Abstract:
A transient voltage surge suppressor is provided to protect equipment with voltage sensitive electronics, such as office equipment, from surges or transients in the multi-phase power distribution network furnishing power. The surge suppressor senses the incoming voltage and electrically disconnects the neutral leads and hot leads of the power network from the neutral lead and hot lead of the office equipment if a voltage surge above an established level is sensed. The suppressor also disconnects its output when a ground connection in the multi-phase power network is disconnected to protect the equipment against excessive voltages. In this situation, the suppressor circuit protects its internal components from damage and possible fire hazard when its output is disabled, so that the suppressor can resume its function when conditions in the power distribution network return to a satisfactory state.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    The present application is a continuation-in-part of prior co-pending U.S. patent application No. 09/311,240 filed May 13, 1999. 
     
    
     
       BACKGROUND OF INVENTION  
         [0002]    1. Field of Invention  
           [0003]    The present invention relates to electrical protective filters or transient voltage surge suppressors (TVSS) for office equipment or any microprocessor-based equipment. These suppressors provide surge filtration to protect the office equipment from surges or transients in the power furnished from the power distribution network.  
           [0004]    2. Description of the Prior Art  
           [0005]    Numerous types of office equipment used in recent years contain electronic chips or components which are sensitive to voltage surges or transients in the power distribution network provided by utility companies. Examples of such types of office equipment include computers, facsimile machines, photocopiers and the like. Devices known as power filters or transient voltage surge suppressors have been developed to protect these types of office equipment from such power surges or transients. U.S. Pat. No. 5,721,661, of which applicant is inventor, is one form of such a power filter.  
           [0006]    Office buildings and other places where such equipment has been used have often been based on a three-phase or center-tap system of power distribution. There are several advantages from the use of this form of power. It allows more power to be delivered to a site, is more easily distributed, and allows two voltage levels (such as 120 volts and 240 volts) to be delivered. Customers can thus use equipment requiring larger amounts of power. These forms of power are a more cost effective way for an electric utility to transmit power to an end user. In three phase or center tap power, in the event of loss of the ground wire or neutral wire connection in the distribution grid, voltage levels provided in the network could increase up to a double level. This is not an uncommon event. Equipment rated at 120 volts could thus be subjected to up to 240 volts. So it could possibly burn out a surge protection component and possibly cause firing the TVSS unit, which could also burn out the connected equipment.  
           [0007]    So far as is known, it was typical to use relatively inexpensive thermal fuses for protective purposes in these situations. These fuses would typically open after response to excess heat for periods of from couple of seconds to several minutes. It may protect the TVSS against firing after burn out, but sensitive electronic chips and circuits of connected equipment were not capable of withstanding such excessive voltage levels for even short fractions of a second, such as a few milliseconds.  
         SUMMARY OF INVENTION  
         [0008]    Briefly, the present invention provides a new and improved protective circuit for electrical apparatus. The protective circuit has hot, neutral and ground leads which are arranged to be placed between corresponding hot, neutral and ground leads of the electrical circuit. The protective circuit includes a voltage surge protection and filtration circuit connected between the hot and neutral leads, also between neutral and ground, and also between the hot lead and ground.  
           [0009]    The voltage surge protection circuit has first and second voltage surge protectors connected in an electrical series relationship with each other. The first and second voltage surge protectors are connected at a common connection or node to each other. The first and second voltage surge protectors are connected between the neutral lead and ground lead to suppress and filter neutral ground noise and transients. If desired, a second set of first and second voltage surge protectors, similarly connected to each other and connected to the first set through a noise isolation transformer or differential transformer may be included.  
           [0010]    The protective circuit also includes a series-connected set of first and second relays connected between the hot and neutral, as well as hot and ground, leads of the protective circuit. The first relay has a switch arm to connect the clamping device, such as an MOV gas tube, Zener or any other type of voltage clamping component, also to connect a filtration component such as capacitor or inductor between the neutral lead and ground lead to suppress and filter the neutral ground (common mode) noises and spikes when the first relay is receiving current. The first relay is typically receiving current when the ground lead is properly connected to ground, also the hot and neutral leads are correctly connected to hot and neutral, not reverse polarity.  
           [0011]    The first relay switch arm opens when current in the first relay circuit is not being received or present, such as when the ground connection of the ground lead is interrupted or broken. Opening the first relay switch arm isolates the electrical apparatus from the power utility. It also protects the voltage surge protectors and filtration components. The protective circuit of the present invention thus protects the voltage surge protectors and filtration components such as MOV&#39;s and capacitors and any type of voltage protector devices (such as a gas-tube, ZENER or the like) between neutral and ground or hot to ground in the voltage surge protector circuit. Protection is provided against over voltage (240 V) when connection to an electrical ground is broken or reverse polarity of hot and neutral causing voltage increase up to 240 V.  
           [0012]    The second relay of the protective circuit also controls a switch arm which is located in a conductor connecting the hot lead of the power utility outlet to the hot lead of the electrical apparatus when the second relay is receiving current. The second relay switch arm opens when current in the second relay is not present, such as when the ground connection of the ground lead is interrupted or a reverse polarity of hot and neutral or when the voltage increases up to 240 V.  
           [0013]    The protective circuit of the present invention also protects all components between hot and neutral and thus protects the electrical apparatus when ground connection to electrical ground is broken or interrupted. Protection occurs against reverse polarity of hot and neutral or when voltage increases up to 240 V, and also in the event of applying 240 volts to hot and neutral without ground connection.  
           [0014]    The protective circuit of the present invention also includes a voltage threshold sensing circuit which detects when the voltage between the hot and neutral lead of the power utility outlet exceeds an established protective level. An electronic switch is connected to the voltage threshold sensing circuit. The electronic switch responds to power from the utility outlet detected as exceeding the threshold and disables the second relay which supplies current to the connected apparatus or microprocessor-based equipment. The electrical apparatus is thus protected by the circuit of the present invention from excess voltage levels between the hot and neutral lead from the power utility outlet. An indicator, such as an LED, also turns on to indicate the abnormality of voltage. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    [0015]FIG. 1 is a schematic electrical circuit diagram of a transient voltage surge suppressor or transformer base filter according to the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0016]    In the drawings, the letter P designates generally a new and improved protective circuit or transient voltage suppressor for electrical apparatus. The protective circuit P functions as a transformer base filter. In the preferred embodiment, the electrical apparatus may take the form of a computer, a copier, a facsimile machine or the like having voltage surge or transient sensitive electronic components, such as computer chips. These types of components are sensitive to voltage surges or transients, as well as abnormal high voltages furnished them by leads from electrical power utilities. It should be understood, however, that the protective circuit P may be used with other electrical apparatus which are sensitive to voltage surges or transients, or to abnormal high voltage.  
         [0017]    The protective or transformer-based filter circuit P has as its inputs a hot lead or terminal  10 , a neutral lead  12 , and ground lead  14 , each of which is connected respectively to a hot lead  16 , a neutral lead  18  and a ground lead  20  of a conventional electrical power utility outlet U. Typically, the embodiment shown in the power provided is conventional 120 volts alternating current potential difference between the hot lead  16  and the neutral lead  18 . It should be understood that the voltage level present could be some other conventional or standard voltage level.  
         [0018]    The protective circuit P includes a voltage surge protective circuit V connected between a hot conductor  10   a  connected to the hot terminal  10  and neutral conductor  12   a  connected to the neutral lead  12 . The voltage surge protective circuit V has a first set of voltage surge protective devices or clamping devices  24  and  26  and a second set of voltage surge protective devices, such as filters or clamps  28  and  30  and also a capacitor  34 . Each of the two sets of voltage surge protective devices is connected in an electrical series circuit between the hot and neutral leads  10  and  12 .  
         [0019]    The series connected clamping devices  24  and  26  of the first set are connected at a node or common connection  32  to each other opposite their respective connections to the hot and neutral leads  10  and  12 . Similarly, the series connected clamping devices  28  and  30  of the second set of the circuit V and also the capacitor  34  are connected to each other at the node  32  and thus to the clamping devices  24  and  26  of the first set. The node  32  is connected to the neutral lead  12  through a noise filter capacitor  34 . The noise filter capacitor  34  may be any rating or capacitance value, such as 2 μf or larger. A current limiting resistor  36  and a second noise filter capacitor  38  are also provided in parallel with capacitor  34  to connect the node  32  to the neutral lead  12 .  
         [0020]    The protective circuit P also includes a relay circuit R composed of a set of a first relay  40  and a second relay  42  connected between the hot and neutral leads  10  and  12 . As is conventional, a protective diode  44  and a filter capacitor  46  are connected in parallel across the relays  40  and  42 .  
         [0021]    As will be set forth, the relay set R protects against several undesirable conditions. The relay set electrically R isolates the electrical apparatus connected to the protective circuit P from transients and protects against over voltage or other undesirable conditions occurring in the power utility. The first relay  40  and second relay  42  protect voltage surge protective devices  24 ,  26 ,  28 , and  30 , and capacitor  34  when ground lead  14  is not connected to building ground  20 . The first relay  40  and the second relay  42  also protect these voltage surge protective devices against high voltages between hot lead  10  and ground lead  14 , and also high voltages between neutral lead  12  and ground lead  14 , such as those occurring when connection to building ground  20  is broken, reverse polarity between hot lead  10   a  and neutral lead  12   a , or disconnection of the neutral lead  12   a.    
         [0022]    In addition, the first relay  40  and the second relay  42  protect voltage surge protective devices  43  and  45  between hot lead  10  and neutral lead  12  against high voltages. The first relay  40  and the second relay  42  as well protect the electrical apparatus at the output of protective circuit P against high voltages. As will be set forth, the first relay  40  and the second relay  42  also protect the other voltage surge protectors and electrical filter components between the protective circuit P against such undesirable conditions.  
         [0023]    The first relay  40  has a relay coil  40   r  controlling the position of a switch arm or contact  40   k . The contact  40   k  of the relay  40  is electrically connected in the neutral conductor  12   a  between the neutral lead  18  of the power utility and the neutral lead  12   b  to the electrical apparatus. As long as the electric ground  14   a  is electrically connected to ground, and also, as long as the connection between the hot and neutral leads  10  and  12  is not reversed, the relay  40  receives current and relay contact  40   k  is in a closed position shown in the drawing.  
         [0024]    The first relay switch arm  40   k  opens when current is not present in the first relay  40  in the event of the undesirable conditions mentioned above. The protective circuit P of the present invention thus protects its voltage surge protectors or clamping devices, as well as its electrical filter elements, as well as any devices between neutral and ground. In addition to the protection provided against these undesirable conditions, the protective circuit P protects and isolates an electrical apparatus which is connected to it from undesirable conditions present on lines from the electrical utility.  
         [0025]    When the ground wire  14   a  is properly connected also the hot and neutral wires are properly connected, then a thyristor  70  is on. The relays  40  turns on and the switch  40   k  is in the position shown in the drawings, and first relay arm  40   k  closes the circuit between the neutral lead  12   a . In this manner any power surges or transients between the hot lead  10  and neutral lead  12  are suppressed by the voltage protective devices  24  and  26 , also by devices  28  and  30  when present. Further, noise and transients also are filtered by capacitors  34  and  38 . In this manner, substantially all electrical noise which may from time to time appear between the hot or neutral leads  10  and  12  is filtered.  
         [0026]    In the event an electrical connection between the ground lead  14  and building ground  20  is interrupted, or if the connection between the hot lead  10  and neutral lead  12  should become improperly connected and polarity thus reversed, or if the neutral lead connection  12  is interrupted or broken, an abnormal situation is present. The voltage levels present can increase to twice their normal level. The relay  40  no longer receives current through thyristor  70  or other electronic switch, such as a transistor. In such a case, the contact  40   k  of the relay  40  opens and moves to an opposite position from that shown. Current cannot flow through it to voltage clamping devices  24 ,  26 ,  28  and  30  or the noise filter capacitors  34  and  38 . Thus, the clamping components of the voltage surge protection circuit V are protected from increased voltage.  
         [0027]    Winding bobbins  41   a  and  41   b  of a differential transformer (or noise isolation transformer)  41  are series connected between hot lead  10   a  and  10   b  and between neutral  12   a  and  12   b , respectively. The noise isolation transformer  41  combines with capacitor  34  to filter the noises between the hot and ground or neutral lead and ground  20 .  
         [0028]    A voltage clamping device  43  is provided to suppress any surges or transient between hot lead  10   a  and neutral lead  12   a  and a clamping device  45  suppresses any surges and transients between hot lead  10   b  and neutral lead  12   b . Capacitors  47  and  49  are furnished for filtering any noise between hot lead  10   b  and neutral lead  12   b  while a resistor  51  discharges the capacitors  47  and  49 .  
         [0029]    The second relay  42  of the relay circuit R includes a coil  42   r  which controls a switch arm or contact  42   k  in hot conductor  10   a  connecting the hot lead  16  of the electrical power utility outlet U to a hot lead output  10   b  connected to the electrical apparatus. So long as the relay  42  is receiving electrical current, the contact  42   k  is closed (as is shown) and electrical power is furnished at the hot lead output  10   b  to the electrical apparatus. In the event that current through the relay  42  is no longer present, such as when the ground connection is interrupted, or polarity between the hot lead  10  and neutral lead  12  becomes reversed, the contact  42   k  of the relay  42  opens. Power is thus inhibited from being present at hot lead  10   b , and the electrical apparatus connected there is protected from voltage surges, over voltage or transients. Also any clamping components between hot lead  10   b  and neutral lead  12   b  are protected against increased voltage.  
         [0030]    The protective circuit P of the present invention also includes a voltage threshold sensing circuit T which detects when the voltage on the hot lead  16  of the electrical power utility outlet U exceeds a set or established voltage threshold. The voltage threshold is established by the relative impedance values of series connective resistors  50  and  52 . The voltage threshold may be adjusted by selecting different impedance values for the two resistors, or by including a variable resistor or rheostat in one or both of the resistors  50  or  52 . A DC filter capacitor  54  is connected in parallel with the resistor  50 . A clamping device  55  is connected between leads  10   a  and  12   a  to limit the voltage drop across the voltage threshold sensing circuit T. The resistor  52  is electrically connected to the neutral conductor  12   a  and neutral lead  12  by a resistor  56 . A diode  58  is present to rectify the AC voltage to DC. A protective fuse  59  may also be provided in lead  10   a  at the input of voltage threshold sensing circuit T.  
         [0031]    A Zener diode  60  is electrically connected to resistors  50  and  52  to sense the voltage threshold level present there. As long as the voltage threshold does not exceed the established threshold, the diode  60  does not conduct. In the event that the voltage threshold level provided to diode  60  exceeds the set level, diode  60  begins to conduct and a transistor or other electrical or electronic switch  62  also begins to conduct. The transistor  62  is normally held in a non-conductive state.  
         [0032]    A collector terminal  62   c  of the transistor  62  is connected to a gate  70   g  of a thyristor  70 , or other suitable electronic switch, such as a transistor, connected in series with the relays  40  and  42 . When the transistor  62  begins to conduct due to the threshold voltage level being exceeded, the current through diode  64  and resistor  66  to the gate  70   g  of the thyristor  70  is drawn to zero. Thyristor  70  is then switched to a non-conductor or off state and current flow through relays  40  and  42  is terminated. In this manner, relays  40  and  42  of the voltage surge protective circuit V are disabled in the event of excess voltage between hot lead  16  and neutral lead  18 , protecting the circuit P and connected apparatus from excessive input voltage.  
         [0033]    Thyristor  70  is normally biased to a conductive state and provides electrical current to relays  40  and  42  by a bias network including diode  64  and resistors  66  and  74 . A diode  78  rectifies the AC to DC and resistor  76  limits the current in relay coils when the thyristor  70  is conductive and thus relays  40  and  42  are receiving current. An alarm indicator  80 , such an LED, is connected through a diode  84  and a resistor  86  to the neutral lead  12   a . The alarm indicator  80  is energized when the relay switch  42   k  is in the open position opposite that shown in the drawings. In the event that contact  42   k  of relay  42  interrupts the flow of power to the electrical apparatus via the hot conductor  10   a , indicator  80  is electrically energized to indicate this alarm condition.  
         [0034]    A normal indicator  90 , such as an LED, is connected between the hot lead  10   b  and the neutral lead  12   b  in series with a diode  92  and a resistor  94 . During normal operation of the protective circuit P when the relays  40  and  42  are receiving current, the relay switch  42   k  is in the position shown in the drawing connecting the hot lead  10   a  through to the hot lead  10   b . Relay switch  40   k  is also in the position shown in the drawing connecting the neutral lead  12   a  through neutral lead  12   b . In this condition, the normal indicator  90  is energized, indicating that conditions are normal for power flow through the protective circuit P to the electrical apparatus.  
         [0035]    It is to be noted that each of the various voltage clamping devices, as well as the electrical filter elements, such as capacitors and inductors, in the protective circuit P are connected between the neutral lead and the ground lead. In this manner, an undesirable effect, such as neutral ground (or common mode) noise and transient spikes are filtered and suppressed by the protective circuit P.  
         [0036]    It should be understood also that the relays  40  and  42  may be separately connected individually between the hot lead  10   a  and neutral lead  12   a , rather than in series as shown in the drawing. In this separate connection, each of the relays  40  and  42  are provided with a separate thyristor or other electronic switch functioning like the thyristor  70 . Each such separate thyristor or electronic switch is of course provided with its own corresponding bias network of the type described above. Also, if desired, one relay with two sets of switch arm contacts may be used as an alternate.  
         [0037]    The foregoing disclosure and description of the invention are illustrative and explanatory thereof, and various changes in the size, shape, materials, components, circuit elements, wiring connections and contacts, as well as in the details of the illustrated circuitry and construction and method of operation may be made without departing from the spirit of the invention.