Paper 33

Pre-standardisation of Interfaces between DC Circuit Breaker and IntelligentElectronic Device to Enable Multivendor Interoperability

M. WANG1, D. JOVCIC2, W. LETERME1, D. VAN HERTEM1, M. ZAJA2, I. JAHN31K.U. Leuven/EnergyVille, Leuven/Genk, Belgium

2University of Aberdeen, Aberdeen, UK3KTH Royal Institute of Technology, Stockholm, Sweden

SUMMARY

DC circuit breakers (DCCBs) are one of the key components to facilitate large meshed HVDCgrids. Driven by the needs for achieving high speed, low loss and low cost, various DCCBtechnologies have been proposed for HVDC applications. Unlike AC circuit breakers (AC-CBs), some DCCBs provide a variety of functions, such as proactive opening or fault currentlimiting (FCL), mainly attributed to the high controllability of the power electronic switchesused in such DCCBs. To enable these functions, the intelligent electronic devices (IEDs) areexpected to provide signals steering these functions in addition to a trip command. Interoper-ability between IEDs and DCCBs from different vendors is considered feasible, but expected tobe more complex than their AC counterparts, due to the different functions provided by variousDCCB technologies. It is therefore crucial to understand which of the functions are essential tofulfil the requirements imposed in HVDC grid protection, and to standardise the interfaces be-tween the IEDs and DCCBs to achieve multivendor interoperability between IEDs and DCCBsprovided by different vendors.

This paper first classifies the DCCB functions into minimally required and auxiliary ones basedon reviewing the existing literature. Then, standardised interfaces between the IEDs and DC-CBs are proposed to enable both types of DCCB functions. An example of such IED is imple-mented in PSCAD/EMTDC to demonstrate that the proposed interfaces are adequate to enableboth minimally required and auxiliary functions using a four-terminal test system. Auxiliaryfunctions of hybrid DCCBs, such as proactive opening, fault current limiting, fast reclosing andreopening, breaker failure internal detection and repeated O-C-O operation are demonstrated bysimulations.

KEYWORDS

HVDC grid protection, DC circuit breaker, intelligent electronic device, standardised interfaces,multivendor interoperability

mian.wang@kuleuven.be

1 INTRODUCTION

Protection against DC faults in meshed high voltage direct current (HVDC) grids is essentialto meet the requirement on security of supply in the future hybrid AC/DC power systems [1].Fully selective HVDC grid protection strategies, utilising DCCBs to protect each componentindividually, are one of the most promising options for large meshed HVDC grids as the al-ternatives like de-energisation a whole HVDC grid imply severe impacts on the connected ACgrids [2].

In recent years, great effort has been put into developing high speed, low loss and low cost DC-CBs, as interrupting a DC current is both necessary and challenging [3, 4]. Depending on thefault current interruption technology used, DCCBs are typically classified as mechanical, hybridand power electronic (PE) types [5]. Unlike ACCBs, some DCCBs provide a large variety offunctions driven by the needs for high speed and low cost, and enabled by the high controllabil-ity of power electronics used in such DCCBs. Common functions of different DCCB technolo-gies have been studied in [6], where the essential functions are modelled and demonstrated on acommon test system. However, the analysis did not include the study of standardised interfacesbetween the IEDs and DCCBs, which would enable a wide range of auxiliary functions such asproactive opening and FCL operation [3, 7]. To enable different DCCB technologies to achievenot only essential but also auxiliary functions, and ensure the interoperability of the HVDC gridprotection system and components, it is necessary to define the required interfaces between theIED and DCCB.

This paper proposes standard interfaces for the main functions of the DCCBs which are pro-posed in the literature. The main functions are, based on a literature review, classified as min-imally required and auxiliary. The principles used for proposing the interfaces are: (1) theinterfaces should provide control of all minimally required functions for any DCCB technol-ogy, (2) the optional interfaces should provide control of all auxiliary functions consideringdifferent DCCB technologies, (3) the interfaces are optional if certain DCCB technology doesnot provide the auxiliary function, and (4) the interface should contain a minimum number ofsignals required for the control of all functions. An example of an IED implementation using theproposed interfaces is demonstrated to achieve both minimally required and auxiliary functionsusing a four-terminal test system in PSCAD/EMTDC. Particularly, this paper demonstrates thefollowing cases: proactive opening and FCL operation of a hybrid DCCB using a current ref-erence signal, fast reclosing during backup operation, fast backup operation using coordinationwith breaker internal failure detection, and repeated O-C-O operation on a overhead line sec-tion.

2 HVDC GRID PROTECTION

In a fully selective protection strategy, a decentralised design of HVDC grid protection systemsis most likely the preferred option compared to a centralised design, as the decentralised designprovides higher reliability and the possibility of employing equipment from multiple vendorsthus encouraging cost reduction through vendor competition [8].

In a decentralised design, each terminal of a DC line is protected by one or more dedicatedIEDs, such as separate IEDs for primary and backup protection. Fig. 1 gives an example ofsuch decentralised design, only showing the fault clearing unit (FCU), the IED for primary pro-tection, and essential signals for DC line and busbar protection. A FCU consists of a residualcircuit breaker (RCB) for isolation, a DCCB for fault interruption and a line inductor for lim-iting the rate-of-rise of the fault current. Depending on the protection algorithms used, a line

2

≈

= ≈MMC MMC

=

U, IIED (line)

IED (line)

IED (line)

IED (line) IED (line)

IED (line)

IED (line)

FCU

U, I measurement

IED (busbar)

...

...

line currents

trip signal toline breakers

MeasurementSignal

IED (busbar)

...

...

line currents

trip signal toline breakers

RCBLline DCCB

Figure 1: Decentralised design of HVDC grid protection systems.

protection IED may use local and/or remote measurements, telecommunication signals fromremote IEDs, and coordination signals with local IEDs in the same substation for fault identi-fication and protection coordination. The interfaces between a DCCB and its associated IEDinclude tripping or closing commands from the IED and breaker status monitoring to the IED.

3 HIGH VOLTAGE DC CIRCUIT BREAKER TECHNOLOGY

Although various DCCB technologies have been proposed in the literature, the most promis-ing ones are mechanical, hybrid and power electronic DCCBs. A 200 kV hybrid DCCB hasalready been put into operation in the Zhoushan 5-terminal HVDC system and 500 kV onesare under construction in the Zhangbei 4-terminal HVDC grid [9, 10]. Third party indepen-dent test of mechanical DCCB prototypes rated at 80 kV has been tested in the PROMOTioNproject [11]. Although at the moment, power electronic DCCBs are limited to low voltage DCimplementations, they may become economically viable at high voltages as the losses of powerelectronic devices decrease in the future [12]. In recent years, innovative breaker topologiesor control methods have been proposed focusing on capability enhancement, cost reduction oradded current flow control capability, e.g., unidirectional or multi-port circuit breakers [13–16].

3.1 Mechanical DCCB

Mechanical DCCBs typically superpose an AC current provided by a resonant circuit on theDC fault current to create zero-crossings, and consequently use a AC breaker for current in-terruption [4, 17–19]. Different implementations focus on circuit design to either speed up theresonance injection process or reduce component requirements and costs.

Two examples of mechanical DCCBs are given in Fig. 2. To interrupt and isolate the faulted line,both the main vacuum interrupter (S1) and the RCB (S2) are required to open. Repeated O-C-Ooperation with acceptable speed is desirable to provide auto-reclosure functions on overheadline sections. This requirement imposes a time constraint on the recharging of the capacitorbanks in the resonant branch (Fig. 2 (a)) and the DC link of the VSC (Fig. 2 (b)). To deal withthis requirement, the examples in [20] make use of a second current injection branch, whichavoids the need to recharge the capacitor of the first branch, and a large DC link capacitorwhich has sufficient stored energy for two consecutive opening operations.

3

VSC

VI(S2)RCBVIRCB

(a) (b)

S3_a Cp_a

S3_b Cp_b CpLpLp

Lline(S1)Lline(S1)(S2)

Figure 2: Examples of mechanical DCCBs. (a) Active resonance [4, 20] (b) VSC assisted resonancecurrent (VARC) [17].

3.2 Hybrid circuit breaker

Hybrid circuit breakers combine the benefit of a low-loss mechanical switch and fast control-lable power electronics, such as examples given in Fig. 3, thus achieving fast operation and lowon-state losses [3, 21]. Alternative circuit topologies using full-bridge or H-bridge submoduleshave been proposed to achieve similar functions as the IGBT-based breaker [22, 23].

(b)

· · ·

UFD (S1) Lline

Main branch (MB, T2)

LCS (T1)

RCB (S2)

(a)

(S2)RCB UFD (S1)

LCS (T1)

Lline

Time delayingbranches

SA11

R11

C11

SA12

R12

C12

C2

R2

Tr1 Tr11

Tr12

Tr2

Figure 3: Examples of hybrid circuit beakers. (a) IGBT-based [3] (b) Thyristor-based [21].

3.3 Power electronics circuit breaker

Power electronics based circuit breakers are capable of interrupting a DC fault current in themicroseconds range, however, at a cost of high on-state losses. An example of such circuit issimilar to the IGBT-based hybrid breaker but without the load current branch [24].

4 DC CIRCUIT BREAKER FUNCTIONS

In the literature, various breaker functions have been proposed additional to the basic function offault current interruption. To ensure interoperability between different breaker technologies, itis beneficial to categorize them into minimally required and auxiliary functions. The minimallyrequired functions are referred to those that any DCCB is required to fulfil for HVDC gridprotection applications regardless of the employed technologies. By contrast, the auxiliaryfunctions are optional by definition and not required for all types of DCCB technologies. Thesefunctions can be used in HVDC grids to improve the performance of the protection system.

4.1 Minimally required functions

The following functions are proposed to be included as minimally required functions.

• Current interruption: interrupt a DC fault current upon receiving a trip order.

4

• Close operation: close upon receiving a closing order.

• O-C-O operation: a DCCB is required to have a repeated O-C-O capability upon receiv-ing trip-closing-trip order from the IED, in case of backup protection or overhead lineapplications.

• Monitoring and communication: a DCCB is required to monitor and communicatebreaker status (such as, open/close and ready-to-operate) to the IED for protection coor-dination.

4.2 Auxiliary functions

The following functions are identified as auxiliary, therefore, optional in HVDC grid protection.

• Proactive opening: refers to the capability of a DCCB to proactively open the loadcurrent branch and commutate the current to the main branch upon receiving an initiatingsignal from the IED, prior to the fault being identified on the line [3]. The DCCB is alsorequired to abort the proactive opening and revert to normal operation, preferably withoutcausing voltage and current transients if the fault is not identified on the line.

• Fast reclosing/reopening: refers to the capability of a DCCB to keep certain compo-nent(s) in close/open position to perform fast reclosing/reopening. For instance, theDCCB can keep the RCB in closed position during an O-C cycle in case of breaker fail-ure backup operation to eliminate the opening and reclosing delay of the RCB, or keepthe load current branch in open position to achieve fast second opening during an O-C-Ocycle [20].

• Fault current limiting (FCL) mode: refers to the capability of a DCCB to control theDC current to desired values during a fault or DC voltage restoration [7, 25–28].

• Breaker failure internal detection: refers to the capability of a DCCB to internallymonitor and detect a breaker failure during current interruption [29].

• Self-protection: this function entails two sub-functions: (1) opening without a trip orderfrom the IED. In case of abnormal operating conditions, such as thermal overloading ofpower electronics or surge arresters, the DCCB may be required to trip without the receiptof an external trip order [20]. (2) maintaining closed state. Although the DCCB is orderedto open by an external trip order, the DCCB closes itself again during the opening processif its internal monitoring predicts the DCCB is not able to interrupt the fault current [6,29].

Other functions such as integrated current flow control and DCCBs with unidirectional faultcurrent interruption have also been proposed in the literature [15, 16]. However, they are notconsidered in this paper as the focus is on the functions related to fault clearing with the highestselectivity.

5 IED INTERFACES

To achieve the minimally required functions and allow for auxiliary functions, the interfacesbetween an IED and DCCB are proposed as shown in Fig. 4. The principles used for proposingthe interfaces are: (1) the interfaces should provide control of all minimally required functionsfor any DCCB technology, (2) the optional interfaces should provide control of all auxiliaryfunctions considering different DCCB technologies, (3) the interfaces are optional if certain

5

DCCB technology does not provide the auxiliary function, and (4) the interface should containa minimum number of signals required for the control of all functions.

The inputs and outputs of a IED are divided into (1) local and remote measurements from mea-surement devices, (2) interfaces between the IED and DCCB, (3) interfaces between the localand remote IEDs for fault identification, and (4) breaker failure detection inputs and outputsbetween the IED and the adjacent IEDs in the same substation.

V_LCL (Np)I_LCL (Np)I_REM (Np)

ST_BRK (Np)ST_RCB (Np)BRK_HLH (Np)BRK_RDY (Np)

Measuredquantities

TW_REM_IN (Np)TRIP_REM_IN (Np)BLK_REM_IN (Np)ISIGN_REM_IN (Np)...

BRK_FAIL_IN (Nl −1)

Remote IED

IEDline

protection

Remote IED

BRK_FAIL_OUT (Np)

Breaker

TRIP_BRK (Np)

BRK_I_REF (Np)TRIP_RCB (Np)

TW_REM_OUT (Np)TRIP_REM_OUT (Np)BLK_REM_OUT (Np)ISIGN_REM_OUT (Np)...

Breaker

Adjacent IEDsAdjacent IEDs

Figure 4: Proposed interfaces between the IED and DCCB (blue: minimally required, magenta: auxil-iary, Np,Nl: the number of poles and lines).

5.1 Local and remote measurements

Depending on the fault detection and identification algorithms, local and/or remote measure-ments may be used. Local voltage and/or current measurements (V_LCL, I_LCL) are typicallyused for non-unit protection algorithms, such as voltage/current derivative and travelling waveextraction [30]. For current differential algorithms, both local and remote currents (I_REM) arerequired [31].

5.2 Interfaces with the remote IED

The interfaces between the local and remote IEDs are required when communication-basedprotection algorithms are used. Examples are travelling wave differential, travelling wave trip-ping and blocking scheme, and current directional comparison [32, 33]. For a travelling wavedifferential algorithm, locally calculated travelling wave signals (TW_REM_OUT) are sentthrough the communication channel to the remote IED to compare the travelling waves. Sim-ilarly, blocking, tripping and current directional signals (BLK_REM_OUT, TRIP_REM_OUT,ISIGN_REM_OUT) are communicated between the local and remote IEDs to assist fault iden-tification.

5.3 Interfaces between the IED and DCCB

Similar to the DCCB functions, the interfaces between the IED and DCCB are divided intominimally required and auxiliary.

Minimally required interfacesThese interfaces (highlighted in blue in Fig. 4) are required for all DCCB technologies to enablethe minimally required DCCB functions.

6

• TRIP_BRK: open (1) and close (0) order to the DCCB. A change from low to highinitiates breaker opening and high to low initiates breaker closing. TRIP_BRK becomes1, if a DC fault is identified on the line or one of the adjacent DCCB has failed, whichrequires backup protection.

• ST_BRK: open (1) and closed (0) status of the DCCB.

• BRK_RDY: indicates ready-to-operate (1) and not-ready-to-operate (0) status. For in-stance, the DCCB may required certain time between a consecutive opening and closingcycle due to thermal limits. The BRK_RDY signal monitors such thermal status of theDCCB and will change from 0 to 1 once it is ready for the next operation.

Auxiliary interfacesThese interfaces (highlighted in magenta in Fig. 4) are optional for all DCCB technologies.Any DCCB technology can make use of these interfaces to enable its auxiliary functions orotherwise disregard them.

• BRK_I_REF: used for initiating a proactive opening (BRK_I_REF = 0) and FCL modewhen a DC fault is detected but not identified on the line. The reference current levelduring FCL operation is typically in the range of 1 – 2 pu. A high value (e.g. 5 pu) can beused to indicate a no-operation status. In the literature, an additional fault detection signalis typically used in combination with the current reference to initiate proactive openingor FCL mode [25, 26]; however, this paper uses only the current reference to minimizethe number of interfaces.

• TRIP_RCB: open (1) and close (0) order to the RCB of a DCCB for fast reclosing orreopening. This external RCB control offers the flexibility to eliminate the time delayintroduced by the RCB operation during reclosing or reopening.

• ST_RCB: open (1) and closed (0) status of the RCB of a DCCB.

• BRK_HLH: remains high (1) is the DCCB is healthy, and changes to low (0) if a breakerfailure is detected internally.

5.4 Coordination signals with adjacent IEDs

Local breaker failure backup detection is performed at the IED and a breaker failure detection(BRK_FAIL_OUT) is sent to the adjacent IEDs to trip the adjacent DCCBs. In the meantime,breaker failure inputs (BRK_FAIL_IN) from the adjacent IEDs are used to trip the DCCB whenany of the adjacent DCCBs fails during a DC fault.

5.5 Example implementations of the IED

An example of the IED implementation in PSCAD/EMTDC for a mechanical and hybrid DCCBis shown in Fig. 5. The IED is composed of four function blocks: breaker monitoring, faultdetection and identification, coordination with local IEDs and breaker failure detection. Breakerfailure internal protection is assumed for both examples to enable fast breaker failure backupprotection.

The main differences of the implementations between mechanical and hybrid DCCBs are thecontrol of the RCB, proactive opening and FCL mode. For mechanical DCCBs, as openingthe RCB is required as part of the fault current interruption process [20], one trip commandTRIP_BRK is sufficient to open or close the DCCB; whereas a separate signal TRIP_RCB is

7

used to operate the RCB for hybrid DCCBs to facilitate fast reclosing or reopening. Corre-spondingly, the status of all components are monitored by ST_BRK for mechanical DCCBs;while for hybrid DCCBs, ST_BRK only monitors the load commutation switch (LCS), the ultrafast disconnector (UFD), and the main breaker (MB) and ST_RCB monitors the status of theRCB.

Fault detection& identification

Local breakerfailure detection BF

BF_INT

FD

FI

Coordination withlocal IEDs

BRK_C

BRK_O

OTH_BF

RCB_C

BRK_HLH

V_LCLI_LCLI_REM

TW_REM_INTRIP_REM_INBLK_REM_INISIGN_REM_IN

BRK_FAIL_IN

Breaker monitoring

BRK_O

BRK_C+−

Breaker monitoring

TRIP_BRK

IED

Σ

(b)(a)

EN_FCLΣ

++

012

5

Ire f0

EN_Proact

Σ+−

ibrIFCLthr

<iRCBIRCBres

IED

at DCCB-side

Local breakerfailure detection BF

BF_INT_OUTBRK_FAIL

Coordination withlocal IEDs

Fault detection& identification

OTH_BF

FD

FI

BRK_FAIL_IN

ST_BRK

BRK_HEALTH

BRK_READY

ST_RCB

V_LCLI_LCLI_REM

TW_REM_INTRIP_REM_INBLK_REM_INISIGN_REM_IN

TRIP_RCB

BRK_I_REF

ST_BRK

BRK_HEALTH

BRK_READY

ST_RCB

BRK_HLHBRK_I_REF

BRK_FAIL_OUT

TRIP_BRK

TRIP_RCB

delay delay

Figure 5: An example of IED implementations. (a) For mechanical DCCB (b) For hybrid DCCB (breakerstatus: 1 open, 0 closed; trip signals: 1 trip, 0 close, unused interfacing signals are marked with gray).

6 TEST SYSTEM

A four-terminal test system is developed to demonstrate the minimally required and auxiliaryfunctions using the proposed interfaces, based on the test system used in [25]. The convertersare modelled with a Type 4 detailed equivalent circuit model as specified in [34], where indi-vidual submodule switching states and capacitor voltages are represented. All converters havethe same power rating of 1265 MVar. During normal operation, MMC2 and MMC4 are operat-ing in active power control mode, exporting 600 MW and 1000 MW, respectively. MMC1 andMMC3 are operating in voltage power droop control mode, importing 1200 MW and 400 MW,respectively. The main parameters of the converter station are listed in Table 1.

Bus 4Bus 3

Onshore ACGrid 2

Cable L24 (100 km)

Cable L14 (300 km)

MMC3 FCU31

FCU34∼≈

=

FCUC3

FCU41

FCU43

Cable L13(350 km)

FCUC3

Offshorewindfarm 2

=

≈

MMC4f1

f2

50%

Bus 1 Bus 2

∼=

≈Onshore AC

Grid 1

Cable L12 (150 km)

Offshorewindfarm 1

MMC1 MMC2FCU12

FCU14≈

=

FCUC1

FCU21

FCURCBLline DCCB

FCU13

600 MW1200 MW

1000 MW400 MW

Figure 6: A four-terminal symmetrical monopolar test system.

8

Table 1: Converter and grid parameters

Parameters Value UnitRated apparent/active power S/PDC 1265/1200 [MVA/MW]Rated DC voltage UDCp,UDCn ± 320 [kV]Rated transformer voltages 400/333 [kV]Transformer leakage impedance 0.18 puArm capacitance Carm 22 [µF]Arm inductance Larm 42 [mH]Arm resistance Rarm 0.6244 [Ω]Converter DC smoothing reactor LDC 10 [mH]

Table 2: Main parameters of the hybrid and mechanical DCCB.

DCCB Parameters Symbol Value

Hybrid

LCS commutation time T oLCS 250 µs

UFD opening/closing time T oUFD/T c

UFD 2/2 msRCB opening/closing time T o

RCB/T cRCB 30/30 ms

UFD/RCB residual current IchUFD/IchRCB 0.01/0.01 kALine inductor Lline 50 mH

Mechanical

Main vacuum interrupter opening/closing time T oV I/T c

V I 8/50 msRCB opening/closing time T o

RCB/T cRCB 8/50 ms

Making switch opening/closing time T oMS/T c

MS 30/8 msMain VI/RCB residual current IchV I/IchRCB 0.01/0.01 kALine inductor Lline 100 mH

6.1 DCCB model

An active resonance injection based mechanical DCCB (Fig. 2 (a)) and an IGBT-based hybridDCCB (Fig. 3 (a)) are modelled as examples for validation, based on models developed in [20,25]. Other types of mechanical and hybrid DCCBs, such as the VSC assisted and H-bridge onesare expected to have comparable performance as the examples. The parameters of the DCCBsare taken from [20], and the most important ones are shown in Table 2.

For the mechanical DCCB, two parallel interruption branches, including mechanical switchesS3_a, S3_b and capacitors Cp_a, Cp_b are modelled for repeated O-C-O operation. One trip signalTRIP_BRK and three breaker monitoring signals ST_BRK, BRK_HLH, and BRK_RDY areused for the mechanical DCCB.

A four-submodule hybrid DCCB with proactive opening, fault current limiting, fast reclosingand fast opening functions is implemented in PSCAD. Trip signals, TRIP_BRK, TRIP_RCB,breaker current reference signal, BRK_I_REF, and breaker monitoring signals are used for thehybrid DCCB. The proactive opening is initiated by a falling edge of the breaker current ref-erence, BRK_I_REF (5 to 0 pu) to start the opening process of the load current branch (Fig. 3(a)). The FCL operation is controlled by BRK_I_REF and breaker internal overcurrent de-tection, and automatically stopped once the breaker current decreases below a pre-determinedthreshold. Details on the IGBT-based hybrid DCCB model can be found in [25].

6.2 IED model

Both primary and local breaker failure backup protection are implemented in each IED. At theDCCB side, breaker failure internal detection is implemented and the BRK_HLH signal is used

9

to communicate the breaker failure status to the associated IED.Primary protectionA two-out-of-three voting scheme with three independent fault detection algorithms is usedin this paper for the primary protection. For line protection IEDs, a non-unit algorithm usingvoltage and current derivative [30], a travelling wave derivative algorithm, and a travelling waveblocking scheme [33] are implemented as examples. For the IEDs associated with the converterDCCBs, a voltage derivative instead of travelling wave blocking scheme is used. The samplingfrequency of the primary protection algorithms is 100 kHz. Derivatives are calculated based on5 samples using the following equation,

dXn =Σ4

i=0X(n− i)−Σ9i=5X(n− i)

5(1)

Local breaker failure backup protectionFast breaker failure protection based on local voltage and current measurements are imple-mented at each line protection IED. The adopted algorithm trains a classifier using linear dis-criminant analysis based on voltage and current data samples, obtained from simulating clearedand uncleared faults along a cable. The classifier is expressed in equation (2), where yth is thethreshold to distinguish cleared and uncleared faults. Detailed description of the algorithms canbe found in [35].

yk = ω1i(k)+ω2u(k)

yth =yd

1 + yd2

2

(2)

where yk: transformed value of the classifier, i(k),u(k): the kth current, voltage sample, ω1,ω2:the voltage and current coefficients, yd

1 and yd2: two closest transformed samples from uncleared

and cleared faults.

Breaker failure internal protectionBreaker internal commutation currents and current derivative criteria are used for internal failuredetection, based on [29]. The LCS and UFD currents are used for monitoring the internalcommutation process for a hybrid DCCB. The breaker failure internal detection functions aregiven in equation (3).

BRK_HLH = 0,

|iLCS|> Ithr, t > ttrip +T o

LCS, or|iUFD|> Ithr, t > ttrip +T o

UFD, or

diCB

dt>−I0, ttrip +T o

UFD < t < ttrip +T2

(3)

where ttrip is the tripping instant. The first two overcurrent criteria operates when the current inthe LCS or UFD is larger than the pre-determined threshold after the opening time has elapsed.The third criterion operates when the current decreases slower than the pre-determined thresh-old, I0. The fault current suppression is expected to happen between ttrip +T o

UFD to ttrip +T2.Similarly, the current in the main vacuum interrupter iV I is used for internal failure detection ina mechanical DCCB.

7 CASE STUDIES

In this section, using the proposed interfaces to enable the aforementioned auxiliary functionsand repeated O-C-O operation is demonstrated by simulation studies.

10

7.1 Proactive opening

A solid pole-to-pole fault at the cable L13 terminal near bus 3 ( f1) is applied at 0 ms in thesimulation. All DCCBs are modelled as hybrid types, while the proactive function of DCCB31is enabled or disabled to demonstrate the impact. The proactive function of all the rest DCCBsare disabled throughout the simulations.

In case 1 where the proactive function of DCCB31 is disabled, the breaker current refer-ence BRK_I_REF remain high (5 pu). On the contrary, in case 2 once the fault is detected,BRK_I_REF changes from 5 to 0 pu, which initiates the proactive opening of the load currentbranch, and the LCS is opened after a presumed commutation delay of 250 µs. Compared tocase 1 where proactive opening is disabled, using proactive opening during primary protectionreduces the breaking current and energy of the DCCB, and the fault interruption time. Thesereductions are more pronounced especially for a slow fault identification.

5 pu 0 pu

TRIP BRK1

TRIP BRK2

BRK I REF1

BRK I REF2

ST BRK1

ST BRK2

Sign

al&

Stat

us

(a) Trip Signal and Breaker Status

0

5

10

250µs

Cur

rent

(kA

)

(b) Breaker CurrentiLCS1 iMB1 iSA1iLCS2 iMB2 iSA2

0

3

6

Ene

rgy

(MJ)

(c) Energy

ESA1 ESA2

0 2 4 6100200300400

time (ms)

V(k

V)

(d) DC Bus3 and MMC3 Voltages of the Positive Pole

ubus1 ubus2uMMC1 uMMC2

Figure 7: Proactive opening of a hybrid DCCB (DCCB31). Subscript 1: proactive opening disabled,subscript 2: proactive opening enabled, fault location: f1.

7.2 FCL operation of hybrid DCCBs

FCL operation of hybrid DCCBs are found to be particularly effective when working with slowDCCBs, such as at the same busbar or converter side [25, 26]. Using FCL operation of theadjacent hybrid DCCBs at the same busbar to a mechanical DCCB is demonstrated in this case.The line breaker DCCB31 is assumed to be a mechanical DCCB. All other DCCBs are assumedto be hybrid ones.

After the trip order, TRIP_BRK31 changes from 0 to 1, the mechanical DCCB starts to open.If the FCL operation is disabled, the current reference BRK_I_REF34 and BRK_I_REFC3

11

remains high, FCL operation of DCCB34 and DCCBC3 are not activated (Fig. 8 (a)). On thecontrary, the current references change from 5 to 2 pu if the FCL operation is enabled, andDCCB34 and DCCBC3 start FCL operation and control the breaker current to 2 pu. The FCLoperation stops automatically by DCCB internal control once the current reduces below a pre-determined threshold after fault clearance by the mechanical DCCB31 (Fig. 8 (b)). Note thatthe arcing voltage of the mechanical DCCB is assumed to be high enough to ensure successfulopening during the FCL operation.

The advantages of using FCL operation of hybrid DCCBs are a reduced breaking current andenergy absorption of the mechanical DCCB, and a decreased fault interruption time. The energydissipated in the mechanical DCCB is reduced from 22.4 MJ to 5.4 MJ by using FCL operationof the adjacent hybrid DCCBs in this particular example.

5 pu

TRIP BRK31

BRK I REFC3

BRK I REF34

Sign

al

(a-1) Trip Signal

05

1015

Cur

rent

(kA

) (a-2) DCCB31 CurrentiCB iV IiLC iSA

−8

−6

−4

−2

0

Cur

rent

(kA

)

(a-3) DCCB34 Current

iCB34

−5

0

5

10

Cur

rent

(kA

)

(a-4) DCCBC3 CurrentiCBC3

0

10

20

Ene

rgy

(MJ)

(a-5) EnergyECB31

0 5 10 15 20−200

0

200

400

time (ms)

V(k

V)

(a-6) DC Bus3 and MMC3 Voltages of the Positive Pole

ubus uMMC

(a) FCL operation disabled

5 pu2 pu

TRIP BRK31

BRK I REFC3

BRK I REF34

Sign

al

(b-1) Trip Signal

05

1015

Cur

rent

(kA

) (b-2) DCCB31 CurrentiCB iV IiLC iSA

−8

−6

−4

−2

0

Cur

rent

(kA

)

(b-3) DCCB34 Current

iMB1 iMB2 iMB3 iMB4iSA1 iSA2 iSA3 iSA4iCB iLCS

−5

0

5

10

FCL operationCur

rent

(kA

)

(b-4) DCCBC3 CurrentiMB1 iMB2 iMB3 iMB4iSA1 iSA2 iSA3 iSA4iCB iLCS

0

10

20

Ene

rgy

(MJ)

(b-5) EnergyECB341 ECB342 ECB343 ECB344ECBC31 ECBC32 ECBC33 ECBC34ECB31

0 5 10 15 20−200

0

200

400

time (ms)

V(k

V)

(b-6) DC Bus3 and MMC3 Voltages of the Positive Pole

ubus uMMC

(b) FCL operation enabled

Figure 8: FCL operation of hybrid DCCBs with a mechanical DCCB, fault location: f1.

7.3 Fast reclosing during backup protection

A solid pole-to-pole fault is applied at the middle of cable L13 ( f2) to demonstrate the fastreclosing function of hybrid DCCBs during backup protection. The line breaker DCCB31 isassumed to have failed during the fault clearing process, and the breaker failure is detected bythe local breaker failure detection at the IED. All DCCBs are hybrid type with a breaker openingtime of 2 ms and a line inductor of 50 mH.

Once the fault is identified by IED13 and IED31, trip signals of the main breakers and RCBs,TRIP_BRK13, TRIP_BRK31, TRIP_RCB13 and TRIP_RCB31 change to high (Fig. 9 (a)).

12

The status of the main breaker and the RCB change to high (open) once they are fully opened(Fig. 9 (b)). The local breaker failure backup protection at IED31 detects a breaker failure, con-sequently, the main breakers of DCCB34 and DCCBC3 are ordered to open by TRIP_BRK34and TRIP_BRKC3, respectively (Fig. 9 (a)). In the meantime, the trip signals of the RCBs(TRIP_RCB34 and TRIP_RCBC3) remain low to enable fast reclosing function. The fault cur-rent in RCB31 reaches below the residual current level once the fault current is interrupted bythe adjacent DCCBs, and the status of RCB31, ST_RCB31 changes to high (open). After a pre-determined reclosing waiting time of 40 ms, the trip signals, TRIP_BRK34 and TRIP_BRKC3change to low and reclose the main breakers.

The fast reclosing function allows for fast voltage and power restoration without opening andreclosing the RCB. The voltage and power restoration time are at least 60 ms shorter thanwithout fast reclosing in the studied case, as it takes 30 ms to open and another 30 ms to reclosethe RCB.

TRIP BRK13TRIP RCB13TRIP BRK31TRIP RCB31BRK FAIL31TRIP BRK34TRIP RCB34TRIP BRKC3TRIP RCBC3

Sign

al

(a) Trip Signals

ST BRK13ST RCB13ST BRK31ST RCB31ST BRK34ST RCB34ST BRKC3ST RCBC3

Stat

us

(b) Breaker Status

−5

0

5

10

-3.86 kA

6.2 kA

Cur

rent

(kA

)

(c) Breaker Current

iCB13 iCB31

iCB34 iCBC3

0 20 40 600

2

4

6

8

107.5 MJ

4 MJ

time (ms)

Ene

rgy

(MJ)

(d) Breaker Energy

ECB13 ECB31

ECB34 ECBC3

Figure 9: Fast reclosing during breaker failure backup protection, fault location: f2.

7.4 Breaker failure internal detection

The simulation conditions are same as in section 7.3, other than that the breaker failure internaldetection function of DCCB31 is enabled.

13

Compared to the local breaker failure detection BF_LCL31, the internal breaker failure detec-tion BF_HLH31 indicates a breaker failure as soon as the commutation time (with a margin of250 µs) has elapsed after receiving the tripping order (Fig. 10 (a)). This leads to faster openingof the backup DCCBs and reduction on the breaking current and absorbed energy as comparedto using local backup detection (Fig. 9 (c)- (d) and Fig. 10 (c) - (d)).

0.5 ms

TRIP BRK13TRIP BRK31

BF LCL31BF HLH31

BRK FAIL31TRIP BRK34TRIP BRKC3

Sign

al(a) Trip Signals

−5

0

5

10

-3.12 kA

4.7 kA

Cur

rent

(kA

)

(b) Breaker Current

iCB13 iCB31

iCB34 iCBC3

0 20 40 600

2

4

6

3.4 MJ

3.16 MJ

time (ms)

Ene

rgy

(MJ)

(c) Breaker Energy

ECB13 ECB31

ECB34 ECBC3

Figure 10: Breaker failure internal detection, fault location: f2.

7.5 Repeated O-C-O operation

The cable section L13 is replaced with a 350 km overhead line, and a permanent pole-to-polefault is applied at the middle of the line ( f2). The de-ionisation time of the overhead line isassumed to be 200 ms in the simulation [36].

7.5.1 Hybrid DCCB

Both cases with the fast reopening function disabled and enabled are compared in the caseof a hybrid DCCB. When the fast reopening function is disabled, the LCS and UFD are closedduring the closing operation. Although the fault is identified again as soon as the main breaker isclosed, the second opening operation needs to wait until finishing the closing operation (Fig. 11(a)). On the contrary, the fast reopening function allows the LCS and UFD remain openedduring the O-C-O operation, and the main breaker interrupt the fault again with a negligibledelay (Fig. 11 (b)) [20]. The breaking current and energy duties during the second openingoperation are considerably small compared to the case with the fast reopening disabled.

14

200 ms

250 µs2 ms 2 ms

TRIP BRK

ST MB

ST RCB

ST LCS

ST UFD //

Sign

al

(a-1) Trip Signal and Breaker Status

0

2

4

//

4.04 kA 4.57 kA

Cur

rent

(kA

)

(a-2) Breaker CurrentiMB iLCSiSA

0 10 20 30 200 210 2200

5

10

//

3.85 MJ10.16 MJ

time (ms)

Ene

rgy

(MJ)

(a-3) Breaker Energy

ECB

(a) Fast reopening disabled

TRIP BRK

ST MB

ST RCB

ST LCS

ST UFD //

Sign

al

(b-1) Trip Signal and Breaker Status

0

2

4

//

4.04 kA0.54 kA

Cur

rent

(kA

)

(b-2) Breaker CurrentiMB iLCSiSA

0 10 20 30 200 210 2200

2

4

//

3.85 MJ 3.88 MJ

time (ms)

Ene

rgy

(MJ)

(b-3) Breaker Energy

ECB

(b) Fast reopening enabled

Figure 11: Repeat O-C-O operation of a hybrid DCCB for a pole-to-pole fault on an overhead linesection, all DCCBs: hybrid type, fault location: f2.

7.5.2 Mechanical DCCB

During the first opening operation, the first resonance injection branch, S3_a, Cp_a is used. Themain vacuum interrupter, the RCB and the making switch, S3_a, start to operate at the same timeafter the trip order is sent to the mechanical DCCB. The status of the RCB becomes open afterthe current in the DCCB reaches to the residual current level. The main vacuum interrupter andthe RCB are closed with a closing mechanical delay of 50 ms after the presumed de-ionisationtime. The fault is again identified as soon the DCCB is closed and the second resonance injec-tion branch, S3_b, Cp_b is used for the opening operation with the same opening sequence. Thebreaking current and energy duties are of similar degree for both opening operations.

200 ms50 ms

8 ms

TRIP BRK

ST VI

ST RCB

ST Sa

ST Sb //

Sign

al

(a) Trip Signal and Breaker Status

02468

//

7 kA 6.45 kA

Cur

rent

(kA

)

(b) Breaker CurrentiV I iSaiSb iSA

0 20 40 200 220 240 260 280 3000

10

20

30

//13.72 MJ

27.82 MJ

time (ms)

Ene

rgy

(MJ)

(c) Breaker Energy

ECB

Figure 12: Repeat O-C-O operation of a mechanical DCCB for a pole-to-pole fault on an overhead linesection, all DCCBs: mechanical type, fault location: f2.

15

8 CONCLUSION

In this paper, the main functions of the DCCBs are classified into minimally required and aux-iliary based on a literature review. To enable both types of functions for various DCCB tech-nologies, standardised interfaces between IEDs and DCCBs were proposed and implemented ina four-terminal test system in PSCAD/EMTDC. The simulation studies demonstrated that theproposed interfaces allow both hybrid and mechanical DCCBs to achieve their designed func-tions. In particular, it is shown that the auxiliary functions of hybrid DCCBs and breaker failureinternal detection have the advantage of reducing breaking current and absorbed energy. In ad-dition, the proposed interfaces were shown capable of enabling various DCCB technologies toachieve multivendor interoperability in a single HVDC grid.

ACKNOWLEDGEMENT

This project has received funding from the European Union’s Horizon 2020 research and inno-vation programme under grant agreement No. 691714.

REFERENCES

[1] D. Van Hertem and M. Ghandhari, “Multi-terminal VSC HVDC for the European super-grid: Obstacles,” Renewable and Sustainable Energy Reviews, vol. 14, no. 9, pp. 3156–3163, Dec. 2010.

[2] PROMOTioN Workpackage 4, “Deliverable 4.1 Definition of test cases and functionalrequirements for DC grid protection methodologies,” Tech. Rep., Feb. 2017.

[3] J. Häfner and B. Jacobson, “Proactive Hybrid HVDC Breakers - a key innovation forreliable HVDC grids,” in Proc. Cigré Bologna Symp., Bologna, Italy, 13–15 Sept. 2011, 8pages.

[4] K. Tahata, S. El Oukaili, K. Kamei, D. Yoshida, Y. Kono, R. Yamamoto, and H. Ito,“HVDC circuit breakers for HVDC grid applications,” in Proc. AORC-cigré 2014, Tokyo,Japan, 27–29 May 2014, 9 pages.

[5] M. Wang, M. Abedrabbo, W. Leterme, D. Van Hertem, C. Spallarossa, S. Oukaili, I. Gram-matikos, and K. Kuroda, “A Review on AC and DC Protection Equipment and Technolo-gies : Towards Multivendor Solution,” in Proc. Cigré 2017 Canada, Winnipeg, Canada,30 Sep. - 6 Oct. 2017, 11 pages.

[6] D. Jovcic, A. Jamshidifar, M. Popov, and S. Liu, “Modelling and Comparison of CommonFunctionalities of HVDC Circuit Breakers,” in Proc. PES GM 2018, Portland, Oregen,USA, 5 – 9, Aug. 2018, 5 pages.

[7] F. Dijkhuizen, “Zoning in High Voltage DC (HVDC) Grids using Hybrid DC breaker,” in2013 EPRI HVDC FACTS Conf., Palo Alto, USA, 28, Aug. 2013, 10 pages.

[8] I. Jahn, F. Hohn, and S. Norrga, “Impact of Measurement and Communication on Pro-tection of MTDC Grids,” in Proc. IET DPSP 2018, Belfast, UK, 12 – 15, Mar. 2018, 5pages.

[9] SGCC, “World’s first set of 200kv dc circuit breaker successfully commissioned,” 29Dec. 2016. [Online]. Available: http://www.cepri.com.cn/release/details_66_771.html

[10] X. Guo, Y. Zhou, N. Mei, and B. Zhao, “Construction and Characteristic Analysis ofZhangbei Flexible DC Grid,” Power System Technology, vol. 42, no. 11, Nov. 2018.

[11] [Online]. Available: https://www.promotion-offshore.net/news_events/news/detail/eu-project-promotion-successfully-demonstrates-ac-short-circuit-generator-based-test-environment-for/

16

[12] D. Johannesson, M. Nawaz, K. Jacobs, S. Norrga, and H. Nee, “Potential of ultra-highvoltage silicon carbide semiconductor devices,” in 2016 IEEE 4th Workshop on WideBandgap Power Devices and Applications (WiPDA), Fayetteville, AR, USA, 7 – 9 Nov.2016, pp. 253–258.

[13] M. H. Hedayati and D. Jovcic, “Reducing peak current and energy dissipation in hy-brid hvdc cbs using disconnector voltage control,” IEEE Transactions on Power Delivery,vol. 33, no. 4, pp. 2030–2038, Aug 2018.

[14] C. C. Davidson, C. D. Barker, J. M. De Bedout, W. Grieshaber, J. W. Bray, and T. J.Sommerer, “Hybrid DC Circuit Breakers Using Gas Discharge Tubes For High VoltageSwitching,” in Proc. Cigré 2017 Canada, Winnipeg, Canada, 30 Sep. - 6 Oct. 2017, 8pages.

[15] A. Mokhberdoran, N. Silva, H. Leite, and A. Carvalho, “Unidirectional protectionstrategy for multi-terminal hvdc grids,” Transactions on Environment and ElectricalEngineering, vol. 1, no. 4, pp. 58–65, 2016. [Online]. Available: https://teee.eu/index.php/TEEE/article/view/71

[16] A. Mokhberdoran, O. Gomis-Bellmunt, N. Silva, and A. Carvalho, “Current flow control-ling hybrid dc circuit breaker,” IEEE Transactions on Power Electronics, vol. 33, no. 2,pp. 1323–1334, Feb 2018.

[17] L. Ängquist, S. Norrga, T. Modeer, and S. Nee, “Fast HVDC breaker using reduced-ratingpower electronics,” in Proc. IET ACDC 2017, Manchester, UK, 14–16 Feb. 2017, 6 pages.

[18] T. Eriksson, M. Backman, and S. Halén, “A low loss mechanical HVDC breaker forHVDC grid applications,” in Proc. Cigré Paris, Paris, France, 24–29 Aug. 2014, 8 pages.

[19] Y. Wang and R. Marquardt, “Performance of a new fast switching DC-Breaker for meshedHVDC-Grids Keywords Main requirements for a HVDC-Breaker HVDC-Breaker Topolo-gies,” in Proc. EPE’15 ECCE-Europe, Geneva, Switzerland, 8 – 10, Sep. 2015, 9 pages.

[20] PROMOTioN Workpackage 6, “Deliverable 6.9 Standard DC CB model verification planand RTDS models,” Tech. Rep., Jan. 2018.

[21] C. C. Davidson, R. S. Whitehouse, C. D. Barker, J.-P. Dupraz, and W. Grieshaber, “A newultra-fast HVDC Circuit breaker for meshed DC networks,” in Proc. IET ACDC 2015,Birmingham, UK, 10-12 Feb. 2015, 7 pages.

[22] Z. Wandi, X. Wei, S. Zhang, G. Tang, Z. He, J. Zheng, Y. Dan, and C. Gao, “Developmentand test of a 200kV full-bridge based hybrid HVDC breaker,” in 2015 17th EuropeanConference on Power Electronics and Applications (EPE’15 ECCE- Europe), Geneva,Switzerland, 08–10 Sep. 2015, 7 pages.

[23] B. Yang, D. Cao, W. Shi, W. Lv, W. Wang, B. Liu, “A novel commutation-based hybridHVDC circuit breaker,” in Proc. Cigré 2017 Canada, Winnipeg, Canada, 30 Sep. - 6 Oct.2017, 8 pages.

[24] J. Magnusson, R. Saers, L. Liljestrand, and G. Engdahl, “Separation of the Energy Absorp-tion and Overvoltage Protection in Solid-State Breakers by the Use of Parallel Varistors,”IEEE Trans. Power Electron., vol. 29, no. 6, pp. 2715–2722, June 2014.

[25] M. Wang, W. Leterme, J. Beerten, and D. Van Hertem, “Using fault current limiting modeof a hybrid DC breaker,” The Journal of Engineering, vol. 2018, pp. 818–823(5), October2018. [Online]. Available: http://digital-library.theiet.org/content/journals/10.1049/joe.2018.0184

[26] D. Jovcic, A. Jamshidi Far, and A. Hassanpoor, “Control Methods for Fault Current Lim-iting Using Hybrid HVDC Breakers,” in Proc. Cigré Paris 2018, Paris, France, 26 – 31Aug. 2018, 10 pages.

17

[27] G. Chaffey and T. C. Green, “Low speed protection methodology for a symmetricalmonopolar HVDC network,” in Proc. IET ACDC 2017, Manchester, UK, 14–16 Feb. 2017,6 pages.

[28] K. Vinothkumar, I. Segerqvist, N. Johannesson, and A. Hassanpoor, “Sequential auto-reclosing method for hybrid hvdc breaker in vsc hvdc links,” in 2016 IEEE 2nd AnnualSouthern Power Electronics Conference (SPEC), Auckland, New Zealand, 5 – 8, Dec2016, 6 pages.

[29] L.-E. Juhlin, “Fast breaker failure detection for hvdc circuit breakers,” US Patent 8947843B2, Feb. 3 2015.

[30] W. Leterme, J. Beerten, and D. Van Hertem, “Non-unit protection of HVDC grids withinductive dc cable termination,” IEEE Trans. Power Del., vol. 31, no. 2, pp. 820–828, Apr.2016.

[31] H. Takeda, H. Ayakawa, M. Tsumenaga, and M. Sanpei, “New protection method for hvdclines including cables,” IEEE Trans. Power Del., vol. 10, no. 4, pp. 2035–2039, 1995.

[32] N. Johannesson and S. Norrga, “Longitudinal differential protection based on the universalline model,” in Proc. Industrial Electronics Society, IECON 2015 - 41st Annual Confer-ence of the IEEE, Yokohama, Japan, 9-12 Nov. 2015, 6 pages.

[33] A. T. Johns, “New ultra-high-speed directional comparison technique for the protection ofe.h.v. transmission lines,” in IEE Proceedings C Generation, Transmission and Distribu-tion, vol. 127, no. 4, 1980, pp. 228–239.

[34] Cigré working group B4.57, “Guide for the Development of Models for HVDC Convertersin a HVDC Grid,” Paris, France, Tech. Rep., Dec. 2014.

[35] W. Leterme, S. P. Azad, and D. Van Hertem, “Fast Breaker Failure Backup Protection forHVDC Grids,” in Proc. IPST 2015, Cavtat, Croatia, 15-18 Jun. 2015, 6 pages.

[36] C. D. Barker, A. G. Adamczyk, R. Gupta, G. Fintzos, R. S. Whitehouse, D. R. Trainer,and N. M. Kirby, “Fault Clearing on Overhead HVDC Transmission Lines,” in Proc. CigréCanada, Toronto, Ontario, Canada, 22 – 24, Sept. 2014, 9 pages.

[37] I. Jahn, N. Johannesson, and S. Norrga, “Survey of methods for selective dc fault detectionin mtdc grids,” in Proc. IET ACDC 2017), Manchester, UK, 14–16 Feb. 2017, 7 pages.

[38] B. Xiang, L. Zhang, K. Yang, Y. Tan, Z. Liu, Y. Geng, J. Wang, and S. Yanabu, “ArcingTime of a DC Circuit Breaker Based on a Superconducting Current-Limiting Technology,”IEEE Transactions on Applied Superconductivity, vol. 26, no. 7, pp. 1–5, Oct. 2016.

[39] B. Pauli, G. Mauthe, E. Ruoss, G. Ecklin, J. Porter, and J. Vithayathil, “Development of ahigh current HVDC circuit breaker with fast fault clearing capability,” IEEE Trans. PowerDel., vol. 3, no. 4, pp. 2072–2080, 1988.

[40] Cigré Joint Working Group A3-B4.34, “Technical Requirements and Specifications ofState-of-the-art HVDC Switching Equipment,” Cigré Technical Brochure, 2017.

18