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1 Assessment of Arc Flash Detection System in Distribution Network Imran bin Hussin College of Engineering, Universiti Tenaga Nasional, Malaysia. Dr Au Mau Teng College of Engineering, Universiti Tenaga Nasional, Malaysia. Abstract The consequences from an arc flash hazard is very severe. As the temperature of an arc can reach four times the temperature of the Sun s surface and occurs very fast, one can get skin burn up to four degree and damaged inner abdominal, permanent blind, hearing impairment and other physical injuries. Arc flash inside breaker compartment can cause breaker explosive blast and destroy costly equipment. To mitigate arc flash hazard is to reduce the fault clearing time. The longer the arc fault is in the system, the more damage would take place, while the damage could be insignificant for a very fast fault clearing time. This paper is intended to utilize IEC61850 communication protocol in current arc protection relaying in which the protocol can run over TCP/IP networks or substation LANs using high speed switched Ethernet to obtain response times below four milliseconds. Unshielded fiber optic connected to a relay at outgoing panel is used to detect arc flash in the busbar, cable and breaker compartments. Trip signal issued from the relay will be transferred to a relay at incomer panel using IEC61850 which will trip its breaker and isolate the whole busbar from the fault. This method reduces transfer tripping time as compared to conventional hard wire method and minimize the material damage, increases operating personnel safety and ensure smooth power restoration. The concept of having built-in arc protection in Over Current Earth Fault (OCEF) relay gives economic value to customer where one relay can serve two functions at one time. Keywords Arc Flash Hazard, Mitigation of Arc Flash Hazard, Arc Flash Relaying, IEC61850 I. INTRODUCTION Consequences of an arcing short circuit or earth fault within a low or medium voltage switchgear can be very serious. An arc can destroy costly equipment, and cause prolonged and expensive downtime. Copper vapor expands to 67,000 times the volume of solid copper producing a considerable pressure wave and sound blast. In some cases, the pressure wave has sufficient energy to snap the heads of 3/8-inch steel bolts and to knock over construction walls [1]. A typical arc flash incident can be inconsequential but could conceivably easily produce a more severe explosion. During the arc flash, electrical energy vaporizes the metal, which changes from solid state to gas vapor, expanding it with explosive force [2]. In addition to the explosive blast, called the arc blast of such a fault, destruction also arises from the intense radiant heat produced by the arc. Surfaces of nearby objects, including people, absorb this energy and are instantly heated to vaporizing temperatures. The effects of this can be seen on adjacent walls and equipment - they are often ablated and eroded from the radiant effects [3]. To the switchgear operators and even bystanders, arc flash can cause the following injuries; firstly skin burns by direct heat exposure. Temperatures at the arc can reach four times the temperature of the Sun's surface. Secondly, the intense UV, visible, and IR light produced by the arc can temporarily and sometimes even permanently blind or cause eye damage to people [4]. II. CAUSES OF ARC Accidents caused by touching a test probe to the wrong surface or slipped tool are the most common cause of an arcing fault [5]. Arc fault can also be caused by sparks due to breakdown or gaps in insulation materials, mal-operation of a switchgear device due to use of substandard parts, improper (loose) busbar or cable joints installation, objects coming into close proximity with the energized bus assembly, overvoltage, corrosion, pollution, moisture, Ferro-resonance and even ageing under electrical stress. Besides that, dirt, dust, grease, corrosion, gas, fluid and other impurities coming into the equipment could also result in an arc short-circuit between one live part and ground or between live parts. Most of these fault reasons can be prevented by appropriate maintenance. But in spite of all precautions, human errors by personnel can also lead to arc faults such as poor service maintenance of switchgear, bridging by tools in the switchgear and forgotten tools inside the compartment. Holes or gaps presence on the panel can be the access for small animal like lizard, rat or even snake to entering the switchgear panel and cause arc flash. Besides that, poor connection inside the switchgear panel could contribute to arc fault, for instance loose connection. Figure 1 shows thermal imaging test conducted towards the switchgear assembly where the hotspot shows the loose connection which prone to cause arc flash. 90

2 avoid hazard area, increase the working distance, usage of arcresistant switchgear as well as current-limiting fuse. While the later approach would aim to reduce the clearing time of arc; in which 5 methods are identified; to reduce Co-ordination Interval (CI) of existing overcurrent (OC) relay, application of high-impedance bus diff protection scheme, or low-impedance bus differential protection, fast bus trip scheme, instantaneous trip element (during maintenance) and arc flash detection. Fig. 1. Thermal imaging of loosed connection on switchgear III. MITIGATION OF ARC FLASH HAZARDS The electrical equation for energy is volts multiplied by current and time. The transition from arc fault to arc flash takes a finite time, increasing in intensity as the pressure wave develops. Therefore, time is critical when it comes to detecting and minimizing the effects of an arc. An arc fault lasting 500ms may cause severe damage to the installation. If the arc lasts less than 100ms the damage is often smaller, but if the arc is eliminated in less than 35ms the damage is almost unnoticed. An arc is developed within a millisecond. Figure 2 shows released energy from an arc (ka 2 s) and it s proportional arc fault time (ms). Fig. 2. Damage from arc flash vs arcing current and time The basic foundation to mitigate are flash is from the incident energy equation where three most obvious mitigating strategies can be taken into consideration; to reduce the fault current (I f), to increase the working distance (D) and to reduce the clearing time (t). In order to achieve these three strategies, there are basically two approaches namely non-relaying or relaying. For the former approach, there are four methods which can be used; A. Non-Relaying Approaches There are four approaches to mitigate arc flash under nonrelaying; to avoid hazard area, increasing the work distance, use of arc resistant switchgear and current limiting use. Avoiding hazard area is the safest way to mitigate the arc flash incident. It can be performed on de-energized equipment. Technology is used to gather information and the operation can be performed without entering the hazard area. Thus, relay event reports can be gathered without exposure to arc flash. Additionally, the Circuit Breaker mechanism would also need to be remote controlled. Disadvantage is this method cannot be applied on energized equipment. Besides that, increasing the working distance has a dramatic effect on the incident energy. Examples of this strategy include remote racking devices, remote operating devices, and the use of extension tools (i.e. hot sticks). However, many tasks may not be able to be accomplished remotely and remote racking devices may not operate as desired. Alternatively, arc-resistant switchgear can be used but it requires designs and construction of current electrical switchgear to be modified in order to withstand blast of arc flash including reinforcement of door and structure, discharge path for blast pressure and material away from personnel working areas and high speed clearing times. However, this type of switchgear does not extinguish arc, plus, it is not designed to preserve the operational condition of the equipment but only to protect operating personnel located outside of the equipment [6]. Last but not least is current limiting fuse which is capable of both limiting the magnitude of fault current and duration provided the fault current is within their current limiting range (typically times the device rating) [7]. Fault currents below this range must be analyzed like non-current limiting. This is because lower level arcing currents can easily result in higher incident energy because the clearing time maybe longer. Current limiting fuse is normally installed in LV system with high speed Circuit Breaker feature, giving fast clearing times which can then reduce incident energy. This would prompt it to operate rapidly that current never reaches it s bolted short-circuit level. B. Relaying Approaches Meanwhile, there are five approaches which can be considered under relaying approach; firstly is to reduce co-ordination interval (CI) of existing over (OC) relay. The principle of this method is that if CI is more than 3s, the tripping time will be reduced. CI is less than 3s is not recommended. If distance between co-ordination devices is low, the T will continue to 91

3 add i.e. highest fault current and longest tripping time yielding towards source (personal working). Secondly is high impedance bus differential protection. The conventional MV protection schemes have traditionally been complemented by implementing busbar differential schemes. The advantages of this scheme are it is fast and secure. Voltage across the internal impedance measured is approximately However, the differential scheme implementations are typically expensive due to extra CT's needed and complicated engineering and wiring. Thirdly is low impedance bus differential protection which is also fast and secure, plus it does not require dedicated CTs like High Impedance Bus Differential Protection scheme. However, there are disadvantages of this low impedance scheme where the relay settings are more complex as each input has independent CT ratio and connection. Furthermore, similar like high impedance busbar differential, this scheme may also be too slow due to its relaying arrangements to ensure safe fault clearance times at arc faults, for instance, operation time of the overcurrent relay controlling the incoming CB may have to be delayed hundreds of milliseconds for selectivity reasons. Fourthly is fast bus trip scheme (use OC + communications). This scheme use existing over current relay with additional communications installed on it. Feeder relays and main relay communicate to signal fault location. Relay co-ordination can be maintained without long time delays. If a fault occurs on feeder, the feeder relay will send a block signal to main relay. It is such a short time delay to look for a block signal. If there is no block signal received, the main Circuit Breaker will trip and the fault will be cleared. Lastly is instantaneous trip element which can be done during maintenance. This is the best and simple solution where instantaneous setting is used within hazard zone. Workers presence indicated with a pushbutton on relay in a form of separate switch, or remote communications. While activated (when workers are in proximity of energized circuits), the change in setting will disable the time co-ordination and will allow Circuit Breaker (CB) to trip without delay. This scheme can be added to new/old installations without adding much expenses. However, this method is limited to maintenance works only [8] IV. ARC FLASH PROTECTION RELAY EVOLUTION Arc flash protection relay is now being revolutionized over the years to improvise its functionality in detecting or clearing arc fault as it has been proven that arc flash protection relaying gives the best solution to mitigate are flash problem over all other solutions. A. Proposed Enhancement of Arc Protection Scheme Using Several IEDs Figure 3 shows overall scheme proposed which utilizes several Over Current Earth Fault (OCEF) relays with built-in arc protection function that send signals to communicate between the relays via IEC61850 communication protocol. Fig. 3. Proposed Arc Protection Scheme One OCEF relay is installed on every outgoing feeder to cover the arc flash protection on that particular panel. Light sensor 1, light sensor 2 and light sensor 3 on the relay channel a fibre optics and a point sensor to locate on every compartment of the panel; cable compartment, breaker compartment and busbar compartment. In addition, a fast tripping output contact is used by the OCEF relay for tripping of the circuit breaker. The OCEF relay protecting the outgoing feeder trips the circuit breaker of the outgoing feeder when detecting an arc at the cable terminations. If the relay protecting the outgoing feeder detects an arc on the busbar or in the breaker compartment via one of the other lens sensors, it will generate a signal to the OCEF relay protecting the incoming feeder using IEC61850 protocol. Upon detecting the signal, the OCEF relay at the incoming feeder trips the circuit breaker of the incoming feeder and simultaneously generates an external trip signal via IEC61850 protocol to all OCEF relays protecting the outgoing feeders, which in turn results in tripping of all circuit breakers of the outgoing feeders. B. Software Configurations PCM600 software is used to configure the arc protection scheme. Step 1: Do IEC61850 configuration for one REM615 relay at outgoing panel as SENDER. Dataset needs to be created where the destination of the signal can be selected to receive the signal established by the relay. In GOOSE controls window, the destination REF615 relay on the incomer panel needs to be selected. There is nothing to be configured in the inputs window as this is sending relay, not receiving. 92

4 At the same time, this relay can also cater for over current and earth fault protection where PHLPTOC1 and PHIPTOC1 function blocks are used to detect over current fault while DEFLPDEF1 and EFHPTOC1 function blocks are used to detect earth fault. So this REM615 relay basically gives two protection at one time i.e. over current and earth fault function as well as arc fault function; giving economic value to the protection relay used at substation. Step 2: Do IEC61850 configuration for one REF615 relay at outgoing panel as RECEIVER. There is no configuration needs to be done on datasets and GOOSE control windows as this is receiving relay, not sending. Inputs window needs to be configured as this will receive the signals (datasets) transferred from the REM615 relay on the outgoing panel. For this case, the datasets have been automatically appear on the Inputs window of REF615 relay on incomer panel when the datasets are defined in datasets and GOOSE Controls window of the REM615 relay on outgoing panel. Similar to REM615 on the outgoing panel, this REF615 relay is also used cater for over current and earth fault protection, so PHxPTOC function blocks are used to detect over current fault while EFxPTOC function blocks are used to detect earth fault. Step 3: Define arc function block for logic configuration. The idea for REM615 relay on the outgoing panel is to detect any arc fault occur on its dedicated busbar compartment, cable compartment or breaker compartment, upon which it will trip its built-in master trip, TRPPTRC, then this tripping signal will be transferred to the REF615 relay at the incomer panel. To detect arc fault, a function block named ARCSARC is used in the logic of the REM615 relay (SENDER) to receive any arc fault input from the relay terminal upon detecting light from an arc by the lens sensors. Step 4: Define logic for REF615 as RECEIVER. For REF615 relay at the incomer panel, it will receive the signal of arc fault trip from REM615 relay on the outgoing panel. The idea is to trip the breaker on the incomer so as to isolate the electricity supply to the whole busbar should the arc fault occur on the busbar compartment. Other than receiving the arc fault trip signal from REM615 relay of the outgoing panel and OCEF function, the REF615 relay also detects arc fault on its busbar compartment, cable compartment and breaker compartment. The same configuration of arc fault function block, ARCSARC is used where upon detecting the arc fault by the lens sensor, the output of the ARCSARC function block will trigger the builtin master trip, TRPPTRC which will operate the relay output contact to trip the breaker of the incomer panel. Step 5: Completion of arc protection scheme test. As the communication protocol used is IEC61850, GOOSERV_BIN function block is used in the application configuration of the REF615 relay (RECEIVER) to receive the incoming GOOSE data (trip signal) from the REM615 relay (SENDER) on the outgoing panel to its application. There are two outputs on the GOOSERV_BIN function block; OUT and VALID. The VALID output indicates the validity of received GOOSE data, which means in case of valid, that the GOOSE communication is working and received data quality bits (if configured) indicate good process data. Invalid status is caused either by bad data quality bits or GOOSE communication failure. While the OUT output passes the received GOOSE value for the application. While the OUT output of the GOOSERCV_BIN function block is used to trigger the built-in master trip, TRPPTRC of the relay which will operate its assigned output contact to trip the breaker of the incomer panel. The output contact will reset automatically once the fault is cleared (non-latched). Step 6: The last step in the configuration is to map the GOOSE signals from REM615 relay on the outgoing panel to GOOSE receive function blocks of the REF615 relay on the incomer panel. This can be done via Signal Matrix Tools in the REF615 relay of incomer panel Step 7: Write configurations to both relays. C. Testing the Arc Protection Scheme Place one REM615 relay for outgoing panel and one REF615 relay for incomer panel. Connect a LAN cable between the two relays for IEC61850 communication medium transfer. Apply a bright light source near the light sensor of the REM615 relay. When the light intensity and current level exceeds the setting set in the relay, this will trigger the ARCSARC function block in the relay, operate the built-in master trip, TRPPTRC and the trip signal will be transferred to the REF615 relay via the IEC61850 communication. Upon receiving this trip signal, the REF615 relay will trip i.e. output contact will operate and this will trip the breaker of the incomer panel. The events should be recorded in the event record inside the relay to retrieve the signals and light channels so as to analyze and qualify the response. Fig. 4. Connection to test arc flash on REM615 and REF615 relay Arc Fault Transfer Using IEC61850 Communication Protocol Arc fault is simulated by projecting camera flashlight to the arc sensor terminal on the rear part of the REM615 relay at outgoing panel. The REM615 relay trips and instantaneously trips the REF615 relay at incomer panel. Tripping of each relay is shown on the LCD display on the relay front HMI. Disturbance recorder is extracted from the relay into the PCM600 software to get the tripping time for each relay so 93

5 that the transfer time (IEC61850) from the outgoing panel to the incomer panel can be calculated. The tripping time of REM615 relay upon detecting arc flash fault on the busbar is recorded as 10:00: hrs while the tripping time of REF615 relay at incoming panel after receiving busbar arc fault trip signal from REM615 relay at outgoing panel is recorded as 10:00: hrs. Transfer time is achieved by calculating the difference between the tripping time of REM615 and of REF615 relay i.e. ( ) s = 0.295s. Time error of 0.102s calculated previously from item 4.1 is subtracted from this value to get the actual transfer time i.e 0.295s 0.102s = 0.193s Arc Fault Transfer Using Hard Wire In this application, the arc fault data is being transferred using hardwire which is connected from binary output of REM615 relay (programmed as Trip CB ) to the binary input of the REF615 relay (assigned as External Trip ). When the REM615 relay has tripped on arc fault, the binary output will simultaneously trip i.e. its Normally Open (NO) contact will close. This will convey the standby positive supply on the binary output to trigger the binary input of the REF615 relay. When the binary input of the REF615 relay has been triggered, the signal will be processed in the microprocessor inside the relay and will give output to trip the relay and trip its respective circuit breaker which finally isolate the system from the arc fault. Arc fault is simulated and the tripping time of both relays shown on the LCD display is taken. Similar to the IEC61850 application, the disturbance recorder for this hard wire test is extracted from the relay into the PCM600 software to get the tripping time for each relay so that the transfer time (hard wire) from the outgoing panel to the incomer panel can be calculated. The tripping time of REM615 relay upon detecting arc flash fault on the busbar is recorded as 9:49: hrs while the tripping time of REF615 relay at incoming panel after receiving busbar arc fault trip signal from REM615 relay at outgoing panel is recorded as 9:49: hrs. Transfer time is achieved by calculating the difference between the tripping time of REM615 and of REF615 relay i.e. ( ) s = 0.404s. Time error of 0.102s calculated previously from item 4.1 is subtracted from this value to get the actual transfer time i.e 0.404s 0.102s = 0.302s Table 1 shows the summary of calculation for the transfer time on both IEC61850 and hard wire application. TABLE 1: SUMMARY OF TRANSFER TIME Relay REM615 (outgoing) Busbar Arc Fault Trip REF615 (incoming) Busbar Arc Fault Trip Test Results (IEC61850) Test Results (hard wire) 10:00: hrs 9:49: hrs 10:00: hrs 9:49: hrs Transfer time 0.295s 0.404s minus time error (0.102s) (-) 0.102s (-) 0.102s Actual transfer time 0.193s 0.302s V. DISCUSSION AND CONCLUSION From the table 1, it can be seen that transfer time from outgoing panel (REM615 relay) to the incoming panel (REF615 relay) using IEC61850 as means of transfer is faster than that using hard wire i.e 0.193s for IEC61850 as compared to 0.302s for hard wire. This proves that IEC61850 communication protocol can give faster transfer time. Subsequently, faster time for the relay at incomer panel to trip its circuit breaker can be achieved in order to isolate the busbar from the arc fault. This is proven to be the fastest way to clear arc fault from the system. Aligned with figure 2, the faster the clearing time the better where damage on the switchgear installation and injury to the operating personnel is reduced to the minimum. The use of IEC61850 communication protocol has benefited a lot to the advancement of arc protection system where the arc fault clearing time has been reduced tremendously. The very fast arc fault clearing time would yield to almost nothing to the affected area, returning back the system to the normal operation without causing any cost of repair. At the end, a good technology does not only prevent arc flash to occur, but it also minimizes material damage, increases operating personnel safety and allows smooth power restoration. Besides that, it also enables redundant, instantaneous and fail-safe arc fault protection fully utilizing fiber-optic technology and flexible, fast overcurrent monitoring for secure protection. This technology will promote quick reaction and cost-effective installation. VI. RECOMMENDATION FOR FUTURE WORK Fiber optic used to detect arc fault along the busbar compartment, breaker compartment and cable compartment is generally very fragile and requires a lot of precaution during the installation as well as during its operation. Damage to any part of the fibre optic would fail the operation of the IEC61850; consequently the arc protection system as a whole would fail to function and the repair of the damaged fibre optic is quite troublesome as it involves the whole energized busbar at the substation. The relay has supervision to detect any mal-operation or cut along the fiber optic laying, but it cannot locate where exactly along the laying that the problem occur. This would require the whole busbar to be de-energized and the whole fiber optic is to be taken out for repair. 94

6 An alternative solution can be recommended where the usage of fiber optic is eliminated. The detection of arc fault is still done by a sensor located at the desired place in the switchgear compartment but the data transferred from the sensor to the arc fault protection relay will be done by using wireless communication media such as Bluetooth etc. This would give better efficiency in terms of communication transfer and the precaution of the sensor is only on the individual panel and not on the whole busbar, easy for maintenance and troubleshooting. ACKNOWLEDGMENT This paper would not have been possible without the help and assistance of several individuals, to whom the author is undeniably indebted. First and foremost, my utmost gratitude to my beloved mother and wife whom their strong support and encouragement I will never forget. My gratitude also sincerely goes to my principal supervisor, Dr Au Mau Teng, without him this thesis would have been impossible. My thanks also goes to my colleagues, Muhamad Dusin and Phang Siew Wey who always give me a bright ideas in the discussion about the topics and who have helped me a lot in the testing of the arc protection relay at lab. And my thanks also goes to the faculty of the Department of the Electrical Engineering of Universiti Tenaga Nasional, and the staff and faculty members that assisted me through writing of this thesis. REFERENCES [1] KM Kowalski-Trakofler, EA Barrett, CW Urban, GT Homce. "Arc Flash Awareness: Information and Discussion Topics for Electrical Workers". DHHS (NIOSH) Publication No D. Accessed January 10, [2] Ken s Safety Section, NEC Digest Spring 2004; Author is Ken Mastrullo, Senior Electrical Specialist, NFPA Electrical Engineering Department. [3] [4] ARC Flash Hazard Analysis and Mitigation by J. C. Das -- IEEE Press 2012 [5] How to Hamper Hazards, IEEE Industry Applications, May/June 2005 [6] Arc Flash Hazard Analysis and Mitigation, Chris Inshaw and Robert Wilson, 2006 Texas A&M Relay Conference. [7] A Total Approach to Arc Flash Compliance, Alan C. Bast, Jeffry L. Bennett, Norman E. Reifsnyder, Richard Mages, Preston Cooper, Power-Gen International 2006 Conference. [8] ABB Buyers Guide, REA 10_ Arc Protection Relay, 1MRS MBG, May