JPS6150073A - Detection of three-phase unbalance - Google Patents

Abstract

PURPOSE:To enable the detection of a three phase unbalance at a high speed with a high sensitivity without being restricted by a sampling timing, by sampling a three-phase instantaneous power at any time to detect hourly changes therein. CONSTITUTION:Three phases of voltages VA, VB and VC and three phases of currents IA, IB and IC in a power system are detected with a transformer PT and a current transformer CT and inputted into an analog/digital converter 2 through a sample holding circuit 1. Output of the converter 2 is inputted into a multiplier and an adder to calculate a 3-phase instantaneous power Pt, which is inputted into a memory and a subtractor. Then, the difference DELTAPt between the 3-phase instantaneous power Pt-1 accumulated in the memory before one sample and the PT is inputted into a comparator and when it exceeds set value delta, a decision signal of 3-phase unbalance is outputted from the timer.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] This invention contributes to grid protection, grid stabilization, etc.
The present invention relates to a phase unbalance detection method.

[Conventional technology]

Conventionally, algorithms for digital protection devices for system protection or system stabilization are based on the 6th grade, 6.2 of ``Protection Relay Engineering, University Course of the Institute of Electrical Engineers of Japan,'' published by Ohm Publishing.
There was a basic calculation algorithm shown in the table in Figure 1. For example, in the case of an overcurrent detection algorithm, if the sum-addition method shown in Fig. 1 is used, the processing flow will be as shown in Fig. 2. t
- Current sample value at time 3 (3 sampling @), t
is the effective value of time t, Nll″lt is the operation counter.

Figure 2 is a flowchart showing the basic calculation algorithm shown in Figure 1, and it is a well-known fact that the effective value calculation shown in the figure is effective only when sampling is performed at a timing of 30 degrees in one cycle of the corresponding frequency. It is.

Therefore, the data t at the current time stored in the normal memory and the data 90' before the current time are calculated by t-3f% effective value, and it is determined whether the effective value t2 is greater than or equal to the set value ε. Depending on the situation, overcurrent detection is performed. In addition, normally, the judgment results are checked several times in a row, taking into consideration the axiality, to create a ``N''. It goes down once every time it is detected.

When the counter N is 3 times or more, the operation of η is detected.

In addition, the algorithm of general digital protection equipment is
As shown in the figure, data with Vc3 sampling always ON (3
(at the time of 0' sampling), all are used to perform the calculation.

Since the algorithm of the conventional three-phase unbalance detection method is configured as described above, it always uses the current data and the data three samplings ago.71) In the case of 7iC, data is missing during calculation. , the calculation becomes invalid for more than three sampling times, and detection is delayed accordingly.

Further, there are restrictions such as the sampling timing being limited to 30° (12 times the fundamental frequency or an integral multiple thereof) vc.

[Summary of the invention]

This invention was made in order to solve the above-mentioned disadvantages of the conventional method, and it samples the three-phase instantaneous force at an arbitrary time and detects whether it becomes temporally distorted or exceeds a certain level. By doing so, high speed and high sensitivity 3
The object of the present invention is to provide a method for detecting phase unbalance.

[The secret case of invention]

Next, to explain this invention in detail, first, when the system is in an equilibrium state, the "width pressure" j of each phase is, and the three-phase instantaneous force pressure Pv = Va (tlX engineering aF + From bfυ× chemical 1+
Vc(tlXICtυ=VmX工mX(sln ωtx
sin(ωt+θ)+5in(ωt-1200)xsi
n(ωt+θ-120°)+5in(ωt-240×
5in (ω = 10-240') Vm
! 08 (2ω at 10-240°) 1-coB (2ω at 10-120) =--Vm

′=! In addition, when the three phases are in an imbalance state, in addition to the above-mentioned DC component, a trigonometric component with twice the frequency is generated.

In addition, even in the load f palpitation equilibrium state, if Vm, m, and θ change while maintaining balance, the above instantaneous magnetic force PMt+
In this case, the rate of change is extremely slow compared to the fluctuation of the trigonometric function described above, so if the time interval is appropriately selected, it can be completely distinguished from the unbalanced state.

Based on the above-mentioned principle, an algorithm for detecting system complaints is, for example, vcfx as shown in the flow shown in Figure 3.
Ru. In the figure, Δt: ΔCt is the current sample value of the A, B, and C phases at the time VC, vAt.

As above, vBt, VCl are vehicle pressure sample values of A, B, and C phases, Pl,, Pl, -1 is the time of the valley, instantaneous vehicle force at time t-1 (data one sample before), ΔPt
is the isometric force change at time t, δ (delta) is the set value, and lA is the honorable mention counter.

In Figure 3, as mentioned above, this algorithm takes advantage of the fact that the three-phase instantaneous magnetic force always has only a DC component,
The three-phase grinding machine At, at the time.

IBt, 工Ct ト3 Phase vomiting pressure VAt, VBt
, vct calculates the 3-phase instantaneous force Pt, and stores it in the memory one sample ago, 'fc 3-phase instantaneous power Pt-
It is determined that the difference ΔPt from 1 is the set value δ. The result of this judgment is used to detect three-phase unbalance in the system.In addition, in the figure, verification is performed multiple times as in the conventional algorithm. (It doesn't have to be M-3.) Also, is the above algorithm in Figure 3? This is a block diagram showing the entire concrete configuration of the protection device when used. In the figure, (1) is a sample and hold circuit, and (2) is an analog/digital converter.

In the above example, all the data from one sample before was used for the power change Δp, 4) calculation, but there is no need to bury l3Jt (, when data is missing, VCri2 samples or 3
All data from before the sample may be used.8Also, in the above actual example, it was explained that the unbalance of the grid is detected based on the amount of power change, but if the instantaneous power itself exceeds a certain value, Have you become a JLI? Furthermore, it goes without saying that the present invention is not limited to the digital calculation shown in FIG. 4, but can be similarly configured with an external calculation.

In addition, this invention is a system protection device or system stabilization device I7.
It is even more effective than VC when applied to

[Original side effect]

As described above, if the unreleased BAVc is detected, changes in the three-phase force, which should be constant in principle, can be detected instantaneously, so three-phase unbalance can be detected at high speed and with high sensitivity. Also, there is no restriction on sampling timing as in conventional methods.

[Brief explanation of drawings]

Fig. 1 is a diagram showing a conventional basic calculation algorithm, Fig. 2 is a flowchart showing an example of the algorithm in Fig. 1, Fig. 3 is a flowchart showing an example of an actual gun of the present invention, and Fig. 4 is a flowchart showing an example of the algorithm of the present invention. It is a block diagram showing an example of the drawing device used. As shown in Figure 3, (At) (At) (At) is the sample link L L Each phase (1') Current, (VAt)
(vnt) (vct) ri The voltage of each sampled phase, (Pt) multiplied by the three-phase instantaneous force, (Pt-1) multiplied by the three-phase instantaneous force one sample before, and (ΔPt) are the above Pt-Pt-
The difference of 1, δ, is a set value. In addition, in each of the above figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] (1) The product of voltage and current sampled from the power grid at the same time is added for three phases to obtain the instantaneous power amount, and an imbalance is determined based on the steep temporal change in this instantaneous power amount. Three-phase unbalance detection method.