Safety enhanced transformer circuit

• US 6,504,691 B1
• Filed: 07/11/2000
• Issued: 01/07/2003
• Est. Priority Date: 07/13/1999
• Status: Expired due to Fees

• Current Assignee: Kabushiki Kaisha Sankyo Seiki Seisakusho
• Original Assignee: Kabushiki Kaisha Sankyo Seiki Seisakusho
• Inventors: Shimizu, Hideki, Matsui, Yoshihiro
• Primary Examiner(s): Jackson, Stephen W.
• Application Number:
  US09/613,734
• Time in Patent Office: 910 Days
• Field of Search: 361/42, 361/45, 361/48, 361/115, 361/38
• US Class Current: 361/38
• CPC Class Codes: H02H 3/162 for ac systems
• CPC Class Codes: H05B 41/2851 for protecting the circuit against abnormal operating conditions

Abstract

A neon transformer includes secondary windings 16 and 17, and a junction 20 therebetween is connected through a voltage detection circuit 41 to a ground terminal 18 of the transformer. A resistive element 54 is connected in shunt with the voltage detection circuit 41. The voltage detection circuit 41 may comprise a series circuit of a Zener diode 52 and a light emitting element 53L of a photocoupler, for example. When a ground fault occurs on the secondary side of the transformer, the location of the ground fault assumes a reference potential, whereby the potential of the junction 20 rises to cause a current flow through the Zener diode 52 and the light emitting element 53L, which renders a light receiving element 53P conductive to pass an energizing current through a relay drive coil 34, thus throwing a relay contact switch 13 from NC to NO, thus interrupting the supply of the a.c. power.

Claims

1. A ground fault protective circuit for detecting a ground connection of a wiring or a load in circuits of secondary windings of a neon transformer, comprising;

a first and a second input terminal to which an AC power supply is connected;

a ground fault voltage detection circuit connected between a neutral point of the secondary windings and a ground terminal of the transformer which is non-responsive to a normal voltage appearing at the neutral point with respect to a ground potential at the ground terminal when the transformer is operated in a normal condition but is responsive to a fault voltage appearing at the neutral point and exceeding the normal voltage when the transformer is operated in an abnormal condition due to occurrence of said ground connection for generating a fault detection output indicating the occurrence of the ground connection in response to the fault voltage; and

a power supply interrupter connected between the first and second input terminals and opposite ends of a primary winding of the transformer and controlled by the fault detection output from the ground fault voltage detection circuit to interrupt the supply of the AC power from the AC power supply to the primary winding, wherein

said normal voltage appearing at the neutral point when the transformer is operated in the normal condition is close to the ground potential.

2. A ground fault protective circuit according to claim 1 in which the ground fault voltage detection circuit comprises:

a switching element connected between the neutral point and the ground terminal, and

a thresholding element which detects whether a voltage appearing at the neutral point with respect to the ground potential at the ground terminal exceeds the normal voltage appearing at the neutral point when said transformer is in the normal condition for turning the switching element in its ON state upon detection of the voltage at the neutral point in excess of the normal voltage.

3. A ground fault protective circuit for detecting a ground connection of a wiring or a load in circuits of secondary windings of a neon transformer, comprising;

a first and a second input terminal connected to opposite ends of a primary winding of the transformer and adapted to be connected to an a.c. power supply;

a ground fault voltage detection circuit connected between a neutral point of the secondary windings and a ground terminal of the transformer for detecting a fault voltage appearing due to said ground connection between the neutral point and the ground terminal which is larger than a normal voltage of a value appearing between the neutral point and the ground terminal when no ground connection occurs;

a power supply interrupter connected with the first and second input terminals and controlled by a detection output indicative of detection of the fault voltage from the ground fault voltage detection circuit to interrupt the supply of the a.c. power from the a.c. power supply to the primary winding; and

the ground fault voltage detection circuit including a switching element connected between the neutral point and the ground terminal, and a thresholding element for turning the switching element on when the voltage between the neutral point and the ground terminal becomes equal to or above the given value; and

the ground fault voltage detection circuit having a rectifier circuit connected between the neutral point and the ground terminal for rectifying a voltage developed therebetween for application to the thresholding element.

4. A ground fault protective circuit for detecting a ground connection of a wiring or a load in circuits of secondary windings of a neon transformer, comprising;

a first and a second input terminal connected to opposite ends of a primary winding of the transformer and adapted to be connected to an a.c. power supply;

a ground fault voltage detection circuit connected between a neutral point of the secondary windings and a ground terminal of the transformer for detecting a fault voltage appearing due to said ground connection between the neutral point and the ground terminal which is larger than a normal voltage of a value appearing between the neutral point and the ground terminal when no ground connection occurs;

a power supply interrupter connected with the first and second input terminals and controlled by a detection output indicative of detection of the fault voltage from the ground fault voltage detection circuit to interrupt the supply of the a.c. power from the a.c. power supply to the primary winding; and

the ground fault voltage detection circuit including a switching element connected between the neutral point and the ground terminal, and a thresholding element for turning the switching element on when the voltage between the neutral point and the ground terminal becomes equal to or above the given value; and

the power supply interrupter having a light emitting element of a photocoupler which is connected in series with a switching element, a series circuit connected between the first and the second input terminal and including a light receiving element of the photocoupler and the relay drive coil, and the relay switching contact which is driven by the relay drive coil and connected in series between the first input terminal and an end of the primary winding to be turned off while forming a relay self-holding circuit which maintains the off condition.

5. A ground fault protective circuit for detecting a ground connection of a wiring or a load in circuits of secondary windings of a neon transformer, comprising;

a first and a second input terminal connected to opposite ends of a primary winding of the transformer and adapted to be connected to an a.c. power supply;

a ground fault voltage detection circuit connected between a neutral point of the secondary windings and a ground terminal of the transformer for detecting a fault voltage appearing due to said ground connection between the neutral point and the ground terminal which is larger than a normal voltage of a value appearing between the neutral point and the ground terminal when no ground connection occurs;

a power supply interrupter connected with the first and second input terminals and controlled by a detection output indicative of detection of the fault voltage from the ground fault voltage detection circuit to interrupt the supply of the a.c. power from the a.c. power supply to the primary winding; and

the neon transformer has a pair of secondary windings each forming a magnetic circuit, the two magnetic circuits having mutually unbalanced magnetic characteristics.

6. A ground fault protective circuit according to claim 5 in which a pair of leakage cores form part of the pair of magnetic circuits of the transformer, the leakage cores having mutually different flux leakage characteristics to provide the unbalance.

7. A ground fault protective circuit for detecting a ground connection of a wiring or a load in circuits of secondary windings of a neon transformer, comprising;

a first and a second input terminal connected to opposite ends of a primary winding of the transformer and adapted to be connected to an a.c. power supply;

a ground fault voltage detection circuit connected between a neutral point of the secondary windings and a ground terminal of the transformer for detecting a fault voltage appearing due to said ground connection between the neutral point and the ground terminal which is larger than a normal voltage of a value appearing between the neutral point and the ground terminal when no ground connection occurs;

a power supply interrupter connected with the first and second input terminals and controlled by a detection output indicative of detection of the fault voltage from the ground fault voltage detection circuit to interrupt the supply of the a.c. power from the a.c. power supply to the primary winding; and

a resistive element connected in shunt with the ground fault voltage detection circuit.

8. A ground fault protective circuit for detecting a ground connection of a wiring or a load in circuits of secondary windings of a neon transformer, comprising;

a first and a second input terminal connected to opposite ends of a primary winding of the transformer and adapted to be connected to an a.c. power supply;

a ground fault voltage detection circuit connected between a neutral point of the secondary windings and a ground terminal of the transformer for detecting a fault voltage appearing due to said ground connection between the neutral point and the ground terminal which is larger than a normal voltage of a value appearing between the neutral point and the ground terminal when no ground connection occurs;

a power supply interrupter connected with the first and second input terminals and controlled by a detection output indicative of detection of the fault voltage from the ground fault voltage detection circuit to interrupt the supply of the a.c. power from the a.c. power supply to the primary winding;

a ground fault protection stop switch; and

a ground fault protection stop circuit connected between the first and the second input terminal and also connected to a ground fault protection stop switch to override the protective function of the ground fault protective circuit when the switch is operated.

9. A ground fault protective circuit according to claim 8, in which the ground fault protection stop circuit comprises a timer which starts upon operation of the ground fault protection stop switch, and interruption stop means which overrides the function of the power supply interrupter to interrupt the supply of the a.c. power during the operation of the timer.

10. A ground fault protective circuit according to claim 9 in which the first input terminal and the second input terminal are adapted to be connected with an active line and a non-active line of an a.c. power supply, respectively, the secondary winding of the transformer having a neutral point, the secondary winding portions located on the opposite side of the neutral point forming a pair of magnetic circuits having magnetic characteristics which are mutually unbalanced, further comprising;

a no-ground connection voltage detection circuit connected between the ground terminal and the second input terminal for detecting a voltage between the ground terminal and the second input terminal; and

a controller for controlling the power supply interrupter in accordance with a voltage detection output from the no-ground connection voltage detection circuit.

11. A ground fault protective circuit for detecting a ground connection of a wiring or a load in circuits of secondary windings of a neon transformer, comprising;

a first and a second input terminal connected to opposite ends of a primary winding of the transformer and adapted to be connected to an a.c. power supply;

a ground fault voltage detection circuit connected between a neutral point of the secondary windings and a ground terminal of the transformer for detecting a fault voltage appearing due to said ground connection between the neutral point and the ground terminal which is larger than a normal voltage of a value appearing between the neutral point and the ground terminal when no ground connection occurs;

a power supply interrupter connected with the first and second input terminals and controlled by a detection output indicative of detection of the fault voltage from the ground fault voltage detection circuit to interrupt the supply of the a.c. power from the a.c. power supply to the primary winding;

the first input terminal and the second input terminal adapted to be connected with an active line and a non-active line of an a.c. power supply, respectively, the secondary winding portions located on the opposite sides of the neutral point forming a pair of magnetic circuits having magnetic characteristics which are mutually unbalanced;

a no-ground connection voltage detection circuit connected between the ground terminal and the second input terminal for detecting a voltage between the ground terminal and the second input terminal; and

a controller for controlling the power supply interrupter in accordance with the voltage detection output from the no-ground connection voltage detection circuit.

12. No-ground connection protective circuit for detecting a no-ground connection of a ground terminal of a neon transformer in which a junction between a pair of secondary windings on the neon transformer is connected with the ground terminal of the transformer or detecting a reverse connection of input terminals, comprising;

an active line input terminal and a non-active line input terminal connected to the opposite ends of a primary winding of the transformer, respectively, and adapted to the connected to an active line and a non-active line of an a.c. power supply, respectively;

a pair of magnetic circuits each formed by one of the pair of secondary windings of the neon transformer and having magnetic characteristics which are mutually unbalanced;

a no-ground connection voltage detection circuit connected between the non-active line input terminal and the ground terminal of the transformer for detecting the voltage between the non-active line input terminal and the ground terminal; and

power supply interrupter connected between the active line input terminal and the non-active line input terminal and controlled by a voltage detection output from the no-ground connection voltage detection circuit for interrupting the supply of the a.c. power from the a.c. power supply to the primary winding.

13. A no-ground connection protective circuit according to claim 12 in which the no-ground connection voltage detection circuit comprises a rectifier circuit having a capacitor at its input which is connected to the ground terminal and a switching element fed with a rectified output from the rectifier circuit to be rendered conductive when the rectfied output is equal to or above a given value, the switching element controlling the power supply interrupter by its conduction.

14. A no-ground connection protective circuit for detecting a no-connection with the ground of a ground terminal of a neon transformer in which a junction between a pair of secondary windings on the neon transformer is connected with the ground terminal of the transformer or detecting a reverse connection of input terminals, comprising

an active line input terminal and a non-active line input terminal connected to the opposite ends of a primary windings of the transformer, respectively, and adapted to be connected to an active line and a non-active line of an a.c. power supply;

a power application detection circuit connected between the active line input line and the non-active line input terminal for detecting the application of the a.c. power between the active line input terminal and the non-active line input terminal;

a power supply interrupter connected between the active line input terminal and the non-active line input terminal and controlled by an output from the power application detection circuit representing the application of the power for interrupting the supply of the a.c. power to the primary winding; and

a no-ground connection voltage detection circuit connected to the active line input terminal and the ground terminal for detecting a voltage between the ground terminal and the active line input terminal to override the function of the power application detection circuit in response to a detection output.

15. A no-ground connection protective circuits according to claim 14 in which the no-ground connection voltage detection circuit comprises a rectifier circuit having its input connected to the ground terminal and including a capacitor at its input, and a switching element connected in shunt with the voltage application detection circuit and including a control electrode which is fed with a rectified output from the rectifier circuit to be turned on when the rectified output is equal to or above a given value.

16. A ground fault protective circuit for detecting the occurrence of a ground fault of a wiring of or a load on a secondary winding on a neon transformer for interrupting the supply of an a.c. power to a primary winding of the neon transformer, comprising;

a first and a second input terminal connected to the opposite ends of the primary winding of the transformer, respectively, and adapted to be connected across an a.c. power supply;

a ground fault protection stop switch; and

a ground fault protection stop circuit connected between the first and the second input terminal and also connected to a ground fault protection stop switch to override the protective function of the ground fault protective circuit when the switch is operated.

17. A ground fault protective circuit according to claim 16 in which the ground fault protection stop circuit comprises a timer which starts when the ground fault protection stop switch is operated, and interruption stop means for overriding the function of the ground fault protection stop circuit to interrupt the supply of the a.c. power during the operation of the timer.

18. A neon sign circuit for lighting neon tubes comprising:

a high voltage transformer having a ground terminal, a primary winding to which A.C. power is supplied and a pair of secondary windings generating a high voltage thereacross, respective first terminals of the secondary windings being connected together to form a neutral point and the other terminals of the respective secondary windings being connected to the neon tubes to be lighted,

a ground fault voltage detection circuit detecting a ground fault which occurs when wires connecting the secondary windings to the neon tubes or the neon tubes accidentally contact ground, the detection circuit generating a detection signal indicative of the occurrence of the ground fault upon detection of a ground fault, and

a power supply interruption controller having a switch and means for controlling said switch in its closed state when the neon sign circuit is under normal condition and turning said switch to its open state to interrupt supply of the power to the transformer in response to the detection signal generated by the ground fault detection circuit,

wherein

said ground fault voltage detection circuit comprises;

a rectifier circuit having a pair of input terminals, one of which is connected to the neutral terminal of the secondary windings and the other of which is connected to the ground terminal of said transformer, and rectifying an A.C. voltage appearing between said pair of input terminals to thereby obtain a rectified D.C. voltage corresponding to said A.C. voltage;

a switching element having on and off states;

a thresholding element having a threshold value for turning said switch means to its on or off state whether the D.C. voltage obtained from said rectifier circuit exceeds said threshold value or not, respectively, said threshold value being predetermined to be larger than the D.C. voltage of a maximum value when said neon sign circuit is under its normal condition but smaller than the D.C. voltage of a value when said ground fault occurs; and

means for transmitting the detection signal responsive to the on state of said switching element to said power supply interruption controller to thereby cause said switch to its open state.