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Causes and Hazards of Arc

The increase of the capacity of the middle and low voltage system, the increase of the cable application, the system resonance over-voltage, the insulation fault, the poor current carrying loop and the human error, etc. often cause arc short circuit fault to the switchgear. The electric arc produced by the internal fault of the switch device increases the pressure and temperature of the switch, and the center temperature of the arc is about 20000 degrees centigrade, which is about 3~4 times of the surface temperature of the sun. If it is not cut off in time, the arc can ignite the device in the switchgear, cause fire, destroy the distribution equipment in a large area, and even destroy the DC system in the substation, causing serious losses and serious personal casualty accidents.

The damage degree of arc fault depends on the electric arc current and the duration time. The energy produced by the arc rises exponentially with time. If the arc duration is more than 100 ms, the released energy will increase sharply, and then the effect of various faults will cause serious damage to the cable of switch equipment, copper bar and steel material. At present, however, the operation time of transformer backup over current protection commonly adopted by medium and low voltage busbar protection is as long as 1.0~2.0s. Adopting transformer backup over current protection locked by feeder instantaneous trip protection, the typical action time is 300ms~500ms. When carrying out protection action and tripping circuit breaker, the switchgear at the scene of the accident may have been burned out of recognition. In the national standard, the class II and III dynamic and thermal stability time of transformers is 0.25s, and the fault cut off time of medium and low voltage busbar is far more than 0.25s. The transformer bears the short distance short circuit fault impact, the electric power produced by the fault current may lead to the winding deformation of the transformer, and the winding is often needed to be replaced, causing serious consequences and losses.

Solution to Arc Protection System

To solve the above problem, Nanjing HONY Electric Automation Co.,Ltd developed China′s first set of rapid protection system for internal faults of medium and low voltage busbar and switchgear. The system adopts the arc detector developed by our company as the core technology, combines the current detection to form the double criterion principle of light detection and electrical detection, accurately detects the arc light signal through some key technologies, such as arc sample, fast data transmission, optical fiber communication, large-scale programming hardware, etc. The outlet of the trip is less than 4ms; the fault is cut off in the bud, so as to achieve the rapid protection of the medium and low voltage busbar. In the arc protection system, "An arc detector for detecting flash arc of switchgear" and "A 100% rapid protection for internal faults of switchgear" have been applied for patent of invention. “An arc protection system”, “A feeder line protection device”, “An arc protection device”, and ”A non electric detection relay” have obtained patent for utility models.

Main features

100% Rapid protection: It can realize the rapid protection for the internal faults of the medium and low voltage busbar and switches.

Selectivity: Arc protection system combines arc protection and high-speed communication network technology. It absorbs the features of arc protection, failure protection and current protection. It is a selective rapid protection system.

Reliability:

Excellent Electromagnetic Compatibility: The arc dectector adopts passive design, all of the units are connected by optical fiber, and the arc signal goes into the arc collection unit through the optical fiber, and the photoelectric conversion is completed in the sample unit. The whole system can pass highest level electromagnetic compatibility test of the national standard and IEC, and can be applied to a variety of complex electromagnetic environment.

Double criteria: The criterion of arc protection is arc and current. The system can be applied in two ways: only to detect arc, detect arc and over current. The threshold of detecting light intensity and current can be adjusted, and the device can be configured according to the actual application so as to further improve the reliability of the device.

Sensitivity: DPR360ARC arc protection system has spectrum identification function, can accurately identify the arc characteristic spectrum, and effectively distinguish it from various light sources in the daily work environment, such as reflected sunlight, lifeliving light, flashlight for overhaul, so as to avoid interference of other light sources on arc protection system, and to improve the sensitivity of the protection device.

Rapid action: Two types of outlets-electromagnetic relays and solid state relays can be selected. In the case of the electromagnetic relay, the outlet time is no more than 8ms, I the case of the solid state relay, the outlet time is no more than 4ms, much faster than the traditional busbar protection.

Intelligent interface: 2-port Ethernet or 2-port CAN is optional; GPS time synchronization can be achieved by self-adaption IRIG-B or second pulse. The communication protocol supports the IEC61850 and IEC60870-5-103 standards, supports the digital process layer IEC61850-9-2 (SMV) and GOOSE high-speed communications, meets the needs of digital substation, and adapts to the future development trend of smart grid.

System Solution

DPR360ARC arc protection system adopts modular design, suitable for a variety of different applications. It can form a simple system with only one main control unit, or a complicated system with several units, applicable for selective arc protection.

System network structure adopts optical fiber star connection mode. Single-mode optical fiber connection is adopted between main control unit and current unit, main control unit and arc unit, main control unit and the arc expander, the arc unit and the arc expander..

The main control unit and the arc detector, the arc unit and the arc detector are connected by a special optical fiber.

The main control unit communicate with the substation monitoring system. The main control unit can be equipped with 2-port Ethernet or 2-port CAN, and the communication protocol supports the IEC61850 standard and the IEC60870-5-103 standard, so that it can easily access to the automation system.

Solution to Busbar Protection

  When arc protection is taken as a medium and low voltage busbar protection, it can consist of 1 or more main control units and a series of auxiliary units according to the system capacity and requirements, so as to realize the main protection when the busbar fault occurs.

Schematic Diagram of System Composition


Figure 1 Configuration Scheme of Busbar Protection System


System Principle Description

                                

             Figure 2 Typical Application Example Diagram of busbar protection system

 

  The transformer low voltage side switch and the busbar chamber of feeder switch, the other bays on the busbar (PT cabinet, isolation cabinet, etc.) belong to the category of busbar. Each bay is installed with arc dectors which access the main control unit directly or through the arc expander; the CTs of transformer low voltage side switch or bustie switch access the main control unit directly or through the current unit, the main control unit trips transformer low voltage side switch or bustie switch directly or through the current unit.

System Parallel Operation

In this mode, 1# transformer powers two section busbars. When the fault occurs at d1 position, the arc dectors (S10-S1n) connected with I busbar monitor the arc flash, and the fault current flows from 1# transformer to the fault point d1, but the bustie switch has no current, the current criterion of 1# transformer is met, but the current criterion of bustie switch is not met, so only arc protection of I busbar region acts, then 1# transformer low voltage side switch (Q2) trips, and bustie switch does not trip. If the fault is not cut off within the specified time, failure protection starts, and 1# transformer high voltage side switch (Q1) trips. When the fault occurs at d2 position, the arc dectors (S20-S2n) connected with II busbar monitor the arc flash, and the fault current flows from 1# transformer to the fault point d2 through bustie switch, the current criterion of both 1# transformer and bustie swtich is met, the current of 1# transformer is only connected with arc dectors (S10-S1n) of I busbar, but the current of bustie switch is connected with both arc dectors (S10-S1n) of I busbar and arc dectors (S20-S2n) of II busbar, so arc protection of bustie switch acts , then bustie switch (Q5) trips, the fault of II busbar is cut off, and I busbar still operates normaly, the selectivity of cutting off fault is achieved. If the fault is not cut off within the specified time, failure protection starts, and transformer high voltage side switchs (Q1 and Q2) trip. It is similar when 2# transformer powers two section busbars.

Configuration and Function of Each Unit

No.

Equipment Name

Function Description

DPR360ARC

Digital arc protection system

Responsible for the collection, measurement, calculation and logical judgment of the input, and realizes the protection logic of the system, communication with the substation monitoring system, self checking and other auxiliary functions.

DPR391ARC

Current Unit

Installed in the incoming switch cabinet, the 3-phase current information can be collected on the spot. 2 rapid relays and 3 conventional relays are installed for local or nearby trip.

DPR392ARC

Arc Expander

Used for connecting arc unit. Each arc expander can access 8 arc units, 8*16=128 arc detecters can be added, so as to achieve the expansion function of the system.

DPR393ARC

Arc Unit

Used when arc detector ports of the main control unit are not enough. Arc unit is installed near the required protection position, and only a pair of ordinary single-mode communication fiber will be needed between arc unit and main control unit or arc expander.

DPR-FAS-D1

Arc Detector

Installed in each bay of the cabinet, photosensitive element detects the sudden increase of light intensity when arc fault occurs, and transmits the optical signal to arc unit or main control unit through a piece of special purpose fiber.

100% Rapid Protection Solution for Internal Faults of Switch Cabinet

Traditional arc protection is realized by “and” gate criterion of current mutation and arc, which can only reflect the fault of busbar chamber of switch cabinet, but cannot protect the switch chamber and cable chamber that are easy to produce fault inside the switch cabinet. To solve the above problem, Nanjing HONY Electric Automation Co.,Ltd offers 100% rapid protection solution for the internal fault of switch cabinet, which realizes selective trip according to the location of the fault in the switch cabinet, and provides comprehensive and rapid protection for the internal faults of the switch cabinet.

100% rapid protection of the internal fault of switch cabinet takes arc detection and fault location as the core technology. Arc detectors are respectively installed in the busbar chamber, switch chamber and cable chamber of switch cabinet  then the fault position can be located accurately. In case of fault on the outgoing feeder of breaker, the switch itself trips to cut off the fault. If the fault occurs on the upper part of the breaker, the breaker of power supply trips, the fault is cut off and isolated, so as to 100% rapid protection of internal fault of switch cabinet is achieved without blind area.

Schematic Diagram of System Composition

 

VFigure 3 100% Rapid protection system configuration schemes for Internal fault of switch cabinet

 

System Principle Description

             

Figure 4 Typical Application Example Diagram of 100% Rapid Protection for Switch cabinet internal fault

 

The system is suitable for enclosed switch cabinet, and can realize selective arc protection for busbar chamber, switch chamber and cable chamber of switch cabinet.

The transformer low voltage side switch and the busbar chamber of feeder switch, the other bays on the busbar (PT cabinet, isolation cabinet, etc.) belong to the category of busbar. Each bay is installed with arc dectors which access the main control unit directly or through the arc expander,, as shown in Figure 4, arc detector is installed in busbar chamber S1.

Each switch chamber of feeder line unit and the bustie switch is equipped with an arc relay, and arc detectors are installed in switch chamber and cable chamber respectively to access arc relay. As shown in Figure 4, arc detectors are installed in switch chamber S2, cable chamber S3.

The main control unit trips transformer low voltage side switch and bustie switch directly or through current unit, the arc relay trips switch of the cabinet directly. The CTs of transformer low voltage side switch and bustie switch access main control unit directly or through current unit.


Figure 5 Logic Sample Diagram of Protection Action for Internal Fault of Switch Cabinet


Based on busbar areas, protection logic is divided. The arc detectors for busbar access main control unit directly, if the fault occurs in d1 position, the fault is within the busbar protection scope, the arc detector S1 in busbar chamber monitors the arc flash and the current criterion is satisfied, then the main control unit will trip transformer low voltage switch and bustie switch instantly according to the set protection logic.

The arc relay communicates with the main control unit by means of two-way fiber. The main control unit trasnsmits current action status of transformer low voltage or bustie to the arc relay according to the operation mode. If the fault occurs in d2 or d3 position, the fault is within the outgoing feeder switch protection scope. If the arc relay monitors arc flash of the arc detector S2 in arc switch chamber or the arc detector S3 in cable chamber, and the current criterion is satisfied, the arc relay trips this switch directly. At the same time, the arc relay trasnmits the fault signal (failture signal) to the main control unit.

If the fault occurs in d4 position, the fault is on the contact position of the breaker, the arc relay monitors arc flash of the arc detector S2 in the switch chamber, and trips this switch directly, but the fault can not be cut off. when the main control unit receives the signal that the arc relay has already acted, after 50~150ms (settable), if the phase current or the negative sequence current or the zero sequence current of power supply which arc relay belongs to is satisfied, the main control unit will trip transformer low voltage switch and bustie switch according to the setting logic, which functions as failure protection.

The main control unit and the arc relay cooperate with each other so as to realize 100% rapid protection for the internal fault of switch cabinet. There is no blind area in the whole switch cabinet and the fault can be cut off selectively, and the power failure area is reduced sharply.

Configuration and Function of Each Unit

No.

Equipment Name

Function Description

DPR362ARC

Main Control Unit

Responsible for the collection, measurement, calculation and logical judgment of the input, and realizes the protection logic of the system, communication with the substation monitoring system, self checking and other auxiliary functions.

DPR391ARC

Current Unit

Installed in the incoming switch cabinet, the 3-phase current information can be collected on the spot. 2 rapid relays and 3 conventional relays are installed for local or nearby trip.

DPR397ARC

Voltage Unit

Installed in the busbar chamber, responsible for sample busbar voltage and zero sequence voltage on the spot.

DPR394ARC

Arc Expander

Used for connecting DPR343 arc unit. Each DPR394 arc expander can access 8 DPR394 arc expanders, and each DPR394 arc expander can access 8 DPR343 arc units. Each arc unit can access four arc detectors. Then 8×8=64 arc units can be added, and 64×4=256 arc detectors can be added. Thus the expansion function of the system can be realized.

DPR396ARC

Arc Expander

Used for connecting DPR395 arc unit. Each DPR396 arc expander can access 8 DPR395 arc units. Then 8×16=128 arc detectors can be added. Thus the expansion function of the system can be realized.

DPR395ARC

Arc Unit

Used for expanding arc detector ports of the main control unit. It can be installed near the required protection position, and only a pair of ordinary single-mode communication fiber will be needed between arc unit and main control unit or arc expander.

DPR343ARC

Arc Unit

Used as arc relay of feeder unit to realize selective trip of the feeder switch. When arc fault occurs in cable chamber or switch chambef of feeder unit, this switch trips instantly, and transmits the arc action signal to the main control unit.

DPR-FAS-D1

Arc Detector

Installed in each bay of the cabinet, photosensitive element detects the sudden increase of light intensity when an arc fault occurs, and transmits the optical signal to arc unit or main control unit through a piece of special purpose fiber.

Arc Protection System Achievements

  Hundreds of sets of arc protection system made by Nanjing HONY Electric Automation Co.,Ltd have been put into operation since 2009, remarkable results have been achieved, and unanimous praise from the user has been won. Some established projects and some projects under construction can be seen in detail in the achievement sheet.

Arc Protection Patent Certificate, Test Report, Identification Certificate, Patent



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