CS232367B1 - Zero Voltage Detector Input Circuit Wiring - Google Patents

Abstract

Connection of a contactless alternating current switch with a reactive load of capacitive nature. The invention falls into the field of heavy current 9 electrical engineering and relates to the synchronization of a contactless switch at zero voltage 1 and eliminates the delay in reconnecting the switch caused by the increased voltage on the load capacitor due to the inductance of the choke in particular. The problem was solved by connecting a resistive divider in parallel to the reactive load with the middle terminal connected to the input of the zero voltage detector. The ratio of the resistive divider is close to the ratio of the voltage on the capacitor to the difference in voltage on it and on the peak voltage of the network. In the drawing, the resistive divider (1) and (2) connected in parallel to the reactive load Z with the middle terminal connected to the input of the zero voltage detector 0 best characterize the invention.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to a circuit of a zero-voltage detector with a limiting resistor connected in parallel to a contactless AC switch of capacitive reactive load consisting of a series connection of at least one capacitor and a choke.

Contactless switches, realized mostly by a pair of antiparallel coupled thyristors and designed for switching of alternating current at reactive load of capacitance character, require exact synchronization of switching time » They are derived from the voltage signal sensed at each pole of the proximity switch and further processed in a zero-voltage detector which directly or after amplification and shaping generates control pulses for the proximity switch thyristors.

Described synchronization and * control of thyristors is suitable only for switching of pure capacitance or resistive capacitance load ·

However, in real cases there are inductances in the circuit switched by a contactless switch. First of all it is the inductance of the mains itself or even inductance of chokes intentionally connected to the switched capacitor circuit · Inductive character of the network is not necessary in most cases. • It cannot be used, however, if a filter or limiting choke is connected to the capacitor in the sewage system, which is necessary, for example, for filter-compensating or compensating devices which

- 2 232 367 use in networks with higher harmonic voltages and currents · In this case, the capacitor produces a voltage higher than the mains voltage by a choke voltage, in the practical examples by 0.8 to 11% ·

The disadvantage of the described connection of the zero-voltage detector only occurs when the contactless switch needs to be switched on again immediately after switching off. A properly functioning zero-voltage detector allows the switch to be turned on only after a certain amount of time required to discharge the capacitor to a voltage lower than the mains voltage amplitude. This unwanted delay can be eliminated by accelerating the capacitor discharge.

The above-mentioned disadvantages are eliminated by the circuit according to the invention, which is based on the fact that a resistive divider from the additional and limiting resistors is connected in parallel to the load via a central outlet connected to the input of the zero-voltage detector.

The advantage of the circuit according to the invention is that it makes it possible to eliminate unwanted delays in switching the switch without interfering with the power circuits while maintaining the critical functions of the neutral voltage detector. The circuit according to the invention reduces the influence of the DC voltage component of the charged capacitor. Immediately after switching off the switch ·

An example of a circuit according to the invention is further described with reference to the drawing in which a reactive load Z in series with a switch S is connected between the poles a and b of the AC power source. A resistive divider consisting of an additional resistor 1 and a limiting resistor 2 the middle terminal is connected to the input of the zero voltage detector D, connected in parallel to the switch S.

The effect of the circuit according to the invention is dependent on the ratio of the value of the additional resistance 1 to the usual value of the limiting resistance 2 ·

- 3 232 367 δία the lower the ratio, the more the capacitor voltage components are suppressed to the zero voltage detector function. · Optimum ratios are achieved when compensating the voltage increase by exactly the reactive voltage of the connected choke, which is fulfilled if 1 to the limiting resistance value 2 is close to the ratio of capacitor voltage to choke voltage, or · to the voltage amplitude difference of the capacitor and the mains · Then the voltage at the zero voltage detector input D becomes zero around the mains voltage amplitude as required noticeably affected when the switch S is switched on for the first time, when the capacitor voltage is approximately zero, or when it is switched on every half-period ·

The invention can be advantageously used ie especially for switching reactive power compensation cells.

Claims (1)

SUBJECT OF THE INVENTION 232 367 Connection of the input circuit of a zero voltage detector with a resistor connected in parallel to a contactless AC switch of capacitive reactive load, consisting of a series connection of at least a capacitor and a choke, characterized in that a resistive divider of additional limiting resistor (1, 2), connected by the middle outlet to the zero voltage detector input (D) ·