JPH03257512A - Automatic power factor adjusting device - Google Patents

Abstract

PURPOSE:To attain the highly accurate control of the power factor by providing a tap to an energizing current detecting CT and taking out a current signal via an appropriate tap in accordance with the load state. CONSTITUTION:The input signals are applied to an automatic power factor adjusting device 3 from both PT1 and PT2, and the CT2 is provided with an intermediate tap. Then two current signals are inputted to the device 3. The device 3 decides to use the current signal of a CT full tap or that obtained from the intermediate tap. Then the controller 3 performs the arithmetic control with use of the decided current signal and outputs a make/break command 4 to a capacitor bank 6 to turn on/off a capacitor. Thus it is possible to attain an automatic power control system with high accuracy regardless of the load state.

Description

[Detailed Description of the Invention] [Object of the Invention] (Field of Industrial Application) The present invention relates to an automatic power factor adjustment device that turns on and off a power factor improvement capacitor in response to load fluctuations in a power receiving and transforming section. It is.

(Prior Art) An example of power receiving and transforming equipment using a conventional automatic power factor adjustment device is shown in FIG.

In Fig. 4, when the load 5 changes, the power factor of the power receiving and transforming equipment changes, so the voltage signal is taken out from PTI and the current signal is taken out from CT2. i3, the automatic power factor adjustment device 3 performs calculations, determines the capacity of the capacitor panchromator in accordance with the preset power factor improvement value, and outputs the corresponding closing/tripping command 4. By doing so, the power factor is improved by turning on and off the capacitor panchromator.

(i[M to be solved by the invention) In the power receiving and transforming equipment shown in Fig. 4, when the load fluctuation is small, problems arise in controlling power factor improvement using the automatic power factor adjustment device 3 and capacitor panchromatic. do not have.

However, if the range of load fluctuation is large, for example, the load capacity may be less than 10% of the receiving and substation equipment capacity,
Alternatively, if the capacity of the power receiving and transforming equipment includes a load capacity that will be added in the future and the initial load capacity is very small compared to the equipment capacity, the control operation may become unstable.

This instability in control operation is due to the fact that the current signal obtained from the CT is small and therefore inaccurate, and the automatic power factor adjustment device cannot maintain good operation.

In other words, the CT ratio of CT2 is determined with respect to the rated capacity of the main transformer 7, so when the load capacity becomes 10% or less, the CT ratio
Due to its characteristics, it is extremely difficult to maintain its accuracy at the same level as when energizing the rated capacity.

In other words, the CT error in the low current range is ±1% at rated current and ±3% at 5% current for IF5 class CT, and when the number of capacitors is controlled according to the energizing current using an automatic power factor adjustment device. In this case, the current change in the low current range and the CT error become close, resulting in unstable operation.

That is, in the rated current range, the width is 2%, and in the 5% current range, the width is 6%, so if there is a 3% current change when 5% current is applied, it is impossible to determine whether this is an error or a current change.

As a result, the operation of the automatic power factor adjustment device becomes unstable, and the input capacity of the capacitor bank may be insufficient, or conversely, the input capacity may become excessive and the power factor may lead.

The present invention has been made in consideration of the above problems.

The purpose is to provide a rational automatic power factor ALJI adjustment device that performs normal control operations even under low loads.

[Structure of the invention]

(Means and effects for solving the problem) The present invention provides a CT for detecting load current in an automatic power factor adjustment device that turns on and off a power factor improvement capacitor in response to load fluctuations in power receiving and substation equipment. A device that provides an appropriate number of taps, selects the tap that corresponds to the load current based on the relationship between the preset current value and the tap, and controls the capacitor on and off according to the current input through the selected tap. This enables highly accurate automatic power factor adjustment regardless of load conditions.

(Example) An embodiment of the present invention is shown in FIG.

In Fig. 1, the input signal to the automatic power factor adjustment device 3 is PT
CT2 is provided with an intermediate tap, and two current signals are input to the automatic power factor adjustment device 3.

Automatic power factor! II adjustment device! ! 3 performs judgment control as shown in the flowchart in Fig. 2, determines whether to use the current signal of the CT full tap or the current signal obtained from the CT intermediate tap, and selects the selected current. Arithmetic control is performed based on the signal, and a closing/tripping command 4 is output to the capacitor panchromator to turn on/off the capacitor.

The current value xA in FIG. 2 must be determined in advance, and is determined in consideration of the accuracy of the transformation ratio with respect to the primary side current value.

Further, the value of the CT intermediate tap is determined in consideration of current detection accuracy at the lowest load when power factor control is performed.

Another embodiment of the invention is shown in FIG.

FIG. 3 shows a case where even more precision is required, and CT
By providing an appropriate number of intermediate taps.

Current can be detected using the most accurate CT transformation ratio, and power factor control can be performed with high accuracy.

〔Effect of the invention〕

As explained above, according to the present invention, a tap is provided on the CT for detecting the conducting current, and the current signal is extracted using an appropriate tap depending on the load condition, so that the current value can be detected with sufficient accuracy no matter the load. Since the automatic power factor adjustment device selects the current signal most suitable for the load condition and performs calculation control, it is possible to perform accurate and optimal power factor control.

[Brief explanation of drawings]

FIG. 1 is a system diagram showing an embodiment of the automatic power factor adjustment device according to the present invention, FIG. 2 is a judgment flow diagram for selecting one of the two detected current signals, and FIG. FIG. 4 is a system diagram showing another embodiment of the present invention in which the power factor adjustment device is further improved in accuracy. FIG. 4 is a system diagram showing an example of a conventional automatic power factor adjustment device. 1... PT 2... CT 3... Automatic power factor adjustment device 4... Closing/tripping command 5... Load 6... Capacitor bank 7... Main transformer (8733)

Claims (1)

[Claims] In an automatic power factor adjustment device that turns on and off a power factor improvement capacitor in response to load fluctuations in power receiving and substation equipment, an appropriate number of taps are provided on the CT for detecting load current, and the taps are adjusted to a preset current value. An automatic power factor adjustment device characterized in that a tap corresponding to the load current is selected based on the relationship with the load current, and a capacitor is turned on and off in accordance with the current input through the selected tap.