JP2540897B2 - Digital type ratio differential relay - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a digital ratio differential relay that protects a bus bar of a power system.

[Conventional technology]

FIG. 3 is a principle configuration diagram of a conventional ratio differential relay disclosed in, for example, Japanese Patent Laid-Open No. 59-035526, in which (1) is a bus of a power system and (2-1) to (). 2-n)
Is a current transformer (hereinafter referred to as CT) that detects the current of each line connected to the bus (1), and (3-1) to (3-n) are CT (2
-1) to (2-n), each of which is an input device for deriving an AC amount I1 to In and an absolute value amount | E1 | to | En | proportional to the current of each line, and the signal _ID is the AC amount. The differential amount obtained by differentially combining (vector combining) I1 to In, the signal | E _R | is the absolute value amount | E1 |
~ | En |, the maximum terminal value is the terminal suppression amount. (12) is a ratio differential relay and is composed of the following circuit elements. (1
3) is the first element for detecting the level of the differential amount I _D , (1
4) is a resistor that outputs the absolute value amount | E ₀ | proportional to the differential amount ID, and (15) is a resistor that outputs the terminal suppression amount | E _R |
(16) is the second element that detects | E _R | − | E ₀ |> K _R , (17) is a signal extension circuit, (18) is a NOT circuit, (19) is an AND circuit,
(20) is an output relay.

Next, the operation will be described. FIG. 3 shows an example applied to a busbar protection device for detecting an accident on a busbar (1) of a power system, which is based on the well-known ratio differential principle. When there is no CT saturation at all times or during an external accident, the first element (13) does not operate because the differential amount I _D is zero, but during an external accident
When the CT saturation is severe, the first element (13) malfunctions. As a countermeasure against this, a second element (16) is provided, which will be described with reference to FIG.

Waveform _IF is an example of the current waveform flowing at the fault point, and the actual fault current waveform is under the most severe conditions for CT saturation. That is, when the accident occurs, the transient DC component current is 100% superposed on the AC component current peak value. If the AC component current is I _FP and the DC component current decay time constant is T, the fault current is Is represented by Waveform I ₁ is an example of the CT secondary current at the external fault end. The primary current of this external fault end (outflow end) CT is waveform I _F , and the magnitude is the same as the magnitude of the fault current. It is in a condition where it is easily saturated. The shaded part of the waveform is CT2
This is the next current waveform, and the dotted line represents the time when CT is not saturated. The waveform I ₂ is the differential current of the error, and if the inflow end CT is unsaturated and only the outflow end (fault end) CT is saturated as the waveform I ₁ as a severe condition, the error differential current I ₂ As a result, a difference between the waveform I _F and the waveform I ₁ will occur, so
The waveform is as shown by the diagonal lines. At this time, the operation input I _{D of} the waveform I _{2 of} FIG. 4 is applied as the input of the ratio differential relay (12) of FIG. 3, and the suppression input | E _R | is the waveform | I ₁ | Since it is applied, the voltages | E ₀ | and | E _R | generated at the resistors (14) and (15) in Fig. 3 are eventually | E ₀ | ∝ | I ₂ |, | E _R | ∝ | I ₁ | Therefore, the waveform of the voltage | E _R | − | E ₀ | becomes the same as the waveform of K ₁ | I ₁ | −K ₂ | I ₂ |.

The second element (16) is designed to switch only when | E _R | − | E ₀ | ≧ K _R and does not operate when | E ₀ |> | E _R | (in an internal accident). Become.

The waveform of | E _R | − | E ₀ | = K ₁ | I ₁ | −K ₂ | I ₂ | disappears when CT is saturated and a differential current I ₂ is generated, as shown in FIG. However, until CT saturation is reached, an output is generated in proportion to the current I ₁ .

The input of the second element (16) is K ₁ | I ₁ | −K ₂ | I ₂ |
The output signal (21) of the second element (16) is K ₁ | I ₁ | at the time t ₁ of the first wave and the time t ₂ + t ₃ of the second wave as shown in FIG.
Switching is performed within the range in which the magnitude of −K ₂ | I ₂ | reaches or exceeds the specified value, an output pulse is generated, and the signal is extended by the signal extension circuit (17) for T ₁ time. Circuit (18)
The signal (22) is a continuous signal as shown in FIG. The extension time T ₁ has a long DC component current decay time T and a short t ₂ + t ₃ of the current I ₁ in the second wave, so that K ₁ | I ₁ | −K ₂ | I ₂ | If the second pulse is not generated because a small third diagram of a signal (21), third wave by increasing the time T _1, or may be allowed引延according to pulse fourth wave.

As described above, even if the CT secondary current is significantly saturated in the first wave due to the residual magnetic flux of the CT, and the saturation continues to occur after the second wave due to the DC component current, the detected value and signal of the second element will be delayed. By properly setting the signal delay time T ₁ of the circuit (17), sufficient countermeasures can be taken.

Note that Fig. 4 shows the waveform at the time of an external accident. Even if the CT is significantly saturated at the time of an internal accident, a differential current is generated at the same time as the accident occurs, and the differential current is the sum of the secondary currents at each power source CT. Since it is always larger than the CT secondary current at each end, it becomes | E ₀ |> | E _R | and the second element (16) cannot detect it.

[Problems to be solved by the invention]

Since the conventional ratio differential relay is configured as above, in order to improve the CT saturation countermeasure performance in the event of an external accident, the detection level of the second element (16) should be set to high sensitivity and signal extension should be performed. It is necessary to lengthen the delay time T ₁ of the circuit (17), but if the constant load current is at or above the detection level of the second element (16), it will become inoperable for the time T ₁ minutes after the occurrence of an internal accident, There was a problem that the operation time was delayed.

The present invention has been made to solve the above problems, and does not always cause an operation delay due to the influence of the load current.
The purpose is to take measures against CT saturation.

[Means for solving problems]

Second operation Max | Int | −ηp · Max {| IDt |, Kp | IDt−α
|}> 0, the third operation Max | Int |> K, and the fourth operation | Max
| Int | −Max | Int−180 ° ||> KT and the fifth operation | IDt |> K1
And at least the fourth calculation output of the fourth calculation output or the fifth calculation output is delayed for a predetermined time and used as a start signal, and the second calculation output, the third calculation output, and the start signal are output. Among these, when the logical product of each output including at least the second operation output and the activation signal is output, this output is delayed by the second signal extending means for a predetermined time, and the output is finalized by the output of the logical product. Lock the motion signal.

[Action]

The fourth calculation in the present invention is to detect the change width of the current, and the fifth calculation is to detect the differential amount. Therefore, there is a feature that the load current does not always respond. Therefore, even if the second calculation output and the third calculation output are always output with the load current, the output that is the logical product of the fourth calculation output and the fifth calculation output is not always output, and an internal accident occurs. When it occurs, there is no need to worry about it being locked for a predetermined time.

For the above reason, the constant K of the third calculation can be set to have sufficiently high sensitivity regardless of the load current, and the performance can be improved as a CT saturation countermeasure in the event of an external accident.

Example of Invention

An embodiment of the present invention will be described below with reference to FIGS. FIG. 2 shows the purpose of the present invention in addition to the performance of a conventional ratio differential relay by applying a digital relay. In the figure, (4-1) to (4-n) are CTs.
An input transformer that receives the secondary currents (2-1) to (2-n) and converts it into an appropriate voltage proportional to the current through a current / voltage conversion circuit (not shown), and (5) is a digital relay. , A filter (6), a sample and hold device (7), a multiplexer (8), an analog / digital converter (9), a memory (10), a microprocessor (11) and the like.

Secondary outputs of the input transformers (4-1) to (4-n) are sampled by the sample-hold device (7) via the filter (6) at the same time and at constant intervals of analog values. The multiplexer (8) sequentially switches the output of the sample and hold device (7), introduces it into the analog / digital converter (9), and converts it into digital data proportional to the analog value instantaneous value by the analog / digital converter (9). upon,
Temporarily store in memory (10). The memory (1
Programs that require computation are also permanently stored in (0), and can be digitally processed in time series by the microprocessor (11).

FIG. 1 shows the operation principle of the digital type ratio differential relay having the above configuration.

In FIG. 1, the current data _Int is CT (2-
1) shows the instantaneous value digital data at time t of the secondary current I ₁ ~I _n of ~ (2-n), and n = 1 to n.
(100) is the first computing means, (101) and (102) are the second and third computing means, and the conventional | E _R | − | E ₀ |> K _R shown in FIG.
This corresponds to the second element (16) for determining. (103) is the fourth
The calculation block (104) is a fifth calculation block, which corresponds to the first element (13) in FIG.

Second calculating means 101 is the ratio differential operation, current data Max | I _nt | of the absolute value of the instantaneous value current data at the time t is I _1t ~I _nt, deriving the maximum value in the calculation The amount of suppression is equivalent to the suppression amount. Current data | I _Dt | is time t
Sum of instantaneous current data I _{1t to Int} at Is derived by calculation and corresponds to the differential amount. The current data | I _Dt-α | is the sum of the instantaneous value current data I _{1t-α to} I _nt-α at time t-α. Although it is an absolute value derived by calculation and is a compensation differential amount for improving the phase characteristic, detailed description thereof is omitted because it is not directly related to the present invention.

Formula Max | I _nt | −ηp · Max {| I _Dt |, Kp | I _Dt−α ｜}
> 0 …… (1) is compared with the maximum value of the suppression amount Max | I _nt | and the differential amount | I _Dt | or Kp | I _Dt−α | (where Kp is a constant). If a constant ηp> 1 is set in the case of an internal accident, | I _Dt
Since | ≧ Max | _Int |, the operation result of equation (1) becomes <0 and is not output.

On the other hand, at the time of an external accident, during the CT unsaturated period, | I _Dt | ≈ 0, so Max | I _nt |> ηp ・ Max {| I _Dt |, Kp | I _{Dt −α} |} Is> 0 and will be output.

The third calculating means (102) detects the level of the suppression amount Max | _Int |, and by performing AND with the output of the equation (1), the conventional | E _R | − | E ₀ |> K _R determination is made. Will be equivalent.

The fourth calculation means (103) detects a change in the suppression amount Max | I _nt |, and the detection method is, for example, | Max | I _nt | −Max | I
_nt−π ||> K _T (where K _T is a constant), Max | I _nt−π | is Max
The amount of suppression 180 degrees before | _Int |

The fifth calculation means (104) detects the level of the differential amount | I _Dt |, and K ₁ is a constant.

The calculation element (110) detects the amplitude value of the differential amount I _D , and the detection method is, for example, (I _Dt ) ² + (I _Dt −90 °).
² > K ₀ (where K ₀ is a constant), and I _Dt −90 ° may be a known vector operation type amplitude value derivation method in which the differential amount is 90 ° before I _Dt , and other amplitude value derivation methods are applied. You may.

(105) is a logical sum (OR) element, and (106) is a logical product (AN
D) element, (107) is first signal extending means, (108) (10
9) is a multiple match timer. (17) is a second signal extending means, (18) is a NOT circuit, (19) is an AND circuit,
These (17), (18) and (19) are the same parts as those of the conventional one shown in FIG.

Next, a description will be given of the principle of the countermeasure of the present invention against the operation time delay due to the influence of the load current, which is a drawback of the above-mentioned conventional embodiment. In order to strengthen the countermeasure against CT saturation, the calculation means (102) in FIG. 3 of FIG. 1 is used in the same manner as the constant K _R in the calculation | E _R | − | E _O |> K _R of the conventional embodiment is made small. Operation M
It is necessary to reduce the constant K of ax | _Int |> K. If the constant K is always less than or equal to the load current, the output of the third calculation means (102) is always output, and the output of the second calculation means (101) is always the differential amount | I _Dt. | Or I _Dt−α | is output because it is zero. However, the fourth and fifth arithmetic means (103) and (104) are added, and the logical product (AND) element (1
If the logical product is taken in 06), the fourth and fifth arithmetic means (103) and (104) do not always output the operation even if the load current is always large, so that the logical product (AND) element (106) The output of is not always output. On the other hand, when an internal or external accident occurs on the bus bar, the magnitude of the current changes, so the fourth calculating means (103) for detecting the change width or the fifth calculating means (104) for detecting the differential amount. Operates, and the operation condition of the logical product (AND) element (106) corresponding to the output condition gate of the second arithmetic means (101), which is an internal / external determination element, is satisfied. The purpose of combining the fourth and fifth calculating means (103) and (104) with the logical element (105) is the change width for detecting the difference in magnitude between the load current and the fault current for a certain period immediately after the occurrence of the fault. Although the detection means (fourth calculation means) (103) operates reliably, it is equal to or longer than the equal time (the change width is detected as in the above example | Max.
| I _nt | −Max | I _{nt − π} | |> K _T ) It is provided because it is possible that the change of the fault current may disappear after more than 1/2 cycle). It is not necessary if the time of the means (for example, timer) (107) is sufficiently long.

Further, if the constant K of the third calculating means (102) and the constant K _T of the fourth calculating means (103) can be the same value, the third calculating means (102) may be omitted. Further, each calculation means (100) (101) (103) (104) (110) in FIG.
Each of the logic elements (105) (106), etc. may be provided individually, or may be composed of a single common CPU (11) as shown in FIG.

In the above embodiment, the change width detection means (fourth calculation means) (103) is set to the maximum value Ma among the absolute values of the end currents _Int.
The change amount of x | I _nt | is detected, but the change amount of the scalar sum Σ | I _nt | of the absolute value of each end current I _nt may be detected. That is, the fourth computing means (103) in FIG.
x | I _nt | −Max | I _nt −180 ° | |> K _T (However, Is the absolute sum of the instantaneous digital value of each terminal current at time _t | I _1t | ~ | I _nt | Is also the scalar sum 180 ° before time t) and I
The change width of _n may be detected.

〔The invention's effect〕

As described above, according to the present invention, as a starting element of the CT saturation countermeasure ratio element (third and fourth calculating means), it is different from the current change width detecting element (fourth calculating means) which is not affected by the load current. Since the configuration is such that the dynamic level detecting element (fifth computing means) is added, a high-performance ratio differential relay with CT saturation countermeasure that does not cause an operation delay phenomenon due to load current can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing the operation principle of a digital ratio differential relay according to an embodiment of the present invention, and FIG. 2 is a system configuration diagram of a digital ratio differential relay utilizing the operation principle shown in FIG.
FIG. 4 is a block diagram showing the principle of a conventional ratio differential relay, and FIG. 4 is a waveform diagram explaining the principle of the conventional ratio differential relay and the present invention. In the figure, (100) is the first computing means and (101) is the second
Calculation means, (102) is a third calculation means, and (103) is a fourth calculation means.
Calculation means, (104) is fifth calculation means, and (107) is first calculation means.
The signal extending means (17) is a second signal extending means. In each figure, the same reference numerals indicate the same or corresponding parts.

Claims (2)

(57) [Claims] 1. A digital type ratio differential relay which converts an instantaneous value obtained by synchronously sampling the current of each terminal of a power system at a constant cycle into a digital value and calculates the digital value according to a predetermined program. Instantaneous value digital amount Int (I1t,
, Int) and the differential value IDt obtained by adding the instantaneous value digital differential value αt before time t and the absolute value of the instantaneous value digital value of each end current at time t. Control amount Max | Int−180 ° | obtained by deriving the maximum value of the suppression amount Max | Int | obtained by deriving the absolute value and the absolute value of the instantaneous value digital value of each end current 180 ° before time t Are obtained by the first calculation means, and the second calculation Max | Int | −η is obtained by the second calculation means.
p · Max {| IDt |, Kp | IDt−α |}> 0 (where ηp and Kp are constants, and Max {| IDt |, Kp | IDt−α | is | IDt | or Kp | IDt−α
│ out of a larger value), the third calculation means calculates the third calculation Max | Int |> K (where K is a constant), and the fourth calculation means calculates the fourth calculation | Max | Int. | −Max | Int−180 ° ||
> KT, and the fifth operation | IDt |> K1 by the fifth operation means.
(However, K1 is a constant), and at least the fourth operation output of the fourth operation or the fifth operation output is extended by the first signal extension means for a predetermined time, and this is used as a start signal, When a logical product of the outputs including at least the second calculation output and the start signal among the second calculation output, the third calculation output, and the start signal is output,
A digital ratio differential relay characterized in that this output is extended for a predetermined time by a second signal extending means, and the final operation signal is locked by the output of the logical product. 2. The fourth calculation means is | Max | Int | −Max | Int−.
180 ° || Replace KT Is the scalar sum of absolute value | I1t | to | Int | of the instantaneous digital value of each terminal current at time t, Is also a scalar sum 180 ° before the time t), and the digital type ratio differential relay according to claim 1.