JPH0640705B2 - Digital reverse power protection relay - Google Patents

Description

The present invention relates to a digital reverse power protection relay applied to parallel operation of a power system.

[Conventional technology]

Conventionally, as this kind of digital reverse power protection relay, there is one shown in FIG.

In the figure, 1 is a service line that receives power from a power company,
2 is a current detecting current transformer, 3 is a power receiving breaker, 4 is a voltage detecting transformer, 5 is a load of the customer, 6 is a generator breaker of the customer, and 7 is a generator of the customer. is there. A digital reverse power protection relay 10 has a current input terminal 11 from the current transformer 2 and a voltage input terminal 12 from the transformer 4, and the current from the current transformer 2 is appropriately supplied by a current / voltage conversion circuit 13. Convert to a proper voltage. Reference numeral 14 is a voltage conversion circuit for converting the voltage from the transformer 4 into an appropriate voltage value, 15 and 16 are analog filter circuits for removing the limited frequency band from the sampling theorem, and 17 is for sampling the input at regular intervals. An A / D conversion circuit for sequentially performing A / D conversion, an operation circuit 18 for executing an operation described later using a sampling amount,
Reference numeral 19 denotes an output terminal of the digital reverse power protection relay 10.

Next, the operation will be described with reference to FIG. First 4th
The figure is a model diagram showing the characteristics of the reverse power protection relay, where V _A is the phase voltage of the A phase introduced from the transformer 4, and I _{A (R)} is the phase current of the A phase introduced from the current transformer 2. Power is being received from the power receiving system. The vector of the phase current I _{A (R)} of the A phase should be illustrated in the same phase direction as the phase voltage V _A of the A phase, but the polarity of the current component is reversed to be introduced in order to detect the reverse power described below. is doing.

In addition, IA _(S) represents the outflow current that flows out from the consumer side to the power receiving system. This is when the power source on the power receiving system side is lost due to an accident in the power transmission and distribution line system on the power receiving system side, or This occurs when the power generated by a customer becomes surplus due to a change in load while the grid is connected.

And Ps shows the allowable value of the reverse electric power which electric power flows out by the said outflow current IA _(S) , and when reverse electric power more than the allowable value Ps of this reverse electric power generate | occur | produces, this is detected by the reverse electric power protection relay, The electric power breaker 3 of FIG. 3 is tripped to disconnect the parallel operation.

Further, θ is a phase angle and indicates a phase difference angle between the phase voltage V _A of the A phase and the phase current I _{A (R)} of the A phase.

Next, the principle of the digital reverse power protection relay will be described with reference to FIG. First, the sampling interval is ωT (ω
When the sampling values of the voltage v and the current i when T = 90 °) are v ₀ , i ₀ , v ₋₁ , i ₋₁ , v ₀ × i ₀ +
The active power component is obtained by performing the operation of v ₋₁ × i ₋₁ by the arithmetic circuit 18.

That is, v ₀ , i ₀ , v _-1 , i _-1 are expressed as follows.

_{v 0 = V A sinωt i 0} = I A sin (ωt-θ) v -1 = V A sin (ωt-90 °) i -1 = I A sin (ωt-90 ° -θ) by substituting them with one another When the formula is expanded by the following formula, the following formula (1) is obtained.

v ₀ × i ₀ + v ₋₁ × i ₋₁ = V _A I _A cos θ (I) Here, the active power component is obtained for V _A I _A cos θ.

The above principle is described in Method C in Table 4-1-3 of Electric Cooperative Research, Vol. 41, No. 4, published in January, 1986.

Whether the obtained power value calculated in this way exceeds the allowable value Ps of the reverse power described in FIG.
The reverse power detection can be performed by making the determination using the formula.

In addition, when electric power is being received here, θ in the equation (1) is 9
Since 0 ° ≦ θ ≦ 270 °, the operation result of the expression (1) is a negative value, and it is understood from the expression (2) that the operation is not performed.

Therefore, in order to suppress the power outflow from the consumer side to the power receiving system as small as possible, the allowable value Ps of reverse power is set to a small value. However, since the rated voltage is usually maintained when the power outflow occurs, a minute current value is taken in to detect the slight reverse power and the calculation of the equation (1) is performed.

However, with a very small current, the DC drift voltage of the electronic circuit elements generated at the outputs of the analog filter circuits 15 and 16 in FIG. 3 cannot be ignored.

Here, the sampling value _i 0 of the current i when the DC drift voltage and _{k, i -1} is _{i 0 = I A sin (ωt} -θ) + k i -1 = I A sin (ωt-90 ° -θ) + k Substituting these into equation (1),
Equation (3) is obtained.

According to the equation (3), when the allowable value Ps of the reverse power is small, the outflow current I _{A (S) to} be detected also becomes small, so the error factors of the two items cannot be ignored.

[Problems to be solved by the invention]

Since the conventional digital reverse power protection relay is configured as described above, if an attempt is made to detect the allowable value Ps of the reverse power while keeping it as small as possible, the outflow current Is also becomes small, which is an adverse effect when the reverse power is detected. There has been a problem that an error occurs due to the DC drift of the electronic circuit element and the accuracy of the reverse power relay is significantly reduced.

The present invention has been made in order to solve the above problems, and is a high-precision digital circuit which is not affected by a DC drift voltage of an electronic circuit element even when detecting a slight reverse power flowing out from a customer system. The purpose is to obtain a type reverse power protection relay.

[Means for solving problems]

The digital reverse power protection relay according to the present invention has a voltage v
And the arithmetic sum average of the active power component obtained from the sampling value of the current i and the arithmetic sum average value of the active power component obtained from the sampling value of the voltage v and the current i of the half cycle before the arithmetic sum average. It is designed to eliminate the influence of the DC drift voltage by using a circuit.

[Action]

The digital reverse power protection relay according to the present invention is a DC drift voltage obtained by calculating the arithmetic sum average value of the active power component calculated by the arithmetic circuit and the arithmetic result of the active power component half cycle before that point by the arithmetic sum average circuit. The error term caused by is set to zero.

Example of Invention

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, the same parts as those in FIG. 3 have the same reference numerals, and in FIG. 1, 20 is the arithmetic sum average of the active power component at a certain time point and the active power half cycle before that time point. Arithmetic and average circuit 100 is a digital reverse power protection relay of the present invention.

Further, FIG. 2 is a waveform diagram for explaining the principle of the present invention, and illustrates the sampling values of the voltage v and the current i when the sampling interval is ωT (ωT = 90 °).

Next, the operation will be described. First, considering the DC drift voltage k in the current component in FIG. 2, each sampling value is expressed by the following equation.

v ₀ = V _A sin ωt i ₀ = I _A sin (ωt-θ) + k v ₋₁ ＝ V _A sin (ωt-90 °) i ₋₁ ＝ I _A sin (ωt-90 ° −θ) + k v _-2 = V _A sin (ωt-180 °) i _-2 = I _A sin (ωt-180 ° −θ) +
k v _-3 = V _A sin (ωt-270 °) i _-3 = I _A sin (ωt-270 ° -θ) + k Here, the sampling value v ₀ of the voltage v and the current i,
When the active power is calculated from v ₋₁ , i ₀ , i ₋₁ and is P ₁ , the following equation is obtained because the same operation as the equation (3) is performed.

Next, the sampling values v ₋₂ , v ₋₃ , i half cycle before the sampling value used to obtain the active power P _1
-2 , i _−3, and the active power is calculated as P ₂ Is obtained.

When the active powers P ₁ and P ₂ obtained as a result are arithmetically averaged by the arithmetic sum averaging circuit 20, the term of the error factor of the DC drift voltage k is eliminated and the following equation (4) is obtained.

(P ₁ + P ₂ ) / 2 = V _A I _A cos θ (4) The result of this equation (4) and the allowable value Ps of the reverse power are determined by the following equation (5) to determine the DC drift voltage. An unaffected digital reverse power protection relay is obtained.

Although the active power is described as V _A I _A cosθ in the above embodiment, it is needless to say that the active power in the case of three-phase AC is 3V _A I _A cos θ, which is multiplied by a constant of 3. Yes.

Further, in the above-mentioned embodiment, the improvement measures are described for the method C in Table 4-1-3 of No. 41, No. 4, No. 41, No. 4, as a reference, but the same idea is applied to other methods. It goes without saying that the characteristics can be improved by adopting the method of obtaining the arithmetic sum average of the operation results before the cycle.

〔The invention's effect〕

As described above, according to the present invention, the arithmetic sum average circuit obtains the arithmetic sum average value of the active power component calculated at a certain time point and the active power component half cycle before that time, and the error caused by the DC drift voltage is obtained. Since the term is set to zero, there is an effect that a highly accurate relay that is not affected by DC drift can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a digital type reverse power protection relay of the present invention, FIG. 2 is a voltage and current waveform diagram for explaining FIG. 1, and FIG. 3 is a conventional reverse power protection relay. FIG. 4 is an explanatory view of an applied power system, FIG. 4 is a characteristic diagram of a general reverse power protection relay, and FIG. 5 is a principle diagram of a conventional reverse power protection relay that obtains a power amount by using a digital amount. In the figure, 15 and 16 are analog filter circuits, and 17
Is an A / D conversion circuit, 18 is an arithmetic circuit, and 20 is an arithmetic sum averaging circuit. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] Claim: What is claimed is: 1. An A / D converter circuit for sampling the voltage and current of an electric power consumer system taken in through an analog filter circuit and converting the voltage into a digital signal, and an operation using an output value from the A / D converter circuit. In the digital reverse power protection relay, the active power component obtained by calculating the output value of the A / D conversion circuit based on the sampling value of the voltage and the current , And a digital type reverse power protection relay which is provided with an arithmetic sum averaging circuit for obtaining an arithmetic mean value of the active power components obtained half cycle before the sampling of the voltage and the current.