JPS5942266B2 - Harmonic component content detection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a detection circuit that detects the content of a harmonic component of a specific order with respect to a fundamental wave component, and is designed to suppress the influence of this harmonic component, especially when protecting a transformer. The present invention relates to a detection circuit included in a ratio differential relay.

Conventionally, there has been a detection circuit of this type as shown in FIG.

In FIG. 1, 1 is a circuit for selecting a fundamental wave component from a signal. In the circuit 1, 2 is a filter that passes the fundamental wave component, 3 is a rectifier circuit that rectifies the output of the filter 2, and 4 is a smoothing circuit that smoothes the output of the rectifier circuit 3.
Reference numeral 5 designates a circuit for selecting the second harmonic component; reference numeral 6 refers to a filter for selecting the second harmonic component from the signal; 7 a rectifier circuit for rectifying the output of the filter 6; and 8 a rectifier circuit. A smoothing circuit smoothes the output of T, and an amplifier 9 amplifies the output of the smoothing circuit 8.

Reference numeral 10 denotes a comparator which introduces the outputs of circuits 1 and 5, that is, the outputs of smoothing circuit 4 and amplifier 9, compares their levels, and outputs an output when the output of circuit 5 exceeds the output.

Next, the operation will be explained with reference to the frequency gain characteristic graph shown in FIG.

Here, it is assumed that the signal Va consists of only the fundamental wave component,
Assuming that the fundamental wave component of the signal Va() is If, and the coefficient when converting the signal Va into a DC signal is 1, the output of the circuit 1 is expressed as Kllfl. Similarly, if the amplification factor of the amplifier 9 is .beta. and the output ratio of the filter 6 to the fundamental wave component is .beta., then the output of the circuit 5 can be expressed as 0.beta.Ifl.times.
On the other hand, if the signal Va is made up of only the second harmonic component If1, the output of the circuit 1 will be α and If2, and the output of the circuit 5 will be 1If2×.

α is the output ratio of the filter 2 to the second harmonic component If2. Therefore, the signal Va whose content rate of the second harmonic component If2 is X is If4+XIf2, and the output of circuit 1 is Kl
lfl+XaKllf2, the output of circuit 5 is K1β1f,
It becomes XK+XKllf2×K.

The comparator circuit 10 outputs an output when the output of the circuit 5 exceeds the output, but in that case, the ideal state is α-β-001.
+F2-1), it becomes K-.

However, in order to approach such a state, it is necessary to increase the selectivity Q of the filters 2 and 6, but doing so causes the disadvantage that the transient response time of the circuit becomes longer.

Also, is there a transient state? In order to prevent the detection circuit from malfunctioning, filter 2 must have a slower response speed than filter 6. If the selectivity of the circuits 1 and 5 is poor, the outputs of the circuits 1 and 5 will change due to the phase difference between the fundamental wave component 1 and the second harmonic component 1f2 of the signal Va.
The detection sensitivity of the detection circuit changes depending on the superimposed phase of the negative fundamental wave component 1 and the second harmonic component 1f2.

FIG. 3 is a block diagram of a conventional detection circuit in which β is attenuated so that the detection sensitivity does not change due to the superimposed phase of the second harmonic component.

In FIG. 3, 11 is a filter for blocking the fundamental wave component (active symbol VaO), and 5' is a circuit for selecting the second harmonic component. Other parts in the figure (well, the same as in Figure 1. (2
) If we pay attention to Equation 1, we can see that the factor that changes the detection sensitivity is α
, β and x. Generally, since X is 0.1 to 0.15, xα is sufficiently small, and reducing β is more effective than reducing α. FIG. 4 is a graph showing frequency gain characteristics of the detection circuit (not shown in FIG. 3).

As is clear from the characteristics shown in Figure 4, the detection circuit improves the effect of the above-mentioned phase change (on detection sensitivity), but it has the disadvantage that the transient response time as a circuit becomes longer. This invention was made in order to eliminate the drawbacks of the conventional ones as described above, and it adds the fundamental wave component in reverse phase to a circuit that selects the harmonic component of a specific order, thereby adding the harmonic component. It is an object of the present invention to provide a harmonic content rate detection circuit that can shorten the transient response time without increasing the Q of the filter by including a circuit for removing the harmonics.

An embodiment of the present invention will be described below with reference to the drawings.

In figure 5? 12 is a phase shifter that shifts the phase of the signal b of the filter, 13 is an amplifier that amplifies the output of the phase shifter 12, and 14
is an adder circuit that adds the output of the amplifier 13 to the output of the filter 6 in such a way that the fundamental wave component contained therein has a negative polarity.Other parts are the same as those shown in FIG. Next, the operation will be explained with reference to FIG.

Now, assuming that the simple symbol Va has a waveform as shown in FIG. 6a, the filter 2 still contains a considerable amount of harmonic components and outputs a signal b as shown in FIG. 6b. The signal b is inputted to the adder circuit 14 via the phase shifter 12 and the amplifier 13. On the other hand, the signal Va is inputted to the filter 6, and from this, as shown in FIG. The signal Vc containing the fundamental wave component is output as a signal C.The signal Vc is input to the 5-adder circuit 14, and the fundamental wave component is added by the negative polarity f and the signal Vb, as shown in FIG. 6d. The signal Vb is approximately composed of the second harmonic component.This operation can be explained using the following equation.

In other words, the active name Va? The fundamental wave component is Vf,a, the second harmonic component is F2a, and the fundamental wave component Vf is the signal Vbl.
, b, the second harmonic component is Vf2bl signal Vcl(a), the fundamental wave component is FO,, the second harmonic component is VfO2, then b so that ・Vflb-Vflc=0
When the phase is shifted by θα and multiplied by α, θd1 becomes phase shifter 12! Since the phase shift angle of Vf2b is α<l, β<l, (compared to the first term 1 to the second term of Equation 4, it is very small and the phases do not match, so the first term 11 The signal Vd of the adder circuit 14, which can be ignored and from which the fundamental wave component has been removed, is sent via the rectifier circuit 7, smoothing circuit 8, and amplifier 9 to the comparator 10 as the output of the second harmonic component circuit TE. Comparator 10
and is compared with the output of circuit 2 of the fundamental wave component.

As is clear from FIG.
Even if the Q of the circuit is lower than that of the conventional circuit, the transient response time of the circuit is approximately 1, which is appropriate because it consists of almost the second harmonic component. What? In the above embodiment, the fundamental wave component is removed by adding the second harmonic component on the output side of the filter that selects it, but the same applies to harmonic components of other orders. As shown in Figure 7, filters 11 and 6 are connected in series, and filter 6 is connected to adder circuit 14.
Alternatively, as shown in FIG. 8, the input of the filter 11 may be introduced from the output side of the filter 2 to obtain the same effect as the embodiment shown in FIG.

As described above, according to the present invention, an adder circuit is provided in the circuit that selects the harmonic component of a specific order, and the fundamental wave component is canceled out and removed. This has the effect of shortening the transient response time and making it easier to set the detection sensitivity.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a conventional detection circuit, Figure 2 is a graph showing the characteristics of the circuit shown in Figure 1, Figure 3 is a block diagram of a conventional detection circuit, and Figure 4 is the circuit shown in Figure 3. FIG. 5 is a block diagram of a detection circuit according to an embodiment of the present invention, FIG. 6 is a waveform diagram of the circuit shown in FIG. 5, and FIGS. FIG. 2 is a block diagram showing an example. 1, 5, 5', 5... circuit, 2, 6, 11...
... Filter, 3, 7 ... Rectifier circuit, 4,
8... Smoothing circuit, 9, 13... Flattener, 10... Comparator, 12... Phase shifter,
14...Addition circuit.

Claims (1)

[Scope of Claims] 1. A first circuit that selects the fundamental wave component from a signal containing a fundamental wave component and a harmonic component of a specific order thereof; and a second circuit that selects the harmonic component from the signal. , a comparison circuit that compares each output of the first and second circuits, and a harmonic component content rate detection circuit that detects the content rate of the harmonic components, the signal derived from the first circuit. A harmonic component content detection circuit characterized in that the second circuit includes an adder circuit that shifts the phase of the fundamental wave component and adds the fundamental wave component with a polarity that cancels out the fundamental wave component in the second circuit. 2. The harmonic component content detection circuit according to claim 1, wherein the adder circuit is cascaded to a filter that selects a harmonic component of a specific order. 3. A harmonic generator according to claim 1, wherein the adder circuit is cascaded to a first filter that blocks a fundamental wave component and a second filter that selects a harmonic component of a specific order. Component content detection circuit.