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BSI PD CLC/TR 50609:2014

BSI PD CLC/TR 50609:2014

$215.11

Technical Guidelines for Radial HVDC Networks

Published By Publication Date Number of Pages
BSI 2014 124
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This Technical Report applies to HVDC Systems having more than two converter stations connected to a common DC network, also referred to as HVDC Grid Systems. Serving the near term applications, this report describes radial HVDC network structures as well as pure VSC based solutions. Both grounded and ungrounded DC circuits are considered.

Based on typical requirements applied to state of the art HVDC converter stations today this report addresses aspects that are specifically related to the design and operation of converter stations and DC circuits in HVDC Grid Systems. The requirements from the AC systems as known today are included. Secondary effects associated with changing the AC systems, e.g. the replacement of rotating machines by power electronic devices, are not within the scope of the present report.

The report summarizes applications and concepts of HVDC Grid Systems with the purpose of preparing the ground for standardization of such systems.

The interface requirements and functional specifications given in this document are intended to support the specification and purchase of multi-vendor multiterminal HVDC Grid Systems.

PDF Catalog

PDF Pages PDF Title
9 Foreword
10 0 Introduction
0.1 The European HVDC Grid Study Group
11 0.2 Technology
0.2.1 Converters
0.2.2 DC Circuit
12 Figure ‎1-1 — Example of an HVDC Grid System having a meshed and radial structure
0.2.3 Technological Focus of the European HVDC Grid Study Group
14 1 Scope
2 Terminology and abbreviations
2.1 General
2.2 Terminology and abbreviations for HVDC Grid Systems used in this report
15 2.3 Proposed Terminology by the Study Group
16 3 Typical Applications of HVDC Grids
3.1 The Development of HVDC Grid Systems
17 3.2 Planning Criteria for Topologies
3.2.1 General
18 3.2.2 Power Transfer Requirements
19 3.2.3 Reliability
21 3.2.4 Losses
23 3.2.5 Future Expansions
3.3 Technical Requirements
3.3.1 General
24 3.3.2 Converter Functionality
25 3.3.3 Start/stop Behaviour of Individual Converter Stations
26 3.3.4 Network Behaviour during Faults
27 3.3.5 DC-AC Interface Requirements
28 3.3.6 The Role of Communication
29 3.4 Typical Applications – Relevant Topologies
3.4.1 General
3.4.2 Radial Topology
30 a) One offshore wind power plant with connection to two (non-synchronized) AC systems
b) Two offshore wind power plants with connections to two AC systems
c) Two offshore wind power plants with cross connected parallel DC sea cables connected to one AC systems
Figure ‎3-1 — Radial HVDC VSC system topologies illustrating possible configurations of the Kriegers Flak Combined Grid Solution
31 3.4.3 Meshed Topology
Figure ‎3-2 — Meshed HVDC Grid System topology with redundancy by means of DC connectors
3.4.4 HVDC Grid Systems Connecting Offshore Wind Power Plants
32 Figure 3-3 — Possible grid-connection topology of approximately 1 000 MW offshore wind power at Kriegers Flak to two onshore not-synchronized AC systems of Denmark-East and Germany
3.4.5 Connection of a wind power plant to an existing HVDC VSC link
Figure 3-4 — Connection arrangements of a new offshore wind power plant to an existing HVDC Grid System
33 4 Principles of DC Load Flow
4.1 General
4.2 Structure of Load Flow Controls
4.2.1 General
4.2.2 Converter Station Controller
34 4.2.3 HVDC Grid Controller
4.2.3.1 General
4.2.3.2 Steady State Load Flow Control
35 4.2.3.3 Dynamic Load Flow Control
36 4.3 Converter Station Control Functions
4.3.1 General
4.3.2 DC Voltage (UDC) Stations
4.3.3 Active Power (PDC) and Frequency (f) Controlling Stations
37 4.4 Paralleling Transmission Systems
4.4.1 General
4.4.2 Paralleling on AC and DC side
4.4.3 Paralleling on the AC side
38 Figure 4-1 — Network showing parallel operation of converters in various configurations (example)
4.4.4 Steady-State Loadflow in Hybrid AC/DC Networks
39 Figure 4-2 — Active power flow through a DC Grid
40 Figure 4-3 — Wheeling active power between the AC and DC grids
4.5 Load Flow Control
4.5.1 DC Voltage Operating Range
41 4.5.2 Static and Dynamic System Stability
4.5.3 Step response
42 Figure 4-4 — Dynamic Response Parameters
4.6 HVDC Grid Control Concepts
4.6.1 General
43 Table ‎4-1 — Requirement for HVDC Grid Controls
47 4.6.2 Voltage-Power Droop Together with Dead Band
4.6.2.1 General
4.6.2.2 Steady State DC Voltage Control
4.6.2.3 Dynamic DC Voltage Control
48 Figure 4-5 — Example of characteristics for five converters connected to a DC grid related to local DC voltage. The small squares are the steady-state operating points of the converters [CIGRE Technical Brochure No 533 [25]]
49 4.6.2.4 Block diagram for droop control with dead-band
50 Figure 4-6 — Block diagram for droop control with dead-band as used in power controlling converters
Figure 4-7 — Block diagram for droop control with dead-band used for the DC voltage controlling converter
4.6.3 Voltage-Current Droop
4.6.3.1 Control of the HVDC Grid Voltage
51 Figure 4-8 — An HVDC converter slope control characteristic
4.6.3.2 HVDC Grid Common Control Block
52 Figure 4-9 — A basic controller for DC converter in a HVDC Grid System
4.6.3.3 Converter Interaction
53 Figure 4-10 — A Two-terminal HVDC Grid System with zero power flow
Figure 4-11 — A Two-terminal HVDC Grid System with power flow A to B
54 Figure 4-12 — Increased demand at Converter B
Figure 4-13 — HVDC Grid Controller optimization of the DC load flow
55 Figure 4-14 — A Two-terminal HVDC Grid System with power flow B to A
4.6.3.4 Power Flow Control
4.6.3.5 Voltage Optimizer
56 4.6.4 Voltage-Power Droop — Control of the HVDC Grid Voltage
Figure 4-15 — Schematic drawing of a HVDC Grid System illustrating the power, voltage and current measurement as applied for Formulae (4-1), (4-2) and (4-3)
57 Figure 4-16 — Overview of a Converter Station Controller
58 Figure 4-17 — Voltage-Current Characteristic of the HVDC Converter Station Controller
Figure 4-18 — Control Characteristic for and
59 Figure 4-19 — Operating Boundaries for Control
Figure 4-20 — Ud-Id Diagram of a HVDC Grid System
4.7 Benchmark Simulations of Control Concepts
4.7.1 Case Study
60 Table 4-2 lists the individual benchmark cases analysed.
4.7.2 Results
Figure 4-21 — Benchmark Model
61 Figure 4-22 — Benchmark grid parameters
Table 4-2 — Benchmark cases
62 Figure 4-23 — Case 8 – Steady State after disconnection of Station A
Figure 4-24 — Case 10 – Steady State values after disconnection of Station C
4.7.3 Conclusions
63 4.7.4 Interoperability
5 Short-Circuit Currents and Earthing
5.1 General
5.2 Calculation of Short-Circuit Currents in HVDC Grid Systems
65 5.3 Network Topologies and their Influence on Short-Circuit Currents
5.3.1 Influence of DC Network Structure
66 a) Point-to-point connection
b) Radial structure
c) Meshed grid
Figure 5-1 — Topologies of HVDC Grid Systems
67 Figure 5-2 — Short-circuit current in a radial network topology with a variable number of converter stations
68 5.3.2 Influence of Line Discharge
Figure 5-3 — Example of Short-circuit current for a line-to-earth fault (earthed cable shield and point-to-point connection)
69 Figure 5-4 — Example of Short-circuit current in case of a line-to-earth fault at an overhead line for a combined overhead line/cable connection (earthed cable shield and point-to-point connection)
5.3.3 Influence of Capacitors
70 Figure 5-5 — Equivalent circuit of a capacitor bank
Figure 5-6 — Example of the Contribution of a capacitor to a short-circuit current
71 5.3.4 Contribution of Converter Stations
72 Figure 5-7 — Current Types of converters
73 Figure 5-8 — Equivalent circuit of the converter for the short-circuit calculation
74 Figure 5-9 — DC side short-circuit current of a MCC Half Bridge type Converter [20]
Figure 5-10 — DC side short-circuit current of a MMC Full Bridge type converter
5.3.5 Methods of Earthing
75 Figure 5-11 — DC line fault cases and grounding methods of the DC circuit
5.4 Secondary Conditions for Calculating the Maximum/Minimum Short-Circuit Current
76 5.5 Calculation of the Total Short-Circuit Current (Super Position Method)
77 Figure 5-12 — Standard approximation function according to [18]
5.6 Reduction of Short-Circuit Currents
78 Figure 5.13 — Measures to reduce short-circuit currents (Single line diagrams) a) system separation b) current limiting reactor c) high-speed decoupling d) HVDC link
6 Principles of HVDC Grid Protection
6.1 General
79 6.2 HVDC Grid System
Figure 6-1 — Principle structure of a HVDC Grid System
80 Table 6-1 — Fault isolation time and breaking device type required
6.3 AC/DC Converter
6.3.1 General
81 Figure 6-2 — Definition of the Points of Common Connection on the AC and DC side
6.3.2 DC System
82 6.3.3 HVDC Switchyard
6.3.4 HVDC System without Fast Dynamic Isolation
6.3.5 HVDC System with Fast Dynamic Isolation
83 6.4 DC Protection
6.4.1 General
6.4.2 DC Converter Protections
84 Figure 6-3 — Typical Protections System for a symmetrical monopole VSC Converter
85 6.4.3 Protective Shut Down of a Converter
86 6.4.4 DC System Protections
6.4.5 DC Equipment Protections
6.5 Clearance of Earth Faults
6.5.1 Clearance of a DC Pole-to-Earth Fault
87 6.5.2 Clearance of a Pole-to Pole Short Circuit
6.5.3 Clearance of a Converter side AC Phase-to-Earth Fault
Figure 6-4 — Clearance of converter side AC phase to earth fault by breaker BL
7 Functional Specifications
7.1 General
88 7.2 AC/DC Converter Stations
7.2.1 DC System Characteristics
7.2.1.1 Voltages
89 7.2.1.2 Short-Circuit Characteristics
7.2.1.3 Insulation Levels
7.2.1.4 Specific Creepage Distances
90 7.2.1.5 Harmonic Voltage Distortion
7.2.1.6 Control Interaction
7.2.1.7 Network Stability Equivalents
7.2.1.8 System Grounding
91 7.2.2 Operational Modes
7.2.2.1 Concept of Fault Clearing
Table 7-1 — Fault isolation time and switching device type required
7.2.2.2 Operational Modes and Operational Options
93 7.2.2.3 Short-Circuit Current Contribution of Converter Station
94 7.2.2.4 DC Side Harmonic Performance Requirements
7.2.2.5 Insulation Coordination
7.2.2.6 Converter Control and Protection
97 7.2.3 Testing and Commissioning
7.2.3.1 General Requirements
7.2.3.2 Factory Tests
7.2.3.3 Site Tests
98 7.3 HVDC breaker
7.3.1 System Requirements
7.3.2 System Functions
7.3.3 Interfaces and Overall Architecture
7.3.4 Service Requirements
7.3.5 Technical System Requirements
99 Table 7-2 — HVDC breaker system requirements
101 Annex A (informative) HVDC – Grid Control Study
103 Figure A.1 — Case 8 voltage values
Figure A.2 — Case 8 current values
104 Figure A.3 — Case 8 power values
106 Figure A.4 — Case 10 voltage values
Figure A.5 — Case 10 current values
107 Figure A.6 — Case 10 power values
108 Annex B (informative) Fault Behaviour of Full Bridge Type MMC
B.1 Introduction
B.2 Test Results
B.3 DC to DC Terminal Faults
109 B.4 DC Terminal to Ground Faults
B.5 Conclusion
110 Figure B.1 — Multi-Modular Full Bridge Voltage Source Converter
111 a) Rectifier End
Figure B.2 (continued)
112 b) Inverter End
Figure B.2 — DC to DC fault at Rectifier
113 a) Rectifier End
Figure B.3 (continued)
114 b) Inverter End
Figure B.3 — DC to DC fault at Inverter
115 a) Rectifier End
Figure B.4 (continued)
116 b) Inverter End
Figure B.4 — DC to Ground fault at Rectifier
117 a) Rectifier End
Figure B.5 (continued)
118 b) Inverter End
Figure B.5 — DC to Ground fault at Inverter
119 a) Rectifier End
Figure B.6 (continued)
120 b) Inverter
Figure B.6 — DC to Ground fault at Inverter (No Converter Protection Action)
121 Bibliography

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BSI PD CLC/TR 50609:2014
$215.11