to the surroundings. Particularly, if a tool is left in the drawer type relay or falls into the relay by mistake, the tool may contact the hot-line portion and cause severe damage such as a short-circuit fault.
Measuring and testing at the rear connector are performed by separately connecting clips to exposed terminals in a grasped state so that proper connection to the testing apparatus results. Accordingly, troublesome work is required, and there is always a fear of electric shock since one's fingers are liable to contact the hot-line portion.
A plug used in the terminal apparatus comprises multiple poles assembled in one body. There are two types of plugs, a test plug used in testing and a connecting plug used in a non-testing state, i.e., during apparatus driving.
Inserting the connecting plug in a bundle results in connection of a circuit in the switchboard side with a circuit in the relay side so that driving is started. If the apparatus required for testing is previously connected to the test plug which is inserted into the terminal apparatus in the bundle, testing can be performed simultaneously at multiple poles.
Any plug can be operated at the front surface of the switchboard as described above; therefore, its operation is performed easily with safety, and the measuring and testing are simplified by simultaneous working of multiple poles.
At present, it is difficult to design and install such a terminal apparatus for the horizontal drawer type relay case because assembling the multiple poles prevents the terminal apparatus from being adequately compact.
The testing apparatus is connected to a test plug, and two lead-in terminals per pole are required to branch the circuit to the relay side and to the switchboard side. Since a tightening tool is likely to be lost, the lead-in terminals are provided with a knob which can be rotatably tightened using one's fingers so that the use of the tightening tool within the switchboard can be avoided. In order to rotatably tighten the knob using one's fingers, the size of the knob must be considerably large. Since the test plug is formed arranging multiple poles in a line, the alignment distance becomes large as the number of poles increases. Furthermore, since many parts such as terminals and knobs are required which necessarily occupy a considerably large area, the testing apparatus cannot be made compact. Particularly in the horizontal relay type case containing stationary elements, many elements are enclosed in one case, and, therefore, the number of poles is numerous and further increases the size of the terminal apparatus.
For example, in the prior art, if a protective relay apparatus composed of three vertical type cases has three stationary elements, the equivalent function of one horizontal type case requires three print cards and three transformers enclosed within it. In this example, there are at least 20 poles in the horizontal type case for the test plug. In addition, the number of terminals and knobs is double the above number. Therefore, 40 sets of terminals and knobs are required.
The area occupied by the terminal apparatus in the horizontal type case is rather small. Since print cards extending in the vertical direction are arranged side by side and enclosed within the case, the width of the terminal apparatus is also small, and the size of the structure to be enclosed adjacent the print cards is also small. Accordingly, the alignment distance between multiple poles in the test plug for the terminal apparatus must be enclosed within the extending height of the print card.
It is difficult to form a test plug having electrode plates for the multiple poles, terminals and knobs within such a restricted area, the number of terminals and knobs being twice that of the number of poles. Therefore, the above-described terminal apparatus is not installed in the horizontal type case, and the rear connector is used in place of the terminal apparatus.
This condition also applies to a terminal apparatus in the conventional vertical type case. That is, the number of the electrode plates for the multiple poles, and the number of terminals and knobs, present problems. In order to reduce the area occupied by the terminals and knobs which are generally used, double knobs in piggy-back relation are effective. This method is intended to reduce the number of knobs by half by solid overlaying and to reduce the area occupied by the knobs on the baseboard.
In this method, both piggy-back knobs have different thread diameters for tightening. The smaller knob, with the smaller thread diameter, can be tightly clamped. However, since the larger knob, with the larger thread diameter, has a small height and also a low number of threads, this latter knob is likely to be loosened. Also, two types of connecting pieces, a larger one and a smaller one having different thread diameters, are required to connect between terminals. Proper use of both types of connecting pieces is troublesome.
The lead wire connected to the testing apparatus during testing is provided with a so-called arrow-shaped chip at its top end. Since the arrow-shaped chip is likely to be readily detached due to loosening at the terminal portion, a larger length lead wire may be provided with a terminal (connecting piece) which has an attaching hole. However, such a connecting piece cannot be inserted before removing both knobs. Also, it is the larger knob which must be connected first, and treatment is, accordingly, inconvenient. The connecting piece for the larger knob is excessively large in size and is likely to be contacted with an adjacent terminal if there is a slight variation in the connecting piece. This is dangerous, particularly when using a connecting piece which has no insulation protection.
Since the electrode plates of the test plug are arranged in a line, the circuit order is distinguished by visual observation. At the knob side connection, however, double knobs in a solid structure are used, and distinguishment of relay side or switchboard side and circuit order cannot be determined by visual observation. Therefore, connection is performed in accordance with a mark. In the double knobs having a solid overlaying structure, however, even if the mark is set forth for both knobs, the mark for the larger knob is hidden by the smaller knob and cannot be seen from above. Accordingly, two different marks are set forth for each position of the baseboard on which knobs are mounted, and the mark corresponding to the larger knob cannot be distinguished by visual observation. Since the mark may be hidden by the lead wire after connection, inconvenience occurs when the connection is checked.
The alignment distance between electrode plates of multiple poles is large. Therefore, forming the baseboard as one body and applying the electrode plates to the baseboard is frequently used to achieve greater strength. However, a long, one-body baseboard may be warped or distorted by contraction or by aging of the resin which forms a part thereof. If the baseboard is warped, an abnormal condition occurs in the contacting state of the electrode plates which are used as contacts during the test plug insertion. Thus, not only a poor contacting state occurs, but, also, smooth inserting or detaching action of the test plug is obstructed.
In order to reduce the alignment distance, the wideth of the electrode plate may be decreased. However, potential transformer circuits (hereinafter referred to as "PT" circuits), as well as CT circuits, have elements which are required to carry a large current during opening. These large current elements exist in a mixed state in the electrode plate. Accordingly, the width of the electrode plates cannot be decreased significantly from the viewpoint of current capacity. Also, the electric insulation distance between electrode plates is considerably large. Therefore, the alignment distance cannot be reduced significantly and, accordingly, remains large.
Due to all of the above-mentioned conditions, the maximum number of poles in the test plug for the conventional, vertical type case is restricted to 10 poles at present. If more than 10 poles are required, the terminal apparatus is arranged in two stages, that is, 10 poles on an uppermost stage and 10 poles on a lowermost stage of the vertical type case. Testing is thus performed by inserting the test plug for 10 poles to the upper and the lower stages, respectively. Furthermore, in the terminal apparatus of the relay, the power source at the input side is generally closed to a relay element side by inserting the above-mentioned connecting plug into the terminal apparatus, and the power source is opened or disconnected from the relay element side by pulling the plug out of the terminal apparatus. Also, as indicated, the test plug may be used rather than the connecting plug when it is desired to conduct various kinds of measurements and tests.
Since the terminal apparatus closes or opens an electric path between the power source and the relay element side by inserting or removing a plug as described above, the contacting state of the contacts in the terminal apparatus is very important. Particularly, in a CT circuit, if the CT secondary side is opened completely for only a brief moment, a serious electric fault occurs. Therefore, the CT secondary side cannot be allowed to open even for a moment. Furthermore, the CT circuit cannot be allowed to open even during a transient state while the connecting or the test plug is being inserted or removed when contacts within the terminal apparatus and the contacts on the plug bounce. Moreover, short-circuit closing contacts of the CT secondary side or circuit must be opened after completely connecting the current element of the relay side to the relay circuit. Also, the CT secondary side must be short-circuited before opening the current element at the relay side. Such conditions must be automatically achieved in the contact mechanism of the terminal apparatus during the insertion and removal of the plug. Since the terminal apparatus has both CT circuits and PT circuits in a mixed state, a control mechanism to facilitate the installation and rearrangement of both circuits is desirable for both workability and circuit change.
Since such a terminal apparatus is installed within the relay and the relay elements occupy a large area, a compact terminal apparatus is inevitably desired. The terminal apparatus is enclosed in the relay and is hidden by a housing of the relay; therefore, the electric contact mechanism is completely invisible from outside. If the contacting state of the CT secondary side can be inspected visually from outside the terminal apparatus, the CT circuit can be readily prevented from opening, which, as mentioned above, is very important.
However, in a conventional terminal apparatus, when the terminal apparatus is enclosed within the relay, the internal electric contact mechanism is hidden by the casing of the relay, although an aperture for inserting a plug may be seen from the front surface of the relay. In order to inspect the contacting state of the short-circuit closing contacts which prevent the CT secondary side from opening, the terminal apparatus is inspected after being drawn out of the relay. Alternatively, an electric test can be performed without withdrawing the terminal apparatus by using an electric conduction test plug (not shown). Most operators perform overall tests through relay elements but do not take the trouble to inspect the internal electric contact mechanism of the terminal apparatus as part of the relay tests. Accordingly, the conventional terminal apparatus has disadvantages in that a poor contacting state of the short-circuit closing contacts is not found until a serious electric fault occurs.