JPS62104422A - Automatic monitoring of 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 Application of the Invention] The present invention relates to an automatic monitoring system for a digital protection relay device, and particularly to an automatic monitoring system for a digital protection relay device suitable for detecting trips due to cable breakage.

[Background of the invention]

First, the system configuration of the digital protection relay device will be explained. Taking generator protection as an example, as shown in FIG.
Broadly speaking, it consists of a voltage transformer 4 that converts current, a current transformer 5, and a cable that connects the voltage and current transformers and the digital protection relay device 7. Next, FIG. 2 shows the internal configuration of the digital protection relay device. The digital protection relay unit includes an input conversion auxiliary transformer 12 that converts input from a voltage and current transformer into a logic level, a filter 13 that removes unnecessary frequency components of voltage and current, and a filter 13 that removes unnecessary frequency components of voltage and current.

A sample holder 14 that holds the current value, a multiplexer 15 that selects the output of the sample holder and inputs it to the A/D converter 16, a calculation unit that calculates the characteristics of various protective relays from the input voltage and current, and memory. unit 1
7. The output unit 18 which outputs the calculation result is configured with multiple units, and the digital protection relay unit is further duplicated, and the unit's contact output 10 is tripped under the AND condition to improve reliability. Furthermore, the digital protection relay device has an automatic monitoring function, and generally has two functions: automatic inspection and constant monitoring. For automatic inspection, lock the -carrier and trip circuits with contact 11X,
Using a separate power supply, apply AC input to the auxiliary transformer circuit,
This is to check that normal arithmetic processing is being performed, and continuous monitoring is performed online to detect malfunctions in the input conversion section, malfunctions in the arithmetic processing section, and malfunctions in the contact input/output section. For this reason, various constant monitoring methods are being applied. Here, a method for constantly monitoring the input converter according to the present invention will be described. Conventional constant monitoring of the input conversion unit is such that if any phase of the three-phase input circuit becomes abnormally high (for example, the filter gain drops or the phase shifts), the three-phase Focusing on the fact that it becomes unbalanced, zero-sequence current (L) is always maintained. ``I-++Ibt+Iet Negative phase current (work,) L=Iat+a2Ibt+aIet Here, Iat, Ibt + I.t calculates the sampling of each phase current at a certain time t (the same applies to voltage), and Io or I2 is If it continues to occur for a certain period of time, it will be detected as a constant monitoring failure and will be trip-locked.The timer counts.
Even in the event of an actual accident involving a generator, etc. .

Since I2 occurs, this is to distinguish it from the occurrence of Io and I2 due to an accident.

Next, the problems of the conventional method described above will be explained. Second
As explained in the figure, the single digital protection relay unit is duplicated, so even if one input circuit becomes abnormal and the relay operates, it will not trip, but the auxiliary transformer may be disconnected or the cable may be disconnected. In the case of a poor contact, a differential current is generated in the generator's current differential relay, so both digital protection relay units operate together and trip. In particular, permanent power plants, etc., use voltage.

Because the current transformer and the protective relay device are far away, the cable distance is long, and the environment is very humid and very bad, so problems with the cable are highly likely.

However, with the conventional constant monitoring method, there is no way to distinguish between tripping due to a generator accident and tripping due to cable trouble, so when a trip occurs, it is necessary to inspect everything from the generator to the cable. Unfortunately, it takes a huge amount of time. In addition, when inspecting digital relays, the present invention shortens the inspection time at the time of trip by displaying them separately from trip charges due to cable breakage, connection failure, etc., and trips due to generator accidents. It is.

[Summary of the invention]

In the event of cable breakage or poor contact, etc., before and after the occurrence,
The current in the phase where the trouble occurs decreases (in the case of a pT circuit,
A similar phenomenon occurs with voltage. ) only. FIG. 4 shows the current vector when the human phase cable is disconnected. On the other hand, when a fault occurs in a grid, the magnitude and phase of the current change before and after the fault occurs. Figure 5 shows how the current vector changes during various types of accidents.

(a) is at the time of a 3-line accident, (b) is at the time of a 2-line accident, fc)
shows the state of vector changes before and after the occurrence of a one-line accident. As is clear from Figures 4 and 5, in the case of cable breakage, etc., if you combine the currents of each phase before and after the trouble occurs, the combination of three-phase balanced currents (for example,
I-, Ib', I. It is conceivable that a change in the current due to power fluctuations or the like can result in a combination of '), but since the cycle of such a phenomenon is 2 to 3 Hz, changes in the current value within a few cycles can be ignored. On the other hand, in the event of an accident,
The combination of currents before and after an accident always results in an unbalanced three-phase current. The present invention focuses on the difference between a cable breakage and an accident, and constantly calculates the negative sequence current based on the current at a certain time t and the current after n cycles (t-1-n). Depending on the presence or absence of negative sequence current, it is possible to distinguish between trips due to cable breakage, etc., and trips due to accidents. FIG. 1 shows a flow diagram according to the present invention. First, the current value at time t, Imt I
Enter Ibt IIet and save. Next, the current value after n cycles, I a(t+++) l Ib(t+n
)+Ie(t+n), and calculate all of the following three sets of negative sequence currents.

Its = Iat + a” Ib(c+++) +
a Ic(L+n) (1) Izb”Ia(
t+n)+aJbt+a Ie(tg) (2
)I2 a = In(t+n)+a' Ibt+ a
Ic(t+++) (3) Calculated here,
La+ Izb, It. In normal times, Iz-=Lb=Le=0 In the event of an accident, La≧, Lb≧, I2e≧ When the cable is disconnected, 2. =0. I2b≧, I2゜≧K (when A phase is disconnected) I2A≧, l2b=O,L. ≧K (when B phase is disconnected) I21≧, Lb≧, I2゜=0 (when C phase is disconnected), so when tripping occurs due to cable disconnection, I2-=O1 or l2b=O1 or I2 ．． :
Since condition O is satisfied, cable breakage is detected based on this condition. There is no need to consider troubles with cables and input converters that occur over multiple phases.
) is used to calculate the negative sequence current. In addition, 3 to 4 cycles is appropriate for n, and this flowchart also has the function of monitoring defects in conventional filters, sample holders, etc.

If the two phases are the current value at time t and the first phase is the current value at (t+n), it is also possible to detect a cable break across the two phases. In the above explanation, the 01 circuit was described, but the same applies to the 91 circuit.

〔Effect of the invention〕

According to the present invention, trips due to cable breakage, poor contact, etc. are displayed to distinguish them from trips due to accidents, thereby shortening the inspection time at the time of trip.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the present invention, Fig. 2 is an explanatory diagram of a digital protection relay system, Fig. 3 is a conventional constant monitoring system, and Figs. 4 and 5 are explanatory diagrams of vectors at the time of cable breakage, etc. and accidents. , FIG. 6 shows a digital protection relay system. DESCRIPTION OF SYMBOLS 1... Step-up transformer, 2... Generator, 3... Neutral point resistance, 4... Voltage transformer, 5... Current transformer, 6...
...Cable, 7...Digital protection relay device, 8
... input converter, 9 ... digital protection relay unit, 10 ... protection output contact, 11 ... automatic monitoring lock contact, 12 ... auxiliary transformer, 13 ... filter, 14 ... Sample holder, 15... Multiplexer, 16... A/D converter, 17... Calculation, memory unit, 18... Output unit, 19... AND gate.

Claims (1)

[Claims] 1. In the automatic monitoring method of digital protection relay equipment, by calculating the negative sequence current from the sampling value at a certain time t and the sampling value after n cycles (t+n) among the input values of each phase of PT and CT. , an automatic monitoring system for digital protection relay devices, characterized by having a function to detect trips caused by cable breaks.