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When observing working grounding of electric grid network, the term should be understood as the totality electrical connections of one step voltage lines and connected the winding generators and power transformers of the same voltage level. Under the protective earthing connection network should be understood the deliberate connection with the land of some points of the network, usually neutral winding parts of transformers, less neutral winding generators, in order to give certain properties to the network, essential for its construction and operation, namely: reducing switching surges, effective protective network valve discharger from atmospheric surges, reducing the isolation of power transformers, simplification of single-relay circuits in the network, extinguishing arc closure to the ground, the possibility of retaining the damaged lines and others in the network acquired the properties listed according to their grounding. Applications received several ways of grounding.
Connecting neutral winding generators, transformers with land should be understood as their adherence to the earthing device installed, the bulk of which is grounding. The latter is a system of non-conductors in contact with ground and designed to transform to the ground. Grounding relatively little resistance and practically does not limit the electric current flow into the ground, and does not distort the stress of three-wire system in relation with land under the earth fault.
Workplace earthing network has no effect on its work in normal conditions. However, if damaged insulation of wires current passes to the ground voltage wires symmetry is violated on the ground. The values of single-circuit current vary widely depending on the grounding system working. This applies also to tension wires on the ground undamaged, with a single short-circuit. Accordingly, the requirements for the protection relay network characteristics valve discharger, the level of isolation power transformers, construction of earth bonds stations and substations, and others. Techno-economic indicators relevant parts grid,also are changed.
Rational relevance
The principles of protectors action of the earth fault are currently used in electrical systems, in many cases the requirements aren’t met. One of the main disadvantages of protectors, reacting to the set the parameters of the regime is the lack of sensitivity, as well as the actions of non-selectivity. The reasons for this situation are: the imperfection of the principles of protection building, a negative correlation parameters of the protected network, low technical characteristics of equipment used to implement protection (zero sequence current transformers, current relay type of RTZ-50 and RTZ-51). In addition, you can also take into account the drawback that the main time earth fault protection does not perform any action (like most other protectors). This work will be aimed at correcting these deficiencies and to develop methods for the replacement of equipment without correcting the deficiencies of protectors.
Goals and Objectives of work
The purpose of the work is the development of technical measures to ensure such quality work protectors of the earth fault, which allows, through greater sensitivity to prevent the outbreak of single circuit to dround, and in some cases – interphase short circuit.
The objectives of the study:
Alleged novelty of scientific and practical value
Developments, that are worked out in this area, most of them are based on the application of mathematical models obsolete. The basis of work is to develop new ways of protectors of the earth fault, which would secure a network and equipment from the adverse effects of the earth fault.
The main content of the work
To compensate capacitive currents, the following ways are used:
compensation by means of located at each Core CZST third windings, which are fed through C capacitor voltage from zero sequence 3U0 from VT installed on the outlets of the generator. As stabilizing winding located on the winding rods CZST blocker are used. These windings are connected in the factory performance counterclaims-consistently are included under-parallel.;
is carried out through the neutral earthing ground-fault neutralizer, resulting inductive resistance which corresponds to capacitive resistance network. Under this mode grounding current network capacity in the place fault is compensated by inductive current reactors, which contribute the arc starvation. If the arc does not arise, the compensation of capacitive current allows to slow down the destruction of isolation and thereby the distance jump in interphase short circuit at the time, sufficient to identify the damaged site and its disconnection of electricity without interruption.
Monophase locking at the compensate network
The number of frames at animation - 6
Net current at the place of locking
where
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neutral potential |
At the time of writing authosynopsis degree work is not yet completed, so the final conclusions of the work haven’t been made yet. However, it can be note, that there was calculated locking current and build its dependence from reactor inductive resistance.
