US3192451A

US3192451A - Power circuit control device

Info

Publication number: US3192451A
Application number: US74140A
Authority: US
Inventors: Green Daniel Andrew
Original assignee: Mine Safety Appliances Co
Current assignee: MSA Safety Inc
Priority date: 1960-12-06
Filing date: 1960-12-06
Publication date: 1965-06-29
Anticipated expiration: 1982-06-29

Description

June 29, 1965 D. A. GREEN POWER CIRCUIT CONTROL DEVICE Filed Dec. 6. 1960 Arron/wife United States Patent O F 1 3,192,451 POWER CIRCUIT CONTROL DEVICE Daniel Andrew Green, Pittsburgh, Pa., assignor to Mine Safety Appliances Company, Pittsburgh, Pa., a corporation of Pennsylvania Filed Dec. 6, 1960, Ser. No. 74,140 7 Claims. (Cl. 317-157) This invention relates' to a system for controlling the power supply to a mining machine.

The invention provides a system whereby when a dangerous concentration of methane gas yis detected 4by a suitable detection device, the alarm information is transmitted all the way back to the distribution box, where the circuits carrying electric power to the machine are opened by a suitable breaker. The control device keeps 4all electrical power shut off at the distribution Ibox until the methane 4concentration in the hazardous area is reduced to a safe level, after which the system will automatically reset the operating circuits tothe mining machine.

These and other objects of the invention will become apparent as the description proceeds.

GENERAL OPERATION In the drawing, which is a diagram illustrating the electrical circuits involved, the letterA indicates a Gas Alarm. This Gas Alarm is mounted on the mining machine, and when the machine encounters an unsafe concentration of methane, the alarm device operates to open switch 10 in the line 11, which with line 12, forms the 250 v. power supply to the mining machine.

Even though the power line is broken bythe opening of switch lil, the presence of high-voltage power potential in the lines 11 and 12 creates a hazard, since sparks may be accidentally produced.

The present invention removes this hazard by opening the power circuit back at the distribution box (usually at a well-ventilated location distant from the working face) substantially simultaneously with the opening of switch 10. This is done by relays under control of the Sensing and Control System B. It should be noted particularly that the alarm signal which triggers the opening of the circuit breaker is the absence of power requirement at the machine. n

The Sensing and Control System also detects the -restored power circuit and thus permits the Automatic Reset System C to close the main circuit breaker applying power to the mining machine. The Automatic Reset System C is not part of this invention but its operation will be described to insure clarity.

NORMAL OPERATING CONDITION When the entire system is in normal operating condition, the circuit breaker 14 is held closed by the circuitbreaker relay 15. The holding circuit through the circuit-4 breaker relay 15 is as follows: from terminal 16, conductor 17, closed contacts 15b ot relay 15, closed contacts 18 operated by an over-load relay, conductor 19, closed contacts Ztlb operated by a time delay circuit (to be described later), coil 15a of relay 15, conductor 21, closed contacts 22b of the load relay 22, and conductor 23 to terminal 24.

In this normal operating condition a current path also exists through the Sensing and Control System as follows: from terminal 24, conductor 23, coil 22a of the load relay 22, conductor 25, closed contacts 26C of the no-loadsensing relay 26, and conductor 27 to terminal 2S.

Thus the normal holding circuit for the circuit-breaker includes the load relay 22 and the circuit-breaker relay 15.

3,192,451 Patented June 29, 1965 ICC The coil 26a of the no-load-sensing relay 26 is shunted across the resistor 29, which is in series with the main power line 11. The resistor 29 is ot very low resistance, and may in fact be a short section of line 11 along which a minute Voltage drop occurs when line 11 is under load. The current owing through coil 26a is suilicient to hold contacts 26e closed, thereby maintaining the load relay coil 22a, and so the coil 15u of the circuit-breaker relay, in energized condition, thus powering the mining machine.

INTERRUPTION or POWER An interruption of power in the lin-es 11 and 12 may be caused in a number of ways, such as by switching off the power at the machine controller, by the accidental cutting of the cable, or by operation of the Gas Alarm A.

Such interruption will cut the current owing in the c-oil 26a of the no-load-sensing relay, causing contacts 26C to open, and sequentially the load relay 22 and the circuit-breaker relay 15 will become de-energized, and the circuit breaker 14 will open. y

A continuity-sensing circuit is arranged for connection across the power lines 11 and 12 through the back contacts 26b of the no-load relay 26. This circuit comprises a relay 30 and a battery which provides a source of low voltage current of small amperage.

When the circuit breaker 14 opened and the no-loadsensing relay 26 became de-energized, the contacts 26h closed, establishing a path for current tlow between power lines 11 and 12 through the continuity-sensing circuit as follows: from terminal 28, conductor 27, contacts 26h, lConductor 31, resistor 32, coil 30a of the continuity-sensing relay, battery 33, conductor 35a to terminal 35.

As stated, the path just traced forms a path for current flow through the continuity-sensing circuit, but current cannot ow across that path until a circuit including lines 11 and 12 is continuous. The presence of this low-power potential in the lines 11 and 12 does not create a spark hazard.

Several blocking diodes 4t) are connected in series in conductor 31 of the continuity-sensing circuit to prevent mainline power from flowing momentarily through coil 30 before contacts 26b are opened.

It will be understood from the above detailed explana-` tion that when the main power circuit is interrupted (as by opening of the switch 10 by the Gas Alarm A) the yfollowing operations result: Y

(1) The no-loadsensing relay 26 becomes -deenergized land permits opening of contacts 26C controlling the load relay 22, thereby causing opening of the circuit breaker.

(2) The no-load-sensing relay 26 permits closing oi' theV contacts 26b to complete the continuitysensing circuit and impress a low voltage current ot small amperage on the conductors of the main power circuit. This continuity-sensing circuit will sense when the main power circuit to the machine has been restored, and will then initiate the reset operation.

RESET OPERATION As soon as the interruption in the power circuit to the machine (lines 11 and 12) is cured, low voltage current from battery 33 can flow through the continuitysensing circuit which has been set up as just described, and through the power lines 11 and 12 to the machine. This low voltage current of small amperage (about 20 ma.) energizes the continuity-sensing relay 30 and closes contacts 3b of that relay. This starts a chain reaction through the delayed-release circuit and the Automatic Reset System to close the circuit breaker 14.

(a) Closing of the circuit breaker through the Automatic eset System C The closing of contacts 36h permits full 25() v. current to liow through the delayed-release circuit as follows: from terminal 35, conductor 35a, contacts 36h, conductor 36, coil 34a of the relay 34, conductor 3'7, conductor 17 to terminal 16. This current energizes the delayed-release relay 34 and closes its contacts 34h, c and d.

The closing of these contacts causes this sequence of operations.

(1) Closing of contacts 34h partially sets up a circuit through the circuit-breaker relay 15. This circuit is not energized until the Automatic Reset System C is energized.

(2) Closing of contacts Mc sets up a temporary holding circuit through the delayed-release relay 34.

(3) Closing of contacts 34d causes energization of the Automatic Reset System C.

Vcloses contacts 45h, which energize closing relay Zt), closing contacts Ztlb. (if lines 11 and 12 were shorted for some reason, relay coil 45C wouldhold open contacts 45]; to prevent circuit breaker 14 from closing.)

Closing of contacts 2Gb permits current to ilow through coil 15a of relay 15 as follows: terminal 38, contacts 34b, conductor 21, coil 15a, contacts 20h, conductor 19, contacts 18, contacts 15C, conductor 46, resistor 47, contacts 421) and conductor 44 to terminal 16.

The completion of this circuit causes relay 1S to close circuit breaker 14, thereby permitting the 250 v. current to again flow through lines 11 and 12 to the machine.

The energization of relay 1S also closes contacts 15b, and the holding circuit through relay 15 which was previously described is now restored, except for contacts 22h.

(b) Reseltlzg of the sensing circuits The current now passing through restored lines 11 and 12 also passes through the no-load-sensing relay 26, energizing that relay, closing contacts 26C and opening contacts 26o.

The closing of contacts 26C completes a circuit through load relay 22;, causing it to close the contacts 22h, which are part of the holding circuit through relay 15, and to open contacts 22e.

The opening of contacts 22C now de-energizes delayedrelease relay 341. This relay had originally become energized by the closing of contacts 3G11, but prior to the time that contacts 30h opened (relay 3l) became rie-energized when contacts 26b opened), the relay 34 had closed its contacts 34C. With these latter contacts closed a temporary holding circuit for relay 34 ran as follows: from contact 24, closed contacts 22e, contacts 34C, conductor 36, coil 34a, conductor 37, to terminal 16. The opening of contacts 22e broke this circuit.

The opening of contacts 26e disconnected the continuity-sensing circuit from the main power line 11-12.

It will be understood from the above detailed explanation that when the interruption in the main power line is cured the following operations result:

(l) The continuity-sensing relay 30 closes a circuit permitting power from the main power source to ilow through the delayed-release relay 3d.

(2) The delayed-release relay 34 closes contacts which partially set up a main holding circuit through the circuit-breaker relay 1'. (Contacts 22h remain open.)

(3) A temporary holding circuit is set up through the delayed-release relay 3ft by way of its contacts 34e.

(4) The delayed-release relay 3d causes energization (through contacts 34a!) of the Automatic Reset System C, which energiaes circuit-breaker relay 15 and closes the circuit-breaker 14.

(5 Current owing through the no-load-sensing relay 26 (a) closes contacts 26e, which energizes coil 22,

closing the contacts 22h in the main holding circuit for the circuit breaker [(2) above], and opening contacts 22e to die-energize relay 34,

(b) opens contacts 26h to disconnect the continuitysensing circuit through relay Si).

(c) The entire syste-m now in normal condition The entire system is now in normal operating condition with current flowing through the power lines 11 and 12, and the important relays in the following condition:

Circuit-breaker relay 15 a Energized.

Holding relay 22 Energized.

No-load-sensing relay 2.6 Energized.

Continuity-sensing relay 30 De-energized.

Delayed-release relay 34 De-energized.

Relays of the automatic reset 13e-energized.

VARIATIONS It has been found that for the no-load-sensing relay 26, there may be substituted a D.C. transistorized voltage amplifier working in the range of 10 to 20 millivolts with adequate override.

CONCLUSION It will be clear to those skilled in the art that the device of the present invention has many advantages, including:

(l) The device operates on an underload basis.

(2) There is no hazardous electric current in the cables to the mining machine as long as the power circuit is interrupted for any reason. During this time the only current in these cables is the low battery current of the continuity-sensing circuit.

(3) The re-set operation takes place automatically at the distribution box (remote from the machine) as soon as the interrupted circuit is restored. This is done without the necessity of using additional cables to the machine or super-imposed radio frequency oscillations. There is no necessity for the machineoperator or an assistant to walk back to the distribution box to reset the circuit breaker.

According to the provisions of the patent statutes, I have explained the principle of my invention and have illustrated and described what I now consider to represent its best embodiment. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

I claim:

1. In a control device which includes a main power circuit having therein a switch controlled by an alarm device, and a circuit breaker normally held closed by a circuit breaker relay, the improvement which comprises:

a load relay arranged in shuntacross the conductors of the main power circuit and between the circuit breaker and the alarm device, the load relay being connected to influence operation of the circuit-breaker relay;

a continuity-sensing circuit arranged in shunt across the conductors of the main power circuit and comprising an independent source of current of low voltage i and small amperage; and a no-load-sensing means arranged in one of the conductors of the main power circuit, and having one pair of contacts in the circuit for the load relay and a second pair of contacts in the continuity-sensing circuit;

the parts being so constructed and arranged that when the alarm device opens the switch in the main power circuit the following operations result:

(1) the no-load-sensing means opens the contacts controlling the load relay, thereby causing the opening of the circuit breaker;

(2) the no-load-sensing means closes the contacts controlling the continuity-sensing circuit, thereby impressing a low voltage current of small arnperage on the conductors of the main power circuit.

2. A device as specified in claim 1 in which a relay located in the continuity-sensing circuit becomes energized when the alarm-controlled switch is closer, whereby an automatic reset of the circuit breaker is initiated.

3. A device as specified in claim 1 in which the independent source of current is a battery.

4. A device as specified in claim 1 in which blocking diodes are connected in series in the continuity-sensing circuit.

5. In a control device which includes a main power circuit having therein a switch controlled by an alarm device, and a circuit breaker normally held closed by a circuit-breaker relay, the improvement which comprises:

a load-relay arranged in shunt across the conductors of the main power circuit and between the circuit breaker and the alarm device, the load relay being arranged for connection in series with the circuitbreaker relay to form a main holding circuit to hold the circuit breaker in closed position when the main power circuit is energized;

a continuity-sensing circuit arranged in shunt across the conductors of the main power circuit and cornprising a continuity-sensing relay and an independent source of current of W voltage and small arnperage;

an automatic reset system arranged across the conductor-s of the main power circuit and between lthe circuit breaker and the main source of power;

a delayed-release circuit arranged across the conductors of the main power circuit and between the circuit breaker and the main source of power and including a delayed-release relay controlled by the continuity-sensing circuit;

and a no-load-sensing relay shunted across a very low resistance in one of the conductors of the main power circuit, and having one pair of contacts in the circuit or the load relay and a `second pair of contacts in the continuity-sensing circuit;

the parts being so constructed and arranged that when the alarm device closes the switch in the main power circuit the following operations result:

(l) the continuity-sensing relay closes a circuit permitting power from' the main power source to ilow through the delayed-release relay;

(2) the delayed-release relay closes contacts which partially set up the main holding circuit through the circuit breaker relay;

(3) a temporary holding circuit is set up through the delayed-release relay;

(4) the delayed-release relay causes energization of the automatic reset system which closes the circuit breaker;

(5) the no-load-sensing relay (a) closes contacts which complete the main holding circuit for the circuit breaker and opens contacts which de-energize the delayed-release relay and (b) opens contacts which disconnect the continuitysensing circuit.

6. A device as specied in claim 5 in which the independent source of current is a battery.

7. A device as specified in claim 5 in which when the switch in the main power circuit opens, the no-load-sensing relay is Vde-energized to cause opening of the circuit breaker and to impress a low voltage current of small ampera'ge from the continuity-sensing circuit on the lines of the main power circuit.

References Cited by the Examiner UNITED STATES PATENTS 2,364,372 12/44 Kenrick 307-81 2,575,053 11/51 Fredrickson 317-44 2,580,858 1/52 Sprengle 317-44 3,090,038 5/ 63 Klein et al. 340-237 MAX L. LEVY, Primary Examiner.

SAMUEL BERNSTEIN,V Examiner. l

Claims

1. IN A CONTROL DEVICE WHICH INCLUDES A MAIN POWER CIRCUIT HAVING THEREIN A SWITCH CONTROLLED BY AN ALARM DEVICE, AND A CIRCUIT BREAKER NORMALLY HELD CLOSELY BY A CIRCUIT BREAKER RELAY, THE IMPROVEMEMENT WHICH COMPRISES: A LOAD RELAY ARRANGED IN SHUNT ACROSS THE CONDUCTORS OF THE MAIN POWER CIRCUIT AND BETWEEN THE CIRCUIT BREAKER AND THE ALARM DEVICE, THE LOAD RELAY BEING CONNECTED TO INFLUENCE OPERATION OF THE CIRCUIT-BREAKER RELAY; A CONTINUITY-SENSING CIRCUIT ARRANGED IN SHUNT ACROSS THE CONDUCTORS OF THE MAIN POWER CIRCUIT AND COMPRISING AN INDEPENDENT SOURCE OF CURRENT OF FLOW VOLTAGE AND SMALL AMPERAGE; AND A NO-LOAD-SENSING MEANS ARRANGED IN ONE OF THE CONDUCTORS OF THE MAIN POWER CIRCUIT, AND HAVING ONE PAIR OF CONTACTS IN THE CIRCUIT FOR THE LOAD RELAY AND A SECOND PAIR OF CONTACTS IN THE CONTINUITY-SENSING CIRCUIT; THE PARTS BEING SO CONSTRUCTED AND ARRANGED THAT WHEN THE ALARM DEVICE OPENS THE SWITCH IN THE MAIN POWER CIRCUIT THE FOLLOWING OPERATIONS RESULT; (1) THE NO-LOAD-SENSING MEANS OPENS THE CONTACTS CONTROLLING THE LOAD RELAY, THEREBY CAUSING THE OPENING OF THE CIRCUIT BREAKER; (2) THE NO-LOAD-SENSING MEANS CLOSES THE CONTACTS CONTROLLING THE CONTINUITY-SENSING CIRCUIT, THEREBY IMPRESSING A LOW VOLTAGE CURRENT OF SMALL AMPERAGE ON THE CONDUCTORS OF THE MAIN POWER CIRCUIT.