SU936157A1 - Device for grounding protection of three-phase four-wire network with solidly grounded neutral - Google Patents

Description

(5) DEVICE FOR PROTECTION AGAINST CIRCUITS ON A THREE-THREE-FOUR-FOUR-WIRE NETWORK WITH DUTCH-GROUNDED NEUTRAL

I

The invention relates to electrical engineering and is intended to protect a three-phase four-wire electrical network with a dead-earthed neutral and repeated grounding of the neutral conductor from ground fault.

A device is known for protecting an electrical network with a dead-earthed neutral against earth faults, which reacts to ground tapes that are provided by a differential transformer covering the phase and neutral wires G11.

However, the need to adjust from suction currents from the neutral conductor to the repeated earthing in operation reduces the real sensitivity of the protection.

Closest to the proposed invention is a device containing a differential current transformer, covering three phase wires and zero for separating

earth leakage current, transformer current-current sensor in a neutral wire, a differentiating unit for generating a tripping signal for the rate of increase (derivative) of leakage current, and a differentiating unit for generating a signal to prohibit a tripping function for the rate of increase (derivative) of the current in the neutral wire, a prohibition and output logic element

10 is the organ acting on the control coil of the switch in the presence of a signal at its input 2.

A disadvantage of the known device is that the appearance of a short 15 times high amplitude noise causes a false alarm of the earth fault protection device.

The purpose of the invention is to increase the reliability of the device by

20 improving its noise immunity;

The goal is achieved by the fact that a three-phase four-wire network with a solidly grounded neutral and re-grounding of the neutral wire containing a differential leakage current transformer and a current transformer in the neutral wire to which the disconnect signaling channel and the channel are connected are protected against earth fault. forming a prohibition signal, consisting each of a series-connected differentiating unit and the first threshold unit, a prohibition unit, an output cat Through a sequentially connected output unit, it is connected to the control input of the switching device, the first and second impulses, the first and second keys, the locking unit, the subtraction unit and the second threshold unit are additionally inserted into each of the two mentioned channels, each VI3 of the two mentioned channels, the input of the first pulse extender is connected to the output of the said differentiating unit, the first input of the first key and the first input of the subtraction unit are connected to the output of the said differential a current transformer, a second input of the first key and an input, a second pulse expander, the output of the first key through a serially connected fixture unit is connected to the second input of the subtractor, the output of the subtractor is connected to the first input of the second key, to the second input of which the output of the second pulse expander is connected and the output of the second key of each of the two mentioned channels through a sequentially connected second threshold unit is connected to the corresponding input of the said prohibition block. The drawing shows a functional diagram of the device. The device consists of a differential leakage current transformer 1, covering three phase and neutral wires, connected to the input of channel A to form a tripping signal and the current transformer 2 to zero, connected to the input of channel B to form a prohibition signal. Each of channels A and B muffles from differentiating unit 3, the first threshold element C, connected to the output of the differentiating unit, the first expander of 5 pulses, the input of which is connected to the output of the first threshold element k, and the output of the expander 5 is connected to the control input of the first key 6, connecting the output 1 of the differential leakage current to the level fixing unit 7, the input of which is connected to one of the inputs of the subtraction unit 8, to the second input of which the output 1 of the differential leakage current is connected, the output of the unit 8 is connected via a key 9 to the threshold element 10 to isolate the current increments, and to the control input of the switch 9, the output of the expander P of pulses is connected, the input of which is connected to the output of the first expander of 5 pulses. The output signals of channels A and B are connected to the inputs of the prohibition element 12, which affects the switching off of the switching device 13, via the output organ Il. The device works as follows. A voltage proportional to the leakage current of the line arises on the secondary winding of the differential leakage current transformer 1. In stationary mode, the voltage at the output of unit 3 is absent, therefore there is no voltage at the output of the threshold element k and the expander 5 pulses, the key 6 is opened and the voltage difference at the inputs of the subtraction unit 8 is zero, the voltage at the output of the subtraction unit 8, the threshold element -10, and therefore channel A is missing. Similarly, channel B operates in a stationary mode. When any wire is shorted to ground, a leakage current rush occurs and, consequently, an output voltage on the secondary winding of the differential transformer 1 of the leakage current. At the output of differentiating unit 3, a voltage pulse appears, the amplitude of which is proportional to the rate of increase of the leakage current. If the amplitude of pulses exceeds the threshold of element 4, the first expander of 5 pulses is triggered, closing key 6, then level fixing unit 7 remembers the voltage value at the start of a leakage current surge. In block 8, the subtraction compares the magnitude of the leakage current at the current time with its value at the moment the current surge starts. When the interval of time determined by the parameters of the expander of 5 pulses expires, the expander of 11 pulses is started and the key 9 is opened for the time determined by the parameters of the expander of 11 pulses. If the mixed signal at the output of the subtraction unit 8 exceeds the setpoint of the threshold element 10, then the output of the element 10 and that of channel A appears to be a shutdown signal. So far, the time of the level fixing unit is chosen so that during the operation of the 11 pulses, the level in the block 7 does not have time to change. The channel B setting of the prohibition signal is selected so that a slight current surge or its absence in the neutral wire does not lead to the prohibition signal and therefore the switching device 13 is disconnected. When switching loads, leakage currents also occur at the output of channel A through is a voltage pulse. However, in this case there is a synchronous inrush of current in the zero percent triggering channel B, at the output of which a signal appears preventing the passage of the pulse of channel 1 to the output block I through the inhibitor circuit 12, and the protection does not activate. Conducting a pulse expander into the circuit for analyzing the magnitude of the increment of the leakage current makes it possible to eliminate the false alarms of the protection from short-term interference of large amplitude (such as lightning). The invention is a device for protection against earth faults of a three-phase four-wire network with a dead-earthed neutral and repeated grounding of a neutral conductor containing a differential leakage current transformer and a current transformer in a neutral wire to which a disconnect signal-forming channel and a ban signal-forming channel, respectively, are connected. each of the serially connected differentiating unit and the first threshold unit, the prohibition unit, the output of which through a successor But the included output unit is connected to the control input of the switching device, characterized in that in order to increase the reliability of the device by improving its noise immunity, the first and second pulse expanders, the first and second keys, the fixing unit are additionally inserted into each of the two mentioned channels the level, the subtraction unit and the second threshold unit; in each of the two mentioned channels, the input of the first pulse expander is connected to the output of the said first threshold unit, the input of the said differential The scoring unit, the first input of the first key and the first input of the subtraction unit are connected to the output of the mentioned differential current transformer, the second input of the first key and the input of the second pulse extender are connected to the output of the first pulse extender, the output of the first key is connected to the second through a serially connected fixing unit. the input of the block you are Mtan, the output of the block of subtraction is connected to the first input of the second key, to the second input of which the output of the second expander of pulses is connected, and the output of the second key is dogo of said two channels by sequentially changing the second threshold unit POD7 key K corresponding vhoduupom mentioned prohibition unit. Sources of information taken into account in the examination 1. The author's certificate of the USSR. No. 391675, cl. H 02 H - 3/16, 1970. 2. USSR author's certificate No. 726617, cl. H 02 H 3/16, 1J77.

Claims (1)

Claim A device for earth fault protection of a three-phase four-wire network with a grounded neutral and repeated ground electrodes of zero wire, containing a differential leakage current transformer and a current transformer in zero wire, to which are connected, respectively, a channel for generating a trip signal and a channel for generating an inhibit signal, each from a series-connected differentiating block and a first threshold block, a prohibition block, the output of which is through a series-connected output the unit is connected to the control input of the switching device, 'characterized in that ”in order to increase the reliability of the device by improving its noise immunity, the first and second pulse expanders, the first and second keys, the level lock block, are additionally introduced into each of the two mentioned channels a subtraction unit and a second threshold block, while in each of the two mentioned channels the input of the first pulse expander is connected to the output of the said first threshold block, the input of the said differentiating block is first the first input of the first key and the first input of the subtraction unit are connected to the output of the mentioned differential current transformer, the second input of the first key and the input of the second pulse expander are connected to the output of the first · pulse expander, the output of the first key through a series-connected block of level fixation is connected to the second input of the subtraction unit , the output of the subtraction unit is connected to the first input of the second key, to the second input of which the output of the second pulse expander is connected, and the output of the second key of each of the two channels through a series-connected second threshold block under ·; keys to the corresponding input of the prohibition block.