EA038734B1 - Device for the protection against single-phase line-to-ground faults in electrical networks - Google Patents

Description

The invention relates to the field of power engineering, namely to power distribution networks operating with isolated, resistive-compensated or resistive-grounded neutral, and is intended for protection against single-phase earth faults (OZZ) in electrical networks of 6-10 kV.

Known protection against single-phase earth faults ZZP-1M, ZZN, containing a zero-sequence current transformer, a matching transformer, a limiting circuit, an AC amplifier, a phase-sensitive amplifier, an actuator in each outgoing feeder and a voltage measuring transformer. The devices represent directional protection in networks with a neutral mode, in addition to compensated, selectively triggered by metallic and stable arc faults, including in power grids with low capacitive currents of earth faults. (http://bmrz-zakharov.narod.ru/2012/OZZ.htm - date of treatment 09/15/2019; _ Shabad M.A.Protection against single-phase earth faults in 6-35 kV networks. Lecture notes. St. Petersburg, PEIPK, 2001. - 52 p.).

The disadvantages of analogs include false alarms of protection in case of intermittent arc faults, as well as large errors and unreliable operation of measuring voltage transformers used in protection and vulnerable to ferroresonant overvoltages in the case of SPC in the power grid, and as a result, a decrease in the efficiency of power supply.

The closest technical solution adopted as a prototype is a device for selective protection against earth faults in electrical networks, containing a zero-sequence current transformer connected through a phase-shifting element, a rectifier and a threshold element to an amplifier, a zero-sequence voltage sensor connected through a trimming resistor with ground, an executive relay, whose contacts are included in the switch circuit, and a second amplifier. In this case, the zero sequence voltage sensor is made of diodes connected to each other according to the 3B scheme and is connected to the phases of the monitored network. The introduction of a high-voltage three-phase rectifier instead of a voltage measuring transformer provides a high-precision determination of the phase (angle) between the vectors of the zero-sequence voltage and the zero-sequence current in the damaged feeder. In the event of an OZZ, in which the zero sequence current in the damaged feeder is directed from the buses to the place of damage (in undamaged feeders, the direction of the currents is opposite), the executive relay by means of both amplifiers is switched on with an effect on disconnecting the damaged feeder or on a signal (patent RU No. 58269, IPC Н02Н 3/00 (2006.01), published: 10.11.2006, bul. No. 31).

The disadvantages of the prototype include the following:

the lack of a function for limiting switching overvoltages that initiate the SPL, as well as their registration in order to determine during the subsequent analysis of overvoltage sources;

reduced electrical safety due to the lack of galvanic isolation between the high-voltage rectifier and the rest of the device;

the complexity and high cost of using a 3B rectifier on each outgoing feeder.

These disadvantages reduce the reliability and safety of power grids, complicate and increase the cost of protection against 033, which significantly reduces the efficiency of power supply.

The objective of the invention is to create a simple and inexpensive device for protection against single-phase earth faults, providing safe and reliable operation of electrical networks with extended functionality and high efficiency of power supply.

The technical result consists in increasing the efficiency of protection against SPL by expanding the functionality of limiting and registering switching overvoltages, simplifying and reducing the cost of the device by installing one zero sequence voltage sensor made of an RC absorber on the busbar section of the power grid, as well as increasing safety by creating a galvanic isolation with the mains by connecting a current transformer between the RC arrester and the rest of the device.

To achieve the technical result, a protection device against single-phase earth faults in electrical networks, containing a switch, a zero sequence current sensor of an outgoing feeder, a zero sequence voltage sensor, a phase detecting module, a voltage relay, a matching unit and an executive relay, according to the invention, a zero sequence voltage sensor is made from an RC damper, the inputs of which are connected to the mains, and the outputs are connected to a common point and grounded through the current transformer, and the secondary winding of the current transformer is connected by means of a matching unit to the input of the additionally introduced signal recorder and to the input of the voltage relay, while the output of the voltage relay is connected to the input of the phase-determining module and to the input of the signal recorder.

The proposed invention is illustrated by a drawing.

The figure shows a block diagram of a protection device against single-phase earth faults in electrical networks, where:

- circuit,

- outgoing feeder,

- 1 038734

- switch,

- zero sequence current sensor (TNP),

- phase-determining module,

- executive relay,

- RC damper,

- voltage relay,

- matching block,

- current transformer,

- signal recorder.

In the power grid 1, each of the outgoing feeders 2 contains a switch 3, a TNP sensor 4, connected by the secondary winding to the input of the phase-determining module 5, the output of which is connected to the executive relay 6, which controls the switch 3. At the same time, it is common for all outgoing feeders 2 connected directly to the power grid 1, is an RC absorber 7 connected by inputs to the mains 1 RC and outputs connected to a common point, grounded through a current transformer 10. Moreover, the secondary winding of the current transformer 10 is connected by means of a matching unit 9 with a signal recorder 11 and a voltage relay input 8 having a time characteristic, outputs which are connected to the input of the phase-determining module 5 and the input of the signal recorder 11.

The proposed invention works as follows.

In normal operation of the power grid 1 without switching overvoltages and OZZ, the outgoing feeders 2, when the switch 3 is on, provide power supply to the consumers, and the TNP 4 sensors, the RC damper 7 and the current transformer 10, detached from the unbalance currents, are energized in the initial state. Also, the phase-determining module 5, the operating relay 6, the voltage relay 8, the matching unit 9 and the signal recorder 11 are in readiness to function when switching overvoltages or OZZ appear.

The occurrence of switching overvoltages in the power grid 1 is accompanied by the fact that a current pulse appears in the RC absorber 7 and the current transformer 10, which is then converted in the matching unit 9 into a voltage pulse. Since the duration of the switching overvoltage does not exceed, as a rule, 10 ms (one half-wave of the fundamental harmonic), and the setting of the delay time in the voltage relay 8 significantly exceeds the specified duration, the signal about the emerging switching overvoltage is only recorded in the signal recorder 11 and does not appear in other elements devices.

The appearance of an OZZ in the power grid 1 leads to the fact that in the RC damper 7, which is, in essence, an undamaged outgoing feeder, as well as through the containers in undamaged feeders, a zero sequence current appears, which passes through the current transformer 10 and its secondary winding, is then converted in the matching unit 9 into the zero sequence voltage Uo. In this case, its phase coincides, by definition, with the phase of the current from the sensor ТНП 4 of the undamaged feeder. Then the signal Uo, exceeding the setting in the voltage relay 8, determined by the current imbalances in the RC absorber 7, and with a delay for the duration of the transient process at SPC, as a rule, by 20-40 ms, enters the phase-determining module 5. Simultaneously and synchronously with this process, it enters the signal from the sensor ТНП 4 and is compared in the phase-determining module 5 with the phase of the signal Uo. In this case, their mutual antiphase state indicates a damaged feeder and the signal generated in this way from the phase-determining module 5 arrives at the operating relay 6 with a subsequent action on the signal or to turn off the damaged feeder by the switch 3. Moreover, the signal Uo is also fed to the signal recorder 11, which fixes the fact of the OZZ in the power grid 1.

Comparative analysis of the proposed device with the prototype shows the following.

1) The use of RC absorber 7 as a zero-sequence voltage sensor Uo is based on its absolute similarity with undamaged outgoing feeders of the mains 1, the currents in the sensors of the consumer goods of which coincide in phase with the indicated zero-sequence voltage Uo. At the same time, the use of an RC damper 7, one per section of the mains buses, instead of a high-voltage three-phase rectifier, which is installed on each outgoing feeder, greatly simplifies and reduces the cost of protection against SPL in power grids.

2) The rationale in the proposed device for an additional function of limiting and registering switching overvoltages arising in the power grid 1 for a number of reasons lies in their manifestation primarily in the RC absorber 7. At the same time, in comparison with nonlinear surge arresters (SPD), which have a very high trigger level, the RC damper 7 limits even the smallest switching overvoltages and dangerous higher harmonics. Thus, the reliability of the device and the power grid as a whole is increased. (http://www.exctr.ru/product/energetika/zahchita-elektrooborudovaniya-6-10kv-otperenapryazheniy/).

3) The introduction of the signal recorder 11 into the device makes it possible to record in time the facts of the appearance and limitation of switching overvoltages. This contributes to the subsequent analysis of the identification of overvoltage sources in order to take preventive measures to prevent overvoltages and increase the reliability of the power grid.

- 2 038734

4) An increase in the level of electrical safety created by the proposed device consists in the fact that the current transformer 10 creates a galvanic isolation between the high-voltage power grid 1 with the RC damper 7 connected to it directly and, accordingly, the rest of the low-voltage elements of the device.

The presented analysis confirms the increase in the efficiency of power supply when using a simple and inexpensive device for protecting power grids from 033 with enhanced functionality for limiting and registering switching overvoltages and ensuring the safety of the power grid, and also proves the novelty and significant advantages of the proposed device in comparison with the prototype for all types of 033.

For the functioning of the proposed device can be used industrial-produced RC-absorbers, measuring coil current transformers of the TKL type, zero sequence current transformers of the TZL and TZR type, as well as equipment, devices and elements of relay protection and signal registration systems widely used in the electric power industry.

Thus, the advantage of the proposed invention is a simple and inexpensive protection device against single-phase earth faults with extended functionality, which ensures safe and reliable operation of electrical networks with a voltage of 6-10 kV in all types of 033 and with neutral modes other than compensated and high efficiency of power supply.

Claims (1)

CLAIM A protection device against single-phase earth faults in electrical networks, containing a switch, a zero sequence current sensor of an outgoing feeder, a phase-detecting module, a voltage relay, a matching unit, an operating relay and a zero sequence voltage sensor, characterized in that the zero sequence voltage sensor is made of an RC absorber, the inputs of which are connected to the mains, and the outputs are connected to a common point and grounded through the current transformer, and the secondary winding of the current transformer is connected by means of a matching unit to the input of the additionally introduced signal recorder and to the input of the voltage relay, while the output of the voltage relay is connected to the input of the phase-detecting module and to the input of the signal recorder.