1. HYBRID DC CIRCUIT BREAKER
ANKIT KHERODIYA AYUSH GUPTA
INSTITUTE OF TECHNOLOGY, NIRMA UNIVERSITY
AHMEDABAD
ABSTRACT
This paper intends to present hybrid circuit
breaker in dc application. For DC circuit breaker
fault current Interruptionis more challenging than
AC due to absence of current zero crossing. In
conventional dc circuit breaker fault current
interruption is performedby increasing the arc
resistance leading to limited endurance & high
current interruption time. This paper presents
redeem of concept to generate zero crossing by
imposing a reverse oscillatory current through
resonance between inductor & capacitor on the
circuit breaker.Hybrid circuit breaker is
combination of conventional circuit breaker and
SSCB(solid state circuit breaker). Hybrid circuit
breaker has advantage of both conventional
circuit breaker & SSCB as it has small on state
resistance as well as short current interruption
time. Analysis & simulation of zero current
crossing is presented using PSCAD/EMTDC, in
which intelligent switching of SSCBis also
considered.
1. INTRODUCTION
The growth of power demands throughout the
world and increasing use of renewable energy
necessitates the transmission of large power over
long distances. HVDC(high voltage direct current)
transmission is well proven technology for long
distance power transmission & interconnection of
asynchronous AC grid. The major advantages of
HVDC transmission is ease of controlling active
power, low short circuit current, low power losses
&less space required compared to AC. However,
the most important reason that limits the
development of HVDC is lack of HVDC circuit
breaker. Circuit breaker is one of the most
important element of DC transmission network to
maintain integrity of system operation. It ensures
the reliability and stability of power system by
isolating faulty section of system. The leading
problem in dc circuit breaker is absence of natural
passage of current through zero. This problem can
be solved by either increasing arc resistance or by
generating current zero. This paper first introduces
DC arc model &various circuit breaker
topologies.Then it discusses an approach to create
current zero by imposing reverse oscillatory
current through resonant commutation circuit.
MCB(Mechanical circuit breaker) is used as main
current path & SSCB is used in commutation
circuit of hybrid circuit breaker .This paper
investigates mathematical modeling and detailed
analysis for HCB(hybrid circuit breaker) and
presents time domain simulation studies for HCB
using PSCAD/EMTDC.
2. DC arc model
The arc model is mathematical description of the
electrical characteristics of arc which is
developed for understanding of the current
interruption process in circuit breaker. According
to Paukert DC empirical arc model which is
applicable for current 0.3A to 100KA & electrode
gap 1 to 200mm arc resistance is equal to
Zg = length of electrode gap
Iarc=arc current
It demonstrates that
1) Arc resistance increases as gap distance
increases.

2. 2) Arc resistance changes rapidly at low current
level and approaches a relatively constant value
at higher current.
The dc arc model simulation for evaluation is
shown in figure.1.
Under normal condition circuit breaker is closed.
Subsequent to fault it opens at t=1.5second &
due to stored energy in inductor high transient
voltage appears across circuit breaker.
Figure 1 DC arc model
Figure 2 Voltage across circuit breaker (arc voltage) circuit breaker operates at 1.5s

3. By this we concluded that opening the circuit
breaker without commutation circuit results
extremely high voltage across circuit breaker
which can leads to failure of circuit breaker.
3. DC circuit breaker topologies
1. Mechanical circuit breaker (MCB) - This
type of circuit breaker has small on state
resistance and long current interruption time
because of movement of mechanical parts
and electric arc.
2. Solid state circuit breaker (SSCB) –This
type of circuit breaker has high on state
resistance and very small current interruption
time but it is not readily available for large
current and voltage application.
3. Hybrid circuit breaker - In this type of circuit
breaker MCB is used as main current path &
SSCB is used as complimentary switch to
assist current interruption.
Hybrid circuit breaker interruption techniques
1. Counter current - In this technique zero
crossing incurrent is created by series
resonance between inductor and capacitor
of commutation circuit.
2. Counter voltage–In this technique current
zero crossing is created by generating a
counter voltage of magnitude same or
greater then supply voltage.
This paper mainly focuses on counter current
interruption technique which is presented as
follows.
4. Active mode DC hybrid circuit
breaker
In revert to above mentioned DC interruption
is more challenging. The main reason is
absence of DC zero crossing.
A DC circuit breaker is required to establish
following requirements.
1.The DC circuit breaker has to interrupt
within a very short interval of time so that due
to high rate of change of current electrical
equipment will not be damaged.
2. The transient voltages generated by circuit
breaker operation should be low enough so as
to maintain breaking capacity of circuit
breaker & successful interruption.
3. The DC circuit breaker should have large
current handling capability without excessive
loss & it should be able to block high current
despite of high potential at terminals.
Above mentioned requirements are not
individually fulfilled by either MCB or SSCB so
in order to take benefits of both circuit breaker
parallel combination of MCB & SSCB is used.
As shown in figure 3 to achieve current zero
crossing LC resonant circuit & SSCB is used
in parallel with MCB.LC resonant circuit injects
counter current & opposes main line current in
the mechanical circuit breaker & hence
current zero crossing is achieved. The
capacitor must be pre-charged & value of L &
C is set such as to get peak magnitude of
counter current greater then fault current. As
shown in figure 3, MOV (metal oxide varistors)
is used in parallel with MCB & commutation
circuit.MOV is used to prevent transient
voltage across MCB which can affect
breakdown strength of circuit breaker.
brk1
RLC
2000e-6 [H]
brk2500e-6 [F]
br3
1.0 [ohm]
5.0 [ohm]
Ib
Ic
Is
a1
5.0 [ohm]
1.0[ohm]
Vc
Ea
Ea1
IMO
SSCB
MCB
MOV
fault at 8
second
breaker 3

4. Figure 3 circuit configuration for active mode
DC-HCB
Figure 4 simulation waveform for active mode
DC-HCB (a) Is (line current) vs t (b) Ic
(commutation capacitor current) vs t (c) Ib
(current through mechanical circuit breaker)
4.1Time interval for fault current
interruption
4.1.1 Pre –fault interval (0 <t< 8sec)
During this interval circuit is under normal
condition line current passes through MCB as
shown in figure 4. line current (Is) is equal to
MCB current(Ib)&current through commutation
capacitor is zero as SSCB is open & capacitor
is pre-charged.
4.1.2 Commutation process interval ( 8< t
<8.01sec)
At the beginning of this interval fault occurs
which leads to increase in line current as
Figure 5 simulation waveform for active mode
DC-HC (a)Vc (commutation capacitor voltage)
vs t (b) Ea1 (voltage across mechanical circuit
breaker) (c) IMO ( current through metal oxide
veristors)
shown in figure 4. At this instant gating signal
sends to SSCB to start commutationprocess.
LC resonant circuit is in series with SSCB so
capacitor discharges its stored energy &
hence counter current is injected into main
conduction path. When counter current (Ic) &
current through MCB (Ib) becomes equal
current zero crossing is produced.at first zero
crossing or second zero crossing MCB opens
& Is commutated from Ib to Ic.

5. 4.1.3 Energy releasing interval (8.1 <t
<8.015sec)
as interruption process completed, turn off
signal sends to SSCB But there is high
amount of energy stored in system
inductance. This energy needs to be
discharged to prevent breakdown of
interrupting medium in circuit breaker. During
this interval this energy release through MOV
which has property of providing low resistance
at high voltage.as shown in figure 4Ic, Ib
becomes zero & (Is=IMOV) line current flows
through MOV till system inductance
discharges its stored energy .
5.CONCLUSION
Following interruption Transient recovery
voltage appears across circuit breaker which
has deleterious effect on circuit breaker.
Based on simulation of DC arc model, we
conclude that DC interruption without
commutation path results in transient voltage
across circuit breaker. This paper discussed
principal of operation and dynamic
performance of DC -HCB and time domain
simulation studies were conducted. based on
simulation studies we conclude that this
approach is far superior then conventional dc
circuit breaker and capable of performing
current interruption for large values of
inductance.
6.ACKNOWLEDGMENT
we would like to express our deepest gratitude
to professor s. c. vora for his guidance and
persistent help. His attitude towards research
encouraged us in writing this paper.
7. REFRENCES
[1] sungmin lee, Hyosung-kim, “A study on
low-voltage circuit breaker”, the journal of Korean
institute of power electronics
[2] T.heinz,V.hinrichsen,L-R jaincke,“Direct current
interruption with commercially available vacuum
interrupters, international symp. On discharge and
electrical insulation in vacuum
[3]Hana a halim,nur Sabina noorpi, nurhakimah m.
mukhtar ,”simulation study of the transient
recovery voltage on circuit breaker”, fifth
international conference on computational
intelligence, modeling and simulation
[4] Jesper Magnusson, Robert sacrs,
larsliljestrand,”separation of the energy absorption
and overvoltage protection in solid state breakers
by use of parallel varistors” IEEE transactions on
power electronics
[5] shang yang, ”Feasibility and simulation study
of DC hybrid circuit breaker”, university of torronto.