Patent Publication Number: US-2007110111-A1

Title: Power system for ultraviolet lighting

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      This invention pertains generally to power systems and, more particularly, to power systems for ultraviolet lighting.  
      2. Background Information  
      Ultraviolet (UV) lights are effective and reliable barriers against, for example, Cryptosporidium and Giardia, which are present in almost all surface waters. These microscopic parasites are resistant to traditional water treatment methods, such as chlorination. Drinking water with these parasites, when ingested, can cause severe abdominal cramps and diarrhea.  
      The cost, for example, of a medium pressure (i.e., with respect to untreated water) UV system for inactivation of Cryptosporidium and Giardia is about $0.05 per 1000 gallons of untreated water as compared to about $0.75 per 1000 gallons for a membrane system and about $0.20 per 1000 gallons for an ozonation system. However, an ozonation system is not as effective as a UV system or a membrane system. Thus, in terms of both cost and effectiveness, the UV system is clearly preferred.  
      Other than UV lights, there are no known alternative electric lights that may be employed to inactivate Cryptosporidium and Giardia.  
       FIG. 1  shows a simplified view of a typical UV disinfection process  2  of a water treatment system  3  for treating, for example, raw water  4  from a river, lake, water reservoir or other untreated water source. The UV disinfection process  2  may include a number of parallel processes  6 , 8 , 10 , which can be added or removed based upon the desired volume of the raw water  4  to be treated. The various series steps of these parallel processes  6 , 8 , 10  include rapid mix  12 , flocculation  14 , sedimentation basins  16 , filters  18 , pumps  20  and UV lights  22 . In turn, the outputs of the parallel processes  6 , 8 , 10  are collected by a number of finished water reservoirs  24 . As a non-limiting example, the various UV lights  22  may include, for example, about 2 to about 20 sets of UV lights.  
      UV lights (e.g., UV lamps) have a known problem when employed as part of a UV disinfection process. When turned on to start the UV disinfection process, UV lights typically take about five minutes to reach full capacity for medium pressure UV systems. Also, after the UV lights are shut down (e.g., due to power sags or power outages), it may take the UV lights between about two minutes to about five minutes to cool down. Hence, after the UV lights are shut off, it will take between about five minutes to about ten minutes between the shutdown time of a set of UV lights to the time where the UV lights could be re-ignited again, and between about seven minutes to about ten minutes for the UV lights to reach full output capacity. Hence, in order to provide a continuous UV disinfection process, in which the finished water output need not be discarded or retreated, it is imperative that a reliable and continuous supply of power be provided to the UV lights.  
      The only known prior proposal of a reliable and continuous power supply for the UV lights of a UV disinfection process is an uninterruptible power supply (UPS)/battery system  26  as shown in  FIG. 2 . The UPS/battery system  26  powers the UV lights  28 , 30  of a UV disinfection process and includes about five minutes to about 15 minutes of battery storage for power sags or power outages. The UPS/battery system  26  includes two medium voltage (MV) power source feeders  32 , 34 , which power two medium-to-low voltage transformers  36 , 38 , respectively. There are two normally closed (NC) drawout circuit breakers  40 , 42  and one normally open (NO) drawout circuit breaker  44  downstream of the transformers  36 , 38 . All three circuit breakers  40 , 42 , 44  are key interlocked as indicated by the two keys (K)  46  operatively associated with at most two of the three circuit breakers  40 , 42 , 44 . Each of the circuit breakers  40 , 42 , 44  can only be closed when one of the keys  46  is inserted. Only two keys  46  are available. Hence, only two of the three circuit breakers  40 , 42 , 44  can be closed at one time. For example, during normal operation, the two NC main circuit breakers  40 , 42  are closed and the tie NO circuit breaker  44  will remain open. When one of the two feeders  32 , 34  is without power, and as a result the corresponding one of the circuit breakers  40 , 42  is open (e.g., in response to an under voltage relay (not shown) either built into the circuit breaker or required by the power company when there is on-site generation in order to prevent the generator from backfeeding the utility), the operator will remove the key  46  from the open circuit breaker (e.g., the circuit breaker  40  connected to the feeder  32  with no power) and insert it in the tie NO circuit breaker  44  (e.g., which was previously open), in order to close it to provide normal alternating current power to the UPS  48  (e.g., which was without power when the main circuit breaker  40  opened due to loss of power from the feeder  32 ). Because of the batteries  74 , 76  in the system  26 , the UV lamps  28 , 30  receive continuous power.  
      Two NC feeder circuit breakers  50 , 52  are upstream of respective UPSs  48 , 54 . These feeder circuit breakers  50 , 52  are normally closed, in order to provide power to the respective UPSs  48 , 54 . A circuit breaker, such as  50  or  52 , on the line side (upstream of the corresponding one of the UPSs  48  or  54 ) is required to open the corresponding one of the UPS feeder lines  56  or  58 , respectively, for: (1) a fault in the corresponding one of the UPSs; or (2) a fault downstream of the corresponding UPS.  
      Two NC drawout circuit breakers  60 , 62  and one NO tie drawout circuit breaker  64  downstream of the UPSs  48 , 54  also employ a key interlock. When one of the UPSs  48 , 54  is unavailable due to maintenance or repair or a fault, then the other one of the UPSs  54 , 48  will provide power to the UV lamps  28 , 30  by the operator closing the tie NO circuit breaker  64  with the key  66 .  
      The NO UPS by-passes  66 , 68  are used only when the respective UPSs  48 , 54  are undergoing repair or maintenance. When the NO UPS by-pass, such as  66 , is closed, it by-passes the UPS  48 . As a result, under this condition, power to the UV lamps  28  or  30  will be “raw” power from the UPS feeder lines  56  or  58  and, thus from the MV power source feeders  32  or  34  (e.g., plant power source; utility power source) with typical unconditioned sags, which may result in the shutdown of the UV lamps  28  or  30 . The power control cabinets  70 , 72 , which provide a suitable higher voltage, power the plural UV lamps  28 , 30 , respectively.  
      The UPS/battery system  26  requires suitable UPSs  48 , 54  plus a suitably sized building (not shown) for storage of the UPS batteries  74 , 76 . The cost of the building, and the operation and maintenance costs of the UPS/battery system  26 , which depend upon the requirements of the UV lamps  28 , 30 , are substantial.  
      A network protector is a special circuit breaker adapted to trip and open a power source, such as a feeder, upon detection of reverse power flow (i.e., power flowing through the power source and out of a network rather than into the network, or, in other words, power flow from the loads toward the networked source). The network protector also includes a control relay, which senses transformer voltages, network voltages and line currents, and executes algorithms to initiate breaker tripping or reclosing action. Trip determination is based on detecting reverse power flow. Examples of network protectors are disclosed in U.S. Pat. Nos. 6,459,554; 5,822,165; and 3,947,728, which are incorporated by reference herein. Examples of network protector relays are disclosed in U.S. Pat. Nos. 6,671,151; 5,844,781; 5,822,165; and 3,947,728.  
      Distribution networks are a type of electrical power distribution system used by utilities and relatively large industrial users to provide highly reliable power by connecting multiple sources of power supply to a common load. Because of the multiple sources, a malfunction of one or more power sources can often be tolerated without impact on the loads. To manage such multiple-source networks, the provision for safe and fully automatic connection of healthy power sources and disconnection of faulty power sources is necessary. Network protectors provide this provision automatically. The overriding goal of a network system including plural network protectors is to electrically connect as many power sources as possible, thereby improving redundancy and, therefore, the reliability of the power sources.  
      There is room for improvement in power systems for ultraviolet lighting.  
     SUMMARY OF THE INVENTION  
      This need and others are met by the present invention, which provides a power system for ultraviolet lighting in which a number of sag ride thru devices include an input powered from a spot network or from one or more busses and an output structured to power a number of ultraviolet lights.  
      In accordance with one aspect of the invention, a power system for ultraviolet lighting comprises: a first network transformer structured to be powered from a first power source and to output a first output; a second network transformer structured to be powered from a second power source and to output a second output; a first network protector inputting the first output of the first network transformer and outputting a third output; a second network protector inputting the second output of the second network transformer and outputting a fourth output; a spot network powered from the third output of the first network protector and from the fourth output of the second network protector; and a number of sag ride thru devices including an input powered from the spot network and an output structured to power a number of ultraviolet lights.  
      The first and second power sources may be medium voltage power sources, and the first and second outputs may be low voltage outputs.  
      The first and second network transformers may include a delta/wye configuration having a delta primary winding structured to be powered from a corresponding one of the first and second power sources and a wye secondary winding outputting a corresponding one of the first and second outputs.  
      The first and second network transformers may include a wye secondary having a central node and a high resistance grounding unit grounding the central node.  
      Each of the first and second network protectors may comprise a network relay, a circuit breaker controlled by the network relay and an arc flash reduction maintenance switch for the circuit breaker.  
      The input of the sag ride thru devices may include a transient voltage surge suppression device.  
      As another aspect of the invention, a power system for ultraviolet lighting comprises: a sub-cycle transfer switch comprising a first input structured to receive a first power source, a second input structured to receive a second power source, and an output powered from one of the first and second inputs; a first transformer including a first output and an input powered from the output of the sub-cycle transfer switch; a second transformer including a second output and an input powered from the output of the sub-cycle transfer switch; a first sag ride thru device including an input powered from the first output of the first transformer and an output structured to power a number of ultraviolet lights; and a second sag ride thru device including an input powered from the second output of the second transformer and an output structured to power a number of ultraviolet lights.  
      As another aspect of the invention, a power system for powering ultraviolet lighting from a plurality of power sources comprises: at least one bus; and a number of sag ride thru devices including an input and an output, the number of sag ride thru devices being structured to be: (a) powered at the input from the at least one bus and to power from the output a number of ultraviolet lights, or (b) powered at the input from one of the power sources and to power from the output the at least one bus which, in turn, powers a number of ultraviolet lights.  
      As another aspect of the invention, a power system for ultraviolet lighting comprises: a first sag ride thru device including an input structured to receive a first power source and an output; a second sag ride thru device including an input structured to receive a second power source and an output; a sub-cycle transfer switch comprising a first input powered from the output of the first sag ride thru device, a second input powered from the output of the second sag ride thru device, and an output powered from one of the first and second inputs; and at least one transformer including an input powered from the output of the sub-cycle transfer switch and an output structured to power a number of ultraviolet lights.  
      As another aspect of the invention, a power system for ultraviolet lighting comprises: a first sag ride thru device including an input structured to receive a first power source and an output; a second sag ride thru device including an input structured to receive a second power source and an output; a first transformer powered from the output of the first sag ride thru device, the first transformer outputting a first output; a second transformer powered from the output of the second sag ride thru device, the second transformer outputting a second output; a first circuit interrupter inputting the first output of the first transformer and outputting a third output; a second circuit interrupter inputting the second output of the second transformer and outputting a fourth output; and a normally open tie circuit interrupter electrically connected between the third output of the first circuit interrupter and the fourth output of the second circuit interrupter, wherein the third output of the first circuit interrupter is structured to power a number of ultraviolet lights, and wherein the fourth output of the second circuit interrupter is structured to power a number of ultraviolet lights.  
      As another aspect of the invention, a power system for ultraviolet lighting comprises: a first transformer structured to be powered from a first power source and to output a first output; a second transformer structured to be powered from a second power source and to output a second output; a first circuit interrupter inputting the first output of the first transformer and outputting a third output; a second circuit interrupter inputting the second output of the second transformer and outputting a fourth output; a normally open tie circuit interrupter electrically connected between the third output of the first circuit interrupter and the fourth output of the second circuit interrupter; a first sag ride thru device including an input powered from the third output of the first circuit interrupter and an output structured to power a number of ultraviolet lights; and a second sag ride thru device including an input powered from the fourth output of the second circuit interrupter and an output structured to power a number of ultraviolet lights.  
      As another aspect of the invention, a low voltage power system for ultraviolet lighting comprises: a first normally closed circuit interrupter structured to receive a low voltage power source and output a first output responsive to predetermined voltage and forward power flow conditions; a second normally closed circuit interrupter structured to receive a low voltage power source and output a second output responsive to predetermined voltage and forward power flow conditions; a tie circuit interrupter electrically connected between the first output of the first circuit interrupter and the second output of the second circuit interrupter; and at least one sag ride thru device including an input powered from one or both of the first and second outputs and an output structured to power a number of ultraviolet lights. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      A full understanding of the invention can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which:  
       FIG. 1  is a simplified block diagram of a typical ultraviolet (UV) disinfection process of a water treatment system for treating raw water.  
       FIG. 2  is a block diagram of an uninterruptible power supply (UPS)/battery system for powering the UV lights of a UV disinfection process.  
       FIG. 3  is a block diagram of a power system for UV lighting in accordance with the present invention.  
       FIGS. 4-10  are block diagrams of power systems for UV lighting in accordance with other embodiments of the invention.  
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      As employed herein, the term “number” shall mean one or an integer greater than one (i.e., a plurality).  
      The present invention is described in association with power systems for ultraviolet (UV) lights of a UV disinfection process, although the invention is applicable to a wide range of power supplies for UV lights.  
      Referring to  FIG. 3 , a power system  80  for ultraviolet lighting  82  includes a bus, such as a spot network  84 , powered from a plurality of power sources, such as for example medium voltage (MV) feeders  86 , 88 , and one or more sag ride thru (SRT) devices, such as  90 , 92 . The SRT devices  90 , 92  include an input  94  powered from the spot network  84  and an output  96  structured to power a number of ultraviolet lights, such as  98  or  100 .  
     Example 1  
      In this example, the spot network  84  powers two SRT devices  90 , 92 , although three of more SRT devices may be employed. Also, the spot network  84  is powered from two feeder systems  102 , 104 , although three or more feeder systems may be employed. Each of the example feeder systems  102 , 104  includes a network transformer,  106  or  108 , and a network protector,  110  or  112 . The first network transformer  106  is structured to be powered from the first MV feeder  86  and to output a first output  114 . The second network transformer  108  is structured to be powered from the second MV feeder  88  and to output a second output  116 . The first network protector  110  inputs the first output  114  of the first network transformer  106  and outputs a third output  118 . The second network protector  112  inputs the second output  116  of the second network transformer  108  and outputs a fourth output  120 . In turn, the spot network  84  is powered from the third and fourth outputs  118 , 120 , and powers the example SRT devices  90 , 92 .  
     Example 2  
      The power sources, such as the example MV feeders  86 , 88 , are MV power sources, and the first and second outputs  114 , 116  are low voltage outputs. In turn, the UV lights  98 , 100  are powered from a suitable low voltage (e.g., without limitation, less than about 1 kVAC; about 480 VAC (US); about 380 VAC (Europe); about 600 VAC (Canada); any suitable low voltage). The inputs to the UV lights  98 , 100  are transformed to a relatively higher voltage through a suitable type of ballast transformer/electronics (not shown) with the actual individual UV lamps  122  being powered at a relatively much higher voltage (e.g., a suitable voltage determined by the manufacturer of the UV lights  98 , 100 ).  
     Example 3  
      As employed herein, the term “network” refers to a low voltage power system including a plurality of power sources wherein the design criterion is to maintain network power with a relatively very high reliability. For example, a typical network includes about four to about eight (not shown) interconnected transformer sources. Each transformer source includes a network protector, such as  110  or  112 , which does not trip into the forward direction (in which power flows through the transformer to the network load), but which does trip relatively very quickly if reverse power flows from the network load to the transformer. A “spot network,” such as  84 , is a relatively smaller network in which there are about two or about three or more transformers connected to a common bus. A typical application is a utility vault (not shown) on a floor of a high-rise building (not shown) or in a water treatment room (not shown). In contrast, a full network has its transformers remotely located from each other.  
     Example 4  
      An example of the SRT devices  90 , 92  (e.g., a sag corrector) is a Sag Ride Through (SRT) product or Sag Corrector product marketed by the Power Quality Solutions Organization (PQSO) of Eaton Electrical, Inc. of Moon Township, Pa.  
     Example 5  
      The example SRT devices  90 , 92  include a voltage source inverter, a bypass circuit and an injection transformer electrically connected in series between an incoming utility supply, such as outputs  114  or  116 , and a load, such as the UV lights  98  or  100 . The SRT devices are high performance, inverter-based active voltage conditioning devices that provide protection to sensitive loads against commonly occurring voltage sags. The SRT device monitors the incoming supply voltage and when it deviates from the nominal voltage level, the SRT device achieves voltage conditioning by injecting the appropriate correction voltage in series with the power supply. The SRT device provides an extremely fast reaction time and sub-cycle response to sag events that would otherwise cause loads to drop out.  
      For example, without limitation, the example SRT device is used to provide continuous power to UV systems under conditions that would otherwise cause the UV system to “shut off”. For example, for a voltage sag of 50% at the input to the SRT device, the output of the SRT device will be regulated above the critical required input voltage that will allow the UV lighting to continue to operate. For this same voltage sag of 50%, without the SRT device, the UV system would “shut off”.  
     Example 6  
      The example SRT devices  90 , 92  correct relatively deep sags in a suitable sub-cycle time. For example, without limitation, input line voltages of about −63%, including phase shifts and distortion, are corrected using a series compensation transformer with dual-conversion voltage injection.  
     Example 7  
      Although  FIG. 3  shows two SRT devices  90 , 92  and two sets of UV lights  98 , 100 , there may be one or more SRT devices and one or more sets of UV lights (e.g., without limitation, six SRT devices and 6-18 sets of UV lights; a variable design function of the design engineer) for each SRT device. For example, a relatively small SRT device may supply one set of UV lights on one treatment reactor (not shown). However, a relatively more cost effective approach is to supply one relatively larger SRT device and feed several UV units (e.g., each UV unit having several individual UV lights, which are all controlled as one unit by the UV manufacturer). Each UV unit includes one or more UV lamp banks each of which is comprised of plural UV lamps and suitable controls to control the brilliance of the UV lamps. If, for example, one of the UV lamps in one of the UV lamp banks fails, then the controls shut-off the affected lamp bank and increase the brilliance of the remaining lamps to maintain the brilliance requirements. If the remaining UV lamps cannot sustain an acceptable level of intensity, then the controls turn them off and direct the untreated water (e.g., the output of the pumps  20  of  FIG. 1 ) to prevent untreated water from being pumped into the water supply (e.g., finished water reservoirs  24  of  FIG. 1 ).  
     Example 8  
      As another example, the UV lights are grouped in sets of three or more. The untreated water flows through a reactor (not shown) at right angles to the UV lights. If a single UV lamp goes out (e.g., as a result of a single phase voltage sag), then a monitoring system (not shown) detects the loss of a UV lamp and the system reports the failure. In this example, even if there may be two other active UV lamps, the system cannot take “credit” for “treating” the untreated water since at least one UV lamp is out. The single phase response and the design of the SRT devices  90 , 92  allow for treatment of a single phase event, two phase events or three phase events, in order that the SRT devices are matched well with this concern.  
     Example 9  
      For redundancy, there may be two or more SRT devices, such as  90 , 92 , and two or more sets of UV lights, such as  98 , 100 , such that if any SRT device or any UV light fails, then the system continues to function.  
     Example 10  
      As another alternative, there may be, for example, one SRT device for the ultraviolet lighting  82  or one SRT device for plural UV lighting systems.  
     Example 11  
      The input MV alternating current (AC) from the feeders  86 , 88  may be any suitable MV (e.g., without limitation, between about 2.4 kVAC and about 75 kVAC).  
     Example 12  
      Non-limiting examples of the network protectors  110 , 112  are model numbers CM52, CMD or CM-22 marketed by Eaton Electrical, Inc. of Pittsburgh, Pa.  
     Example 13  
      The example three-phase network transformers  106 , 108  include a delta/wye configuration having a delta primary winding  124  structured to be powered from a corresponding one of the feeders  86 , 88  and a wye secondary winding  126  outputting a corresponding one of the first and second outputs  114 , 116 . The wye secondary winding  126  has a central node (e.g., neutral or wye point)  128  which is: (a) grounded through a high resistance grounding unit  130  ( FIG. 5 ); (b) directly electrically connected to ground  132  (i.e., solidly-grounded (not shown)); or (c) ungrounded. Alternatively, the network transformers  106 , 108  may include a delta connected secondary winding (not shown).  
      Statistically, most faults that occur are single line-to-ground faults (e.g., one phase to ground) in which one of the three-phase conductors shorts to ground (e.g., a metal cabinet; a conduit; a ground rod). If the neutral point  128  is solidly tied to ground, then the most common ground fault will allow very high currents to flow. Hence, the circuit must be tripped off line, in order to reduce the risk of catastrophic failure. However, if that neutral point  128  to ground is electrically connected through a relatively high ohmic resistor, then this resistor will limit the current to an extremely low value (e.g., typically under 5 A). In this example, the power system  136  ( FIG. 5 ) continues to operate without catastrophic failure and, thus, does not have to open any protective device in order to clear the fault. This provides much better continuity of service.  
       FIGS. 4 and 5  are examples of other power systems  134  and  136 , respectively, for UV lighting. In  FIG. 4 , the power system  134  for ultraviolet lighting  138  includes two busses, such as power busses or feeders  140 , 142 , powered from a plurality of power sources, such as MV feeders  144 , 146 , and one or more SRT devices, such as  148 , 150 . The SRT devices  148 , 150  include respective inputs  152 , 153  powered from one of the corresponding power busses or feeders  140 , 142 , and an output  154  structured to power a number of ultraviolet lights, such as  156  or  158 .  
     Example 14  
      The example power system  134  of  FIG. 4  includes a MV sub-cycle transfer switch  160  and two or more transformers, such as secondary unit substation type transformers  162 , 164 . The output  166  of the transfer switch  160  is electrically connected to transformers  162 , 164 , which power the respective SRT devices  148 , 150 . The transfer switch  160  and the transformers  162 , 164  replace the network transformers  106 , 108  and network protectors  110 , 112  of  FIG. 3 .  
      The sub-cycle transfer switch  160  includes a first input  168  structured to receive the first MV feeder  144 , a second input  170  structured to receive the second MV feeder  146 , and an output  166  powered from one of the first and second inputs  168 , 170 . The first transformer  162  includes a first output  172  and an input  174  powered from the transfer switch output  166 . The second transformer  164  includes a second output  176  and an input  178  powered from the transfer switch output  166 . The first SRT device input  152  is powered from the first output  172  of the first transformer  162 . The second SRT device input  153  is powered from the second output  176  of the second transformer  164 .  
      The configuration of the count of SRT devices, such as  148  and/or  150 , and the count of UV lights, such as  156  and/or  158 , may be the same as was described above in connection with the different examples of one or more SRT devices  90 , 92  and UV lights  98 , 100  of  FIG. 3 .  
     Example 15  
      The first and second power sources are MV feeders  144 , 146 , and the first and second SRT devices  148 , 150  are low voltage SRT devices.  
     Example 16  
      The three-phase first and second transformers  162 , 164  include a delta/wye configuration having a delta primary winding  180  powered from the transfer switch output  166  and a wye secondary winding  182  outputting a corresponding one of the first and second outputs  172 , 176 . The wye secondary winding  182  has a central node (e.g., neutral or wye point)  184  which is: (a) grounded through a high resistance grounding unit  130  ( FIG. 5 ); (b) directly electrically connected to ground  132  ( FIG. 5 ); or (c) ungrounded.  
     Example 17  
      An example of the MV sub-cycle transfer switch  160  is model MVSTS marketed by Eaton Electrical, Inc. of Greenwood, S.C. Here, sub-cycle means, for example, that the transfer switch  160  senses loss of power and quickly transfers from a normal power source (e.g., MV feeder  144 ) to an alternate power source (e.g., MV feeder  146 ) and does so in less than one cycle (e.g., less than about 1/60 second for an example 60 Hz power source). As such, the load will never know that the transfer switch  160  has transferred its output  166  from the normal power source to the alternate power source.  
     Example 18  
      A plurality of pumps (e.g., pumps  20  of  FIG. 1 ) may be operatively associated with the ultraviolet lighting  138 . The sub-cycle transfer switch  160  includes an output  186  structured to disable the pumps upon loss of both of the first and second MV feeders  144 , 146 .  
     Example 19  
      The output  186  which shuts down the pump(s) (e.g., pumps  20  of  FIG. 1 ) is not required in the power system  80  of  FIG. 3  if a sufficient number of feeder systems  102 , 104  are provided, thereby increasing reliability of the spot network  84 .  
     Example 20  
      The power system  136  of  FIG. 5  is somewhat similar to the power system  80  of  FIG. 3 . Here, the example high resistance grounding unit  130  is a type C-HRG unit, model number F4WNDNNSF, marketed by Eaton Electrical, Inc. of Asheville, N.C.  
     Example 21  
      Alternatively, if the C-HRG type of grounding is not employed, then the power system may be solidly grounded, but may be subject to damage and/or tripping when there is a single line to ground fault.  
     Example 22  
      Alternatively, if the C-HRG type of grounding is not employed, and the power system is completely ungrounded, then in response to a ground fault, the voltage can escalate and result in insulation failure and/or other significant damage.  
     Example 23  
      In  FIG. 5 , the circuit breaker  188  of the network protectors  110 ′, 112 ′ includes an optional Arc flash Reduction Maintenance Switch (ARMS)  189 , which is marketed by Eaton Electrical, Inc. of Greenwood, S.C. The network protectors  110 ′, 112 ′ also include a network relay  190 , which controls the circuit breaker  188 .  
     Example 24  
      An example of an arc flash reduction maintenance switch is disclosed by U.S. patent application Publication No. 2005/0219775, which is incorporated herein by reference. The maintenance switch, such as  189 , which includes a normal position to select a specified trip function of the circuit breaker  188  and a maintenance position to select a maintenance trip function, overrides the specified trip function with the maintenance trip function. This results in reduced arc energy in a fault during a trip with the maintenance trip function as compared to arc energy during a trip with the specified trip function.  
     Example 25  
      The example UV lighting power system  136  includes a number of high power devices. Hence, there is a relatively very high available arc flash energy. If, for example, a worker might cause an arc flash incident, then the energy would be relatively high. As such, the worker would have to wear relatively excessive personal protective equipment since the worker can cause the fault and be exposed to a dangerous situation. The ARMS function of the ARMS  189  allows the worker to significantly reduce the risk and exposure to arc flash incidents. As such, most of the time, the worker does not have to wear the relatively excessive personal protective equipment.  
     Example 26  
      Alternatively, if the ARMS function is not employed, then the worker should always work on the equipment with the extra personal protective equipment in view of increased safety concerns and/or risks.  
     Example 27  
      The power system  136  of  FIG. 5  includes optional transient voltage surge suppressers (TVSSs)  192 , such as example Clipper models, such as CPS250480DSG, at the inputs  152 , 153  of the respective SRT devices  90 , 92 . The Clipper Power System (CPS),  250  kA surge protector, rated for a delta connected power system would be applied (if using the high resistance grounding unit  130  of  FIG. 5 ) because the line-to-ground voltage may approach the line-to-line voltage during a ground fault condition which would fail the MOVs in the surge protector. Alternatively, a wye rated surge protector would be used on a solidly grounded power system. The example CPS is marketed by Eaton Electrical, Inc. of Calgary, Canada. The TVSS  192  is essentially a very special low voltage lightning arrester designed to protect electronic loads. The TVSS typically has six elements inside (e.g., three elements connected phase-to-ground, and three elements connected phase-to-phase with other variations available).  
     Example 28  
      If the TVSSs  192  are not employed, and if a transient voltage travels into the power system  136 , then there is the high risk of failing the electronics of the SRT devices  90 , 92 .  
     Example 29  
      Each of the SRT devices  90 , 92 , 148 , 150  of  FIGS. 3-5  preferably includes a suitable upstream circuit interrupter  194  (e.g., circuit breaker; fused switch).  
     Example 30  
      Referring to  FIG. 6 , a power system  80 ′ for ultraviolet lighting  82  includes a bus  84 ′ powered from a plurality of power sources, such as, for example, MV feeders  86 , 88 , and one or more SRT devices, such as  90 , 92 . The power system  80 ′ is the same as the power system  80  of  FIG. 3 , with two exceptions. First, the networks protectors  110 , 112  of  FIG. 3  are replaced by suitable circuit interrupters, such as draw-out circuit breakers  110 ″, 112 ″, respectively. Second, the spot network  84  of  FIG. 3  is replaced by a bus  84 ′ in which a normally open tie circuit interrupter (e.g., without limitation, tie switch; tie circuit breaker; tie fused switch)  85  is electrically connected between the circuit interrupter outputs  118 ′, 120 ′. This main-tie-main arrangement allows the UV lights  98 , 100  on one system to be fed from either of the transformers  106 , 108 .  
     Example 31  
       FIG. 7  shows a power system  134 ′ for ultraviolet lighting  138 . The power system  134 ′ is similar to the power system  134  of  FIG. 4  except that the low voltage SRT devices  148 , 150  are eliminated and suitable medium voltage (MV) SRT devices  148 ′, 150 ′ are disposed upstream of the inputs  168 , 170  of the MV sub-cycle transfer switch  160 . In particular, the input  152 ′ of the first MV SRT device  148 ′ is structured to receive the first MV feeder  144 , and the input  153 ′ of the second MV SRT device  150 ′ is structured to receive the second MV feeder  146 . The first input  168  of the MV sub-cycle transfer switch  160  is powered from the output  154 ′ of the first MV SRT device  148 ′, and the second input  170  of the MV sub-cycle transfer switch  160  is powered from the output  154 ′ of the second MV SRT device  150 ′. The first output  172  of the first transformer  162  is structured to power a number of ultraviolet lights  156 , and the second output  176  of the second transformer  164  is structured to power a number of ultraviolet lights  158 .  
     Example 32  
       FIG. 8  shows a power system  80 ″ for ultraviolet lighting  82 . The power system  80 ″ is similar to the power system  80 ′ of  FIG. 6  except that the low voltage SRT devices  90 , 92  are eliminated and suitable medium voltage (MV) SRT devices  90 ′, 92 ′ are disposed upstream of the transformers  106 , 108 . In particular, the input  94 ′ of the first MV SRT device  90 ′ is structured to receive the first MV feeder  86 , and the input  94 ′ of the second MV SRT device  92 ′ is structured to receive the second MV feeder  88 . The primary winding  124  of the first transformer  106  is powered from the output  96 ′ of the first MV SRT device  90 ′, and the primary winding  124  of the second transformer  108  is powered from the output  96 ′ of the second MV SRT device  92 ′. Similar to  FIG. 6 , the normally open tie circuit interrupter (e.g., without limitation, tie switch; tie circuit breaker; tie fused switch)  85  is electrically connected between the circuit interrupter outputs  118 ′, 120 ′. This allows the MV SRT devices  90 ′, 92 ′ to supply power to the transformers  106 , 108 , which, in turn, power the UV lighting  82 . The main-tie-main arrangement allows the UV lights  98 , 100  on one system to be fed from either of the transformers  106 , 108 .  
     Example 33  
      Referring to  FIG. 9 , a low voltage power system  80 ′″ for ultraviolet lighting  82  includes a bus  84 ″ powered from a plurality of power sources, such as, for example, low voltage feeders  86 ′, 88 ′, and one or more SRT devices, such as  90 , 92 . The power system  80 ′″ may be employed where there is no available MV power and the UV lighting system requirements are less than about 500 kVA. The power system  80 ′″ is the same as the power system  80 ′ of  FIG. 6 , with three exceptions. First, the transformers  106 , 108  of  FIG. 6  are eliminated since the low voltage feeders  86 ′, 88 ′ are used in place of the MV feeders  86 , 88 . Second, the circuit interrupters  110 ″, 112 ″ are replaced by respective normally closed (NC) circuit interrupters  110 ′″, 112 ′″, as will be described. Third, a normally closed (NC) tie circuit interrupter  85 ′ is electrically connected between the circuit interrupter outputs  118 ″, 120 ″. This arrangement allows the UV lights  98 , 100  on one system to be fed from either or both of the low voltage feeders  86 ′, 88 ′. Otherwise, from the bus  84 ″, the power supply to the SRT devices  90 , 92  and the ultraviolet lighting  82  is the same as in the medium voltage power system  80 ′ of  FIG. 6 .  
      Operation of the low voltage power system  80 ′″ is as follows. The low voltage feeders  86 ′, 88 ′ (e.g., less than or equal to about 600 VAC) feed the low voltage NC circuit interrupters  110 ′″, 112 ′″. The bus  84 ″ receives power from both of the two low voltage feeders  86 ′, 88 ′ through the NC circuit interrupters  110 ′″, 112 ′″ when the NC tie circuit interrupter  85 ′ is closed. When one of the low voltage feeders  86 ′, 88 ′ is unavailable or faulted, a corresponding reverse current relay (“67”)  196  opens the corresponding circuit interrupter  110 ′″ or  112 ′″ connected to the unavailable or faulted feeder. The NC circuit interrupters  194  feed the SRT devices  90 , 92  and, thus, the ultraviolet lighting  82 . Since the tie circuit interrupter  85 ′ is normally closed, power to the bus  84 ″ and, hence, to the SRT devices  90 , 92  and ultraviolet lighting  82  is maintained (i.e., without any interruption).  
      It is believed that the structure of the power system  80 ′″ is reliably applicable to only two low voltage power sources, such as  86 ′, 88 ′.  
     Example 34  
      Referring to  FIG. 10 , a low voltage power system  80 ″″ for ultraviolet lighting  82  includes a bus  84 ″ powered from a plurality of power sources, such as, for example, low voltage feeders  86 ′, 88 ′, and one or more SRT devices, such as  90 , 92 . The power system  80 ″″ is the same as the power system  80 ′″ of  FIG. 9 , with three exceptions. First, the normally closed (NC) tie circuit interrupter  85 ′ is replaced by a normally open (NO) tie circuit interrupter  85 ″. Second, the reverse current relays (“67”)  196  are not employed. Third, under/over voltage relays (“27/59”)  198  are employed. A corresponding under voltage condition (e.g., loss of source) is detected by the “27” relay function, which causes its corresponding main circuit interrupter to open and the NO tie circuit interrupter  85 ″ to close. Upon restoration of power, the “59” relay function may optionally initiate an automatic transfer back to the original circuit conditions.  
      This arrangement allows the UV lights  98 , 100  on one system to be fed from either or both of the low voltage feeders  86 ′, 88 ′. Otherwise, from the bus  84 ″, the power supply to the SRT devices  90 , 92  and the ultraviolet lighting  82  is the same as in the medium voltage power system  80 ′ of  FIG. 6 .  
      It is believed that the structure of the power system  80 ″″ is reliably applicable to only two low voltage power sources, such as  86 ′, 88 ′.  
      The disclosed power systems  80 , 80 ′, 80 ″, 80 ′″, 80 ″″, 134 , 134 ′, 136  provide reliable power to the UV lighting  82  or  138 , but at about less than one-half of the cost, at about one-half of the space, and without the maintenance problems associated with the UPS/battery system  26  of  FIG. 2 . For example, the SRT devices  90 , 92 , 148 , 150  (e.g., in the size range of 100 kW and higher) and MV sub-cycle transfer switch  160  or the network protectors  110 , 112 , 110 ′,  112 ′ have about one-half to about three quarters of the lifecycle cost of a UPS system with significantly less maintenance and electrical losses. UPS systems have several drawbacks in industrial applications because of footprint space (e.g., larger by about two times in some cases) plus UPS systems are more sensitive to heating and cooling requirements (e.g., batteries, such as  74 , 76  of  FIG. 2 , at greater than about 70° F. can lose half of their life for every increase of 10° F.). The power electronics on a UPS are essentially very similar to an SRT device, except that the SRT device generally uses more standard magnetic components (e.g., reactors; transformer; filters) and is generally in bypass until required by the load (e.g., for four or five line cycles once every few weeks). This allows the SRT device to be relatively very efficient (e.g., greater than 99%) while in a standby mode. Alternatively, the UPS units of  FIG. 2  are typically about 93-96% efficient) and their losses contribute to lifecycle costs.  
      While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the claims appended and any and all equivalents thereof.