Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
2002-01-16
2003-11-18
Wu, Daniel J. (Department: 2632)
Communications: electrical
Condition responsive indicating system
Specific condition
C318S757000, C318S778000, C340S525000, C340S648000, C340S657000, C340S659000, C340S664000, C361S002000, C361S012000
Reexamination Certificate
active
06650245
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a multi-functional hybrid contactor, and more particularly, to a multi-functional hybrid contactor having a function of an electronic motor protection relay (EMPR) and a function of selectively starting a motor in a direct starting mode or a soft starting mode.
2. Description of the Background Art
In general, a method for starting a motor includes a direct starting method for supplying a power source voltage directly to a motor by using a relay and a relay contact and a soft starting method using a semiconductor switch device.
The direct starting method has a problem that, since the power source voltage is directly supplied to the motor, much surge current is caused on power supplying to damage a motor and a contact of a contactor is also damaged.
In order to protect the motor against the surge current generated in starting a motor for improving the direct starting method, a method has been proposed in which a motor is started by a so-called ‘star connection’ in its starting and the star connection is converted into a so-called ‘delta connection’ to operate the motor in an operation that a stable power source voltage is supplied, as shown in FIG.
1
.
FIG. 1
illustrates a motor control apparatus adopting the prior art.
As shown in
FIG. 1
, a motor control apparatus includes: a circuit breaker (MCCB: Molded case circuit breaker)
11
for conducting or cutting off a source current inputted from a three-phase power source terminal (R, S, T); an electronic motor protection relay (EMPR)
14
for monitoring an inverted phase, a phase deficiency, an unbalance of phases, an overload or an over current during an operation of a motor
16
so as to determine whether there is an error in the source current supplied to the motor
16
and protect the motor
16
; a power supply contactor (MC
M
)
15
for switching-controlling the three-phase current applied to the motor
16
through coils U, V and W of the motor
16
from the electronic motor protection relay
14
; and an operation contactor (MC
D
)
17
for switching-controlling the current applied to the motor
16
through coils X, Y and Z of the motor
16
from the electronic motor protection relay
14
; a starting contactor (MC
S
)
18
being connected to the coils X, Y and Z of the motor
16
and turned on in starting; and an auxiliary circuit
13
being connected to the three contactors
15
,
17
and
18
and sequence-controlling ON/OFF of the contactors
15
,
17
and
18
.
The operation of the motor control apparatus constructed as described above will now be described.
First, in a state that three-phase alternating current (abbreviated AC hereinafter) is being supplied as three contacts of the molded case circuit breaker
11
are closed, when a user presses a starting switch
12
connected to the auxiliary circuit
13
in order to operate the motor
16
, the electronic motor protection relay
14
supplies three-phase power current, and at the same time, starts to continuously monitor the current being supplied to a circuit of the motor
16
.
At this time, the auxiliary circuit
13
magnetizes a power supplying contactor controlling relay (not shown) and a starting contactor controlling relay (not shown) installed therein to close the power supplying contactor and the starting contactor
18
, and accordingly, the motor
16
assumes a so-called ‘star connection’ (i.e., ‘Y connection’) configuration and starts rotating.
Subsequently, when a predetermined time elapses after the motor
16
is started, the auxiliary circuit stops the magnetization of the starting contactor controlling relay to open (OFF) the starting contactor
18
and magnetize an operating contactor controlling relay to close the operation contactor
17
.
Then, as the connection configuration of the motor
16
is changed to a so-called ‘delta connection’, a rated voltage is supplied to the motor
16
.
Meanwhile, when the motor
16
starts rotating and a current flows, the electronic motor
16
protection relay
14
continuously measures the current flowing to the motor in order to determine whether there occurs an error in the power current.
If an error is detected from the power current, a cut-off signal is transmitted from the motor protection relay
14
, passing the auxiliary circuit
13
, to the power supplying contactor
15
, so that the power supply contactor
15
is opened to cut off the power being supplied to the motor
16
.
However, though the conventional motor control apparatus having the so-called star/delta connection' configuration converting method advantageously reduces the surge current, it fails to have a complete soft starting characteristic. In addition, in order to reduce the surge current, three contactors, one timer for switching starting and operating and three contactor controlling relay are required only to complicate its structure and enlarge its volume.
Moreover, in case that the motor is frequently opened and closed, the contact of the contactor and the motor may be damaged due to an arc generated at the contact of the contactor.
Furthermore, the conventional motor control apparatus can not be applied to a motor which has no function of converting to the ‘star-delta connection’.
That is, in general, in case of a motor having a rated voltage of 3-phase 380V or 440V, if a rated voltage is 220V, the motor is operated in a delta connection configuration, while if a rated voltage is 380V or 440V, the motor is operated in a star connection configuration.
Accordingly, in case that a rated voltage of the motor is 220V, the star-delta soft starting method can be adopted. But, in case that a rated voltage is 380V or 440V, since the ‘star connection’ itself is a condition for applying a rated voltage to the coil of a motor, an appropriate motor needs to be specially manufactured in order to apply the star-delta connection method.
As one solution to the problems, a solid-state switched soft starter (SSSS) method for controlling a level of a voltage applied to a motor or a variable voltage variable frequency (VVVF) method for converting a voltage by a frequency is used.
However, such equipment is more expensive compared to the apparatus operated in a star-delta connection method, and there are difficulties in its application.
In addition, as for the SSSS constructed with only semiconductor switches, during current conducting, heat is generated due to a loss at the both ends of a switch and thus a large heat sink is required to cool the heat, resulting in an increased size of the motor control apparatus.
FIG. 2
is a schematic block diagram of a hybrid contactor in accordance with the prior art.
As shown in
FIG. 2
, a soft starting type motor control apparatus using a hybrid contactor to prevent an arc current generated at the instant when a mechanical relay contact is turned off, including: a main contact
40
of a contactor connected between an AC power source
30
and a load (motor)
60
; a relay
50
for controlling switching of the main contact
40
of the contactor; a switch unit
23
having silicon controlled rectifiers (SCR
1
and SCR
2
), that is, semiconductor switching devices, connected in parallel in an inverse direction at the main contact
40
and turned on at a time just before and at a time just after the main contact
40
is closed in order to supply a load current; a snubber
22
for restricting a spike voltage generated at both ends of the switch unit to be below a predetermined value; a driving coil voltage controller
80
for outputting a coil driving voltage (V_coil) to the relay
50
, detecting a level change of an input driving voltage (V-input), and outputting a gate driving pulse stream (Vx); and gate driving units
21
and
70
being driven by the gate driving pulse stream (Vx) and supplying a drive signal to the switching unit.
The snubber
22
includes a resistance R
3
, a condenser C
3
and a varistor (ZNR
1
) restraining an over current.
FIG. 3
is a detailed block diagram of the driving coil voltage controller of FIG.
2
.
As
LG Industrial Systems Co. Ltd.
Pham Lam
Wu Daniel J.
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