Download Extending the Application Field of Vacuum Circuit Breakers to Generators for Capacities up to 400 MW

ISSN 0040-6015, Thermal Engineering, 2018, Vol. 65, No. 4, pp. 200–207. © Pleiades Publishing, Inc., 2018.
Original Russian Text © K. Venna, Yu.P. Gusev, E.P. Oknin, G.Ch. Cho, 2018, published in Teploenergetika.
ELECTRICAL PART OF THERMAL
AND NUCLEAR POWER PLANTS
Extending the Application Field of Vacuum Circuit Breakers
to Generators for Capacities up to 400 MW
K. Vennaa, *, Yu. P. Gusevb, **, E. P. Okninb, and G. Ch. Chob
aSiemens,
bNational
Berlin, 13629 Germany
Research University Moscow Power Engineering Institute (NRU MPEI), Moscow, 111250 Russia
*e-mail: [email protected]
**e-mail: [email protected]
Received September 7, 2017; in final form, September 27, 2017
Abstract⎯The progress that has been achieved in the development and manufacture of vacuum circuit breakers opens the possibility of using them for a wider range of applications at power plants, including as generator
circuit breakers. Such characteristics of modern vacuum circuit breakers as increased breaking capacity and
high switching life are factors that make them closer in competitiveness to SF6 circuit breakers for generators
with capacities up to 400 MW. The article considers problem aspects relating to clearing of short-circuit faults
in the generator voltage circuits and interruption of out-of-phase making currents and no-load currents of
generator transformers. Conditions leading to a longer period of time to the moment at which the switched
current crosses zero are considered. It is pointed out that, unlike the IEC/IEEE Standard 62271-37-013,
GOST (State Standard) R 52565-2006 does not specify the requirements for generator circuit breakers in full.
The article gives the voltage drop values across the arc for different design versions of vacuum circuit breaker
contacts and shows the effect the arc in a vacuum circuit breaker has on the time delay to the moment at which
the current crosses zero. The standardized parameters of transient recovery voltage across the generator circuit breaker contacts are estimated along with the contact gap electric strength recovery rates ensured by
modern arc quenching chambers. The switching overvoltages arising when vacuum circuit breakers interrupt
short-circuit currents and no-load currents of generator transformers are analyzed. The article considers the
most probable factors causing the occurrence of switching overvoltages, including current chopping, repeated
breakdowns of the circuit breaker contact gap, and virtual current chopping. It is found that, unlike repeated
breakdowns and virtual current chopping, an actual current chopping does not give rise to dangerous switching overvoltages. The article also determines the vacuum circuit breaker application field boundaries in which
dangerous switching overvoltages may occur that would require additional measures for limiting them.
Keywords: vacuum generator circuit breaker, switching overvoltage, transient recovery voltage, current chopping, time delay to the current zero crossing moment, voltage drop across the arc
DOI: 10.1134/S0040601518040092
The conditions under which generator circuit
breakers operate are more intense than those of circuit
breakers used in medium voltage electric networks.
Significantly more stringent requirements in terms of
rated current, rated breaking current, DC component
in the breaking current, and transient recovery voltage
parameters are posed to generator circuit breakers.
However, standard [1] that is currently in force for circuit breakers stipulates the need of agreeing the
requirements for circuit breakers between the manufacturer and customer on a number of parameters.
Sometimes, lack of information available to the customer results in the fact that the requirements for generator circuit breakers (primarily those produced by
foreign manufacturers) made according to international standards, in particular, standard [2], are specified incorrectly. Previously, power plants in Russia
used MGG and VGM oil generator circuit breakers
and VVG and VVOA air-blast generator circuit breakers for rated currents ranging from 2000 to 3000 A and
rated breaking currents ranging from 45 to 160 kA [3].
Type KAG load interrupters were installed in the circuits of the largest generators. Later on, minimum-oil
and air-blast circuit breakers were replaced by SF6
generator circuit breakers and SF6 generator systems,
which are presently a standard solution used in
upgrading or new construction. Vacuum circuit breakers are used in the circuits of small-capacity generators; however, the application of these circuit breakers
for large-capacity generators is restrained due to the
following drawbacks that were inherent in the firstgeneration vacuum circuit breakers:
(1) increased levels of switching overvoltages,
(2) insufficiently high rated currents and rated
breaking currents of these circuit breakers, and
200
EXTENDING THE APPLICATION FIELD OF VACUUM CIRCUIT BREAKERS
201
Is.c
SC current DC component
Time delay interval
to the current zero
crossing moment
τ
Fig. 1. Generator short circuit current Is.c versus time τ.
(3) a low breaking capacity when there is an
increased content of the DC component in the
switched current.
Modern vacuum circuit breakers are already free
from these drawbacks. It was as far back as in 1988 that
vacuum generator circuit breakers successfully passed
independent short-circuit (SC) current breaking tests
with a delay to the moment at which the current
crosses zero caused by the DC component at a level of
120%. Good progress has been achieved in control of
switching overvoltages. The vacuum circuit breakers
proposed by Siemens can be used in the circuits of
generators for capacities up to 400 MW.
Modern vacuum circuit breakers have become free
from the bottlenecks they had at the early stage of their
development and have advantages over their SF6
counterparts: they permit a larger number of load current switching cycles, they feature a faster recovery of
contact gap electric strength, they need a smaller
amount of maintenance work, they are friendly to the
environment, and have a low cost [4, 5]. At present, vacuum circuit breakers for rated currents up to 12500 A
and rated breaking currents up to 100 kA are serially
produced [5]. They have successfully passed tests for
conformity to the requirements of international standard [2]. The use of vacuum circuit breakers allows
more efficient and reliable operation of upgraded and
newly constructed power plants to be secured.
Below, the characteristics of modern vacuum generator circuit breakers and the conditions of using
them at generator–transformer-type power plants are
considered in more detail.
Interrupting an SC fault current in the generator
voltage circuit is the heaviest mode of circuit breaker
operation. Depending on the SC fault location, the
current from the generator or power unit transformer
due to the feed from the grid and from the power
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plant’s other generators will flow through the circuit
breaker for a short period of time. Each of these cases
has its specific features that are of interest in considering the SC current interruption process by a vacuum
circuit breaker.
Owing to a high content of the DC component in
the SC current from the generator in the case of a shortcircuit fault between the generator and transformer, the
resulting instantaneous current curve shifts with respect
to the horizontal line corresponding to the zero value of
current. Due to low resistance and high inductance of
the generator stator winding, the SC current’s DC component decays quite slowly. The periodic component of
the SC current from the generator, which is characterized at the SC fault initial stage by the direct-axis subtransient time constant, can decay more rapidly than
the DC component, which is characterized by the time
constant of the SC current DC component. The initial
value of the DC component in each phase depends on
the SC occurrence phase angle and can reach the periodic component’s amplitude value. Thus, by the instant
at which the circuit breaker contacts begin moving
apart, the SC current’s slowly decaying DC component
may exceed the amplitude of the periodic component,
and the SC current will not cross zero for a few cycles
(Fig. 1), during which the circuit breaker will not interrupt the current.
The resistance of electric arc between the circuit
breaker contacts facilitates more rapid decaying of the
switched current DC component. As the SC current
DC component decays, the resulting current shifting
amplitude decreases, and the circuit breaker interrupts
the SC current during its first crossing of zero value.
The time delay between the moment the circuit
breaker contacts start moving apart to the moment the
instantaneous current crosses zero results in the fact
that the arc burns for a longer period of time, and that
202
VENNA et al.
Is.c, rel.units
8
Circuit breaker contacts
parting moment
2
1
6
4
2
0
–2
20
40
60
80
100
120
140
τ, ms
–4
Fig. 2. Interrupted SC current value versus time [2]. 1—DC
component of the interrupted SC current; 2—interrupted
SC current.
the arc chute and circuit breaker contacts experience
additional heating.
Standard [1] does not specify requirements for circuit breakers in regard to disconnecting the circuits
under the conditions in which the instantaneous current crosses zero after a time delay. Standard [2] specifies two standardized values of the DC component in
the SC current from the generator by the moment the
circuit breaker contacts start moving apart, which are
equal to 110 and 130%. The electric arc that ignites
after the circuit breaker contacts are parted from each
other adds external resistance to the SC circuit, as a
result of which the time constant becomes smaller, the
DC component decays more rapidly, and the time
delay to the moment the instantaneous current crosses
zero becomes shorter. Despite the fact that the voltage
drop across the arc is small in comparison with the circuit breaker operating voltage, the former has a noticeable effect on the SC current interruption process
(Fig. 2).
The extent to which the circuit breaker arc affects
the shift of the resulting instantaneous SC current
depends on the voltage drop across the arc. Vacuum
circuit breakers are characterized by the shortest distance between the contacts and by the lowest voltage
drop across the arc in comparison with circuit breakers
of other types. The results obtained from tests of vacuum generator circuit breakers have shown that the
average voltage drop across the arc does not exceed
100 V for Type AMF contacts, which generate an axial
magnetic field [6], and 120–150 V for Type TMF contacts, which generate a transverse magnetic field [7].
In [5], the results obtained from simulating the process
of interrupting the SC current from a generator are
presented for estimating the effect the arc in a vacuum
circuit breaker has on the SC current interruption process. The arc burning time between the contacts of two
circuit breaker poles is equal to 80 and 29 ms for the
voltage drop across the arc equal to zero and 100 V,
respectively, after which the instantaneous current
reaches zero value and the SC fault is cleared (Fig. 3).
With an SC fault between the generator and circuit
breaker, the SC current periodic component shows
hardly any decay due to remoteness of the SC fault
location from the power sources. The DC component
in the SC current does not exceed the amplitude of its
periodic component by the time the circuit breaker
contacts part from each other, due to which the instantaneous current will cross zero without time delay
(Fig. 4).
As a rule, the current from the transformer that
flows through the circuit breaker is higher than the SC
current from the generator in the case of an SC fault on
the generator voltage side due to feed from the grid and
from the power plant’s other generators. The SC currents from the transformer produce significant electrodynamic impacts on the generator circuit breaker
and determine the circuit breaker rated breaking currents. The ability of vacuum generator circuit breakers
to interrupt SC currents up to 100 kA [5] is a factor that
extends their application field at power plants.
The quenching of the arc in a circuit breaker pole is
accompanied by the growth of the transient recovery
voltage (TRV) across its contacts. The TRV growth
rate depends on the frequency of the TRV high-frequency component, which is proportional to the natural oscillation frequency of the generator or power
unit transformer loops. Due to the difference between
the capacitances of the generator and transformer
phases (with the commensurable inductances of their
windings), the transformer loop has a higher frequency of its natural oscillations. In view of this circumstance, the TRV in the case of an SC fault between
the generator and circuit breaker has a higher growth
rate. Thus, standard [2] specifies the required TRV
parameters separately for SC currents from the generator and from the transformer. In the first case, the
required voltage recovery rate does not exceed 2 kV/μs,
whereas it may reach 5 kV/μs in the second case. At the
moment in which the arc in the circuit breaker pole is
extinguished, the voltage is close to its amplitude
value, because the switched circuit is inductive in
nature and because there is a low content of DC component in the breaking current. Superposition of
amplitude voltage on the high-frequency component
results in higher peak values of the TRV in interrupting
the SC current from the transformer.
Out-of-step connection of the generator done as a
result of errors committed in arranging the secondary
circuits gives rise to high equalizing currents. Interruption of equalizing currents entails the occurrence of a
TRV across the generator circuit breaker contacts, the
parameters of which are essentially higher than those
of the TRV that occurs in interrupting SC currents. In
accordance with [2], the circuit breaker shall be
designed for an increased voltage under the conditions
of out-of-step connection; it shall ensure the possibility to perform out-of-step connection with subsequent
disconnection of the generator. In the most unfavorTHERMAL ENGINEERING
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EXTENDING THE APPLICATION FIELD OF VACUUM CIRCUIT BREAKERS
203
(a)
I, kA
100
3
1
50
0
0.04
0.06
0.08
0.10
0.16 τ, s
0.14
0.12
−50
−100
2
4
6
5
−150
(b)
I, kA
3
100
1
50
0
0.04
0.06
0.08
0.10
0.12 τ, s
−50
−100
2
4
5
6
−150
Fig. 3. Interruption of the generator current I in the case of a three-phase SC fault and voltage drop across the arc equal to (a) 0 V
and (b) 100 V. Phases: 1—А; 2—В; 3—С; 4—SC fault occurrence instant; 5—parting the circuit breaker contacts; 6—clearing the SC
fault.
able case, the TRV peak value resulting from circuit
breaker disconnection under out-of-phase conditions
is produced when the high-frequency voltage component is superimposed on twice the generator phase
voltage. Clearly, the peak voltages produced in this
mode will exceed their values in the case of clearing an
SC fault in the generator voltage circuit. Thus, standard [2] specifies the standard TRV peak value with
respect to the circuit breaker’s highest operating voltage in the out-of-phase switching mode equal to
2.6 relative units and equal to 1.84 relative units in the
SC clearing mode with the commensurable TRV
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growth rate in both cases. The standardized TRV
parameters are given for the standardized breaking
current, the value of which in the out-of-phase mode
is determined by the difference between the voltage
phasors at the generator terminals and at the terminals
of the transformer low voltage winding and between
the grid equivalent impedance and the generator subtransient reactance. The grid impedance is commensurable with the generator subtransient reactance, and
the current resulting from out-of-phase connection of
the generator will not be significantly higher than the
SC current from the generator even if the generator is
204
VENNA et al.
Is.c
SC current DC component
τ
Fig. 4. Short-circuit current from the transformer versus time.
connected in the opposite-phase mode [8]. In accordance with [1, 2], the standardized breaking current
shall be no less than 50% of the circuit breaker rated
breaking current, which corresponds to a phase mismatch angle equal to 90 el. deg. The actual breaking
current may be significantly higher than its standardized value. Thus, with the phase mismatch angle equal
to 90 el. deg, the breaking current can make 63% of the
circuit breaker rated breaking current [9].
Interruption of current in a circuit breaker that
occurs before the expected moment at which the
instantaneous power frequency current crosses zero,
called current chopping, is characteristic for all types of
circuit breakers. Instability of arc discharge at low current values and intense dissipation of the arc column
energy in the circuit breaker chute under the effect of
electromagnetic or gas blasting are factors causing the
current chopping phenomenon [10, 11]. The current
chopping phenomenon can initiate repeated ignitions
of the arc in the circuit breaker and the occurrence of a
high-frequency current component.
The current chopping phenomenon causes the
energy stored in the switched circuit inductances to be
discharged onto the capacitance of live parts with
respect to ground and gives rise to overvoltages. The
overvoltage amplitude is directly proportional to the
chopped current Ich and inversely proportional to the
capacitance. The chopping current of vacuum circuit
breakers depends on the material of their contacts [12],
because the arc burns in the vapors of metal vaporized
from the cathode surface under the effect of high temperature. Figure 5 shows the possible chopping current
values for different media and the distribution of its
occurrence probability P for vacuum circuit breakers.
It can be seen from Fig. 5a that the vacuum generator circuit breakers with contacts made of chro-
mium–copper compositions [5, 13] ensure the lowest
chopping current in comparison with that in using
other media. A low chopping current allows switching
voltages to be limited to a level that does not pose danger for electrical machines provided that no repeated
arc ignition and voltage escalation occur [14, 15].
In what follows, we consider the conditions under
which repeated arc ignitions occur in a vacuum circuit
breaker. A vacuum differs advantageously from other
arc quenching media in the steepness of the impulse
breakdown voltage growth curve. In comparison with
SF6 generator circuit breakers operating at a pressure
of 0.5 MPa, the vacuum circuit breaker impulse breakdown voltage is higher by more than a factor of two
than that of SF6 circuit breakers at the distances characteristic for the initial stage of parting the circuit
breaker contacts. Thus, the vacuum circuit breakers
produced by Siemens that comply with the requirements of standard [2] ensure the contact gap electrical
strength recovery rate more than 10 kV/μs. Nonetheless, repeated breakdowns in disconnecting a circuit
occur even in vacuum circuit breakers. Cases in which
the circuit breaker pole (phase С) contacts begin to
part at less than 0.5 ms before the current zero crossing
moment (Fig. 6a) are the most dangerous ones. After
the current has been interrupted, the circuit breaker
contacts still continue to part, and the contact gap
electrical strength continues to grow. This period of
time involves a danger of repeated breakdowns to
occur with generation of a high-frequency current
component. Repeated arc ignitions entail voltage
escalation and a growth of the high-frequency current
amplitude. Due to the inductive and conductive couplings between the phases, a high-frequency current
arises also in phases A and В, which may also be a factor causing virtual chopping of current in them (see
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EXTENDING THE APPLICATION FIELD OF VACUUM CIRCUIT BREAKERS
(а)
205
(b)
Air-blast
circuit breakers
20
Ich, A
Vacuum circuit breakers
(with Cu–Bi contacts)
15
Minimum-oil
circuit
breakers
P
0.4
10
Bulk-oil
circuit breakers
5
0.3
SF6 circuit
Vacuum circuit breakers
breakers
(with Cu–Cr
contacts)
0.2
0.1
0
0
1
2
3
4 Ich, A
Fig. 5. (a) Chopping current for different arc quenching media and (b) probabilistic distribution of chopping current in vacuum
circuit breakers with contacts made of Cu–Cr composition [16].
Iint
Ic
(а)
Ic
(b)
Ic
A
fnom = 50 Hz I
B
B
C
τ
Ic
High-frequency
current zero
crossing moment
IA
Fig. 6. Induced virtual current chopping [16]. (a) Interrupted currents of phases А, В, and С versus time and (b) switching state
of the disconnected circuit at the virtual chopping current occurrence instant.
Fig. 6a). This may give rise to an overvoltage with a
ratio of up to six phase voltages applied to the turn and
main insulations of the generator and transformer.
Based on the results from tests of medium voltage
vacuum circuit breakers produced by Siemens that
involved interruption of inductive currents, which
were reported in [16], the conditions under which
dangerous overvoltages may occur due to repeated
contact gap breakdowns entailing virtual current
chopping have been determined. Figure 7 shows the
voltage frequency fa across the circuit breaker contacts
as a function of the interrupted current rms value Iint
for 12 kV electrical installations. Overvoltages may
occur if the interrupted current parameters lie in the
separated zone of the diagram. Cases involving disTHERMAL ENGINEERING
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connection of neutral grounding transformers with arc
suppression coils, motors in their starting mode, and
shunting reactors are dangerous in terms of switching
overvoltages. The dangerous range of interrupted current rms values is from 20 to 600 A. Thus, interruption
of an SC current by a vacuum circuit breaker does not
entail the occurrence of dangerous switching overvoltages. This statement is also valid for disconnection of
idle generator transformers with magnetization currents below 20 A (which corresponds to transformers
with capacities equal to or less than 100 MVA):
repeated arc ignitions and dangerous switching overvoltages do not occur. For power units of a larger
capacity, vacuum circuit breakers with several parallelconnected arc chutes per pole are produced.
206
VENNA et al.
fa, kHz
8
100
50
6
10
5
5
3
1
0.5
0
1
0.5
5 10
7
4
2
50 102
5 × 102
5 × 103
5 × 104
Iint, A
Fig. 7. Diagram showing interruption of inductive currents in 12 kV electrical installations [16]. Transformers: 1—idle, 2—of electric arc furnaces, 3—for neutral grounding with arc suppression coils, and 6—with short-circuited secondary windings; 4—motors
in the starting mode; 5—shunting reactors; 7, 8—short-circuit faults in the network and in connections equipped with reactors.
Overvoltages caused by repeated breakdowns and
virtual current chopping were observed in disconnecting the idle transformer of the Kama hydroelectric
power plant’s unit [14]. An analysis of the test conditions indicates that there are additional factors that
affect the interruption process. The domestically produced vacuum generator circuit breakers were
equipped with arc chutes produced by Siemens. Poor
technical state of the vacuum circuit breaker drive may
become a factor causing a degraded gap strength
recovery rate at the initial stage of interruption and
giving rise to dangerous switching overvoltages. Disconnections of the power plant auxiliary electric
motor performed before finishing its startup with a
startup current lower than 600 A were accompanied by
repeated breakdowns and entailed the occurrence of
overvoltages with ratios equal to 3.0 and 2.7 of the
amplitude phase voltage with the availability of overvoltage limiters [15].
Dangerous switching overvoltages caused by the
operation of vacuum generator circuit breakers may
occur in disconnecting the power unit’s idle transformer if the current interrupted by the arc chute
exceeds a certain threshold value. The threshold current value for the vacuum circuit breakers produced by
Siemens is 20 A. Owing to the use of several parallelconnected arc chutes in circuit breakers for rated currents up to 14 kA, the threshold current value does not
occur as a rule, and repeated arc ignitions and dangerous overvoltages do not occur in the course of disconnection. Hence, there is no need to mandatorily provide protection from overvoltages by installing overvoltage limiters or R-C circuits.
CONCLUSIONS
(1) Vacuum generator circuit breakers outperform
the currently used SF6 circuit breakers in the majority
of their characteristics. Owing to the state-of-the-art
technologies for manufacturing vacuum arc chutes
and low chopping current values, protection from the
overvoltages caused by the operation of vacuum circuit
breakers is not a must. The progress achieved in the
vacuum circuit breaker manufacturing technology
opens the possibility to use these circuit breakers at
power plants in the circuits of generators with capacities up to 400 MW.
(2) Wide-scale application of vacuum generator
circuit breakers is hindered by the preconceived attitude of some specialists to their manufacturing technology stemming from the negative experience gained
from using first-generation vacuum circuit breakers
and incorrect choice of circuit breakers. To secure reliable operation of vacuum generator circuit breakers,
they should be selected with due regard to the results
from calculations of the periodic and DC short-circuit
current components and the parameters of transient
recovery voltage.
REFERENCES
1. GOST R 52565-2006. Alternating-Current CircuitBreakers for Voltages from 3 to 750 kV. General Specifications (Standartinform, Moscow, 2007).
2. IEC/IEEE 62271-37-013 High-Voltage Switchgear and
Controlgear — Part 37-013: Alternating-Current Generator Circuit-Breakers (Int. Electrotechnical Commission, 2015).
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EXTENDING THE APPLICATION FIELD OF VACUUM CIRCUIT BREAKERS
3. P. A. Sheiko, “6–24 kV generator circuit breakers. The
problem of choice and application,” Nov. Elektrotekh.,
No. 2, 70–72 (2006).
4. A. N. Nazarychev, “Analysis of main advantages of the
use of vacuum circuit breakers,” Energoekspert, No. 4–
5, 58–63 (2007).
5. K. Venna, N. Anger, and T. Kleinert, “Role of vacuum
generator circuit breaker in improving the plant efficiency & protecting the generators up to 450 MVA,” in
Proc. POWER-GEN Europe 2016, Milan, June 21–23,
2016 (PennWell, 2016).
6. Test Order No. 14-00626, Hochspannungs- und Schaltleistungsprüfungen, Schalter-3AH36 (Siemens AG, 2015).
7. R. K. Smith, R. W. Long, and D. L. Burminghan,
“Vacuum interrupters for generator circuit breakers
they’re not just for distribution circuits breakers anymore,” in Proc. 17th CIRED Conf. on Electricity Distribution, Barcelona, May 12–15, 2003 (CIRED, 2003).
8. S. A. Ul’yanov, Electromagnetic Transients in Electric
Systems. Textbook (Energiya, Moscow, 1970) [in Russian].
9. D. Braun and G. Koeppl, “Transient recovery voltages
during the switching under out-of-phase conditions,”
in Proc. Int. Conf. on Power Systems Transients (IPST
2003), New Orleans, Sept. 28 – Oct. 2, 2003.
10. W. M. C. van den Heuvel, Doctoral Dissertation in Engineering (Technische Hogeschool Eindhoven, Eindhoven, 1966). doi 10.6100/IR76586
THERMAL ENGINEERING
Vol. 65
No. 4
2018
207
11. M. Murano, S. Yanabu, H. Ohashi, H. Ishizuka, and
T. Okazaki, “Current chopping phenomena of medium
voltage circuit breakers,” IEEE Trans. Power Appar.
Syst. 96, 143–149 (1977).
12. R. D. Garzon, High Voltage Circuit Breakers. Design and
Applications (CRC, New York, 2002). doi 10.1109/
MEI.1998.730820
13. G. Evdokunin and S. Titenkov, “Overvoltages in
6(10) kV grids are caused by both vacuum and SF6 circuit breakers,” Nov. Elektrotekh., No. 5, 27–29 (2002).
14. V. S. Larin, A. K. Lokhanin, and P. A. Sheiko, “A study
of switching overvoltages caused by the work of vacuum
generator circuit breakers VGG-10 and VGGm-10 at
Kamskaya GES,” Elektrichestvo, No. 9, 31–40 (2011).
15. Degtyarev I. L. Candidate’s Dissertation in Engineering (Novosibirsk State Technical Univ., Novosibirsk,
2006).
16. A. Mueller, “Switching phenomena in medium voltage
systems. Good engineering practice on the application
of vacuum circuit-breakers and contactors,” in Proc.
2011 Eur. Conf. on Electrical and Instrumentation Applications in the Petroleum & Chemical Industry (PCIC
Europe), Rome, June 7–9, 2011 (IEEE, New York,
2011).
Translated by V. Filatov