# Field Experiments on 10 kV Switching Shunt Capacitor Banks Using Ordinary and Phase-Controlled Vacuum Circuit Breakers

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## Abstract

**:**

## 1. Introduction

**Figure 1.**An explosion involving switching 10 kV shunt capacitor banks with vacuum circuit breakers (VCBs). (

**a**) Testing site; and (

**b**) burnt capacitors.

## 2. Analytical Analysis

_{sa}(t), U

_{sb}(t), and U

_{sc}(t) are the power sources. R is the internal resistance of source. K

_{a}, K

_{b}, and K

_{c}are the circuit breakers. L is the series inductance, and C are the shunt capacitor banks. In a 10 kV ungrounded neutral system, the typical values of these parameters are as follows: U

_{sa}(t) = 8.165sin(100πt) kV, U

_{sb}(t) = 8.165sin(100πt + 120°) kV, U

_{sc}(t) = 8.165sin(100πt − 120°) kV, R = 0.2 Ω, C = 27.14 µF, L = 9.90 mH. The reduced circuit in Figure 2b can be obtained with the assumption of simultaneous switching on/off for the three-phase circuit breakers.

**Figure 2.**Circuit of switching shunt capacitor banks. (

**a**) Symmetrical three-phase circuit; and (

**b**) reduced circuit.

#### 2.1. Closing Operation

_{0}is the value of the initial capacitor voltage, U

_{cm}is the steady voltage of capacitor ${U}_{\mathrm{cm}}=\frac{{U}_{\mathrm{sm}}}{\mathsf{\omega}C\sqrt{{R}^{2}+{(\mathsf{\omega}L-1/\mathsf{\omega}C)}^{2}}}$, ${\mathsf{\omega}}_{0}=1/\sqrt{(LC)}$, and ${\mathsf{\omega}}_{0}$ is the oscillation frequency. The amplitude of the closing current and voltage are given as:

_{cm}, and the closing current may reach 11 ${I}_{\mathrm{cm}}$ in the most serious case.

_{0}is the value of the initial capacitor current. Therefore, closing at ${\mathsf{\theta}}_{\mathrm{c}}={0}^{\mathrm{o}}$ significantly decreases the closing current by comparing Equation (7) with Equation (5).

#### 2.2. Opening Operation

_{sm}after arc extinguishing if capacitor the discharge is ignored. The transient recovery voltage of the circuit breaker contacts will be as follows:

_{sm}after half a cycle ($\mathsf{\omega}t=\mathsf{\pi}$). If the dielectric recovery voltage is less than 2U

_{sm}at this moment, the re-striking and subsequent high-frequency oscillation will occur. The high-frequency voltage and current of the capacitor are given as follows:

_{sm}at i

_{c}(t) initially crossing zero during high-frequency oscillation. In the same moment, the overvoltage of capacitor will be maintained at 3U

_{sm}if the arc extinguishes. After a half cycle, the transient recovery voltage of the contacts reaches 4U

_{sm}. If re-striking occurs again, the maximum value of U

_{c}(t) will reach 5U

_{sm}. With this analogy, the overvoltage of the capacitor becomes 3 p.u., 5 p.u., 7 p.u., and so on.

## 3. Phase-Selecting Control Strategy for 10 kV Ungrounded Capacitor Banks

_{0}, the breakers of phase A and phase B close at t

_{ab}, and the breaker of phase C closes at t

_{c}. t

_{Ad}, t

_{Bd}, and t

_{Cd}are the closing delay times, respectively.

_{b}as shown in Figure 5). The strategy for opening capacitor banks is to open one phase and then to open the other two phases when the current of the first-pole-to-clear reaches zero (5 ms later than the first phase). Figure 5 shows the sequence of opening capacitor banks with phase selection. The breaker receives the opening signal at t

_{0}, the breaker of phase B opens at t

_{b}, and breakers of phase A and phase C opens at t

_{ac}. t

_{Ad}, t

_{Bd}, and t

_{Cd}are the opening delay times, respectively. t

_{Ao}, t

_{Bo}, and t

_{Co}are the times between the moving contact starting to move and the moment the moving and static contacts are completely separated.

## 4. Field Test Results and Discussion

Parameters | Phase A | Phase B | Phase C | Total |
---|---|---|---|---|

Power frequency | 50HZ | 50HZ | 50HZ | - |

Rated power of capacitors | 2004 kVAR | 2004 kVAR | 2004 kVAR | 6012 kVAR |

Number of capacitors | 6 | 6 | 6 | 18 |

Number of groups | 3 | 3 | 3 | 9 |

Number of capacitors in each group | 2 | 2 | 2 | 6 |

Capacitance of each capacitor | 27.14 µF | 27.14 µF | 27.14 µF | - |

Rated voltage of each capacitor | $11/\sqrt{3}$ kV | $11/\sqrt{3}$ kV | $11/\sqrt{3}$ kV | - |

Rated power of each capacitor | 334 kVAR | 334 kVAR | 334 kVAR | - |

Series reactor rate of shunt capacitor bank | 5% | 5% | 5% | 5% |

Rated power of reactors | 100.2 kVAR | 100.2 kVAR | 100.2 kVAR | 300.6 kVAR |

Number of reactors | 3 | 3 | 3 | 9 |

Number of groups | 3 | 3 | 3 | 9 |

Number of reactors in each group | 1 | 1 | 1 | 3 |

Inductance of each reactor | 9.90 mH | 9.90 mH | 9.90 mH | - |

Rated voltage of each reactor | 10 kV | 10 kV | 10 kV | - |

Rated power of each reactor | 33.4 kVAR | 33.4 kVAR | 33.4 kVAR | - |

Quality factor (Q) of the reactor | 50 | 50 | 50 | - |

No. | Operation | Breaker | Group | Voltage Base Value (kV) | Current Base Value (A) |
---|---|---|---|---|---|

Case 1 | Switching on | Without phase selection (#653) | 1 | 8.165 | 155.56 |

Case 2 | Switching on | Without phase selection (#653) | 1–3 | 8.165 | 466.69 |

Case 3 | Switching on | With phase selection (#65301) | 1 | 8.165 | 155.56 |

Case 4 | Switching off | Without phase selection (#653) | 1 | 8.165 | 155.56 |

Case 5 | Switching off | Without phase selection (#653) | 1–3 | 8.165 | 466.69 |

Case 6 | Switching off | With phase selection (#65301) | 1 | 8.165 | 155.56 |

#### 4.1. Case 1

**Figure 8.**Waveforms of the closing current and capacitor voltage in Case 1. (

**a**) Current waveform; and (

**b**) voltage waveform.

#### 4.2. Case 2

**Figure 9.**Waveforms of the closing current and capacitor voltage in Case 2. (

**a**) Current waveform; and (

**b**) voltage waveform.

#### 4.3. Case 3

_{1}when their line voltage U

_{ab}crosses zero, and then phase C is closed after 5 ms at t

_{2}when its phase voltage crosses zero. The transient voltage of phase C from t

_{1}to t

_{2}is equal to the neutral voltage of the shunt capacitor banks. Thus, the zero-crossing switching strategy is achieved. Almost no high-frequency voltage oscillation occurs in this case, and the corresponding maximum of the high-frequency oscillation voltage is very low (about 0.76 p.u.). The time error of the phase-controlled circuit breaker for closing the shunt capacitor banks is below ±0.2 ms.

#### 4.4. Case 4

_{3}, and phase B is the first-pole-to-clear. The transient currents of phase A and phase C are always equal, but in the opposite direction, after the current of phase B decreases to zero at the moment of t

_{4}, which is also the time of the contacts of phase A and phase C start to separate. The breaking arc duration of phase B is Δt

_{1}= 1.7 ms (Δt

_{1}= t

_{4}− t

_{3}). After a quarter of a cycle (5 ms), the currents of phase A and phase C both reach zero at the moment of t

_{5}. Thus, the phenomenon of the power frequency extinguishing arcing is observed. Statistical results according to our field tests show that the breaking arc duration of the first-pole-to-clear (phase B in this test) is almost 1.0–4.5 ms.

**Figure 10.**Waveforms of the closing current and capacitor voltage in Case 3. (

**a**) Current waveform; and (

**b**) voltage waveform.

**Figure 11.**Waveforms of the opening current and capacitor voltage in Case 4. (

**a**) Current waveform; and (

**b**) voltage waveform.

#### 4.5. Case 5

_{6}, and phase B is also the first-pole-to-clear. The breaking arc duration of phase B is Δt

_{2}= 4.1 ms (Δt

_{2}= t

_{7}− t

_{6}). The currents of phases A and C are equal but opposite in direction from t

_{7}to t

_{8}, during which the current of phase B reaches zero. After t

_{8}, the currents of the three phases remain zero.

**Figure 12.**Waveforms of the opening current and capacitor voltage in Case 5. (

**a**) Current waveform; and (

**b**) voltage waveform.

#### 4.6. Case 6

_{3}= 2.67ms) later than its last current zero-crossing point at t

_{9}, and phase B is the first-pole-to-clear. The transient currents of phase A and phase C are always equal, but in the opposite direction, after the current of phase B decreases to zero at the moment of t

_{10}, which is also the time that the contacts of phase A and phase C start to separate. The breaking arc duration of phase B is Δt

_{4}= 7.4 ms (Δt

_{4}= t

_{10}− t

_{9}). After a quarter of a cycle (5 ms), the currents of phase A and phase C both reach zero at the moment of t

_{11}. Therefore, the power frequency extinguishing arcing still occurs in this case. Statistical results according to our field tests indicate that the breaking arc duration of the first-pole-to-clear (phase B in this test) is about 7.5 ms, and the time error of the phase-controlled circuit breaker for opening shunt capacitor banks is below ±0.3 ms.

**Figure 13.**Waveforms of the opening current and capacitor voltage in Case 6. (

**a**) Current waveform; and (

**b**) voltage waveform.

## 5. Conclusions

- ≫
- The overcurrent of closing 10 kV shunt capacitor banks was about 2.12 p.u. with phase selection, and it was far below than those of ordinary VCBs (4.04 p.u. for Case 1 and 4.49 p.u. for Case 2). Moreover, high-frequency voltage oscillation did not occur for switching on shunt capacitor banks when phase-controlled VCBs were used.
- ≫
- The overvoltage of opening 10 kV shunt capacitor banks was about 1.57 p.u. with phase selection, and it was below those of ordinary VCBs (2.26 p.u. for Case 4 and 2.23 p.u. for Case 5).
- ≫
- The arc duration of closing shunt capacitor banks without phase selection was about 1.0–4.5 ms. However, for the phase-controlled VCBs, the circuit breaker of the first-pole-to-clear was opened 2–3 ms later than its last current zero-crossing point, which result in an average of 7.5 ms arc duration of first-pole-to-clear.
- ≫
- The time error of phase-controlled VCBs for opening and closing shunt capacitor banks was below ± 0.3 ms. Furthermore, the higher arc duration increased the fracture gap distance of phase-controlled VCB contacts, and the probability of prestrike and re-ignition was reduced. This can contribute to keeping the power system safe and achieving steady operation.

## Acknowledgments

## Author Contributions

## Conflicts of Interest

## References

- Dullni, E.; Shang, W.K.; Gentsch, D. Switching of capacitive currents and the correlation of restrike and pre-ignition behavior. IEEE Trans. Dielectr. Electr. Insul.
**2006**, 13, 65–71. [Google Scholar] [CrossRef] - Glinkowski, M.; Greenwood, A.; Hill, J.; Mauro, R.; Varneckes, V. Capacitance switching with vacuum circuit-breakers—A comparative-evaluation. IEEE Trans. Power Deliv.
**1991**, 6, 1088–1095. [Google Scholar] [CrossRef] - Jones, R.A.; Fortson, H.S. Consideration of phase-to-phase surges in the application of capacitor banks. IEEE Trans. Power Deliv.
**1986**, 1, 240–244. [Google Scholar] [CrossRef] - Witte, J.F.; DeCesaro, F.P.; Mendis, S.R. Damaging long term overvoltages on industrial apacitor banks due to transformer energization inrush currents. IEEE Trans. Ind. Appl.
**1994**, 30, 1107–1115. [Google Scholar] [CrossRef] - Bruns, D.P.; Newcomb, G.R.; Miske, S.A.; Taylor, C.W.; Lee, G.E.; Edris, A.A. Shunt capacitor bank series group shorting (CAPS) design and application. IEEE Trans. Power Deliv.
**2001**, 16, 24–32. [Google Scholar] [CrossRef] - Anderson, E.; Karolak, J.; Wisniewski, J. Application of modern switching methods in reactive power compensation systems. Prz. Elektrotechniczny
**2012**, 88, 1–5. [Google Scholar] - Bonfanti, I. Shunt Capacitor Bank Switching, Stressesand Test methods (2nd part) (Cigre WG 13-04). Electra
**1999**, 183, 13–41. [Google Scholar] - Mcgranaghan, M.F.; Reid, W.E.; Law, S.W.; Gresham, D.W. Overvoltage protection of shunt-capacitor banks using MOV arresters. IEEE Trans. Power Appar. Syst.
**1984**, 103, 2326–2336. [Google Scholar] [CrossRef] - Pflanz, H.M.; Lester, G.N. Control of overvoltages on energizing capacitor banks. IEEE Trans. Power Appar. Syst.
**1973**, 92, 907–915. [Google Scholar] [CrossRef] - Boehne, E.W.; Low, S.S. Shunt capacitor energization with vacuum interrupters—A possible source of overvoltage. IEEE Trans. Power Appar. Syst.
**1969**, 88, 1424–1443. [Google Scholar] [CrossRef] - Surge Protective Devices Committee. Surge protection of high-voltage shunt capacitor banks on AC power-systems survey results and application considerations. IEEE Trans. Power Deliv.
**1991**, 6, 1065–1072. [Google Scholar] - Das, J.C. Analysis and control of large-shunt-capacitor-bank switching transients. IEEE Trans. Power Appar. Syst.
**2005**, 41, 1444–1451. [Google Scholar] - Zadeh, M.K.; Hinrichsen, V.; Smeets, R.; Lawall, A. Field emission currents in vacuum breakers after capacitive switching. IEEE Trans. Dielectr. Electr. Insul.
**2011**, 18, 910–917. [Google Scholar] [CrossRef] - Smeets, R.P.P.; Thielens, D.W.; Kerkenaar, R.W.P. The duration of arcing following late breakdown in vacuum circuit breakers. IEEE Trans. Plasma Sci.
**2005**, 33, 1582–1588. [Google Scholar] [CrossRef] - Yang, Q.; Ouyang, S.; Sima, W.X.; Xi, S.Y.; Kang, H.F.; Yang, M. Mechanism of overvoltage induced by fast switching on-off 10 kV shunt capacitors using vacuum circuit breakers. High Volt. Eng.
**2014**, 40, 3135–3140. (In Chinese) [Google Scholar] - Yang, Q.; Zhang, Z.H.; Sima, W.X.; Yang, M.; Wei, G.W. Field experiments on overvoltage caused by 12 kV vacuum circuit breakers switching shunt reactors. IEEE Trans. Power Deliv.
**2015**. [Google Scholar] [CrossRef] - CIGRE (International Council on Large Electric systems) Working Group A3, 07. Controlled Switching of HVAC Circuit Breaker: GUIDANCE for Further Applications Including Unloaded Transformer Switching, Load and Fault Interruption and Circuit-Breaker Updating; CIGRE: Paris, France, 2004. [Google Scholar]
- Mahurkar, T.M.; Murali, M. Suppression of capacitor switching transients using symmetrical structure transient limiter [SSTL] and its applications. In Proceedings of the International Conference on Computation of Power, Energy, Information and Communication, Chennai, India, 16–17 April 2014.
- Filion, Y.; Coutu, A.; Isbister, R. Experience with controlled switching systems (CSS) used for shunt capacitor banks: planning, studies and testing accordingly with CIGRE A3-07 Working Group Guidelines. In Proceedings of the Quality and Security of Electric Power Delivery Systems Conference, Montreal, PQ, Canada, 8–10 October 2003.
- Borghetti, A.; Napolitano, F.; Nucci, C.A.; Paolone, M.; Sultan, M.; Tripaldi, N. Transient recovery voltages in vacuum circuit breakers generated by the interruption of inrush currents of large motors. In Proceedings of the International Conference on Power Systems Transients (IPST2011), Delft, The Netherlands, 14–17 June 2011.
- Ding, F.H.; Duan, X.Y.; Zou, J.Y.; Liao, M.F. Controlled switching of shunt capacitor banks with vacuum circuit breaker. In Proceedings of the International Symposium on Discharges and Electrical Insulation in Vacuum (ISDEIV 2006), Matsue, Janpan, 25–29 September 2006.
- Ning, D.; Yonggang, G.; Jingsheng, Z.; Jirong, N.; Shuhua, Y.; Guozheng, X. Protections of overvoltages caused by 40.5 kV vacuum circuit breakers switching off shunt reactors. High Volt. Eng.
**2010**, 36, 345–349. (In Chinese) [Google Scholar] - Roseburg, T.; Tziouvaras, D.; Pope, J. Controlled Switching of HVAC Circuit Breakers: Application Examples and Benefits. In Proceedings of the 61st Annual Conference for Protective Relay Engineers, College Station, TX, USA, 1–3 April 2008.
- Reid, J.F.; Tong, Y.K.; Waldron, M.A. Controlled Switching Issues and the National Grid Company’s Experience of Switching Shunt Capacitor Banks and Shunt Reactor; August Session; CIGRE: Paris, France, 1998; pp. 223–231. [Google Scholar]
- Jones, S.; Gardner, K.; Brennan, G. Switchgear issue in deregulated electricity industries in Australia and New Zealand; August Session; CIGRE: Paris, France, 2000; pp. 1–6. [Google Scholar]
- Nordin, R.; Holm, A.; Norberg, P. Ten Years of Experience with Controlled Circuit Breaker Switching in the Swedish Regional Network; August Session; CIGRE: Paris, France, 2002; pp. 21–23. [Google Scholar]
- Li, D. Study on forepart re-strike rate of 35kV vacuum circuit breaker in the closing-opening process of capacitor group. High Volt. Eng.
**2002**, 28, 22–23. (In Chinese) [Google Scholar] - Yan, X.L.; Li, Z.B.; Wang, C.Y.; Liu, B.Y.; Wang, H. Analysis on characteristics of phase-selectable circuit breaker for switching capacitor banks in UHV power transmission project. Power Syst. Technol.
**2014**, 38, 1772–1778. [Google Scholar] - Liu, S.H. Analysis and simulation study on overvoltage of shunt power capacitor. Master’s thesis, South China University of Technology, Guangdong, China, 2011. [Google Scholar]
- Zhong, X. Study on the transition process of closing shunt capacitors in 10 kV power system. Master’s Thesis, Chongqing University, Chongqing, China, 2010. [Google Scholar]
- Insulation Co-Ordination—Part I: Definitions, Principles and Rules; IEC Std. 60071-1:2006; IEC (the International Electrotechnical Commission): Geneva, Switzerland, 2006.

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**MDPI and ACS Style**

Sima, W.; Zou, M.; Yang, Q.; Yang, M.; Li, L.
Field Experiments on 10 kV Switching Shunt Capacitor Banks Using Ordinary and Phase-Controlled Vacuum Circuit Breakers. *Energies* **2016**, *9*, 88.
https://doi.org/10.3390/en9020088

**AMA Style**

Sima W, Zou M, Yang Q, Yang M, Li L.
Field Experiments on 10 kV Switching Shunt Capacitor Banks Using Ordinary and Phase-Controlled Vacuum Circuit Breakers. *Energies*. 2016; 9(2):88.
https://doi.org/10.3390/en9020088

**Chicago/Turabian Style**

Sima, Wenxia, Mi Zou, Qing Yang, Ming Yang, and Licheng Li.
2016. "Field Experiments on 10 kV Switching Shunt Capacitor Banks Using Ordinary and Phase-Controlled Vacuum Circuit Breakers" *Energies* 9, no. 2: 88.
https://doi.org/10.3390/en9020088