SU519808A1 - Current Delay Protection Device - Google Patents

Description

The invention relates to electrical engineering, namely, relay-controlled devices with dependent time lag.

A device of current protection with a dependent response characteristic is known, which contains in two phases intermediate saturated transformers, to the secondary windings of which rectifier bridges and an active-capacitive circuit with a gas discharge device and an output relay 1 are connected. The disadvantage of this device is that the thermal protection characteristics do not match. characteristics of the protected electrical installations, due to the exponential charge law of the integrating capacitor, in the low accuracy of the protection due to unstability of the gas discharge device in the relay circuit and the exponential charge law of the capacitor, as well as in the difficulty of coordinating the temporal characteristics of the protection of adjacent transmission lines.

The closest in technical means and achievable results is a time-dependent current-time protection device containing current sensors, sources of stable voltage, an integrating capacitor with transistors in the charge and discharge circuits, a threshold element, and an output organ 2. The disadvantage of this device is 2

The consistency is low reliability due to the complexity of the circuit.

The purpose of the invention is to increase the reliability of protection. This is achieved by improving the matching of the characteristics of the protection and the object to be protected by switching on the circuit with the common base of said transistors, the input terminals of which are connected to the indicated sources.

Diagram of the device shown in the drawing.

In the secondary circuits of the current transformers of the protected electrical installation, transreactors 1 are connected with rectifying bridges 2, the outputs of which in all phases are connected in parallel and shunted by a smoothing capacitor 3. These outputs are through a limiting circuit consisting of a resistor 4 and a zener diode 5, and an adjustable resistor 6 , connected to the emitter circuit of the transistor 7, included in the amplifier circuit with a common base. An integrating capacitor 8 is connected in series with the collector circuit of this transistor to a source of stabilized voltage. In parallel, there are two circuits connected to it: the first consists of transistors -9 and 10, a resistor 11 and a reacting organ — a polarized relay 12; the second circuit consists of a transistor 13, adjustable a resistor 14 and a zener diode 15. The first circuit is a comparison device

the voltage on the capacitor 8 with the voltage on the zener diode 16. The base of the transistor 7 is connected to the zener diode 17 and through a resistor 18 to a constant voltage source.

The device works as follows.

When the currents of the electrical installation are lower than the protection setting, the discharge current of the integrating capacitor 8 flowing in the collector circuit of transistor 13 will be greater than the charging current of capacitor 8 flowing in the collector circuit of transistor 7.

In this mode, the capacitor 8 will not be charged and the reacting organ 12 will be de-energized. For protection currents exceeding the set current, the collector current of transistor 7 will be greater than the collector current of the transistor.

13 and the difference of these currents will cause the charge of the capacitor 8, the voltage of which is directly proportional to the charging current and inversely proportional to the capacitance of the capacitor 8. When the voltage on the capacitor 8 is equal to the zener diode 16, then the transistors

9 and 10 will open and the reacting element 12 will operate, after which the capacitor 8 is discharged through the collector circuit of the transistor

13 current slightly lower emitter current of this transistor. In the case of short-time overcurrent of the protected electrical installation, the capacitor 8 will not have time to charge before the voltage of the key device triggered with the reacting element 12 and the device will not work. After current decrease

the capacitor 8 is discharged through the collector circuit of the transistor 13.

The technical and economic efficiency of the device application is due to the increased reliability of protection, the accuracy of its temporal characteristics, the improvement of its temporal characteristics to the characteristics of electrical installations being fenced and consists in reducing erroneous protection reactions, which entails an increase in the reliability of electricity supply to electrical consumers.

Claims (1)

Invention Formula A time-dependent current-time protection device containing current sensors, stable voltage sources, an integrating capacitor with transistors in the charge and discharge circuits, a threshold element and an output organ, characterized in that, in order to improve reliability by improving the protection characteristics and the protected object, said transistors are connected according to a common base circuit, the input terminals of which are connected to the indicated sources. Sources of information taken into account in the examination: 1 Auth. St. No. 306525, cl. H 02h 3/16, 1970. 2 J.P. Greivulis et al. “Semiconductor current and voltage relays, M., Energie, 1970, p. 93, fig. 59.