WO2022105017A1 - Arc flash hazard calculation method, arc flash hazard reduction method, and fault detection method - Google Patents

Abstract

An arc flash hazard calculation method, an arc flash hazard reduction method, and a fault detection method. According to the arc flash hazard calculation method for a multi-source power supply system, a time-phased arc current calculation method is provided according to the type composition condition of the multi-source power supply system, so as to perform time-phased arc flash accident energy and arc flash protection boundary calculation, and thus, the accuracy is higher. According to the arc flash hazard calculation method for the multi-source power supply system, a protection device responsible for tripping within a time period can be found according to the time period corresponding to the maximum arc flash accident energy, and the effect of reducing the maximum arc flash hazard can be achieved by reasonably reducing the action time limit of the protection device or modifying protection configuration. According to the fault detection method for the multi-source power supply system, when it is monitored that the real-time arc flash accident energy is greater than the maximum accident energy of a corresponding position or device, an alarm warning is generated.

Description

Arc Flash Hazard Calculation Method, Arc Flash Hazard Reduction Method and Fault Detection Method technical field

The invention relates to the field of power supply, in particular to an arc flash hazard calculation method of a multi-source power supply system, a method for reducing the arc flash hazard of a multi-source power supply system, a fault detection method for a multi-source power supply system, a microcomputer system of a multi-source power supply system, and a multi-source power supply system. computer.

Background technique

Existing research has proved that the arc flash accident energy is related to the short-circuit current and arcing time (ie, the action time limit of the protection device). In a more complex system (such as a multi-source power supply system), after a short-circuit fault occurs on a certain section of the line, it may be protected by multiple adjacent protection devices at the same time. It may lead to different arc flash accident energy at the fault point in different time periods, and different arc flash hazard degrees. The algorithm provided in the IEEE 1584-2002 standard is widely used in the existing arc flash hazard calculation methods, which is suitable for the situation in the radioactive network powered by a single power supply, and the calculation of the arc flash hazard in the multi-source power supply system is not accurate enough. The problem is that the arc flash accident energy generated after the fault is usually overestimated, resulting in the inability to choose appropriate personal protective equipment and other economic losses. Since the factors that will affect the calculation results in the multi-source power supply system are not fully considered, it is necessary to Further improvements.

SUMMARY OF THE INVENTION

The purpose of the present invention is to overcome the defects of the prior art and provide an arc flash hazard calculation method of a multi-source power supply system with higher accuracy, which can be used for the selection of personal protective equipment, reducing arc flash hazards and fault detection.

To achieve the above object, the present invention has adopted the following technical solutions:

An arc flash hazard calculation method for a multi-source power supply system. Multiple power supplies respectively form power supply circuits through bus bars and cables for supplying power to load equipment. There is a protection device, and there is a protection device between the connected busbar and the load equipment,

S1: Determine the equipment where the fault occurs, and the n power sources that supply the equipment with the fault and the power types of the n power sources, n>=2;

Obtain the cut-off time _{t 1} , t ₂ , . ₁ , I ₂ , ..., In , calculate the sum I _sum of the short-circuit contribution currents of the _n power sources to the equipment where the fault occurs;

S2: Arrange the cut-off times t ₁ , t ₂ , . . . , t _n of the n power supplies to the short-circuit contribution current of the fault-occurring bus from small to large, and arrange the short-circuit contribution currents I ₁ , I ₂ , . . . I _{n is} combined to obtain short-circuit contribution currents I ₁ , I ₂ ,..., I _z at times t ₁ , t ₂ ,..., t _z ;

S3: Calculate the arc current I _arc,1 , I _arc,2 ,..., I _arc,z in each time period from 0 to t ₁ , t ₁ to t ₂ ,..., t _z-1 to t _z ;

For the period 0 to _t1 ,

Calculation method of arc current I _arc,1 of power supply system below 1kV:

The calculation method of the arc current I _arc,1 of the power supply system of 1kV and above is:

lg I _arc,1 = 0.00402+0.983lg I _sum (2)

For the period from _ty-1 to ty, 1< _y <=z,

Calculation method of arc current I _arc,y of system below 1kV:

The calculation method of the arc current I _arc,y of the system of 1kV and above is:

In formulas (1) and (2), S is 0.153 for the open arc, and -0.097 for the arc in the box; V is the system voltage; G is the phase spacing;

S4: According to the arc currents I _arc,1 , I _arc,2 , ..., I _arc,z in each time period, calculate the normalized arc flash accident energies En, ₁ , En, ₂ , ... respectively in each time period , E _n,z ;

The calculation method of the normalized arc flash accident energy En _,y is:

lg E _n,y = k ₁ +k ₂ +1.081lg I _arc,y +0.0011G (3)

In formula (3), k ₁ takes -0.792 for open arcs, -0.555 for box arcs; k ₂ takes 0 for ungrounded systems or high-resistance grounded systems, and -0.113 for grounded systems, and G is the phase spacing;

S5: Select an appropriate distance correction factor x according to the type of faulty equipment, and calculate the actual accident energy E ₁ , E ₂ , ..., E _z and arc flash protection boundaries DB _,1 , DB _,2 , ..., D _B,z ;

For the period 0 to _t1 ,

For the period from _ty-1 to ty, 1< _y <=z,

In formulas (4) and (5), C _f is 1.0 for systems above 1kV and 1.5 for systems below 1kV, D is the distance between the arc center and the human body, and x is the distance correction factor;

S6: _Compare the _magnitudes of the actual accident energies E ₁ , E ₂ , .

Preferably, in step S1, if the fault-occurring device is a load device, there are n power sources in the system to supply power to the load device, the n power sources do not include distributed power sources, and there is only a unidirectional short-circuit current flow when a fault occurs at the load device Then, the cut-off time t ₁ , t ₂ , ..., t _n of the short-circuit contribution current of n power sources to the fault-occurring equipment are all the action time limit t of the protection device of the line where the load equipment is located. The short circuit contributes the currents I ₁ , I ₂ , . . . , _In .

Preferably, in step S1, if the fault-occurring device is a load device, there are n power sources in the system to supply power to the load device, and the n power sources include m distributed power sources, 0<m<=n, and m distributed power sources are obtained The cut-off time t _DG,1 , t _DG,2 , ..., t _DG,m , the cut-off time of the remaining nm power supplies to the short-circuit contribution current of the fault-occurring equipment are all the action time limit t of the protection device of the line where the load equipment is located, we get The cut-off times t ₁ , t ₂ , . . . , t _n of the n power sources contribute to the short circuit of the fault-occurring equipment.

Preferably, in step S1, if the fault-occurring device is a bus, there are n power sources in the system supplying power to the bus, and the n power sources do not include distributed power sources, and the cut-off time t of the short-circuit contribution current of the n power sources to the fault-occurring bus is obtained. _bf,1 , t _bf,2 , . . . , t _bf,n , obtain the cut-off times t ₁ , _{t 2} , .

Preferably, in step S1, if the fault-occurring device is a bus, there are n power sources in the system to supply power to the bus, and the n power sources include m distributed power sources, 0<m<=n, to obtain the removal of m distributed power sources The time is t _DG,1 , t _DG,2 , ..., t _DG,m , obtain the cut-off time t _bf1 , t _bf2 , ..., t _{bf nm} of the remaining nm power supplies to the short-circuit contribution current of the faulted bus, and obtain n The cut-off time t ₁ , t ₂ , . . . , t _n of the power supply to the short circuit of the faulty busbar contributes the current.

The present invention also provides a method for reducing the arc flash hazard of a multi-source power supply system. The above-mentioned arc flash hazard calculation method of the multi-source power supply system is used to obtain the actual accident energy of a certain position or a certain equipment in the multi-source power supply system in each period of time. The maximum accident energy _{E max in} E ₁ , E ₂ , _. Time limit or modify the protection configuration of the multi-source power supply system used.

The present invention also provides a fault detection method for a multi-source power supply system. The above-mentioned arc flash hazard calculation method for a multi-source power supply system is used to obtain the maximum accident energy E caused by arc flash at each position and each device in the multi-source power supply system. _max ; monitor the arc flash accident of the multi-source power supply system, obtain the location or equipment where the arc flash accident occurred, and the arc flash accident energy; compare the arc flash accident energy with the maximum accident energy E _max of the corresponding location or equipment, if the arc flash accident occurs If the accident energy is greater than the maximum accident energy E _max of the corresponding location or equipment, an alarm will be issued.

A microcomputer system of a multi-source power supply system includes a processor, and the processor executes the steps of the fault detection method of the multi-source power supply system of the present invention.

A computer includes a processor that executes the steps of the arc flash hazard calculation method for a multi-source power supply system of the present invention.

The arc flash hazard calculation method of the multi-source power supply system of the present invention provides an arc current calculation method by time period according to the type and composition of the multi-source power supply system, and performs the calculation of the arc flash accident energy and the arc flash protection boundary by time period. Compared with the calculation method in the existing standard, the inventive method calculates the multi-source power supply system with higher accuracy.

The arc flash hazard calculation method of the multi-source power supply system of the present invention, by applying the arc flash hazard calculation method of the present invention, and by calculating the arc flash accident energy by time period, the responsible trip in this time period can be found according to the time period corresponding to the maximum arc flash accident energy By reasonably reducing the action time limit of the protection device or modifying the protection configuration, the effect of reducing the maximum arc flash hazard can be achieved.

In the fault detection method of the multi-source power supply system of the present invention, when a certain position or equipment in the system fails, the arc flash accident energy calculated in real time when the system is running is compared with the existing protection configuration before the system is put into operation. , compare the maximum accident energy obtained in advance by the arc flash hazard calculation method of the multi-source power supply system of the present invention, when the monitored real-time arc flash accident energy is greater than the maximum accident energy of the corresponding location or equipment, an alarm will be given. If an alarm occurs signal, it means that some protection devices may refuse to act and fail to trip in time, causing the arc current at the fault point to be too high, causing the accident energy to exceed the maximum value, so as to detect the fault, improve safety, and reduce the damage caused by At this time, it may be necessary for the staff to manually remove the fault point in time, and the protective clothing and personal protective equipment that should be worn when overhauling the fault point should be selected based on the accident energy calculated in real time.

Description of drawings

1 is a single-line diagram of a system according to an embodiment of the present invention;

Fig. 2 is the single-line diagram of the dual power supply system of the present invention;

Detailed ways

The specific embodiments of the method for calculating the arc flash hazard of the multi-source power supply system of the present invention are further described below in conjunction with the embodiments of the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention, and do not limit the protection scope of the present invention.

As shown in Figure 1-2, a multi-source power supply system includes multiple power sources, including non-distributed power sources and/or distributed power sources, and multiple power sources respectively form power supply circuits through bus bars and/or cables for supplying loads to the load. When supplying power to the equipment, a protection device is arranged between the power supply and the connected busbars, a protection device is arranged between the connected busbars, and a protection device is arranged between the connected busbars and the load equipment.

The existing algorithms are close to mature for the calculation of arc flash hazards in radioactive networks powered by a single power supply, but for the calculation of arc flash hazards in multi-source networks, more factors that will affect the calculation results need to be considered. Not enough to deal with these more complex situations. The invention provides an arc flash hazard calculation method of a multi-source power supply system. According to the design structure type of the multi-source power supply system, a targeted analysis is carried out, and a calculation method of arc current by time period is provided. The calculation method of the flash protection boundary adopts the method of the present invention to calculate the multi-source power supply system, and obtains a result with higher accuracy, so as to carry out more targeted protection.

In the method for calculating arc flash hazards of a multi-source power supply system of the present invention, a plurality of power supplies respectively form a power supply circuit through bus bars and/or cables for supplying power to load equipment, a protection device is provided between the power supplies and the connected bus bars, and a protection device is provided between the power supplies and the connected bus bars. There is a protection device between the busbars, and there is a protection device between the connected busbar and the load equipment.

S1: Determine the fault-occurring device, the n power supplies that supply the fault-occurring device and the power types of the n power supplies, n>=2;

Obtain the cut-off time _{t 1} , t ₂ , . ₁ , I ₂ , ..., In , calculate the sum I _sum of the short-circuit contribution currents of the _n power sources to the equipment where the fault occurs;

For example, in case 1, in step S1, if the fault-occurring device is the load device, there are n power sources in the system to supply power to the load device, the n power sources do not include distributed power sources, and there is only a unidirectional short-circuit current when a fault occurs at the load device flow, then the cut-off times t ₁ , t ₂ , . . . , t _n of the n power supplies to the short-circuit contribution current of the fault-occurring equipment are all the action time limit t of the protection device of the line where the load equipment is located.

For example, in case 2, in step S1, if the fault-occurring device is a load device, there are n power sources in the system to supply power to the load device, and the n power sources include m distributed power sources, 0<m<=n, and m distributed power sources are obtained. The cut-off time of the power supply t _DG,1 , t _DG,2 , ..., t _DG,m , the cut-off time of the remaining nm power supplies to the short-circuit contribution current of the fault-occurring equipment is the action time limit t of the protection device of the line where the load equipment is located, The cut-off times t ₁ , t ₂ , . . . , t _n of the n power supplies to the short-circuit contribution current of the fault-occurring equipment are obtained.

For example, in case 3, in step S1, if the fault-occurring device is a bus, there are n power sources in the system supplying power to the bus, and the n power sources do not include distributed power sources, obtain the cut-off time of the current contributed by the n power sources to the short-circuit of the fault-occurring bus. t _bf,1 , t _bf,2 , . . . , t _bf,n , obtain the cut-off times t ₁ , _{t 2} , .

For example, in case 4, in step S1, if the fault-occurring device is a bus, there are n power sources in the system supplying power to the bus, and the n power sources include m distributed power sources, 0<m<=n, obtain the The cut-off time is t _DG,1 , t _DG,2 , ..., t _DG,m , and the cut-off time t _bf1 , t _bf2 , ..., t _{bf nm} of the remaining nm power supplies to the short-circuit contribution current of the faulty bus is obtained, and n is obtained. The cut-off time t ₁ , t ₂ , . . . , t _n of each power supply contributes to the short circuit of the faulted bus.

S2: Arrange the cut-off times t ₁ , t ₂ , . . . , t _n of the n power supplies to the short-circuit contribution current of the fault-occurring bus from small to large, and arrange the short-circuit contribution currents I ₁ , I ₂ , . . . I _{n is} combined to obtain short-circuit contribution currents I ₁ , I ₂ ,..., I _z at times t ₁ , t ₂ ,..., t _z ;

S3: Calculate the arc current I _arc,1 , I _arc,2 ,..., I _arc,z in each time period from 0 to t ₁ , t ₁ to t ₂ ,..., t _z-1 to t _z ;

For the period 0 to _t1 ,

Calculation method of arc current I _arc,1 of power supply system below 1kV:

The calculation method of the arc current I _arc,1 of the power supply system of 1kV and above is:

lg I _arc,1 = 0.00402+0.983lg I _sum (2)

For the period from _ty-1 to ty, 1< _y <=z,

Calculation method of arc current I _arc,y of system below 1kV:

The calculation method of the arc current I _arc,y of the system of 1kV and above is:

In formulas (1) and (2), S is 0.153 for the open arc, and -0.097 for the arc in the box; V is the system voltage; G is the phase spacing;

S4: According to the arc currents I _arc,1 , I _arc,2 , ..., I _arc,z in each time period, calculate the normalized arc flash accident energies En, ₁ , En, ₂ , ... respectively in each time period , E _n,z ;

The calculation method of the normalized arc flash accident energy En _,y is:

lg E _n,y = k ₁ +k ₂ +1.081lg I _arc,y +0.0011G (3)

In formula (3), k ₁ takes -0.792 for open arcs, -0.555 for box arcs; k ₂ takes 0 for ungrounded systems or high-resistance grounded systems, and -0.113 for grounded systems, and G is the phase spacing;

S5: Select the appropriate distance correction factor _x according to the type of faulty equipment, and calculate the actual accident energy E ₁ , E ₂ , ..., E _z and the arc flash protection boundary DB _,1 , DB _,2 , ..., D _B,z ;

For the period 0 to _t1 ,

For the period from _ty-1 to ty, 1< _y <=z,

In formulas (4) and (5), C _f is 1.0 for systems above 1kV and 1.5 for systems below 1kV, D is the distance between the arc center and the human body, and x is the distance correction factor;

S6: _Compare the _magnitudes of the actual accident energies E ₁ , E ₂ , .

The arc flash hazard calculation method of the multi-source power supply system of the present invention conducts targeted analysis according to the design structure type of the multi-source power supply system, and provides a time-based arc current calculation method, time-based arc flash accident energy, and arc flash protection. The boundary calculation method adopts the method of the present invention to calculate the multi-source power supply system, obtains a result with higher accuracy, and conducts a more accurate assessment of the arc flash hazard in the multi-source power supply system.

The owner of the power supply system can use the calculated maximum value E _max and its corresponding arc flash protection boundary for the production of arc flash protection signs, the compilation of work permit forms, and the selection of personal protective equipment for employees.

The arc flash hazard calculation method of the multi-source power supply system of the present invention can be used to reduce the maximum arc flash hazard, and a method for reducing the arc flash hazard of the multi-source power supply system is provided. The flash hazard calculation method _obtains the maximum accident energy E _max and the time period corresponding to the maximum accident energy E _max in the actual accident energy E ₁ , E ₂ , . Find the protection device responsible for tripping based on the time period corresponding to the maximum accident energy E _max , reduce the action time limit of the protection device or modify the protection configuration of the multi-source power supply system, which can reduce the maximum arc flash hazard. The action time limit of the protection device can be reduced as much as possible. Of course, how much time is reduced should be reasonable. The action time limit of the protection device also needs to be compatible with other protection devices in the multi-source power supply system and meet the corresponding standards.

The arc flash hazard calculation method of the multi-source power supply system of the present invention can be calculated manually, preferably by a computer processor. The present invention provides a computer, including a processor, and the processor executes the arc flash of the multi-source power supply system of the present invention. Steps in the Hazard Calculation Method.

The arc flash hazard calculation method of the multi-source power supply system of the present invention can be used for the detection of fault points, and a fault detection method of the multi-source power supply system is provided, which can be used for the microcomputer system of the multi-source power supply system. The management, control and monitoring of the multi-source power supply system, including detecting the current and voltage of the multi-source power supply system, and calculating the arc flash accident energy, etc., are the prior art in the art and will not be repeated here. Before the multi-source power supply system is put into operation, according to the protection configuration of the existing multi-source power supply system, the arc flash hazard calculation method of the multi-source power supply system of the present invention is used to obtain the arc flash occurrence at each position and each equipment in the multi-source power supply system. The maximum accident energy E _max caused by the flash; store the maximum accident energy E _max corresponding to each position and each equipment in the storage unit of the microcomputer system; after the system is officially put into operation, monitor the arc flash accident of the multi-source power supply system, and use the microcomputer The system calculates the arc flash accident energy in real time, and obtains the location or equipment where the arc flash accident occurs, as well as the arc flash accident energy; compares the arc flash accident energy with the maximum accident energy E _max of the corresponding location or equipment. If it is greater than the maximum accident energy E _max of the corresponding location or equipment, it will alarm.

According to the protection configuration of the multi-source power supply system, if the protection device operates normally, the protection function is that the arc flash accident energy is greater than the maximum accident energy E _max , and no alarm will occur. If an alarm signal occurs at this time, it means that Some protection devices may refuse to act and fail to trip in time, causing the arc current at the fault point to be too high and causing the accident energy to exceed the maximum value. At this time, it may be necessary for the staff to manually remove the fault point in time, and the protective clothing and personal protective equipment that should be worn when overhauling the fault point should be selected based on the accident energy calculated in real time.

The following is for the purpose of calculating the arc flash hazard when a three-phase metallic short-circuit fault occurs at the load device A or the bus A in the three-phase AC multi-source power supply system. It is assumed that all protection devices are properly protected. The equipment protection in the source power supply system is divided into the following situations for discussion.

①Situation 1: There are n power supplies in the system to supply power to the load device A, the n power supplies do not contain distributed power supplies, n>=2, and only a unidirectional short-circuit current flows when a fault occurs at the device A, such as the equipment A is at the end of the feeder. At this time, there is generally only one protection device on the line where the device A is located, which is the main protection of the device A, and the action time limit of the protection device is t.

Step 1: Obtain the action time limit _t of the protection device of the device A, and obtain the cut-off times t ₁ , t ₂ , . The action time limit t of , calculates the sum I _bf of the short-circuit contribution currents of the non-distributed power supply 1, the power supply 2, . . . , and the power supply n to the fault point, and obtains I _sum . The calculation method of I _bf belongs to the prior art, for example, I _bf can be calculated according to the method of "GB/T 15544.1-2013 Three-phase AC System Short-Circuit Current Calculation Part 1: Current Calculation".

Step ₂ : Divide the time period, arrange the cutoff times _{t 1} , _{t 2} , . _{, . _ _ _ _ _} For case 1, there is only one period from 0 to t, and the short-circuit contribution current at time t is I _bf , that is, I _sum .

Step 3: Calculate the arc current I _arc flowing through the fault point in each time period. For case 1, there is only one period from 0 to t. According to the sum of short-circuit contribution currents I _bf , calculate the arc current from 0 to t period. I _arc .

For the system arc current I _arc below 1kV, the calculation method is:

The calculation method of arc current I _arc for 1kV and above systems is:

lg I _arc = 0.00402+0.983lg I _bf (2)

In formulas (1) and (2), I _arc is the arc current, in kA; S is 0.153 for the open arc, and -0.097 for the arc in the box; I _bf is the sum of the short-circuit contribution current, in kA; V is the system Voltage, in kV; G is the phase spacing, in mm.

Step 4: Calculate the normalized arc flash accident energy E _n according to the arc current I _arc , that is, the accident energy when the arc center is 610 mm away from the human body and the arcing time is 0.2 s.

The calculation method of the normalized arc flash accident energy _En (J/cm ² ) is:

lg E _n =k ₁ +k ₂ +1.081lg I _arc +0.0011G (3)

In formula (3), En is the normalized arc flash accident energy when the arc center is 610mm away from the human body and the arcing time is 0.2s, J/cm ² ; k ₁ is _-0.792 for an open arc, and -0.792 for an arc in a box. 0.555; k ₂ is 0 for an ungrounded system or a high-resistance grounded system, and -0.113 for a grounded system; I _arc is the arc current; G is the phase spacing, mm.

Step 5: Select an appropriate distance correction factor _x according to the type of faulty equipment (refer to IEEE 1584-2002 5.3 Table 4 for selection standards), and calculate the actual accident energy _E and arc flash protection boundary DB in each time period. For case one, there is only one period from 0 to t.

The calculation method of the actual accident energy E (J/cm ² ) in a certain period is:

_The calculation method of the arc flash protection boundary DB (mm) in a certain period is:

In equations (4) and (5), E _n is the normalized arc flash accident energy when the arc center is 610 mm away from the human body and the arcing time is 0.2 s, in J/cm ² ; C _f is 1.0 for systems above 1kV, and for The system of 1kV and below takes 1.5; t is the duration of the period, in s; D is the distance between the arc center and the human body, in mm; x is the distance correction factor.

Step 6: Compare the magnitude of the actual accident energy in each time period, and obtain the maximum value E _max and its corresponding arc flash protection boundary. According to the maximum value and the corresponding arc flash protection boundary, the selection of personal protective equipment and the production of arc flash warning signs can be carried out.

Step 7: Find the protection device responsible for tripping based on the time period corresponding to the maximum accident energy E _max . On the basis of meeting the design requirements and standard regulations, reduce the action time limit of the protection device or modify the protection configuration used to reduce Maximum arc flash hazard. Or store the calculated maximum accident energy E _max in the storage unit of the microcomputer system, for the microcomputer system to monitor the arc flash accident of the multi-source power supply system, and compare the arc flash accident energy with the maximum accident energy E _max of the corresponding location or equipment, If the arc flash accident energy is greater than the maximum accident energy E _max of the corresponding location or equipment, it will alarm.

②Situation 2: There are n power sources supplying power to device A in the system, n power sources include m distributed power sources, n>=2, 0<m<=n, and there is only one-way power supply in the event of a fault at device A A short-circuit current flows, for example if device A is at the end of the feeder. At this time, there is generally only one protection device on the line where equipment A is located, which is the main protection of equipment A, and the action time limit of the main protection is set as t. After a fault occurs, according to the provisions of IEEE Std.1547, each distributed power source will be preferentially cut off, and the cut-off time of m distributed power sources is t _DG,1 , t _DG,2 , ..., t _DG,m , the corresponding distribution The type power supply is denoted as DG ₁ , DG ₂ , ..., DG _m .

Step 1: Obtain the cut-off times of m distributed power sources as t _DG,1 , t _DG,2 , ..., t _DG,m , and the cut-off times of the remaining nm power sources are the action time limits of the protection devices of the lines where the load equipment is located t, the cut-off times t ₁ , t ₂ , . . . , t _n of the n power supplies to the short-circuit contribution current of the device A are obtained. According to "GB/T 15544.1-2013 Three-phase AC System Short-Circuit Current Calculation Part 1: Current Calculation", calculate the short-circuit contribution current I _DG1 , I of m distributed power sources DG ₁ , DG ₂ , ..., DG _m to the fault point _DG2 , . . . , I _DGm , calculate the sum I _sum of the short-circuit contribution currents of all n power sources to the fault point.

Step ₂ : Divide the time period, arrange the cutoff times _{t 1} , _{t 2} , . , . . . and In are combined to obtain the short _- circuit _{contribution currents I 1 , I 2} , . For the second case, the cut-off times t _DG,1 , t _DG,2 , ..., t _DG,m of each distributed power source are arranged from small to large, and the short-circuit contribution currents I _DG1 , I of the distributed power sources with the same cut-off time are arranged. _DG2 , ..., I _{DGm are} combined to obtain the short-circuit contribution currents I ₁ , I ₂ , ..., I _k at time t ₁ , t ₂ ... , t _k , if m=n, then t ₁ , t ₂ ... , t _k are t ₁ , t ₂ , ..., t _z , if m<n, then t ₁ , t ₂ , ..., t _k , t are t ₁ , t ₂ , ..., t _z . An easy-to-understand way is to arrange the cut-off times t _DG,1 , t _DG,2 , ..., t _DG,m of each distributed power source in a row from small to large (times with the same value are arranged adjacent to each other in any order) , in the second row correspondingly arrange the short-circuit contribution current of each distributed power source to the fault point, and make a table. Then the columns in the table with the same value for each period of time are merged into a new column. In a new column, the first row is the time value, and the second row is the sum of the short-circuit contribution currents corresponding to the column with the same time value. Finally, rename the time and short-circuit contribution current in the table by column from left to right, as shown in the table below.

t 1	t 2	…	tk
I 1	I 2	…	I k

Step 3: Calculate the magnitude of the arc current flowing through the fault point in each time period. The calculation method is the same as formula (1) and formula (2).

Therefore, for the period 0 to _t1 ,

Calculation method of arc current I _arc,1 of system below 1kV:

lg I _arc,1 = S+0.662lg I _sum +0.0966V+0.000526G

+0.5588V(lg I _sum )-0.00304G(lg I _sum )

The calculation method of arc current I _arc,1 for 1kV and above systems is:

lg I _arc,1 = 0.00402+0.983lg I _sum

For the period _t1 to _t2 ,

Calculation method of arc current I _arc,2 of system below 1kV:

lg I _arc,2 =S+0.662lg(I _sum -I ₁ )+0.0966V+0.000526G

+0.5588V(lg(I _sum -I ₁ ))-0.00304G(lg(I _sum -I ₁ ))

The calculation method of arc current I _arc,2 for 1kV and above systems is:

lg I _arc,2 =0.00402+0.983lg(I _sum -I ₁ )

For the period t _k-1 to t _k ,

Calculation method of arc current I _arc,k of system below 1kV:

The calculation method of the arc current I _arc,k of the system of 1kV and above is:

Until time t _k , all distributed power sources are cut off. If m=n, that is, all power sources are distributed power sources, then jump directly to step 4; if m<n, then for the period from t _k to t,

Calculation method of arc current I _arc,t of system below 1kV:

The calculation method of the arc current I _arc,t of the system of 1kV and above is:

Step 4: According to the arc current in each time period, calculate the normalized arc flash accident energy En _{,1 ,} E _{n ,2} , . The accident energy when the time is 0.2s, the calculation method is the same as formula (3). If m<n, the normalized arc flash accident energy En _{,t shall also be calculated for the period from tk to t .}

Step 5: Select the appropriate distance correction factor x according to the type of faulty equipment (refer to IEEE 1584-2002 5.3 Table 4 for the selection standard), and calculate the actual accident energy and arc flash protection boundary in each time period. The calculation method is the same as formula (4), Formula (5).

Therefore, for the period 0 to _t1 ,

For the period _t1 to _t2 ,

…      …

…      …

For the period t _k-1 to t _k ,

If m<n, for the period from t _k to t,

Step 6: Compare the actual accident energy in each time period, and obtain the maximum value E _max and its corresponding arc flash protection boundary. According to the maximum value and the corresponding arc flash protection boundary, the selection of personal protective equipment and the production of arc flash warning signs can be carried out.

Step 7: Find the protection device responsible for tripping based on the time period corresponding to the maximum accident energy E _max . On the basis of meeting the design requirements and standard regulations, reduce the action time limit of the protection device or modify the protection configuration used to reduce Maximum arc flash hazard. Or store the calculated maximum accident energy E _max in the storage unit of the microcomputer system, for the microcomputer system to monitor the arc flash accident of the multi-source power supply system, and compare the arc flash accident energy with the maximum accident energy E _max of the corresponding location or equipment, If the arc flash accident energy is greater than the maximum accident energy E _max of the corresponding location or equipment, it will alarm.

③Situation 3: If the fault-occurring device is a bus, there are n power sources in the system supplying power to the bus (or sub-bus) A at the same time, and the n power sources do not include distributed power sources, n>= 2, and the fault occurs on the bus (or At the sub-busbar) A, the faulty busbar is called the faulty busbar. At this time, each main protection device of the faulty busbar will cut off the short-circuit contributing branch connected to the faulty busbar respectively.

Step 1: According to "GB/T 15544.1-2013 Three-phase AC System Short-Circuit Current Calculation Part 1: Current Calculation", calculate the short-circuit contribution current I _bf,1 , I _bf,2 ,… , I _bf,n , namely the short-circuit contribution currents I ₁ , I ₂ , . . . , I _n of n power sources to the faulty busbar are obtained. Calculate the sum I _sum of the short circuit contribution currents of all power sources to the faulty bus.

According to the protection configuration of each main protection device of the faulty bus, determine the cut-off time t _bf,1 , t _bf,2 , ..., t _bf,n of the n power sources to the short-circuit contribution current of the fault bus, and obtain the n power sources for the fault bus The cut-off times t ₁ , t ₂ , . . . , t _n of the short-circuit contribution current.

Step ₂ : Arrange the cut-off times _{t 1} , _{t 2} , . _{n is combined} to obtain the short _- circuit contribution _{currents I 1 ,} I ₂ , . In case 3, the cut-off times t bf _{, 1} , t _{bf , 2} , . _{, I bf , 2 , . _} An easy-to-understand way is to arrange the cut-off time of each power supply to the short-circuit contribution current of the faulty busbar in a row from small to large (times with the same value are arranged adjacent to each other in any order), and in the second row correspondingly arrange each power supply for the fault. The short-circuit contributions of the busbars are tabulated. Then the columns in the table with the same value for each period of time are merged into a new column. In a new column, the first row is the time value, and the second row is the sum of the short-circuit contribution currents corresponding to the column with the same time value. Finally, rename the time and short-circuit contribution current in the table by column from left to right, as shown in the table below.

t 1	t 2	…	tk
I 1	I 2	…	I k

Step 3: According to Step 3 in Case 2, calculate the magnitude of the arc current at the faulty busbar in each time period between 0 and _tk .

Step 4: According to Step 4 in Case 2, calculate the normalized accident energy at the faulty bus in each time period between 0 and _tk .

Step 5: According to Step 5 in Case 2, calculate the actual arc-flash accident energy and arc-flash protection boundary at the faulty bus in each time period between 0 and _tk .

Step 6: Compare the magnitude of the actual accident energy in each period between 0 and t _k , and obtain the maximum value E _max and its corresponding arc flash protection boundary. According to the maximum value and the corresponding arc flash protection boundary, the selection of personal protective equipment and the production of arc flash warning signs can be carried out.

Step 7: Find the protection device responsible for tripping based on the time period corresponding to the maximum accident energy E _max . On the basis of meeting the design requirements and standard regulations, reduce the action time limit of the protection device or modify the protection configuration used to reduce Maximum arc flash hazard. Or store the calculated maximum accident energy E _max in the storage unit of the microcomputer system, for the microcomputer system to monitor the arc flash accident of the multi-source power supply system, and compare the arc flash accident energy with the maximum accident energy E _max of the corresponding location or equipment, If the arc flash accident energy is greater than the maximum accident energy E _max of the corresponding location or equipment, it will alarm.

④Situation 4: There are n power sources in the system supplying power to the busbar (or sub-busbar) A at the same time, and the n power sources include m distributed power sources, n>=2, 0<m<=n, the fault occurs in the busbar ( or demultiplexer) A.

At this time, according to the regulations of IEEE Std.1547, m distributed power sources will be preferentially cut off, and the cut-off time of m distributed power sources is t _DG,1 , t _DG,2 , ..., t _DG,m , and the corresponding distributed power sources are The power sources are denoted DG ₁ , DG ₂ , . . . , DG _m , during which the remaining (nm) non-distributed power sources will continue to contribute short-circuit current to the faulty bus. After all the distributed power sources are cut off, the remaining (nm) non-distributed power sources will be cut off successively to the short-circuit contribution current of the faulty bus. In step 1, the cut-off times of m distributed power sources are obtained as t _DG,1 , t _DG,2 , ..., t _DG,m , and the cut-off times t _bf1 , t of the remaining nm power sources to the short-circuit contribution current of the faulty bus are obtained _bf2 , ..., t _{bf nm} , obtain the cut-off times t ₁ , t ₂ , ..., t _n of n power sources to the short-circuit contribution current of the faulty bus, calculate the short-circuit contribution current of the non-distributed power sources 1 to (nm) to the faulty bus I _bf,1 , I _bf,2 ,..., I _bf,nm , calculate the short-circuit contribution current I _DG1 , I _DG2 ,..., I _DGm of m distributed power sources DG ₁ , DG ₂ ,..., DG _m to the fault point , calculate the sum I _sum of the short-circuit contribution currents of all _n power sources to the fault point, and obtain the short-circuit contribution currents I ₁ , I ₂ , . calculate.

Step 1: If m=n, that is, all of them are distributed power sources, then follow steps 1 to 6 in case 2 to complete subsequent calculations. If m<n, for m distributed power sources DG ₁ , DG ₂ , . . . , DG _m , follow steps 1 to 5 in case 2 to complete subsequent calculations, and obtain 0-t _k before m distributed power sources are all cut off The arc current in each period, as well as the corresponding standardized accident energy, actual arc flash accident energy and arc flash protection boundary. For nm non-distributed power sources, first calculate the short-circuit contribution current of non-distributed power sources 1 to (nm) to the faulty bus according to "GB/T 15544.1-2013 Three-phase AC System Short-Circuit Current Calculation Part 1: Current Calculation" I _bf,1 , I _bf,2 ,..., I _bf,nm ; then according to the protection configuration of each main protection device of the faulty busbar, determine the cut-off time t of the non-distributed power sources 1 to (nm) to the short-circuit contribution current of the faulty busbar _bf1 , t _bf2 , ..., t _{bf nm} . Finally, according to steps 1 to 5 in case 2, calculate the magnitude of arc current, the magnitude of normalized accident energy, the magnitude of actual accident energy and the magnitude of arc flash protection boundary in each period between 0 and _tk .

Step 2: For ( _nm ) non-distributed power sources, arrange the cut-off times t _bf1 , t _bf2 , . The short-circuit contribution currents I _bf,1 , I _bf,2 , ..., I _bf,nm of the non-distributed power supply are combined to obtain the short-circuit contribution current I _p at the time t _p,1 , t _p,2 ... , t _{p,h ,1} , I _p,2 , ..., I _p,h . An easy-to-understand way is to _arrange the cut-off times t _bf1 , t _bf2 , . Adjacent arrangement), in the second row correspondingly arrange the short-circuit contribution current of each non-distributed power source to the faulty bus, and make a table. Then the columns in the table with the same value for each period of time are merged into a new column. In a new column, the first row is the time value, and the second row is the sum of the short-circuit contribution currents corresponding to the column with the same time value. Finally, rename the time and short-circuit contribution current in the table by column from left to right, as shown in the table below.

tp ,1	tp ,2	…	t p,h
I p,1	I p,2	…	I p,h

Step 3: According to the short-circuit contribution currents I _p,1 , I _p,2 , ..., I _p,h , calculate the arc current at the fault busbar in each time period between t _k and t _p,h , and the calculation method The same formula (1), (2).

Therefore, for the period t _k to t _p,1 ,

Calculation method of arc current I _arcp,1 of system below 1kV:

The calculation method of the arc current I _arcp,1 of the system of 1kV and above is:

For the period t _p,1 to t _p,2 ,

Calculation method of arc current I _arcp,2 of system below 1kV:

The calculation method of arc current I _arcp,2 for 1kV and above systems is:

…       …

…       …

For the period t _p,h-1 to t _p,h ,

Calculation method of arc current I _arcp,h of system below 1kV:

The calculation method of the arc current I _arcp,h of the system of 1kV and above is:

Step 4: According to the arc currents I _arcp,1 , I _arcp,2 ,…,I _arcp,h , calculate the normalized accident energy at the fault busbar, the actual arc value in each time period between t _k and t _p,h Flash accident energy size and arc flash protection boundary size. The arc current in each time period between 0 and _tk , as well as the corresponding standardized accident energy, actual arc flash accident energy and arc flash protection boundary are calculated according to steps 1 to 5 in case 2.

Step 5: Compare the actual accident energy in each time period between 0 and t _k and between t _k and t _p,h . According to the maximum value and the corresponding arc flash protection boundary, the selection of personal protective equipment and arc flash can be carried out. Production of warning signs.

Step 6: Find the protection device responsible for tripping based on the time period corresponding to the maximum accident energy E _max . On the basis of meeting the design requirements and standard regulations, reduce the action time limit of the protection device or modify the protection configuration used to reduce Maximum arc flash hazard. Or store the calculated maximum accident energy E _max in the storage unit of the microcomputer system, for the microcomputer system to monitor the arc flash accident of the multi-source power supply system, and compare the arc flash accident energy with the maximum accident energy E _max of the corresponding location or equipment, If the arc flash accident energy is greater than the maximum accident energy E _max of the corresponding location or equipment, it will alarm.

The arc flash hazard calculation method of the multi-source power supply system of the present invention is further described below based on the embodiment of FIG. 1. The embodiment is a small multi-source power supply system, which is powered by two mains and one distributed power supply. System one-line diagram. Circuit breakers 3, 4, 7, 8, 9 and 10 in this system constitute typical directional protection. The operation time limits of circuit breakers 3, 4, 7, 8, 9 and 10 are obtained as t ₃ , t ₄ , t ₇ , t ₈ , t ₉ and t ₁₀ , respectively. When a three-phase short-circuit fault occurs at bus 1, in order to meet the selectivity of protection, t ₇ <t ₁₀ ; when a three-phase short-circuit fault occurs at bus 2, in order to meet the selectivity of protection, t ₈ <t ₉ ; bus 3 When a three-phase short-circuit fault occurs at the location, t ₉ <t ₃ , t ₁₀ <t ₄ .

The multi-source power supply system of this embodiment includes distributed power sources, and when a three-phase short-circuit fault occurs at the load 3, it belongs to the second case in the method of the present invention. At this time, the distributed power source is preferentially cut off, and then the circuit breaker 11 is disconnected as a protection device to provide main protection for the load 3 . The voltage level at the load 3 is 380V, and a reasonable protection configuration has been completed. The action time limits of the circuit breakers 18 and 11 are respectively t ₁₈ and t ₁₁ .

The calculation is completed according to the calculation step of the second case in the inventive method, and the action time limit of the main protection of the load 3 is t=t ₁₁ .

Step 1: Calculate the short-circuit contribution current I _DG1 of the distributed power sources to the load 3 , and calculate the sum I _sum of the short-circuit contribution currents of all the power sources to the load 3 .

Step 2: Divide the time period to obtain the short-circuit contribution current of the distributed power source to the load 3 in each time period. One way is to make a table according to the description in step 2 of case 2, where t ₁ =t ₁₈ and I ₁ = _{ID G1} in the table.

Step 3: Calculate the arc current of the fault point in each period.

During the period from 0 to _t1 ,

lg I _arc,1 = S+0.662lg I _sum +0.0966V+0.000526G

+0.5588V(lg I _sum )-0.00304G(lg I _sum )

During the period from t ₁ to t,

lg I _arc,t =S+0.662lg(I _sum -I ₁ )+0.0966V+0.000526G

+0.5588V(lg(I _sum -I ₁ ))-0.00304G(lg(I _sum -I ₁ ))

Step 4: Calculate the normalized accident energy of the fault point in each time period.

During the period from 0 to _t1 ,

lg E _n,1 =k ₁ +k ₂ +1.081lg I _arc,1 +0.0011G

During the period from t ₁ to t,

lg E _n,t =k ₁ +k ₂ +1.081lg I _arc,t +0.0011G

Step 5: Select the appropriate distance correction factor x according to the type of faulty equipment (refer to IEEE 1584-2002 5.3 Table 4 for the selection standard), and calculate the actual accident energy and arc flash protection boundary in each time period.

During the period from 0 to _t1 ,

During the period from t ₁ to t,

Step 6: Compare the sizes of E ₁ and E _t , and select suitable personal protective equipment according to the hazard risk level corresponding to the larger accident energy (for selection criteria, refer to NFPA 70E-2009 Table 130.7(C)(10)).

2) The system of the embodiment includes a distributed power source, and when a three-phase short-circuit fault occurs at the bus bar 3, it belongs to the fourth case in the method of the present invention. At this time, the distributed power supply is preferentially cut off. Then, according to the principle of directional protection, the action time limits of circuit breakers 3, 4, 7, 8, 9 and 10 are set as t ₃ , t ₄ , t ₇ , t ₈ , t ₉ and t ₁₀ respectively, in order to ensure the protection selection , should satisfy t ₇ <t ₁₀ <t ₄ , t ₈ <t ₉ <t ₃ . Assuming that the voltage level at the bus bar 3 is 380V and a reasonable protection configuration has been completed, the action time limit of the circuit breaker 18 is t ₁₈ . Distributed power supply cut-off time t ₁ =t ₁₈ , and the distributed power supply contributes current I ₁ = _{ID G1} to the short circuit of bus bar 3 during the period from 0 to t ₁ .

The calculation is completed according to the calculation step of the fourth case in the inventive method.

Step 1: Calculate the short-circuit contribution currents I _bf,1 , I _bf,2 of the mains 1 and 2 to the bus 3, and determine the cut-off time t _bf1 , t _bf2 . Let t _bf1 =t _bf2 .

During the period from 0 to _t1 ,

lg I _arc,1 = S+0.662lg I _sum +0.0966V+0.000526G

+0.5588V(lg I _sum )-0.00304G(lg I _sum )

lg E _n,1 =k ₁ +k ₂ +1.081lg I _arc,1 +0.0011G

Step 2: Divide the time period to obtain the short-circuit contribution current of the non-distributed power source to the bus bar 3 in each time period. Make a table according to the instructions in Step 2 of Scenario 4. Since t _bf1 =t _bf2 , t _p,1 =t _bf1 =t _bf2 , I _p,1 =I _bf,1 +I _bf,2 in the table.

Step 3: Calculate the arc current at the busbar 3 during the period from t ₁ to t _p,1 .

During the period from t ₁ to t _p,1 ,

lg I _arcp,1 =S+0.662lg(I _sum -I ₁ )+0.0966V+0.000526G

+0.5588V(lg(I _sum -I ₁ ))-0.00304G(lg(I _sum -I ₁ ))

Step 4: Calculate the normalized accident energy magnitude, actual accident energy magnitude and arc flash protection boundary at busbar 3 in each period from t ₁ to t _p,1 .

During the period from t ₁ to t _p,1 ,

lg E _np,1 = k ₁ +k ₂ +1.081lg I _arcp,1 +0.0011G

Select an appropriate distance correction factor x according to the type of faulty equipment (refer to IEEE 1584-2002 5.3 Table 4 for selection standards), and calculate the actual accident energy and arc flash protection boundary in each time period.

During the period from t ₁ to t _p,1 ,

Step 5: Compare the magnitude of E ₁ and E _p,1 , and select personal protective equipment according to the hazard risk level corresponding to the larger accident energy (for selection criteria, refer to NFPA 70E-2009 Table 130.7(C)(10)).

Figure 2 is a single-line diagram of a dual-source power supply system, which is used to illustrate the improvement points of the arc flash hazard calculation method of the multi-source power supply system.

As shown in Figure 2, a dual power supply system, the system is powered by power supply A and power supply B at the same time. When a fault occurs at position 4, in order to meet the selectivity of protection, the action time limit of the protection device is extremely poor, then compared with power source A, the action time limit of the main protection circuit breaker 4 of the line where position 4 is located should be smaller than the backup protection circuit breaker 3 action time limit. When a fault occurs at position 2, compared to power source B, the action time limit of the main protection circuit breaker 3 of the line where position 2 is located should be shorter than the action time limit of the backup protection circuit breaker 4, thus creating a contradiction.

In order to solve the above contradictions, directional elements can be added, so that after a fault occurs, the circuit breakers 1, 3, and 5 can only detect the short-circuit contribution current provided by the power source A, and the circuit breakers 2, 4, and 6 can only detect the short-circuit contribution current provided by the power source. The short-circuit contribution current provided by B. Therefore, in order to satisfy the selectivity of protection, the circuit breakers 5, 3, and 1 can be operated in sequence, and the circuit breakers 2, 4, and 6 can be actuated in sequence, and no contradiction will arise.

Based on the characteristics of the multi-source power supply system, it is required to install directional elements in certain positions, and the calculation results of arc flash hazards may also change. For example, when the position 5 fails, the circuit breaker 6 will detect the short-circuit contribution current provided by the power source B, and the circuit breaker 5 will detect the short-circuit contribution current provided by the power source A. Since the action time limit of circuit breaker 5 and circuit breaker 6 may be different, the total fault current at position 5 will change in different time periods, resulting in changes in the calculation result of arc flash hazard. Moreover, if the short-circuit contribution current of one side of the power supply is very small, and only the overcurrent protection function or the delayed current quick-break protection function of the main protection device on that side can be triggered, the action time limit will be larger. For another example, if the multi-source power supply system contains distributed power supply, according to IEEE Std.1547, the distributed power supply should be removed first when the distribution network fails, so that the distributed power supply will no longer provide short-circuit contribution to the fault point after a short period of time. At this time, the main protection action time limit of the fault point and the cut-off time of the distributed power supply must be extremely poor. In these complex situations, if the calculation is performed according to the traditional arc flash hazard algorithm in the existing single power supply system, that is, the total short-circuit contribution current of the fault point and the action time limit of the latest main protection device are substituted into the calculation, the get overly conservative results.

By using the arc flash hazard calculation method of the multi-source power supply system of the present invention, based on the action time limit of the protection device and the cut-off time of the distributed power supply, the short-circuit contribution current is divided and summarized by time periods, and the arc flash hazard calculation is performed, which can avoid the above problems. , to get more accurate results.

It should be noted that before using the method of the present invention, the following points should be noted:

(1) Clarify the types of all power supplies in the multi-source power supply system, and determine the corresponding calculation method in the present invention according to the specific power supply composition.

(2) Ensure that there is a reasonable protection configuration in the multi-source power supply system, and can obtain the operating current and operating time limit of the protection device when a fault occurs.

(3) The protection device in the multi-source power supply system may have directional elements, so it is necessary to clarify the current direction detected by the protection device under multiple power supply modes.

(4) The method of the present invention is suitable for arc flash hazard calculation under the maximum working condition of the system, and the parameters used are subject to the values under the maximum working condition of the system.

(5) Since the grounding fault is usually rapidly transformed into a three-phase short-circuit fault, causing more serious arc flash hazards, the method of the present invention can address the situation where a three-phase short-circuit fault occurs.

The present invention also provides a microcomputer system of a multi-source power supply system, comprising a processor, and the processor executes the steps of the fault detection method of the multi-source power supply system of the present invention, and can also execute the arc flash of the multi-source power supply system of the present invention. Steps in the Hazard Calculation Method.

The above content is a further detailed description of the present invention in conjunction with specific preferred embodiments, and it cannot be considered that the specific implementation of the present invention is limited to these descriptions. For those of ordinary skill in the technical field of the present invention, without departing from the concept of the present invention, some simple deductions or substitutions can be made, which should be regarded as belonging to the protection scope of the present invention.

Claims (9)

1. An arc flash hazard calculation method for a multi-source power supply system. Multiple power supplies respectively form power supply circuits through bus bars and cables for supplying power to load equipment. A protection device is provided, and a protection device is provided between the connected busbar and the load equipment, which is characterized in that:

   S1: Determine the fault-occurring device, the n power supplies that supply the fault-occurring device and the power types of the n power supplies, n>=2;

   Obtain the cut-off time _{t 1} , t ₂ , . ₁ , I ₂ , ..., In , calculate the sum I _sum of the short-circuit contribution currents of the _n power sources to the equipment where the fault occurs;

   S2: Arrange the cut-off times t ₁ , t ₂ , . . . , t _n of the n power supplies to the short-circuit contribution current of the fault-occurring bus from small to large, and arrange the short-circuit contribution currents I ₁ , I ₂ , . . . I _{n is} combined to obtain short-circuit contribution currents I ₁ , I ₂ ,..., I _z at times t ₁ , t ₂ ,..., t _z ;

   S3: Calculate the arc current I _arc,1 , I _arc,2 ,..., I _arc,z in each time period from 0 to t ₁ , t ₁ to t ₂ ,..., t _z-1 to t _z ;

   For the period 0 to _t1 ,

   Calculation method of arc current I _arc,1 of power supply system below 1kV:

   

   The calculation method of the arc current I _arc,1 of the power supply system of 1kV and above is:

   lg I _arc,1 = 0.00402+0.983lg I _sum (2)

   For the period from _ty-1 to ty, 1< _y <=z,

   Calculation method of arc current I _arc,y of system below 1kV:

   

   The calculation method of the arc current I _arc,y of the system of 1kV and above is:

   

   In formulas (1) and (2), S is 0.153 for the open arc, and -0.097 for the arc in the box; V is the system voltage; G is the phase spacing;

   S4: According to the arc currents I _arc,1 , I _arc,2 , ..., I _arc,z in each time period, calculate the normalized arc flash accident energies En, ₁ , En, ₂ , ... respectively in each time period , E _n,z ;

   The calculation method of the normalized arc flash accident energy En _,y is:

   lg E _n,y = k ₁ +k ₂ +1.081lg I _arc,y +0.0011G (3)

   In formula (3), k ₁ takes -0.792 for open arcs, -0.555 for box arcs; k ₂ takes 0 for ungrounded systems or high-resistance grounded systems, and -0.113 for grounded systems, and G is the phase spacing;

   S5: Select an appropriate distance correction factor x according to the type of faulty equipment, and calculate the actual accident energy E ₁ , E ₂ , ..., E _z and arc flash protection boundaries DB _,1 , DB _,2 , ..., D _B,z ;

   For the period 0 to _t1 ,

   

   

   For the period from _ty-1 to ty, 1< _y <=z,

   

   

   In formulas (4) and (5), C _f is 1.0 for systems above 1kV and 1.5 for systems below 1kV, D is the distance between the arc center and the human body, and x is the distance correction factor;

   S6: _Compare the _magnitudes of the actual accident energies E ₁ , E ₂ , .
2. The arc flash hazard calculation method for a multi-source power supply system according to claim 1, wherein in step S1, if the fault-occurring device is a load device, there are n power supplies in the system to supply power to the load device, and none of the n power supplies Including distributed power sources, when a fault occurs at the load equipment, only a short-circuit current in one direction flows, then the cut-off times t ₁ , t ₂ , ..., t _n of n power sources to the short-circuit contribution current of the fault equipment are all load equipment. According to the action time limit _t of the protection device of the line, calculate the short-circuit contribution currents I ₁ , I ₂ , .
3. The arc flash hazard calculation method for a multi-source power supply system according to claim 1, wherein in step S1, if the fault-occurring device is a load device, there are n power sources in the system to supply power to the load device, and the n power sources include m distributed power sources, 0<m<=n, obtain the cut-off time t _DG,1 , t _DG,2 , ... , t _DG,m of m distributed power sources, and the contribution of the remaining nm power sources to the short circuit of the faulted equipment The current cut-off time is the action time limit t of the protection device of the line where the load equipment is located, and the cut-off times t ₁ , _{t 2} , .
4. The arc flash hazard calculation method for a multi-source power supply system according to claim 1, wherein in step S1, if the fault-occurring device is a bus, there are n power sources in the system to supply power to the bus, and the n power sources do not include distribution t bf,1 , t bf,2 , ... , t bf,n to obtain the cut-off time t _bf,1 , t _{bf, 2} , ... , t _bf,n of n power sources to the short-circuit contribution current of the faulted bus, and obtain the cut-off time of n power sources to the short-circuit contribution of the faulted bus t ₁ , t ₂ , ..., t _n .
5. The arc flash hazard calculation method for a multi-source power supply system according to claim 1, wherein in step S1, if the fault-occurring device is a bus, there are n power sources in the system to supply power to the bus, and the n power sources include m Distributed power supply, 0<m<=n, the cut-off time to obtain m distributed power supplies is t _DG,1 , t _DG,2 ,..., t _DG,m , obtain the short-circuit contribution of the remaining nm power supplies to the faulty busbar The current cut-off times t _bf1 , t _bf2 , . . . , tbf _nm are used to obtain the cut-off times t ₁ , _{t 2} , .
6. A method for reducing the arc flash hazard of a multi-source power supply system, characterized in that: a certain position or a certain position in the multi-source power supply system is obtained by using the arc flash hazard calculation method of the multi-source power supply system according to any one of claims 1-5. The maximum accident energy E _{max among} the actual accident energies E ₁ , E ₂ , _.

   Find the protection device responsible for tripping based on the time period corresponding to the maximum accident energy E _max , reduce the action time limit of the protection device or modify the protection configuration of the adopted multi-source power supply system.
7. A fault detection method for a multi-source power supply system, characterized in that: the arc flash hazard calculation method for a multi-source power supply system according to any one of claims 1-5 is used to obtain the arc flash occurrence at each position and each device in the multi-source power supply system. The maximum accident energy E _max caused by the flash;

   Monitor the arc flash accident of the multi-source power supply system to obtain the location or equipment of the arc flash accident and the energy of the arc flash accident;

   Compare the arc flash accident energy with the maximum accident energy E _max of the corresponding position or equipment, and alarm if the arc flash accident energy is greater than the maximum accident energy E _max of the corresponding position or equipment.
8. A microcomputer system of a multi-source power supply system, comprising a processor, characterized in that: the processor executes the steps of the fault detection method of the multi-source power supply system according to claim 7 .
9. A computer, comprising a processor, characterized in that: the processor executes the steps of the method for calculating the arc flash hazard of a multi-source power supply system according to any one of claims 1-5.

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