SU560287A1 - Device to protect the contact network from leakage current - Google Patents

Description

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The invention relates to the field of protection of electrical equipment and networks against short circuits and dangerous current leaks, in particular, to systems for protecting contact networks of locomotive mine haulage.

Devices are known that are used to control and protect contact networks from emergency operation, built on the principle of applying a high-speed operating current to the operating current of the network.

Of the known devices for monitoring and protecting contact networks, the closest in technical essence to the invention is a device for protecting a contact network from current leaks.

In the specified device, the primary converter is the object itself (contact network), since it directly converts the leakage conductivity value into an increment of the amplitude and phase of the operational current supplied to the measuring circuit of the relay protection unit. Therefore, the magnitudes of the increments of the amplitude and phase of the operative current depend not only on the leakage conductivity, but also on the transmission coefficient of the contact network. The magnitude of this coefficient of transmission is not constant and during the operation of the network changes with changing number of electric locomotives working on the line, changing the length of the network and other factors. As a result, leakage protection sensitivity also changes, which adversely affects the quality of protection performance. Increased sensitivity leads to unjustified re-protection and frequent false positives, lowering sensitivity worsens the security of operation of the protected network. The invention is stabilized by

protection sensitivity. The goal is achieved by the fact that in the protection device of contact networks against current leakage, the comparator is made with a tunable threshold, and its output is connected to a moving contact

the second key, to the first fixed contact of which the input of the said filter is connected, and to the second fixed contact an actuator is connected. The drawing shows a diagram of the proposed device.

The device includes an emergency imitation unit 1, containing in series a reference leakage resistor 2 and an accessory filter 3, which transmits only the operating current of the free frequency. The emergency imitation unit is connected via key 4 to the protected object 5 and into the output of the measuring unit 6. To the output of the measuring device.

unit 6 is connected the first input of the comparat3

pa 7. The second input of the comparator 7 is connected to one of the fixed contacts of the key 8 through a low-pass filter 9. To the other fixed contact of the key 8, the safety actuator 10. The output of the comparator is connected to the movable contact of the key 8. By the operation of the key 4 and the key 8, which collectively form a switch, controls the synchronization node P.

The non-nodic actions generated by the synchronization node 1 ensure synchronous and common-mode operation of key 4 and key 8. The switch switching time period is less than the required protection performance time. In response to iodiodic simulations of the emergency mode of the network arising from the closure of key 4, the measuring unit 6 generates a sequence of pulse output signals, the amplitude of which depends on the transmission coefficient of the network. These signals are sent to one of the inputs of the comparator 7, working as a relay element with a tunable response threshold. The role of the tunable threshold is played by the voltage on the second input of the comparator.

When the device is put into operation, the threshold voltage is zero, so the original pulse signals arriving at the first input of the comparator 7 cause periodic triggers of the comparator — pulses appear at its output, but the polarities coincide with the signal at the first input. As a result, the voltage of the threshold generated at the output of the filter 9 will gradually increase until it exceeds the amplitude of the pulses coming from the measuring unit. As soon as this happens, the pulses at the output of the comparator will disappear, and the threshold voltage will begin to smoothly decrease until the amplitude of the pulses at the first input of the comparator becomes less. The comparator will start responding again to the imitations of an emergency, the voltage at the filter output will again increase, and so on. By choosing the parameters of the circuit elements, the oscillations of the output voltage of the filter can be made small, whereby the threshold of the relay element will be maintained by the rabbi amplitude of 4

the input signals of the measuring circuit, due to the imitation of an emergency sitz-ation. With a sufficiently slow change in the transmission coefficient of the object recorded, it changes the amplitude of these signals, the threshold will be adjusted in accordance with it. Due to the adjustment of the threshold of the relay element, the sensitivity of the protection system is constant, independent of the transmission coefficient

object and is determined by the resistance of the resistor 2.

The control of the state of the object of protection by this device is performed in the intervals between simulations, when the key 4 is open, and

Key 8 is in the right position. In case of a sudden leakage, the resistance of which is less than or equal to the resistance of the resistor 2, the comparator, acting on the output signal, acts on the actuator 10, and the latter de-energizes the network.

Due to the fact that the sensitivity of the proposed constant device, false alarms and deterioration of protection due to the measurement of the conversion properties of the protected network are eliminated. This ultimately enhances the safety of network operation and improves the reliability of power supply.

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Claims (1)

Invention Formula Device to protect the contact network from current leakage, containing a synchronization unit, controlling the operation of two keys, the measuring unit, the input of which is connected to the emergency imitation unit through the first key and to the protected object directly, and the output connected to the first the input of the comparator, to the second input of which the output of the low-pass filter is connected, and the executive body, characterized in that, in order to stabilize the sensitivity, the comparator is made with a tunable threshold, and its output is connected to the moving contact of the second key, to one fixed contact of which is connected the input mentioned filter, and to another fixed contact, an executive o) gan.