CN113612225A - Medium-voltage power supply reliability effect evaluation method - Google Patents

Abstract

The invention belongs to an evaluation method, and particularly relates to a method for evaluating reliability and effect of medium-voltage power supply. It includes: the method comprises the following steps: collecting data; step two: adjusting power grid parameters; step three: synthesizing voltage and current; step four: fitting a curve; step five: selecting a main curve; step six: normalizing the curve; step seven: merging the main parameter normalization curves; step eight: calculating a threshold range; step nine: and (6) evaluating. The invention has the following remarkable effects: according to the effect evaluation method, the medium-voltage reliability is evaluated in a reverse mode from the power utilization effect through evaluating the power utilization effect of each device in the power grid. In the method execution process, the main performance parameters of the electric equipment are selected, so that the evaluation result and the effect of the electric equipment are directly hooked, the evaluation result is reliable and accurate, the multi-dimensional evaluation is changed into simple numerical comparison by selecting the main curve, normalizing and combining the curves, and the evaluation result is simple and understandable.

Description

Medium-voltage power supply reliability effect evaluation method

Technical Field

The invention belongs to an evaluation method, and particularly relates to a method for evaluating reliability and effect of medium-voltage power supply.

Background

The power grid is an important form of energy supply in modern society, and many devices, whether industrial or civil, are highly dependent on the power supply of the power grid.

However, for systematic reasons, the effect of the power supply from the power grid cannot meet the requirements of all the electrical consumers. Firstly, in terms of power supply form, power supply of a power grid is an energy supply form of centralized power generation, then power transmission is carried out through the power grid, and power is used by an end user. In order to ensure the power supply efficiency, the power generation devices of the power grid are often arranged in a centralized manner, and use coal, water power, nuclear energy, wind energy, solar energy or other power generation modes. And on the basis of the consideration of efficiency, high-voltage or ultrahigh-voltage transmission is adopted in the transmission process according to the transmission power and different trans-regional distances. Therefore, before the end user uses electricity, the most originally generated electric energy is converted and processed for many times, and the generated electric pollution influences the electricity utilization effect of the end user. Secondly, in terms of the power consumption demand mode of the end user, the power consumption demands of different users are different, and the power consumption demands of different devices are also different, for example, the sensitivity of the motor to current and frequency is higher, the sensitivity of the lighting device to voltage is higher, and the sensitivity of the high-precision electronic device to voltage and frequency is higher.

The prior art only adds a voltage stabilizer in front of the electric equipment to deal with the condition of electric power pollution. However, this processing method cannot adjust the demand of the electric equipment in real time, and cannot allow the power generation and power management unit to grasp the direction of power adjustment in real time.

Therefore, a method for evaluating reliability effect of medium voltage power supply is needed.

Disclosure of Invention

The invention provides a method for evaluating reliability and effect of medium-voltage power supply aiming at the defects of the prior art.

The invention is realized by the following steps: 1. a method for evaluating reliability effect of medium voltage power supply is characterized by comprising the following steps:

the method comprises the following steps: data collection

Collecting data separately for each device in the grid and the grid;

step two: adjusting grid parameters

Respectively adjusting the grid voltage, the grid current and the grid frequency of a power grid to stop all electric equipment in the power grid from working, and simultaneously recording all relevant parameters;

step three: voltage current synthesis

Synthesizing the recorded voltage and current;

step four: fitting of curves

By a resultant voltage u_tSynthesized current I_tGrid frequency f_tMain performance parameter S of ith equipment_iat、S_ibt、S_ictRespectively fitting to respectively obtain main performance parameter curves of the ith equipment;

step five: selecting a main curve

Obtaining derivatives of three curves of the same performance parameter of the same equipment, taking the absolute value of an extreme value, and selecting the curve corresponding to the maximum absolute value of the extreme value as a main curve;

step six: curve normalization

Performing curve normalization on the main curve corresponding to each performance parameter of each device;

step seven: merging the main parameter normalization curves;

step eight: calculating a threshold range;

step nine: and (6) evaluating.

2. The method of claim 1 for evaluating the reliability effect of a medium voltage power supply, wherein: the first step comprises the following steps of,

for the grid, the following parameters were collected: network voltage u_1t、u_2t、u_3tGrid current I_1t、I_2t、I_3tFrequency of the grid f_tWherein u is_1t、u_2t、u_3tThree voltages representing three-phase alternating current, I_1t、I_2t、I_3tRepresenting three currents of three-phase alternating current, t being time, i.e. u_1tRepresenting the voltage of the first phase at time t, u_2tRepresenting the voltage of the second phase, u, at time t_3tRepresents the voltage of the third phase at time t; i is_1tRepresenting the current of the first phase at time t, I_2tRepresenting the current of the second phase at time t, I_3tRepresenting the current of the third phase at time t; f. of_tRepresenting the frequency of the grid at time t,

for each device in the grid, the following parameters are collected: s_1at、S_1bt、S_1ct、S_2at、S_2bt、S_2ct、S_3at、S_3bt、S_3ct、…S_iat、S_ibt、S_ictWherein i represents the serial number of the equipment, and if n electric equipment in the power grid are provided, the value range of i is [1, n]，S_iat、S_ibt、S_ictRespectively representing the main performance index of the ith equipment at the time t, wherein S_iatThe value of (A) must be significant, S_ibtAnd S_ictThe value of (a) is not necessarily significant, and when not significant, it is-1,

the main parameters of the equipment are the main parameters of the equipment during normal operation;

in the step, t is time, the interval between t and t +1 is 1 second, and when the value of t is less than or equal to 3000, sampling is continuously carried out; and when the value of t is more than 3000 and all the devices in the power grid continuously and normally work, executing the subsequent steps besides sampling in each cycle.

3. A method of assessing the reliability effectiveness of a medium voltage power supply as claimed in claim 2, characterized by: the third step includes the following steps,

the resultant voltage u is calculated by the following formula_t

The resultant current I is calculated by the following formula_t

4. A method of assessing the reliability effectiveness of a medium voltage power supply as claimed in claim 3, characterized by: the fifth step includes the following steps,

step five, different performance parameters are respectively carried out,

when the same value appears, the main curve is selected according to the priority of voltage > current > frequency.

5. The method of claim 4 for evaluating the reliability effect of a medium voltage power supply, wherein: the sixth step includes the following contents that,

let g_iat(x) Is the main parameter S of a device with sequence number i_iatWherein x is one of voltage u, current I, and frequency f, the specific determination method is obtained according to the calculation of step five,

then the curve f is normalized_iat(x) The calculation method of (2) is as follows:

where min { g }_iat(x) Is g_iat(x) Max { g } of_iat(x) Is g_iat(x) The maximum value of (a) is,

similarly, the main parameter S of the device with serial number i can be obtained_ibtNormalized curve f of_ibt(x)，

Similarly, a normalized curve of all the main parameters of all the devices can be obtained.

6. The method of claim 5 for evaluating the reliability effect of a medium voltage power supply, wherein: the seventh step includes the following steps,

solving a main parameter normalization curve merging function f of the equipment i by using the following formula_it(x)

f_it(x)＝P₁f_iat(x)+P₂f_ibt(x)+P₃f_ict(x)

Wherein f is_iat(x)、f_ibt(x) And f_ict(x) Is the main parameter normalization curve of the device i obtained by calculation in the sixth step, and certainly, if the device i has no corresponding main parameter, the corresponding item number is directly omitted,

P₁、P₂and P₃Is a coefficient, and the three values can be determined by any one of the following methods:

the first method is as follows: external giving

If the staff member can determine the weight relationship of several main parameters, the weight proportion of three parameters can be directly and externally given,

if the staff can not determine the weight relation of several parameters, a fixed value can be directly used, and the typical value given in the application is P₁：P₂：P₃＝5:3:2

The second method comprises the following steps: determining a weight ratio based on the values of several primary parameters

When | max { (f)_iat(x))″}|+|max{(f_ibt(x))″}|+|max{(f_ict(x) ")" | is not equal to 0, P is₁、P₂And P₃Is calculated by the following formula

Wherein (f)_iat(x) "represents a pair function f_iat(x) Second derivative, max { (f)_iat(x) -) "(denotes (f)_iat(x) "of, | max { (f)_iat(x) ")" | denotes max { (f)_iat(x) Absolute value of ""), analogous to (f)_ibt(x) "represents a pair function f_ibt(x) Second derivative, max { (f)_ibt(x) -) "(denotes (f)_ibt(x) "of, | max { (f)_ibt(x) ")" | denotes max { (f)_ibt(x) Absolute value of "); (f)_ict(x) "represents a pair function f_ict(x) Second derivative, max { (f)_ict(x) -) "(denotes (f)_ict(x) "of, | max { (f)_ict(x) ")" | denotes max { (f)_ict(x) The absolute value of ")" (ii) the absolute value of,

if | max { (f)_iat(x))″}|+|max{(f_ibt(x))″}|+|max{(f_ict(x) ")", | 0, then P₁＝P₂＝P₃＝1/3，

Of course if there are only two main parameters, then P₁＝P₂＝1/2，

If there is only one main parameter, then there is no need for the main parameter normalization curve merging through this step.

7. The method of claim 6 for evaluating the reliability effect of a medium voltage power supply, wherein: the step eight includes the following contents that,

normalizing curve merging function f to main parameters of equipment i_it(x) And solving an upper limit and a lower limit, wherein the upper limit and the lower limit are boundary thresholds of the device i for the medium-voltage electric mass.

The method for evaluating the reliability effect of the medium voltage power supply comprises the following steps,

when a new voltage and current frequency in the power grid occurs at the next moment, calculating a main parameter normalization curve merging function f of each device by using the fitting formula_it(x) And if the calculation results are all within the threshold range of the step eight, judging that the medium-voltage quality is qualified, and otherwise, judging that the medium-voltage quality is unqualified.

The invention has the following remarkable effects: according to the effect evaluation method, the medium-voltage reliability is evaluated in a reverse mode from the power utilization effect through evaluating the power utilization effect of each device in the power grid. In the method execution process, the main performance parameters of the electric equipment are selected, so that the evaluation result and the effect of the electric equipment are directly hooked, the evaluation result is reliable and accurate, the multi-dimensional evaluation is changed into simple numerical comparison by selecting the main curve, normalizing and combining the curves, and the evaluation result is simple and understandable.

Detailed Description

A method for evaluating reliability and effect of medium-voltage power supply comprises the following steps:

the method comprises the following steps: data collection

For the grid, the following parameters were collected: network voltage u_1t、u_2t、u_3tGrid current I_1t、I_2t、I_3tFrequency of the grid f_tWherein u is_1t、u_2t、u_3tThree voltages representing three-phase alternating current, I_1t、I_2t、I_3tRepresenting three currents of three-phase alternating current, t being time, i.e. u_1tRepresenting the voltage of the first phase at time t, u_2tRepresenting the voltage of the second phase, u, at time t_3tRepresents the voltage of the third phase at time t; i is_1tRepresenting the current of the first phase at time t, I_2tRepresenting the current of the second phase at time t, I_3tRepresenting the current of the third phase at time t; f. of_tRepresenting the frequency of the grid at time t.

For each device in the grid, the following parameters are collected: s_1at、S_1bt、S_1ct、S_2at、S_2bt、S_2ct、S_3at、S_3bt、S_3ct、…S_iat、S_ibt、S_ict. Wherein i represents the equipment serial number, if the number of the electric equipment in the power grid is n, the value range of i is [1, n]。S_iat、S_ibt、S_ictRespectively representing the main performance index of the ith equipment at the time t, wherein S_iatThe value of (A) must be significant, S_ibtAnd S_ictThe value of (b) is not necessarily meaningful, and when not meaningful, it takes the value of-1.

The primary performance indicator is not necessarily a primary parameter of the device. The main parameters of the equipment are the main parameters of the equipment during normal operation, and generally comprise current, voltage, power and the like; the main performance index refers to the effect evaluation dimension of providing a certain function for the outside by taking the equipment as a whole. In different application scenarios, the main performance index of the equipment may be different, as long as the main performance index of the equipment is determined before the method is performed.

In order to achieve unified calculation and improve efficiency, at most three main performance indexes are given to each device, and of course, a person skilled in the art can set more performance index dimensions as required.

For example, the main function of an electric fan is to blow air, so that the main performance index is the rotating speed, and the S of the electric fan_7atIt is the speed of the fan (assuming that the equipment number of the fan is 7), and generally the fan has no other main performance indexes, so S_7btAnd S_7ctAll values of (a) are-1; the main parameters of the electric fan can comprise rated voltage, rated current, rated power and the like, and the parameters are not parameters influencing the most main use function of the electric fan and are not main performance indexes.

If the main function of the electric lamp is illumination, and the main performance index is brightness, the S of the electric lamp is_8atIt indicates the brightness of the lamp (assuming that the equipment number of the lamp is 8), and the parameters of the rated voltage, the rated current, the rated power and the like of the lamp are not the main performance indexes of the lamp.

Also, as still an electric lamp, in some special cases, in addition to the need for lighting, heat is released to the lampWith the limitation, then S of the lamp_9atIndicates the brightness of the lamp, S_9btShowing the heat emission of the lamp (assuming the device number of this lamp is 9), S_9ctHas a value of-1.

The time t in this step is set arbitrarily according to the different precision of the equipment in the power grid, and the interval between t and t +1 is 1 second in general. When the value of t is less than or equal to 3000, continuously sampling; and when the value of t is more than 3000 and all the devices in the power grid continuously and normally work, executing the subsequent steps besides sampling in each cycle.

Step two: adjusting grid parameters

Regulating the network voltage u of a network in each case_1t、u_2t、u_3tGrid current I_1t、I_2t、I_3tFrequency of the grid f_tAnd all the electric equipment in the power grid stops working.

The purpose of this step is to examine the main performance parameter conditions of the consumer in extreme conditions, as well as the corresponding grid parameters.

Because most of the electric equipment cannot bear electric energy exceeding rated voltage and rated current, when the voltage or the current reaches the rated voltage limit or the rated current limit (the upper limit and the lower limit are respectively carried out), the electric equipment is actively disconnected through the switch so as to protect the safety of the electric equipment. The main performance parameters of the device recorded at this time are used as valid data for subsequent calculations.

Step three: voltage current synthesis

The resultant voltage u is calculated by the following formula_t

The resultant current I is calculated by the following formula_t

Step four: fitting of curves

By a resultant voltage u_tSynthesized current I_tGrid frequency f_tMain performance parameter S of ith equipment_iat、S_ibt、S_ictAnd respectively fitting to respectively obtain main performance parameter curves of the ith equipment.

The fitting in this step is performed on data whose main performance parameter is not-1, that is, the main performance parameter of the i-th device should have meaning.

For example, for the ith device, the device has two significant main performance parameters S_iatAnd S_ibt. According to the preceding step requirement, S of the device_ictThe value is always-1, so the subsequent calculation is only for S_iatAnd S_ibtThe process is carried out. For the first performance parameter S_iatRespectively with a combined voltage u_tSynthesized current I_tGrid frequency f_tFitting, three curves can be obtained: voltage performance curve K_iau(t), Current Performance Curve K_iaI(t), frequency Performance Curve K_iaf(t) of (d). Similarly, a second performance parameter S can be obtained_ibtThree curves of (a): voltage performance curve K_ibu(t), Current Performance Curve K_ibI(t), frequency Performance Curve K_ibf(t)。

Step five: selecting a main curve

And (3) solving derivatives of the three curves of the same performance parameter of the same equipment, taking the absolute value of the extreme value, and selecting the curve corresponding to the maximum absolute value of the extreme value as a main curve.

The above process is performed separately for different performance parameters.

When the same value appears, the main curve is selected according to the priority of voltage > current > frequency.

For example, for the ith device, the device has two significant main performance parameters S_iatAnd S_ibtObtaining corresponding parameters S according to the step four_iatThree curve voltage performance curve K_iau(t), Current Performance Curve K_iaI(t), frequency Performance Curve K_iaf(t) and correspondingParameter S_ibtThree curve voltage performance curve K_ibu(t), Current Performance Curve K_ibI(t), frequency Performance Curve K_ibf(t) of (d). Curve K versus voltage performance at this time_iau(t), Current Performance Curve K_iaI(t), frequency Performance Curve K_iaf(t) respectively obtaining derivatives, respectively taking absolute values of extreme values, and comparing the three values, wherein the curve corresponding to the maximum value is taken as a parameter S_iatThe main curve of (2). Similar vs. voltage performance curve K_ibu(t), Current Performance Curve K_ibI(t) respectively obtaining derivatives, respectively taking absolute values of extreme values, and comparing the three values, wherein the curve corresponding to the maximum value is taken as a parameter S_ibtThe main curve of (2).

Step six: curve normalization

And carrying out curve normalization on the main curve corresponding to each performance parameter of each device. The method comprises the following steps:

let g_iat(x) Is the main parameter S of a device with sequence number i_iatWherein x is one of voltage u, current I, and frequency f, the specific determination method is obtained according to the calculation of step five.

Then the curve f is normalized_iat(x) The calculation method of (2) is as follows:

where min { g }_iat(x) Is g_iat(x) Max { g } of_iat(x) Is g_iat(x) Is measured.

Similarly, the main parameter S of the device with serial number i can be obtained_ibtNormalized curve f of_ibt(x)。

Similarly, a normalized curve of all the main parameters of all the devices can be obtained.

Step seven: principal parameter normalization curve merging

Solving a main parameter normalization curve merging function f of the equipment i by using the following formula_it(x)

f_it(x)＝P₁f_iat(x)+P₂f_ibt(x)+P₃f_ict(x)

Wherein f is_iat(x)、f_ibt(x) And f_ict(x) The main parameter normalization curve of the device i is obtained by calculation in the sixth step, and if the device i does not have corresponding main parameters, the corresponding item number is directly omitted.

P₁、P₂And P₃Is a coefficient, and the three values can be determined by any one of the following methods:

the first method is as follows: external giving

If the staff member can determine the weight relationship of several main parameters, the weight proportion of three parameters can be directly given externally.

If the staff can not determine the weight relation of several parameters, a fixed value can be directly used, and the typical value given in the application is P₁：P₂：P₃＝5:3:2

The second method comprises the following steps: determining a weight ratio based on the values of several primary parameters

When | max { (f)_iat(x))″}|+|max{(f_ibt(x))″}|+|max{(f_ict(x) ")" | is not equal to 0, P is₁、P₂And P₃Is calculated by the following formula

Wherein (f)_iat(x) "represents a pair function f_iat(x) Second derivative, max { (f)_iat(x) -) "(denotes (f)_iat(x) "of, | max { (f)_iat(x) ")" | denotes max { (f)_iat(x))Absolute value of "", like (f)_ibt(x) "represents a pair function f_ibt(x) Second derivative, max { (f)_ibt(x) -) "(denotes (f)_ibt(x) "of, | max { (f)_ibt(x) ")" | denotes max { (f)_ibt(x) Absolute value of "); (f)_ict(x) "represents a pair function f_ict(x) Second derivative, max { (f)_ict(x) -) "(denotes (f)_ict(x) "of, | max { (f)_ict(x) ")" | denotes max { (f)_ict(x) Absolute value of "").

If | max { (f)_iat(x))″}|+|max{(f_ibt(x))″}|+|max{(f_ict(x) ")", | 0, then P₁＝P₂＝P₃＝1/3，

Of course if there are only two main parameters, then P₁＝P₂＝1/2，

If there is only one main parameter, then there is no need for the main parameter normalization curve merging through this step.

Step eight: threshold range is calculated

Normalizing curve merging function f to main parameters of equipment i_it(x) And solving an upper limit and a lower limit, wherein the upper limit and the lower limit are boundary thresholds of the device i for the medium-voltage electric mass.

Step nine: evaluation of

When a new voltage and current frequency in the power grid occurs at the next moment, calculating a main parameter normalization curve merging function f of each device by using the fitting formula_it(x) And if the calculation results are all within the threshold range of the step eight, judging that the medium-voltage quality is qualified, and otherwise, judging that the medium-voltage quality is unqualified.

Claims (8)

1. A method for evaluating reliability effect of medium voltage power supply is characterized by comprising the following steps:

the method comprises the following steps: data collection

Collecting data separately for each device in the grid and the grid;

step two: adjusting grid parameters

Respectively adjusting the grid voltage, the grid current and the grid frequency of a power grid to stop all electric equipment in the power grid from working, and simultaneously recording all relevant parameters;

step three: voltage current synthesis

Synthesizing the recorded voltage and current;

step four: fitting of curves

By a resultant voltage u_tSynthesized current I_tGrid frequency f_tMain performance parameter S of ith equipment_iat、S_ibt、S_ictRespectively fitting to respectively obtain main performance parameter curves of the ith equipment;

step five: selecting a main curve

Obtaining derivatives of three curves of the same performance parameter of the same equipment, taking the absolute value of an extreme value, and selecting the curve corresponding to the maximum absolute value of the extreme value as a main curve;

step six: curve normalization

Performing curve normalization on the main curve corresponding to each performance parameter of each device;

step seven: merging the main parameter normalization curves;

step eight: calculating a threshold range;

step nine: and (6) evaluating.

2. The method of claim 1 for evaluating the reliability effect of a medium voltage power supply, wherein: the first step comprises the following steps of,

for the grid, the following parameters were collected: network voltage u_1t、u_2t、u_3tGrid current I_1t、I_2t、I_3tFrequency of the grid f_tWherein u is_1t、u_2t、u_3tThree voltages representing three-phase alternating current, I_1t、I_2t、I_3tRepresenting three currents of three-phase alternating current, t being time, i.e. u_1tRepresenting the voltage of the first phase at time t, u_2tRepresenting the voltage of the second phase, u, at time t_3tRepresents the voltage of the third phase at time t; i is_1tRepresenting the current of the first phase at time t, I_2tIndicates the second time of tCurrent of phase, I_3tRepresenting the current of the third phase at time t; f. of_tRepresenting the frequency of the grid at time t,

for each device in the grid, the following parameters are collected: s_1at、S_1bt、S_1ct、S_2at、S_2bt、S_2ct、S_3at、S_3bt、S_3ct、…S_iat、S_ibt、S_ictWherein i represents the serial number of the equipment, and if n electric equipment in the power grid are provided, the value range of i is [1, n]，S_iat、S_ibt、S_ictRespectively representing the main performance index of the ith equipment at the time t, wherein S_iatThe value of (A) must be significant, S_ibtAnd S_ictThe value of (a) is not necessarily significant, and when not significant, it is-1,

the main parameters of the equipment are the main parameters of the equipment during normal operation;

in the step, t is time, the interval between t and t +1 is 1 second, and when the value of t is less than or equal to 3000, sampling is continuously carried out; and when the value of t is more than 3000 and all the devices in the power grid continuously and normally work, executing the subsequent steps besides sampling in each cycle.

3. A method of assessing the reliability effectiveness of a medium voltage power supply as claimed in claim 2, characterized by: the third step includes the following steps,

the resultant voltage u is calculated by the following formula_t

The resultant current I is calculated by the following formula_t

4. A method of assessing the reliability effectiveness of a medium voltage power supply as claimed in claim 3, characterized by: the fifth step includes the following steps,

step five, different performance parameters are respectively carried out,

when the same value appears, the main curve is selected according to the priority of voltage > current > frequency.

5. The method of claim 4 for evaluating the reliability effect of a medium voltage power supply, wherein: the sixth step includes the following contents that,

let g_iat(x) Is the main parameter S of a device with sequence number i_iatWherein x is one of voltage u, current I, and frequency f, the specific determination method is obtained according to the calculation of step five,

then the curve f is normalized_iat(x) The calculation method of (2) is as follows:

where min { g }_iat(x) Is g_iat(x) Max { g } of_iat(x) Is g_iat(x) The maximum value of (a) is,

similarly, the main parameter S of the device with serial number i can be obtained_ibtNormalized curve f of_ibt(x)，

Similarly, a normalized curve of all the main parameters of all the devices can be obtained.

6. The method of claim 5 for evaluating the reliability effect of a medium voltage power supply, wherein: the seventh step includes the following steps,

solving a main parameter normalization curve merging function f of the equipment i by using the following formula_it(x)

f_it(x)＝P₁f_iat(x)+P₂f_ibt(x)+P₃f_ict(x)

Wherein f is_iat(x)、f_ibt(x) And f_ict(x) Is the step ofSixthly, calculating a main parameter normalization curve of the equipment i, wherein if the equipment i does not have corresponding main parameters, the corresponding item number is directly omitted,

P₁、P₂and P₃Is a coefficient, and the three values can be determined by any one of the following methods:

the first method is as follows: external giving

If the staff member can determine the weight relationship of several main parameters, the weight proportion of three parameters can be directly and externally given,

if the staff can not determine the weight relation of several parameters, a fixed value can be directly used, and the typical value given in the application is P₁：P₂：P₃＝5:3:2

The second method comprises the following steps: determining a weight ratio based on the values of several primary parameters

When | max { (f)_iat(x))″}|+|max{(f_ibt(x))″}|+|max{(f_ict(x) ")" | is not equal to 0, P is₁、P₂And P₃Is calculated by the following formula

Wherein (f)_iat(x) "represents a pair function f_iat(x) Second derivative, max { (f)_iat(x) -) "(denotes (f)_iat(x) "of, | max { (f)_iat(x) ")" | denotes max { (f)_iat(x) Absolute value of ""), analogous to (f)_ibt(x) "represents a pair function f_ibt(x) Second derivative, max { (f)_ibt(x) -) "(denotes (f)_ibt(x) Maximum of) ")The value, | max { (f)_ibt(x) ")" | denotes max { (f)_ibt(x) Absolute value of "); (f)_ict(x) "represents a pair function f_ict(x) Second derivative, max { (f)_ict(x) -) "(denotes (f)_ict(x) "of, | max { (f)_ict(x) ")" | denotes max { (f)_ict(x) The absolute value of ")" (ii) the absolute value of,

if | max { (f)_iat(x))″}|+|max{(f_ibt(x))″}|+|max{(f_ict(x) ")", | 0, then P₁＝P₂＝P₃＝1/3，

Of course if there are only two main parameters, then P₁＝P₂＝1/2，

If there is only one main parameter, then there is no need for the main parameter normalization curve merging through this step.

7. The method of claim 6 for evaluating the reliability effect of a medium voltage power supply, wherein: the step eight includes the following contents that,

normalizing curve merging function f to main parameters of equipment i_it(x) And solving an upper limit and a lower limit, wherein the upper limit and the lower limit are boundary thresholds of the device i for the medium-voltage electric mass.

8. The method of claim 7 for evaluating the reliability effect of a medium voltage power supply, wherein: the step nine includes the following contents that,

when a new voltage and current frequency in the power grid occurs at the next moment, calculating a main parameter normalization curve merging function f of each device by using the fitting formula_it(x) And if the calculation results are all within the threshold range of the step eight, judging that the medium-voltage quality is qualified, and otherwise, judging that the medium-voltage quality is unqualified.