JPS62178118A - Digital protective relay - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a digital protective relay that calculates resistance and inductance (or reactance) from voltage and current.

[Conventional technology]

FIG. 5 is a diagram illustrating the principle of the Mo element of a conventional digital protective relay as shown in, for example, Mitsubishi Electric (Vol. 54, No. 11, 1980), published by Mitsubishi Electric, November 1980.

As shown in the figure, the difference vector (z i -?) between the current vector i multiplied by the impedance and the voltage vector * is calculated, and the voltage vector! It is determined whether the phase difference between the two is within 90°.

If the phase is within 90', within the circumference indicated in the operating range,
It turns out that a voltage vector* is included.

Expressing this in a formula, the phase difference γ between current and voltage and the impedance angle θ are 121·1ilc.
os(θ-7) > lvl, 1 no l cn
s (θ−γ) ■゛11
1, it is determined that it is within the circle.

The means for realizing this using a digital protective relay will be explained next.

AC voltage U(t) and AC current 1(t) at the same time,
Sampling is performed at a sampling interval T, where T is a time equivalent to 30 degrees in electrical angle.

When the alternating current 1(t) is advanced by θ, the following equation is obtained.

1(t)・eJ″=(cos・1(t)−(Sinl
・1(t-8T) ■The two vectors are the reference vector Upo 1(t) and the calculation vector Upol(t
), then Upol(t) = U(t)
■Uop(t) = l no 1 ・1(t)・
ejθ−U([)=1 of 1−(−1(t) of cal)−
(sin a)-1(t-aT))-ut)
■ is obtained. Two vectors Upol(t) and U
The condition that op(t) is within 90° can be determined by formula (2).

Upol (t-87) Uop (t-8T) + Upol (
t) ・Uop(t) > 0 0Equations (2), (2), and (2) described above are all valid on the condition that the frequencies of the alternating voltage and the alternating current are constant.

[Problem that the invention seeks to solve]

However, in recent power systems, due to the increase in the number of cable systems and static capacitors for power factor improvement, when a system fault occurs, free oscillating harmonic voltages and currents that resonate with the reactance of the power transmission lines are generated. The order of harmonics is approaching that of the fundamental wave, and the content rate has become very large.Therefore, the above equation (2), which focuses only on the fundamental wave, has a very large error and cannot be used as a practical protective relay. In addition, since the fundamental wave requires a processing time equivalent to 90 degrees of electrical angle, there is a limit to how high the speed can be increased.

This invention was made to solve the above-mentioned problems, and allows for accurate determination even when the content of low-order harmonics is large. Furthermore, the calculation processing time is shortened, allowing for high-speed determination. The purpose is to obtain a digital protective relay that can

[Means for solving problems]

The digital protective relay according to the present invention is provided with a voltage integration circuit and a current integration circuit that derive time-integrated values of voltage and current, and samples the current values and the outputs of the voltage integration circuit and the current integration circuit, respectively, and digitalizes them. By using the converted data and solving two-dimensional simultaneous equations using AC theory, the resistance component and inductance component (reactance component) are determined.

[Effect]

The two-dimensional simultaneous equations in this invention either require a voltage integral value and a current integral value, or are provided with dedicated integral circuits for deriving the respective integral values, and the outputs of these integral circuits are also
It uses a means of sampling at the same time and with the same period as other currents.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
In the figure, (1) is the power system, (2) is the voltage transformer,
(3) is a current transformer, which introduces the voltage and current of the power system, respectively. (4) and (5) are input converters for obtaining voltage values that are easy to process, and (6) and (7) are integrating circuits that convert the outputs of input converters (4) and (5) For obtaining the temporal integral value, (8), (9),
QO is a sample and hold circuit that holds the instantaneous value of the input voltage at regular intervals, and Oυ is a multiplexer that sequentially switches the input and passes the voltage value to the analog/digital converter shown in the next stage (2). Q3 is an arithmetic unit that processes the digitized numerical values using a predetermined arithmetic method in the memory circuit shown in a4).

Now, assuming an impedance in which a resistor R and an inductance L are connected in series, and if the current flowing through the voltage U1 across the impedance is i, the waveforms shown in FIGS. Furthermore, the time integral of the waveforms of voltage U and current i is f tJ(
t) d and f i (t)dt, the waveforms are y) and y), respectively.

If these waveforms (a), y), ni) are sampled at a constant period T,...;(t-2T), 1(t-T)
, 1(t),...f U (t −2T)dt.

∫U(t-T)dt, ∫U(t)dt,..., ri
(t-2TMt, f; (t-T)dt.

, I''1(t)dt is obtained.

According to electrical theory, the relationships of formulas ■ to ■ are established.

di (t-2T) U (t-27) = R-i (t-27) 10L・□
■t di (t-T) U (t-T') = R-1 (t-T) 10L・□
■t a [By time-integrating these equations, the 0-0 equation can be obtained.

f u(t-2TMt= R-f 1(t-2r)dt
+L・(t-2T) f U(t-
T) at= R-∫i(t-T)dt +L-r (t
-r) [Phase]∫U(tMt = R-
f t(t)at+L-1(t) @Generally, if time t-1t (I is an integer), the [phase] formula is obtained.

∫U(t-lT)dt= R-∫i(t-1'r)dt
+Li(t-lT) (Ji■~[Phase] Since the equation is expressed as a general equation that is not related to frequency, it holds true in any frequency range.

Now, if we treat the 0 equation and the [phase] equation as two-dimensional simultaneous equations, and solve them using the determinant, we will obtain the equation (2) and the [F] equation.

Therefore, as shown by the right-hand sides of equations ri and 0, the time and t
The resistance component R and the inductance component can be directly calculated from each sampled value of -IT.

Since the values of R and L are independent of frequency, they can be calculated accurately even if harmonics are superimposed on the voltage or current.

Furthermore, the value of the integer l can be any value < ,! =1
In this case, R and L can be calculated in the shortest period.

It is well known that the reactance value can be obtained by multiplying the inductance obtained by this equation 0 by the angular velocity.

Figure 8 illustrates the calculation procedure of the [phase] formula, where the sampling values ∫U(t)dt, ∫U(t t'r)cit
, t(t), i(t lT)−∫i(t)dt,
, ri(t-lT)dt as illustrated, multiplication processing (18-1), (18-2), (18-J),
(18-4) and subtraction processing (19-1) (19-2)
This shows that the process can be performed using the following steps: and division processing. Although not shown, equation 0 can be expressed similarly.

FIG. 4 shows an example of an integrating circuit for obtaining an integral value, where Q is an operational amplifier, the wire is a resistor, and the wire is a capacitor. Is this integrator circuit known? Is it an operational amplifier? Assuming that the amplification factor of the sword is very large, Uo(t) = −−∫
UI(t)dt=-∫U(t)dtQ, and if the resistor γ and capacitor C are appropriately selected, K=1, and an output signal obtained by integrating the input signal can be obtained.

In addition, in the above example, it was explained that the two-dimensional simultaneous equations at the sampling times of time t and t-lT are solved as shown by equations 0 and 0. It may be.

Furthermore, in the above embodiment, the resistance component R and the inductance component are calculated, but it is also possible to store R and L in the memory αΦ and judge the magnitude of the calculation result. Furthermore, it is also possible to determine the phase difference between voltage and current from R and L.

In addition, in the above embodiment, it was explained that voltage and current are introduced in one amount each, but voltage and current obtained by the relationship between phases and lines in the power system, relationships including zero phase, etc. The same effect as in the above embodiment can be obtained.

In addition, in the above embodiment, it was explained that resistance and inductance are determined, but considering that the inductance value of power systems, especially power transmission lines, is proportional to the distance of the power transmission lines, digital protective relays are used to measure the resistance and inductance of power transmission lines. It is possible to estimate the distance to the accident point, and it can also be used as a failure point locator.

〔Effect of the invention〕

As described above, according to the present invention, the voltage and current are input, and the time integral values of the voltage and current are obtained to calculate the simultaneous equations at two times. Moreover, it is possible to obtain a digital protective relay that is not affected by frequency.

[Brief explanation of drawings]

FIG. 1 is a digital protective relay according to an embodiment of the present invention, FIG. 2 is a diagram showing the sampling relationship of voltage, current, voltage integral, and current integral, and FIG. 3 is a processing flow diagram for determining the resistance component. FIG. 4 is an example of an integrating circuit, and FIG. 5 is a principle diagram of a conventional Moh element. In the figure, (1) is the power system, (2) is the voltage transformer,
(3) is a current transformer, (4) and (5) are input converters, (
6), (7) are integral circuits, (s), (9),
an is a sample hold circuit, Qυ is a multiplexer, (6) is an analog-to-digital converter, a is a computing unit,
αΦ is a memory circuit, Qυ is an operational amplifier, a wire is a resistor, and a wire is a capacitor. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] In a protective relay that performs sampling-to-digital conversion of the voltage and current of a power system at a constant cycle and then performs arithmetic processing based on the converted values, there is provided a voltage integrator circuit that derives a time-integrated value of voltage and a time-based current. and a current integrator circuit for deriving a specific integral value, and the digital protective relay captures the voltage, the current, and the outputs of the voltage integrator circuit and the current integrator circuit at the same time and at the same sampling period T, respectively. The outputs of the current, voltage integration circuit, and current integration circuit at sampling time t and sampling time t-IT separated by a predetermined number of samples l are expressed as i(t), i(t-IT), and ∫U( t) dt, ∫U(
t-lT)dt, ∫i(t)dt, ∫i(t-lT)d
When t, the following formula R = [∫U(t)dt・(t-lT)-∫U(t-lT
)dt・i(t)]/[∫i(t)dt・(t-lT)
−∫i(t-lT)dt・i(t)]L=[∫i(t)
dt・∫U(t-lT)dt-∫i(t-lT)dt・
∫U(t)dt]/[∫i(t)dt・i(t-lT)
-∫i(t-lT)dt·i(t)] or an equation equivalent thereto to measure or determine the resistance and inductance of a power system.