IEC PAS 61975:2004

PUBLICLY
IEC
AVAILABLE
PAS 61975
SPECIFICATION
First edition
Pre-Standard
2004-08
System tests for high-voltage
direct current (HVDC) installations

Reference number
IEC/PAS 61975:2004(E)
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PUBLICLY
IEC
AVAILABLE
PAS 61975
SPECIFICATION
First edition
Pre-Standard
2004-08
System tests for high-voltage
direct current (HVDC) installations

” IEC 2004  Copyright - all rights reserved
No part of this publication may be reproduced or utilized in any form or by any means, electronic or
mechanical, including photocopying and microfilm, without permission in writing from the publisher.
International Electrotechnical Commission, 3, rue de Varembé, PO Box 131, CH-1211 Geneva 20, Switzerland
Telephone: +41 22 919 02 11 Telefax: +41 22 919 03 00 E-mail: inmail@iec.ch Web: www.iec.ch
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For price, see current catalogue

– 2 – PAS 61975 © IEC:2004 (E)

CONTENTS
Part 0: Executive Summary. 4

Part 1: General. 11

1.1 Statement of Purpose . 13

1.2 Structure of the HVDC System. 15

1.3 Structure of the Control and Protection System. 16
1.4 Logical Steps of Commissioning . 17
1.5 Structure of System Testing. 19
Part 2: Off-Site Tests. 20
2.1 Steady State Performance of the Controls . 23
2.1.1 Measurements.24
2.1.2 Control and Protective Sequences. 24
2.1.3 Steady Stale Performance Tests. 25
2.2 Dynamic Performance Tests. 27
2.2.1 Controls-Step Responses . 29
2.2.2 Control Mode Transfer. 31
2.2.3 AC System Interaction/Control. 33
2.2.4 Commutation Failures and Valve Misfires . 34
2.2.5  AC Filter, Transformer and Reactive Element Switching. 36
2.2.6 AC and DC System Faults . 37
2.2.7 Islanding.41
2.3 Functional Performance Tests . 43
2.4  Type Tests on the Control and Protection Equipments . 46
Part 3: Converter Tests . 50
3.1 Converter Unit Tests . 52
3.2 Converter Station Tests. 54

3.2.1 HV Energization or AC Filters, Capacitor Banks and Shunt Reactors . 54
3.2.2 Open Line Test of the DC Switchyard. 55
3.2.3  Load Tests. 57
3.3 Open Line Tests on the DC Transmission Circuit. 61
Part 4: End-to-End-Tests. 63
4.1 Changing the DC System Configuration, Off Voltage . 67
4.2 Start and Stop Sequences and Steady State Operation at Minimum
Power.69
4.3 Protective Blocking and Tripping Sequences . 73
4.4 Power and Current Ramping . 76
4.5 Reduced Voltage Operation. 78

PAS 61975 © IEC:2004 (E) – 3 –

Part 5: Steady-State Performance and Interference Tests. 81

5.1 Harmonic Performance and Filter Components Rating . 83

5.2 Audible Noise . 86

5.3 Overload/Temperature Rise . 88

5.4 Interference .90

5.5 Earth Electrode. 92

Part 6: Operation and Integration Tests . 9

6.1 Changes of DC Configuration. 98
6.1.1 Tests from Monopolar Metallic Return Operation. 100
6.1.2 Tests from Monopolar Earth Return Mode. 101
6.1.3 Tests from Bipolar Operation . 101
6.2 Control Performance. 103
6.2.1 Step Response . 105
6.2.2 Control Mode Transfer. 110
6.2.3 AC System Interaction / Control. 113
6.2.4 Commutation Failure . 116
6.3 Switching AC Side Fillers and Transformers. 119
6.4 Loading Tests. 121
6.5 AC and DC System Staged Fault Tests. 124
6.6 Loss of Telecommunications, Auxiliaries, or Redundant Equipment 129
6.6.1 Loss of Telecommunications between Terminals . 129
6.6.2 Loss of Auxiliary Power Supplies. 132
6.6.3 Loss of Redundant Equipment. 134
Part 7: Trial Operation. 135
Part 8:  System Test Plan and Documentation. 138
8.1 Plant Documentation and Operating Manuals . 139
8.2 System Study Reports and Technical Specifications . 139
8 3 Inspection and Test Plan . 139
8.4 System Test Program . 141
8.5 Test Procedures for each Test. 142

8.6 Documentation of System Test Results. 142
8.7 Deviation Reports. 143

– 4 – PAS 61975 © IEC:2004 (E)

INTERNATIONAL ELECTROTECHNICAL COMMISSION

____________
SYSTEM TESTS FOR HIGH-VOLTAGE DIRECT CURRENT (HVDC)

INSTALLATIONS
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising

all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with an IEC Publication.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
A PAS is a technical specification not fulfilling the requirements for a standard but made
available to the public.
IEC-PAS 61975 was submitted by the CIGRÉ (International Council on Large Electric
Systems) and has been processed by subcommittee 22F: Power electronics for electrical
transmission and distribution systems, of IEC technical committee 22: Power electronic systems
and equipment.
The text of this PAS is based on the This PAS was approved for
following document: publication by the P-members of the
committee concerned as indicated in
the following document
Draft PAS Report on voting
22F/96/NP 22F/101/RVN
Following publication of this PAS, which is a pre-standard publication, the technical committee
or subcommittee concerned will transform it into an International Standard.

PAS 61975 © IEC:2004 (E) – 5 –

An IEC-PAS licence of copyright and assignment of copyright has been signed by the IEC and
CIGRÉ and is recorded at the Central Office.

This PAS shall remain valid for an initial maximum period of three years starting from 2004-
08. The validity may be extended for a single three-year period, following which it shall be

revised to become another type of normative document or shall be withdrawn.

– 6 – PAS 61975 © IEC:2004 (E)

PART 0: EXECUTIVE SUMMARY
Abstract
This document which gives guidance on all aspects of system tests for HVDC

installations (excluding multiterminal HVDC systems), has been prepared by

CIGRE WG 14.12. It is structured in eight parts.

The guide should give potential users guidance, regarding which course of
action should be taken in planning commissioning activities.
Structure of the tests and a brief statement of the purpose of the individual group
of tests is presented.
Introduction
Commissioning an HVDC system is a very complex task which may affect more
than the actual contract parties. The complexity and the diversified areas of
concern during system testing require thorough planning and scheduling,
cooperation of all parties involved, and complete and structured documentation.
System testing completes commissioning of an HVDC system.
It allows the supplier to verify the suitability of the station equipment installed

and the functional completeness of the system; adjustments and optimization
can be made.
The user is shown that the requirements and stipulations in the contract are met
and that there is correlation with studies and previous off-site testing.

PAS 61975 © IEC:2004 (E) – 7 –

In adapting the HVDC system to the "real world" (the connected AC systems)

various constraints may exist, which require coordination within the economic

schedules of the AC system operators.

System testing proves to the public that tolerable values of phenomena

concerning public interest are not exceeded.

Five (5) major aspects are subject to system testing:

- HVDC station equipment and DC line/cable/bus incl. earth electrode, if any
- HVDC controls and protection
- Environmental considerations
- AC/DC system interaction
- System performance
The following diagram shows the interrelation between these aspects:

– 8 – PAS 61975 © IEC:2004 (E)

Acceptance tests shall be defined between supplier and user in advance and

may be performed at an appropriate time during the test schedule.

The testing sequence is best scheduled starting at local level with simple tests

before Involving additional locations and the transmission system and more

complex tests,
A system test plan has proven itself as a good means for planning and
scheduling.
Complete and organized documentation of the system tests is to the benefit of
both the supplier and the user, it shall form part of the project documentation
and contain al! necessary oscillograms, logs, etc, and if necessary a
commentary and references.
Structure of System Testing
System testing should follow the structure of the HVDC system, starting from the
smallest, least complex operational unit and shall end with the total system in
operation.
The first step, to ensure proper function, is to debug and to test the control
system during off-site tests. Because of the complex nature of the HVDC
system, this requires a simulator. Where applicable it is recommended to run

commissioning tests and acceptance tests during the off-site tests in a similar
way to those performed later at site. In such a way off-site tests can serve as
reference for the site tests.
PAS 61975 © IEC:2004 (E) – 9 –

System Tests for HVDC Installations

Before system commissioning can begin at site, preconditions concerning
subsystem tests, operator training and safety Instructions, system test plan and
test procedures, and all necessary test equipment must be fulfilled.
After all preconditions are fulfilled, each converter unit is commissioned
separately during the converter unit test. Open-circuit tests and/or short-circuit
tests are possible for this purpose. Converter station tests also include
energization of the AC filter, DC yard energization and back-to-back tests.
Back-to-back tests allow full active power with the nominal DC voltage, firing

angles, harmonics, etc. whilst still disconnected from the second AC system.
Certain control, relaying and instrumentation changes as welt as temporary DC
switchyard changes may be required for back-to-back tests.
Before end-:o-end tests are performed, it is advisable to perform an open line
test and shorted line tests with the DC transmission line. This test can be
repeated from both ends to verify the integrity of the DC line.

– 10 – PAS 61975 © IEC:2004 (E)

End-to-end tests involve both stations and the transmission Tine. With this

operation, power is transmitted for the first time. This test usually start on a

monopolar basis, with full bipolar operation being the final step.

Having the complete system running properly, steady state verification tests can

be performed. With normal operating ramp settings and automatic switching

sequences in place the effect of a number of disturbances on the DC side of the

system as well as in the AC systems may be checked.
Operation and Integration tests verify the transient and fault recovery behaviour
of the HVDC system-Correct operation of the HVDC system over an extended
period of time is checked during the trial operation.
The HVDC system tests are now completed, all functions have been verified and
the HVDC system is ready to be handed over to the owners. The acceptance
tests necessary to verify whether acceptance criteria have been met may have
been performed all or in part during the commissioning period.

PAS 61975 © IEC:2004 (E) – 11 –

PART 1: GENERAL
Introduction
This document deals with all aspects of system tests of HVDC systems. System

tests start when all relevant subsystems have been precommissioned and are
ready for operation. They end with full acceptance of the system for operation in
the power systems.
This document provides background information for IEC to produce standards
for system testing. It is structured in eight parts:
1. General
2. Off-site Tests
3. Converter Tests
Commissioning of converter units, verification of steady state performance
of units, switching tests
- converter unit tests
- converter station tests.
4. End-to-End Tests
Commissioning of the transmission system, verification of station
coordination.
5. Steady-State Performance and Interference Tests
Verification of steady-state performance and interference caused by the
HVDC-system.
– 12 – PAS 61975 © IEC:2004 (E)

6. Operation and Integration Tests

Operational and fault tests, verification of dynamic performance and

interaction between the DC and AC systems.

7. Trial operation
8. System test plan and documentation

The guide also covers interrelation with off-site system tests. Preconditions of
system tests wit] be established.
Part 1 General will address the purpose of this document, the HVDC system
structure, the control and protection structure, the logical steps of commissioning
and the structure of system testing of HVDC system. Parts 2 to 7 comprise
individual paragraphs on general test objectives, information on test procedures,
as well as detailed descriptions of the individual tests, including as appropriate
the following;
- Specific objectives per test
- Test procedures
- Test acceptance criteria
- Preconditions for the test
- References to system studies/specifications
- References to off-site tests
- Special conditions
Part 8 describes the documentation normally required to adequately perform the
system tests. This primarily consists of the following:
- Plant documentation
- Inspection and test plan (ITP)
- System study reports/technical specifications
- System test program
- Test procedures for each test
- Documentation of system test results

PAS 61975 © IEC:2004 (E) – 13 –

- Deviation report
The guide should give potential users guidance, regarding which course of

action should be taken in planning commissioning activities. The tests described

in the guide may not be applicable to all projects, but represent a range of

possible tests which should be considered.

1.1   Statement of Purpose
System testing completes the commissioning of an HVDC system.
It allows the supplier to verify the suitability of the station equipment installed
and the functional completeness of the system; adjustments and optimization
can be made.
The user is shown that the requirements and stipulations in the contract are met
and that there is correlation with studies and previous off-site testing.
For the user, the completion of system testing marks the beginning of
commercial operation of the HVDC system.
In adapting the HVDC system to the "real world" (the connected AC systems)
various constraints may exist, which require coordination within the economic
schedules of the AC system operators.
System testing proves to the public that tolerable values of phenomena
concerning public interest are not exceeded.
Five (5) major aspects are subject to system testing:

- HVDC station equipment and DC line/cable/bus incl. earth electrode, if any
- HVDC controls and protection
- Environmental considerations
- AC/DC system interaction –
- System performance
– 14 – PAS 61975 © IEC:2004 (E)

The following diagram shows the interrelation between these aspects:

Thorough and complete system testing of the above components can be
achieved with the tests described in the eight parts of the guide.
Acceptance tests shall be defined between supplier and user in advance and
may be performed at an appropriate time during the test schedule.
System testing may affect more than the actual contract parties. Those parties
shall be informed in time.
The complexity and the diversified areas of concern during system testing
require thorough planning and scheduling, cooperation of all parties involved, as

well as complete and organized documentation.
The testing sequence is best scheduled starting at local level with simple tests
before involving additional locations and the transmission system and more
complex tests. A system test plan (probably as part of a site test plan) has
proven itself as a good means for planning and scheduling.

PAS 61975 © IEC:2004 (E) – 15 –

Complete and organized documentation of the system tests is to the benefit of

both the supplier and the user, it shall form part of the project documentation

and contain all necessary oscillograms, logs, etc., and if necessary a

commentary and references.
1.2   Structure of the HVDC System

From a functional point of view an HVDC system consists of a sending terminal

and a receiving terminal, each connected to an AC-system. The two terminals
have one or several converters connected in series on the DC side and in
parallel on the AC side. The terminals are connected by a transmission line or
cable or a short piece of busbar (Back-to-Back station). Multiterminal systems
are not addressed in this document

– 16 – PAS 61975 © IEC:2004 (E)

1.3   Structure of the Control and Protection System

Each of the converter units can be controlled individually. To make the system

function as a transmission system the converter units should be controlled in a

coordinated way by a second level of the control system. Coordinated controls

and protection are essential for the proper function of HVDC systems.

PAS 61975 © IEC:2004 (E) – 17 –

1.4   Logical Steps of Commissioning

System commissioning should follow the structure of the HVDC system, starting

from the smallest, least complex operational unit, usually a 12-pulse converter,

and shall end with the total system in operation.

The first step, to ensure proper function, is to debug and test the control system

during factory system tests. Because of the complex nature of the HVDC

system, this requires a simulator. Where applicable, it is recommended to run
commissioning tests and acceptance tests in addition to ail limiting design cases
on the simulator in a similar way to those done later at site. In such a way
simulator tests can serve as reference for the site tests.
Before system commissioning can begin at site the following preconditions
should be fulfilled.
- All subsystems tested and commissioned including AC filters and the
converter transformers with special attention to possible transformer/AC filter
resonance during energizing
- Sufficient training of operating personnel
- Operating instructions for the station available to the operators
- Personnel, plant safety and security instructions made
- System test plan and documentation (part 8) ready and agreed upon
- AC/DC power profiles agreed for each test
- Any AC/DC system operating restrictions identified
- Operator voice communications available

- All necessary test equipment calibrated and operational
- Procedures for the preparation and evaluation of test results agreed upon
After all preconditions are fulfilled, each converter unit is commissioned
separately. Open-circuit tests and/or short-circuit tests are possible for this
purpose. Steady-state performance and interference tests may start at this
instant; however, they can be performed one by one at any convenient other
place dying the system test program, in order to minimize duplication of tests.

– 18 – PAS 61975 © IEC:2004 (E)

If possible, as a next step the converters in each station should be connected

back-to-back. This allows full active power with the nominal DC voltage, firing

angles, harmonics, etc. whilst still disconnected from the second AC system.

Certain control, relaying and instrumentation changes as well as temporary DC

switchyard changes may be required for back-to-back tests.

Before full end-to-end tests are performed, it is advisable to perform an open line

test and shorted line tests with the DC transmission line. This test can be

repeated from both ends to verify the integrity of the DC line.
End-to-end tests will then be conducted. These tests involve both stations and
the transmission line. With this operation power is transmitted for the first time.
This test is usually done on a monopolar basis first, with full bipolar operating
being the final step.
Having the complete system running properly in steady state operation, with
normal operating ramp settings and automatic switching sequences in place the
effect of a number of disturbances on the DC side of the system as well as in the
AC systems may be checked. Operation and integration tests verify the transient
and fault recovery behaviour of the HVDC system.
The HVDC system tests are now completed, all functions have been verified and
the HVDC system is ready to be handed over to the owners. The acceptance
tests necessary to verify whether acceptance criteria have been met may have
been performed all or In part during the commissioning period- To avoid
unnecessary duplication of such tests, careful consideration should be given in
advance as to when acceptance tests are carried out.

If acceptance tests are still outstanding or acceptance tests have to be repeated
due to modifications they should be performed at this time, or following trial
operation, as appropriate.
Finally it has to be ensured that the system also operates correctly over an
extended period of time. This is checked during the trial operation.

PAS 61975 © IEC:2004 (E) – 19 –

1.5 Structure of System Testing

– 20 – PAS 61975 © IEC:2004 (E)

PART 2: OFF-SITE TESTS
General
Introduction
This part describes the testing of the control equipment prior to it being shipped

to site. The following tests are outlined:
2.1 Steady state performance of the controls
2.2 Dynamic performance tests
2.3 Functional performance tests
2.4 Type tests on the control and protection equipments
Subsequent to the Routine Testing of the HVDC-System Control and Protection
equipment it is normal practice to check the steady state, the functional and the
dynamic performance of this equipment prior to it being shipped to site. These
tests provide the opportunity to set up the parameters of the control circuits
(though these set tings may have to be fine tuned later at site) and to obtain a
preliminary check on the performance of the equipment relative to the specified
requirements.
Performance of the protective functions of the converter, during various
simulated faults, can also be checked. This enables the equipment to be partly

commissioned off-site. It also provides the opportunity to detect and correct
hardware and software errors or deficiencies in the control and protection
systems.
PAS 61975 © IEC:2004 (E) – 21 –

To carry out the dynamic performance tests it is necessary to have a real time

HVDC simulator which includes representation of the AC systems, AC filters,

converter equipment, DC smoothing reactors, DC lines and DC filters. The

extent of the system representations should be sufficient to replicate resonances

as determined from previous studies. In general, a comprehensive simulation will

enable thorough fault tracing to be done and allow effective commissioning at

site.
As defined in Part 1 of this guide the control equipment is arranged in a
hierarchical structure and only the representative sections which will affect the
dynamic performance would be used for the dynamic tests. These controls would
be the closed loop control sections of the HVDC System Controls (Master
Control), Station Control, Pole Controls and Converter Control. The
telecommunication system and the valve base electronics would be appropriate.
The Valve Base Electronics would be appropriately simulated. Conventional
protection equipment would be omitted i.e. that for AC filters, DC filters and
converter transformers but the protection for the DC system would be included.
The control equipment as defined above needs not necessarily be that supplied
for the contract.
The real time simulator may also be used for the functional performance tests
but other forms of simulation e.g. by software models, are possible. For the
functional performance tests the complete control system shall be tested. Fault
recorders and Sequence of Event Recorders which are "stand alone
equipments" may not be included for the Functional Performance Tests. If these
recorders are not used the validity of output signals to these equipments would

be checked during the tests.
Finding and correcting hardware and software errors in the control system is an
important function of off-site testing. Such faults are easier to find and correct
off-site rather than during commissioning. Correcting such faults reduces the
probability of disturbing the Customers' power system during site commissioning.

– 22 – PAS 61975 © IEC:2004 (E)

The principles for off-site testing of the control system are as follows:

a) Controls, as defined above, should be present and connected in an identical

manner to the final site configuration. Possible exceptions are simple interface

equipment, Fault Recorders and Sequence of Events Recorders.

b) It is desirable that the test team acts independently from the equipment

design team to verify correct operation of the control system. The test team

shall include representatives from the commissioning group, the design
group and the test group. It is recommended that the customer takes a
significant role in this testing team in order to provide valuable experience
in training customers staff.
c) During the test period the equipment being tested shall be under the control
of the test team leader and no changes should be made without his
approval. Changes to the equipment should be recorded in conformity with
the defined Quality Assurance (QA) procedures, thus ensuring that the
tests are carried out on a known state of hardware and software.
d) An off-site test plan including AC system representations, DC configurations
and tests to be performed shall be mutually agreed between the manufacturer
and the customer in advance of the commencement of the tests.
Type testing, if required, can be carried out to demonstrate performance over the
specified environment, with variations of power supply voltage and simulation of
faults on auxiliary systems, to demonstrate the stability of the control and the
accuracy of protection settings. In addition it may be possible to demonstrate

interference immunity of the control and protection equipment, together with the
communication interface.
General Test Objectives
1. To check the steady state, the functional and the dynamic performance
of the control equipment and, if required, to carry out some of the type
tests for the control and protection equipment,
2. To make preliminary settings of the control parameters.

PAS 61975 © IEC:2004 (E) – 23 –

3. To provide confirmation of the design specifications and study results for

the control and protection equipment and also to provide test data for

comparison with that obtained during the operation and integration tests

defined in PART 6 of the guide.

4. To find and correct errors and deficiencies in the control and protection

hardware and software.
Preconditions for the Tests
1. For the functional performance tests the control and protection
equipment shall have passed all its routine tests.
2. For the functional performance tests the control and protection cubicles
shall be interconnected In the "as site" configuration.
3. An off-site test plan including AC system representations, DC
configurations and tests to be performed shall be mutually agreed
between the manufacturer and the customer in advance of the
commencement of the tests.
4. The studies defining the control strategies shall have been completed.
2.1   Steady State Performance of the Controls
Introduction
Before the functional and the dynamic performance test can be performed, the
steady state performance of the control equipment shall have been
demonstrated.
– 24 – PAS 61975 © IEC:2004 (E)

2.1.1 Measurements
General
The following measurements should only be regarded as typical since they will

vary with different control system designs.

Test Objectives
To confirm that the correct measurements are transmitted to the appropriate
points within the control equipment.
Test Procedure
All measurements shall be checked for appropriate level, polarity, phasing and
sequence at both source and destination.
- Line side voltage/test supply for valve firing;
- Valve winding currents;
- DC current and voltage;
- di/dt if applicable;
- Alpha and Gamma responses;
- Active and reactive power;
- Frequency.
2.1.2 Control and Protective Sequences
General
The sequences described in the Test Procedure can be checked with the
converter system off-load.
PAS 61975 © IEC:2004 (E) – 25 –

Test Objectives
To ensure that the operational sequences of the valve control and protection are

correct.
Test Procedure
Check that the correct sequence of events, with appropriate timings take place
during deblocking/blocking of the converter system.
Check that the valve firing pulse sequences sent to the firing controls are correct
Check that forced retard, valve refire and blocking signals are generated in the
correct locations and are transmitted to the correct locations.
Formation of bypass pairs should be checked if applicable.
2.1.3  Steady State Performance Tests Test Objectives
To ensure that the basic control functions meet the designed performance. The
following tests should be regarded as typical since they may vary with different
designs of control equipment.
Test Procedure
Verify the DC voltage and current static characteristics.

– 26 – PAS 61975 © IEC:2004 (E)

With the converter system deblocked check:

- Alpha and gamma order calibration;

- With the voltage and frequency of the AC systems varied over their normal

ranges of operation confirm that the current order can be varied over the full

range, DC voltage and current can be confirmed at different levels of currents

order, and that any prescribed limits are maintained;

- that the power order can be varied over the full range, the derived current
order may be confirmed at different levels of power order;
- block the rectifier and confirm the current error calibration and the correct re-
sponse of the gamma control loop.
Reduced DC Voltage Operation
Manual or automatic reduction of DC voltage may be required to reduce stresses
on DC cables when the power transfer level is being reduced, or to reduce the
possibility of flashover of overhead DC lines during extreme weather conditions
or conditions of excessive contamination.
Manual reduction will simply be cone by a selector switch operating the tap
changer control. With automatic operation check that the reduction occurs under
the designed conditions.
Protective shut-down
With minimum current order setting and the converter system deblocked apply a
protective blocking signal at the rectifier. Repeat with maximum continuous

current order setting. Confirm that correct blocking sequence occurs followed by
circuit breaker tripping if required. Repeat for protective blocking at the inverter
and with reversed power flow if appropriate.
Test Acceptance Criteria
For all the above tests the performance should conform to the system studies
and the design parameters.
PAS 61975 © IEC:2004 (E) – 27 –

2.2   Dynamic Performance Tests

Introduction
For the dynamic performance tests only the closed loop controls of the HVDC

System Control (Master Control), Station Control, Pole Controls and Converter

Controls would be used. The telecommunication system shall be adequately

simulated. Protection for the DC system would also be included. Tests would be

performed using a real time HVDC Simulator. The control equipment hardware
used for the representation need not necessarily be that supplied for the
Contractor, but should be functionally identical. If the idea is to check software
and hardware problems, they should be supplied by the Contractor's equipment.
Test Objectives
1. To check that measurements for the controls are of the correct
magnitude and phasing.
2. To check that the sequences for deblocking/blocking, the firing sequence
for the valves, and the signals for forced retard, refire bypassing and
blocking are correct.
3. To check the stability and response of the controls during transient
disturbances.
4. To make preliminary settings of the control parameters.

5. To check the correct operation of the protective functions for various
types of faults in the DC system and the associated AC systems.
6. To find and correct any hardware deficiencies and software errors.
7. To check the interaction between the AC and DC systems under all
relevant operating conditions.
8. Crosscheck against digital studies for consistency.

– 28 – PAS 61975 © IEC:2004 (E)

Preconditions for the Tests
In addition to the general preconditions the following must be fulfilled.

1. The preliminary control parameters as defined by the controls design

study have been installed.
2. The set points, thresholds and time delays of the protective relays as

defined by the protection co-ordination study have been checked by
injection tests.
3. The steady state performance defined in section 2.1 shall have been
demonstrated.
Test Procedures
The procedure for each of the following tests will be described separately in
each section.
2.2.1 Control - Step Response
2.2.2 Control Mode Transfer
2.2.3 AC System Interaction/Control
2.2.4 Commutation Failures and Valve Misfires
2.2.5 AC Filter, Transformer and Reactive Element Switching
2.2.6 AC and DC System Faults
2.2.7 Islanding
All tests for optimization and verification of the controls and protection dynamic
performance require a similar recording and monitoring set-ups as listed below,
in cases where additional or different set-ups are required these are listed in the
individual sections.
The results of these tests will be used as references for the end-to-end tests and
the operation and integration tests at site and it is desirable that similar
recording equipment and test report formats are used for both test sequences.

PAS 61975 © IEC:2004 (E) – 29 –

Where practical the following should be monitored:

- Current or power order
- DC current
- DC voltage
- Alpha order
- Alpha response
- Gamma response
- Control mode identification
- AC busbar voltages and frequency
- Valve winding AC currents
- DC power
- Reactive power
- Forced retard, blocking and initiation commands
- Valve firing sequence
- Tap position indications (if available)
2.2.1  Controls-Step Respons
...