WO2018122630A1

WO2018122630A1 - Contact assembly for a switchgear

Info

Publication number: WO2018122630A1
Application number: PCT/IB2017/054557
Authority: WO
Inventors: Hrishikesh S BRAMHAPURIKAR; Bhushan KULKARNI; Ramesh VISWANATHAN IYER; Nilesh BAJIRAO LOKHANDE
Original assignee: ABB Schweiz AG
Current assignee: ABB Schweiz AG
Priority date: 2016-12-29
Filing date: 2017-07-27
Publication date: 2018-07-05
Anticipated expiration: 2019-06-29

Abstract

The invention provides a contact assembly for a switchgear. The contact assembly has a first contact with at least two cylindrical pin contact elements, wherein a first cylindrical pin contact element is coaxial to a second cylindrical pin contact element. The second contact has a tulip assembly with at least two sets of contact fingers. Contact fingers of a first set of contact fingers are mounted on a first cylindrical contacting element, and contact fingers of a second set of contact fingers are mounted on a second cylindrical contacting element of the second contact. The two cylindrical contacting elements of the second contact are coaxial. When the two contacts engage, current flows in parallel through contact fingers of the first set of contact fingers engaged with the first cylindrical pin contact element and contact fingers of the second set of contact fingers engaged with the second cylindrical pin contact element.

Description

CONTACT ASSEMBLY FOR A SWITCHGEAR

FIELD OF THE INVENTION

[001] The present invention relates to switchgear, and more specifically to a contact assembly for a switchgear.

BACKGROUND OF THE INVENTION

[002] Compact circuit breakers with higher current ratings, at similar or reduced form factors are desired. In such switchgear, the contact assembly (e.g. a tulip contact assembly) has a spring to hold contacts in a particular shape, and apply contact pressure, wherein the contacts (e.g. made from copper) also help in heat dissipation. For example, a copper strip pair contact may be bound with a helical spring in a circular shape. Taking another example, copper finger contacts may be held by a leaf spring in a circular shape.

[003] Such arrangements work fine for heat dissipation in circuit breakers having rating upto 2500 A. However, a heat sink needs to be added to extract heat from vacuum interrupter (VI) contacts and the copper flexibles for circuit breakers with rating above 2500A, even for ~40°C ambient application.

[004] The heat sink is required despite the significant amount of copper used in the busbars in such circuit breakers. Even with a heat sink and the significant amount of copper used in the busbars to dissipate the heat generated in the VI contacts and isolation contacts under natural cooling principle, ratings of 4000A and above may not be reachable for ~50°C ambient application. Such may be the case event if there is significant pole distance (e.g. 275 mm pole distance).

[005] Therefore, it is difficult to further reduce the panel and circuit breaker width under natural cooling. This adds to the limitation of retaining desired dielectric performance at ~75kVp when such heat sink is used and it makes it practically impossible to attain higher insulation levels of ~95kVp without increasing the form factor and the cost.

SUMMARY OF THE INVENTION

[006] An aspect of the present invention provides a contact assembly for a switchgear. The contact assembly comprises a first contact and a second contact that can engage for current flow through the first contact and the second contact. The first contact can be a fixed contact (e.g. fixed on a switchgear panel), while the second contact can be a movable contact (e.g. fixed on a vacuum interrupter assembly), and vice versa (i.e. the first contact can be movable, while the second contact is fixed). It is also possible that both the contacts are movable contacts. The contact assembly can have one or multiple pairs of fixed and movable contacts.

[007] The first contact has at least two cylindrical pin contact elements. A first cylindrical pin contact element of the at least two cylindrical pin contact elements, is coaxial to a second cylindrical pin contact element of the at least two cylindrical pin contact elements. Thus the first contact has at least two pins (or pin elements), wherein one pin is an outer cylindrical pin, and the second is an inner cylindrical pin. The first contact can be a single molded pin (i.e. casted as a single component) having the two cylindrical pin contact elements. Alternately, the second cylindrical pin contact element can be bolted with the first cylindrical pin contact element. The first contact can have a plurality of straight slots for heat dissipation. Such slots can be distributed evenly about a periphery of the first contact. For example, the first contact may have 12 to 14 slots distributed evenly about a circumference of the first contact.

[008] The second contact has a tulip assembly. The tulip assembly comprises at least two sets of contact fingers. Contact fingers of a first set of contact fingers (first tulip) are mounted on a first cylindrical contacting element of the second contact, and contact fingers of a second set of contact fingers (second tulip) are mounted on a second cylindrical contacting element of the second contact. Here, the first cylindrical contacting element and second cylindrical contacting element of the second contact are coaxial. Thus, the second contact has at least two tulips (or sets of contact fingers arranged cylindrically using a spring), wherein one tulip is an outer tulip mounted on an outer contact arm, and the second is an inner tulip mounted on an inner contact arm of the second contact. Similar to the first contact, the contact arm components (in the second contact) can be singular (i.e. a single mold), or connected to each other using connecting members (e.g. bolts).

[009] The contact fingers of the first tulip and the second tulip can be identical. Here, the first set of contact fingers can have a first number of contact fingers (e.g. 30, 32, 34 etc.), while the second set of contact fingers can have a second number of contact fingers (e.g. 4, 6, 8 etc.). Alternately, each contact finger of the first set of contact fingers can have a first current carrying capacity (e.g. 75A), while each contact finger of the second set of contact fingers has a second current carrying capacity (e.g. 50A).

[0010] The first contact and the second contact engage for current flow through the first contact and the second contact. For example, the two contacts can be engaged in a service position, while remain disengaged (e.g. isolated) in a test position. When the two contacts are engaged, current flows in parallel through the contact fingers of the first tulip engaged with the first cylindrical pin contact element, and the contact fingers of the second tulip engaged with the second cylindrical pin contact element.

[0011] An aspect of the present invention provides the switchgear with the contact assembly. The switchgear can have a circuit breaker assembly with one or more vacuum interrupters. For example, the circuit breaker assembly can have three poles, wherein each pole has a vacuum interrupter. The contact assembly provides for current flow between a switchgear panel and a vacuum interrupter of the one or more vacuum interrupters (e.g. of circuit breaker assembly). The first contact of the contact assembly can be a fixed contact attached with the switchgear panel, while the second contact is a movable contact attached with the circuit breaker assembly. Here, a contact of the vacuum interrupter can be exposed for heat dissipation.

BRIEF DESCRIPTION OF DRAWING

[0012] Fig. 1 illustrates a circuit breaker with a heat sink.

[0013] Fig. 2 illustrates a pin contact of the circuit breaker with the heat sink

[0014] Fig. 3 illustrates a switchgear with a contact assembly, in accordance with an embodiment of the present invention.

[0015] Fig. 4 illustrates a side view of the contact assembly, in accordance with an embodiment of the present invention.

[0016] Fig. 5 illustrates a sectional view of the contact assembly, in accordance with an embodiment of the present invention.

[0017] Fig. 6 illustrates a side view of a first contact of the contact assembly, in accordance with an embodiment of the present invention.

[0018] Fig. 7A and 7B illustrate side and front views of the first contact of the contact assembly, in accordance with another embodiment of the present invention.

[0019] Fig. 8 illustrates a sectional view of the first contact of the contact assembly, in accordance with an embodiment of the present invention. [0020] Fig. 9 illustrates a side view of a second contact of the contact assembly, in accordance with an embodiment of the present invention.

[0021] Fig. 10 illustrates a front view of the second contact, in accordance with an embodiment of the present invention.

[0022] Fig. 11 illustrates a sectional view of the second contact, in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION

[0023] A vacuum interrupter (VI) in a circuit breaker with rating of 3150 A, typically has a resistance of 6-8 microohm without silver plating of the VI stems. Therefore, the heat generated at a rating of 3150A is typically 60 watts to 80 watts (W). Rest of the circuit breaker typically has resistance of about 2 microohms. This constitutes for 20W of heat generated. The joints of tulip and switchgear pin has resistance of about 0.5 - 0.75 microohm each. Two such tulip + pin joints occur per phase. Therefore, one phase of the circuit breaker will have 1 - 1.5 microohm resistance resulting into heat dissipation of 10-15W.

[0024] Most of the heat is conducted through the contact arm via the tulip + switchgear pin joint. The heat sink is used to have rating of 3150A, as the ability of the joint is limited to transfer the heat at elevated temperatures. The joint also acts as a source of heat and thereby limits the area for heat radiation.

[0025] Therefore, it is required to have two compensators for the heat management within specified safe limits (e.g. as specified by a standard).

[0026] Here, there are two ways to do it: • To increase the area of the heat conduction: It is needed to increase the contact arm section. However, it is found that the same is more than adequate. But the ratio of the cross section to the surface area for radiation is limited due to high amount of copper used.

• To increase the parallel paths of current flow in the tulip: This is possible by adding more fingers to the tulip. This will work in two ways. First, it will bring down the effective current flow per finger resulting in the reduction of the self- heat generation. Therefore, it will be able to conduct more heat coming from the VI to the switchgear. Secondly, adding more fingers will also add more surface area to radiate the heat out from the contacts, faster.

[0027] Reduction of the heat dissipated from the circuit breaker to the surrounding by avoiding the heat sink, will provide a temperature cushion to the circuit breaker chamber.

[0028] Consider a circuit breaker shown in Fig. 1. In the circuit breaker, the pole pitch may remain as high as around 275 mm, when a heat sink (102) is provided on the top side of the pole. The heat sink (102) may be an Aluminum heat sink coated with epoxy / PU powder. The heat sink limits the compaction of pole pitch to 275mm. It is difficult to further reduce the pole pitch of the circuit breaker due to the heat sink. Also, the fixed contact (106) is a single bolt pin holding (as shown in Fig. 2). Accordingly, there is current and heat concentration at center.

[0029] There are also specially machined bolts (108) for heat transfer, which add to cost. There is accordingly a need to modify the heat dissipation arrangement of such a circuit breaker, in order to have higher rating while having similar or reduced size (e.g. same / reduced pole pitch). [0030] The present invention provides a solution to reduce heat generated and dissipated from a circuit breaker. Aspects of the present invention relate to a contact assembly for a switchgear. The switchgear can have a circuit breaker assembly with one or more vacuum interrupters. For example, the circuit breaker assembly can have three poles, wherein each pole has a vacuum interrupter. The contact assembly provides for current flow between a switchgear panel and a vacuum interrupter of the one or more vacuum interrupters.

[0031] Fig. 3 shows the switchgear with the contact assembly of the present invention. As shown in Fig. 3, the contact assembly comprises two pairs of contacts, wherein each pair of contacts has a first contact (302) and a second contact (304). Here, a single pole circuit is represented, and a switchgear may have one or three poles. Accordingly, there may be corresponding number of contact pairs.

[0032] The first contact may be a fixed contact (e.g. to be fixed with the switchgear panel), while the second contact may be a movable contact (e.g. fixed with the circuit breaker assembly). It should be apparent that the contacts may be arranged such that they are swapped, i.e. the first contact is designed to be movable, while the second contact is fixed (i.e. on the switchgear panel). It is also possible to have both the contacts as movable contacts. The contact assembly may have different number of contacts than shown in Fig. 3. For instance, there may be more than two pairs of first contact and second contact (e.g. six pairs, two pairs for each phase).

[0033] As can be seen in Figs. 6 and 7A, the first contact has a cylindrical shape. Further, the first contact has a plurality of straight slots (such as 602). These slots can be distributed evenly about a periphery of the first contact. For instance, the slots can be arranged in a cylindrical shape as shown in Fig. 6. These slots can provide ventilation, and thereby assist in heat dissipation. Also, straight slots provide more gaps for ventilation as compared with circular openings (202, shown in Fig. 2). The number of slots in the first contact may be varied (e.g. from 8 to 16). For example, there may be 12 slots for ventilation.

[0034] The first contact has two or more pin contact elements (conductive elements). The conductive elements can be metallic (e.g. made from Copper, Aluminum etc.). Further the conductive elements can have predetermined shape. For example, the first contact can have a first pin contact element (802), and a second pin contact element (804). Each pin contact element provides for a contact surface. For example, an outer peripheral surface, or an inner peripheral surface of 802, or 804 can act as a contact surface. The second pin contact element can be coaxial to the first pin contact element, with a common axis (502) as shown in Fig. 5. The two pin contact elements can be connected with each other using one or more connections. For instance, the second pin contact element can be bolted using bolts through openings (such as 806) as shown. Alternately, as can be seen in Fig. 5, the first contact can be a single molded contact having the two cylindrical pin contact elements.

[0035] Thus the first contact provides a dual pin that can be attached with a single bolt, with uniform current and heat transfer at the outer periphery. There may be openings to enable attachment of the first contact (e.g. 808 for attachment with a switchgear). It should be apparent that there could be variations in the design of the first contact. For example, in place of the cylindrical pin contact elements, there could be conical pin contact element (as is apparent from Fig. 5).

[0036] The first contact is designed such that components of the first contact engage with corresponding components of the second contact for current and heat flow. The second contact has a plurality of contact fingers (902) attached with a contact arm (904) as shown in Fig. 9. The contact arm can have a bare copper surface for higher radiation. Alternately, the arm can be painted for improved radiation performance. [0037] The plurality of contact fingers can have a first set of contact fingers (1002) and a second set of contact fingers (1004). The first set of contact fingers (first tulip) can have contact fingers arranged in a predetermined shape (e.g. circular / cylindrical towards the outer side as 1002 shown in Fig. 10). Similarly, the second set of contact fingers (second tulip) can have contact fingers arranged in a predetermined shape (e.g. circular / cylindrical towards the inner side as 1004 shown in Fig. 10). In the embodiment shown in Fig. 10, the first set of contact fingers and the second set of contact fingers are co-centric, with the second set located in the inner side.

[0038] The first set of contact fingers can have a greater number of contact fingers (e.g. 25 - 35), as compared to the second set of contact fingers (e.g. 2 - 10). This is because the diameter of the first tulip is greater than the diameter of the second tulip. Also, the capacity of the contact fingers in the first set can be same (identical) or different (e.g. higher) as compared to that of the contact fingers of the second set. The second set of contact fingers provide for additional (and parallel) flow for current (as compared with a single set of contact fingers (110) shown in Fig. 1). Thus, when the first contact and the second contact are in an engaged position, the contact fingers of the first set of contact fingers engage with the first cylindrical pin contact element, and the contact fingers of the second set of contact fingers engage with the second cylindrical pin contact element (as can be seen in Fig. 5). This enables current to flow in parallel through the first tulip and through the second tulip. This assists in having a higher current and heat transfer ability, as compared with the circuit breaker shown in Fig. 1.

[0039] The second contact can have one or more conductive elements (similar to the first contact) for current and heat flow. The conductive elements (of contact arm 904) can provide for current and heat flow between VI contact (306) and the first contact. For instance, the contact arm of the second contact can have a first cylindrical contacting element (1102), and a second cylindrical contacting element (1104) for current and heat flow as shown in Fig. 11. Here, the second cylindrical contacting element is coaxial to the first cylindrical contacting element, with common axis 502 as shown in Fig. 5. Also, the two cylindrical contacting elements can be connected with each other using one or more connections. For instance, the second cylindrical contacting element can be connected using bolts though opening (such as 1106) as shown in Fig. 11. Such openings may also assist in heat dissipation. Alternately, the entire contact arm can be singular (i.e. cast in one piece) as for the first contact.

[0040] There can be additional components for heat dissipation in the switchgear. The VI support contact (306) can be exposed (not shown in figures) for enhanced heat dissipation. For example, one or more slots may be provided on the VI support contact (306) for heat dissipation from the VI to the ambient environment.

[0041] Thus the circuit breaker of the present invention has increased surface area to radiate heat in contact pin (elements) of switchgear and contact arm of the circuit breaker. Further, there are more contact touch points (i.e. more contact fingers) for current and heat flow, which also provides for upgradation of current rating of the circuit breaker. In addition, the slots provide more area in the pin for ventilation of hot gases. All these result in having a circuit breaker without heat sink, which provides for compaction of the circuit breaker pole center (distance) / panel size. The busbar length is also reduced (in each phase) due to size reduction of the panel, which provides for reduction of the footprint of the distribution substation, while having similar / higher current and heat transfer as compared with the earlier circuit breakers.

Claims

1. A contact assembly for a switchgear, the contact assembly comprising:

a first contact (302) with at least two cylindrical pin contact elements, wherein a first cylindrical pin contact element (802) of the at least two cylindrical pin contact elements is coaxial (502) to a second cylindrical pin contact element (804) of the at least two cylindrical pin contact elements; and

a second contact (304) with a tulip assembly, wherein the tulip assembly comprises at least two sets of contact fingers, wherein contact fingers of a first set of contact fingers (1002) are mounted on a first cylindrical contacting element (1102) of the second contact, and contact fingers of a second set of contact fingers ( 1004) are mounted on a second cylindrical contacting element (1104) of the second contact, wherein the first cylindrical contacting element and second cylindrical contacting element of the second contact are coaxial (502),

wherein the first contact and the second contact engage for current flow through the first contact and the second contact, wherein the current flows in parallel through:

the contact fingers of the first set of contact fingers engaged with the first cylindrical pin contact element, and

the contact fingers of the second set of contact fingers engaged with the second cylindrical pin contact element.

2. The contact assembly of claim 1, wherein the first contact is a single molded pin having the two cylindrical pin contact elements.

3. The contact assembly of claim 1, wherein the second cylindrical pin contact element is bolted with the first cylindrical pin contact element.

4. The contact assembly of claim 1, wherein the first contact comprises a plurality of straight slots for heat dissipation, distributed evenly about a periphery of the first contact.

5. The contact assembly of claim 1, wherein the contact fingers of the first set of contact fingers and the second set of contact fingers are identical, and the first set of contact fingers comprises a first number of contact fingers, and the second set of contact fingers comprises a second number of contact fingers.

6. The contact assembly of claim 1, wherein each contact finger of the first set of contact fingers has a first current carrying capacity, and each contact finger of the second set of contact fingers has a second current carrying capacity.

7. A switchgear, the switchgear comprising:

a switchgear panel;

a circuit breaker assembly with one or more vacuum interrupters; and a contact assembly for current flow between the switchgear panel and the one or more vacuum interrupters, wherein the contact assembly comprises:

a first contact (302) with at least two cylindrical pin contact elements, wherein a first cylindrical pin contact element (802) of the at least two cylindrical pin contact elements is coaxial (502) to a second cylindrical pin contact element (804) of the at least two cylindrical pin contact elements; and a second contact (304) with a tulip assembly, wherein the tulip assembly comprises at least two sets of contact fingers, wherein contact fingers of a first set of contact fingers (1002) are mounted on a first cylindrical contacting element (1102) of the second contact, and contact fingers of a second set of contact fingers (1004) are mounted on a second cylindrical contacting element (1104) of the second contact, wherein the first cylindrical contacting element and second cylindrical contacting element of the second contact are coaxial (502),

8. The switchgear of claim 7, wherein the first contact is a fixed contact attached with the switchgear panel, and the second contact is a movable contact attached with the circuit breaker assembly.

9. The switchgear of claim 7, wherein a contact of each vacuum interrupter is exposed for heat dissipation.