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TB 657 2016 Guidelines for the preparation of "connection agreements" or "Grid Codes" for multi-terminal schemes and DC Grids

In the light of recent advancement of HVDC technology and the prospect of DC grid projects a need to address the required guide lines to develop the DC grid codes has arisen. Grid Codes or network codes are a set of rules and guidelines that govern a power system environment with multiple stakeholders, which describe e.g. the technical requirements that the equipment must fulfil in order to be integrated in the system and the rules and guidelines for interactions between the systems and stakeholders under steady state or abnormal operation conditions. This brochure provides recommendations on the models of interactions between the stakeholders and activities from planning to operation including technical aspects of planning, building and operation of a DC grid. Based on these recommendations a specific (set of) grid code(s) can be developed for the DC grid. The focus of this document is on the MTDC grids, and not on the HVAC networks which are connected to these DC grids. The objective of this brochure is to support the concerned stakeholders i.e. system planners, system operators (SO) and system users, to develop their own particular DC grid code.

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TABLE OF CONTENTS

1 STAKEHOLDERS AND ACTIVITIES FROM PLANNING TO OPERATION OF DC GRIDS

   1.1 Introduction

   1.2 Overview of Planning Activities

      1.2.1 Long and Med. Term Development Planning

      1.2.2 DC Grid Planning

      1.2.3 HVDC Project Specific – Technical Specification

   1.3 Description of Project Specific Execution Activities

      1.3.1 Design

      1.3.2 Manufacturing and Construction

      1.3.3 Commissioning

   1.4 Overview of Operation Activities

      1.4.1 Short and medium term Operation

      1.4.2 Real Time Operation

      1.4.3 Protection

   1.5 Description of Stakeholders / Actors

      1.5.1 DC Grid Users

      1.5.2 Regulator

      1.5.3 DC Grid Asset Owners

      1.5.4 AC/DC Power System Planner

      1.5.5 DC Grid Specification Provider

   1.6 Description of Designer & Implementation Stakeholder

      1.6.1 HVDC Consultancy Providers

      1.6.2 HVDC Project

      1.6.3 HVDC Technology Provider

   1.7 Description of Operator Stakeholder

      1.7.1 AC Grid Operator

      1.7.2 DC Grid Operator

2 PLANNING CODE - OVERVIEW

   2.1 Principles for planning a DC Grid

      2.1.1 Basic principles

      2.1.2 Methodology for planning a DC Grid

      2.1.3 AC & DC Network Development Plan

      2.1.4 Preliminary technical considerations for planning a DC Grid

         2.1.4.1 Fault handling

         2.1.4.2 Energy Balance

         2.1.4.3 Power flow control

         2.1.4.4 Standardization and Inter-operability with different components

   2.2 Planning criteria of the DC Grid

      2.2.1 Introduction

      2.2.2 Technical Criteria

      2.2.3 Contingencies

         2.2.3.1 Contingency definitions

         2.2.3.2 System definition

         2.2.3.3 Response to N-k outages

      2.2.4 Planning minimum and max. capacities for power exchange in a DC node

   2.3 Technical performances of the DC Grid

      2.3.1 Steady state DC voltages

      2.3.2 Transient and temporary DC voltage profiles

      2.3.3 Steady-state DC current

      2.3.4 Maximum Short circuit current

      2.3.5 Inrush Currents

      2.3.6 Overload capability

      2.3.7 DC harmonic performance

      2.3.8 Insulation Coordination

      2.3.9 Measurement Tolerances

      2.3.10 Modelling of DC Grids

3 CONTROLS AND PROTECTIONS:

   3.1 Steady state characteristics

   3.2 Normal operation control modes

   3.3 DC Grid primary control

   3.4 DC Grid secondary control

   3.5 DC current regulation and control

   3.6 Stability

   3.7 Response during system dynamics and transients

   3.8 System energization

   3.9 Fault ride-through

   3.10 Under-voltages

   3.11 Over-voltages

   3.12 Detection of DC faults

   3.13 Protection against local and system faults

   3.14 Response after a DC fault clearing

   3.15 Compatibility with the existing DC Grid

   3.16 Model of Converter Controls and Cables

      3.16.1 Model compatible with existing simulation tools

      3.16.2 Simulation studies to be performed

   3.17 Reliability and Availability Requirements

4 OPERATION CODE FOR DC GRIDS

   4.1 DC Grid operating states and codes;

      4.1.1 Normal mode of operation (Green):

      4.1.2 Alert mode of operation (Yellow):

      4.1.3 Emergency mode of operation (Red):

   4.2 Normal operation state, connection and disconnection of converter stations and cables

      4.2.1 Security criterion:

   4.3 Energizing of subsystems or components from the DC side

      4.3.1 Energizing of subsystems or components from the AC side

   4.4 Operation during and after fault conditions

      4.4.1 Faults on the AC side;

      4.4.2 Faults on the DC side;

   4.5 Alert mode of Operation under DC voltage contingencies

   4.6 Emergency procedures in case of forced outages

   4.7 Operation and maintenance of the grid

   4.8 Dispatching regulations

   4.9 Energy balance

   4.10 Contribution to the DC ancillary services (centralized control, damping…)

   4.11 Performance checking and monitoring

   4.12 Information on scheduled outages

   4.13 Congestion management

   4.14 Ancillary Services

   4.15 Ancillary Services for DC Grids

      4.15.1 DC Energy Balance and Reserves

      4.15.2 DC transmission capacity reserve and power flow control

      4.15.3 DC Loss Compensation

      4.15.4 Energizing of DC subsystems, DC black start and restoration

   4.16 References

5 CONNECTION CODE

   5.1 Right of access to the DC grid

   5.2 Regulatory considerations

   5.3 Access procedure

   5.4 Connection procedure

   5.5 Operation Notification Procedure

   5.6 Operational Interface Agreement

6 DATA EXCHANGE CODE

   6.1 Introduction

   6.2 Long Term Planning data

   6.3 Pre-Project phase

   6.4 Project Specific Execution

   6.5 Operation of DC Grid

ACRONYMS AND ABBREVIATIONS