JPH05336668A - Independent operation detector - Google Patents

Abstract

PURPOSE:To make it possible to detect independent operation of a low power plant regardless of frequency fluctuation. CONSTITUTION:An independent operation processing section receiving bus voltage VB of high power system and bus voltage VP of low power power plant comprises relays 251, 252 for detecting phase difference between voltages VB and VP having wide and narrow detecting zones respectively, timers T1 and T2 receiving outputs from the phase difference detecting relays and preventing erroneous detection, and an OR circuit OR1 producing a logical sum of the outputs from the timers T1 and T2, wherein independent operation is detected based on the phase difference between the voltages VB and VP.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an islanding operation detecting device for a small power plant.

[0002]

2. Description of the Related Art FIG. 8 shows a conventional small power plant connected to a large power system. In FIG. 8, PO is a large power supply, 1 is a large power system bus, 2 ₁ and 2 ₂ are power transmission lines connected to the large power system bus 1, and 3 is a high power system 1 via a power transmission line 2 _1. The connected small power generation station, 4 is a bus of the small power generation station 3, and 5 is a distribution line connected to the small power generation station bus 4.

In such a power system, in the event of a power system accident or the like, an automatic recovery operation is performed from the high power source terminal after the accident system is separated. In this automatic restoration operation, if the small power plant at the end of the system has a local load and maintains unstable operation, the restoration operation cannot be performed.

Therefore, an isolated operation detection relay 6 is provided in the small electric power plant 3 to detect that the small electric power plant 3 is in an isolated operation and disconnects the generator AG of the small electric power plant 3 from the system. ing.

Conventionally, the isolated operation detection relay 6 is composed of a frequency drop detection relay UFR and a frequency rise detection relay OFR, and incorporates the power plant bus voltage V _P detected by the transformer PT ₃ to obtain a frequency difference from the basic frequency f of the transmitted power. Δf (number H
z) is detected, and a trip command for the circuit breaker CB ₃ for interconnection with the power transmission line 2 ₁ is issued.

[0006]

However, depending on the state of power transmission to the local load L after islanding, the power may be balanced and the frequency fluctuation may be small. In such cases, it may not be detected by settling (the number H _Z variation detection) frequency reduction detection relay UFR and frequency rising detection relay OVR.

The present invention has been made in view of the above-mentioned problems of the prior art, and an object of the present invention is to balance power in an extremely balanced manner in a power transmission state to a local load after islanding. An object of the present invention is to provide an islanding operation detection device capable of detecting islanding even when the fluctuation is small.

[0008]

In order to achieve the above object, the islanding operation device according to the present invention is an islanding operation detecting device in an interconnection system of a large power system and a small power generation station, and a large power system busbar. An independent operation processing unit to which a voltage signal and a small power plant bus voltage signal are input is provided, and the independent operation processing unit detects the phase difference between the large power system bus voltage and the small power bus voltage. A phase difference detection relay and a second phase difference detection relay with a small detection zone, and a long time limit first timer and a short time limit for inputting a detection signal of the first and second phase difference detection relays for preventing erroneous detection. Second
And a logical product circuit that outputs an islanding operation detection signal by the logical sum of the outputs of the first and second timers.

The first and second phase difference detection relays may be constructed by adding a filter to the digital phase difference relay.

[0010]

[Operation] Since the islanding operation processing unit detects the phase difference between the large power system bus voltage and the small power bus voltage by the phase difference detection relay, the power is balanced by the power transmission state to the local load after islanding. It is possible to detect an islanding operation when the frequency fluctuation is small.

Since the first phase difference detection relay has a large detection zone, it detects a phase difference in which the phase difference gradually widens. The long-timed first timer blocks an erroneous detection output of the first phase difference detection relay during power fluctuations such as when an accident is removed.

Since the second phase difference detection relay has a small detection zone, it detects a phase difference in which the phase difference suddenly spreads. The second timer with a short time period prevents the output of the erroneous detection of the second phase difference detection relay at the time of power fluctuation such as accident elimination.

Therefore, if the outputs of the first and second timers are output from the AND circuit, the islanding operation can be reliably detected regardless of the speed of change in the phase difference.

If an appropriate digital filter is added to the digital phase difference relay, the phase difference can be calculated accurately.

[0015]

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows the overall system configuration, FIG. 2 shows the circuit of an isolated operation system, and FIG. 3 shows the processing contents of the isolated operation processing unit. The same parts as those shown in FIG. 8 of the related art are designated by the same reference numerals, and the duplicate description thereof will be omitted.

1 to 3, 10 is a transformer PT ₁
The high-power system terminal device to which the voltage V _B of the high-power bus line 1 detected at step 20 is input, and 20 is the low-power power plant bus voltage V _P detected at the transformer PT ₃ and the voltage V _B data from the terminal device 10 are transmitted on the transmission line. It is an islanding operation detection device input via 19.

The terminal device 10 processes the voltage V _B input via the analog interface A / I in the terminal processing unit 12, and connects the parallel-serial code conversion unit P / S, the transmission unit 14, and the optical transmitter E / O. It is configured to output to the transmission path 19 via the.

The islanding operation detection device 20 receives the voltage V _B data input from the transmission line 19 via the optical receiver O / E, the transmission section 22, and the serial-parallel code conversion section S / P and the analog interface A / I. The islanding operation processing unit 24 performs islanding operation detection processing on the basis of the voltage V _P input via the output, and the output unit D / O outputs a disconnection command.

As shown in FIGS. 3 and 4, the islanding operation processing unit 24 detects the phase difference between the zones 1 and 2 in which the phase difference detection zones for detecting the phase difference between the voltages V _B and V _P are different. It is composed of relays 25 ₁ and 25 ₂ and false detection prevention timers T ₁ and T ₂ to which the outputs thereof are input, and a logical sum circuit OR ₁ which outputs a disconnection command by the logical sum of outputs of the timers T ₁ and T _2. There is.

Next, details of the islanding operation processing unit 24 will be described with reference to FIGS.
This will be described with reference to FIG.

The basic idea of this islanding operation detecting device is as follows:
The fact that a small electric power plant (hereinafter simply referred to as a small electric power plant) is separated from the electric power system to become an independent system depends on detecting the phase difference between the small power plant bus voltage and the large power system bus voltage. judge. This system cannot detect only when the frequency of a small power plant that has become an independent system is completely synchronized with the system frequency and has a predetermined phase difference, and can be detected otherwise.

Determining Zones of Phase Difference Detection Relays 25 ₁ and 25 _{2 In} order to increase the detection sensitivity of the isolated operation state, it is preferable that the detection zone of the phase difference detection relay is wide. There is a risk of erroneous detection during power fluctuations such as. Therefore, the islanding operation processing unit 24 functions as two types of digital phase detection relays of zone 1 and zone 2 having different phase detection zones, and is used as follows.

(1) Zone 1: Detection when frequency gradually changes The detection target is when the phase difference between the large power system power source bus voltage and the small power plant bus voltage gradually increases. Although the detection zone is relatively wide, a long timed timer T ₁ is used so as to prevent erroneous detection during power fluctuations such as when an accident is removed.

(2) Zone 2: Detection when the frequency changes abruptly The small power plant bus voltage vector rotates at the difference frequency between the two voltages with reference to the large power system bus voltage. When the frequency difference is large, the time during which the single-system voltage vector exists in zone 1 becomes short and cannot be detected by the long-timer timer, so a short-timer timer is required. Therefore, the detection range is set to a narrow phase range that does not erroneously detect power fluctuations when an accident is removed, and a short time limit timer T ₂ is added to this.

(1) Determination of zone 1 <Error factor> RT error ... 2 ° Relay error ... 6 ° SP synchronization deviation: 2 ° Input transformer-analog section error: 3 ° Calculation error: 1 ° It is necessary to allow for an error of °.

The voltage phase shift between the large power system and the small power plant is
Considering the worst case of 30 °, the phase shift detection angle becomes 38 °. This has a margin, and is set to 60 °. The timer is a variable timer of 0.1 to 10.0 seconds (step 0.1).

(2) Determination of zone 2 Since it is unlikely that the voltage phase difference between the large power system and the small power plant house bus will be 90 ° or more even during power fluctuations, the detection angle of zone 2 is 90 °. To do.

Zone 2 is mainly intended for detection of a sudden frequency shift. The relationship between the spread width φ of the detection zone, the frequency difference Δf, and the detection timer T _{2 is} as follows.

(1 / Δf) × (φ / 360) = T _{2 In} order to detect a large frequency shift, it is necessary to shorten the timer. Table 1 shows the relationship between the frequency shift, which is the detection limit, and the timer.

[0031]

[Table 1]

On the other hand, conventional customer relays UFR, OFR
Because of settling there with the degree "rated ± 1~3H _Z", the phase difference detection relay in accordance with the present method, thinking that to detect a range of "rated ± 3~5H _Z", which saw a slight margin in this It is necessary to set the timer. Therefore, the range of timer settling is set to 0.01 to 1.00 second (step 0.01).
The relationship between the conventional relay UFR and OFR system and the detection range of this system is as shown in FIG.

As a result of investigating a method for obtaining a phase difference between power supplies having different frequencies by digital calculation, by adding an appropriate digital filter to the output result of the calculation in the phase difference detection relay which has been generally used conventionally,
It was found that the phase difference can be calculated with high accuracy.

Phase Difference Calculation Method There are various methods for digitally calculating the phase difference between two AC electric quantities, which has been adopted in the conventional digital relay, but as shown in FIG. 6, either method is compared. The phase difference is accurately obtained only when the two electric quantities have the same frequency, and an error occurs in trying to obtain the phase difference between the electric quantities having different frequencies. Two electric quantities are represented by the following equations.

A (t) = Asin (ω ₀ t) b (t) = B sin (ω ₀ t + Δωt) Further, the electric quantity A side is defined as the fundamental frequency, and sampling is performed at a frequency 12 times the frequency of the electric quantity A. If it does, the sampling data in each point (n) is expressed by the following equation.

[0036]

[Equation 1]

Specific data at n = 0.1, ..., 3, ..., 6 are shown below.

(Hereinafter, t ₀ is an arbitrary time, so the subscript 0 at time t is omitted)

[0039]

[Equation 2]

Here, the product of the sampling data at each point is obtained.

[0041]

[Equation 3]

It can be seen visually that each equation is divided into a term that vibrates at an angular velocity of -Δωt and a term that vibrates at 2ω ₀ t + Δωt. Here, in order to eliminate the term that oscillates at 2ω ₀ t + Δωt, a ₀ · b ₀ + a ₃ · b ₃ is obtained. This corresponds to a digital filter operation for removing harmonics.

FIG. 7 shows a calculation block diagram of the digital relay.

Output of digital filter DF ₁

[0045]

[Equation 4]

From the above equation, the term oscillating at 2ω ₀ t + Δωt is attenuated by tan {(Δω / ω ₀ )  (π / 4)} times, but cannot be completely eliminated.

By the way, when Δω / ω ₀ = 0.2,
This is 0.1584 (= 15.8%), which is a considerable error.

Output of Digital Filter DF _{2 In} order to further attenuate this term, the following calculation is performed.

A ₀ = a ₀ · b ₀ + a ₃ · b ₃ A ₃ = a ₃ · b ₃ + a ₆ · b ₆ A ₀ + A ₃ = 2 · cos (−Δωt−2 · β) · cos ² (β ) −2 · cos (2ω ₀ t + Δω ₀ t + 2 · β) · sin ² (β) Accordingly, the vibration term of 2ω ₀ t + Δωt is tan ² {(Δ
It is attenuated by ω / ω ₀ ) · (π / 4)} times. By the way, Δ
When ω / ω ₀ = 0.2, 0.02508 (= 2.5
%), It will be considerably attenuated.

Output of digital filter DF ₃ To further attenuate this, B ₀ = A ₀ + A ₃ = a ₀ · b ₀ +2 · a ₃ · b ₃ + a ₆ · b ₆ B ₃ = A ₃ + A _{6 = a 3 · b 3 +2 ·} a 6 · b 6 + a 9 · b 9 Distant, B ₀ + B ₃ may be calculated.

[0051]

[Equation 5]

Therefore, B ₀ + B ₃ ≈4 · cos (−Δωt
-3 · β) As a result, the vibration term of 2ω ₀ t + Δωt is t
It is attenuated up to an ⁴ {(Δω / ω ₀ ) · (π / 4)} times.
By the way, when Δω / ω ₀ = 0.2, 0.0006
3 (= 0.06%).

The algorithm for obtaining the cosine (cos θ) of the phase difference: θ between the two electric quantities has been developed, and the method for obtaining the sine (sin θ) is as follows.

A ′ ₀ = a ₀ · b ³ −a ₃ · b ₀ A ′ ₃ = a ₃ · b ₆ −a ₆ · b ₃ B ′ ₀ = A ′ ₀ + A ′ ₃ = a ₀ · b ₃ − _{a 3 · b 0 + a 3} · b 6 -a 6 · b 3 ≒ 2 · si n (-Δω 0 t-2 · β) B '3 = A' 3 + A '6 = a 3 · b 6 -a 6 _{· b 3 + a 6 · b} 9 -a 9 · b 6 ≒ 2 · si n (-Δω 0 t-4 · β) B '0 + B' 3 = a 0 · b 3 -a 3 · b 0 +2 · a for the _{3 · b 6 -2 · a 6} · b 3 + a 6 · b 9 -a 9 · b 6 ≒ 4 · sin (-Δωt-3 · β) error, is exactly the same as that for determining the cosine.

Summarizing the above, C ₀ = B ₀ + B ₃ ≈4ABcos (−Δωt−3 · β) = 4ABcos θ (1) C ′ ₀ = B ′ ₀ + B ′ ₃ ≈4ABsin (−Δωt−3 · β) ) = − 4ABsin θ (2)

[0056]

[Equation 6]

Although θ changes with time t, it can be sufficiently confirmed in the confirmation timers T ₁ and T _{2 of} the phase difference detection relays 25 ₁ and 25 ₂ .

Further, 3β is a fixed error, but the problem is eliminated by giving a margin to the characteristic.

The relationship between the relay characteristics and the expressions (1) and (2) is as follows.

[0060]

[Equation 7]

The phase difference detection relay output of zone 1 is output as the logical sum of zone 1-1 and zone 1-2.

As described above, since the phase difference between the voltages of the large power system and the small power plant is detected by using the phase difference detectors having different phase difference detection zones, regardless of the speed of frequency change. Since it is possible to reliably detect a frequency change with little fluctuation, it is possible to reliably detect an islanding operation even if the frequency change is small when the islanding operation is performed.

[0063]

EFFECTS OF THE INVENTION Since the present invention is configured as described above, a minute frequency shift can be detected with high sensitivity by a phase difference, so that power is extremely balanced in a power transmission state to a local load after islanding. Even when the frequency fluctuation is small, islanding operation can be detected.

[Brief description of drawings]

FIG. 1 is a configuration explanatory view showing an entire system according to an embodiment.

FIG. 2 is a block circuit diagram showing an isolated operation detection system.

FIG. 3 is a block circuit diagram showing processing contents of an islanding operation processing unit.

FIG. 4 is an explanatory diagram of a phase difference detection zone.

FIG. 5 is an explanatory diagram comparing a frequency detection range with a conventional method.

FIG. 6 is a diagram showing two electric quantities and sampling data.

FIG. 7 is a calculation block diagram showing a calculation of a relay.

FIG. 8 is a structural explanatory view showing an entire system of a conventional example.

[Explanation of symbols]

1 ... high-power system bus 2 _1, 2 ₂ ... transmission line 3 ... low-power plant 10 ... large power system terminals 12 ... terminal processing unit 14, 22 ... transmission unit 19 ... transmission line 20 ... isolated operation detecting apparatus 24 ... Independent operation processing unit

Claims (2)

[Claims] 1. An islanding operation detection device in an interconnection system between a large power system and a small power station, comprising an islanding operation processing unit to which a large power system bus voltage signal and a small power station bus voltage signal are input. The islanding operation processing unit includes a first phase difference detection relay having a large detection zone and a second phase difference detection relay having a small detection zone for detecting the phase difference between the high power system bus voltage and the small power bus voltage. And a long-time first timer and a short-time second timer for preventing erroneous detection to which the detection signal of the second phase difference detection relay is input, and the logical sum of the outputs of the first and second timers. And an AND circuit that outputs an isolated operation detection signal. 2. The first and second phase difference detection relays are digital phase difference relays and are expressed by the following formula: C ₀ = 4ABcos (−Δωt−3β) C ₀ ′ = 4ABsin (−Δωt−3β) where β = (Δω / Ω ₀ ) ・ (π / 4) A is the maximum instantaneous value of the bus voltage of the large power system B is the maximum instantaneous value of the bus voltage of the small power power plant ω ₀ = angular velocity of the system frequency Δω = a digital filter of the angular velocity of the frequency difference The islanding operation detection device according to claim 1, wherein the device is additionally provided.