KR810000009Y1 - Distribution transformer secondary circuit interrupter having an improved bimetal - Google Patents

Abstract

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Description

Secondary Circuit Breaker for Distribution Transformer

1 is a perspective view of an inlet distribution transformer,

2 is a perspective view of a secondary circuit breaker used in a distribution transformer,

3 is a plan view of the circuit breaker of FIG. 2 with the contacts closed;

4 is a side view of the circuit breaker shown along the line IV-IV of FIG.

5 is a side view of the bimetal,

6 is a view of a bimetal of the prior art.

7 is a view of a bimetal.

The present invention improves the structure of a bimetal so as to deflect the bimetal largely with low power consumption in a circuit breaker for a distribution transformer for controlling a medium power distribution power of a feeder line having a bimetal thermal trip element. will be.

The circuit breaker of the present invention is particularly suitable for distribution transformers used in distribution systems with protection devices that prevent or limit overload current damage of transformers and their accessories. Transformers that are fully self-contained have circuit breakers on the secondary or undervoltage side for protection against damage from overload currents. If the load current becomes dangerously high, the secondary circuit breaker disconnects the transformer from the load.

Common circuit breakers have three basic characteristics: (1) Low and load signaling devices (2) Incremental adjustment (3) Trip devices for opening the contacts of the circuit breakers at preset overloads.

The bimetal element is connected in series in the circuit breaker. As the load current flowing through the circuit breaker increases, the low overload point is reached, and in this the bimetal element is sufficiently deflected to operate the traffic light outside the transformer compartment.

Traffic lights attached to the transformer visually indicate that the secondary circuit breaker is about to trip. That is, the traffic light turns on at an overload lower than the overload required to trip the circuit breaker, indicating that the load current is approaching the trip level. As the load stage continues to increase, the bimetal element is further deflected to reach the second overload point where the circuit breaker trips and opens. The tripping of the circuit breaker protects the transformer from severe damage from excessive current flow. Since the bimetallic element is also affected by the ambient temperature of the oil surrounding it, the pre-set oil temperature must also be able to produce the necessary deflection to activate the traffic lights or trip the breaker. It is desirable to deflect the bimetal element as needed while minimizing the power lost in the bimetal element during operation. Bimetallic elements used in circuit breakers of the prior art generally have a structure in which power consumption is proportional to their length.

According to the present invention, the circuit breaker has a first fixed contact, a second fixed contact spaced apart from the first fixed contact, a bridge contact device, an elongated contact arm, and a bridging arm on the arm. a contact means is attached, and the brush contact device closes or opens the electrical circuit between the first fixed contact point and the second contact point (when opened, the bridge contact device is separated from both the first contact point and the second contact point). The arm is pivoted about an axis. A primary latch means connected to the elongated contact arm to engage the contact arm in the closed state, and a second engagement device to maintain the binding state of the first binding device; latch means and bimetal actuating meang, which consist of elongated bimetals, one end of which is relatively stationary and the other end of which is connected to the circuit breaker in response to the When the trip level is exceeded, the binding of the second binding device is released, and the bimetal is made to have a structure in which power consumption is increased near a relatively fixed end rather than near the deflected end. It consists of

In inlet transformers, this circuit breaker, which uses a bimetal thermal trip element (consisting of power dissipated at the base of the bimetal) to open the circuit breaker under various overload conditions, can be placed inside the transformer compartment. It is convenient.

This circuit breaker forms a series circuit from a movable contact that can open and close a fixed contact, through a transformer, to a low voltage terminal located in the transformer enclosure. The movable contact is spring biased in the open direction, but is connected to the stationary contact by the engagement mechanism so that the circuit breaker is in contact with the stationary contact.

The bimetal drive device arranged in series in the transformer circuit is connected so that when the current flowing through the bimetal exceeds the overload trip value, the bimetal drive device moves the binding device to the unlocked position to trip and open the circuit breaker. . Bimetals are also affected by the ambient oil temperature and will be deflected if the oil is heated for some reason. The operating handle of the circuit breaker lies outside the transformer compartment and is connected to the operating mechanism of the circuit breaker. In addition, the traffic light contacts of this circuit breaker are closed when a current flows through the circuit breaker that exceeds a small overload rather than a trip value overload. Traffic light contacts are connected to a traffic light placed outside of the box to visually indicate that a low overload condition is continuing. Once the traffic light circuit is activated, the traffic light circuit is not automatically reset but can be reset by moving the operating knob from the off position to the normal on position. In other words, with the circuit breaker on, the traffic light contacts are reset by moving the handle past the on position without moving the knob toward the off position. This prevents the circuit breaker from accidentally tripping when resetting the traffic light circuit.

The transformer secondary circuit breaker described above uses a single toggle and a latching mechanism to operate two or three poles. In the above-described transformer, the circuit breaker contact is located under the bimetal sensing element, so if oil leaks from the transformer for any reason, the bimetal is first exposed to the oil and the circuit breaker while the contact is still under oil. Trips. This sequence of operations prevents arcing of the contacts in explosive gas spaces above the reduced oil level.

The movable contact is located at the end of a long contact arm, which is pivoted around an axis so that the circuit can be opened by closing the circuit or by dropping it from the fixed contact by attaching the contact to the fixed contact. Let it go. The first binding device is connected to an elongated contact arm to engage the movable contact in the closed position. The second binding device is provided to keep the first binding device in the engaged state.

A bimetallic drive that reacts according to the current and / or oil temperature is provided for releasing the second binding device when a predetermined condition is exceeded. Obercenter toggele, spring-biased in the direction of collapsed position, is connected to the long contact arm, and if the circuit breaker is normally closed, the first binding device It is in an extended center (overcenter extended position). When the second binding device is loosened due to an overload current or an excessively high oil temperature, the first binding device moves to the position where the binding is loosened, causing the spring-loaded toggle to fall and snapping the circuit breaker with a snap action. To open.

An object of the present invention is to introduce a circuit breaker for a distribution transformer in which a trip of the circuit breaker is controlled by a bimetal having a structure in which power is intensively consumed at the base of the bimetal.

This invention is demonstrated by an Example, referring drawings.

FIG. 1 shows a self-protected columnar distribution transformer 10 that includes a circuit breaker 20. Transformer 10 includes an enclosure or tank 11 with arrester 12 and primary high pressure bushing 16. A secondary bushing, such as a low pressure bushing 15, is attached to the transformer enclosure 11 and the transformer load is connected to it. The traffic light 17 is mounted on the enclosure 11 and is electrically connected to the circuit breaker to operate at a predetermined low overload. The iron core and coil assembly 18 are embedded in an enclosure with the circuit breaker 20 attached thereto. The required primary winding lead 14 is connected to the high pressure bushing 16 from the iron core and coil assembly 18. Enclosure 11 is partially filled with insulating liquid dielectric 19, such as transformer oil. Circuit breaker 20 and assembly 18 of iron core and coil are immersed in insulating oil 19. Secondary wiring 22 from the iron core and coil assembly 18 is connected to the input terminal attached to the circuit breaker 20. Conductor 24 connects the output terminal of circuit breaker 20 to the low voltage bushing 15 attached to the transformer tank 11. The appropriate load is then connected to the low voltage terminal 26 of the distribution transformer 10.

2 to 4 show a circuit breaker 20 attached to the metal base 30. Carver 32 partially surrounds the sensing and tripping elements of the circuit breaker for protection during handling. Lead 22 of the iron core and coil assembly 18 is attached to the circuit breaker input terminal 34. An electrical conductor 24 disposed between the circuit breaker 20 and the transformer low voltage bushing 15 is attached to terminal 36 of the circuit breaker 20.

The circuit breaker terminal 34 is connected to the fixed contact 38. Circuit breaker terminal 36 is connected to fixed contact 40 via electrical conductor 42 and bimetal 44. The fixed contacts 38 and 40 of each pole are spaced apart. The bridge contact 46 is provided to make an electrical connection between the fixed contacts 38 and 40 when the circuit breaker is closed. Therefore, if the circuit breaker 20 is closed, the electric circuit is made from the terminal 34 to the circuit breaker terminal 36 through the fixed contact 38, the bridge contact 46, the fixed contact 40, the electrical conductor 42, and the bimetal 44. The bridge contact device 45 includes a movable bridge contact 46 attached to one part thereof to make an electrical connection between the fixed contacts 38 and 40 when the circuit breaker is closed.

The bridge contact is located under the bimetal 44. This is a very desirable feature. This is because, if for some reason, the transformer oil leaks, the bimetal is first exposed to the gas space above the oil, which heats up the metal and trips the breaker even if the contacts 46, 38, and 40 are still under the oil.

This operating sequence is preferred because it prevents arcing of the contacts in the explosive gas space above the reduced oil level.

The angular pole of the circuit breaker 20 is given an elongated contact arm 48, one end of which is firmly fixed to the shaft 50. The shaft 50, which can be made of metal, connects together the elongated contact arms 48 of all poles of the circuit breaker 20 to move simultaneously. In other words, the contact arms 48 are connected to the shaft 50 together and move simultaneously. The bridge device 45 is connected to the opposite end of the shaft 50 of the elongate contact arm 48. The insulator 52 is arranged at the end of the contact arm 48 such that the contact arm 48 is electrically insulated from the contact bridge arrangement 45. Spring 54 in contact device 45 provides a constant contact pressure so that bridge contact 46 can properly contact fixed contacts 38 and 40. As shown in the figure, if any one of the poles of the circuit breaker 20 is opened, all other poles must also be opened.

The shaft 50 is rotatably and firmly supported by a bracket 55 attached to the metal base 30. The fixed contacts 38 and 40 are electrically insulated from the substrate 30 by the insulating plate 56 secured to the substrate 30. The terminal 36 is connected to the insulating plate 58 firmly fixed to the board 30. Electrical conductor 42 is insulated from substrate 30 by transformer oil 19 and insulating plates 56 and 58 which fill the space of circuit breaker 20 during normal operation. In general, the L-shaped conductor 42 has its short legs attached to one leg of bimetal 44. The other leg of the bimetal 44 is attached to the terminal 36 in the shape of a magnet.

A single operating mechanism 60 is provided for operating all the poles of the circuit breaker 20. The implement 60 is connected to one of the elongated contact arms 48, which, when moved according to the position of the implement 60, also moves the other elongated contact arm 48 connected via the shaft 50. A single actuator 60 for all poles is attached to the side plates 62 and 64 which are firmly attached to the support base 30. The implement comprises a U-shaped actuator 66, the two legs of which are pivotally connected to the side plates 62 and 64 at points 68 and 70, respectively.

The first binding device 72 is rotatably connected to the shaft 74 located between the side plates 62 and 64. One pair of toggle links 76 and 78 is connected to the elongated contact arm 48, the other end of the toggle is connected to the first binding device 72, and the multiple spring 80 is connected to the knee of toggle 82 and U. It is connected between the upper parts of the mold 66 so that the contact arm 48 is snapped when the first binding device 72 is released. Toggle links 76 and 78 are connected to each other so that they can be rotated by curved pivot pins 82. The lower toggle 76 has its bottom connected to an elongated contact arm 48 by a pivot pin. At the top of the pair of toggle links 78 is formed a U-shaped slot which fits around the shaft 86 connected to the first binding device 72. That is, since the first binding device 72 is disposed between the pair of toggle 78, the support shaft is fitted into the U-shaped slot formed in the upper toggle link 78. A spring holder is attached to the bent pin 82 to bind the lower ends of the plurality of springs 80. The shaft 90 is fixed on the U-shaped portion 66 and the upper end of the spring 80 is attached thereto. The upward force generated in the spring 80 causes the toggle link 78 to engage the shaft 86 in the first binding device 72.

When the circuit breaker is assembled, the ends of the pair of links 78 are twisted to ensure engagement with the pin 86. The first binding device 72, which can be released, is held bound by the second binding device. The second binding device 92 is biased toward the unbound state by the torsion spring. When the second binding device 92 is left unbound, the first binding device 72 is released and, under the force of the spring 80, rotates the shaft 74 around to knock down the toggles 76-78 and lifts the long contact arm 48.

When the breaker is closed, the second engagement device 92 is prevented from moving to an unbound position when it is closed by the cam surface surface 96 that is part of the trip bar mechanism 98. As shown in FIGS. 3-4, when the circuit breaker is normally closed, a portion 106 of the second binding device 92 is reset by the cam surface 96 (reset against the cam surface 96).

When the trip bar mechanism is rotated counterclockwise by a predetermined angle, the cam surface 96 exits the opening 100 of the second binding device 92 and the second binding device 92 is rotated in the direction of loosening the first binding device 72. Loosen and trip circuit breaker 20 to open. The trip bar mechanism 98 is connected to be rotated by the current sensitive device when the current through the circuit breaker 20 exceeds a preset value.

At each pole of the circuit breaker 20 there is a separate trip device comprising a current sensitive bimetal element 44 through which the load current of the associated pole flows. That is, the bimetal element 44 is electrically connected in series with the breaker contacts 38, 40, 46 of the circuit of the circuit breaker 20. FIG. Bimetal 44 is generally U-shaped and has adjusting screw 102 in the bend. The bridge of bimetal 44 is connected to fixed conductor 42 and the other leg of bimetal 44 is connected to fixed terminal 36. The adjusting screw 102 is arranged to be in contact with the insulator 104 of the trip bar mechanism 98 when the bimetal 44 is deflected. For example, when an overload occurs below 500% of the normal rated current, the bimetal element is heated and deflected toward trip bar mechanism 98.

When the bimetal element is deflected by the current flowing through it, the rounded edge of the adjusting screw 102 binds the insulating plate 104 attached to the trip bar mechanism 98, so that the trip bar 98 rotates counterclockwise to reach the trip state and the second binding The circuit breaker 20 trips open because the device 92 is released. The cam portion 96 of the trip bar mechanism 98 exits the latching surface 106 to release the second binding device 92. The first binding device 72 then rotates around the pivot 74 to move the operating line of the spring 80 to the left of the toggle rotating bend 82 to knock down the toggles 76-78 and open the circuit breaker 20 in a snap action.

The construction of the bimetallic thermal element 44 used in the circuit breaker 20 submerged in oil must satisfy the following two conditions.

(1) Even if a given oil temperature varies by (ΔT), the required deflection must occur (2) and the required deflection must also be caused by the flow of current given for a specified period of time.

The bimetal thermal trip element of the prior art has a structure having a linear power consumption distribution along its length as shown in FIG.

The bimetal of the structure according to the principles of the present invention is deflected as necessary while reducing power consumption as shown in FIG. Bimetal 44 made according to the principle of the present invention is formed of a narrow portion of the support end and a relatively wide portion 45 of the deflection end. Reference is made to FIG. 5 which shows a biased bimetal to better understand the present invention. Assuming a 2 ″ bimetal with a given thickness, the required deflection can be obtained from the following formula.

Where F is the constant L is the bimetal length ΔT is the temperature change t is the bimetal thickness.

For example, ΔT = 100 ℉

Let's assume that at the tip as shown in Figure 5

Now we analyze the phenomenon when the current flows through the bimetal. Assume that the current is consumed by one watt in each of the two one inch portions X and Y. In this case, of course, the temperature of the bimetal must be increased to 100 ° F.

For analysis we can assume that the bimetal is divided into two parts X and Y. Global bias can be thought of as the sum of your biases. The bottom X will deflect as follows.

The top will deflect the same as the bottom. However, since the upper part is effectively attached to the tangent of the lower end, it will be further deflected as it is deflected into the steel extension. The top will therefore be deflected by adding 0.010 "times the distance and the slope.

The slope is calculated as follows.

L = 1, so the bias due to slope is 0.02 ″.

Although bimetals of the same thickness are used where the same deflection occurs with a change in the oil temperature of ΔT, but instead of bimetals having a uniform heat distribution along the bimetal, the use of concentrated heat in the lower part of the bimetal has the advantage of overall deflection. If 1.5 watts are consumed at X and 0.5 watts are consumed at Y, then the entire 2 watts is consumed equally but the bias is increased.

The lower deflection will increase directly proportional to the temperature proportional to the power consumed, assuming a short time.

Therefore, the deflection due to the lower temperature is as follows.

The tangential deflection is as follows.

The deflection by the top is as follows.

Therefore, the overall deflection is

Of course, this is greater than the 0.040 ″ deflection caused by the uniform power distribution.

As a direct indication of power saving, calculating the power consumption required for a deflection of 0.040 "using the above structure, in which the lower power consumption is three times the upper power consumption, it is 1.2 watts at the bottom, 0.4 watts at the top, and 1.6 watts total. . In this particular case, 2 to 0.4 watts is saved, which is a 20% reduction.

The calculation for the 0,040 ″ bias is as follows.

Slope at the midpoint,

To fit the above equation, the thickness must of course be equal, while the width must be changed to reduce power consumption.

The watts consumed vary depending on the width, so

Therefore, the ratio of the width of 0.4 watts to the width of 1 watt is as follows.

Similarly, the ratio of the width of the lower 1.2 watts to the lower 1.0 watts is

The structure of the prior art bimetals relative to the structure of the new bimetal is shown in FIGS.

Of course, many of the above-described changes can be developed for a particular situation. However, it will have a common feature that the power consumed is concentrated in the relatively lower fixed part of the bimetal.

Claims (1)

A circuit breaker as described in the text and as shown in the figures, wherein the circuit breaker is characterized in that the power consumption is made larger at the relatively corrected end portion than at the end portion where the bimetal structure is deflected.