JPH0572168B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an overcurrent relay having inverse timing characteristics used for overload protection.

[Technical background of the invention]

In recent years, various proposals have been made to protect motors and transformers from overload using electronic circuits. For example, the electronic overload protection device proposed in Japanese Patent Application Laid-Open No. 1728/1983 uses the square of the current i of the device i ² for the purpose of accurately simulating the thermal behavior of the device to be protected.
In this method, the main circuit is disconnected if the integral result, ∫ ^tn ₀ i ² dt, becomes larger than the allowable value determined by the equipment.

As the inventor explains using Figure 3 of the above-mentioned publication, when a relatively large overcurrent continues for a short time and then changes to near the rated current, the conventional method This comparison shows that it is an effective method.

[Problems with background technology]

According to the above proposal, since the integral calculation is started after i > i _o , the magnitude of the steady-state current that would have been heating the equipment before overload is reflected in the integral calculation result. It can be said that it has not been taken into account.

In other words, in general, the smaller the load on equipment during steady state, the lower the
Despite having the characteristic of tolerating large short-term overloads, the proposed method performs protective operation in the same operating time regardless of whether the operating state before overload is no load or rated load. This is a serious problem when implementing overload protection.

[Purpose of the invention]

The present invention has been made to solve the above-mentioned problems, and the operating characteristics change in the same manner as the equipment characteristics depending on the magnitude of the steady-state load, and not only enables more accurate overload characteristics, The object of the present invention is to provide an overcurrent relay that prevents equipment from being turned on again depending on the degree of overload of the equipment, and that improves maintenance and testability of built-in elements.

[Summary of the Invention] The present invention provides an overcurrent relay whose operating characteristics take into account the current value at a steady load before an overload state occurs, and for this purpose, a value KI ² proportional to the input current I is provided. K′( ^{KI 2} ₋
Calculate S _o-1 ) + S _o-1 , (where K' is a positive constant),
The result of these additions is set as S _o , and by comparing this S _o with an operation judgment level previously held internally, it is determined whether or not to send a trip signal. .

[Embodiments of the invention]

Example 1 An example will be described below with reference to the drawings. FIG. 1 is a block diagram of an embodiment of an overcurrent relay according to the present invention.

In Figure 1, 1 is an amount of electricity proportional to the square of the amount of current I introduced from the power system by a known means.
A first means of calculating KI ² by a known means such as a multiplier, and 2 is the amount of electricity obtained by the first means.
KI ² is introduced and the second means calculates the addition result S _o by the signal processing means shown in FIG. 2, _which will be described later. 3 shows a third means for sending out a tripping signal using the determination means shown in FIG. 3 and described later.

FIG. 2a shows an example of the configuration of the second means in the embodiment of FIG. 1, and the input quantity is an analog electrical quantity.
An analog/digital (A/D) converter that converts KI ² into a digital quantity, 5 reads the electric quantity KI ² converted into a digital quantity, and combines this value with the internally held numerical value S _o-1. , according to the processing procedure shown in the flowchart of Figure 2b,
This is a microcontroller that calculates the addition result S _o and is composed of a microcomputer, etc.

Next, the flowchart shown in FIG. 2b will be explained. First, step 6 is an initialization procedure, which specifically includes a procedure for giving an initial value to the addition result S _o .
Step 7 is a procedure to save the addition result S _o as S _o-1 . Step 8 is a procedure for reading the electric quantity KI ² converted into a digital quantity by the A/D converter.
Step 9 uses the data of KI ² and S _o-1
A procedure for calculating K′ (KI ² −S _o-1 )+S _o-1 , (K′ is a positive constant) and setting the result as S _o is shown below. step
10 shows a procedure for making the addition result S _o the output of the second means.

FIG. 3a shows an example of the configuration of the third means in the embodiment of FIG. 11 reads the input amount S _o and calculates the third value from this value and the internally held numerical value L _T.
This is a microcontroller that determines whether or not to send a tripping signal according to the processing procedure of the flowchart shown in FIG. b, and is composed of a microcomputer or the like.

In the flowchart of Figure 3b, the steps
12 is the procedure to read the input amount S _o . Step 13 is a procedure for determining the magnitude relationship between the read input amount S _o and the planned value L _T . Step 14 is a procedure to block the trip signal. Step 15 is a procedure for sending a trip signal.

Next, the operation of the second means will be explained. It has already been mentioned that the addition result S _o of the second means is calculated by the following equation.

S _o = K′ (KI ² − _{S o-1} ) + S _o-1 …(1) When this is transformed, the following equation (2) is obtained.

S _o −S _o-1 = K′(KI ² −S _o-1 ) …(2) The left side of equation (2) represents the increase/decrease in the addition result S _o in the time (Δt) for one round of processing in the flowchart. ing.

Here, if this time Δt is an extremely short time, equation (2) can be approximated by the following equation.

dS/dt=K'( ^KI2 -S)...(3) Using this approximate expression, how S _o changes when the input current I changes will be explained.

(1) When the input current I changes like a step function. Figure 4a shows the case where the input current changes from zero like a step function. In this case, the function value S is the time at which the change occurs. When t=0, it is expressed as S=KI ² (1−e ^−K ′ ^t ) (4).

That is, it can be said that the function value S asymptotically approaches KI ² with a constant time constant.

The time at which this function value S becomes the planned value L _T can be determined by solving KI ² (1-e ^-K ′ ^t )≧L _T as t≧-1/K′log (1-L _T /KI ² ) It is expressed as

Therefore, the larger the input current I is, the shorter the time it takes for the function value S to reach the expected value L _T .

Figure 4b shows the case where the input current changes from I' in a step function manner, and the function value S in this case is S = (KI ² - K (I′) ² (1−e ^-K ′ ^t )+K(I′) ²
...(5) The function value S in this case is the planned value
In the same way ^, for times when L _{T or} ^more
′) ² ) Under the conditions illustrated here, I>I', K(I') ² <L _T <KI ² , L _T −K(I') ² /K(I ² )−K(I') ² <L Since _T /KI ² holds, −1/K′log(1−L _T −K(I′) ² /KI ² −K(I′)
² ) <-1/K′log(1 −L _T /KI ² ), and therefore the case with a prior current I′ is better than the case with no prior current (as shown in Figure 4a). ), the time for the function value S to reach the expected value L _T is shorter.

(2) If the input current I becomes an intermittent overcurrent,
FIG. 4c shows a case where the input current is intermittently overcurrent, and the function value S in this case changes exponentially as shown. This is clear from the fact that "the function value S follows the input quantity KI ² as a linear function" in FIGS. 4a and 4b, and detailed explanation will be omitted.

As is clear from the figure, when the input current I becomes an intermittently overcurrent, the function value S follows the input with a fixed time constant.

Therefore, in this case, the time required for the function value to reach the expected value L _T is shorter than in the case shown in FIG. 4a.

As described above, the relationship between the input current I and the function value S roughly also holds true for the relationship between the input current I and the addition result _So.

Next, the operation of the third means will be explained. Third
The means compares the addition result S _o obtained by the second means with the scheduled value L _T , and when S _o L _T , a tripping signal is sent. When S _o < L _T , the tripping signal is blocked. It is something.

Here, the value of the planned value L _T is the rated current I _o of the protected equipment
, it is generally chosen that L _T > KI ² _o .

Next, the effects of this embodiment will be explained.

(1) When the input current I changes as shown in Figure 4a, in this case the output of the second means
S _o increases with time like S shown in the figure.
After time t=-1/Klog (1-L _T /KI ² ), S _o becomes larger than L _T , and therefore a trip signal is sent by the third means, and a disconnection signal (not shown) is generated. trip the device and perform overload protection on the equipment.

(2) If the input current I changes as shown in FIG. 4b, in this case the output S _o of the second means
increases with time like S shown in the figure. Time t = 1/K'log(1-L _T -K(I') ² /KI ² -K(I'
) After ² ), S _o becomes larger than L _T , so the third
A tripping signal is sent from the means, and a disconnector (not shown) is tripped to perform overload protection of the equipment.

Figure 5 shows an example of the _operating time characteristics _of ^this overcurrent _relay . This figure shows the characteristics when the constant is selected.

As is clear from the drawings, the relay of the present invention has a slow operation time when the steady load current I' of the protected equipment is small, and
When I' is large, the operating time characteristic is fast, so that overload protection can be performed with higher accuracy than those proposed in the past.

(3) Even when the input current I changes as shown in Figure 4c, the output S _o of the second means increases and decreases with time as shown in the figure, so for example, a short-term overload can occur. Even if a long-term overload continues to occur after an overload has occurred, the history of short-term overloads remains in the addition result S _o , and therefore the relay operating time is reduced to the extent that a long-term overload occurs. The speed increases depending on the value of S _o , which is the addition result of the times at which the It can be said that there is no concern about the occurrence of problems such as delays in load protection.

As explained above, this embodiment has the feature that the operating characteristics change in the same manner as the equipment characteristics, especially depending on the magnitude of the steady-state load, so it has a higher performance than the previously proposed ones. The present invention realizes an overcurrent relay that enables accurate overload protection.

Embodiment 2 FIG. 6 is a block diagram of another embodiment of the overcurrent relay according to the present invention.

In FIG. 6, parts having the same functions as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. 16 introduces the electricity quantity KI ² obtained from the first means, and the seventh
The addition result is obtained by the signal processing means shown in the figure and will be described later.
This is the second means of calculating S _o . And this second
The means includes means for setting the addition result S _o to a predetermined value when an external command signal is received from an external device or a control switch (not shown).

FIG. 7a shows a configuration example of the second means in the embodiment of FIG. 6, and the reference numeral 4 corresponds to FIG. 2a. 17 is the electrical quantity KI ² converted into a digital quantity
Read this value and the internally held number
A micro-processor that calculates the addition result S _o by adding S _o-1 according to the processing procedure in the flowchart described later.
It is a controller and is composed of a microcomputer, etc. Furthermore, it has a function of forcibly setting the addition result S _o to a specific value based on external command conditions.

FIG. 7b is a flowchart explaining the process,
Steps 6, 7, 8, 9 and 10 are similar to FIG. 2b. Step 18 is a procedure to determine the presence or absence of an external command; if there is no external command, steps 7, 8, and
9 and 10, the process is similar to that shown in FIG. 2b. If it is determined in step 18 that there is an external command, the process moves to step 19, where the addition result is forcibly set to S _o =A.

Here, the following values can be considered as the value of A.

A=0 A=K A=L _T +α (α is positive or negative) These specific explanations will be given later.

Next, the effect will be explained. First, if there is no external command, it is obvious that the embodiment is the same as the embodiment shown in FIG. 1, which has already been explained, and the explanation will be omitted. Therefore, the operation when there is an external command will be explained below.

When A=0 In this case, as is clear from the flowchart, the output S _o of the second means becomes S _o =0 as in step 6 for initialization, so in the third means, The S _o L _T condition does not hold, and no tripping signal is sent from the relay.

Case of A=K In this case, the output S _o of the second means becomes S _o =K as is clear from the flowchart. This is equal to the value of the addition result S _o when the rated current I _o is constantly flowing through the relay. Therefore, in general, the S _o L _T condition is not satisfied and no trip signal is sent.

In the case of A=L _T +α In this case, the output S _o of the second means becomes S _o = L _T +α as is clear from the flowchart. If α>0, it means that the value of the addition result S _o is set to a value slightly larger than the operation determination level L _T .

Therefore, the condition of S _o >L _T is satisfied, and a tripping signal is sent by the third means.

When α<0, it means that the value of the addition result S _o is set to a value slightly smaller than the operation determination level L _T .

Therefore, the condition S _o L _T does not hold, and no tripping signal is sent from the relay.

Next, before explaining the effects of this embodiment, the background technology will be explained. That is, in a relay such as the present invention in which the internal state (specifically, the value of S _o ) depends on past input conditions (specifically, the history of input current I) and whose time constant is long, There is a problem in that it takes a long time to test the relay.

Here, the operating time of the relay is measured by measuring the operating time from zero input (called the cold characteristic) as shown in Figure 4a, and the operating time from the presence of input (called the hot characteristic) as shown in Figure 4b. However, in any case, in order to accurately measure the operating time, the internal state of the relay must be steady, that is, the value of the addition result S _o must be almost constant. It is necessary to be familiar with it. For this reason, it is generally necessary to maintain this for a longer time than the internal time constant, with zero input in the former case, and with input (steady value) in the latter case, and then measure the operating time. be. However, as shown in the example in Figure 5,
The internal time constant is usually as large as several hundred seconds,
It is not efficient to require such a long time for one test.

Therefore, the present embodiment is intended to improve such unreasonableness, and since the internal state of the relay can be instantaneously set by an external command, a long time is not required for one test as described above.

For example, in order to measure the operating time from zero input, it is sufficient to give an external command with A=0, then apply a predetermined current I and measure the operating time; In order to measure the operating time, an external command may be given with A=K, and then a predetermined current I may be applied to measure the operating time. Also, by giving an external command as A = L _T + α (α > 0) and checking the operation of the relay at this time, the operating side can be inspected as A = L _T + α (α < 0).
It can be said that the maintainability of the relay is improved compared to the conventional method because it is possible to inspect the non-operating side by giving an external command as follows and confirming that the relay is not operating at this time. Or A=L _T +α(α><
If an external command is given as 0) and then a current of I√L _T /K is applied to measure the operating value and return value, the operating value and return value test can be performed in a very short time.

As explained above, this embodiment is an overcurrent relay for overload protection, which has the features of the embodiment shown in Fig. 1, as well as superior functions that improve maintenance and testing work compared to the conventional one. can be realized.

Embodiment 3 FIG. 8 is a block diagram of another embodiment of the overcurrent relay according to the present invention. Reference numerals 1 and 2 have the same functions as in FIG. 1, and the explanation thereof will be omitted.

20 is a third means, which introduces the addition result S _o obtained by the second means 2 and displays a display for waiting for the shutoff connected to the protected machine to be turned on.

FIG. 9a shows an example of the configuration of the third means in the embodiment of FIG. 8, and 21 reads the input amount S _o and uses this value and the operation judgment levels L _T , L held internally in advance. _I (however, L _T > L _I ), this is a microcontroller that determines whether or not to send a trip signal and display signal according to the processing procedure in the flowchart shown below, and is controlled by a microcomputer, etc. It is composed of Incidentally, 22 is a display device for displaying a standby state for turning on the cutter or disconnector.

FIG. 9b is a flowchart explaining the process,
Step 12 is the same as that shown in FIG. 3, so its explanation will be omitted. Steps 23 and 24 show procedures for determining the magnitude relationship between the read input amount S _o and the operation determination levels L _T and _LI , respectively. Here, step 25 shows a procedure for sending a tripping signal and lighting the indicator 22 in the case of S _o L _T. Also, step 26 is L _T > S _o
In the case of L _I , without sending a trip signal,
A procedure for lighting only the display 22 will be shown. Step 27 shows a procedure for not sending out both the trip signal and the display signal when S _o <L _I.

The difference between this embodiment and the embodiment shown in FIG. 1 already explained is in the configuration of the third means, and in particular, in the display for waiting for the shutoff to be turned on. . That is, in the relationship between the input current I of the relay and the tripping signal, there is no difference between this embodiment and the embodiment shown in FIG. 1 already described. Therefore, the explanation of the effects of this embodiment will be limited to the display, which is the characteristic part.

First, the necessity of waiting for the turn-on of the breaker will be explained using the example shown in FIG. 10.

Figure 10 shows a power outage in the system connected to equipment that is in rated operation for some reason, and as a result, the equipment is disconnected from the system by an undervoltage detection protection device (not shown), and then the power outage is restored. When the device is reinserted into the grid, the starting current generated at this time satisfies the S _o L _T condition, which causes a trip signal to be sent and the circuit breaker (CB) to trip. , indicating that the device has been disconnected from the grid.

Note that during rated operation, the addition result S _o is relatively close to the operation judgment level L _T.
Therefore, if the power is turned on again after being stopped for a short time, the resulting starting current will exceed the overload protection level of the device.

This means that equipment that has been separated from the grid due to overload may attempt to rejoin the grid and fail, causing unnecessary disturbance to the grid and prolonging the outage of the equipment. Undesirable.

In the past, to prevent this problem, it was necessary to wait for a while before turning on the circuit breaker again and wait for the equipment to sufficiently recover from the overload condition. Naturally, the demands are strong.

This embodiment solves the above-mentioned problems, and by clearly informing the operator whether or not the equipment can be re-injected, the probability of re-insertion failure is significantly reduced.

The operation of this embodiment will be explained using the example shown in FIG.

Figure 11 shows that a power outage occurs for some reason in the system connected to equipment that is in rated operation, and as a result, the equipment is temporarily disconnected from the system by an undervoltage detection device (not shown), and then the power outage occurs. It shows that he has recovered.

As is clear from the figure, the addition result S _o gradually decreases from a nearly constant value during rated operation during a power outage. However, when the power is restored, S _o >L _I , and therefore the indicator 22 remains lit. As time passes further, the addition result S _o further gradually decreases until S _o <L _I , and the display 22 turns off. Therefore, the operator turns on the equipment again, and at this time a starting current is generated as described above, but since the addition result S _o is sufficiently smaller than the operation judgment level L _T , S _o does not exceed L _T . Therefore, the equipment will not be cut off again when it is turned on again.

In short, if we compare the magnitude of the value of S _o when the CB is re-closed in Figures 10 and 11, the former is S _o L _T and the latter is S _o L _I (L _T > L _I ), and it can be said that the latter has more margin against the overload limit of the equipment. Therefore, it is generally not possible for a relay to respond to a short-term overcurrent (this takes into account inrush current, etc.) immediately after the circuit breaker (CB) is re-closed and send out a tripping signal again. The latter (this embodiment) cannot occur, and rejoining failure can be made almost impossible.

As described above, in addition to the features of the embodiment shown in FIG. 1, this embodiment can realize an overload protection relay that can prevent failure in re-attachment of equipment.

Embodiment 4 FIG. 12 is a circuit diagram showing the application of another embodiment of the present invention, in which 28 is a bus bar, 29 is a bridge breaker (CB), 30 is a current transformer (CT), and 31 is a circuit diagram of the present invention. In the overcurrent relay according to the embodiment, 32 indicates a device to be protected against overload. Here, the breaker 29 is controlled by a trip signal and a closing signal sent from the overcurrent relay 31. That is, the circuit breaker is opened by a trip signal, and the closing command of a device (not shown) that issues a closing command is invalidated by a closing signal, and the circuit breaker is maintained in an open state.

The configuration of the overcurrent relay 31 is the first one described above.
The electrical quantity KI ² is obtained by the means described above, and the second
The addition result S _o is obtained by the means shown in FIG. 13A, and the tripping signal and closing prevention signal are sent out by the third means shown in FIG. 13a.

Note that since the first means and the second means have already been described, the third means, which is a characteristic part of this embodiment, will be explained.

In Fig. 13a, the input amount S _o is read, and this value and the operation judgment level L _T held internally in advance,
A microcontroller that determines whether to send a tripping signal and a closing prevention signal based on L _C (where L _T >L _C ) according to the processing procedure of the flowchart shown in FIG. 13b, It is composed of a microcomputer, etc.

Step 23 of the flowchart shown in Figure 13b
and 34 indicate a procedure for determining the magnitude relationship between the input amount _So read and the operation determination levels L _T and L _C respectively. Step 35 shows a procedure _for sending out a tripping signal and sending out a closing prevention signal in the case of _SOLT . Also, step 36 is L _T > S _o
Without sending a trip signal in the case of L _C ,
The procedure for sending only the input prevention signal is shown. Furthermore, step 37 shows a procedure in which both the tripping signal and the closing prevention signal are not sent when S _o <L _C .

The difference between this embodiment and the embodiment shown in FIG. 8 already explained is in the configuration of the third procedure, and in particular, the one in FIG. In contrast, the device of this embodiment sends a closing prevention signal directly to the switch or disconnector.

Therefore, the explanation of the effects of this embodiment will be limited to this characteristic part, the input prevention signal.

The necessity of waiting for the injection of the heat cutter has already been explained, and in the embodiment shown in FIG. 8, an improvement method for the case where the heat cutoff is inputted via a human system has been described. This embodiment provides a method for improving the problem in the case where the cutter and disconnector are automatically turned on.

The response of this embodiment can be easily understood by replacing the operation determination level L _I with L _C and the lighting of the display with the sending of the input prevention signal in the response of the embodiment shown in FIG.

That is, to explain this embodiment in the same manner as in FIG. 11, which has already been explained, a power outage occurs in a system connected to equipment that is in rated operation for some reason, and as a result, an undervoltage detection device (not shown) detects This shows how equipment is briefly disconnected from the grid, and then the power outage is restored. At this time, the addition result S _o is a substantially constant value during rated operation, but gradually decreases during a power outage. However, when the power is restored, S _o >L _C , so the closing prevention signal continues to be sent, the closing circuit is interlocked, and the breaker will not close. Next, with the passage of time, the addition result S _o gradually decreases, and eventually S _o < _LC , the closing prevention signal is restored, and the interlock of the closing circuit is released.

As a result, if there is a command to close the breaker,
The breaker will be automatically turned on. Then, due to the above-mentioned shutoff and disconnection, the addition result S _o increases due to the starting current, but S _o
L _T is not reached and therefore no trip signal is sent.

In short, in this embodiment, instead of issuing a warning to the operator as in the embodiment shown in FIG. It can be said that this is the same as the embodiment shown in FIG.

Embodiment 5 FIG. 14 is a circuit diagram showing the application of another embodiment of the present invention, and since the symbols 28, 29, 30 and 32 have the same functions as those already explained in FIG. omitted. 38 is the overcurrent relay of this embodiment according to the present invention, and 39 is a temperature sensor, which measures the ambient temperature of the protected device, the ambient temperature of the contents stored in the protected device, or the ambient temperature of the protected part of the protected device. , and sends the measurement result to the overcurrent relay 38 as a temperature signal θ. The configuration of the overcurrent relay 38 is such that the electrical quantity KI ² is obtained by the first means described above, the addition result S _o is obtained by the second means described above, and the third By this means, the temperature signal θ obtained from the temperature sensor 39 is also used to send out the trip signal.

Here, since the configurations of the first means and the second means have already been described, the third means, which is a characteristic part of this embodiment, will be explained.

FIG. 15a shows an example of the configuration of the third means of the relay shown in FIG. 14, and 40 reads both the input amount S _o and the temperature signal θ, and calculates these values and the operation stored in advance. This is a microcontroller that determines whether or not to send a tripping signal based on the judgment level L _T ,k (k>0) according to the processing procedure shown in the flowchart shown in FIG. Consisted of.

In the flowchart shown in FIG. 15b, step 41 shows the procedure for reading the temperature signal θ, and step 42 shows the procedure for reading the input amount that has been read.
A procedure for determining the magnitude relationship between S _o and θ and the operation determination level L _T is shown. The other steps 12, 14, and 15 are the same as those described above with reference to FIG. 3, so their explanation will be omitted.

Note that the difference between this embodiment and the embodiment shown in FIG. The point is that the reference amount for this is controlled by the temperature signal θ.

That is, in the third means, the addition result S _o obtained in the second means, the temperature signal θ, and the operation judgment level are used.
Using L _T , a trip signal is sent when S _o (L _T −kθ).

When S _o < (L _T −kθ), no trip signal is sent.

It is something. Here, k>0 is selected, and the operation judgment level L _T is generally set to satisfy (L _T −kθ ₁ )>KI ² ₁ when the continuous operating current I ₁ is the ambient temperature θ ₁ of the protected equipment. Select accordingly. Since the value of (L _T −kθ) described above increases as the ambient temperature decreases, it can be said that the lower the ambient temperature, the greater the value of the addition result S _o and the tripping signal will be sent from the relay. Therefore, it can be seen that the overcurrent relay of this embodiment operates with a larger input current I as the ambient temperature is lower, and the operating time becomes slower for the same overcurrent.

For example, when the input current I changes as shown in Figure 4a, the operating time of the relay can be calculated by partially modifying the above equation, t=-1/K'log(1-L _T -kθ/ KI ² ).

Figure 16 shows the operating time characteristics of this overcurrent relay. Here, when the ambient temperature θ = 30°C, the device continuously allows a current of 1.15 times the rated current _Io , and when the ambient temperature θ is 0.8% for every 1℃ decrease
Assuming that overload is allowed, L _T = (1 + 0.008 x 30) x K x (1.15 x I _o ) ² k = 0.008 x K x (1.15 x I _o ) ² 1/K' = 700 This shows the characteristics when seconds (time constant) are selected.

Generally, power equipment can be subjected to a greater load as the ambient temperature decreases.

For example, the following explanation is given in the Overload Operation Guidelines for Power Transformers (Noboru Ooka and Sadao Maekawa, "Transformers", published by Tokyo Denki University Press, 1968). In other words, ``For every 1 degree Celsius drop in the maximum daily temperature of the cooling air from 30 degrees Celsius, the overload can be applied by 0.8% of the rated output.This is independent of the cooling method; In this case, 0.8×(30−
10)=16% can be overloaded. However, even if the cooling air or cooling water is below 0℃,
It is not possible to overload more than . By the way, conventional overload protection overcurrent relays rely solely on the magnitude of the device's current to detect overloads, regardless of the ambient temperature. Even if the equipment has increased margin against overload, it is possible that the equipment will stop operating under certain current conditions, and conversely, if the ambient temperature rises, the equipment may have less margin against overload. Even when the current is gone, protection is delayed because only the current conditions are looked at, and there are concerns that this could lead to malfunctions that could damage the equipment. However, in this embodiment, since the ambient temperature θ is taken into account as an operation determination condition, the occurrence of such problems can be significantly reduced compared to the prior art.

Embodiment 6 FIG. 17 shows another embodiment of a modified overcurrent relay according to the present invention. The only difference in this embodiment is that the way the input current is taken in is modified and the position at which the squared value is calculated is changed.

That is, as the configuration is shown in FIG. 17a, 43 is an input circuit that introduces a current I from the power system by a known means and sends out an amount of electricity √I that is proportional to the amount of current, and 44 is an input circuit. An analog-to-digital (A/D) conversion circuit converts the electrical quantity √I obtained from 43 into a digital quantity, and 45 reads the electrical quantity √I converted into a digital quantity, and converts this value and the numerical value held internally. From S _o-1 , No. 17
This is a microcontroller that performs arithmetic processing according to the processing procedure of the flowchart shown in FIG. b, and determines whether or not to send out a tripping signal.

In the flowchart of FIG. 17b, steps 6, 7, 9, 13, 14, and 15 have the same functions as those shown in FIGS. 2b and 3b,
The explanation will be omitted. Note that in step 46, the amount of electricity converted into a digital amount by the A/D converter 44 is
The procedure for reading I is shown. Further, step 47 shows a procedure for calculating this square value KI ² using the data of √I.

Therefore, the operation of this embodiment is as follows.

First, the input circuit 43 converts the introduced electric power system current I into an electric quantity √I. Next, this electric quantity √I is converted into a digital quantity by an A/D converter 44 and introduced into a microcontroller 45, where a square value KI ² is obtained. Furthermore, this data
From KI ² and So _-1 , calculate K′(KI ² −S _o-1 )+S _o-1 , and use the result as the addition result _So. And this
A tripping signal is sent out when S _o is equal to or higher than the operation determination level L _T , and conversely, no tripping signal is sent out when S _o is less than L _T . After this, the data S _o
Replace with S _o-1 and repeat the same operation.

This is because the embodiment shown in Fig. 1 converts the amount of current I into the amount of electricity KI ²
In contrast, in this embodiment, the current amount I is converted to the electrical amount √I, then A/D converted, and the process is performed using the value KI ² . The value √I is further squared and processed as KI ² . Therefore, this example and the first
There is no essential difference from the embodiment shown in the figure, only the positions of the square calculation and A/D conversion have been swapped.
Needless to explain, the effect obtained is the same as in Fig. 1. In other words, the present invention is not characterized in that the electrical quantity KI ² is A/D converted, but rather the electrical quantity √I is A/D converted as in the embodiment shown in FIG. , it goes without saying that the configuration may be such that the square value KI ² is obtained by digital calculation.

In each of the above embodiments, a single-phase current was used to simplify the explanation, but instead of this, two-phase or three-phase currents may be introduced, and a symmetrical current synthesized from these may be used. Furthermore, as the current I, not only an effective value but also an average value or a maximum value may be used.

〔Effect of the invention〕

As explained above, according to the present invention, the operating characteristics are changed according to the magnitude of the steady-state load, and the possibility of re-starting is determined according to the degree of overload. This not only provides good overload protection, but also provides an overcurrent relay that is easy to maintain and test.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the overcurrent relay according to the present invention, FIG. Fig. 3b is a flowchart explaining the operation; Fig. 4a is a diagram illustrating the operating time when the input current changes from zero as a step function; Fig. 4b is a diagram explaining the operating time when the input current changes from a predetermined value as a step function, FIG. 4c is a diagram explaining the operating time when the input current changes intermittently, and FIG. Example diagram of operating time characteristics of overcurrent relay,
FIG. 6 is a block diagram of another embodiment, FIG. 7a is a block diagram of the second means in FIG. 6, FIG. 8 is a block diagram of still another embodiment, FIG. 9a is a block diagram of the third means in FIG. Figure 11: Diagram explaining the necessity of waiting for the connection of the cutter and disconnector.
12 is a circuit diagram showing an application of another embodiment of the present invention, and FIG. 13a is a diagram illustrating a configuration example of the third means of the overcurrent relay shown in FIG. 12. , FIG. 13b is a flowchart explaining the operation of the overcurrent relay of FIG. 12, FIG. 14 is a circuit diagram showing application of another embodiment of the present invention, and FIG. 15a
is an example of the configuration of the third means of the overcurrent relay shown in FIG. 14, FIG. 15b is a flowchart explaining the operation of the overcurrent relay shown in FIG. 14, and FIG. Fig. 17a is a diagram showing an example of operating time characteristics of a relay, and Fig. 17b is a configuration diagram of another embodiment.
is a flowchart illustrating the operation of the embodiment of FIG. 17a. 1...first means, 2...second means, 3,2
0... Third means, 4, 44... A/D converter, 5, 11, 17, 21, 33, 40, 45...
... Microcontroller, 22 ... Display, 28
... bus bar, 29 ... wire breaker, 30 ... current transformer,
32... Protected equipment, 31, 38... Overcurrent relay, 39... Temperature sensor.

Claims (1)

[Claims] 1. In an overcurrent relay having an inverse time characteristic used for overload protection, a value proportional to the square of the current.
a first means for calculating KI ² ; a second means for calculating the addition result S _o by adding the value calculated by the first means; and a value calculated by the second means is a predetermined value. and third means for producing an output when the above-mentioned conditions occur, and the second means adds the calculated value KI ² of the first means to the calculated value S _{o -} of the second means before the present time. The value K′ (KI ² − S _o-1 ), which is proportional to the difference from ₁ (K and K′ are positive constants), and the calculated value before the current time
An overcurrent relay characterized in that it adds S _o-1 . 2. The overcurrent relay according to claim 1, wherein the predetermined value is a constant value. 3. The overcurrent relay according to claim 1, wherein the predetermined value decreases as the ambient temperature of the protected part or the object stored therein increases. 4 In overcurrent relays with inverse time-limiting characteristics used for overload protection, a value proportional to the square of the current
a first means for calculating KI ² ; a second means for calculating the addition result S _o by adding the value calculated by the first means; and a value calculated by the second means is a predetermined value. and third means for producing an output when the above-mentioned conditions occur, and the second means adds the calculated value KI ² of the first means to the calculated value S _{o -} of the second means before the present time. The value K′ (KI ² − S _o-1 ), which is proportional to the difference from ₁ (K and K′ are positive constants), and the calculated value before the current time
The overcurrent relay is characterized in that the _second means is added with a means for forcibly setting the calculated value to a specific value by an external command. . 5 In overcurrent relays with inverse time-limiting characteristics used for overload protection, a value proportional to the square of the current
a first means for calculating KI ² ; a second means for calculating the addition result S _o by adding the calculated value of the first means;
and a third means for generating first and second outputs corresponding to the respective predetermined values when the values exceed a second predetermined value, and a fourth means for tripping the breaker by the first output. and a fifth means for preventing the closing of the breaker by the second output, the first predetermined value is set larger than the second predetermined value, and the second predetermined value is set to be larger than the second predetermined value. The addition of the means is a value K _′ ^{(KI 2 −}
S _o-1 ), (where K and K' are positive constants) and a previously calculated value S _o-1 . 6 In overcurrent relays with inverse time-limiting characteristics used for overload protection, a value proportional to the square of the current
a first means for calculating KI ² ; a second means for calculating the addition result S _o using the calculated value of the first means;
a third means for generating first and second outputs corresponding to the respective predetermined values when the predetermined values of and a fifth means for displaying that the second output is waiting for the shutoff to be turned on, the first predetermined value is set to be larger than the second predetermined value, and the second predetermined value is set to be larger than the second predetermined value. The addition of the means is a value K _′ ^{(KI 2 −}
S _o-1 ), (where K and K' are positive constants) and a previously calculated value S _o-1 .