Electricity supply of the rural settlement

Contents

TASK

SUMMARY

O G L A IN L E N AND E

INTRODUCTION

1. Calculation of electrical loads of the settlement

2. Power Determination and Transformer Selection

3.Electric calculation of 10kV overhead line

4. Comparison of voltage deviation table

5.Electric calculation of 0.38 kV overhead line

6. Design of 0.38kV, 10kV and 10/0.38kV substation

7. Calculation of short-circuit currents

8. TC substation equipment selection

9. Short Circuit Current Protection

9.1. TP transformer protection

9.2. Protection of 0.38 kV lines outgoing from TP1:

9.3. 10 kV VL protection

10. Coordination of protections

12. Individual task

LIST OF LITERATURE

Summary

In this course project, the calculation of the power supply of the agricultural facility is given.

In the first chapter of the project, the electrical loads of the settlement are calculated and transformers are selected.

The second chapter consists of calculating the 10 and 0.38 kV network. The calculation is performed to select the grade and section of the power transmission line wires .

The third chapter calculates the emergency operation modes. There is also a selection of equipment.

Chapter Four - Short Circuit Current Protection. In the last, fifth chapter of the feasibility study.

Introduction

All agricultural facilities and residential buildings use electric energy.

Overhead transmission lines cover almost all settlements. However, this does not mean the cessation of work on their construction. The electrical load in agriculture is constantly increasing, there is a need to expand the lines. Their new construction in the village is increasingly being replaced by systematic reconstruction. At the same time, part of the overhead lines is replaced by underground cable lines.

Electricity supply to productive enterprises and settlements in rural areas has its own characteristics compared to electricity supply to industry and cities. The main one is the need to bring electricity to a huge number of relatively low-power facilities. As a result, the length of networks is many times higher than in other sectors of the national economy.

The above illustrates the importance of agriculture's electricity supply. The economic efficiency of the use of electricity in agriculture and in the household of the rural population depends to a large extent on its rational solution. This should be done in compliance with all requirements, rules, electricity standards.

1. Types of damages and abnormal operation modes of generators.

Damage of stator winding. Multiphase short circuits are among the most severe types of damage to the generator. They are accompanied by large currents several times higher than the nominal current of the generator. To protect against multiphase short circuits causing significant damage in the stator, all generators with a power of more than 1000 kW with the presence of individual phase leads from the neutral side are provided with longitudinal differential protection acting to disconnect the generator. On low-power generators for protection against multiphase short circuits, it is allowed to use simpler devices of maximum current protection or cut-off installed on the side of the generator leads, as well as circuit breakers or fuses.

Single-phase ground faults (to the generator housing) in generators with a stator winding voltage above 1000 V, operating with an isolated neutral, are accompanied by the passage of small currents at the point of damage compared to multiphase short-circuit currents. However, long current passage and arc burning at the closing point on the generator housing can lead to insulation burnout and significant melting of the active steel of the stator, after which a long repair with the replacement of damaged steel will be required. Based on the experience of operation and special tests, it was established that in case of damage in the stator winding, a ground fault current of up to 5 A usually does not lead to significant steel damage. Therefore, with ground fault currents in the generator voltage network less than b A, ground fault protection is usually performed with a signal action. If the ground fault currents exceed b A, the protection must act to disconnect the generator.

On low-power generators with a voltage of up to 1000 V, operating with a grounded neutral, protection from single-phase short circuits, which are accompanied by large currents, acts to disconnect.

In the generator stator, there may also be closures between turns of the same phase. Currents passing at the point of damage are commensurate with currents of multiphase short circuits. On generators having output parallel branches, for protection against winding faults, transverse differential protection is installed, which acts to disconnect the generator. On generators that do not have output parallel branches, protection against turn faults is not established, since its implementation in this case is relatively difficult, and also because turn faults in the generator stator that are not accompanied by single-phase ground fault or multiphase short circuit are very rare.

Rotor winding damage. The ground fault at one point of the excitation circuit does not affect the normal operation of the generator, the current at the point of damage does not pass, and the symmetry of the magnetic flux is not disturbed. However, the presence of one ground fault poses a potential danger to the generator, since in the event of a ground fault at the second point of the excitation circuit, part of the winding will be short-circuited.

Ground fault at two points of excitation circuit is accompanied by strong vibration due to violation of magnetic flux symmetry. An arc at the closing point can cause damage to the rotor winding and steel.

To prevent damage to generators, protection against ground faults at one point of the excitation circuit of hydrogenerators should be provided with a shutdown action, and turbine generators (with water cooling of the rotor winding of any power, and with other cooling systems with a capacity of 300 MW and above) with a signal action.

Protection against ground faults in two points of the excitation circuit is installed only on turbine generators.

Abnormal modes. Overloading the stator with a current larger than the nominal one entails overheating and destruction of the winding insulation, which as a result can lead to damage (short circuit or ground fault). In operation, powerful turbogenerators with direct cooling of windings are increasingly being introduced, while the cooling medium (hydrogen, water) circulates inside the current-carrying rods, thereby providing better cooling conditions and higher current densities. Generators with smaller sizes and better economic characteristics are produced by the domestic industry of four types: TVF, TVV, TGV, TVM. The design of these generators is such that they allow significantly less overload than indirect cooling generators. In order for duty personnel to take timely measures to unload the generator, current overload protection acting on the signal is installed on it.

With external short circuits, when overload currents can reach large values, even their short-term passage poses a danger to the stator winding. To prevent damage to the generator by the overload current, if the external short circuit is not turned off by the protection of lines or transformers, the maximum current protection with or without voltage starting acting on the generator shutdown is used.

The most severe consequences for the generator can occur with external asymmetric short circuits (two-phase or single-phase). In this case, the inequality (non-symmetry) of currents in the stator phases causes increased heating of the rotor and vibration of the generator, which can cause its damage. Unsymmetry of stator currents can also occur due to a break in one of the phases or a failure to switch on/off one of the phases. The allowable duration of the return sequence current generator, s, can be determined according to the following expression:

where I2 * 2 is the multiplicity of the current of the reverse sequence with respect to the nominal current of the generator; A is a constant value for generators of this type, the values ​ ​ of which are given below: for turbogenerators with indirect cooling of TV2 - 29 type, TV type - 20; for turbogenerators with direct cooling of TVF type - 15, TGV, TVM, TVV types (with the exception of TVB1000 4 and TVB12002) - 8, TVB10004 and TVB12002 types - 6; for hydrogenerators with indirect cooling - 40 Generator protection from external asymmetric short-circuit and asymmetric modes is performed by current protection of the reverse sequence acting on the signal and on disconnection.

Overload by rotor current. Overload protection of the rotor is provided only on turbogenerators with direct winding cooling. This protection must remain in effect during generator operation, both on primary and standby excitation. Overload protection of the rotor is also installed on hydrogenerators with indirect cooling of windings with a capacity of more than 30 MW. Protection usually acts with two shutdowns: from a smaller one - to unloading the generator (through an automatic excitation regulator), and from a larger one - to disconnecting the generator and quenching the field.

Abnormal modes also include the operation of a synchronous generator without excitation (for example, when the ATS is turned off), the so-called asynchronous mode. When operating in asynchronous mode, the generator speed increases and the stator current ripples. Most indirect cooling turbogenerators, with the exception of machines with set teeth of rotors, can operate for a long time (up to 30 minutes) in asynchronous mode with a load of up to 60% of the nominal. For turbogenerators with direct winding cooling up to 300 MW, it is allowed to operate in asynchronous mode with a load of not more than 40% of the nominal. In most cases, the asynchronous mode of operation of hydraulic generators is accompanied by a significant decrease in voltage and large oscillations, at which the stator current can be several times higher than the nominal value. Therefore, in case of loss of excitation, the hydraulic generator must be turned off, or immediately take measures to restore normal mode.

An increase in voltage at the terminals of the stator winding can lead to a violation of insulation and the occurrence of damage in the windings of the generator or transformer of the generator-transformer unit. A voltage increase dangerous for insulation occurs due to the disappearance of the magnetic flux of the stator reaction and an increase in the rotation speed of the unit, which occurs when the load is relieved. On units with turbine generators with a capacity of 160 MW or more, voltage increase protection is provided, which is activated when the generator is disconnected from the network. Protection acts on suppression of generator field and exciter

On units with hydraulic generators, voltage increase protection acts to disconnect the generator and AGP. Protection action for unit shutdown is permitted.