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The basic principles of controlled switching and synchronous vacuum circuit breaker application in local distribution networks

09.03.2019

The basic principles of controlled switching and synchronous vacuum circuit breaker application in local distribution networks

The basic principles of controlled switching and synchronous vacuum circuit breaker application in local distribution networks

Dmitry Shevtsova, Dmitry Pavluchenko, Evgeny Prohorenko

Novosibirsk State Technical University, 20 Prospekt K. Marksa, Novosibirsk, 630073, Russia

admitriy_shevtsov@mail.ru

Keywords: controlled switching, synchronous vacuum circuit breaker, switching overvoltages.

Abstract. The paper is devoted to the solution of the switching overvoltages problem in distribution networks by application synchronous vacuum circuit breaker. The basic principles of controlled switching are considered. The example of vacuum circuit breaker application realizing principles of synchronous switching is presented. It is shown, that synchronous vacuum circuit breaker is reliable and effective device for overvoltages reduction.

   Introduction

  When distribution electric networks are switched, overvoltages having negative influence on power equipment are possible to occur. This problem can be solve by using devices with controlled (synchronous) switching.

  Now there are known the following controlled switching devices: «Switchsync» [1] and «Switching Control Sentinel (SCS)» [2] of ABB, «Point on Wave Control» [3] and «Digital Zero Voltage Closing (ZVC)» [4] of Joslin Hi-Voltage, etc. But all mentioned devices cannot be applied in distribution networks of 6 (10) kV. In Russia in All-Russian Electrotechnical Institute named after V.I.Lenin the vacuum circuit breaker, combined with vacuum controlled arrester, is developed [5]. This solution also is focused for special application.

  Developed device fully realizing the principles of controlled switching in distribution networks of 6 (10) kV is synchronous vacuum circuit breaker EX-BBC SMARTIC 6(10)-20/1000 [6]. This circuit breaker is versatile device and can be used for any load switching. The operation of synchronous vacuum circuit breaker is based on the principles of synchronous switching presented below.

  Basic principles of controlled switching

  In comparison with common switching, controlled switching has a number of technical and economic advantages: reducing of inrush currents, elimination of dangerous switching overvoltages, lowering of the number of equipment failures, decreasing of the number of regular maintenance and increasing of life time for switching devices [7].

  Controlled switching devices shall comply with strict requirements on stability of closing time and opening time. Scattering of operating times for these devices shall be in the range of ± (1-2) ms without dependence on load type, switching type and ambient temperatures [8].

  Controlled opening is realized by contact separation at the definite instant before the moment of zero crossing for breaking current. In this case, arcing time is significantly reduced, because energy release during arcing greatly decreases. Controlling the instant of contact separation prevents circuit breaker failures and decreases influence on the power supply system.

   1.png

Fig. 1. Principles of controlled opening

   Fig. 1 shows principles of controlled opening [7]. A command for circuit breaker opening is generated at random time tcommand and transmitted to a switching controller. This command is delayed by a controller for a certain period Ttotal. The time interval Ttotal consists of a controller response time Tresp and an intentional synchronization time Tsync. The time interval Tsync is determined in relation to the instant of current zero and depends on an opening time of a circuit breaker Topening and a time of contact separation tseparate for a specified distance to provide required electric strength of a contact gap.

 

Ttotal=Tresp+Tsync,                                                                                                                              (1)

 

Tsync=N∙Tzero-Tarcing-Topening,                                                                                                              (2)

 

  where Ttotal – time delay for an opening command, ms; Tresp – response time of a switching controller, ms; Tsync – synchronization time for a current-based opening command, ms; N – the number of half-cycles; Tzero – duration of a half-cycle, ms; Tarcing – arcing time, ms; Topening – opening time of a circuit breaker, ms.

  Accurate control of tseparate, which indicates the instant of total contact separation, actually determines Tarcing. The opening time Topening is an interval between the instant of energizing the coil of a circuit breaker mechanism and the beginning of contact separation. N∙Tzero is the number of half-cycles required to achieve positive values of Tsync in accordance with equation (2).

  Controlled closing is realized by contact closing at the definite instant after the instant of zero crossing for power supply voltage. Controlled closing of a reactive load by a circuit breaker allows minimizing inrush currents.

 

2.png 

Fig. 2. Principles of controlled closing

    For realizing controlled closing, a switching controller monitors power supply voltage. A command for circuit breaker closing is generated at random time tcommand. Fig. 2 illustrates principles of controlled closing of an inductive load [7]. An optimal time for closing is at a voltage peak, provided that duration of prestriking at closing is not greater than a half-cycle. A controller delays a closing command for a period of Ttotal which consists of a controller response time Tresp and an intentional synchronization time Tsync.

  A controller produces the time delay Tsync related to the instant of power supply voltage zero. This time delay is determined by (3) taking into account a closing time of a circuit breaker Tclosing and a time of prestriking Tprestriking. Current starts to flow at the instant of tmake. A time interval Tm depends on tmake and the following instant of power supply voltage zero.

 

Ttotal=Tresp+Tsync,                                                                                                                              (3)

 

Tsync=N∙Tzero-Tm-(Tclosing-Tprestriking)=N∙Tzero-Tm-Tmaking,                                                                     (4)

 

  where Ttotal – time delay for a closing command, ms; Tresp – response time of a switching controller, ms; Tsync – synchronization time for a voltage-based closing command, ms; N – the number of half-cycles; Tzero – duration of a half-cycle, ms; Tm – time interval between the beginning of prestriking and the first voltage zero, ms; Tclosing – time interval between energizing a closing coil and mechanical contact touching, ms; Tprestriking – time of prestriking, ms; Tmaking – time interval between energizing a closing coil and prestriking, ms.

  Algorithms of controlled switching

  In a three-phase AC network, each phase voltage crosses zero at different instants. Thus, to minimize switching transients, special algorithms of switching are used.

In the case of solid neutral grounding, the algorithm of controlled switching is as follows. Phase switching shall be done sequentially at the instants of voltage zero for each phase with a time delay determined by the following equation [7];

 

t1=1/(360∙f)∙60=1/(360∙50)∙60=0,0033[s],                                                                                      (5)

 

where f – network frequency, f = 50 Hz.

  In the case of an ungrounded network, two-phase switching shall be done simultaneously. Then, after 90 electrical degrees, switching of the third phase shall be performed. It is also possible to switch one phase at the instant of zero crossing. And then, perform switching of the last two phases with delay of 90 electrical degrees.

 

t2=1/(360∙f)∙90=1/(360∙50)∙90=0,005[s].                                                                                        (6)

 

3.png

 

Fig. 3. Time intervals of phase switching sequence

   

  Fig. 3 presents time intervals of phase switching sequence for different types of neutral grounding. It provides conditions for minimizing switching transients.

   Example of vacuum circuit breaker application

   Synchronous vacuum circuit breaker EX-BBC SMARTIC 6(10)-20/1000 has been placed for trial operation in local distribution network. The basic parameters of this circuit breaker are shown in table 1. The main purpose of this trial operation was controlled switching algorithms testing and their impact to the switching overvoltages reduction.

 

Table 1. Circuit breaker parameters


Parameters

Value

Voltage frequency, [Hz]

50

Nominal voltage, [kV]

10

Nominal current, [A]

1000

Nominal breaking current, [kA]

20

Total break time, [s]

0,09

Opening time, [s]

0,07

Closing time, [s]

0,1

   The voltage of local distribution network is 10 kV with insulated neutral. This network is characterized by great length and branching and mainly consists of cables, overhead lines and distribution substation of 10/0,4 kV with primarily domestic supply. Such synchronous vacuum circuit breaker location is typical for urban electric networks and is characterized by relatively low levels of overvoltages due to the features of switched load and the large length of the protected feeder. In this case, there are no conditions for emergence of critical overvoltages, however this case allows to identify optimal algorithms of controlled switching and to evaluate the reliability and effectiveness of synchronous vacuum circuit breaker.

   Simulation results

  Matlab Simulink has been used for electrical network and applied switching devices modeling. The simulation was made for the overvoltages estimation for the traditional (noncontrolled) and controlled switching and for optimal controlled switching algorithms determination.

  According to the results of simulation the maximum overvoltages for traditional switching is not more than 2,2 p.u. [9]. Such overvoltages do not have negative influence to the power equipment.

  The algorithm A-5ms-BC (phase A then 5ms delay then phases B and C simultaneously) with current synchronization is selected as the best algorithm of controlled circuit breaker opening [9]. The simulation results of synchronous opening shows that overvoltages are not occurred in this case.

Application results

During the period of trial operation some scheduled and short-circuit switchings were carried out. It shown, that synchronous vacuum circuit breaker is reliable and effective device for overvoltages reduction, both for switching off short-circuit current, and for scheduled switching.

 

4.png

Fig. 4. The voltages waveforms of controlled circuit breaker opening 

  Fig. 4 shows the voltages waveforms of scheduled controlled circuit breaker opening. It demonstrates the applied controlled opening algorithm: at first (at 19 ms) phase A was deactivated, later after 5 ms (at 24 ms) phases B and C simultaneously were disconnected. The overvoltages are not occurred during the switching.

   Conclusions

   The basic principles of controlled switching are considered. The application of synchronous vacuum circuit breaker realizing these principles as reliable and effective device for overvoltages reduction in urban electric networks 6-10 kV is presented. Using the controlled switch algorithm A-5ms-BC with current synchronization allowed eliminating completely overvoltages.

   Acknowledgements

This work has been supported by the Department of Industry, Innovation and Entrepreneurship City Hall of Novosibirsk (Agreement No 67-14).

  References

[1].             ABB ID 1HSM9543 22-01 en. Controlled switching. Buyer’s & Application Guide, 2009.

[2].             ABB ID 2GNM11001B. Product Brochure. Switching Control Sentinel, 2008.

[3].             Joslin Hi-Voltage ID DB 750-205. Product Brochure. Transmaster: Electric Arc Furnace Switches, 2007.

[4].             Joslin Hi-Voltage ID DB 750-510. Product Brochure. Digital Zero Voltage Closing (ZVC): Control for Capacitor Switching, 2003.

[5].             D.F.Alferov, G.S.Belkin, Yu.A. Goryushin, V.N.Ivakin, V.P. Ivanov, V.G. Kirakosov, V.I. Kochkin, A.A.Maslov, O.P.Nechayev, V.A.Sidorov. Control device of capacitor voltage regulator, Utility model patent №55222 RF, Opubl. v Byul., 21 (2006), (in Russian).

[6].             E.V. Prokhorenko, S.I. Odokiyenko, I.A.Lebedev. Synchronous vacuum circuit breaker, Patent for invention № 2432635 2011, Opubl. v Byul., 30 (2011), (in Russian).

[7].             A.A. Achitaev, D.A. Pavluchenko, E.V. Prohorenko, D.E. Shevtsov. Application of synchronous switching for limitation of switching overvoltage, Glavnyy energeti. 3 (2014) 50-56, (in Russian).

[8].             L.G. Kleparskaya. Controlled Circuit Breakers, Energiya, Moscow, 1973, (in Russian).

[9].             A.A. Achitaev, D.A. Pavluchenko, E.V. Prohorenko, D.E. Shevtsov. Using synchronous vacuum switch in urban electro power networks, Glavnyy energetik. 7 (2014) 46-52, (in Russian).



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