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Abstract

Introduction

TPS

Electrical Network 6-10 kV occupies most cell in the energy about 78% of all power lines. Most of these lines are used to supply high-power electric motors, is also used to power transformer units and consists of a cable transmission lines that pass operation in severe conditions (effect of moisture, sharp differences of temperatures and high overvoltage that caused by single-phase ground fault (PTG)). Overvoltage accelerates deterioration of the insulation of cables and equipment, which ultimately leads to failure. PTG arc is the most common case. Long passing arc PTG, and ultimately leads to the interfacial closures, which implies that fire cables.

1. Urgency of the problem

It is impossible to determine with great accuracy the fault zone using standard protection PTG.

Everything else it works after closures. In this emergency shutdown [2] of the damaged area is not always correct, as it can affect the stability of the system.

For the system to be stable we need to eradicate instances of sudden breakdown of the insulation due to its deterioration, which subsequently leads to failure of expensive equipment. It's very important to develop a defense that is capable of providing continuous monitoring of the insulation. To achieve such results, it is necessary to revise the standard protection systems, to explore new methods of controlling the operation of the power system and explore new protection based on microprocessor technology. Today's energy needs in a reliable protection with the parameters that have been listed above to the production of electricity was more reliable and most importantly cheap.

2. This paper investigates the following research issues and challenges

  1. Study on the mathematical model the system and check the reliability of this model new protection.
  2. Consider always available in networks with isolated neutral capacitive components of leakage current.
  3. Assess and compare with other methods of reliability analysis protections.
  4. Development of algorithms triggering of safety devices protected system.
  5. Conduct a comprehensive physical model testing device protection.

3. Existing species protection from PTG

3.1 Zero sequence protection

ZSP is able to measure the voltage and run off the line with PTG, only when one line departs from the busbar. This embodiment comparing with the other possesses small importance qualities - high-frequency component in the [1] zero-sequence voltage is practically not seen that gives an advantage in its functioning. For example, when the PTG is shown, which extends in the subsequent intermittent or discontinuous edges. Also, the protection mode does not affect arcing reactor. But when there is a connection with the tires, it will be applied as a non-selective alarm (alert about the manifestation of PTG in the circuit while not showing the damaged connection).

3.2 Non-directional current protection

In certain situations the reliability can be achieved using non-directional protection zero sequence.

Current, resulting in the non-directional protection responds, be set up, [6] taking into account the effect of the capacitive current connection, in most cases, the data protection helpless at the connections with high capacitive current.

Particular attention is cause non-directional protection ZS on the "relative measure". This protection is able to act when there PTG stress occurs ZS, is also able to compare the current ZS of protected area. Where there is the fundamental harmonic current ZS more is damaged. This protection is not normally able to operate using a line or arc suppression coil if enough connections to busbars.

3.3 Directional protection

Directional protection has a greater range of operation as compared to non-directional protection, able to operate with the ZS voltage harmonics currents. Fault currents of directional protection shall be much lower than that of non-directional protection because it was originally built up from their own capacitive currents. As a result, directional protection obtained sensitivity and efficiency.

Block diagram of directional protection type ZZP-1M

Fig.1. Block diagram of directional protection type ZZP-1M

Directional protection has a large family of devices. These include remote protection that can operate on the conductivity of the chain [3] of ZS and their individual components. Also here there are devices that respond to the power direction and magnitude of the current ZS. Also under study are the protection, triggered by the interval work instantaneous values of the harmonic components of voltage and current ZS. The big problem is the complexity of this protection setup settings. Officially, there is no way to calculate the selected settings. In practice, in order to expose the settings should be set at the beginning of the minimum setpoint. If the defense does not work properly, it is necessary to roughen the settings until such time as the protection will not work consistently. Such a method greatly reduces the operation of this protection and reduces its effectiveness. Manufactured protections PTG leads maximum sensitivity protection. The bottom line is that the defense can perceive currents PTG about 0.2-0.3 A. That inherently leads to confusion operatives because they do not take into account the actual conditions of protection. The problem is the imbalance in the presence of a real network, i.e. a production system there are signals that are responsive to the defense as PTG. If not all of these features protection may not work properly. It is important to study because of this protection.

3.4 Protection, retaining current cash

If the system of arc suppression coils (ASC), the use of directional and non-directional protection is an inefficient way. Excellent result in this situation gives protection application analyzing applied current with a frequency different from the industrial. For example, you can cause the connection to the network neutral current source 25 hertz and analyze currents with the same frequency in the protected accessions.

Operation protection of the system in the steady state of PTG, as well as generators is due to the applied current at 25 Hz. In the role of the source of current control is applicable electromagnetic frequency divider. Its winding is connected in series with the primary winding of the ASC. By using more than one reactor in the system, include their outputs (connected by the pre-ground) via a frequency divider output winding.

Protection using the

Fig.2. Protection using the "imposed" current
(animation: 7 frames, 5 cycles of repetition, 44.3 kilobytes)

In the case of semi-conductor transmission line used as filter current relay with a nominal range of low frequencies in the area connected to the cable TTNP. Contrast to the current unbalance frequency filter residual current (50 Hz) and affect the quantity (25 Hz) facilitates detuning unbalance and prevents zagrubenie current.

Negative protection feature working on a method of "imposed" current, have impact on the stability of the error protection CTs ZS which increases with decreasing nominal frequency; also arises from the complexity of the compound auxiliary power sources present in the system if some of the ASC, located at different sites; the presence of external alternating arc PTG hard to rebuild from the natural harmonic component due to the variation range of the current depends on the method of neutral grounding, and network settings; need to accede to the source "superimposed current", which greatly complicates the primary circuit switching; PTG point location and more

Electrical Network 6-10 kV

3.5 Absolute and relative measurement

The most common defenses in the systems of 6-10 kV, current protection is an absolute measurement, working on an analysis of the level of higher harmonics in the currents of the system and compares it with the desired setpoint. A protection of the measurement relative working on a comparison [5] levels of higher harmonics in the currents ZS of all accessions chain under consideration.

Protection of absolute measurement is not reliable in the case of variability composition and level of higher harmonics in the currents of ZS, which is the norm for networks 6 - 10 kV operating companies.

Conclusions

Based on the foregoing, it becomes apparent importance of the study of new systems of protection against PTG 6-10 kV networks with isolated neutral. Because in my master thesis is the question of new high-performance protection at 6-10 kV networks with isolated neutral. For safe operation in automated control systems of the production process.

At a writing of the given abstract master's work is not finished yet. Definitive end: January, 2015. The full text of work and materials of a theme can be received from the author or his supervisor after the named date.

References

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  2. Циркуляр Ц–01–88 О повышении надежности сетей 6 кВ собственных нужд энергоблоков АЭС
  3. Шабад М.А. Защита и автоматика электрических сетей агропромышленных комплексов, Ленинград, Энергоатомиздат, 1987.
  4. Правила устройства электроустановок. — М. Энергоатомиздат, 1985. — 640 с.
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  6. Шуин В.А. Гусенков А.В. Защиты от замыканий на землю в электрических сетях 6–10 кВ. — НТФ «Энергопрогресс» 104с. ил. [Библиотечка электротехника: Вып. 11 (35)]
  7. M. Muhr, R. Strobl, R. Woschitz. Entladestrommethode — Ein Prufverfahren fur kunststffisolierte Mittelspannungskabel.