Electricity: magnetically operated switches – magnets – and electr – Electromagnetically actuated switches – Plural independently operable switches
Reexamination Certificate
2001-11-07
2004-09-21
Donovan, Lincoln (Department: 2832)
Electricity: magnetically operated switches, magnets, and electr
Electromagnetically actuated switches
Plural independently operable switches
C200S050010, C335S132000
Reexamination Certificate
active
06794967
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a magnetic contactor(electromagnetic switch device) for star-delta connections, and more particularly to an electromagnetic switch device designed to be used for a star-delta starter adapted to start up a three-phase electric motor in order to allow the motor to be driven at its full speed within a short period of time.
BACKGROUND ART
As well known, star (Y)-delta (&Dgr;) starters, which are used to start up an electric motor, serve to establish a star connection for the electric motor upon the start-up of the electric motor, thereby reducing starting current and starting torque required in the start-up of the electric motor to a ⅓ level, while switching the connection for the electric motor into a delta connection after completion of the-start-up of the electric motor so that the electric motor is driven-in the delta connection state. Such star-delta starters are widely used in a variety of industrial fields in order to protect electric motors and peripheral devices thereof from overload.
Star-delta starters are classified into a contact type using an electromagnetic switch device adapted to switch electric contacts by use of electromagnets, and a non-contact type using a semiconductor switch device. The type using an electromagnetic switch device is more widely used.
FIGS. 1
a
,
1
b
and
2
illustrate a conventional electromagnetic switch device and a star-delta starter using the electromagnetic switch device, respectively.
FIG. 1
a
is a perspective view illustrating the electromagnetic switch device, and
FIG. 1
b
is a cross-sectional view taken along the line A—A of
FIG. 1
a
.
FIG. 2
is an equivalent circuit diagram illustrating the star-delta starter.
As shown in
FIGS. 1
a
and
1
b
, the conventional electromagnetic switch device, which is denoted by the reference character C, includes a body
1
, and a cover
2
separably attached to an upper surface
1
a
of the body
1
. Three pairs of terminals
3
are disposed on the upper surface
1
a
of the body
1
in such a fashion that the terminals of each terminal pair are arranged at opposite sides of the body
1
, respectively, while being insulated from one another. Electric power lines not shown are connected to the terminals
3
, respectively. Isolating plates
4
are arranged at opposite sides of the cover
2
to isolate adjacent ones of the terminals
3
.
Three pairs of fixed contacts
5
are also provided. Each fixed contact
5
is arranged at an end of an associated one of the terminals
3
extending toward a central portion of the body
1
. The fixed contacts
5
are insulated from one another. A vertical moving member
6
is arranged at the central portion of the body
1
in such a fashion that it is upwardly and downwardly movable. Three pairs of moving contacts
7
insulated from one another are mounted to the vertical moving member
6
at opposite sides of the vertical moving member
6
in such a fashion that each of the, moving contacts
7
selectively comes into contact with an associated one of the fixed contacts
5
so that it is short-circuited or opened with respect to the associated fixed contact
5
. A compression coil spring
8
is arranged around the vertical moving member
6
between the upper surface
1
a
of the body
1
and the moving contacts
7
in such a fashion that it always urges the vertical moving member
6
upwardly.
A fixed core
9
is arranged at a lower portion of the body
1
. A coil
10
is wound around the fixed core
9
in order to form an electromagnet. Above the fixed core
9
, a moving core
11
is arranged in such a fashion that it moves vertically along with the vertical moving member
6
in accordance with a magnetization of the electromagnet.
The conventional star-delta starter using electromagnetic switch devices having the above mentioned configuration includes an electromagnetic switch device C
1
for a main circuit, an electromagnetic switch device C
2
for a star circuit, and an electromagnetic switch device C
3
for a delta connection, which are connected together as shown in the equivalent circuit diagram, of FIG.
2
and activated by a timer (not shown) to start up a three-phase electric motor M.
When current flows through the coil
10
of the electromagnetic switch device C
2
for the star circuit upon starting the three-phase electric motor M, the electromagnet formed by the fixed core
9
and coil
10
is magnetized by virtue of the current.
Accordingly, the electromagnet generates a magnetic force greater than the resilience of the spring
8
, so that the vertical moving member
6
and moving core
11
are downwardly moved. As a result, the moving contacts
7
, which also move downwardly, come into contact with the fixed contacts
5
, respectively.
When the electromagnetic switch device C
1
for the main circuit is activated in accordance with the same procedure as mentioned above, a star connection is established for the three-phase electric motor M, so that the three-phase electric motor is started up using starting current and starting torque reduced to a ⅓ level. At the same time, the timer not shown begins to operate in order to count the drive time of the three-phase electric motor M.
After a predetermined period of time elapses, the current flowing through the coil
10
of the electromagnetic switch device C
2
for the star connection is cut off by an operation of the timer. At the same time, current flows through the coil
10
of the electromagnetic switch device C
3
for the delta connection.
In this state, the magnetic force of the electromagnet formed by the fixed core
9
and coil
10
of the electromagnetic switch device C
2
for the star connection disappears. As a result, the vertical moving member
6
is upwardly moved along with the moving core
11
and moving contacts
7
by virtue of the resilience of the spring
8
, thereby causing the moving contacts
7
to be separated from the fixed contacts
5
.
Meanwhile, the electromagnet formed by the fixed core
9
and coil
10
of the electromagnetic switch device C
3
for the delta connection is magnetized by virtue of the current flowing through the coil
10
. As a result, the moving contacts
7
are downwardly moved, so that they come into contact with the fixed contacts
5
, respectively.
Accordingly, the electromagnetic switch device C
3
for the delta connection is short-circuited to electric power lines at its one-side terminals
3
. As a result, the three-phase electric motor M is switched to the star connection state to a delta connection state, so that it is driven at a full speed.
In the star-delta starter having the above mentioned configuration, each of its electromagnetic switch devices is used only for a single purpose, that is, a star connection or a delta connection. For this reason, the conventional star-delta starter cannot implement a desired system unless at least two electromagnetic switch devices are used, even when those used for the main circuit are not taken into consideration.
As a result, the conventional star-delta starter involves high-manufacturing and installing costs and a large occupation space.
The conventional star-delta starter also involves a complex wiring for the connection between the electric motor and the electromagnetic switch device used. Such a complex wiring may result in a possibility of erroneous connections. In particular, such a wiring may be easily damaged by an external force applied thereto, thereby resulting in an erroneous operation of the starter or a damage of the electric motor.
DISCLOSURE OF INVENTION
Therefore, an object of the invention is to solve the above mentioned problems involved in the prior art, and to provide an electromagnetic switch device for star-delta connections which includes two electromagnets arranged in its body and two switching units operating in accordance with respective magnetization states of the electromagnets in order to selectively establish a star connection or a delta connection for a three-phase electric motor, so that it can reduce insta
Donovan Lincoln
Shin Dong-A Electric Corp.
Snell & Wilmer L.L.P.
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