JPS6327934B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION An object of the present invention is to provide a control device suitable for controlling a group of capacitors having different capacities in an automatic power factor control device for improving the power factor.

Calculation of power factor in electricity bill is based on one month's
The average power factor is calculated based on the integrated value of KWH and KVAVH. You can receive a discount on charges according to the percentage by which the average power factor exceeds 85%. If the average power factor is 100%, the contract electricity rate
You can get a 15% discount. Therefore, it is necessary to control the capacitor so as not to generate delayed reactive power. Although there are no pricing restrictions on leading reactive power, if the power factor becomes too advanced, it may result in an increase in power supply voltage, waveform distortion, and other negative effects on the load. Therefore, in order to obtain an advantageous rate discount without adversely affecting the load, it is necessary to appropriately control the capacitance of the capacitor.

Figure 1 shows the skeleton of power reception. SW is the main switch, SL ₁ , SL ₂ , SL ₃ are switches that control the supply of electricity to each load, MS is the main switch for the power factor correction capacitor (hereinafter abbreviated as capacitor), S ₁ ~ S ₄
is a switch that controls opening and closing of individual capacitors C ₁ to C ₄ . _L1 to _L4 are reactors. The power factor can be improved by controlling the capacitors C ₁ to _{C 4} according to the load condition, that is, the delayed reactive power condition. Conventionally, this control device generally uses a meter relay equipped with a mechanical element, but since the closing value and opening value are set at only one point each regardless of the number of control capacitor groups, it is common to use meter relays with mechanical elements. In some cases, appropriate control cannot be performed, and control is limited to equal group capacities or groups with relatively small differences in capacity. For example, 100KVA x 2 groups,
The control method for controlling a total of four groups of capacitors (200KVA x 2 groups) is shown in Figure 2. In Figure 1, capacitors C ₁ and C ₂ are 100KVA, and C ₃ and C ₄ are 200KVA.
The closing setting value of the capacitor is the opening setting value. As the load increases, the active and reactive power consumed increases, and at the point where the reactive power matches the level of , switch on S ₁ and connect capacitor C ₁ (100KVA) to the grid. Since the input value and open value in the case of different group capacitances are set by the maximum capacitor capacity, the reactive power remains at the point when capacitor _C1 is input. Furthermore, as the load increases, the reactive power decreases. At the point where the value matches, capacitor C ₂ (100KVA) is connected to the grid following capacitor C ₁ . The reactive power at this point is . As the load increases further, the capacitor C ₃
(200KVA) is input, but in this case, the input setting value is set in advance based on 200KVA, so the reactive power value at the time of input is control. Similarly, capacitor _C4 is injected at point. Next, let's take the open case as an example. When the load decreases and the reactive power reaches the point and matches the open value, capacitor _C4 is opened. Similarly, capacitors C ₃ to C ₁ are opened, but
Although the capacitance of capacitors C ₂ and C ₁ is small, since the capacitance is set based on the capacitance of capacitors C ₃ and C ₄ , it is difficult to open the capacitor even when the load becomes light, and the leading power factor decreases extremely. It is clear from FIG. 2 that this is not only a cause for concern, but also causes the power factor at light loads to drop more than necessary.

The present invention compensates for the above-mentioned drawbacks and provides a device having a control method that always performs appropriate control even in the case of different group capacitances. This amount of change is approximately equivalent to the capacitor capacitance, so this amount of change is detected as the capacitor capacitance, and based on this value, the closing setting value and opening setting value are set for each capacitor group. It is something to do. For example, if the reactive power (hereinafter abbreviated as Q value) value of the capacitor C ₁ shown in Figure 1 is Q ₁ before it is turned on, and the value after it is turned on is a lagging phase Q ₂ , then capacitor C ₁ capacitance = Q ₁ −Q ₂ , so
Store this value as the capacitance of capacitor _C1 ,
Next, this _C1 will be the factor that determines the set value when opening and closing. If the value after input is leading, Q ₁
+Q ₂ . Similarly, the capacitances of capacitors C ₂ to _{C 4} are memorized. The above control can be achieved by using an inexpensive microcomputer such as a one-chip microcomputer.

Next, FIG. 3 showing an embodiment of the present invention will be described. RST is a three-phase distribution line. 1 is a transformer, 2 is a current transformer, and 3 is a transducer that detects the reactive power value on the load side of the distribution line based on the transformer 1 and the current transformer 2. 4 sets the center value of the adjustment width. Alternatively, it is a setting section for setting the value at which the capacitor is charged for the first time. 5 is a microcomputer, and 6 is a switch S ₁ to 6 shown in FIG.
This is an output section that gives commands to _S4 and indicates whether switches _S1 to _S4 are on or off. A case in which the first setting value applied to each group is determined by the maximum capacitance as in the conventional case under the capacitor conditions described in the conventional example is shown and explained in FIG. 4 in comparison with FIG. 2. The maximum capacity setting is input into the microcomputer 5 using a digital switch or the like. The adjustment width is capacitor capacity x 1.5, and the ratio of open value and closed value is 1:2.
Considering the case, {close set value = capacitor capacity x 1.0 open set value = capacitor capacity x 0.5} Therefore, after detecting the capacitor capacity, the microcomputer 5 calculates the set value according to the capacitance. can be found. Further, reactive power can be easily detected by known means, for example, by using a pulse generating means proportional to the reactive power value and inputting this pulse into the microcomputer 5. In Fig. 4, the initial input setting value is
The first time when the capacitors C ₁ to _{C 4} are turned on, when the reactive power that matches this set value reaches the point, the capacitor C ₁ (100KVA) is turned on, and the reactive power becomes . When the load increases further, capacitor C ₂ (100KVA) is added, and the point is reached. Similarly, capacitor C ₃ (200KVA) is applied at point , and capacitor C ₄ (200KVA) is applied at point . At this time, the changes A to D in the reactive power when the capacitors C ₁ to _{C 4} are turned on are stored in the device as the capacitance of each capacitor. Next, consider the case where the load decreases. At this time, the open circuit value of capacitor _C4 is given by D = capacitor capacity as described above.
The value is calculated by multiplying by 0.5. That is, 100KVAR becomes the open setting value. At the point where the reactive power is reduced, capacitor _C4 is released. In the case of capacitor _C3 , the capacitance is the same as that of capacitor _C4 , so the open value is , and it is opened at the point. However, in the case of capacitors C ₂ and C ₁ , the capacitance is 100 KVA, so naturally the changes A and B are also half of C and D, and the open setting value is 50 KVA. In other words, this is the set value for opening capacitors C ₂ and C ₁ , and C ₂ and C ₁ are opened at a reactive power value that matches this value. The same idea applies when the capacitors are next turned on, and the input values of capacitors C ₁ and C ₂ become , while C ₃ and C ₄ remain the same. On the other hand, if the values of capacitors C ₁ to _{C 4} are all different, four levels will be provided for both the closing setting value and the opening setting value.

As explained above, the present invention detects the change in the reactive power value due to capacitor closing (or opening) for each group, replaces this change with the capacitor capacity, and adjusts the capacitance of each capacitor based on this value. By automatically calculating and controlling the corresponding closing setting value and opening setting value by a microcomputer, appropriate control can be performed according to the capacitance of each capacitor even in the case of different group capacitances. This also means that there is no need to stick to a group of capacitors of equal capacitance as in the past, and this is highly practical.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing a skeleton of power reception, Fig. 2 is an explanatory diagram showing an example of a conventional control method, Fig. 3 is a block diagram showing a circuit configuration according to an embodiment of the present invention, and Fig. 4 is a diagram showing the same control method. It is an explanatory diagram showing an example of a method. 3... Transducer, 4... Setting means (setting section), 5... Control means (microcomputer), 6... Output means (output section).

Claims (1)

[Claims] 1. In an automatic power factor control device that controls the opening and closing of multiple groups of power factor improvement capacitors with different capacities, a transducer that detects reactive power on the load side of a distribution line, a microcomputer, and a first power factor improvement device are used. a setting means such as a digital switch that inputs into the microcomputer the value at which the power factor correction capacitor is turned on; and an output means such as a relay that turns on and off the switch for the power factor correction capacitor according to commands from the microcomputer. Each time a power factor correction capacitor is connected or opened, the amount of change in reactive power is detected, this amount of change is replaced as the capacitance, and the next turn-on or opening set value is calculated based on this value. automatic power factor control device.