IEC TR 63368:2024

IEC TR 63368 ®
Edition 1.0 2024-09
TECHNICAL
REPORT
colour
inside
Control and protection systems for high-voltage direct current (HVDC) power
transmission systems – Off-site real-time simulation testing

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IEC TR 63368 ®
Edition 1.0 2024-09
TECHNICAL
REPORT
colour
inside
Control and protection systems for high-voltage direct current (HVDC) power

transmission systems – Off-site real-time simulation testing

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.240.99  ISBN 978-2-8322-9712-4

– 2 – IEC TR 63368:2024 © IEC 2024
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 7
3.1 Terms and definitions . 7
3.2 Abbreviated terms . 7
4 Test environment . 8
4.1 General . 8
4.2 Real-time simulator . 8
4.2.1 General . 8
4.2.2 Simulation interface devices . 8
4.2.3 Simulation model . 9
4.3 HVDC control and protection devices . 11
4.3.1 Control devices . 11
4.3.2 Protection devices . 11
4.3.3 Measurement devices . 12
4.3.4 Monitoring devices . 12
4.3.5 Fault recording devices . 12
4.3.6 Valve base control devices . 12
5 Steady state control tests . 12
5.1 General . 12
5.2 DC switching sequence tests . 13
5.3 Energization of reactive power components . 13
5.4 Energization of converter transformers. 13
5.5 Open line test of HVDC control system . 13
5.6 Deblock-block performance tests . 13
5.7 Operator control mode transfer tests . 14
5.8 Operation status tests . 14
5.9 Tap changer control tests. 14
5.10 Reactive power control tests . 14
5.10.1 Reactive power component switching function tests . 14
5.10.2 Reactive power curve tests . 14
5.11 Power ramping tests . 15
5.12 Overload tests . 15
5.13 Metallic and ground return configuration and transfer tests . 15
5.14 Reduced voltage operation tests . 15
5.15 Tests of static characteristic curves of converters . 15
5.16 PQ diagram tests of VSC-HVDC converters . 15
6 Dynamic control tests . 16
6.1 General . 16
6.2 Power step test . 16
6.3 Current step test . 16
6.4 Voltage step test . 16
6.5 Gamma step test . 17
6.6 AC system related tests . 17

6.6.1 AC disturbance tests . 17
6.6.2 AC/DC interaction tests . 17
6.7 Stability control function tests . 18
6.8 Power system restoration test . 18
6.9 Grid code tests . 18
7 Protection tests . 19
7.1 General . 19
7.2 Trip signal logic tests . 19
7.3 Converter unit area protection tests . 19
7.4 DC bus area protection tests . 19
7.5 DC filter area protection tests . 20
7.6 DC line area protection tests . 20
7.7 Switch protection tests . 20
7.8 Other protection tests . 20
8 Redundancy and reliability of control and protection system tests . 21
8.1 General . 21
8.2 Redundant system failure tests . 21
8.3 System monitoring and switching tests . 21
8.4 Electromagnetic interference tests (optional) . 22
8.5 IT security . 22
9 Special tests for VSC . 23
9.1 General . 23
9.2 Control system delay (optional) . 23
9.3 Valve control and protection function tests . 23
9.3.1 Valve control function test . 23
9.3.2 Valve protection function tests . 24
9.4 STATCOM tests . 24
10 Test report . 24
Annex A (informative) Examples of protection areas and faults . 25
Annex B (informative) A typical test method for control system delay . 28
Bibliography . 30

Figure 1 – Relationship between clauses and test phases. 6
Figure A.1 – Typical faults in a LCC HVDC substation
(IEC/TR 60919-2:2008/AMD1:2015, Figure 7) . 26
Figure A.2 – Typical faults in a VSC HVDC substation (example – symmetrical
monopole shown in single phase) . 27
Figure B.1 – Composition of control system delay . 28
Figure B.2 – The real-time simulation test scheme for control system delay . 29

– 4 – IEC TR 63368:2024 © IEC 2024
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
CONTROL AND PROTECTION SYSTEMS FOR HIGH-VOLTAGE DIRECT
CURRENT (HVDC) POWER TRANSMISSION SYSTEMS –
OFF-SITE REAL-TIME SIMULATION TESTING

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
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IEC TR 63368 has been prepared by subcommittee 22F: Power electronics for electrical
transmission and distribution systems, of IEC technical committee 22: Power electronic systems
and equipment. It is a Technical Report.
The text of this Technical Report is based on the following documents:
Draft Report on voting
22F/763/DTR 22F/787/RVDTR
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this Technical Report is English.

This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
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• reconfirmed,
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of its contents. Users should therefore print this document using a colour printer.

– 6 – IEC TR 63368:2024 © IEC 2024
INTRODUCTION
It has been the mainstream practice of HVDC transmission system engineering to build a
real-time simulation test system with actual control and protection (C&P) devices to test the
functionality of various functions of the HVDC C&P system.
In order to provide practical guidance for the functional tests of HVDC transmission systems,
this document covers the real-time test environment, functional performance tests, and the test
report.
In order to construct the test system in the test preparation phase, Clause 4 introduces the off-
site real-time simulation test environment of the functional performance tests (FPT), including
the real-time simulator, the C&P system for test purposes, the interface devices and their
connection relationships, and the simulation models.
Clause 5 introduces the test practices and test methods of HVDC steady state control functions.
Clause 6 introduces the test practices and test methods of HVDC dynamic control functions,
whose main concerns are dynamic responses of DC voltage, DC current and DC power.
Clause 7 introduces the test practices and test methods of DC protection, whose main concerns
are DC protection logic and threshold values.
Clause 8 introduces the reliability tests of C&P systems, including redundancy tests and related
system switching tests, with the test practices and test methods described in detail.
Clause 9 introduces the special test practices and test methods for VSC-HVDC. In order to
thoroughly test the unique functions of VSC-HVDC, it can be necessary to add some specific
tests to be decided case by case.
Clause 10 introduces test reports. It includes mainly the contents of a test report.
The above clauses introduce various possible functionalities which do not apply to every HVDC
project mandatorily as a whole. It is the purchaser's task to select the appropriate
project-specific combination of functionalities. This document describes various possibilities;
however, it is important that project-specific needs be clearly defined by the purchaser. The
relationship between clauses and test phases is shown in Figure 1.

Figure 1 – Relationship between clauses and test phases

CONTROL AND PROTECTION SYSTEMS FOR HIGH-VOLTAGE DIRECT
CURRENT (HVDC) POWER TRANSMISSION SYSTEMS –
OFF-SITE REAL-TIME SIMULATION TESTING

1 Scope
This document provides guidance on off-site real-time simulation tests of control and protection
(C&P) systems for HVDC power transmission systems. The off-site real-time simulation tests
are carried out after the testing of C&P devices and prior to on-site system tests.
This document covers point-to-point, back-to-back, and multi-terminal HVDC systems of line
commutated converters (LCC), voltage-sourced converters (VSC) and hybrid HVDC
technologies.
In order to provide practical guidance for the functional performance tests of HVDC power
transmission systems, this document covers the test environment, the contents and methods of
functional performance tests, and the test report.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following
addresses:
• IEC Electropedia: available at https://www.electropedia.org/
• ISO Online browsing platform: available at https://www.iso.org/obp
3.1 Terms and definitions
3.1.1
control system delay
total time delay of the control link, including sampling delays, transmission delays and signal
processing time of all control devices
3.2 Abbreviated terms
C&P Control and protection
EHV Extra high voltage
EMT Electromagnetic transient
FPGA Field-programmable gate array
FPT Functional performance test
GRTS Ground return transfer switch
HIL Hardware in loop
HMI Human machine interface
HVDC High-voltage direct current

– 8 – IEC TR 63368:2024 © IEC 2024
IGBT Insulated-gate bipolar transistor
I/O Input / output
LCC Line-commutated converter
MMC Modular multilevel converter
MRTB Metallic return transfer breaker
MTDC Multi-terminal HVDC transmission system
RTS Real-time simulator/simulation
SCADA Supervisory control and data acquisition
SER Sequence of event recording / Sequence of event recorder
SM Sub-module
STATCOM Static synchronous compensator
SVC Static var compensator
TCSC Thyristor controlled series compensation
VDCOL Voltage dependent current order limitation
VSC Voltage-sourced converter
4 Test environment
4.1 General
The test environment is used for providing various power system conditions. The system
conditions are based on real-time simulation for testing the functionality including dynamic
behavior of an HVDC C&P system. It commonly includes RTS with models and delivered C&P
devices of a specific HVDC project.
4.2 Real-time simulator
4.2.1 General
RTS refers to real-time digital simulators based on electro-magnetic transient (EMT) algorithm.
RTS is used to model HVDC main circuits, adjacent AC system(s), and adjacent HVDC system(s)
as required by the purpose of the test, to connect actual C&P devices with simulation interfaces.
It runs models with sufficient simulation cycle time, stably and continuously, strictly in real-time
in every simulation time step.
4.2.2 Simulation interface devices
4.2.2.1 General
Simulation interface devices are used to connect C&P devices, with RTS for establishing
closed-loop HIL simulation systems. The protocols used for the communication among RTS,
the C&P devices and the simulation interface devices are dependent on the actual project and
type of simulator in use.
4.2.2.2 I/O interface devices
Simulation interface devices are used for establishing the I/O communications with RTS.
Generally, there are two types of interface techniques used for commercial RTS nowadays:
analog interface and digital interface.
1) Analog interface: the interface connections are performed through wires connected to the
I/O interface cards of RTS.
2) Digital interface: the interface connections are performed through digital system buses, and
in most of the applications, physically established via optical fibers.

4.2.2.3 Other special interfaces for RTS tests
1) Power amplifiers can be used to amplify RTS analog output signals to ensure the interface
adaptation to the C&P devices designed for the actual interfaces on site. It is optional and
dependent on the measurement input design of the C&P devices.
2) Disconnectors and earthing switches with slow operating time are usually not represented
in RTS. Instead, they are simulated in other suitable ways such as by AC and DC switch
simulator in the form of relay or digital system.
4.2.2.4 Valve interfaces for MMC-HVDC
In order to test the functions of the MMC valve base control device, appropriate interface
devices could be provided for RTS. These devices are optional, and if needed, used for
translating the packets of MMC sub-module on/off commands from the MMC valve base control
device into a specific form adapting to the MMC models in RTS.
4.2.3 Simulation model
4.2.3.1 General
The simulator model must be adapted for the specific project and for the planned testing.
Generally, the detailed characteristics of equipment in the model match the testing purposes.
The simulation model is generally composed of one or more of the following in 4.2.3.2.
4.2.3.2 Model of HVDC main circuit
4.2.3.2.1 LCC converter and transformer
The LCC converter and transformer are generally integrated with one component or two
individual models according to the test requirement.
The component simulates the key characteristics of the converter and transformer, including
compensation algorithm, firing angle, and extinction angle measurement.
4.2.3.2.2 MMC converter and transformer
The large number of sub-modules creates an excessive computational burden for the EMT
simulation of MMC-HVDC systems, especially in real-time environments. For the HIL test, the
exchange of large numbers of capacitor voltages and individual firing pulses presents a
communication challenge for the simulation model and the external physical control devices. In
order to meet the requirements of MMC-HVDC simulation and testing, various types of models
based on both processors and FPGAs have been developed using vast parallel computation
techniques, which can model the MMC converter with up to thousands of sub-modules.
The time step of the MMC converter model on FPGA is usually less than 10 μs. In this case,
the transformer can be modelled as an interface model for decoupling the MMC converter in
small time step from the main network in large time step.
If the MMC converter model and the main network use the same time step, a traditional
transformer model can be used to connect the MMC converter model and the main network.
4.2.3.2.3 HVDC transmission line and electrode line or metallic return conductor
Generally, the distributed parameter frequency-dependent model is used in RTS for HVDC
overhead lines, HVDC cables, and the electrode line or metallic return conductor. The model
parameters are in accordance with the actual project. For stability and accuracy purposes, the
phase domain frequency dependent line model can be utilized to model DC lines and cables.

– 10 – IEC TR 63368:2024 © IEC 2024
4.2.3.2.4 Reactive power components
Reactive power components in an LCC-HVDC converter station can be modelled as integrated
components or individual equipment branches. Integrated components are recommended for
high efficiency in resources.
The breakers of reactive power components are modelled individually in accordance with HVDC
reactive power control.
4.2.3.2.5 DC filter
The DC filter and its current measurements are modelled in detail in RTS if DC filter protection
is to be tested.
4.2.3.2.6 Pre-insertion resistor
If used in the actual project, the pre-insertion resistor and its resistor bypass breaker are
modelled to perform a converter energization test.
4.2.3.3 Model of interconnecting AC system(s)
4.2.3.3.1 General
The connected AC system can be modelled as a simplified static voltage source or as a dynamic
equivalent model in accordance with the need for specific tests.
4.2.3.3.2 AC system: Simplified static voltage source model
Simplified static voltage source models are used to simulate the connected AC system. In this
model, the short circuit impedance of the connected AC system is configured. The dynamic
behavior of the AC system is not considered and simulated in this model, e.g., angular stability.
However, a harmonic current path must be provided in the source model to ensure the numerical
stability of the simulation.
4.2.3.3.3 AC system: Dynamic equivalent model of AC systems
To simulate the dynamic and transient interactions between the DC system and the connected
AC system or between the new DC system and other existing DC systems, a dynamic equivalent
model of the AC system is required. It is noteworthy that these interaction studies are optional
in RTS and can be done in offline simulation. The advantage of the interaction study on RTS is
the high fidelity brought by the real control devices in the loop. This type of AC system model
depends on the project requirements.
For example, a dynamic equivalent model preserves the essential transmission network,
including AC transmission lines, transformers, and large-scale generators at a high voltage
level. Other parts of the AC system can be reasonably simplified.
As part of the dynamic equivalent model of the AC system, real-time simulation models of
adjacent HVDC C&P systems could be included to verify the interaction with existing HVDC
transmission systems, such as multi-HVDC infeed systems.
4.2.3.4 Adjacent HVDC systems
It is noteworthy to consider the requirement of modeling adjacent (in the context of electrical
distance) HVDC systems and power electronic equipment if the necessity is demonstrated and
a detailed model or a replica is available.

The interactions between an HVDC system being tested and other adjacent HVDC transmission
systems (especially when they are part of a multi-HVDC infeed system) are typically
investigated by means of EMT offline studies. Alternatively, they can be verified or performed
in a real-time test environment, provided the resources on the RTS are adequate.
4.2.3.5 Model validation
4.2.3.5.1 General
The goal of model validation is to evaluate whether the model and its parameters can be
simulated with the necessary precision for the tests to be performed.
4.2.3.5.2 Validating main circuit equipment models
The main circuit equipment models based on the design specifications, including LCC and VSC
converters, DC lines/cables, high speed switches, and AC/DC filters, can be verified by
comparison with the results of offline software simulation.
4.2.3.5.3 Validating short-circuit ratio (SCR) and dynamic equivalent model
When equivalent AC voltage sources are used to simulate the adjacent AC power grids
connected with the HVDC system, SCR can be compared with the pre-calculated values.
While the static equivalents focus on representing the exact steady state performances of the
actual AC power systems, the dynamic equivalents aim at representing both the exact steady
state and dynamic performances of the actual AC system, from the perspective of HVDC
converter stations.
4.2.3.5.4 Validating HVDC control and protection system model
If the C&P models of adjacent C&P systems mentioned in 4.2.3.4 are included in the real-time
simulation, it is necessary to validate these HVDC C&P models.
The HVDC C&P models can be software providing basic C&P functions such as closed-loop
power control, closed-loop current control, and valve control. The software models are usually
simplified from the actual control and protection system functions and do not include all the
details.
The validation of the offline software models can be started from the individual closed-loop
control functions. In order to validate the algorithms, it can be ensured that the logic and control
response is consistent with the offline models, the control replicas or the software programs.
After this validation is successful, the dynamic performances of the offline software models are
validated by normal operation tests and system disturbance tests. The important system
parameters and control device outputs are compared in detail, such as the AC/DC voltages,
currents, active power, and reactive power.
4.3 HVDC control and protection devices
4.3.1 Control devices
Based on the requirements of tests, the control system devices to be tested are consistent with
the requirements of the actual project configuration and design. However, in case of optional
dynamic control tests, system redundancy is not necessarily required.
4.3.2 Protection devices
The protection devices to be tested, including the pole protection, the valve group protection,
the DC line protection, and the optional DC filter protection, are consistent with the actual
project configuration and design.

– 12 – IEC TR 63368:2024 © IEC 2024
4.3.3 Measurement devices
The measurement devices to be tested are used to collect signals for the C&P system. These
devices are optional in the RTS C&P test system. If FPT needs to test related functions, the
necessary measurement devices are included.
4.3.4 Monitoring devices
The monitoring system to be tested includes the monitoring system servers, the monitoring
network interface device, the operator workstations, and the synchronous clock system.
4.3.5 Fault recording devices
The fault recording system to be tested includes the delivered fault recorder equipment of a
specific HVDC project. Generally, the fault recording system is used for analysis and verification.
Meanwhile, the capability of the fault recording system can be checked during the RTS test.
The test of the fault recording system is optional. The specific fault recording system delivered
to an HVDC project can be tested along with the control/protection devices by the real-time
simulator if necessary.
4.3.6 Valve base control devices
There are two kinds of valve base control devices: the LCC valve base control device and the
VSC valve base control device.
The LCC valve base control device is optional in RTS. Normally the thyristors in the same arm
are assumed to switch simultaneously, therefore, the valve base control device is not needed
in the simulation and testing. If FPT needs to test related functions, the valve base control
device can be represented by the special valve control functions provided by the manufacturers
for the actual project, using either the equivalent devices or the equivalent function model in
RTS.
The VSC valve base control devices switch every sub-module inside the RTS model individually.
Therefore, the VSC valve base control device provided for the actual project is used in RTS for
the test.
5 Steady state control tests
5.1 General
The steady state control functions include DC switching sequences, reactive power components
energizing, the converter transformer energizing, the open line test, deblock/blocking, control
mode switching, reactive power control, steady state performance, power ramping, stability
control function, overloading, metallic and ground return configuration and switching, and
voltage reduction operation, as applicable.
Please note that it is possible that not all functions will be applicable for every project. The
objective of the functional performance tests for steady state control is to verify whether these
applicable functions meet the design specifications.
All of the functions described in 5.2 to 5.16 can be verified in the real-time simulation test
system while some of them can also alternatively be verified on-site or in a non-real-time
simulation environment. The test items performed in the real-time simulation test are selected
based on mutual agreement between the project owner and the manufacturer.

5.2 DC switching sequence tests
The sequential control operations by manual and automatic orders can smoothly switch the
HVDC system into the different operating states that are required. Meanwhile, the test verifies
whether the interlocks for different operation switching meet the designed specification. The
sequential operations triggered by the orders include all required HVDC system operation
modes (monopolar metallic return, monopolar ground return, or open line test) and DC filter
connection/isolation, as/if applicable.
5.3 Energization of reactive power components
The functional performance tests for energization of reactive power components are to:
1) Verify whether the energization and dis-connection of the reactive power components are
correct.
2) Verify whether the influence on the AC systems during the energization/dis-connection is
acceptable.
These tests are carried out in manual mode. The operator issues a manual command to switch
on or off the reactive power component to verify whether the corresponding component is
switched on/off correctly.
5.4 Energization of converter transformers
The tests of energization of converter transformers are to:
1) Evaluate the magnitude of inrush current.
2) Verify the impact on HVDC devices already in operation in the same station.
5.5 Open line test of HVDC control system
The open line test (OLT) function confirmation in the real-time simulation verifies that this
control function is implemented as designed and verifies the protection functions in case of a
DC line being short circuited to ground. If the OLT function does not exist in a specific project,
this test is not applicable.
5.6 Deblock-block performance tests
The deblock-block performance tests are to:
1) Verify that the HVDC system can deblock smoothly without any unexpected disturbance
under different power control modes with a single pole (or multiple poles).
2) Verify that the single pole (or multiple poles) of the HVDC system can be blocked stably
without any unexpected disturbance at different power control modes.
3) Verify the stable and undisturbed deblocking of the blocked valve groups when other valve
groups are in operation, and smooth DC power transfer after the successful deblock.
4) Verify that a certain operating valve group can achieve stable and undisturbed blocking
when several valve groups are in operation, and that DC power can be transferred smoothly
after the successful block.
5) Verify a converter station being put into or out of operation as designed while the others
remain in operation for a MTDC system.
6) Verify the deblock-block performance when inter-station communication is lost, if required.

– 14 – IEC TR 63368:2024 © IEC 2024
5.7 Operator control mode transfer tests
The operator control mode transfer tests are to:
1) Verify that the interlocking and selection of master control, slave control, and different
control locations of converter stations are correct in different operations, as applicable and
designed.
2) Verify that the toggle of control modes of reactive power components at the rectifier or
inverter has no influence on the steady-state operation.
3) Verify that the transitions between different power control modes are smooth and as
expected.
5.8 Operation status tests
Operation status tests are to verify whether the HVDC steady operating points are compliant
with the results of system design studies, such as the main circuit parameter report.
5.9 Tap changer control tests
The tap changer control tests are to:
1) Verify whether HVDC control could perform the tap-changer control functions correctly over
the entire designed operating range.
2) Verify whether the tap-changers of single-phase transformers are operated synchronously
in different control modes and from different control locations.
3) Verify whether the tap-changer control could avoid unexpected false trips in case of
un-synchronized tap-changer positions during operation.
5.10 Reactive power control tests
5.10.1 Reactive power component switching function tests
The reactive power control tests in LCC-HVDC are to:
1) Verify the reactive power component switching coinciding with the designed reactive power
control under U mode and Q mode in the process of power ramp up/down.
ac
2) Verify another reactive power component with the same type being switched on
automatically while the one in service becomes unavailable, when expected so.
3) Verify the low-load reactive power optimization function, if specified, is the same as
designed.
5.10.2 Reactive power curve tests
This Subclause 5.10.2 applies to VSC-HVDC.
The reactive power curve tests are carried out for the VSC-HVDC converter stations. The
reactive power control of VSC-HVDC have several modes, e.g., the Q mode and the U mode.
ac
These modes are designed according to the specification and system study report in the form
of corresponding reactive power curves, which represent the relationships between I and U .
q ac
I is the amplitude of the current in the q-axis of the d-q coordinate system.
q
In Q mode, the control target is the exchange of reactive power of the converter with the
connected AC system at the defined point of control. In U mode, the control target is the
ac
voltage of the AC bus at the defined point of control.
The reactive power curve tests are to verify that the control system is working correctly with the
designed strategies at different AC voltages.

5.11 Power ramping tests
The power ramping tests are to:
1) Verify whether the DC power can be manually ramped up or down in different operation
modes.
2) Verify the DC power ramping function based on the automatic power curves under different
power control modes, when so designed.
3) Verify that the reaction of power ramping pause, control mode switching and communication
fault between converter stations during the process of power ramping meets the designed
specifications.
5.12 Overload tests
For HVDC projects with overload capabilities considered, the overload tests are performed.
Generally, the overload tests are to verify whether the HVDC system overload functions are
correct in the conversion processes of different operation modes, the changes of DC power,
DC voltage, and firing angle.
5.13 Metallic and ground return configuration and transfer tests
This Subclause 5.13 applies to the projects in which the function is specified by design.
The metallic-ground return configuration and transfer tests are to verify whether the metallic
and ground return configurations of the DC system can correctly be transferred from one to the
other and vice-versa within the designed limits of MRTB and GRTS components.
5.14 Reduced voltage operation tests
This Subclause 5.14 applies to the projects in which the function is specified by design.
The reduced voltage operation tests are to:
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