Methods and apparatus for transferring electrical power

BACKGROUND OF THE INVENTION

This invention relates generally to electrical power transfer and, more particularly, to electrical power transfer switches.

Many businesses use transfer switches to switch between power sources which supply power to the business. For example, from a public utility source to a private secondary supply. Critical equipment and businesses, such as hospitals, airport radar towers, and high volume data centers are dependent upon transfer switches to provide continuous power. More specifically, in the event that power is lost from a primary source, the transfer switch shifts the load from the primary source to an alternate source in a minimal amount of time to facilitate providing continuous electrical power to such equipment and businesses.

At least one known transfer switch utilizes a “make-beforebreak” switch to transfer the load from the primary source to the alternate source. The make before break switch includes dual main contacts which require dual shafts and a plurality of actuators. Transfer switches including dual main contacts and dual shafts may also include dual solenoids to drive the shafts. In the event one of the solenoids fails, the main contacts may remain in an undesired position thereby preventing the transfer switch from activating to enable the business to switch to an alternate power supply.

BRIEF DESCRIPTION OF THE INVENTION

In one aspect, a method for manufacturing a transfer switch is provided. The method includes providing a transfer switch including a first shunt contact and a second shunt contact, and operationally coupling a shunt solenoid to the first shunt contact and the second shunt contact such that when the solenoid is electrically activated the first shunt contact electrically couples a first source to a load and the second shunt contact electrically couples a second source to the load in a first pre-determined amount of time.

In another aspect, an apparatus for transferring power from a first source to a second source is provided. The apparatus includes a first shunt contact, a second shunt contact, and a shunt solenoid operationally coupled to the first shunt contact and the second shunt contact such that when the shunt solenoid is electrically activated the first shunt contact electrically couples a first source to a load and the second shunt contact electrically couples a second source to the load in a first pre-determined amount of time.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1

is a diagram of a power system including a transfer switch.

FIG. 2

is an illustration of one embodiment of a transfer switch that may be used with the power system shown in FIG.

1

.

FIG. 3

is a side view of the transfer switch shown in FIG.

2

.

FIG. 4

is a perspective view of a portion of the transfer switch in

FIG. 2

in a first operating position.

FIG. 5

is a perspective view of a portion of the transfer switch in

FIG. 2

in a second operating position.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1

illustrates a power system

8

which includes a transfer switch

10

used to selectively switch between a plurality of power sources, e.g. between a power source

12

and a power source

14

, to supply electrical power to a load

16

. For example, in one embodiment, load

16

is a hospital, airport radar tower or other electrical power user that desires a substantially uninterrupted power supply. Load

16

, via switch

18

, draws power from source

12

under normal operating conditions. If, for example, power source

12

fails or becomes inadequate to supply load

16

, load

16

is transferred via switch

18

to draw power from source

14

. When source

12

again provides sufficient power, load

16

may be transferred via switch

18

to resume drawing power from source

12

. The foregoing description of transfer switch

10

operation is exemplary only, and additional functions may be performed by transfer switch

10

.

FIG. 2

is a transfer switch

18

that may be used with power system

8

(shown in FIG.

1

). Transfer switch

18

includes a plurality of main contact phase compartments

20

. More specifically, switch

18

includes one phase compartment

20

for each phase of power entering transfer switch

18

. Compartments

20

are mechanically coupled together with a plurality of mechanical fasteners. In the exemplary embodiment, transfer switch

18

includes three phase compartments

20

. Transfer switch

18

also includes a main finger shaft

24

, a first shunt contact shaft

26

, and a second shunt contact shaft

28

. Finger shaft

24

, first shaft

26

and second shaft

28

extend from a first side

30

of transfer switch

18

to a second side

32

of transfer switch

18

. In one embodiment, finger shaft

24

, first shaft

26

and second shaft

28

are rotatably coupled to transfer switch

18

using a mechanical fastener (not shown), such as, but not limited to, a bolt and a nut, a mechanical clip or any other suitable fastener.

FIG. 3

is a side view of transfer switch

18

. Transfer switch

18

includes a single coil shunt contact solenoid

40

mechanically coupled to transfer switch

18

, a first shunt linkage

42

, a second shunt linkage

44

, and a third shunt linkage

46

. First shunt linkage

42

includes a first end

50

rotatably coupled to first shunt shaft

26

, and a second end

52

rotatably coupled to third linkage

46

. Second shunt linkage

44

includes an opening

60

, a first end

62

rotatably coupled to second shunt shaft

28

and a second end

64

rotatably coupled to third linkage

46

. Solenoid

40

is controlled by a controller (not shown).

Solenoid

40

includes a plunger

70

and a spring

72

. Plunger

70

also includes a connector

74

which extends through opening

60

to couple connector

74

in slidable contact with second shunt shaft

28

. Transfer switch

18

also includes a first limit switch

80

and a second limit switch

82

mechanically coupled to transfer switch

18

.

FIG. 4

is a perspective view of a portion of transfer switch

18

in a first operating position

90

.

FIG. 5

is a perspective view of a portion of transfer switch

18

in a second operating position

92

. Phase compartment

20

includes a first source bus

100

, a second source bus

102

, and a load bus

104

mounted in a housing

106

. In the exemplary embodiment, housing

106

is fabricated from a non-conductive material and electrically isolates each first source bus

100

, second source bus

102

, and load bus

104

. First source bus

100

includes a first contact

110

, a second contact

112

, and a third contact

114

that are each electrically coupled to a power source such as source

14

(shown in FIG.

1

). Second source bus

102

includes a first contact

120

, a second contact

122

and a third contact

124

each electrically coupled to a source such as source

12

(shown in FIG.

1

). Load bus

104

includes a first contact

130

, a second contact

132

, and a third contact

134

each electrically coupled to a load, such as load

16

(shown in FIG.

1

).

Phase compartment

20

also includes a finger assembly

140

mechanically coupled to finger shaft

24

. Finger assembly

140

includes a movable finger

142

and two contact pads

144

mounted on finger

142

. Finger assembly

140

also includes an electrical conductor

146

, such as a braid assembly attached to finger

142

to electrically couple finger

142

to load bus

104

as finger

142

is re-positioned. In the exemplary embodiment, finger

142

is symmetrical about a centerline

148

.

Phase compartment

20

also includes a first shunt contact

150

and a second shunt contact

152

that are each positioned within phase compartment

20

. First shunt

150

is mechanically coupled to first shunt shaft

26

, and second shunt contact

152

is mechanically coupled to second shunt shaft

28

. First shunt contact

150

includes a first contact

160

and a second contact

162

. First contact

160

and second contact

162

are electrically isolated from shunt shaft

26

by an electrically non-conductive device (not shown). Second shunt contact

152

includes a first contact

170

and a second contact

172

which are electrically isolated from shunt shaft

28

. In an alternative embodiment, first shunt contact

150

and second shunt contact

152

are fabricated such that electrical current is transferred through first shunt contact

150

and second shunt contact

152

without the use of contacts

160

,

162

,

170

, and

172

, respectively.

During use, when the controller senses the available power from either source

14

or source

16

. More specifically, the controller monitors a phase differential between source

12

and source

14

to determine when source

12

and source

14

are in approximate synchronism and when the available power is below a pre-set value. When source

12

and source

14

are approximately in synchronism, the controller causes solenoid

40

(shown in

FIG. 2

) to actuate thereby retracting plunger

70

(shown in

FIG. 2

) into solenoid

40

to move first shunt contact

150

and second shunt contact

152

from first operating position

90

(shown in

FIG. 4

) to second operating position

92

(shown in FIG.

5

). In first operating position

90

, first shunt contact

150

and second shunt contact

152

are “open” such that contacts

150

and

152

do not conduct electricity. In second operating position

92

, first shunt contact

150

rotates such that first shunt contacts

160

and

162

electrically couple with contacts

112

and

130

, respectively, thereby allowing electricity to flow from first power source

12

to load

16

. Additionally, second shunt contact

152

is rotated such that second shunt contacts

170

and

172

electrically couple with contacts

122

and

132

, respectively, thereby allowing electricity to flow from second power source

14

to load

16

. For example, retracting plunger

70

causes second shunt linkage

44

(shown in

FIG. 2

) to translate to move third linkage

46

(shown in FIG.

2

). As third linkage

46

is re-positioned, first shunt linkage

42

(shown in

FIG. 2

) is rotated at approximately the same rate as second shunt linkage

44

. Because first shunt contact

150

is coupled to first shunt shaft

26

, and second shunt contact

152

is coupled to second shunt shaft

26

, actuating solenoid

40

causes contacts

150

and

152

to translate from a non-conducting state to a conducting state to enable electricity to flow from first power source

12

to load

16

and from second power source

14

to load

16

.

In the exemplary embodiment, shunt contact

150

and shunt contact

152

are rotated together such that buses

100

and

102

respectively, are electrically coupled to load bus

104

when source

12

and source

14

are approximately synchronized. Shunt contacts

150

and

152

remain in a closed position for a first pre-determined amount of time. In one embodiment, shunt contacts

150

and

152

are closed between approximately seventy five milliseconds and approximately one hundred and twenty five milliseconds. In another embodiment, shunt contacts

150

and

152

are closed approximately one hundred milliseconds.

When first shunt contact

150

and second shunt contact

152

are in the closed position, i.e. conducting electricity, a single coil solenoid (not shown) coupled to finger

142

is activated to cause finger

142

to traverse from a first finger position

200

to a second finger position

202

. For example, if finger

142

is in position

200

, contacts

120

and

144

are electrically coupled such that electricity flows from power source

14

to load

16

. Furthermore, activating the finger solenoid causes finger

142

to traverse to position

202

such that contacts

110

and

144

are coupled to enable power to flow from source

12

to load

16

.

In one embodiment, main finger

142

traverses from first finger position

200

to second finger position

202

in a second pre-determined amount of time. In one embodiment, main finger

142

traverses from first position

200

to second position

202

between approximately sixty milliseconds and approximately seventy milliseconds. In the exemplary embodiment, the first pre-determined amount of time, i.e. amount of time shunt contacts

150

and

152

remain closed, is greater than the second pre-determined amount of time, i.e. time required for main finger

142

to traverse from first position

200

to second position

202

. When a main finger shaft of main finger

142

reaches second position

202

, another limit switch, such as limit switch

80

or limit switch

82

signals solenoid

40

to cut off. Spring

72

then extends plunger

70

causing shunt contacts

150

and

152

to return to an “open” position. For example, if finger

142

is in position

200

, when finger

142

traverses to second position

202

, finger

142

depresses first limit switch

80

and power to solenoid

40

is terminated, allowing energy stored within spring

72

to force plunger

70

out of solenoid

40

, thereby moving linkage

46

causing first shunt contact

150

and second shunt contact

152

to return to an open position. In another embodiment, if finger

142

is in second position

202

, when finger

142

traverses to first position

200

, finger

142

depresses first limit switch

82

and power to solenoid

40

is terminated, allowing energy stored within spring

72

to force plunger

70

out of solenoid

40

, thereby moving linkage

46

causing first shunt contact

150

and second shunt contact

152

to return to an open position.

In the exemplary embodiment, transfer switch

18

facilitates transferring load

16

from source

12

to source

14

, in phase, and without a loss of power to load

16

. Furthermore, transfer switch

18

includes only the main finger shaft coil and coil of solenoid

40

which can both operate as an open or a closed transition switch. In the event of a shunt contact failure, switch

18

can continue to operate as an open transition switch. Additionally, shunt contacts

150

and

152

are not required to be the same ampacity as the main contacts, nor have a load breaking or an arc quench capability.

Transfer switch

18

is adaptable for a two-pole, a three-pole, and a four-pole modular configuration with minimal additional hardware. Symmetrical and one-piece design of parts such as compartments

20

facilitate reducing a number of components, thus facilitating cost reductions.

Additionally, transfer switch

18

facilitates reducing the inertia of a shunt contact train. For example, during a closed transition operation without direct frequency control of the alternate source, the alternate source, typically a generator set, is usually set to a tenth of a hertz higher than the alternate source (a utility). An electronic controller monitoring the phase differential between the primary source and the alternate source will determine when the two are in synchronism. At that point a shunt signal will be issued causing the load to be connected to both the primary source and the alternate source and the main finger to transfer. Since shunt contacts

150

and

152

are physically smaller than bus

100

and bus

102

, shunt contacts

150

and

152

facilitate shunting the circuit more rapidly. Therefore, a length of time before shunting with a subsequent shifting to a more out of phase condition is reduced. This is beneficial to the load not seeing an electrical anomaly.

While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.