TWI509924B - A method to solving the protective coordination curve intersection of electromechanical overcurrent relays in power delivery networks with the customized characteristic curve equation - Google Patents

Description

Method for solving the intersection of electromagnetic over-current electro-hydraulic protection coordination curve of transmission and distribution network by characteristic curve custom formula

The invention is a method for solving the intersection of the electromagnetic over-current electric raft protection coordination curve of the transmission and distribution network by using the characteristic curve custom formula, and deducing the protection coordination curve adjustment program through the characteristic curve customization formula, which can be used for the traditional electromagnetic type phase-to-phase The current electric power is adjusted with the traditional electromagnetic grounding overcurrent electric current to solve the situation that the upper and lower coordination curves are crossed due to the poor coordination setting, so that the power failure range is not caused when the fault occurs. The expected expansion will affect the quality of power supply.

Due to the economical reliability and good coordination of overcurrent electric power, if properly coordinated, it can provide a proper protection and coordination mechanism for the transmission and distribution networks. When there is a problem in the transmission and distribution network, it can be isolated with the least fault in the shortest time. The area is used to troubleshoot problems, so that the transmission and distribution network can continue to maintain the best power quality.

The key to a well-established transmission and distribution network protection coordination mechanism is how to determine the optimal coordination sequence of the power lines in the transmission and distribution networks, and the optimal time calibration for each power trip time. . At present, mainstream commercial software packages (such as ASPEN OneLiner) for power systems do not support the calculation of overcurrent 驿 值 value for protection coordination design. Therefore, in practice, the advantages and disadvantages of overcurrent 驿 protection coordination settings are still mainly It is based on experienced senior electric engineers. However, this kind of manual calculation method is not only time-consuming and labor-intensive. For the more complicated transmission and distribution network structure, in addition to the more complicated calculation process, it is not easy to get appropriate protection coordination settings.

In practice, one of the most common coordination problems encountered with overcurrent cymbals is the intersection of protection coordination curves. If the upstream and downstream overcurrent protection coordination curves cross each other, in the event of a fault, within a certain fault current range, the backup power (ie, the upstream power) will be prior to the main power supply (ie, the downstream power supply). The action, resulting in an unexpected expansion of the power outage range, is not allowed in design. Used to borrow The commercial power system software, such as ASPEN's OneLiner software package, draws a protection coordination curve according to the original design value, and then visually checks the figure to determine whether the coordination curve intersects. If the curve is found to cross, the staff will The trial and error method adjusts the delay value of the relevant power by manual calculation to solve the intersection. In this way, not only is it cumbersome and time consuming, but it also changes the original design parameters, such as the above and downstream coordination time interval (CTI).

The overcurrent current used in the transmission line protection of transmission and distribution networks is mainly based on digital type and traditional electromagnetic type. Among them, the characteristic curve of the digital overcurrent electric raft is represented by a single action characteristic curve equation, such as the IEC and IEEE standard inverse time type digital electric yoke characteristic curve formula, because it is an electronic device, therefore, the setting is convenient and accurate. As for the conventional electromagnetic overcurrent electric cymbal, the action principle is to generate a vortex current of different phase difference on the induction turntable by applying an electric current to the induction coil of the electromagnet, and form an induced rotational torque on the induction turntable to close the movable contact. The upstream and downstream protection coordination functions are achieved by adjusting the length of the closed path between the moving contact and the fixed contact. Because it is a mechanical device, it also produces inertia and friction effects. Therefore, it is impossible to accurately express the characteristic curve in a single formula like a digital type of electric power. Usually, the manufacturer will provide the relevant characteristic curve obtained from the experiment in the instruction manual. However, It is inconvenient and inaccurate in use. In addition, the industry still provides a characteristic curve custom formula for the traditional electromagnetic over-current electro-hydraulic simulation.

At present, when dealing with the intersection of the upstream and downstream overcurrent protection coordination curves, for the digital type of electric power, it is based on the IEC or IEEE standard inverse time type digital electric characteristic curve expression to improve the upstream digital position of the intersection of the coordination curve. For current-type power 驿, it is based on the characteristic curve data provided by the manufacturer, and self-built related database to process the upstream electromagnetic overcurrent gong that intersects the coordination curve, but has not tried to be used for analog electromagnetic The characteristic curve of the characteristic curve of the overcurrent current characteristic curve is used to adjust the delay value of the electromagnetic overcurrent current.

Based on the above, the present invention proposes a method for solving the intersection of the electromagnetic overcurrent and electric power protection coordination curves of the transmission and distribution network by using the characteristic curve custom formula, and deducing the protection coordination curve adjustment procedure through the characteristic curve customization formula for solving Due to the improper setting of protection coordination, the crossover problem of the upstream and downstream electromagnetic overcurrent electro-hydraulic coordination curves is solved. By recalculating the appropriate delay value of the upstream electromagnetic type electrocution that crosses the curve, the new curve is no longer There are cross-over situations to provide a complete coordination mechanism for transmission and distribution network protection.

The method of the invention mainly adjusts the traditional electromagnetic type phase-to-phase overcurrent electric raft and the traditional electromagnetic type grounding overcurrent electric raft, and can be used for solving various transmission and distribution network forms (such as: radial transmission grid road, ring transmission) The protection coordination curve of the network and the distribution network is crossed, and can achieve the following effects: 1. There is no need to replace the existing electromagnetic overcurrent battery; 2. The original design parameters are not changed, 譬 above, downstream Coordinated time interval (CTI); 3. Improve the integrity of transmission and distribution network protection coordination; 4. Improve the efficiency of transmission and distribution network protection coordination; and 5. Improve the accuracy of transmission and distribution network protection coordination.

The method of the present invention will now be described as follows:

Equations (1) and (2) are the expressions of the IEC and IEEE standard inverse-time digital electric characteristics, and the formula (3) is the characteristic curve. The custom formula can be used to simulate the inverse-time electromagnetic type characteristic curve.

Among them, t eMule action time

L , TD delay value

i current transformer secondary side fault current

I _n current tap value

M starting current multiple, M = i / I _n

A, B, P, K constant

Table 1 lists the values recommended by the Basler Power Company for the constants A, B, K, and P of the characteristic curve (3) relative to the different counter-time type CO electromagnetic overcurrents. Among them, CO-2 is Short Inverse, CO-5 is Long Inverse, CO-6 is Definite Inverse, and CO-7 is Intermediate. Moderately Inverse, CO-8 is Inverse, CO-9 is Very Inverse, and CO-11 is Extremely Inverse.

"Picture 1" is a CO-8 inverse electromagnetic type overcurrent current characteristic curve drawn based on the data provided by the manufacturer. "Picture 2" is a characteristic curve drawn by CO-8 in a custom formula (where A=8.9341, B=0.17966, K=0.028, P=2.0938). "Picture 3" compares the difference in characteristic curves drawn by the two methods. Comparing the same delay value (for example, 1.0), it can be clearly seen from "3" that the two curves are extremely different. Therefore, the characteristic curve custom formula cannot be directly used to replace the manufacturer curve because the error is too large before the correction delay value is set.

Table 2 is the correction data of the characteristic curve of the characteristic curve in the delay value, which is provided by Basler Power Company. The first column in the table is the delay value of the electromagnetic overcurrent ,, and the remaining columns are the correction data of the CO 模拟 simulated by the custom formula corresponding to the first column calibrated value. For example, taking the CO-7 electromagnetic overcurrent gong as an example, if the delay value calculated by the characteristic curve of the characteristic curve is 3.0, the corrected delay value can be obtained by looking up Table 2. In addition, if the target value to be corrected falls between the first column and the second index value, the corresponding correction value may be calculated by interpolation or Curve Fitting. "Fig. 4" is a comparison with the original CO-8 curve after the CO-8 modified delay time value is simulated by the simulation formula. It can be seen from the figure that the original index value of 1.0 and the modified formula are 0.7, and the two curves are quite similar. Therefore, the custom formula can be directly replaced by the manufacturer after the corrected delay value. The curve.

The standard anti-time action characteristic curve equation mainly includes three variables, such as delay set value (TD), electric action time (t) and starting current multiple (M). Therefore, according to the problem to be processed, the three The relationship between them is expressed in an appropriate form. In order to facilitate the method of solving the intersection of the coordination curve, the delay value of the formula (3) is expressed as a function of the electric motor action time and the starting current multiple as a variable, as shown in the formula (4). Equation (5) is used to calculate the new starting current multiple of the upstream electric power. Under the condition that the upstream overcurrent electric current operation time is maintained (that is, the operation time=T), the formula (4) is for the pre-adjustment and the adjustment. The two cases can be expressed as equations (6) and (7), respectively. Then, formula (8) can be derived from equations (6) and (7) for calculating the new delay flag value of the upstream power.

Wherein, the starting current multiple of the upstream electric current of the M _B

Current tap value of I _NB upstream power

CT analogy of CT _B upstream power

I _F reference fault current, coordinating the near-end fault current of the downstream electric power in the middle

TD _B = g ( T , M _B ) (6)

TD _{B 1} = g ( T , M _{B 1} ) (7)

Wherein, the starting current multiple of the upstream power adjustment of the M _B

M _B1 upstream power 驿 adjusted starting current multiple

Delay value before TD _B upstream power adjustment

Delay value of TD _B1 upstream power adjustment

T upstream power grid original setting action time

g(T, M _B ) Substituting the action time (t=T) of the upstream electric enthalpy and the multiple of the starting current (M=M _B ) into the formula (4), the obtained function value before adjustment

g(T, M _B1 ) substitutes the action time (t=T) of the upstream electric enthalpy and the multiple of the starting current (M=M _B1 ) into the formula (4), and the obtained adjusted function value

The invention is used for solving the protection coordination curve adjustment procedure of the curve intersection, and adjusting the upstream electric power delay time value of the upper and lower electromagnetic type overcurrent electric 驿 coordination center of the intersection of the occurrence curves by formulas (5) and (8). Then, according to Table 2, the adjusted delay value is corrected, and then the software program for drawing the coordination graph is used to stagger the intersection characteristic curve, so that the transmission and distribution network can be protected by good coordination. A situation in which an overcurrent current malfunction occurs and the downstream power supply is affected. "Fig. 5" is a flowchart of the protection coordination curve adjustment procedure for solving the intersection of the upstream and downstream electromagnetic overcurrent electric enthalpy coordination curves, and the flow chart is described in detail below:

(Step 100): input the system parameter data used by the protection coordination design to the software program with the function of drawing the coordination graph to generate the coordination graph.

The aforementioned software program can be a commercial professional coordination graph drawing software (such as ASPEN's OneLiner), or a self-developed non-commercial program. The aforementioned system parameter data includes system voltage, bus bar voltage, bus bar position information, line rated value, fault current, ratio of current ratio, coordination time interval, protection type, protection position information, protection power驿Time metric value, end demarcation point position information, and end demarcation point time metric value.

(Step 200): Examine whether the coordination graph has an intersection of upstream and downstream coordination curves.

If not, it means that no adjustment or adjustment has been completed, otherwise it proceeds to step 300 to start processing the intersection.

(Step 300): Determining the fixed position of the upstream electric 驿 coordination curve of the electromagnetic overcurrent 驿 coordination center to be adjusted

For the power coordination coordination of the protection coordination curve, the near-end fault current I _F of the downstream power supply is coordinated with the reference fault current and the upstream power-off operation time T _{B of} the power coordination coordination center, Determine the position of the fixed point on the upstream power coordination curve as a reference point for curve adjustment, as shown in Figure 6.

(Step 400): Calculate the new starting current multiple of the upstream electric power

According to the reference fault current I _F and the CT turns ratio of the upstream electric power and the adjusted current tap value, the new starting current multiple of the upstream electric power can be obtained from the formula (5).

(Step 500): Calculate the new delay flag value of the upstream power device

The new start delay value of the upstream power is obtained by substituting the multiple of the initial current before the adjustment of the upstream power and the delay value and the multiple of the starting current obtained in step 400 into the formula (8). In Figure 6, TD _P is the original coordination curve of the downstream power, and TD _B is the original coordination curve of the upstream power. The curve indicated by the dotted line by the fixed point is the coordination curve of the upstream power corresponding to the new delay index value, TD _B1 is the result of the first adjustment, and TD _B2 is the result of the second adjustment. It can be clearly seen from the figure that the adjusted coordination curve will gradually deviate from the original intersection, and since the adjusted curve passes through the fixed point of step 300, the adjustment mode does not change the original action time of the upstream power supply. _B and the upstream and downstream coordination time interval CTI.

(Step 600): Correct the delay flag value after the upstream power adjustment

The new delay flag value calculated in step 500 is modified according to Table 2. If the target value to be corrected falls between the first column and the second index value, the corresponding correction value can be calculated by interpolation or Curve Fitting. Then return to step 100 to draw an adjusted coordination graph to check if the intersection has been eliminated.

Fig. 6 shows a schematic diagram of the intersection of the upper and lower electromagnetic type overcurrent electric enthalpy coordination curves by the protection coordination curve adjustment program of the present invention. In the figure, TD _B1 is the result of the first adjustment, and TD _B2 is the result of the second adjustment. As can be clearly seen from the figure, the crossover has been eliminated when adjusting to TD _B2 .

The features and implementations of the present invention are described in detail with reference to the preferred embodiments.

In order to demonstrate the specific feasibility of the method of the present invention, and to enable those skilled in the art to fully grasp the technical content of the method, it can be implemented accordingly, and an embodiment is specifically described below (see "Figure 7" to " Figure 9): According to the foregoing process relating to the method of the present invention, a single-loop secondary transmission network road having seven bus bars as shown in "Fig. 7" is first constructed, and the seven bus bars are respectively A BUS , B BUS, C BUS, D BUS, E BUS, F BUS and G BUS name. The busbars have a voltage rating of 69 KV. The system constant of A BUS is Z ₁ =0.000+j1.432Ω, Z _o =0.001+j31.251Ω. The safe current is 1200A. Other line parameters and overcurrent-related information are shown in Table 3. The overcurrent devices used include ABB's CR-8, CRP-8 electromagnetic overcurrent, and GE's IBC51 and IBCG51 electromagnetic overcurrent.

The method of the present invention will now be described by taking the phase-to-phase overcurrent current protection coordination setting of the clockwise direction of the loop as an example. First check the ring routing A BUS #620 → B BUS #620 → C BUS #620 → D BUS #610 → E BUS #610 → F BUS #620 → G BUS #620 clockwise 67 electric 驿 characteristic curve cross Need to adjust. The protection coordination graphs shown in Figure 8 and Figure 9 are drawn by ASPEN's OneLiner software. Among them, Figure 8 is the protection coordination curve of the original design, and Figure 9 This is the adjusted protection coordination graph. The curve No. 7 in the second figure is the characteristic curve of A BUS, No. 6 is the characteristic curve of B BUS, No. 5 is the characteristic curve of C BUS, and the rest is analogous. In "Fig. 8," curve No. 7 intersects the three curves of No. 4, No. 5, and No. 6, respectively, where the three-phase short-circuit fault currents are 2100A, 2800A, and 3500A. Therefore, the intersection of the curves needs to be processed to avoid malfunctions.

The delay value of the A BUS #620:67 electromagnetic overcurrent is adjusted by the method of the invention. Coordination of A BUS#620:67 power after the A BUS#620:67 electric current tap value is gradually increased from 5A to 6A and 7A The curve no longer intersects with the coordination curve of its downstream power. "Picture 9" is the protection coordination graph redrawed by the OneLiner software with the optimal delay value setting after the A BUS #620:67 power adjustment. As is clear from the figure, after the method of the present invention is used, the intersection of the curves generated by the original protection coordination design no longer exists.

While the present invention has been described above in terms of the preferred embodiments thereof, it is not intended to limit the invention, and the invention may be modified and modified without departing from the spirit and scope of the invention. The scope of patent protection of the invention is subject to the definition of the scope of the patent application attached to the specification.

CTI‧‧‧Upstream and downstream coordination time interval

CT _B ‧‧‧CT ratio of upstream electric power

I‧‧‧current secondary current fault current

I _n ‧‧‧current tap value

I _NB ‧‧‧current tap value of upstream electric

I _F ‧‧‧ Near-end fault current of downstream power

L‧‧‧Electric delay time value

M‧‧‧ starting current multiple

M _B ‧‧‧Initial current multiplier

t‧‧‧Electric time

T _B ‧‧‧Upstream eMule action time

T _P ‧‧‧Downstream eMule action time

TD‧‧‧Electricity delay flag

TD _B ‧‧‧Upstream eMule delay flag

TD _B1 ‧‧‧After the first adjustment of the upstream power delay value

TD _B2 ‧‧‧After the second adjustment of the upstream power delay value

TD _P ‧‧‧Downstream eDonkey delay value

Step 100‧‧‧Enter the system parameter data used in the protection coordination design into the software program with the function of drawing the coordination graph to generate the coordination graph

Step 200‧‧‧Check whether the coordination curve has the intersection of the upstream and downstream coordination curves

Step 300‧‧‧Determining the fixed-point position on the coordination curve of the upstream electric enthalpy of the electromagnetic overcurrent 欲 coordination

Step 400‧‧‧ Calculate the new starting current multiple of the upstream electric

Step 500‧‧‧ Calculate the new delay value of the upstream power unit

Step 600‧‧‧ Amend the delay value of the upstream power meter adjustment

The first picture is based on the CO-8 inverse electromagnetic type drawn by the data provided by the manufacturer. Current characteristics curve.

Figure 2 is a plot of the characteristic curve drawn by CO-8 using a custom formula.

Figure 3 compares the difference in the characteristic curves plotted by the two methods (manufacturer data and custom formula).

Figure 4 is a comparison of the CO-8 curve of the CO-8 modified by the simulation formula with the corrected CO-8 curve.

Figure 5 is a flow chart of the protection coordination curve adjustment procedure for solving the intersection of the upstream and downstream electromagnetic overcurrent electric enthalpy coordination

Figure 6 is a schematic diagram of the intersection of the upper and lower electromagnetic type overcurrent electric enthalpy coordination curves with the protection coordination curve adjustment program of the present invention.

Figure 7 is a schematic diagram of a transmission grid path of an embodiment.

Figure 8 is a schematic diagram showing the intersection of the coordination curves of the embodiments.

Figure 9 is a schematic diagram of the coordination curve of the adjustment of the embodiment.

Step 100‧‧‧Enter the system parameter data used in the protection coordination design into the software program with the function of drawing the coordination graph to generate the coordination graph

Step 200‧‧‧Check whether the coordination curve has the intersection of the upstream and downstream coordination curves

Step 300‧‧‧Determining the fixed-point position on the coordination curve of the upstream electric enthalpy of the electromagnetic overcurrent 欲 coordination

Step 400‧‧‧ Calculate the new starting current multiple of the upstream electric

Step 500‧‧‧ Calculate the new delay value of the upstream power unit

Step 600‧‧‧ Amend the delay value of the upstream power meter adjustment

Claims (12)

A method for solving the intersection of the electromagnetic over-current electric raft protection coordination curve of the transmission and distribution network by the characteristic curve custom formula, which is to re-balance the coordination curve formed in the original protection coordination design and the downstream electromagnetic over-current 驿 value The adjustment to the curve no longer crosses, so that the fault does not cause improper action, resulting in an unexpected expansion of the power outage range and affecting the quality of the power supply; wherein the protection coordination curve adjustment procedure is mainly derived through the characteristic curve customization formula, and the original protection coordination In the design, the electromagnetic over-current electric raft is crossed above and below the coordination curve, and the adjustment is not crossed until the coordination time interval of the original design is changed. The characteristic formula of the characteristic curve is as follows: Among them, the t-type electro-hydraulic action time, the TD-system delay value, the M-system start-up current multiple, the A, B, P, and K-series constants; and the characteristic curve of the characteristic curve is through the A, B, and K, P constants to simulate different inverse-time CO electromagnetic overcurrents; The CO-2 in the table is the Short Inverse, the CO-5 is the Long Inverse, the CO-6 is the Definite Inverse, and the CO-7 is the Intermediate Inverse. Moderately Inverse, CO-8 is Inverse, CO-9 is Very Inverse, and CO-11 is Extremely Inverse. For example, the method of characterizing the characteristic formula to solve the intersection of the electromagnetic type overcurrent and electric power protection coordination curve of the transmission and distribution network as described in the first paragraph of the patent application scope is mainly for the intersection of the coordination curve and the downstream electromagnetic overcurrent.驿 Coordination adjustments. The method for solving the intersection of the electromagnetic overcurrent and electric power protection coordination curves of the transmission and distribution network, as described in the second paragraph of the patent application scope, is mainly for the intersection of the coordination curve and the downstream electromagnetic overcurrent.驿 Coordinate the adjustment of the upstream electromagnetic type overcurrent 对. For example, the method for solving the intersection of the electromagnetic over-current electro-hydraulic protection coordination curve of the transmission and distribution network by the characteristic curve custom formula described in the third paragraph of the patent application scope is to coordinate the electromagnetic over-current electro-hydraulic coordination for the protection coordination curve. The electric power is used to coordinate the near-end fault current of the middle and the downstream electric power as the reference fault current and the upstream electric power regenerative action time of the electric power coordination center, and determine the fixed position of the upstream electric power coordination curve as a curve adjustment Reference point; then by changing the current tap value of the upstream electric pole, obtaining different index values of the electric pick, and then correcting the set value to gradually adjust the position of the upstream coordination curve passing the fixed point to make it Deviate from the intersection of the original upstream and downstream coordination curves until they no longer intersect. For example, the method of characterizing the characteristic formula to solve the intersection of the electromagnetic over-current electro-hydraulic protection coordination curve of the transmission and distribution network, as described in the fourth paragraph of the patent application scope, wherein the selection method of the fixed point can make the original design and the downstream coordination time The distance remains unchanged. For example, the method of characterizing the characteristic formula to solve the intersection of the electromagnetic overcurrent and electric power protection coordination curve of the transmission and distribution network, as described in the fourth paragraph of the patent application scope, wherein the selection of the range of the current tap value does not affect the electromagnetic type. Sensitivity of overcurrent. The method for solving the intersection of the electromagnetic overcurrent and electric power protection coordination curve of the transmission and distribution network, as described in the sixth paragraph of the patent application scope, wherein the current tap value is selected within the range of the current tap value, According to the current tap value set by the electromagnetic overcurrent electric appliance manufacturer, the size is small to large. The order is adjusted successively until the intersection is eliminated. The method for solving the intersection of the electromagnetic overcurrent and electric power protection coordination curve of the transmission and distribution network is solved by the characteristic formula of the characteristic curve described in item 4 of the patent application scope, wherein the calculation of the new delay indication value of the electromagnetic type electrophoresis is performed by The overcurrent current current tap value is changed, so that the overcurrent current starting current multiple is changed accordingly, and then the original delay value, the original moving current multiple value, and the adjusted starting current multiple value are obtained, and the adjusted value is obtained. The new delay flag is used, and the new delay flag is obtained using the following formula: Among them, M _B is the starting current multiple before the upstream power adjustment, M _B1 is the starting current multiple after the adjustment of the upstream power, the delay value before the adjustment of the upstream power of the TD _B system, after the upstream power adjustment of the TD _B1 system The delay value is set, the operating time of the T- line upstream power setting, g(T, M _B ) is substituted into the following formula for the operation time (t=T) and the starting current multiple (M=M _B ) of the upstream power unit. The obtained function value before adjustment, g(T, M _B1 ) is the adjusted function value obtained by substituting the action time (t=T ) of the upstream electric power and the multiple of the starting current (M=M _B1 ) into the following formula. ; Among them, the t-type electric cymbal operation time, the g-system adjusted function value, the M-system starting current multiple, and the A, B, P, and K-series constants. The method for solving the intersection of the electromagnetic over-current electro-hydraulic protection coordination curve of the transmission and distribution network according to the characteristic formula of the characteristic curve mentioned in item 8 of the patent application scope, wherein the calculated new delay type of the upstream electromagnetic type electro-hydraulic is calculated The value must be corrected after the following table is used; for example, taking the CO-8 electromagnetic overcurrent device as an example, if the delay value calculated by the characteristic curve of the characteristic curve is 1.0, after the table is checked, The corrected delay flag is 0.7; The CO-2 in the table is the Short Inverse, the CO-5 is the Long Inverse, the CO-6 is the Definite Inverse, and the CO-7 is the Intermediate Inverse. Moderately Inverse, CO-8 is Inverse, CO-9 is Very Inverse, and CO-11 is Extremely Inverse. For example, in the method of claim 9, the characteristic formula of the characteristic curve is used to solve the method of intersecting the electromagnetic over-current electro-hydraulic protection coordination curve of the transmission and distribution network, and if the correction value to be corrected falls within the first column of the table. When the value is between the two values, the corresponding correction value can be calculated by interpolation or Curve Fitting. For example, the method of characterizing the characteristic curve to solve the intersection of the electromagnetic overcurrent and electric current protection coordination curve of the transmission and distribution network, as described in the first paragraph of the patent application, is directed to the traditional electromagnetic phase-to-phase overcurrent electric raft and the traditional electromagnetic type grounding. The current coil is adjusted for its coordination curve. The method for solving the intersection of the electromagnetic overcurrent and electric power protection coordination curve of the transmission and distribution network according to the characteristic curve characteristic formula mentioned in the first paragraph of the patent application is applied to solve the radial transmission network road, the ring transmission network road or The protection coordination curve of the distribution network crosses.