JPH0270233A - System protector - Google Patents

Abstract

PURPOSE:To realize a highly reliable protector by interrupting a load on condition that three requirements of voltage, apparent power variation of load and apparent power variation rate of load are satisfied for a specific time. CONSTITUTION:A first block 1 judges that the voltage is lower than a set value K1 while a second block 2 detects that the apparent load power variation is larger then a set value K2 and a third block 3 detects that the time variation rate of the apparent load power is higher than a set value K3. When these three requirements are satisfied, output from on AND gate 4 goes to 1 and when such condition continues longer than the set time T1 of a timer element 5, a load interruption command is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a system protection device that is installed in a substation of a power system and shuts off load transmission lines according to system conditions.

(Prior art) As power sources become larger and more remote, and power systems become larger and more complex, 2. Stable operation of power grids is becoming increasingly important.

On the other hand, social demands for improved supply reliability are increasing due to the problems of computers and other devices that require high-quality power, and due to the increasing sophistication of urban functions.

Here, the following factors can be considered as factors that worsen supply reliability. First, focusing on the system configuration, it is difficult to locate power sources in areas with heavy loads due to social factors. Therefore, power sources have to be located far from load areas, resulting in uneven distribution of loads and power sources.

This involves transmitting large amounts of power via long-distance transmission lines, and in addition to the stability associated with active power, there is a tendency for the ability to maintain a stable load-side voltage to deteriorate as well.

Furthermore, focusing on the characteristics of system loads, the reactive power characteristics of air conditioning loads, which account for a large proportion of the demand during peak summer power hours, can be cited.

Conventionally, one measure to prevent a voltage drop when a voltage drop occurs due to an increase in load is to cut off part of the load. This is a load cutoff that detects voltage and performs voltage control in addition to frequency control within the separated system when system separation occurs due to the spread of a system fault.

(Problems to be Solved by the Invention) As described above, in the conventional system, the load is simply cut off by detecting a drop in voltage.

However, when looking at the characteristics of the air conditioning load, it is similar to the induction motor load, and it has an operating characteristic in which the amount of reactive power consumed increases sharply when the voltage drops below a certain value. vinegar,
This tendency is even more pronounced in recent inverter type air conditioners (coolers).

FIG. 2 shows the reactive power characteristics with respect to the voltage of the load, where the vertical axis shows the reactive power Q, and the horizontal axis shows the voltage ■.

Characteristic (2) shown in the figure is a light load such as an incandescent light bulb, and is close to the characteristic of a constant impedance load, so that the reactive power Q consumed decreases as the voltage decreases.

Characteristic (2) is an induction machine load, and since the active power is kept constant, if the voltage decreases, the reactive power increases.

Therefore, when looking at the load comprehensively, the characteristics ■ and characteristics ■
However, if we consider a specific time period, especially in the summer, the proportion of air conditioning load increases, and the characteristic becomes close to (2).

In this case, when the voltage falls below the rated value VQ and drops below the voltage V corresponding to the minimum value Qm of the reactive power Q, the reactive power Q shows an increasing tendency, which in turn causes the voltage to drop further. Acts on the direction. At this time, due to the increase in load, the active power increases and the voltage decreases.

Therefore, a new problem in system operation is the voltage drop problem caused by the reactive power characteristics of the air conditioning load during peak demand in the summer.In particular, if the drop in system voltage is left as it is, the voltage of the entire system will further drop, causing the so-called so-called There are even cases where voltage instability occurs and the grid cannot be operated stably.

In order to prevent system voltage drops during heavy loads such as during summer peak demand periods, it is insufficient to apply conventional methods that detect only simple voltage drops, and a system protection device with a new operating principle is needed. It was hoped that it would appear.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a system protection device capable of stably supplying power during peak demand in summer.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the present invention provides a system that reduces the system voltage and that the amount of change in the apparent power of the system load is equal to or greater than a predetermined value, and that the system load A cutoff command is issued to the load when each condition that the rate of change of the apparent power with respect to time is equal to or greater than a predetermined value continues for a predetermined period of time.

To explain the configuration of the present invention with reference to FIG. 1, there is a first condition 1 that is satisfied when the magnitude of the voltage ■ is less than or equal to the first set value, and the amount of change in the apparent power of the load is equal to the second set value. The second condition 2, which holds true when the apparent power of the load is 2 or more, and the third condition 3, which holds true when the rate of change of the apparent power of the load with respect to time is 3 or more, the third set value. The configuration is such that a cutoff command is issued to the load on the condition that the fourth set value T1) or more is satisfied.

(effect) FIG. 3 is a diagram explaining the present invention in detail.

As shown in FIG. 3(a), the voltage ■ decreases and becomes equal to or less than the first set value by 1 at time C1, and the first condition is satisfied.

Furthermore, the voltage continues to drop, and the apparent power of the load (S=P+JQ) increases as shown in FIG. 3(b), and at time m
sl, s2 sSo in l, m2, m3...
l l S.

) becomes the second set value 2 or more at time c2, and the second condition is satisfied.

Here, SO is the apparent power of the load in a steady state a certain period of time ago, and Δt is the change calculation interval.

As the voltage decreases, the rate of increase in apparent power also increases Δtls
ol Δt I SO) increases, and at time C3, the third set value becomes 3 or more, and the third condition is satisfied.

Here, at time t4, when the time during which the three conditions are satisfied simultaneously becomes equal to or longer than the fourth set value T1,
Outputs a cutoff command to the load.

(Example) Examples will be described below with reference to the drawings.

FIG. 4 is a block diagram of an embodiment of the system protection device according to the present invention. In FIG. 4, the same parts as in FIG. 1 are designated by the same reference numerals. The structural feature of this embodiment is that a fourth condition 6 is added as a lock function in the event of a short circuit or ground fault in the system, and 6-1, 6
-2 conditions through the OR circuit 7 to the inhibit circuit 4.
-1 prohibition condition.

6-1, which is one of the fourth conditions, is that the voltage drop is less than 1 to 5 or less at the first set value, and
The other condition, 6-2, is a case where the voltage change rate is significantly less than 6 and there is a sudden voltage drop. Inhibit circuit 4- via OR circuit 7
The configuration is such that the output of 1 is locked.

In short, such a configuration is adopted because the voltage drop phenomenon when a short circuit or ground fault occurs in the power system is outside the scope of the present invention.

The setting value of 1 is, for example, about 0.9 PU, but in addition, it is about 0, which is the lower limit of normal operation of the grid.
．． 95 PU may be adopted.

In this case, K5 is set to 0.6 to 0.7 PU so that K5 < K1 is satisfied as described above.

For example, the value of K6 is set to 10 PU/sec to distinguish it from short circuits and ground faults.
shall be.

The voltage drop phenomenon under this type of load condition (which has the same characteristics as an induction motor load when looking at the entire system) is relatively slow, on the order of minutes in terms of numbers, so it occurs over time. The set value T1 may be on the order of minutes.

The other configurations and functions are the same as those shown in FIG. 1 except for the locking function in the event of an accident, so their explanation will be omitted.

The embodiment configured in this manner has a function of locking load cutoff when a short circuit or ground fault occurs, and a more reliable system protection device can be realized.

FIG. 5 is a diagram showing an example of application to a system.

In the figure, 8 is the system protection device explained in FIG. 4, and is connected to the high voltage bus 9 and the low voltage bus 10 via voltage transformers 14 and 16 for high voltage and low voltage buses, respectively. 11 is a transformer, which has a high voltage side breaker CBH and a low voltage side breaker CB.
L is installed between each bus bar. 12 is a load transmission line, each circuit breaker CB1, CB2 to CBn and each current transformer 15
It is connected to the low voltage bus 10 via.

Next, I will explain how it works. First, the high voltage f is applied via the transformer 14.
While introducing the f# line voltage V1, a current I Tr passing through the transformer 11 is introduced via the current transformer 13, and the apparent power for determination is calculated from the high voltage bus voltage and the transformer passing current.

On the other hand, while introducing the low voltage bus voltage v2 via the transformer 16, the current 1. I2...
In is introduced, and the power factor of the load on each power transmission line is calculated using these.

In this way, when the voltage condition and the apparent power condition satisfy the operating conditions of the system protection device 8 described above, a cutoff command is output to a specific power transmission line.

In this case, the cutoff command preferentially selects and cuts off the power transmission line with a poor lagging power factor (large lagging reactive power).

FIG. 6 is a diagram showing still another example of application to the system. In this application example, there is no power transmission line to be cut off at observation substation A, so the determination result of the system protection device under observation is transmitted through the transmission system, and the target power transmission line is cut off on the slave side.

In FIG. 6, parts corresponding to those in FIG. 5 are given the same reference numerals.

A is a visual inspection substation and B is a subsidiary substation, and they are electrically connected by a power transmission line 17.

8-1 is a new system protection device installed at substation A, 8
-2 is the secondary system protection device installed at substation B, 18
is a micro transmission system that connects the new example and the child side, and the load cutoff command is transmitted via this transmission system.

In this case, the protection function in the grid protection device 8-1 is the same as that shown in Fig. 4, and the resulting cutoff command is transmitted to the grid protection device 8-2, where the load on each transmission line is Taking the power factor into consideration, cut off the specified power transmission lines that should be cut off.

That is, a power transmission line with a poor lagging power factor is selected and cut off preferentially.

As can be seen from the above application examples, according to this embodiment, even if a voltage drop phenomenon occurs during peak summer demand when there is a large load on induction motors such as coolers, the voltage drop is not the only detection condition as in the past. , changes in the apparent power of the load and the rate of change in the apparent power of the load with respect to time are also taken into account.

Therefore, it is possible to optimally cut off the load to prevent a voltage drop phenomenon, and highly reliable system protection can be achieved.

[Effects of the Invention] As explained above, according to the present invention, the magnitude of the voltage has decreased to below the set value, the change in the apparent power of the load has become equal to or greater than the set value, and the change in the apparent power of the load has been achieved. Each of the conditions for the rate to exceed the set value is met, and these three
Since the system is configured to issue a shutdown command to the load when the condition has elapsed for a predetermined set time, it is possible to provide the most reliable system protection device as a countermeasure against overloads such as during peak summer demand.

[Brief explanation of the drawing]

FIG. 1 is a functional block diagram of the system protection device of the present invention,
Fig. 2 is a reactive power characteristic diagram of the entire system with respect to load voltage, Fig. 3 is a diagram explaining the present invention in detail, Fig. 4 is a configuration diagram of an embodiment of the grid protection device according to the present invention, FIG. 5 is a diagram showing an example of application to a system, and FIG. 6 is a diagram showing another example of application to a system. 1...First condition 2...Second condition 3.
...Third remainder ff-4...AND circuit 5...Timer element Figure 1 Patent applicant Tokyo Electric Power Company (and one other person) Representative Patent attorney Norio Ishii Figure 2 +5 Figure 6

Claims (1)

[Claims] A first condition that holds true when the magnitude of the grid voltage is less than or equal to a first set value, a second condition that holds true when the amount of change in apparent power of the grid load is greater than or equal to a second set value, and the grid load When the third condition, which is satisfied when the time rate of change of the apparent power of A system protection device that is characterized by issuing a power-off command.