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Enhance Grid Reliability With Hybrid HVDC Breaker
electrical-engineering-portal
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Content
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How does Hybrid HVDC Breaker work? (VIDEO)
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Proactive control
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Comparison/Summary

Introduction
The advance of voltage source converter-based (VSC) high-voltage direct current (HVDC) transmission systems
makes it possible to build an HVDC grid with many terminals
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This advantage makes an HVDC grid more attractive
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Consequently, fast and reliable HVDC breakers are needed to isolate faults and avoid a collapse of the
common HVDC grid voltage
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In order to minimize disturbances in converter operation, particularly the operation of stations
not connected to the faulty line or cable, it is necessary to clear the fault within a few milliseconds
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Hybrid HVDC Breaker Construction
The hybrid HVDC breaker consists of an additional branch, a bypass formed by a semiconductor-based load
commutation switch in series with a fast mechanical disconnector
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After fault clearance, a disconnecting circuit breaker interrupts the residual current and isolates the faulty line
from the HVDC grid to protect the arrester banks of the hybrid HVDC breaker from thermal overload
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When an HVDC fault occurs,
the load commutation switch
immediately commutates the
Figure 1 - Hybrid HVDC breaker main components
current to the main HVDC
breaker and the fast
disconnector opens
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The mechanical switch isolates the load commutation switch from the primary voltage across the main HVDC
breaker during current breaking
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A successful commutation of the line current into the main HVDC breaker path requires a voltage rating of the
load commutation switch exceeding the on-state voltage of the main HVDC breaker, which is typically in the kV
range for a 320 kV HVDC breaker
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The transfer losses of the hybrid HVDC breaker concept are thus significantly reduced to a percentage of the
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losses incurred by a pure semiconductor breaker
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The fast disconnector will be exposed to the maximum pole-to-pole voltage
defined by the protective level of the arrester banks after first being in open position while the main HVDC
breaker opens
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Proactive control
Proactive control of the hybrid HVDC breaker allows it to compensate for the time delay of the fast disconnector,
if the opening time of the disconnector is less than the time required for selective protection
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LCS denotes load commutation switch

commutation is initiated by the hybrid HVDC breaker’s built-in overcurrent protection as soon as the HVDC line
current exceeds a certain overcurrent level
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To extend the time before the self-protection function of the main HVDC breaker trips the hybrid HVDC breaker,
the main HVDC breaker may operate in current limitation mode prior to current breaking
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Pulse mode operation of the main HVDC breaker or sectionalizing the main HVDC breaker as shown in Figure 2
will allow adapting the voltage across the main HVDC breaker to the instantaneous HVDC voltage level of the
HVDC grid
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On-line supervision allowing maintenance on demand is achieved by scheduled current transfer of the line
current from the bypass into the main HVDC current breaker during normal operation, without disturbing or
interrupting the power transfer in the HVDC grid
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Due to the proactive mode, over-currents in the line or superior switchyard protection will activate the current
transfer from the bypass into the main HVDC breaker or possible backup breakers prior to the trip signal of the
backup protection
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2 ms
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If not utilized for backup protection, the
hybrid HVDC breakers automatically return to normal operation mode after the fault is cleared
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0 kA in an HVDC grid with
rated voltage of 320 kV and rated HVDC transmission current of 2 kA
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The fast disconnector and main HVDC breaker are designed for switching voltages exceeding 1
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u
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The main HVDC
breaker consists
of several
HVDC breaker
cells with
individual
arrester banks
limiting the
maximum
voltage across
each cell to a
specific level
during current
breaking
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Figure 3 - Design of 80kV main HVDC breaker cell

Two stacks are required to break the current in either current direction
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Due to the large di/dt stress during current breaking, a mechanical design with low stray inductance is required
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5 kV voltage rating [6] enables a compact stack design and ensures a
stable short circuit failure mode in case of individual component failure
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Optically powered gate units enable operation of the IGBT HVDC breaker independent of current and voltage
conditions in the HVDC grid
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For the design of the auxiliary HVDC breaker, one IGBT HVDC breaker position for each current direction is
sufficient to fulfill the requirements of the voltage rating
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Series connected,
redundant IGBT HVDC breaker positions improve the reliability of the auxiliary HVDC breaker
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Since the auxiliary
HVDC breaker is continuously exposed to the line current, a cooling system is required
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Comparison
Existing mechanical HVDC breakers are capable of interrupting HVDC currents within several tens of
milliseconds, but this is too slow to fulfill the requirements of a reliable HVDC grid
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To overcome these obstacles, ABB has developed a hybrid HVDC breaker described above
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Resource: ABB Grid Systems, Technical Paper Nov’2012: The Hybrid HVDC Breaker – An innovation
breakthrough enabling reliable HVDC grids

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