Requirements for Protection and Control Systems for Landsnet’s Customers

Version 1.0 approved on 11.08.2023, ERS

Introduction

This document outlines the requirements for Landsnet's customers regarding control and protection equipment. The aim is to ensure that faults in the customers’ systems have as insignificant impact on the transmission system as possible.
For this purpose, Landsnet specifies the same requirements, regarding control and protection, to its customers as Landsnet does to the transmission system.

The Grid System

The Icelandic transmission grid consist of a 220 kV main grid in the South-West and NorthEast part of the country, a 132 kV ring connection surrounding the island that connects the two 220 kV networks and 132-, 66- and 33 kV that make up the regional transmission-network.
The Icelandic Grid is a directly grounded system and Landsnet’s protection philosophy is arranged accordingly. All customers must be connected to the transmission system via transfomer with a directly grounded star-point on the transmission grid side.

System Requirements to Customers

Validity:

These principles apply to new stations as well as refurbishing and extensions of existing stations.

Requirements for protection:

Using these principles, it is possible to fulfill the protection requirements set by Landsnet. Tripping a faulty component shall have as little effect on the operation of the transmission system as possible. Fault-clearing shall impose no risk to humans, property or system components.
The protection- and control systems shall be designed so that the risk of unwanted operation is minimized.

1. All short-circuits and winding faults shall be detected by at least two independent protection systems.
2. One of the two protection systems must fulfill requirements on minimum fault-clearing time of 100 ms and selectivity.
3. Under normal circumstances all short-circuits shall be cleared selectively. The following faults might cause unselective tripping:
   1. A fault in the protection system, both redundant and non-redundant.
   2. A fault in the circuit breaker.
   3. A fault between circuit breaker and current transformer.
   4. A broken conductor fault.
4. The protection system shall, under normal circumstances, isolate a faulty component from the rest of the power system.
5. All components in the 220 kV, 132 kV and 66 kV shall have a non-directional earth fault protection with RXIDG-characteristic
6. The protection system shall not trip during transient, dynamic, or abnormal stationary conditions caused by: fault clearing, switching, islanding, energizing, load shedding or loss of production units.
7. The protection of system components on voltage levels below 66 kV shall be selective against the protections in the main transmission system.
8. The current transformers used for protection purposes shall be of class 5P and must be designed not to reach CT-saturation under any circumstances based on the respective short-circuit power in the system.
9. The control and protection for the HV switchgear shall be done in a secure way following common practices i.e., regarding interlocks, trip logic etc.

Control and Protection

Transformers 30MVA or larger must be controlled via single pole control equipment.

A summary document showing the main functions of Control and Protection can be found in the appendix. The table is not finite but is meant to show the main philosophy. Each case shall be evaluated individually.

When connecting a new Customer to the Grid, some electrical connection for control, interlock and signaling might be required.

Landsnet will provide further information on control and protection upon request.