JPH09215179A - Method for deciding limitation of load on line - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control the conduction current on a line just to a maximum level within thermal limit while taking account of weather conditions by delivering a feeder interruption command when a predicted temperature of the line after a predetermined time later is increasing over a decision level or when an estipated temperature exceeds the decision level for a predetermined time or longer continuously. SOLUTION: When a temperature θn+j1 of a line after a predetermined time later predicted while taking account of weather conditions has increasing trend and a decision is made that the highest allowable temperature θL is reached surely (decision of event 2), or when a decision is made that a temperature θn . of the line estimated while taking account of weather conditions has exceeded a dangerous level θH for a predetermined time or longer (decision of event 1), a feeder interruption command is delivered by determining that the load must be limited with no delay through a so-called predictive decision method. According to the method, the conduction current on a line can be limited just to a maximum level within thermal limit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric line load limit determination method for determining whether or not there is a need for load limit based on the thermal limit of an electric line having a stranded wire structure such as an overhead transmission line.

[0002]

2. Description of the Related Art Conventionally, in this kind of electric line, since it is not possible to detect the electric wire temperature itself and directly grasp the thermal limit thereof, in general, the energizing current of the electric line is detected,
Whether or not there is a need for load limitation is determined based on the magnitude of the energizing current, and the result of this determination selectively cuts off the power supply to each load feeder of the transmission line to implement the load limitation.

In this case, the temperature of the electric wire is
It is necessary to limit the load based on a certain current value because the amount of current that can be transmitted (the amount of current flowing) varies depending on the weather conditions such as solar radiation, for example, even when the current is the same, the amount of current that can be transmitted is different in summer and winter. If the reference current value is set assuming a harsh summer, the load limit will be applied at a current amount well before reaching the limit in winter, and effective use of the electric line can be achieved only by determining the presence or absence of There is no inconvenience.

On the other hand, the applicant of the present application filed Japanese Patent Application No. 7-67.
As described in the specification and drawings attached to the application for No. 09 application, the temperature monitoring method of the electric line has already been invented to estimate the electric wire temperature of this kind of electric line in consideration of the energizing current and the meteorological condition,
I am applying.

In the temperature monitoring method of the above-mentioned application, the estimated value of the internal temperature of the electric wire of the monitoring line is calculated from the energization current of the electric line to be monitored (hereinafter referred to as the monitoring line), and the surrounding temperature such as temperature and insolation intensity is calculated. The calculated value of the wire surface temperature of the monitoring line is calculated from the meteorological conditions, and the temperature difference between the inside and the wire surface of the monitoring line is calculated from the difference between the two estimated values. The temperature difference is calculated by adding the temperature difference.

In this case, when abnormal overheating due to overcurrent occurs, the amount of heat generated inside the electric wire becomes larger than the amount of heat generated on the electric wire surface, and the electric wire temperature is changed from the temperature obtained by adding the temperature difference to the set value of the electric wire surface temperature. It can be estimated without actual measurement.

Since the electric wire temperature is estimated in consideration of the current flowing through the electric line and the weather condition, the temperature of the monitoring line is monitored in consideration of the weather condition.

[0008]

In the case of the conventional load limiting determination method for this kind of electric line, even if the electric wire temperature is estimated in consideration of the weather condition by the temperature monitoring method of the above-mentioned application, the present condition of the electric line is Since only the temperature of the wire is estimated, it is not judged that the load must be restricted until the wire temperature actually exceeds the temperature at which the load must be restricted, and vice versa. Is caused, and as a result, the excess or deficiency of the load limitation is frequently repeated, which causes a so-called control hunting phenomenon.

Moreover, it is not easy to set the reference level for judgment, and if this level is set low, the load can be surely limited, but the electric current of the limit capacity actually allowed is passed through the electric line to transmit power. There are some problems that cannot be implemented.

According to the present invention, whether or not there is a need for load limitation is determined without delay so that the current flowing through the electric line can be controlled from the thermal limit to the maximum allowable current without deficiency in consideration of weather conditions. This is an issue.

[0011]

In order to solve the above-mentioned problems, in the load-limit judging method of the electric line of the present invention,
The judgment level for load limitation of the electric line is set to a dangerous temperature higher than the maximum allowable temperature of the electric line, and the current temperature of the electric line is periodically estimated from the current flowing current of the electric line and the meteorological condition, and a fixed time is also set. When the temperature after is predicted, and the predicted temperature after a certain period of time has risen above the judgment level in a continuous trend of multiple times, or when the estimated temperature of the electric line continuously exceeds the judgment level for a predetermined time or longer , It determines that the load on the electric line needs to be limited and outputs a feeder cutoff command.

Therefore, the predicted temperature after a certain period of time in consideration of the weather conditions of the electric line shows a continuous upward trend, and when it is determined that the dangerous temperature will be reached without fail, or when the electric wire in consideration of the weather conditions is taken into consideration. When it is judged that the estimated temperature of the road is higher than the dangerous temperature for a certain period of time or more, it is judged by a so-called predictive judgment method that there is a need for load limitation without delay, and a feeder cutoff command is output and the electric line The energizing current is limited to the proper amount.

To further improve the determination accuracy,
Set the 1st stage judgment level of the load limit of the electric line to the maximum allowable short-time use temperature of the electric line, and set the 2nd stage judgment level of the load limit of the electric line to a dangerous temperature higher than the maximum allowable temperature for short time use. , The current temperature of the electric line is estimated periodically from the current flowing current of the electric line and the weather condition, and the temperature after a certain time is predicted, and the predicted temperature after the certain time is continuously increasing several times. When the estimated temperature of the electric line becomes equal to or higher than the second stage determination level, when the estimated temperature of the electric line continuously becomes equal to or higher than the second stage determination level for a first predetermined time or longer,
When the first stage judgment level is continuously exceeded for the second predetermined time longer than the predetermined time, it is determined that the load limitation of the electric line is necessary and the feeder cutoff command is output.

Therefore, in this case, whether or not there is a need for load limitation is determined by setting the first stage determination level set to the maximum allowable short-time use temperature of the electric line and the dangerous temperature of the electric line higher than this level. The determination is performed by providing two determination levels including the determined second determination level.

The two-stage judgment shows that the predicted temperature after a certain period of time in consideration of the weather condition of the electric line shows a continuous upward trend, and if it is judged that the dangerous temperature will be certainly reached as it is, the weather condition Not only when it is determined that the estimated temperature of the electric line in consideration of the condition is equal to or higher than the dangerous temperature for the first predetermined time or more, and further, the estimated temperature of the electric line in consideration of the weather condition is the second predetermined time. Even if the maximum allowable temperature for a short time is reached and the dangerous temperature may be reached soon, it is determined that there is a need to limit the load, the so-called predictive determination method does not delay, and extremely accurately,
A feeder cutoff command is output by determining whether or not there is a need to limit the load, and the current flowing through the electric line is limited without excess or deficiency.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Regarding one embodiment of the present invention,
Description will be made with reference to FIGS. 1 to 4. First, the estimation and prediction of the temperature of the electric line (electric wire temperature) in consideration of the energizing current and the weather conditions will be described.

The estimation and prediction of the electric wire temperature is performed by estimating the present electric wire temperature as described below, and further presuming that the present event (current, solar radiation, temperature, etc.) continues until a predetermined time J1 elapses. To do.

Estimation of Current Temperature In general, the amount of heat generated in an object in a unit time dt (generated heat amount) is the sum of the amount of heat that raises the object temperature by the unit temperature dθ and the amount of heat released to the outside, and The time change of temperature is performed by using the heat quantity (heat quantity) Q [KW] generated in the object within a unit time, the heat capacity C [KW seconds / ° C] of the object and the heat dissipation coefficient H [KW / ° C] as parameters. Θ
When the temperature is [° C.] and the elapsed time is t [seconds], the heat transfer equation <1> of the following equation 1 is given.

[0019]

[Equation 1] Q · dt = C · dθ + H · θ · dt (1)

The heat transfer formula <1> is Q / H = θma
If x, the general solution θ is expressed by the following equation <2>.

[0021]

## EQU00002 ## .theta. =. Theta.max .multidot. {1-exp (-t / T)} ... <2>

As is clear from the equation <2>, the temperature θ of the object is determined by a functional equation in which the rising saturation temperature θmax (= Q / H) and the time constant T (= C / H) are constants. t
Changes exponentially with respect to.

The electric wire temperature of the stranded wire electric line also changes with a constant time constant in accordance with the exponential function characteristic of the expression <2> due to the change in the amount of heat, and the electric wire temperature with respect to the temperature θ of the expression <2>. It can be estimated from the temperature calculation of the simple exponential function of.

In this case, if the change in the wire temperature based on the energizing current and the change in the wire temperature based on the weather conditions are individually predicted and added together, the current wire temperature can be estimated in consideration of the energizing current and the weather conditions. You can do it.

Then, the electric wire temperature based on the energized current can be estimated by the calculation of the following exponential function expression <3>.

[0026]

Equation 3] θin = {Δθimax (In / Imax ) k -θi n-1} · [1-exp {- (t n -t n-1) / Ti}] + θi n-1 = (Δθi-θi n _{-1) · {1-exp (} -Δt / Ti)} + θi n-1 ... <3> tn in the formula, tn _-1, ... a respective value of Hatsugi. t _n , t _n-1 : n-th (current), _n-1 (previous) computation time [minutes] Δt: computation (sampling / control) time interval (= t _{n
-T n-1) θi n,} θi n-1: the time t _n, t _n-1 of the estimated temperature [° C.] an In: Detection value of the current sensor at time t _n (measured line current value)
[A] Imax: Reference value of energizing current (nominal allowable current value) [A] Δθimax: Saturation temperature rise value at Imax [° C] Ti: Time constant of temperature change due to energizing current change k: Current conversion index

The exponent k of (In / Imax) in the formula
Is the current conversion index, which is almost 2 for electric lines.

Further, in the above-mentioned application, Δθmax, θ
Although the electric wire temperature is obtained with in as the amount of heat, since the temperature and the amount of heat are in a proportional relationship, the calculation formula for this amount of heat is substantially the same as the exponential function formula <3>.

Next, when temperature and solar radiation intensity are considered as meteorological conditions, the wire temperature θa based on the temperature and solar radiation intensity
n and θsn are the same as in Exponential formula <3>
It can be estimated by the calculation of exponential function equations <4> and <5>.

[0030]

## EQU00004 ## .theta.an = (An-.theta.an _-1 ) .multidot. {1-exp (-. DELTA.t / Ta)} +. Theta.an _-1 ... <4>

[0031]

Equation 5] θsn = (Δθsmax · Sn-θs n-1) · [1-exp {- (t n -t n-1) / Ts}] + θs n-1 = (Δθs-θs n-1) · {1-exp (-Δt / Ts )} + θs n-1 ... <5> both exponential formula <4> is a θan _-1, θsn _-1, ... the values of Hatsugi of <5>. θan, θan ₋₁ : Estimated temperature [° C] based on air temperature at times tn and tn ₋₁ San, San ₋₁ : Estimated temperature [° C] based on solar radiation at times tn and tn ₋₁ An: Measured temperature at time tn [ ℃] Sn: Measured solar radiation intensity at time tn [KW / m ² ] Δθsmax: Solar radiation intensity saturation temperature rise value Ta: Temperature change time constant due to temperature change Ts: Temperature change time constant due to solar radiation intensity change

Then, by adding the respective wire temperatures θin, θan, and θsn by the following equation (6), the wire temperature (estimated temperature) θn at time tn in consideration of the energizing current and the weather condition is obtained.

[0033]

[Equation 6] θn = θin + θan + θsn… <6>

Prediction of temperature after a certain time From the present time (time tn), for example, a certain time J of about 1 to several minutes
Wire temperature (predicted temperature) θi _{(n + J1)} , θa based on the energizing current, temperature, and solar radiation intensity at time tn _{+ J1} after 1
_{(n + J1)} , θs _{(n + J1)} are parameters Δθimax, (In / Imax) ² , Ti of the exponential function formula <3> and parameters An, Ta, ΔSmax of the exponential function formulas <4>, <5>.・ S
Fixing n and Ts to the current values, tn in the formula is tn _{+ J1} ,
We can predict tn- ₁ as tn _{-1 + J1} .

Further, the predicted temperatures θi _{(n + J1)} , θ
a _{(n + J1)} and θs _{(n + J1)} are estimated θin and θa of the calculation formula <6>
By substituting for n and θ sn, it is possible to obtain the predicted temperature θ n _{+ J1} after the fixed time J1 in consideration of the energization current and the weather condition.

Then, the set time interval (for example, 0.
5 minutes), the calculations of the equations <3> to <6> are repeated, and the current estimated temperature at every moment and the predicted temperature after a fixed time from that are obtained.

Next, determination of whether or not there is a need for load limitation based on the estimated and predicted wire temperature will be described.

In this embodiment, in order to make a highly accurate judgment, the first stage judgment level and the second stage judgment level are set as the load limit judgment levels, and the load limit is required by the two-stage judgment described below. Determine the presence or absence of sex.

When the electric line is a transmission line, the first stage determination level is set to the maximum allowable short-time use temperature (short-time use level) θ _L of the transmission line, and the second stage determination level is the first level.
Set to a dangerous temperature θ _H that is higher than the stage judgment level.

Further, as conditions for determining that the load limitation is necessary, first, second, and third main conditions and sub-conditions described below are set.

First and second main conditions for immediate shutoff using the second stage judgment level (dangerous temperature θ _H ) as a judgment criterion (i) First main condition (judgment condition for event 1) This condition is Estimated temperatures at times tn _-2 , tn _-1 , and tn three times in succession are θn _-2 , θn _-1 , and θn, and predicted temperatures after respective constant times J1 are θn _{-2 + J1} and θn _{-1 + J1.} , Θn
_{Assuming + J1} , this three consecutive predicted temperatures θ
n _{−2 + J1} , θn _{−1 + J1} and θn _{+ J1} are as shown in FIG.
An upward trend (θn _{-2 + J1} <θn _{-1 + J1} <θn _{+ J1} ) is shown, and both are in the second stage judgment level (hazardous temperature θ _H ).
That is all.

(Ii) Second main condition (condition for backing up the judgment condition of event 1) As shown in FIG. 3, this condition is such that the estimated temperature rises to the second-step judgment level at time tx, for example, and thereafter. The estimated temperature is maintained at or above the second-stage determination level, and from time tx, for example, 1 to
Time tn _-2 (T after the lapse of a certain time J2 of about several minutes)
1n _-2 hours later), tn _-1 (T1n _-1 hour later), tn (T1n
After three hours, the estimated temperatures θn ₋₂ , θn ₋₁ , and θn for all three times are equal to or higher than the second-stage determination level, in other words, equal to or higher than the second-stage determination level (dangerous temperature θ _H ). That is, the state continues for a first predetermined time, that is, a predetermined time J2 or more.

Incidentally, in this case is not a condition is to show the estimated temperature rise between them, corresponding to the condition as long as the way downward trend indicates danger temperature theta _H or more as in Figure 3.

Third Main Condition Using Judgment Level of 1st Stage (Maximum Allowable Temperature θ _L ) (Judgment Condition of Event 2) This condition has a margin more than the case of the first and second main conditions. As shown in FIG. 4, the estimated temperature rises to the first stage determination level (maximum allowable temperature θ _L ) and then the estimated temperature is maintained at the first stage determination level or higher as shown in FIG. , Time tn _-2 (T2n _-2 hours later), tn _-1 (T2n _-1 hour later), after a lapse of a predetermined time J3 as a second predetermined time longer than the predetermined time J2 from the time ty.
Estimated temperatures θn _-2 , θ three times consecutively after tn (after T2n time)
Both n ₋₁ and θn are equal to or higher than the first stage determination level, in other words, the state of the first stage determination level (maximum allowable temperature θ _L ) or higher continues for a certain time J3 or longer.

Sub-Condition Based on Excessive Energizing Current (Evaluation Condition for Current Emergency Value) This condition is the energizing current In at the time tn (current) of the electric line.
Is an emergency value Im · βmax or more.

Im is a reference current value for each wire,
βmax is a wire emergency value coefficient larger than the minimum current guarantee coefficient βmin of the electric line, and both are constant values specific to the electric line.

This sub-condition is that the above-mentioned constant time J of the above-mentioned electric line is set in a situation such as winter when the temperature is low and the solar radiation intensity is weak.
The predicted temperature after 1 becomes low, and if the judgment is made only from the predicted temperature and the estimated temperature, there is a possibility that load limiting may not be performed even if an excessive current far exceeding the allowable current of the electric line flows. Therefore, it is provided to avoid this situation.

Next, regarding the implementation structure of this determination method,
This will be described with reference to FIG. In FIG. 1, the temperature determination unit 1 performs the determination based on the first, second, and third main conditions and the determination of the next first and second resets.

(I) First Reset This reset is to release the load limitation based on the first and second main conditions. The condition is that the predicted temperature is once the second stage judgment level (danger temperature θ Even if the temperature rises to _H ), the predicted temperature θn after a certain time J1 at the time tn
_{+ J1} is lower than the second-stage judgment level.

If the reset condition is satisfied, it is predicted that the electric wire temperature will certainly be lower than the dangerous temperature θ _H without load limitation when a certain time J1 has passed from the present (tn). , Reset the judgment output of the second main condition to prevent useless load limitation.

(2) Second reset This reset is to release the load limitation based on the third main condition. The condition is that the estimated temperature is once the first stage judgment level (maximum allowable temperature θ _L ). Even after rising to
This means that the predicted temperature θn ₊ J1 after the constant time J1 at the time tn becomes lower than the first-stage determination level.

If this reset condition is satisfied,
When a certain time J1 has elapsed from the current time (tn), it is predicted that the wire temperature will certainly be lower than the maximum allowable temperature θ _L without load limitation, so the judgment output of the third main condition is reset and wasteful. Prevent load shedding.

Then, if the first, second, and third main conditions are satisfied, a logical 1 (hereinafter referred to as "1") indicating that load limitation is required from each of the AND gates 2, 3, and 4 of the temperature determination unit 1. ) Is output, and if it corresponds to the first and second resets, the temperature determination unit 1 outputs a reset signal of "1". Further, the current determination unit 5 performs the determination based on the sub-condition and the determination of the next third reset.

This third reset is to release the load limitation based on the sub-condition, and the condition is that the conduction current In
Is 1.1 times (In · 1.1) smaller than Im · βmax, and the conduction current In is sufficiently smaller than the emergency value.

If the sub-condition, the third reset, is satisfied, the current judgment unit 5 resets the judgment signal of "1", which is the same as the judgment signals of the AND gates 2 to 4, and the first and second reset conditions. The reset signal of "1" similar to the signal is output.

Further, each judgment signal and the reset signal are supplied to the limit command section 6, the judgment signals of the AND gates 2 and 3 are latched in the signal holding section 8 via the OR gate 7, and the reset signal of the first reset condition is set. The signal is supplied to the output OR gate 9 via the signal holding unit 8 until the signal holding unit 8 is reset.

Similarly, the judgment signal of the AND gate 4 is latched by the signal holding unit 10 and given to the OR gate 9 via the signal holding unit 10 until the signal holding unit 10 is reset by the reset signal of the second reset condition. To be

The determination signal of the current determination unit 5 is latched by the signal holding unit 11, and the signal holding unit 11 is reset until the signal holding unit 11 is reset by the reset signal of the current determination unit 5.
Is given to the OR gate 9.

Therefore, the OR gate 9 of the limit command unit 6
Outputs the feeder cutoff command of "1" until it is canceled by the reset signal when it is predicted that the load limitation is required, when either the main condition or the sub condition is satisfied.

Based on this cutoff command, the load control circuit 12
Shuts off each load feeder of the system in order according to the set order.

Therefore, in the case of this embodiment, the second stage determination level (dangerous temperature θ _H ) at which the load feeder needs to be immediately shut off by the determination of the first main condition based on the predicted temperature after a fixed time. Whether or not the load limitation is necessary is predictively determined based on the reference, and a delay in the determination when the energized current rapidly increases to reach the dangerous temperature within a short time is prevented.

At this time, when the temperature of the electric line is accurately estimated and predicted in consideration of meteorological conditions, and the predicted temperature tends to increase three times, that is, a plurality of times consecutively exceeds the second-stage judgment level. Since it is determined that the load limitation is necessary only in the above case, fluctuations due to transient fluctuations, disturbances, etc. can be eliminated and highly accurate judgment can be performed.

When the estimated temperature (current temperature) continuously reaches the second-stage judgment level for a certain period of time or longer and has already reached the dangerous temperature, the load is immediately limited by the judgment of the second main condition. It is judged necessary.

Furthermore, when the estimated temperature continues to be above the first stage judgment level (maximum allowable temperature θ _L ) for a certain period of time or longer and eventually reaches a dangerous temperature, the load is determined by the judgment of the third main condition. Since it is determined that the restriction is necessary, the prediction determination can be performed with higher accuracy than the so-called two-step determination.

In the judgment of the second and third main conditions, the condition is that the estimated temperature is higher than or equal to the judgment levels of the first and second stages a plurality of times (three times) in succession. Of course, it is possible to eliminate the influence of disturbance and the like.

Therefore, the so-called two-step judgment based on the first and second-step judgment levels is used to make a predictive judgment which has not been conventionally made, thereby making it possible to accurately judge whether there is a need for load limitation without delay. Based on this determination, the load feeder can be shut off without excess or deficiency, and the amount of current flowing through the electric line can be limited so that the temperature becomes the maximum temperature allowed in consideration of weather conditions.

Moreover, when the amount of the energized current becomes abnormally large, the load feeder is shut off because it is determined that the load limitation is necessary even by the determination of the sub-condition, so that the accuracy of determination and control is further improved.

By the way, in order to simplify the judgment, etc., the second stage judgment level (the dangerous temperature θ
It is also possible to determine whether the load limitation is present or absent by performing only the determination of the first and second main conditions based on _H ).

Further, the wire temperature may be estimated by the same method as that of the above-mentioned application. At this time, if the influence of wind is added as a weather condition, the estimation can be performed with higher accuracy. Further, the first stage determination level, the second stage determination level, each fixed time period, etc. may be set according to the electric line or the like.

[0070]

The present invention has the following effects. First, in the case of claim 1, the predicted temperature after a certain time in consideration of the weather conditions of the electric line shows a continuous rising tendency,
If it is determined that the dangerous temperature will be reached without fail as it is, or if it is determined that the estimated temperature of the electric line in consideration of weather conditions has been above the dangerous temperature for a certain period of time,
A so-called predictive determination method can be used to output a feeder cutoff command when it is determined that the load must be limited without delay, and the conduction current of the electrical line must be limited to the maximum capacity within the thermal limit without excess or deficiency. You can

According to the second aspect of the present invention, whether or not it is necessary to limit the load is determined by the first stage judgment level set to the maximum allowable short-time use temperature of the electric line and the dangerous temperature of the electric line higher than this level. The determination is performed by providing two determination levels with the second determination level set to.

The two-stage judgment shows that the predicted temperature after a certain period of time in consideration of the weather conditions of the electric line shows a continuous upward trend, and if it is judged that the dangerous temperature will be certainly reached as it is, the weather conditions will be changed. Not only when it is determined that the estimated temperature of the considered electric line is equal to or higher than the dangerous temperature for the first predetermined time or longer, and further, the estimated temperature of the electric wire temperature in consideration of the weather condition is short for the second predetermined time or longer. Even when the maximum allowable temperature for time use is reached and the dangerous temperature may be reached soon, it is determined that load limitation is necessary, and the predictive determination method does not delay and extremely accurate load reduction is necessary. It is possible to output the feeder cutoff command by determining the presence or absence of the current, and it is possible to more accurately limit the current flowing through the electric line without excess or deficiency.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is an explanatory diagram of the change over time of the electric wire temperature for explaining the determination of the first main condition of FIG.

FIG. 3 is an explanatory diagram of the change over time of the electric wire temperature for explaining the determination of the second main condition of FIG. 1.

FIG. 4 is an explanatory diagram of the change over time of the electric wire temperature for explaining the determination of the third main condition of FIG. 1.

[Explanation of symbols]

θn ₋₂ , θn ₋₁ , θn Estimated temperature θn _{−2 + J1} , θn _{−1 + J1} , θn _{+ J1} Predicted temperature θ _L 1st stage judgment level (maximum allowable temperature) θ _H 2nd stage judgment level (hazardous temperature )

Claims (2)

[Claims] 1. A judgment level of load limitation of an electric line is set to a dangerous temperature higher than a maximum allowable temperature of the electric line, and the current of the electric line is periodically determined from a current flowing current and a weather condition of the electric line. When the temperature predicted for a certain period of time is predicted and the predicted temperature after the certain period of time becomes higher than or equal to the determination level with a tendency to continuously increase for a plurality of times, or the estimated temperature of the electric line continues for a predetermined period of time or more. The load limit determination method for an electric line, which is characterized in that it is determined that the load limit of the electric line is required and a feeder cutoff command is output when the load level exceeds the determination level. 2. A first stage judgment level of load limitation of an electric line is set to a maximum allowable short-time use temperature of the electric line, and a second stage judgment level of load limitation of the electric line is set to the maximum short-time use allowable temperature. Set a dangerous temperature higher than the temperature, periodically estimate the current temperature of the electric line from the current flowing current and weather conditions of the electric line, and predict the temperature after a certain time, When the predicted temperature continuously rises a plurality of times and becomes equal to or higher than the second stage determination level, or when the estimated temperature of the electric line continuously becomes equal to or higher than the second stage determination level for a first predetermined time or more, or When the estimated temperature of the electric line continuously becomes equal to or higher than the first stage judgment level for a second predetermined time longer than the first predetermined time, it is determined that the load limitation of the electric line is necessary. It is special to output the feeder cutoff command. The method of determining the load limit of the electric line to be collected.