EP2145369A1

EP2145369A1 - Zero sequence current generator

Info

Publication number: EP2145369A1
Application number: EP07834948A
Authority: EP
Inventors: Alexei Mikhailovich Chaly; Vyacheslav Nikolaevich Gorelov; Alexander Nikolaevich Inyachin
Original assignee: "Tavrida Electric Industrial Group"
Current assignee: "Tavrida Electric Industrial Group"
Priority date: 2007-04-28
Filing date: 2007-04-28
Publication date: 2010-01-20
Also published as: EA200901464A1; CN101711447A; WO2008133543A1; EA016235B1; EP2145369A4

Abstract

A facility for an identification of an earth-fault feeder in networks with an isolated neutral comprises filters of zero sequence currents, which are included in a circuit of each outgoing filter, and the filter of the zero sequence voltage, which is connected to busbars. A generator of zero sequence current is connected to busbars through a switch, which is controlled by means of control and operation module, which is connected to the zero sequence voltage filter and which accomplishes temporarily closing the above- mentioned switch, when zero sequence voltage exceeds its definite level. The control and operation module comprises a time delay and provides with an identification of one phase-to-ground fault with respect to the zero sequence. The zero sequence current generator comprises a reactor with three-phase non-saturable iron circuit and with windings, which are connected in star with a grounded neutral. To the control and operation module there is connected a drive in the form of series-connected selector and vacuum switching module with three vacuum switches.

Description

ZERO SEQUENCE CURRENT GENERATOR

Description Field of the Invention The present invention is related to the electrical engineering when discriminating earth fault protection in networks with isolating neutral is required.

Prior Art

In these networks, identification of fault feeder is a difficult task, especially if fault earthing resistance is high and few feeders are supplied by power transformer. Variable configuration of the network leads to additional difficulties.

If earth fault protection does not indicate fault feeder, then feeders connected to the busbar section are sequentially switched off, and fault feeder is indicated when zero-sequence voltage disappears. This method is too continued and leads to high cost of energy not supplied.

A facility including three-phase group of high-voltage resistors, connected to busbar system for short time, has been earlier proposed (RU

2157038 C1). These resistors provide active current drawing through earthing point. As a result zero-sequence currents in healthy feeders are of capacitive type, but in a fault feeder zero-sequence current has a significant active component. Phase difference between zero-sequence current and zero-sequence voltage, being measured for various feeders, shows the fault feeder, and afterwards three-phase group of resistors can be switched off.

The disadvantages of the above mentioned innovation are using of power earthing resistors, that shall be protected by specially designed relays, and too sophisticated algorithm to study the correspondences of signals generated by current transformers of different feeders. The other innovation proposed by Moskovsky Zavod Electroschit

(Moscow, Russia) includes a earthing transformer mounted in a metal enclosed cabinet and connected to busbars through K-104M switchgear (refer to the leaflet of "Moskovsky Zavod Electroschit"). The earthing transformer is of 63kVA rated power, high-voltage windings are star- connected with star-point available, low-voltage windings are delta- connected. The star-point of high-voltage winding is earthed through bank of resistors of IOOOhm or 150Ohm active resistance (for 7.2kV or 12kV rated voltage respectively).

The non-optimal design and operation make the earthing transformer be oversized and heavy. The necessity for earthing of the star-point via active resistance requires high-powered resistors in the bank. Additionally, the transformer and switching device are mounted in two separate cabinets. To interconnect these cabinets the jumper cable is used. The disadvantages of this solution are the large overall dimensions, high cost and low reliability.

The target of the present innovation is effective and compact arrangement, reliably generating zero-sequence current by means of three-phase non-saturable reactor. This current is adequate to identify a fault feeder. The advantages of the innovation are simple design, low mass, dimensions and cost of zero-sequent current generator. The latter is a part of ETALON-type switchgear patented in Russian Federation (2217851 ).

Technical problem of the invention is making an efficient current generator of a zero-sequence, and also expansion of an arsenal of current generators of a zero-sequence.

The technical effect of the invention consists in simplification of a construction, heightening of speed and reliability, cutting of overall dimensions and mass, security of optimum arrangement, heightening of safety of upkeep.

Summary of the Invention The present invention is related to the electrical engineering, namely to the apparatuses, providing the selective earth fault protection in isolated neutral system. According to the claimed invention, zero-sequence current is effectively generated due to three-phase three-core non-saturable reactor, temporarily connected to busbars, when zero-sequence voltage is detected by controlgear. Zero-sequence current is inversely proportional to the sum of zero-sequence and earth-fault impedances. The three-leg core of the reactor is designed so as not to give rise to zero-sequence magnetic flux. As a result, zero-sequence impedance is determined solely by leakage inductive reactance of the windings, and zero-sequence impedance is inconsiderable. The three-phase non-saturable reactor is disconnected from busbars after a faulty outgoing feeder has been selected by earth-fault protection. The reclose of the switching module is blocked until earth fault is cleared, and zero-sequence voltage goes to zero.

The essence of the invention is in that the facility for identification of a earth-fault feeder in networks with isolated neutral including filters of zero sequence currents in each outgoing feeder, the filter of the zero sequence voltage connected to busbars, generating zero sequence current and connected to busbars through normally open three-phase switching module controlled by the protection relay connected to the zero sequence voltage filter temporarily closing the above-mentioned switching module when zero sequence voltage exceeds the definite level, and differing by time-delay in the protection relay and zero sequence current is generated by three-phase non-saturable reactor having one group of star- connected windings with earthed star-point, Thus the above-mentioned zero sequence current and voltage filters are connected a specific protection relay sensitive to zero sequence active power.

Besides the current generator of a zero-sequence in a three-phase web with an isolated neutral contains a reactor with a three-rod not saturated magnetic circuit and with windings, joint in a star with an earthed neutral, and also the normally-opened module high-voltage, supplied by a drive, hooked up to the module of monitoring both control, and executed by the way sequentially of joint selector and vacuum switching module with three vacuum interrupters, and selector is executed with three armature arms, with three isolated stationary contacts, with three earthed conclusions and with three conclusions, joint with buses, and the switching module is executed with three conclusions, joint with armature arms of the selector and with three conclusions, joint with windings of a reactor, Thus the module of monitoring and control is executed with an opportunity of identification of a single-phase circuit closing on ground on voltage of a zero-sequence. And it is supplied with a unified body by the way of case with a compartment of modular buses and with disposed sequentially from the top downward by low-tension compartment, high-voltage compartment and compartment of a reactor, thus in a compartment of modular buses disposed behind a high-voltage compartment, the devices of basic interment, current wires and connectors of modular buses are disposed, in a low-tension compartment are disposed the module of monitoring and control, and also the follow-up installed bodies of the signalling system and indication, in a high-voltage compartment are disposed the switching module and selector, interlocked with it, and in a compartment of a reactor - reactor and connective conductors.

Besides the each compartment is supplied with the valve of drop of excessive pressure.

And the high-voltage compartment is executed with a window from high-strength transparent polycarbonate and is supplied with an operating mechanical mimic disposed with an opportunity of overseeing by it through a window.

The transformer has a simple and compact design and low cost. The high-voltage module, the reactor, and control gear are united in a single cabinet. The functionality of high-voltage module is sufficient for both switching operations and safety maintenance of the reactor. Additionally, the currents /a, /b and /c (see Fig.1), drawing through phase windings of the reactor, are temporary and inductive hat prevents overheating of the windings and, as a result, provides high reliability of the apparatus.

Brief description of drawings Fig.1 is a single-line circuit diagram of the zero-sequence current generator.

The movable contacts of selector can be manually placed in either Earthed, or Isolated, or Engaged position. Permanently selector is in the Engaged position, and the switching module is switched off. As shown on Fig.2, that is a cross-section of the cabinet where the generator arranged, the cabinet includes high-voltage module compartment 1 , busbar compartment 2, reactor compartment 3, that are power compartments, and low-voltage compartment 4.

Switching module 5, selector 6, selector driver 7, upper part of bushing insulators 8, and upper terminals 9 of central conductors are placed in high-voltage module compartment.

Lower part of bushing insulators 10, lower terminals 11 , flexible interconnecting wires 12, and three-phase non-saturable reactor 13 are arranged in reactor compartment. The reactor is fastened to horizontal rails disposed from front to rear.

Support insulators of busbars 14 and busbar connectors, imbedded in solid insulation, are located in busbar compartment.

All the power compartments above are equipped with safety valves intended for positive pressure release and providing the endurance of the cabinet against the internal arc.

The controlgear 15, terminals for wiring and interconnection with protection and control system are mounted inside the low-voltage compartment.

Fir.3 shows the overall view of the cabinet from the front side. The high-voltage compartment has an inspection window covered with transparent polycarbonate sheet, that makes selector and mimic circuit diagram visible. The elements 1 and 2 of mimic circuit diagram display positions pof contacts of switching module and selector respectively. The interlocking handle 3, preventing wrong operations of personnel, is accessible from the front panel as well.

The best embodiment of the of the Invention

When earth-fault occurs, the controlgear identifies it by zero- sequence voltage. After program-controlled time delay, that is necessary for probable arc self-extinction of phase-to-earth fault, the switching module is closed. Being connected to busbars, the three-phase non- saturable reactor goes into unbalanced operation, caused by three-core design of the reactor, and zero-sequence current In (see Fig.1), depending upon both phase voltage and earth-fault impedance, draws through the neutral of the reactor.

The reactor is designed so as to limit zero-sequence current In below the level of 4OA, that does not compound the fault, on the one part, and is adequate for effective earth-fault protection, on the other part.

After a time, that is sufficient for determination of a fault outgoing feeder, the controlgear opens the switching module and, thereby, disconnects the three-phase reactor from busbars. At origin of single-phase earth-fault in a neutral there is a current of a zero-sequence, and in phase wires - its constituting. The module of monitoring and control (is, for example, by a timing unit) identifies availability of damage on voltage of a zero-sequence in a neutral (on a transmitter of voltage of a zero-sequence), but does not allow to establish and to disconnect an injured phase. After programmed endurance of time indispensable for provision of self-extinguibility of an arc of single-phase earth-fault, the module of monitoring and control yields insert of the module high-voltage. Thus the contacts of vacuum interrupters of the switching module are made, and the contacts of the selector are installed by its mechanical drive in a standing of linking of the switching module with modular buses. At origin of single-phase earth-fault the module of monitoring and control identifies this damage on voltage of a zero- sequence, the filter which one is erected in a transformer case KRU of a series "ETALON", hooked up to sectional section of modular buses. After some endurance of time indispensable for provision of self-extinguibility of an arc of single-phase earth-fault, the module of monitoring and control yields insert of the switching module, and the voltage of modular buses is hooked up to a three-phase reactor. Thus the three-phase three-rod not saturated reactor falls in an asymmetrical condition, and in its neutral the current In, depending from a voltage to neutral of a web, resistance in a damaged area and induced drag of a dispelling of windings of a reactor is shaped.

The design data of a reactor are picked so that the current magnitude Jn constituted not less more 40 A, that on the one hand, does not reduce in development of emergency in a damaged area, and with other - it is enough for the sure actuation of current guards of a zero-sequence. For operation last on each association, hooked up to section of modular buses, the filters of a zero-sequence are erected.

There is a hook up of voltage of modular buses to a three-phase not saturated reactor (for example, three-rod heart). Thus, last falls in an asymmetrical condition and in its neutral the indicated current Jn by magnitude up to 40 A, depending from a voltage to neutral of a web and resistance in a damaged area is shaped. The generator (is padding to a flowing past current) shapes in injured linking (injured phase) a short-time current of a zero-sequences representing a part of a current Jn. Its magnitude is defined in design data of a reactor and is proportional to the total of resistance to a zero-sequence of a three-phase reactor and resistance in a damaged area. In a three-rod magnetic circuit the magnetic flux of a zero-sequence, therefore, resistance to a zero-sequence of a reactor minimumly is not directed, as is defined only by induced drag of a dispelling of its windings, and the voltages on windings do not exceed a linear line voltage bisected on V3 . The current magnitude of a zero- sequence shaped in an injured phase, does not reduce in development of emergency and is sufficient for actuation of current guards of this phase. After some time, sufficient for identification of single-phase earth-fault on the injured feeder, the module of monitoring and control disconnects the switching module and detaches a reactor from modular buses of section.

After working guards, after time indispensable for identification of single-phase earth-fault on the injured feeder on actuation of guards, the module of monitoring and control yields lockout of the module high- voltage. Thus the contacts of vacuum interrupters of the switching module are unlocked, and the contacts of the selector are erected by its mechanical drive in a neutral standing up to a bulk-channel reclosing after elimination of damage.

The bulk-channel reclosing of the module high-voltage is blocked before elimination of damage and miss of voltage of a zero-sequence in a web, that takes place after actuation of evocative guards of an injured phase. The three-item selector can be in one of following locked positions:

The module switching electrically «ls "included" - is connected to modular buses.

The module switching «ls "isolated" - is isolated.

«ls "grounded" - winding of a reactor can be grounded, if the principal contacts of the module switching are made.

In a normal condition the selector is in a standing «ls "included", the principal contacts of the switching module are broken.

As the magnetic circuit of a three-phase not saturated reactor is executed three-rod, in the magnetic flux of a zero-sequence is not directed, and the resistance to a zero-sequence of a reactor is defined only by induced drag of a dispelling of its windings.

It is if necessary serviceability checks and upkeeps of inventory disposed in a case, the contacts of the selector are translated in an earthed standing. On the part of a facade a compartment of the module high-voltage isolated by the removable forward panel having a rectangular window. The window is enclosed by a leaf of high-strength transparent polycarbonate, that allows to supervise of devices and operating mechanical mimic. Last maps a state of contacts of the switching module and standing of armature arms of the selector. On the forward panel of a compartment the handhold « is inferred Is switched - off and the assignment by which one - is disabled » to prevent error operations of an operator by operation with the selector and switching module.

The valves of drop of excessive pressure disposed in a unmanned band of each compartment of a case, ensure local demanded a structural strength. Field of localization is each compartment separately.

Parameters of the device: Voltage rating, κE3 - 6 or 10

Current rating of modular buses, And - 1600

Current of spalling resistance of modular buses,

Effective value, KA - 31.5

Time of weep of a current of spalling resistance, with - 3 Current of electrodynamic stability of modular buses, peak, KA - 80

Overall dimensions, mm

Height - 2008

Depth - 762

Breadth on front - 330 Weight, kg - 370

The efficient device for detection of association with earth-fault in a web with an isolated neutral and current generator of a zero-sequence thus is created, and also the arsenal of current generators of a zero- sequence dilated. Thus the construction is simplified, boosted speed and reliability, the overall dimensions and mass are reduced, the opportunity of optimum arrangement is provided, the safety of upkeep boosted.

Industrial Applications This invention is implemented by means of all-purpose equipment, which is widespread in industry.

Claims

1. The facility for identification of a earth-fault feeder in networks with isolated neutral including filters of zero sequence currents in each outgoing feeder, the filter of the zero sequence voltage connected to busbars, generating zero sequence current and connected to busbars through normally open three-phase switching module controlled by the protection relay connected to the zero sequence voltage filter temporarily closing the above-mentioned switching module when zero sequence voltage exceeds the definite level, and differing by time-delay in the protection relay and zero sequence current is generated by three-phase non-saturable reactor having one group of star-connected windings with earthed star-point,

2. The facility according to Claim 1 , characterized in that the above- mentioned zero sequence current and voltage filters are connected a specific protection relay sensitive to zero sequence active power.

3. The facility according to Claim 1 , characterized in that the current generator of a zero-sequence in a three-phase web with an isolated neutral contains a reactor with a three-rod not saturated magnetic circuit and with windings, joint in a star with an earthed neutral, and also the normally-opened module high-voltage, supplied by a drive, hooked up to the module of monitoring both control, and executed by the way sequentially of joint selector and vacuum switching module with three vacuum interrupters, and selector is executed with three armature arms, with three isolated stationary contacts, with three earthed conclusions and with three conclusions, joint with buses, and the switching module is executed with three conclusions, joint with armature arms of the selector and with three conclusions, joint with windings of a reactor, Thus the module of monitoring and control is executed with an opportunity of identification of a single-phase circuit closing on ground on voltage of a zero-sequence.

4. The facility according to Claim 1 , characterized in that it is supplied with a unified body by the way of case with a compartment of modular buses and with disposed sequentially from the top downward by low-tension compartment, high-voltage compartment and compartment of a reactor, thus in a compartment of modular buses disposed behind a high-voltage compartment, the devices of basic interment, current wires and connectors of modular buses are disposed, in a low-tension compartment are disposed the module of monitoring and control, and also the follow-up installed bodies of the signalling system and indication, in a high-voltage compartment are disposed the switching module and selector, interlocked with it, and in a compartment of a reactor - reactor and connective conductors.

5. The facility according to Claim 4, characterized in that each compartment is supplied with the valve of drop of excessive pressure.

6. The facility according to Claim 4, characterized in that the high- voltage compartment is executed with a window from high-strength transparent polycarbonate and is supplied with an operating mechanical mimic disposed with an opportunity of overseeing by it through a window.