JPH088742B2 - AC filter equipment protection relay - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AC filter equipment protection relay provided to protect AC filter equipment provided with a high-pass filter for removing a plurality of harmonics.

<Prior art> In order to remove harmonics generated in the power transmission system,
AC filter equipment may be connected to the conductive system in parallel with the ground.

The AC filter equipment may be a dedicated filter for removing a single frequency or a dual-purpose filter for simultaneously removing a plurality of harmonics. Also, both filters may be used together.

For example, when there are a large number of expected harmonics, the required number of the former dedicated filters are installed for the major harmonics (the ones with a large power component), and the many harmonics with a small number of power components are installed. One of the latter combined filters is installed for.

The dedicated filter and dual-purpose filter described above have a heat capacity corresponding to the power of the expected harmonics. May be overloaded. Therefore, an AC filter equipment protection relay is provided to protect these filter equipment.

In this case, the setting criterion of the operation threshold of the AC filter equipment protection relay becomes a problem. With a dedicated filter, the frequency is fixed, so it is relatively easy to determine the threshold value, but with a dual-purpose filter, since many frequencies are handled, each harmonic component flowing into the resistor in the dual-purpose filter The diversion ratio of will have to be taken into consideration.

That is, if the current value of each harmonic component flowing into the resistor in the dual-purpose filter is k (k = 1 to n), the total power consumed by the resistor in the filter is proportional to Σ (βk k) ² . Here, k is the harmonic order, and βk is the shunt ratio of the kth harmonic flowing into the resistor.

Therefore, the AC filter equipment protection relay is
(Βk k) ² must be calculated and compared with a threshold value to make a decision.

<Problems to be Solved by the Invention> However, in order to perform the above calculation, each coefficient βk must be obtained in advance. Therefore, it is necessary to secure a memory capacity for storing the coefficient βk. Also,
A means (digital filter or the like) for detecting each harmonic current k is required, which complicates the configuration of the protection relay.
Furthermore, since it takes a long calculation time to calculate the above Σ (βk k) ² , it is not preferable for the AC filter equipment protection relay that requires quick processing.

Of course, if the current flowing through the resistor in the dual-purpose filter can be directly measured, the above problem can be solved, but since the filter is integrally incorporated in one sealed housing, it is generally necessary to insert a sensor for measuring the current. Have difficulty.

The present invention has been made in view of the above problems,
The purpose thereof is to quickly and accurately protect an AC filter equipment equipped with a high-pass filter in which a capacitor C and a coil L are connected in series, and a resistance R for damping is connected in parallel to the coil L. It is an object of the present invention to provide an AC filter equipment protection relay having a simple configuration that can be achieved.

<Means for Solving the Problems> The AC filter equipment protection relay of the present invention for achieving the above object is a current detection unit for detecting a current flowing through a high-pass filter, and a low signal included in a detection signal of the current detection unit. Shunt correction means having a differentiating circuit for removing frequency components, arithmetic processing means for calculating an effective value based on an output signal of the shunt correction means, and a circuit breaker command when the arithmetic processing means detects an effective value exceeding a threshold value. A command means for outputting a signal is provided, and the time constant of the differentiating circuit is set to be equal to the time constant determined by the coil L and the resistor R of the high-pass filter that constitutes the AC filter equipment.

<Operation> The high-pass filter that constitutes the AC filter equipment is a series circuit of the capacitor C and the coil L as shown in FIG. 1, and the resistor R is connected in parallel to the coil L. If the current of the nth harmonic flowing through the entire high-pass filter is n, the current shunting to the coil L is 2n, and the current shunting to the resistor R is 1n, the current 1n is Becomes Here, ωo is the angular frequency of the fundamental wave. Electric current
The absolute value of 1n is Becomes

Therefore, the diversion ratio βn in which the current n of the nth harmonic flows to the resistor R is Becomes

On the other hand, assuming that the differentiating circuit has a capacitor C1 and a resistor R1 as illustrated in FIG. 2, the gain G (jnωo) of the differentiating circuit is It is represented by. The absolute value of the gain is Becomes At this time, if the time constant C1 R1 is selected such that R / ωo L = 1 / ωo C1 R1, that is, C1 R1 = L / R, the differentiating circuit makes the shunt ratio βn for the nth harmonic. It behaves like an amplifier circuit with a gain of.

Therefore, if the effective value is calculated for the output of the differentiating circuit, the amount of heat consumed by the resistor R can be known, and when it is detected that this effective value exceeds the threshold value, the circuit breaker command signal is output. If output, it is possible to properly protect the AC filter equipment.

<Embodiment> An embodiment will be described in detail below with reference to the accompanying drawings.

FIG. 3 is a circuit diagram of the filter equipment 2 connected in parallel to the power transmission line 1 and the protection relay 1 for protecting the filter equipment 2.

The filter equipment 2 is a series circuit of a capacitor C and a coil L, and has a high-pass filter 2 in which a resistor R is connected in parallel to the coil L. The capacitor C and the coil L are connected in series because they have high impedance with respect to the fundamental wave. The reason why the resistor R is inserted is to lower the Q of the resonance circuit of the capacitor C and the coil L so as to function as a high pass filter.

The current flowing through the high pass filter 2 is detected by the current coil 3 and input to the AC filter equipment protection relay 1.

AC filter equipment protection relay 1 is a current conversion transformer
11, a differentiation circuit 12 including a capacitor C1 and a resistor R1, an effective value calculation circuit 14 that calculates an effective value, a comparison processing circuit 1 that compares the calculated effective value with a threshold value and outputs a circuit breaker command signal 1.
5 and time limit circuit 16.

The time constant C1 R1 of the differentiating circuit 12 satisfies C1 R1 = L / R ... Using the values of the coil L and the resistance R of the high-pal filter 2.

Cutoff angular frequency of high-pass filter 2 no ωo
Is selected as no ωo = R / γL (γ is a constant, 3.6 at frequency 50Hz, 3 at frequency 60Hz), so the above equation becomes C1 R1 = 1 / no γωo ... . For example, basic frequency 60Hz, no = 24, C = 0.01μ
If F, then using the formula, R1 = 3.68 kΩ.

The rms value calculation circuit 14 is the same as a commonly used rms value calculation circuit, for example, one that is converted to an rms value by a bridge rectification circuit, one that uses a resistor and a thermocouple, and rectified by a bridge rectification circuit. 2 by rear diode
RMS / DC that passes through a power line circuit and uses an operational amplifier
It is possible to use an analog type such as a converter (Burr Brown, 4340 etc.) or a digital type such as that which obtains an effective value by digital calculation after sampling and digital conversion.

The comparison processing circuit 15 outputs a command output when it receives an effective value input equal to or more than a threshold value for a certain period of time counted by the time limit circuit 16. The comparison processing circuit 15 may output a command if it determines that the value obtained by integrating the effective value input over a certain period of time is equal to or greater than the threshold value.

In the AC filter equipment protection relay with the above configuration,
Since the time constant C1 R1 of the differentiating circuit 12 is set so as to satisfy the above expression, the differentiating circuit 12 determines, as already described, the shunt current βn to the resistor R for the nth harmonic.
Outputs a voltage signal proportional to.

Therefore, by performing an effective value calculation on the output of the differentiating circuit 12, a signal proportional to the power consumed by the resistor R can be taken out. If the comparison processing circuit 15 issues a command output based on this signal, the shunt ratio βn is calculated and stored as previously considered, and Σ (βk
k) The process of calculating ² is unnecessary, the relay configuration is simplified, and the calculation time is shortened.

Note that the present invention is not limited to the above-described embodiments, and for example, a differentiating circuit is configured by using a coil L and a resistor R, as long as the gist of the present invention is not changed,
For example, various design changes can be made.

<Effects of the Invention> As described above, according to the AC filter equipment protection relay of the present invention, the AC filter equipment is detected by the simple means of detecting the current flowing through the high-pass filter, passing it through the differentiating circuit, and calculating the effective value. The Joule heat generated in the resistance of can be correctly estimated.

Therefore, as conventionally thought, it is not necessary to store the diversion ratio βk of the current flowing through the resistor, and the means for detecting each harmonic current k is not required, and the AC filter equipment protection relay capable of rapid processing can be obtained. Can be realized.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram showing a specific configuration of an AC filter equipment protection relay, FIG. 2 is a circuit diagram showing a specific configuration of a differentiating circuit, and FIG. 3 is an AC filter equipment protection relay. It is a circuit diagram which shows one Example. 1 ... AC filter equipment protection relay, 2 ... AC filter equipment, 3 ... Current detector, 12 ... Differentiation circuit, 14 ... Effective value calculation circuit, 15 ... Comparison processing circuit

Claims (1)

[Claims] 1. A relay for protecting an alternating current filter equipment having a high-pass filter in which a capacitor C and a coil L are connected in series, and a resistance R for damping is connected in parallel to the coil L, which is a high-pass filter. Current detecting means for detecting a current flowing through the current detecting means, shunt ratio correcting means having a differentiating circuit for removing low frequency components included in the detection signal of the current detecting means, and calculation for calculating an effective value based on the output signal of the shunt ratio correcting means. The processing means and the command means for outputting a circuit breaker command signal when the arithmetic processing means detects an effective value exceeding a threshold value, and the time constant of the differentiating circuit is the high-pass filter of the AC filter equipment. An AC filter equipment protection relay, which is set to have a time constant determined by the coil L and the resistance R.