Electricity: motive power systems – Induction motor systems – Primary circuit control
Reexamination Certificate
2002-10-04
2004-11-16
Ro, Bentsu (Department: 2837)
Electricity: motive power systems
Induction motor systems
Primary circuit control
C318S781000
Reexamination Certificate
active
06819075
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a single-phase induction motor and, more particularly, to a voltage-controlled electronic relay for starting a single-phase induction motor.
2. Description of the Related Art
Conventionally, a single-phase induction motor that is operated with single-phase AC power includes an operation coil and a starting coil. The starting coil becomes conductive only at the moment when the motor starts to provide a starting rotary power to the motor and is maintained in OFF state when the motor is in its normal operation state after started. A device for turning on/off the starting coil of the single-phase induction motor is called a centrifugal switch or starting relay. A voltage-controlled electronic relay employs the characteristic that the voltage induced across both ends of the starting coil increases as the speed of revolution of the motor is raised. That is, the voltage-controlled relay provides power to the starting coil at the initial stage where the induction motor is supplied with power, and then detects the voltage induced across the starting coil to cut off the power applied to the starting coil when the induced voltage becomes higher than a predetermined level (when the motor reaches its normal operation state). In case that a heavy load is applied to the motor during its normal operation so that the motor becomes a constraint state, the voltage induced across the starting coil is lowered. The relay senses this induced voltage and provides power to the starting coil when the voltage becomes lower than a predetermined level to start the motor again. Here, the induced voltage turning off the relay is relatively high and the induced voltage turning on the relay again is relatively low, the difference between the two voltages being called ‘hysteresis width’.
A conventional voltage-controlled electronic relay for starting the single-phase induction motor includes the voltage-controlled electronic relay disclosed in Korean Pat. No. 91-2458 applied by the applicant. This voltage-controlled relay includes a single-phase induction motor
110
, and an electronic relay circuit
120
for turning on/off the starting coil of the motor, as shown in FIG.
1
.
Referring to
FIG. 1
, the single-phase induction motor
110
has operation coils W
1
and W
2
and the starting coil W
3
. The operation coils W
1
and W
2
are connected such that they directly receive commercial AC power (AC 110V) through power input ports L
1
and L
2
but the starting coil W
3
accepts the power via a starting capacitor SC and the electronic relay
120
.
The electronic relay
120
that is a switch for applying the power to the starting coil W
3
through the starting capacitor SC is constructed of a triac
121
and a control circuit for triggering the gate of the triac
121
. The control circuit includes a power supply unit
122
for supplying power to circuit elements of the relay, a control signal generator
123
for sensing the voltage across the starting coil W
3
to generate an ON/OFF control signal, and a triggering unit
124
for triggering the gate of the triac
121
according to the output of the control signal generator
123
.
The power supply unit
122
consists of a diode D
2
for rectifying the AC power applied through connection ports T
1
and T
2
, a filter capacitor C
4
for filtering the output of the diode D
2
, distribution resistors R
7
and R
8
, a zener diode ZD and a filter capacitor C
2
, to supply power Vcc to NAND gates M
1
, M
2
, M
3
and M
4
.
The control signal generator
123
is constructed of a diode D
1
and distribution resistors R
1
and R
2
for sensing the voltage across the starting coil W
3
, a resistor R
3
for controlling the hysteresis width and two NAND gates M
1
and M
2
, to sense the voltage induced across the starting coil W
3
to generate the control signal for turning on/off the triac
121
. The triggering unit
124
includes NAND gates M
3
and M
4
for creating oscillation according to the control signal and a transistor TR for interrupting a pick-up coil PC, the pick-up coil PC triggering the gate of the triac
121
. Here, the output of the NAND gate M
2
is positively fed back to the NAND gate M
1
through the resistor R
4
to widen the hysteresis width and the capacitor C
3
and resistor R
5
negatively feeds back the output of the NAND gate M
4
to create oscillation. In
FIG. 1
, reference symbols R
4
and R
9
designate current-limiting resistors and C
1
represents a filter capacitor.
When the AC power is applied to the induction motor
110
having the aforementioned configuration, the power Vcc is supplied to the circuit elements through the power supply unit
122
to operate the electronic relay
120
. The voltage induced across the starting coil W
3
is applied to the NAND gate M
1
through the diode D
1
connected to the connection port T
3
, the distribution resistors R
1
and R
2
and the hysteresis width controlling resistor R
3
. At this time, a low-level signal is inputted to the NAND gate M
1
at the initial stage because the voltage induced across the starting coil W
3
is low. The NAND gate M
1
inverts this low input signal into a high signal to transmit it to the NAND gate M
3
. By doing so, the oscillation circuit configured of the NAND gates M
3
and M
4
oscillate. The oscillating signal of the NANG gate M
4
turns on/off a transistor TR to interrupt the primary coil of the pick-up coil PC so that a signal voltage capable of triggering the gate of the triac
121
is induced to the secondary coil of the pick-up coil PC, to thereby turn on the triac
121
. When the triac
121
is turned on, the starting coil W
3
is provided with the AC power through the triac
121
and the starting capacitor SC to start the single-phase induction motor
110
.
When the speed of revolution of the motor
110
increases according to the starting operation thereof, the voltage induced across the starting coil W
2
is also raised gradually. If this induced voltage reaches a predetermined voltage set by the hysteresis width controlling resistor R
3
, the level of the signal applied to the NAND gate M
1
becomes high so that the NAND gate M
1
outputs a low-level signal. This interrupts the oscillation operation of the NAND gates M
3
and M
4
and triggering of the gate of the triac
121
through the pick-up coil, to thereby turn off the triac
121
.
When the triac
121
is turned off, the AC power applied to the starting coil w
3
through the starting capacitor SC is cut off, and the induction motor
110
is operated only by the operation coils W
1
and W
2
.
FIG. 2
is a circuit diagram of another voltage-controlled electronic relay for starting the single-phase induction motor. The operation of the circuit of
FIG. 2
is similar to that of the circuit shown in
FIG. 1
, excepting that a resistor R
10
and a capacitor C
6
are connected in parallel between the gate and cathode of the triac to be connected to the secondary coil of the pick-up coil PC and the output signal of the NAND gate M
4
is transmitted to the primary coil grounded through a capacitor C
5
, to control the triac.
The conventional voltage-controlled electronic relay described above can control the positive feedback characteristic of the NAND gate and the intensity of input signal to widen the hysteresis width up to 75V that is above half the power supply voltage. Accordingly, the starting device can be stably operated even in a power equipment area where voltage variation is severe. In addition, there is no generation of arc and the device can be installed in any place. However, the conventional relay has problems that the voltage applied to the NAND gates M
1
to M
4
is not stable and the triac may be damaged due to impulse noise.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a voltage-controlled electronic starting relay for a single-phase induction motor, which has a spark killer for removing impulse noise, connected in parallel with a triac, to protect th
Kim In-Seok
Kim Young-Jun
LandOfFree
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