Circuit breaker

When a current of a distribution line is increased to about two times of a rated current of a circuit breaker, the circuit breaker is operated to open the distribution line with a comparatively long time lag such as 100 seconds by a long time-lag tripping circuit of the circuit breaker, on the other hand, in case that a current of 80-90% of the rated current have continuously flowed before the current is increased as mentioned above, the time lag which is set in the long time-lag tripping circuit is shortened.

FIELD OF THE INVENTION AND RELATED ART STATEMENT 
1. Field of the Invention 
The present invention relates generally to a circuit breaker, and more 
particularly to a circuit breaker having an over-current tripping device. 
2. Description of the Related Art 
A circuit breaker in the prior art is disclosed in the Japanese Published 
Unexamined Patent Application Sho 60-32211 or Japanese Utility Model Sho 
55-29931, for example. In these prior art, when an over-current flows in 
distribution lines of an electric power by accident of an electrical 
equipment which is connected to the distribution lines or the distribution 
lines itself, the over-current is detected by a current transformer which 
is mounted on the distribution lines. The detected signal of the current 
transformer is inputted to a processing circuit, and when the current 
exceeds a predetermined value of the current, an output signal is issued 
and is applied to a timer circuit. The timer circuit outputs an output 
signal after a predetermined time period. The output signal is applied to 
the gate of a thyristor, and an over-current tripping coil is excited by 
turn-ON of the thyristor, and thereby contacts of the circuit breaker are 
opened. 
A circuit block diagram of a conventional general circuit breaker is shown 
in FIG.4. Referring to FIG.4, a current transformer 21 is mounted on an 
alternating current distribution line 11. An output signal of the current 
transformer 21 is rectified by a full-wave rectifier 30. A voltage 
regulating circuit 500 is connected across a positive output terminal 31 
and a negative output terminal 32 of the rectifier 30 through a resistor 
40 for detecting a current flowing the voltage regulating circuit 500. The 
voltage regulating circuit 500 is provided with a center terminal 5c which 
is grounded. Therefore, the voltage regulating circuit 500 outputs a 
positive voltage +V at a terminal 5a and a negative voltage -V at a 
terminal 5d with respect to the center terminal 5c. A differential 
amplifier 60 is composed of an operational amplifier 63 and resistors 64, 
65, 66 and 67. A voltage across both the terminals of the resistor 40 is 
converted to a signal which is produced across the ground and the output 
terminal of the differential amplifier 60. 
A timer circuit 70 is composed of a long time-lag tripping circuit 170, a 
peak value converting circuit 210, an effective value converting circuit 
211, a short time-lag tripping circuit 220 and an instant tripping circuit 
230. The output signal of the operational amplifier 63 is applied to the 
peak value converting circuit 210, the effective value converting circuit 
211 and the instant tripping circuit 230. The output signal of the peak 
value converting circuit 210 is applied to the short time-lag tripping 
circuit 220, and the output signal of the effective value converting 
circuit 211 is applied to the long time-lag tripping circuit 170. The 
respective output terminals of the long time-lag tripping circuit 170, the 
short time-lag tripping circuit 220 and the instant tripping circuit 230 
are connected together, and are coupled to a terminal 70a of a switch 55. 
The other terminal of the switch 55 is coupled to a coil of a switch 120. 
A tripping coil 80 is coupled to a coil of a switch terminal 31 of the 
rectifier 30 and one terminal 80A of the switch 120. The other terminal 
80b of the switch 120 is coupled to the negative terminal 5d of the 
voltage regulating circuit 500. A shut-off mechanism 100 is driven by the 
tripping coil 80 which is activated by a close of the switch 120, and a 
contact 201 is opened by the shut-off mechanism 100. 
An operation inhibiting circuit 50 is connected across the positive output 
terminal 5a and the negative output terminal 5d of the voltage regulating 
circuit 500, when the output voltage of the voltage regulating circuit 500 
is lower than a predetermined value, the switch 55 is opened to inhibit 
operation of the shut-off mechanism 100. 
A voltage which is induced in the current transformer 21 by an alternating 
current flowing through the distribution line 11 is rectified by the full 
wave rectifier 30. The output current of the rectifier 30 flows the 
voltage regulating circuit 500 and the resistor 40, and a constant DC 
voltage is issued from the voltage regulating circuit 500. Thus, the full 
wave rectified current corresponding to the current 1a of the distribution 
line 11 flows through the voltage regulating circuit 500 and the resistor 
40. The positive voltage +V and the negative voltage -V are issued from 
the respective terminals 5a and 5d of the voltage regulating circuit 40 
with respect to the grounded center terminal 5c. The electric power for 
the differential amplifier 60 is supplied by the voltage regulating 
circuit 500, and a voltage Vin across both the terminals of the resistor 
40 are inputted to the respective input terminals of the differential 
amplifier 60 through the resistors 64 and 66, respectively. 
The output signal of the differential amplifier 60 is applied to the 
instant tripping circuit 230 and also to the short time-lag tripping 
circuit 220 through the peak value converting circuit 210, and also to the 
effective value converting circuit 211. 
An output voltage Ex of the effective value converting circuit 211 is 
applied to the long time-lag tripping circuit 170. 
In the above-mentioned timer circuit 70, as shown in FIG. 6, the instant 
tripping circuit 230 activates the shutoff mechanism 100 with a short time 
lag of 20 msec when a large current which is larger than a current I.sub.H 
flows. The short time-lag tripping circuit 220 activates the shutoff 
mechanism 100 with a time lag of 100 msec when a current which is lower 
than the current I.sub.H but is higher than a current I.sub.M flows. The 
long time-lag tripping circuit 170 activates the shutoff mechanism 100 
with a time lag of 100 sec when a current I.sub.L which is lower than the 
current I.sub.M but is higher than a rated current I.sub.L flows. 
FIG. 5 is the circuit block diagram of the long time-lag tripping circuit 
170 in the conventional circuit breaker. The output voltage Ex is inputted 
to a comparator 35 of the long time-lag tripping circuit 170. When the 
output voltage Ex is equal to a reference voltage Ey of a reference 
voltage setting circuit 37, a switch 36 which is operated by the output of 
the comparator 35 is opened, and electric charge into a capacitor 38 is 
started. 
For instance, when the current flowing the distribution line 11 is 200 
amperes, if the output voltage Ex is 0.5 V, the reference voltage Ey of 
the reference voltage setting circuit 37 is set to 0.6 V. Then, when the 
output voltage Ex of the effective value converting circuit reaches 0.6 V, 
the switch 36 of the comparator 35 is opened, and electric charge to the 
capacitor 38 is started. In the above mentioned case, the current flowing 
the distribution lines is estimated to 240 amperes. 
On the other hand, the output voltage Ex is applied to a voltage-current 
converting circuit 44 and is converted to a current Ib. 
In the voltage-current converting circuit 44, the current Ib is in 
proportion to the square of the output voltage Ex. For example, when the 
voltage Ex is 0.5 V, the current Ib is 1 .mu.A, and when the voltage Ex is 
1 V, the current Ib becomes 4 .mu.A. 
When the voltage e1 of the capacitor 38 exceeds a reference voltage E2 of a 
reference voltage setting circuit 42 for setting a time period in long 
time-lag tripping operation, an output signal is issued from the 
comparator 41. The time period is 100 sec when the current I of the 
distribution line 11 is two times of the rated current, for example as 
shown in FIG.6. 
For example, in case that a current of 80% of the rated current flows 
continuously, the circuit breaker is not tripped. However, the wires of 
the distribution lines are heated by the current. In the above mentioned 
state, when the current is increased to two times of the rated current, as 
mentioned above, the circuit breaker is tripped after 100 seconds. 
Whereas, the wires are considerably heated by the continuous current of 
80% of the rated current, and the wires are further heated in high 
temperature by the current of two times of the rated current during the 
additional time period of 100 seconds. Thus the wire is liable to be 
damaged by unexpected temperature rise. 
OBJECT AND SUMMARY OF THE INVENTION 
An object of the present invention is to provide a circuit breaker wherein 
a time lag in a long time-lag tripping operation of a tripping device is 
shortened in case that a current which is substantially equal to a rated 
current flows during a long time period prior to increase of the current 
above the rated current. 
The circuit breaker in accordance with the present invention comprises: 
a first switch for opening or closing an distribution line, 
a current transformer for detecting a current of the distribution line, 
a rectifier for rectifying a detected signal of the current transformer, 
a voltage regulating circuit connected across a positive terminal and a 
negative terminal of the rectifier, 
detecting means for detecting an output current of the rectifier, 
a differential amplifier for amplifying the output of the detecting means, 
a timer circuit for producing a time lag corresponding to the current of 
the distribution line, 
a second switch to be operated by an output of the timer circuit, 
a tripping coil connected to the second switch for driving the first 
switch, wherein 
the timer circuit comprises: 
a first reference voltage setting circuit for issuing a first reference 
voltage for setting the rated current, 
a second reference voltage setting circuit for issuing a second reference 
voltage which is lower than the first reference voltage, 
a first comparator for comparing an output voltage of the differential 
amplifier with the first reference voltage, 
a second comparator for comparing the output voltage of the differential 
amplifier with the second reference voltage, 
a voltage-current convertor for converting the output voltage of the 
differential amplifier to a current, 
a capacitor for charging the current from the voltage-current convertor, 
a current leaking means connected in parallel to the capacitor, 
a third switch connected in parallel to the capacitor and to be opened by 
an output of the first comparator, 
a fourth switch connected in parallel to the capacitor and to be opened by 
an output of the second capacitor, 
a third reference voltage setting circuit for issuing a reference voltage 
for setting a time lag in a long time-lag tripping operation, and 
a third comparator for comparing a terminal voltage of the capacitor with 
the reference voltage of the reference voltage setting circuit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A block diagram of an embodiment of the circuit breaker in accordance with 
the present invention is shown in FIG. 1. Referring to FIG. 1, a current 
transformer 21 is mounted on an alternating current distribution line 11. 
An output signal of the current transformer 21 is rectified by a full-wave 
rectifier 30. A voltage regulating circuit 500 is connected across a 
positive output terminal 31 and a negative output terminal 32 of the 
rectifier 30 through a resistor 40 for detecting a current flowing the 
voltage regulating circuit 500. The voltage regulating circuit 500 is 
provided with a center terminal 5c, which is grounded. Therefore, the 
voltage regulating circuit 500 outputs a positive voltage +V at a terminal 
5a and a negative voltage -V at a terminal 5d with respect to the center 
terminal 5c. A differential amplifier 60 is composed of an operational 
amplifier 63 and resistors 64, 65, 66 and 67. A voltage across both the 
terminals of the resistor 40 is converted to a signal which is produced 
across the ground and the output terminal of the differential amplifier 
60. 
A timer circuit 77 is composed of a long time-lag tripping circuit 270, a 
peak value converting circuit 210, an effective value converting circuit 
211, a short time-lag tripping circuit 220 and an instant tripping circuit 
230. The output signal of the operational amplifier 63 is applied to the 
peak value converting circuit 210, the effective value converting circuit 
211 and the instant tripping circuit 230. The output signal of the peak 
value converting circuit 210 is applied to the short time-lag tripping 
circuit 220, and the output signal of the effective value converting 
circuit 211 is applied to the long time-lag tripping circuit 270. The 
respective output terminals of the long time-lag tripping circuit 270, the 
short time-lag tripping circuit 220 and the instant tripping circuit 230 
are connected together, and are coupled to a terminal 70a of a switch 55. 
The other terminal of the switch 55 is coupled to a coil of a switch 120. 
A tripping coil 80 is connected between the positive terminal 31 of the 
rectifier 30 and one terminal 80A of a switch 120. The other terminal 80b 
of the switch 120 is coupled to the negative terminal 5d of the voltage 
regulating circuit 500. A shut-off mechanism 100 is driven by the tripping 
coil 80 which is activated by close of the switch 120, and a contact 201 
is opened by the shut-off mechanism 100. 
An operation inhibiting circuit 50 is connected across the positive output 
terminal 5a and the negative output terminal 5d of the voltage regulating 
circuit 500. When the output voltage of the voltage regulating circuit 500 
is lower than a predetermined value, the switch 55 is opened to inhibit 
operation of the shut-off mechanism 100. 
FIG. 2 is a circuit block diagram of the long time-lag tripping circuit 
270. Referring to FIG. 2, an output voltage Ex of the effective value 
converting circuit 211 is applied to the respective input terminals 35c 
and 35d of comparators 35a and 35b. A switch 36a is operated by the output 
of the comparator 35a, and a switch 36b is operated by the comparator 36b. 
A reference voltage Ey of a reference voltage setting circuit 37a is 
applied to an input terminal 35e of the comparator 35a. A voltage Ez which 
is a voltage made by diving by the reference voltage Ey 48 and 49, is 
applied to an input terminal 35f of the comparator 35b. Each one terminal 
of the switches 36a and 36b is connected together and is coupled to an 
input terminal E1 of the comparator 41. The other terminal of the switch 
36a is grounded through a bias power source 45. The bias power source 45 
is composed of a battery 47 which is grounded at its negative terminal and 
an oppositely poled diode 46 which is coupled by its cathode to the 
positive terminal of the battery 47. The other terminal of the switch 36b 
is grounded. A capacitor 38 and a resistor 39 are connected between the 
input terminal E1 of the comparator 41 and the ground. A voltage-current 
conversion circuit 44 is connected between the input terminal 35c of the 
comparator 35a and the input terminal E1 of the comparator 41. A reference 
voltage power source 42 for setting a long time-lag is coupled to an input 
terminal E2 of the comparator 41. 
Operation of the embodiment is elucidated hereafter. 
A voltage which in induced in the current transformer 21 by an alternating 
current flowing the distribution line 11 is rectified by the full wave 
rectifier 30. The output current of the rectifier 30 flows the voltage 
regulating circuit 500 and the resistor 40, and a constant DC voltage is 
issued from the voltage regulating circuit 500. Thus, the full wave 
rectified current corresponding to the current 1a of the distribution line 
11 flows the voltage regulating circuit 500 and the resistor 40. The 
positive voltage +V and the negative -V are issued from the respective 
terminals 5a and 5d of the voltage regulating circuit 40 with respect to 
the grounded center terminal 5c. The electric power for the differential 
amplifier 60 is supplied by the voltage regulating circuit 500, and a 
voltage Vin across both the terminals of the resistor 40 are inputted to 
the respective input terminals of the differential amplifier 60 through 
the resistors 64 and 66, respectively. A gain A of the differential 
amplifier 60 is given by 
EQU A=Vout/Vin=Rout/Rin. 
The output signal of the differential amplifier 60 is applied to the 
instant tripping circuit 230, and through the peak value converting 
circuit 210 to the short time-lag tripping circuit 220 and through the 
effective value converting circuit 211 to the long time-lag tripping 
circuit 270. 
FIG. 3 is a graph showing operation of the circuit breaker in accordance 
with the present invention. Referring to FIG. 3, when a current flowing in 
the distribution line 11 exceeds the current I.sub.H, a voltage Vin 
corresponding to the current of the voltage regulating circuit 500 
increases and an output voltage Vout of the differential amplifier 60 
significantly increases. Consequently, the instant tripping circuit 230 is 
immediately activated, and the switch 120 is closed within 20 
milliseconds. The current range which is larger than the current I.sub.H 
is named "current range of instant tripping". 
When the current of the distribution line 11 is smaller than the current 
I.sub.H but is larger than a current I.sub.M as shown in FIG. 3, the short 
time-lag tripping circuit 220 is activated, and the switch 120 is closed 
within 100 milliseconds. The current range between the current I.sub.M and 
I.sub.H is "current range of short time-lag tripping". 
When the current of the distribution line 11 is smaller than the current 
I.sub.M but is larger than a current I.sub.L shown in FIG. 3, the long 
time-lag tripping circuit 270 is activated as shown hereafter. Referring 
to FIG. 2, the output voltage Ex from the effective value converting 
circuit 211 is inputted to the comparators 35a and 35b. When the output 
voltage Ex reaches a reference voltage Ez of the reference voltage setting 
circuit 37b, the switch 36b is opened by the output of the comparator 35b. 
Then, the capacitor 38 is charged by the output current Ib of the 
voltage-current converting circuit 44. In this time, since the switch 36a 
is closed, the terminal voltage E1 of the capacitor 38 does not exceed the 
voltage E1 of the power source circuit 45. Since the voltage E1 of the 
power source circuit 45 is lower than the output voltage E2 of the 
reference voltage setting circuit 42, the output terminal of the 
comparator 41 remains low level. 
When the current Ia of the distribution line 11 is 200 A which is a rated 
current of the circuit breaker, for example, the output voltage Ex of the 
effective value converting circuit 211 is set to 0.5 V, and the reference 
voltage Ey and Ez of the reference voltage setting circuit 37a and 37b are 
set to 0.6 V and 0.4 V, respectively. In this case, when the output 
voltage Ex of the effective value converting circuit 211 reaches 0.4 V, 
the switch 36b of the comparator 35b is opened and charge to the capacitor 
38 is started. 
In the above-mentioned condition, when the current Ia flowing the 
distribution line 11 is 160 A, which is 80% of the rated current 200 A, 
the distribution line 11 is gradually heated. However, the distribution 
line 11 is not damaged by heating since the current is lower than the 
rated current of the circuit breaker. The output voltage Ex is 0.4 V (80% 
of 0.5 V), and the switch 36b of the comparator 35b is opened. Therefore, 
the capacitor 38 is charged by the output of the voltage-current 
converting circuit 44. 
Subsequently, when the current Ia of the distribution line 11 is increased 
to 400 A which is double as large as the rated current 200 A, for 
instance, the output voltage Ex of the effective value converting circuit 
211 becomes 1 V, and exceeds the reference voltages Ey and Ez. 
Consequently, the switch 36a is opened. The output current Ib of the 
voltage-current converting circuit 44 flows in the capacitor 38 because of 
open state of the switch 36a. Since the capacitor 38 is already charged 
until the voltage E1 of the power source circuit 45, the capacitor 38 is 
further charged so that the terminal voltage of the capacitor 38 reaches 
the output voltage Ex from the voltage E1. When the voltage E1 of the 
capacitor 38 exceeds the voltage E2 of the reference voltage setting 
circuit 42, the output signal of the comparator 41 turns to high level, 
and the switch 120 is closed. Consequently, the tripping coil 80 is 
activated, and the contact 201 is opened through the shut-off mechanism 
100. 
As mentioned above, when the current of the distribution line 11 is 
increased to 200% of the rated current from 80% of the rated current, the 
voltage E1 of the capacitor 38 is already retained to the voltage E1 which 
is equal to the voltage of the power source circuit 45. Therefore, a time 
period wherein the voltage E1 exceeds the reference voltage E2 of the 
reference voltage setting circuit 42 is shortened as a result, the 
time-lag in the long time-lag tripping operation is also shortened as 
shown by a dotted line in the graph of FIG. 3. 
On the other hand, when the current 1a of the distribution line 11 is 
rapidly increased to a valuse twice as large as the rated current from a 
comparatively low current, both the switches 36a and 36b are 
simultaneously opened. Since the voltage E1 of the capacitor 38 is 
retained to zero until opening of the switches 36a and 36b, a long 
charging time is required. Therefore, the circuit breaker is operated by 
the long time-lag operation which is similar to the operation as shown in 
FIG. 6 as shown by the solid line in the graph of FIG. 3. In 
above-mentioned case, the distribution line 11 is not heated by the low 
current prior to increase of the current. On the contrary, in case that 
the current of 80% of the rated current has been flowing before increase 
of a double of the rated current and hence the distribution line 11 has 
been considerably heated, the time lag of the long time-lag tripping 
operation is shortened in comparison with state which is not heated, and 
thereby unexpected trouble is effectively prevented. 
In case that the current 1a of the distribution line 11 is comparatively 
small such as 10%-20% of the rated current, the output voltage of the 
voltage regulating circuit 500 is low and operation of the timer circuit 
70 is liable to be unstable. In order to prevent mal-operation of the 
timer circuit 77 in the abovementioned state, the switch 55 of the 
operation inhibiting circuit 50 is opened, and thereby closing operation 
of the switch 120 is blocked. 
In the embodiment, the effective value converting circuit 211 can be 
replaced by the peak value converting circuit 210. 
Although the invention has been described in its preferred form with a 
certain degree of particularity, it is understood that the present 
disclosure of the preferred form has been changed in the details of 
construction and the combination and arrangement of parts may be resorted 
to without departing from the spirit and the scope of the invention as 
hereinafter claimed.