JPS61288731A - Reactive power compensation system - 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 Industrial Application] This invention provides a reactive power compensation system that absorbs reactive power generated on the load side by connecting a capacitor and an accelerator in parallel to the secondary side of a step-down transformer. Regarding.

[Conventional technology]

FIG. 2 is an operational principle diagram for explaining the reactive power compensation operation in such a system.

In other words, assuming that the temporal change in reactive power QF of the load (generally considered as delayed phase reactive power) is shown as shown in the same figure (A), the reactive power QL taken by the variable reactor is
(Long phase) is as shown in the same figure (B), when QF increases, Q
L is decreased, and when QF is decreased, QL is increased. In other words, by controlling Qb so that QF + QL remains constant, regardless of the reactive power of the load, the reactive power Qs of the system can be reduced as shown in (e) of the same figure, as shown in (c) of the same figure. , Qs = QF + QL - Qa':: It is made to be constant. Note that Qo is the reactive power (phase advance) taken by the fixed capacitor, and is constant as shown in FIG. At this time, when the system voltage fluctuation Δ■ is expressed as a unit quantity with the system reactance being Xs, it becomes constant ΔV2Qs−Xs, and voltage fluctuation (so-called flicker phenomenon) is suppressed.

[Problem that the invention seeks to solve]

By the way, in the above system, if the reactive power of the load or its fluctuation is zero, Q? =0, or (
b - becomes constant, and (b, becomes maximum. At this time, in general, Qr, -Qa becomes and the reactor current becomes maximum, and the loss (proportional to the square of the voltage) also becomes maximum. In other words, when the load is on a steelmaking arc furnace, the molten steel is taken out after each melting process, and raw material scrap is put in after the furnace is repaired, so the downtime is about 20 to 30 minutes. In a load that occurs every two hours, it is not preferable to increase the loss by increasing the output of the reactive power compensator's accelerator to its maximum output during this stop period because it wastes power and increases the power bill. As a countermeasure, a method of opening and closing using a breaker may be considered, but there are problems such as disturbances in the system voltage due to the life of the breaker and the inrush current of the capacitor that occurs at startup.

Therefore, it is an object of the present invention to easily reduce the load loss mainly caused by the reactor due to the stoppage of the load, etc., by a simple and inexpensive means.

[Means for solving problems]

A step-down transformer that can step down the voltage and a detector that detects when the reactive power of the load or its fluctuation has become zero are provided.

[Effect]

When the detector detects that the reactive power of the load or its fluctuation has become zero, the transformer lowers its secondary voltage, mainly reducing the current flowing through the reactor to reduce its loss. In the figure, 3 is a reactor, 4 is a thyristor switch, and 5 is a capacitor.
These constitute a well-known reactive power compensator. Note that its operation is as explained in the [Prior Art] section. Therefore, this embodiment is characterized in that it is provided with a transformer 1 capable of stepping down the voltage, such as an on-load tap change transformer, and a reactive power detector 6.

In addition, 2 in the same figure is a load with large fluctuations such as an arc furnace, and 7
8 is a voltage detector, 8 is a current detector, and 9 is a tap changer driving device.

That is, the reactive power detector 6 determines the reactive power QF of the load 2 from the voltage and current values detected by the voltage detector 7 and the current detector 8, and detects whether this reactive power or its fluctuation is zero. When this is zero, a signal to that effect is sent out, which causes the tap changer drive device 9 to operate, lowering the tap voltage of the transformer 1 and reducing the current flowing through the reactor 3, reducing its loss. to reduce the At this time, as a matter of course, the current flowing through the capacitor 5 is also reduced, which causes the capacitor 5 to
The loss caused by this is also reduced. Note that the tap voltage of the transformer 1 is set so that it can be lowered to about 1/2, for example, and when the capacitor 5 is turned on, the tap voltage of the step-down transformer 1 is lowered to this lowest tap before being turned on. In other words, the inrush current Im (transient maximum value) when starting the capacitor is:
It is expressed as Here, Em is a steady voltage, 2 is a circuit impedance, 'XL is a circuit reactance, XO is a capacitor reactance, ω is an angular frequency (-2πf), and α is a coefficient. Therefore, by turning on the steady voltage Ernt at the lowest tap of the step-down transformer 1, the inrush current of the capacitor can be proportionally reduced, thereby making it possible to reduce the voltage drop in the system.

〔Effect of the invention〕

According to the present invention, not only is there an advantage that electric power and electric power charges can be saved in loads such as steelmaking arc furnaces and electric railway loads (such as loads that have frequent and relatively long outage periods), but also In cases where the power supply system is weak and the system voltage drop becomes a problem when the capacitor is turned on,
The effect of reducing this can be obtained.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an embodiment of the present invention, and FIG. 2 is a general operating principle diagram for explaining reactive power compensation operation. Code explanation 1...Step-down transformer, 2...Load, 6...
...Reactor, 4 ... Thyristor switch, 5 ... Capacitor, 6 ... Reactive power detector, 7 ... Voltage detector, 8・・・・・・
- Current detector, 9...Tap changer drive device. Agent Patent Attorney Akio Namiki Agent Patent Attorney Kiyoshi Matsuzaki If1

Claims (1)

[Claims] A system that compensates for the reactive power generated on the load side by connecting a capacitor and a variable reactor in parallel on the secondary side of a transformer that can step down, and the reactive power on the load side or its fluctuation becomes zero. The present invention is characterized by comprising a detecting means for detecting this, and when the detecting means detects this, the secondary voltage of the transformer is lowered to reduce losses due to the variable reactor and the capacitor. Reactive power compensation system.