JP2889667B2 - AC filter overload detection device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an AC filter overload detection device used for a relay or the like that protects AC filter equipment from overload.

(B) Conventional Technology Conventionally, for example, in a DC transmission AC / DC converter, an AC filter facility for reducing a harmonic current superimposed on a system has been provided. Such an AC filter usually combines a single-tuned filter for each order for low-order harmonics of 13th or less and a high-pass filter for high-order harmonics exceeding 13th order. Is the economics and the reactive power at the fundamental of the filter,
In consideration of the resonance of the filter and the system at the time of the tuning deviation due to the frequency change of the AC system, etc., the distribution of the capacitors to the respective shunts, the sharpness (Q), etc. are determined so that the filter effect is maximized. .

In general, the capacity and the like of an AC filter are designed in advance according to the content of the harmonic current generated on the AC system side in the AC / DC conversion facility, but the harmonic current is superimposed on the system by another route. As in the case, an unpredictable harmonic current component may flow into the AC filter, and the AC filter may be overloaded. Therefore, in the related art, a temperature sensor is directly attached to the reactor that generates the most heat in the AC filter to detect an overheated state of the reactor.

(C) Problems to be Solved by the Invention However, the method using the temperature sensor cannot detect a rapid temperature rise. Conventionally, a current transformer is provided in each shunt of the AC filter, and an overcurrent of each shunt is detected from the output of the current transformer. However, only the total current flowing in such an AC filter is used. The heat loss of the AC filter could not be determined, and thus the overload determination could not be made.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an AC filter overload detection device that accurately determines the heat loss of an AC filter by calculation and detects an overload state.

(D) Means for Solving the Problem A particularly problematic problem in overloading the AC filter is the heat generated by the reactor and the resistor. Therefore, in order to perform overload protection, an ideal method is to monitor heat loss including harmonic components represented by the following equation.

Where n is the harmonic order, In is the harmonic component of the current, and Rn
Is the equivalent resistance for each harmonic.

However, the heat loss due to the fundamental wave current (n = 1) exists as the base with little fluctuation, and the heat rise may be considered to be determined by the harmonic component. Therefore, the change of the heat loss in the harmonic component may be detected.

An AC filter overload detection device according to the present invention is a device that is connected to a current transformer provided on a ground wire of an AC filter that absorbs a harmonic current of a predetermined order or a higher harmonic. A filter that passes a frequency component of a higher order harmonic current to be absorbed among currents flowing into the filter, a quantizing unit that samples an output signal of the filter at fixed time intervals and performs A / D conversion; Heat loss calculating means for calculating the heat loss of the AC filter due to the harmonic current of the order based on the respective sampling data by the following equation: (However, R is the equivalent resistance of the AC filter, i (m) is the sampling data of the current, m is the number of the sampling data when one cycle is equally divided into 2 l) The difference between the calculated heat loss and a predetermined value Means for determining the overload state of the AC filter by comparison.

(E) Function FIG. 1 shows an example of the configuration of the AC filter overload detection device of the present invention. In FIG. 1, reference numeral 7 denotes an AC filter circuit including a capacitor Co, a reactor Lo, and a resistor Ro, which is connected between the system and the ground. A current transformer CT is connected to the ground wire of the AC filter circuit 7, and the AC filter overload detecting device 6 detects an overload state of the AC filter from an output signal of the current transformer CT. In this example, the AC filter overload detection device 6 includes an auxiliary CT for further changing the output of the current transformer CT, a filter 2, a sample and hold circuit 3, an A / D conversion circuit 4, and an arithmetic processing circuit 5. Allows the frequency component of the harmonic current of the order absorbed by the AC filter circuit 7 in the voltage conversion signal of the output current of the auxiliary CT to pass. Sample hold circuit 3 and A /
The D conversion circuit 4 corresponds to a "quantizing means", and samples the output signal of the filter 2 at regular time intervals.
Convert to digital data. The arithmetic processing circuit 5 corresponds to “heat loss calculating means” and “overload state determining means”, and performs a root-mean-square calculation of each sampled data in one cycle of the harmonic current to thereby obtain a heat loss due to a harmonic component of the AC filter. Is obtained, and when the value exceeds a predetermined set value, a detection signal is output on the assumption that an overload condition has occurred.

The calculation means performs the heat loss calculation as follows. First, the square value of the harmonic current component flowing through the AC filter circuit 7 appearing as the output signal of the filter 2 can be obtained by the following equation.

Here, ω = 2πf, where f is the frequency of the harmonic, i (t)
Is current, i (m) is current sampling data, and m is 1
This is the number of sampling data when the cycle is equally divided by 2l.

Therefore, the amount of heat generated by the harmonic current of the AC filter circuit 7 is obtained by the following equation.

Here, R is the equivalent resistance of the AC filter circuit 7.

(F) Embodiment FIG. 3 shows a circuit diagram of an AC filter equipment according to an embodiment of the present invention, and FIG. 4 shows a configuration of an AC filter overload detection relay.

In FIG. 3, the circuit composed of the capacitor C1, the reactor L1, and the resistor R1 is an AC filter for the fifth harmonic, and the circuit composed of the capacitor C2, the reactors L21, L2, and the resistor R2 is an AC filter for the seventh harmonic. , Both AC filters are connected to the bus via circuit breaker CB1. Condesa C
3.The circuit consisting of the reactor L3 and the resistor R3 is an AC filter for the 11th harmonic, the capacitor C4, the circuit consisting of the reactors L41 and L4 and the resistor R4 is the AC filter for the 13th harmonic, and the capacitor C5 and the resistor R5 The circuit composed of the reactor L5 is an AC filter for higher harmonics, and this AC filter is connected to the bus via a circuit breaker CB2. Also,
Current transformers denoted by CT1 to CT5 are provided on the ground wire of each AC filter.

The AC filter overload detection relay shown in FIG. 4 is a device connected to each of the current transformers CT1 to CT5 shown in FIG. 3 to detect the overload state of each AC filter. In Fig. 4, CT11
To CT15 are auxiliary current transformers respectively connected to the outputs of the current transformers CT1 to CT5 shown in FIG. 21 to 25 are auxiliary current transformer CT
These are a band-pass filter and a high-pass filter that allow only the tuning frequency component of each AC filter in the output signals of 11 to CT15 to pass. A multiplexer 26 selects an output signal of each filter, a sample and hold circuit 27 samples and holds the output signal, and an A / D conversion circuit 28 converts the sampling signal into digital data,
The data is stored in a predetermined area of the RAM 31 by DMA transfer. CPU29
Performs overload detection control of the AC filter by executing a program written in the ROM 30 in advance.
The RAM 31 is provided with an area for storing sampling data and other working areas for calculating an effective value. The operation panel 33 is a panel including an operation unit for setting a set value for determining an overload state and a display unit for displaying a detection result of the overload state, and the interface circuit 32 controls the operation unit. The printer 35 records the load state of each AC filter, and the interface circuit 34 controls the printer. The contact output circuit 36 trips a circuit breaker or the like according to the output when an overload state is detected.

The current flowing in each of the AC filters provided with the converters CT1 to CT4 shown in FIG. 3 is dominated by a fundamental component and a single harmonic current of each order.
24 may be a filter that blocks at least the fundamental wave component. On the other hand, in addition to the fundamental wave component, four higher harmonic currents of 24 ± 1 and 36 ± 1 flow into the AC filter provided with the current transformer CT5 shown in FIG. In the AC filter for the second harmonic, the heat generated by the resistor R5 connected in parallel to the reactor L5 rather than the reactor L5 poses a problem. Therefore, the shunt ratio of the signal detected by the current transformer CT5 that shunts to the resistor R5 must be considered. The frequency characteristic of the shunt ratio has a high-pass filter characteristic, and the high-pass filter 25 shown in FIG. 4 functions as a circuit for correcting the frequency characteristic of the shunt ratio.

Further, the sample-and-hold circuit 27 shown in FIG. 4 performs high-frequency sampling at a frequency at least twice the harmonic frequency to be detected, and the A / D conversion circuit 28 sequentially stores the digital data in the buffer area of the RAM 31. I do. CPU
Numeral 29 determines the overload state of the AC filter by performing the calculation shown in the expression (3) or (5) on the sampling data for one cycle of the harmonic signal stored in the buffer area and comparing it with the set value. .

(G) Effects of the Invention According to the present invention, since the heat generation of the AC filter can be obtained by calculation, a rapid rise in temperature can be quickly detected to protect the AC filter. In addition, since the heat generated by the AC filter is determined by the heat loss itself due to the harmonic current flowing through each AC filter, overload detection can be performed in accordance with the substance of the heat resistance of the AC filter. In addition, there is no error in principle as compared with a calculation method by Fourier integration or a method by matrix calculation, and digital calculation by a square root square root procedure is not required, so that the calculation is easy and the time required for the calculation is relatively short. There is an advantage that it is short and a common calculation method can be adopted for each shunt.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration example of the present invention, and FIG. 2 is a diagram provided for describing the operation thereof. FIG. 3 is a circuit diagram of an AC filter facility to which an AC filter overload relay according to an embodiment of the present invention is applied, and FIG. 4 is a configuration diagram of an AC filter overload relay according to an embodiment of the present invention.

Claims (1)

(57) [Claims] 1. A device connected to a current transformer provided on a ground wire of an AC filter for absorbing a harmonic current of a predetermined order or a higher harmonic wave, wherein the current flowing into the AC filter is A filter for passing the frequency component of the harmonic current of the order to be absorbed, a quantizing means for sampling the output signal of the filter at a constant time interval, and performing A / D conversion; and Heat loss calculating means for determining the heat loss of the AC filter due to the harmonic current of the order by the following equation: (However, R is the equivalent resistance of the AC filter, i (m) is the sampling data of the current, m is the number of the sampling data when one cycle is equally divided into 2 l) The difference between the calculated heat loss and a predetermined value Means for determining an overload state of the AC filter by comparison, and an AC filter overload detection device comprising: