WO1998011767A1 - Solid state switching device arrangement for silicon transfer switch - Google Patents

Abstract

A silicon transfer switch (10) having a compact and modular arrangement of solid state switch components (14) within the switch boxes (10). The components are arranged in modular half-stack assemblies (14) such that the half-stacks can be loaded into and out of compartments (12) within the switch boxes (10) in an efficient and timely manner. The cooling system minimizes temperature and pressure gradients in the flow of air to the electronic components arranged in the stacks (14) so as to provide uniform cooling of the components. The compact and modular arrangement of the switch components optimizes electrical interconnection between components, mechanical clamping forces, thermal cooling, magnetically coupled solid state switch device firing and temperature management within the system.

Description

SOLID STATE SWITCHING DEVICE ARRANGEMENT FOR SILICON TRANSFER SWITCH

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. Serial Number 08/710,291 , filed September 16, 1996, the disclosure of which is herein incorporated by reference.

BACKGROUND OF THE INVENTION The present invention relates to a silicon transfer switch for providing an uninterrupted transfer of power between two sources in the event of a voltage sag or disturbance in one of the power sources. More specifically, the present invention relates to a silicon transfer switch having an improved arrangement of solid state switching components in series, wherein a compact and modular arrangement of electrical components and heat sinks provides for optimized cooling with minimal pressure losses in the flow of cooling air, as well as a low noise environment.

Silicon transfer switches are known in the art. These switches are designed to provide an uninterrupted power source to facilities where any interruption in power could result in significant loss. Such facilities include industrial plants that perform continuous manufacturing operations, hospitals, airports, military bases and data communications centers, where an uninterrupted power supply is critical to facility operation. Generally, the switch comprises two power source switch boxes, wherein the preferred power source is input into one of the switch boxes and an alternative power source is input into the other switch box. Inside each switch box is an arrangement of solid state switching devices, such as thyristors, with the electrical components of each switch box being connected to controller electronics housed in a controller box (generally positioned between the switch boxes). The solid state switching devices in each box are designed to provide transfer of the power service from the preferred power source to the alternative power source in the event of a disturbance or voltage sag that is detected in the preferred power source.

The controller electronics in the controller box provides the necessary input and output information to turn the switch device in one of the switch boxes to an "on" position, while turning the switch device in the other box to an "off" position so that the power source flowing into the "on" switch is supplied to the load. Typically, transfer from the preferred AC power source to the alternate AC power source will occur within a fraction of a power cycle. However, controlling and monitoring the operation of the solid state switch devices must be done in a significantly elevated voltage environment. Specifically, control/monitoring in such an environment includes at least three key aspects, namely, thyristor failure detection, simultaneous thyristor triggering and thyristor temperature monitoring.

In the large applications noted above, the power requirements are such that a large number of electrical components are necessary to provide a satisfactory switch. Some known power requirements can be as much as a 36 kV and 600 amp service. Generally, the arrangement of components in each of the switch boxes comprises as many as eight or more solid state switching devices arranged in series so as to provide a switch capable of operation in the required high voltage, high current environment. Due to the significant amount of heat generated by the solid-state switch components within each switch box, the components must be cooled.

Unfortunately, considering the necessity for a large number of solid state switch components to satisfy the large voltage and current requirements, combined with the necessity for cooling apparatus to provide significant cooling of the electronic components, known switches generally comprise a cumbersome arrangement of parts. The switch components are stacked in a column-like arrangement that takes-up a large volume of space and make accessibility to the components for inspection and repair difficult. Moreover, the components are arranged in a fixed environment wherein it is necessary to replace an entire switch box in the event of a catastrophic failure of one of the key switch components. In known switches, replacement of the components in a switch box can take up to 8 hours, and in some cases replacement of the entire switch box is required.

Generally, thyristor failure detection in a high voltage anti-parallel switch is difficult when detection is to be made while the switch is conducting. This condition requires that the shorted thyristor condition be established from signals indicating elevated current flow in both directions. Conventional current monitoring incorporated an air-core current transformer type winding. Such a winding, however, required transmission of the coil voltage against the high common mode potential difference at die computer or monitor circuit, where signal analysis can be performed on an instant by instant basis. In order to trigger a thyristor gate to turn it on, a current-pulse of a few amperes is applied during forward voltage bias conditions. Such a current pulse is required to rise to a maximum level in 1 microsecond and remain at that level for 12 to 40 microseconds, also called a hard gate pulse. In a series string of anti-parallel thyristors, gate signals must be applied simultaneously to avoid voltage break-down in a late turning on valve. To assure simultaneous valve triggering in a series of thyristors, the gate current is often coupled from a series of pulse current transformer type CTs with a common primary current winding. This arrangement, however, neither precludes nor detects the loss of a gate signal due to failure of one of the gate-level firing pulse transformer type CTs. The temperature of the junction of a thyristor limits its operational capability and reliability if certain temperature limits are exceeded for longer than certain prescribed times. Direct detection of the junction temperature is not possible with present technology and must instead be estimated. Estimation of thyristor junction temperature requires knowledge of the heat generation, thermal impedance of the thyristor heat sink assembly, and the actual temperature at the point to which the thermal impedance is known. Accurate temperature measurement of the thyristor heat-sink has been the best means for estimating the junction temperature of the thyristor. However, an instrumentation problem exists for such a temperature measurement. Since the heat-sink itself conducts current between adjacent thyristors, the heat-sink is at an elevated voltage potential, many orders of magnitude above the level of the temperature signal for any known transducer. Additionally, conventional active temperature measurement transducers require some electrical power in order to operate. Moreover, analog signals of some transducers may be inaccurately transduced due to the common mode voltage limitations and due to noise.

As discussed, it is critical that the electronic switch components be maintained in a cool environment. In view of the massive size of the switch boxes, it has heretofore been difficult to provide an effective air cooling system within the switch box. Since the solid state switching devices are arranged in a substantially high column, or stack, it is known to be difficult to provide a cooling air system that can overcome the significant pressure gradient in the flow of air along the height of the stack such that the components at the top, bottom and middle of the stacks are all effectively cooled. In order to overcome the adverse effects of pressure losses in the flow of cooling air over the component stacks it is necessary to provide a system of high-power fans and a complex arrangement of ducts to evenly distribute the flow of cooling air over all the components in the stack. These requirements add to the cumbersome nature of the boxes and require that the boxes be excessively large. In addition to the substantial cost and manufacturing complexity of the boxes with such an air cooled system, operation of the cooling system in the boxes is known to be prohibitively loud in view of the vibrations of the apparatus.

A liquid cooling system is known to be an alternative to an air cooled system to maintain operation of the switch below the maximum sustainable temperature for the electronic switch components. Unfortunately, like the known air cooling systems, liquid cooling systems also have known disadvantages that make operation of such a system complex and costly. Since fluids used in liquid cooling systems are conductors of electricity (as opposed to air, which is a known insulator), the cooling system must be insulated from the electronic switch components. In view of the cumbersome arrangement of the component stacks, it is burdensome, as well as costly, to install and maintain the cooling apparatus in addition to the insulation apparatus to shield the cooling system components from the electronic components that are designed to protect.

Finally, considering the sensitivity of the electronic switch components, e.g. , thyristors, to environmental contaminants such as dust and the like, it is necessary to maintain the switch components in a clean environment. Since switches are generally operated in dirty environment, maintenance of a clean environment within the switch boxes is of primary importance. Unfortunately, due to the massive size of the known switch boxes, it is difficult and costly to provide adequate sealing members that effectively prevent contamination of the switch components by dust and dirt.

Accordingly, a need still exists for a silicon transfer switch having solid state switching components disposed in a compact, modular arrangement to provide for efficient repair or replacement of the components, wherein the components within the switch box are effectively sealed from environmental contaminants and are cooled by an efficient and quiet cooling system. Furthermore, a need still exists for methods and apparatus for controlling and monitoring solid state switches which also overcome the problems of high common mode potential difference, detecting the loss of a gate signal due to failure of one of the gate-level firing pulse transformer type CTs and which accurately measure temperature.

SUMMARY OF THE INVENTION

Accordingly, it is the general object of the current invention to provide a silicon transfer switch having solid state switching components disposed in a compact, modular arrangement to provide for efficient repair or replacement of the components, wherein the components within the switch box are effectively sealed from environmental contaminants and are cooled by an efficient and quiet cooling system. Furthermore, it is the general object of the current invention to provide methods and apparatus for controlling and monitoring solid state switches which also overcome the problems of high common mode potential difference, detecting the loss of a gate signal due to failure of one of the gate-level firing pulse transformer type CTs and which accurately measure temperature.

Briefly, this object, as well as other objects of the current invention, is accomplished in a silicon transfer switch having at least two switch boxes and one controller box, the controller box having a control circuit therein, each of the switch boxes receiving a power supply therein, each of the switch boxes, comprising: at least one valve compartment; two half-stack switch valves disposed in each valve compartment, each half- stack switch valve comprising a plurality of solid state switch devices arranged into two columns, each half-stack switch valve having means for applying compressive forces to the solid state switch devices, the solid state switch devices being electronically coupled to the power supply and the control circuit; and cooling means for cooling the solid state switch devices, wherein the silicon transfer switch provides for transferring power service to a downstream load from the power supply into one of the switch boxes to the power supply of another of the switch boxes.

According to one preferred embodiment of the invention, the solid state switch devices are thyristors. According to another preferred embodiment of the invention, thyristors are air cooled by a flow of cooling air across heat sinks that are mechanically coupled to the thyristors.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is perspective view of a switch box having one half-stack thyristor valve disposed in a valve compartment of a switch box in accordance with the invention.

Figure 2 shows a switch box with the thyristor valves removed.

Figure 3 shows an arrangement of switch boxes and a controller box of a silicon transfer switch in accordance with the invention.

Figure 4 shows a front view of a half-stack thyristor valve. Figure 5 shows the portion of the half-stack thyristor valve labeled A-A in

Figure 4.

Figure 6 illustrates a perspective view of a heat sink in accordance with the invention.

Figure 7 shows a side view of a half-stack thyristor valve. Figure 8 shows a side-rear perspective view of one half-stack thyristor valve disposed in a valve compartment of a switch box.

Figure 9 illustrates operation of a cooling system in accordance with the invention.

Figure 10 shows a side-rear perspective view of a half-stack thyristor valve in accordance with the invention.

Figure 11 is a schematic diagram of a control and monitoring circuit in accordance with the invention.

DESCRD7TION OF THE PREFERRED EMBODIMENT

Referring to FIGS. 1 and 2, switch box 10 has three main valve compartments 12 into which a plurality of half-stack thyristor valves 14 are disposed, as discussed in detail below. Referring to FIG. 3, at least two switch boxes 10, having a plurality of half-stack thyristor valves 14 therein, and a controller 16 form a silicon transfer switch for transferring power essentially uninterrupted from a preferred power source to an alternative power source. The controller 16 comprises a variety of circuitry, mechanical switches, isolators and the like, as described in further detail below. The electronic components of the half-stack thyristor valves in the switch boxes 10 are connected to control circuits in the controller 16 via connectors 17. The silicon transfer switch operates to detect a voltage sag or disturbance in a preferred power source 18 supplied to a downstream load (not shown), turn the power source 18 to an "off" position, and turn an alternative power source 20 to an "on" position such that power supply to the downstream load is transferred to the alternative power source without interruption of service at the load. The present invention is not intended to be limited to a silicon transfer switch having only two switch boxes 10 and any number of switch boxes can be used in the switch depending upon the power requirements. As is known in the art, an industrial power source for delivering high tension voltage is distributed in a three phase (A/B/C) package through three separate inputs. Thus, referring again to FIGS. 1 and 2, switch box 10 has three main valve compartments 10, into which the half-stack thyristor valves 12 are arranged in the manner described below, such that each one of the three phase connectors (A/B/C) is connected to the half-stack thyristor valves in a corresponding main valve compartment.

Prior to the description of the arrangement of the half-stack thyristor valves 14 into the switch box 10, the half-stack thyristor valves will be described with reference to FIGS. 4-7. Each half stack thyristor valve 14 is made-up of two columns of four solid state switching devices, which are preferably thyristors 22. However, the present invention is not intended to be limited to thyristors as the solid state switching components, and other components such as GTOs, IBGTs and triacs which provide for solid state switching can be used as alternatives to thyristors in the half stack valve assemblies.

Each of the two columns of thyristors in each half-stack thyristor valve also includes a plurality of heat sinks 24 disposed between the thyristors 22. Each heat sink 24 is preferably extruded aluminum comprising a base 26 and fins 28 integrally extending from the base. The heat sink also includes four vertical ligaments 30, with two of the ligaments being symmetrically displaced about the lateral center-line of the heat sink and one ligament at each edge of the base 26 on the outside of the fins 28. The outer end of the ligaments 30 extends beyond the outer end of the fins 28, as shown in FIG. 5.

In each column of the half-stack, the heat sinks are arranged from top-to- bottom such that a single heat sink 24 is disposed above the first thyristor 22. The base 26 is positioned opposite the top surface of the thyristor such that the fins 28 and ligaments 30 of the heat sink face in upward direction toward the top of the column. The base 26 of the heat sink is fitted with dowel holes 32, while the top surface of the thryistor is also fitted with corresponding holes. Accordingly, the heat sink is positioned in place with respect to the thyristor by the insertion of dowel pins into the matching holes of the heat sink and thryistor and any sliding between the heat sink and thyristor is obviated and each column is maintained in coplanarity relative to the thyristor center line.

Moving in a direction down the columns of each half-stack thyristor valve, two heat sinks are disposed between the first thyristor at the top of a column and the next thyristor down in the column. The base of one of the heat sinks is secured to the bottom surface of the top thyristor by the described dowel pin arrangement and the base of the other heat sink is similarly secured to the top surface of the next thyristor in the column. Accordingly, the two heat sinks are positioned with the vertically opposed fins. The outer ends of the four ligaments 30 of one heat sink contact the outer ends of the ligaments of the other heat sink. In a preferred embodiment, a glued tenon joint 34 is formed between the two inner ligaments 30 of the opposed heat sinks 24. The tenon joint is comprised of a slit in each of the two inner ligaments of each heat sink, the slit being about two inches in length and about 0.25 inches deep. A filler piece is disposed in the slits between opposed ligaments and secured into position by an epoxy glue. As shown in FIG. 7, the heat sinks in one of the columns of the half-stack thyristor valve is mechanically coupled to the opposing heat-sinks in the other column by clamps 36.

Due to the compact arrangement of the components within the half-stack thyristor valve, and the intimate contact between the ligaments of the opposed heat sinks (as described above), current is conducted effectively through the half stack without arcing of the voltage across the heat sinks and series connection of the components within the half-stack can be effectuated in the manner described below.

Moving further down each of the columns in the half-stack thyristor valve 14, the thyristors 22 and heat sinks 24 are arranged and secured within the column in the manner described above such that two opposed heat sinks are disposed between the second and third thyristors and between the third and fourth thyristors from the top of the column. A single heat sink is secured to the bottom surface of the bottom thyristor such that fins and ligaments of this heat sink face toward the bottom of the arrangement.

As is known in the art, the solid state switch components, such as the thyristors described herein, must be packaged under substantial pressure. For some applications, the solid state switch components must be packed under a pressure of up to about 20,000 pounds (10 tons). In order to apply the packing pressure to the thyristors in the preferred arrangement of the half-stack thyristor valves, the thyristor columns are clamped together as shown in FIGS. 4 and 7. A pair of opposed outer pressure plates 38 are disposed at the top and bottom of each column. As shown, the pressure plates 38 cover both of the columns in a half-stack thyristor valve. Another pair of opposed inner pressure plates 40 are disposed in each column adjacent to the top and bottom heat sinks 24 such that the pressure plates contact and rest on the outer ends of the ligaments 30 of these heat sinks. The inner pressure plates 40 have rounded corners to reduce local electric stress.

The opposed outer pressure plates 38 are clamped together by four electrically insulated long tension rods 42 on each side of the half-stack thyristor valve and corresponding tension rod nuts 44. Insulated material is required for the tension rods to provide maximum impulse strength of the insulated valve arrangement from ground, and to reduce the size, as well as the mechanical stress and deflection, of the outer pressure plates.

Referring still to FIGS. 4-7, an expanding screw clamp 46 is coupled to the inner pressure plates 40 of each of the thyristor - heat sink columns for providing a tension force in the tension rods 42, which in-turn provides the required compressive force to the heat sink - thyristor column. The screw clamps 46 include a clamping nut 48, clamping disc 50 and clamping bearing 52. Springs 54, preferably Bellville type springs, are coupled between the clamping disc 50 and the upper inner pressure plate 40. A post insulator 56 is coupled between the clamping bearing 52 and the upper outer pressure plate 38 of each column to insulate the clamping means and the components in the column from the outer pressure plate 38. Similarly, a post insulator 56 is coupled between the lower inner pressure plate 40 and the lower outer pressure plate 38 to insulate the components in the column from the lower outer pressure plate 38. Post insulators 56 can be made of any suitable insulating material such as poly concrete, porcelain, or other polymeric materials. Upon turning of the clamping nut 48, the screw clamp 46 is actuated to provide tension in the tension rods 42, which results in a compressive force applied to each column of the half-stack thyristor valve arrangement. The springs 54 allow for thermal expansion of the apparatus in the columns, as well as compressive force control. In view of the compact arrangement of the apparatus within the columns, the tension rods 42 can be disposed in close proximity to the columns so as to optimize uniformity of the application of compressive forces to the column and maintain coplanarity of the column relative to the thyristor center line. The four vertical ligaments 30 of the heat sinks 24 are dimensioned in height and width, and are displaced at a distance from the lateral center line of the heat sink, to manage compressive stress and minimize deflection in the heat sink surface. With this arrangement of the apparatus in the half-stack thyristor valve, clamping pressure of up to about 10 tons can be maintained. Moreover, considering the dowel and tenon joint couplings between the heat sinks and thyristors and between opposed heat sinks, as many as six thyristors can be provided in each column such that coplanarity of the column is maintained relative to the thyristor center line upon application of 10 tons of compressive force.

Referring to FIGS. 1-2, 4, and 7-10, the half-stack thyristor valve 14 is fitted with four roller wheels 58 coupled to the upper outer pressure plate 38. Each one of the half-stack thyristor valves 14 is mounted into one side of the valve compartments 12 by the engagement of the roller wheels 58 onto stationary guide rails 60 extending along the top of the front and back of each valve compartment 12. In order to load the half-stack thyristor valves 14 into the valve compartments 12 of the switch box 10, a portable guide rail assembly 62 is mechanically coupled to the stationary guide rails 60 and the half-stacks are delivered to the portable guide rail assembly such that roller wheels 58 are positioned into the portable guide rail assembly 62 and the half-stack is rolled into position in the valve compartment 12 along the stationary guide rails 60. A stop (not shown) at the end of the end of the stationary guide rails 60 limits the travel of the half- stack in the front and back sections of the valve compartment. In order to remove one or more of the half-stacks from the switch box 10 in the event of catastrophic failure of one of components, or for routine maintenance or the like, the half-stack can be removed by rolling the half-stack out of the valve compartment and onto a portable guide rail assembly for delivery to a maintenance vehicle or the like, and a substitute half-stack could be loaded in the switch box in a quick, routine and efficient manner. It should be noted that the stationary guide rails used for loading the half stack thryistor valves into the switch box could be positioned at the bottom of the valve compartments (with the roller wheels being assembled onto the bottom of the half-stacks) such that the half-stacks could be loaded into the switch box in the same described manner. In view of the compact, modular arrangement of the half-stacks and the provisions for loading the stacks into the switch box along rails, removal and replacement of a half-stack can be effectuated in about two hours. One of ordinary skill in the art will appreciate this significant decrease in the time required for replacement of the components of known solid state switch devices, which could take as long as 8 hours. Moreover, one of ordinary skill in the art will appreciate that maintenance of the switch components can be effectuated in an efficient manner. It should be noted that the present invention is not intended to be limited to placement of the compact modular half-stack thyristor valve assemblies into the switch box using the described rail assembly and other means for loading of the half-stack assemblies into the switch box are within the scope of the invention.

The electrical interconnections for assembly of the silicon transfer switch can also be made quickly and efficiently in view of the compact, modular arrangement of the solid state switching devices within the switch boxes. Referring to FIGS. 8-10, once the half-stack thyristor valve 14 is loaded into the valve compartment 12 an electrical connector plug 64 fitted into the valve compartment 12 is connected to a corresponding power supply socket 66 on the rear of the half-stack to form a plug and socket joint 67. The connector plug 64 is coupled into a bus compartment 68 at the bottom of the switch box and the couplings are sealed so as to seal the bus compartment from the main valve compartment. The connector plug 64 is connected to one phase of the power source input 65 (FIG. 9) in a known manner such that the power supply is input into the half-stack thyristor valve. It will be understood by those of skill in the art that a similar arrangement of electrical connection components is provided for hooking up a half-stack thyristor valve into the rear portion of the valve compartment 12, as well as into the front and rear portions of the other valve compartments in the switch box. One of ordinary skill will also understand that the valve compartments and the bus compartments of the switch box will be fitted with exterior walls (not shown) that are sealed to prevent contamination of the valve compartments from the environment outside the switch box. Referring to FIGS. 9-10, when the half-stack thyristor valves are loaded in a back-to-back arrangement into their respective front and rear portions of a valve compartment 12, electrical connection between the half stacks is accomplished by coupling series connection sockets 70 at the rear of each half-stack. Accordingly, the four thyristors in one of the columns of the half-stack thyristor valve 14 in the front portion of the valve compartment 12 can be connected in series to the four thyristors in one of the columns of the half-stack thyristor valve 14 in the front portion of the valve compartment 12 through the series connection sockets 70. Similarly, the other four thyristors from the front half- stack can be connected in series to the other thyristors in the rear half-stack. Series connection of these multiple thyristor levels provides for a solid state switch that can withstand voltage levels up to about 36 kilo-volts. In this arrangement, the opposed thyristors in the columns that make up the half-stack thyristor valves are electrically connected by an anti-parallel connection.

Referring to FIGS. 4 and 7-10, four printed circuit boards 72 are contained within a half-stack thryistor valve, wherein one of the circuit boards 72 is disposed in the stack adjacent a pair of anti-parallel thyristors 22. Two gate firing tubes 74 are mechanically coupled to the front side of a half-stack thyristor valve by plastic retaining clips 75 on the top and bottom circuit boards in the stack (FIG. 1). It should be noted that the gate firing tubes 74 have been removed from the illustration in FIG. 9 for clarity. A main insulating current transformer is disposed in transformer boxes 76. Multiple gate firing current transformers, one per thyristor, and a secondary current loop of the main insulating current transformer are disposed within the gate firing tubes 74. The current transformers are electronically interconnected and connected to the printed circuit boards, which are in turn connected to controller circuitry in the controller box 16 through a series of fiber optic and electrical cables (not shown). The gate firing tubes 74 also provide mechanical support for the fiber optic connections. Snubber circuits are disposed in the vertical panels 82 and are electrically connected across the thyristors 22 to limit over- current and over- voltage occurrences. Firing of the thyristors is effectuated magnetically through an isolated current loop. Fast rise-time trigger currents are delivered from a pulse amplifier that is magnetically coupled through the main insulating current transformer. The valve firing arrangement provides for power application in an environment where it may be unacceptable to use trigger power from the snubber circuits prior to the turn-on process of the thyristors. Operation of the circuitry for control and monitoring of the thyristor valve firing is described in further detail herein.

Operation of the cooling system for the switch box 10 is described with reference to FIGS. 1-2, 5 and 9-10. Each of the half-stack thyristor valves 14 includes a baffle 80 mechanically secured to the rear of the half-stack assembly and vertical panels 82 are assembled onto the baffle 80. The sockets 66, 70 are sealed through openings in the baffle 80 and sealed openings in the baffle expose the vertical fins 28 of the heat sinks 24 through the baffle 80 within the confines of the vertical panels 82. Sealed accommodations for the wires and cables used to establish the various electrical connections of the valve firing and monitoring equipment are also provided in the baffle 80.

When the front and back opposed half-stack thyristor valves 14 are loaded into position in a valve compartment 12 of the switch box 10, the opposed baffles 80 at the rear of each half-stack form a plenum 84 between them (FIG. 9). The baffles 80 are sealed into position within the valve compartment 12 to effectively seal the plenum 84.

At the top of the switch box, above the upper wall 85 of each of the valve compartments 12, an air blower chamber 86 is disposed above a cold side air inlet plenum 88. An internal cool air blower 90 is disposed in the air blower chamber 86, with one cool air blower positioned above each valve compartment 12. Cooling air 91 from the cool air blower 90 is input into a cool air duct 92 that extends through the cold side air inlet plenum 88 and into flow communication with the plenum 84 such that cooling air flows into the plenum 84.

The chimney-like effect of the flow of cooling air into the plenum provides for a substantially uniform flow of cooling air 91 into the entrance of each of the heat sinks at the rear of the baffle and across the fins of the heat sinks. Temperature and pressure gradients in the flow of cooling air inside the sealed plenum 84 are minimized such that a substantially even flow of cooling air 91 is distributed into all of the heat sinks from the top to the bottom of the columns within a half-stack thyristor valve.

The flow of cooling air 91 exits the heat sinks as a flow of hot air 94 into a hot air side plenum 96. The flow of hot air 94 is exhausted into a sealed hot air return exhaust duct 98. The hot air return exhaust duct 98 is in flow communication with a heat exchanger 100 disposed in the air blower chamber 86, with one heat exchanger 100 above each half-stack thyristor valve 14. Ambient outside air 102 from outside the switch box 10 is drawn into the heat exchanger 100 through the cold side air inlet plenum 88. Accordingly, the high temperature air in the heat exchanger is partially cooled and exhausted out of the switch box through external air flow fan assemblies 104 arranged on a platform 106 at the top of the switch box.

One of ordinary skill in the art will appreciate another advantage of the described air cooling system wherein the electrical bus connections of the switch are contained at the cool air side plenum 84 and are not exposed to the hot air at the hot air side plenum 96. Also, the cylindrical design of the gate firing tube 74 provides a smooth exterior for air-flow and pressure recovery. Furthermore, operation of the described cooling system provides for quite operation of the switch box assembly.

The compact and modular arrangement of the split half-stack thryistor valves allows for quick and efficient maintenance or replacement of the switch components. The complete valve stack assembly, including the clamping components and the electrical firing components, can be removed from service by disengaging the plug and socket connections and loading of the assembly onto a portable guide rail system. The system within the switch box is cooled efficiently with a compact arrangement of the cooling system components. The electrical bus work and plug and socket connections are isolated from a high temperature environment in a cold air side chimney-like plenum. Thus, a silicon transfer switch in accordance with the invention provides a compact and modular switch assembly capable of providing uninterrupted power service to a downstream load.

Referring now to Fig. 11, the electronic circuit used to detect thyristor failure during normal closed conditions, to detect the presence of a gate signal and to monitor heat sync temperature is disclosed. Generally, detection and monitoring circuit

200 is disposed on printed circuit board 72 which is shown in Figs. 4, 7 and 10 as being provided at each level of the half-stack arrangement. Since each circuit board 72 contains an identical electronic circuit, only one description of circuit 200 need be made.

In order to detect gate current, circuit 200 generates a gate current reception signal which provides feedback to the firing controller located in controller 16 (Fig. 3). Such feedback indicates to the firing controller that a gate signal was received at each thyristor level. The firing controller can quickly remove gate signals from the series stack of thyristors 22, if a gate signal from any given thyristor is not received. Such action serves to be protective of the stack voltage with-stand integrity due to failure of a valve to begin conducting current.

The gate reception signal is developed magnetically using toroidal pulse transformers 202 and 204 positioned around the gate current leads of thyristors 22. It will be recalled previously that these toroidal pulse transformers are arranged in tubes 74 for electrical connection with transformers 76. The voltage signals from two anti-parallel thyristor gate reception transformers 206 and 208 are regulated by resistors 210 and 212 and rectified by diodes 214 and 216. The two signal currents are wired OR'ed and current limited by resistor 218 into a single fiber-optic light emitting diode 220. The circuit settings are chosen to detect only the hard-gate pulses and to reject typical picket fence maintenance pulses.

In relation to monitoring the temperature of heat sync 24 (not shown), a temperature sensor 222 is attached to heat sync 24. Temperature sensor 222 thereby provides a method of digitally transducing the heat sync temperature which temperature information will be transmitted to controller 16 at ground potential. However, in order to power temperature sensor 222, a 5 volt DC power supply is generated from a gate pulse signal produced from the regulated voltage drop of zener diode 224. This gate pulse is sustained between pulses by energizing smoothing capacitors 226 through 230. This 5 volt supply is applied to temperature sensor 222.

In the preferred embodiment, temperature sensor 222 is a variable duty cycle oscillator, whose duty cycle varies linearly with temperature. The variable duty cycle temperature signal is modulated with a fixed frequency oscillator 232 whose output is on the order of 200 kHz. The oscillated signal is OR'ed with the gate reception signals described previously. This technique provides both temperature information and gate reception information on one fiber optic channel, namely LED 220. The variable duty- cycle transducer represents a digital transducer method which is inherently accurate, depending only on the duty-cycle rather than the frequency of oscillations. It may be appreciated at this point that the output of LED 220 will be reflective of the oscillated temperature signal so long as gate reception signals are present. Should one of the gate reception signals cease, the modulated temperature information signal will also cease, thereby indicating a gate signal loss.

Circuit 200 also discloses thyristor failure detection circuitry. The circuitry of the present invention eliminates conventional signal analysis by using a high coercive force toroidal magnetic core 240 and 242 and a potential wilding 244 and 246. The cores and windings are arranged to detect the change in thyristor current flowing through the center of the toroidal magnetic structure. With unidirectional current flow in the thyristor, i.e. , during normal operation, the magnetic core is saturated in one direction. In such a situation, no voltage is generated in the toroidal windings 224 and 246. If thyristors 22 fail, however, and begin conducting in both directions, the magnetic force will traverse the magnetic hysteresis loop of cores 240 and 242 from positive to negative saturation for each cycle of current. As a result, twice each cycle the core associated with the failed thyristor jumps from positive to negative or negative to positive saturation. This jump from one saturation point to another generates a small voltage on the toroidal winding (244 or 246) sufficient to light a light emitting diode 248. This light can be transmitted fiber optically and converted to a digital sense signal for simple detection by controller 16. The thyristor failure detection system is very sensitive depending on the magnetic properties of the core. Core materials can be chosen that exhibit high remnant magnetic flux at very low magnetizing current levels. It is possible to arrange for detection of thyristor failure down to the order of two amperes of current flow in a system rated for 600 amperes. In the preferred embodiment, toroidal cores 240 and 242 are formed from a nickel-iron saturable core material which comprises approximately 40 to

50 percent nickel (grain-oriented). It is specifically preferred that such material be Orthonol, a common trade name for this material. Even more particularly, it is preferred that the cores be formed from square Orthonol. Square Orthonol is described as a material which is a grain-oriented 50 percent nickel-iron alloy available in various thicknesses for tape wound cores and bobbing cores. It is manufactured to meet exacting circuit requirements for very high squareness and high core gain and is said to have been used in saturable reactors, high gain magnetic amplifiers, bi-stable switching devices and power invertor-convertor applications. Other applications are said to have included time delays, flux counters and transducers demanding extremely square hysteresis loops.

In order to exploit the pulses generated by cores 240 and 242, circuit 200 includes a level electronic monitoring system. For open-thyristor failure detection, the sharing resistor across the level is split into a voltage divider whose voltage signal is present at terminals 250 and 252. This voltage signal is current limited with resistor 254 and voltage limited with back-to-back zener diodes 256 and 258. The current limited and voltage limited signal is applied to a full-wave rectifier bridge 260. The DC rectified voltage output is logically OR'ed with the two voltage signals from the anti-parallel thyristor failure current detectors 240 and 242 through diodes 262 and 264. The combined voltage is presented to a current limiting and voltage clamping circuit 264 to provide signal current during failure detection to a fiber optic light emitting diode 248.

The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification, as indicating the scope of the invention.

Claims

CLAIMS:

1. A silicon transfer switch having at least two switch boxes and one controller box, said controller box having a control circuit therein, each said switch box receiving a power supply therein, each said switch box, comprising: at least one valve compartment; two half-stack switch valves disposed in each said valve compartment, each said half-stack switch valve comprising a plurality of solid state switch devices arranged into two columns, each said half-stack switch valve having means for applying compressive forces to said solid state switch devices, said solid state switch devices electronically coupled to said power supply and said control circuit; and cooling means for cooling said solid state switch devices, wherein said silicon transfer switch provides for transferring power service to a downstream load from the power supply into one of said switch boxes to the power supply of another of said switch boxes.

2. The silicon transfer switch according to claim 1, wherein said solid state switch devices are thyristors.

3. The silicon transfer switch according to claim 2, wherein each said column has four thyristors connected in series, and four thyristors from one of said columns of one of said half-stack switch valves in said valve compartment is electronically connected in series to four thyristors from one of said columns of said other half-stack switch valve in said valve compartment.

4. The silicon transfer switch according to claim 1 , wherein said cooling means provides for air cooling of said solid state switch devices.

5. The silicon transfer switch according to claim 1, each said half-stack switch valve further having wheels thereon, said valve compartment having guide rails therein, wherein said half-stack switch valves hang in said valve compartment by coupling said wheels in said guide rails.

6. A switch box for a silicon transfer switch, comprising: at least one valve compartment; two half-stack switch valves disposed in each said valve compartment, each said half-stack switch valve comprising a plurality of solid state switch devices arranged 5 into two columns, each said half-stack switch valve having means for applying compressive forces to said solid state switch devices; and cooling means for cooling said solid state switch devices.

7. A switch box for a silicon transfer switch, comprising: at least one valve compartment; and 0 two half-stack switch valves disposed in each said valve compartment, each said half-stack switch valve comprising a plurality of solid state switching devices and heat sinks arranged into two columns, each said solid state switching device having first and second sides, one of said heat sinks mechanically secured to each of said first and second sides, each said column having means for applying compressive forces to said solid state 5 switching devices and said heat sinks within said column.

8. The switch box according to claim 7, each said heat sink having a base and a plurality of fins extending from said base, each said fin having a fin end, each said heat sink further having a plurality of ligaments extending from said base, each said ligament having a ligament end extending beyond said fin ends, at least two of said heat o sinks arranged in said columns to be opposed with said ligament ends of one of said heat sink contacting said ligament ends of said opposing heat sink.

9. The switch box according to claim 8, wherein said ligament ends of opposing heat sinks are joined by a tenon joint.

10. The switch box according to claim 8, said base of each said heat sink 5 having heat sink dowel holes therein, each said first and second sides of said solid state switching device having switching device dowel holes therein, said heat sinks being mechanically secured to said first and second sides by doweling together said heat sink dowel holes and said switching device dowel holes.

11. A thyristor failure detector for detecting the failure of a thyristor, said dector comprising: a core arranged so that the saturation characteristics of said core change in response to current passing through said thyristor; and a coil, attached to said core, wherein as current flows through said thyristor in both positive and negative directions said core generates a voltage on said coil.

12. The detector of Claim 11, further comprising a light emitting diode, wherein said light emitting diode is energized in reposnse to said voltage generated on said coil.

13. The detector of Claim 11 , wherein said core comprises square

Orthonol.

14. A gate signal detector, for use in detecting the presence of a gate signal to a thyristor, said detector comprising: a toroidal pulse transformer positioned in proximity to the gate of a thyristor, said transformer having an output, for generating a voltage signal at said output when a gate signal is present at said thyristor; and an indicator for providing an indication signal in response to said voltage signal.