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Rio Tinto Alcan ISAL Smelter in Iceland Expansion Project

Introduction

The power intensive industry, which is characterised here as manufacturersneeding more than 7 MWh/t of theiroutput product, is highly dependent on the technological development of the manufacturing companies in the areas of products conveying, transforming, switching and controlling power at medium and high voltages.

It is of mutual benefit to these companies to cooperate for continuousimprovements of quality and efficiency of their products and processes. For Rio Tinto Alcan (RTA), HSE (Health-Safety-Environment) aspects of their equipment and production processesare paramount in their evaluationfor construction and operationpotential.

The engineering and production technique of ABB in the field of SF6 insulated switchgear, has presently reached such a level that smelters

with high HSE-demands combined with high demands of availabilityand reliability of equipment, cantake confidence in choosing medium voltage switchgear.

The specific properties of SF6 are further outlined below.

Electrical Properties

The excellent dielectric properties of SF6 are attributable to the electronegative character of its molecule. It has a pronounced tendency to capture free electrons forming heavy ions with low mobility, making the formation of electron avalanches very unlikely. The dielectricstrength of SF6 is about 2,5 times higher than that of atmospheric air under the same conditions, and this leads to space demand of only 1/10th of conventional air insulated switchgear. This fact is decisive for

economical considerations in many cases for voltage levels of 33 kV and higher.

Chemical Properties

SF6 can be heated to 500°C without decomposition in the absence of catalytic metals. SF6 is non-flammable. Therefore, the risk of ignition caused by an SF6 switchgear malfunction is practically zero, as well as the risk of damage caused by an external fire is as limited as possible. The fault current interruption capability of SF6 is excellent. In its pure state, SF6 is nontoxic, and this is regularly confirmed on new gas prior to delivery, by placing mice in a gas mixture of 80 % SF6 and 20% oxygen for a period of 24 hours (biological test recommended by IEC 376).

220kV AIS Footprint

Operation and Maintenance

The temperature within an arc in the interruption chamber can be 15 000K. However, only minor decomposition remnants are present after each interruption. CIGRE WG 23.10 is working on an SF6 recycling guide, covering purity criteria for SF6 SWG. Criteria for handling of SF6 are based on IEC 376 Standards for safety of personnel and environment.

These factors contribute in minimizing emissions to the atmosphere. The normal leakage rate of HV Switchgear can be expected to be 0,1 % - 0,5 % per year.

Only authorised personnel are entitled to work with SF6 in Iceland and other EEA (European Economic Area – an outer Layer of the EU) countries, as mandated by an EU directive. Two electricians of our substation staff have passed through tests after theoretical and practical training of SF6 Gas Treatment with ABB nearMannheim in Germany.

RTA ISAL have acquired special equipment which is dedicated for the sampling, testing, emptying and refilling purposes.

RTA ISAL keeps track of its mass of gas by annually weighing the reserve gas and by having SF6 gas detectors in the switchgear room and in the cable cellar connected to the alarm system of the substation. The pressure gauges of each gas compartment are read off once a week. They are also equipped with a warning and alarm/trip level.

Environmental Aspects

SF6 does not contribute significantly to stratospheric ozone depletion, as it contains no chlorine, which is the main agent in ozone catalysis, nor to the Greenhouse effect, because the quantities present in the atmosphere are very small.

SF6 has infrared absorption characteristics and is considered a minuscule Greenhouse gas, due to its very long lifetime in the atmosphere. It's contribution to global warming however is very small, due to the extremely low concentration of SF6 in the atmosphere.

Assessment on Engineering:

The experience of most, if not all, users of SF6 switchgear, for a wide range of operating conditions, is that this technology has brought advantages in performance, size, weight, global costs and reliability.

However, for this endeavour to be implemented, it is necessary to perform a rigid risk analysis. This is carried out jointly by knowledgeable consultants with experience on operation, the operators and maintenance staff of the owner, and the manufacturer. The findings of such risk analysis and an SQRA (Semi Quantitative Risk Analysis) shall form the basis for the engineering of the switchgear.

The modern SF6 Switchgear, as for instance manufactured by ABB in Germany, is an extremely safe equipment against Arc Flash. In spite of this, the standard policy of RTA ISAL is to control it remotely from the control rooms.

Switchgear Room:

The IPU project (ISAL Production Upgrade) needed space for the installation of 13 bays of 60 kV Circuit Breakers on double busbar. Due to the limited space available near the seaside, accommodating an air insulated switchgear would not have been possible without costly landfill. The gas-insulated switchgear (GIS) technology offered a feasible solution on the available land. It was therefore decided to construct a concrete building beside the two 220/60 kV, 200 MVA, bays for the Step-down transformers feeding each half of both 60 kV busbars. The link from the

ABB’s latest development in GIS has been to reduce the overall footprint drastically

Out of the total contribution of allagents, the contribution of SF6 (lessthan one part in ten thousand, 0,1promille) is negligible.

secondary of these Step-downs is an SF6 insulated busbar.

Control System

ISAL‘s main substation is supervised by an Allen-Bradley Control Logix controller, SuperMaster, that monitors the status of high voltage and auxiliary equipment, interfaces with Landsnet, the national grid operator, and controls transformer cooling, filter banks and collects usage data (energy, water consumption, etc.). Landsnet can enforce automatic curtailment of plant load remotely from their National Control Centre. The required load reduction is divided among the potlines and adjusted for plant power variations by the SuperMaster.

The new high voltage (HV) equipmenttransformers, 220kV air-insulated switchgear (AIS) and 60kV gas-insulated switchgear (GIS) are controlled and supervised by ABB Relian protective relays. A communication gateway, ABB COM600, passes information between the protective relays (status, process values, commands, etc.) and SuperMaster, as well as the InTouchSCADA system. In case of failure of the plant‘s SCADA system, the COM600 can be used for supervision and control of the HV equipment.

Each of the potlines is controlled,

protected and supervised by its respective potline current controller. PL1 and PL2 are controlled by state ofthe art A-B Control Logix controllers and PL3 by an ABB Controller (PSR). The existing diode rectifer units of PL1 and PL2 are directly controlled by their potline controllers, but rectifier units of potline 3 are each controlled by anABB PSR. In case of a potline master controller failure, all rectifier units can be operated manually in stand-alone mode.

The new rectifier units are each controlled by a specialized ABB AC800 PEC rectifier controller. The new units fulfill the same requirement, as the existing ones, of being able to provide current to their potline in the absence of a potline controller, in a stand-alone mode.

Communications:

As the IPU project was one of integrating new equipment with existing equipment, several communication paths had to be developed.

• SuperMaster / COM600 communicate through a serial link using the IEC 60870- 5-101 protocol. A ProSoft module for the Control Logix platform is used

This technique demanded a high degree of precision in the civil part and in installation of transformers and switchgear. Avoiding cable connection here, offers the possibility of undistorted condition analysis of the transformers among other benefits.

On the GIS, the local manoeuvring cubicles have indicators for the position of the respective switches. However, for safety reasons, normally the manoeuvring of the switches takes place at the substation’s SCADA system, or in one of the two new Control Rooms constructed by IPU.

The GIS-room is fitted with an overhead crane. This was integrated

with the installation of the switchgear, and can be utilized in repair of the switchgear if required.

The GIS is not particularly maintenance demanding, but ISAL intends to incorporate it in its switchgear maintenance scheme, recording the pattern of the control circuit of the trip coils, the pattern of the main current under the interruption period and to record the length of the total interruption period.

This article was originally published in Aluminium World Journal, produced by Global Media Communication Ltd.

and software was developed to pass information and commands back and forth.

• InTouch SCADA / COM600 as well as Relian / COM600 communicate over Ethernet using the IEC 61850-8-1 protocol. Paths 1) and 2) are completely independent, allowing the SuperMaster to supervise operation and to generate redundant alarms/ warnings in case of break down of COM600 / SCADA communications.

• SuperMaster / PML power monitoring devices ION 7600 communicate through an RS-485 link using the Modbus RTU protocol. A ProSoft module for the Control Logix platform is used and software was developed to collect data from the intelligent power meters. Supervision and redundant control of plant power transformer OLTC voltage regulators (21 kV) is also done via a Modbus link.

• InTouch SCADA / PML power monitoring devices communicate over Ethernet. A proprietary Schneider Electric (ex. Power Measurement Limited of Canada) ION Enterprise system collects detailed data from the ION 7600 meters, transients, sag/swell, power quality and historical data into a MS SQL database.

• Potline Controllers PL1 and PL2 / AC 800 PEC rectifier controllers communicate over Ethernet using the EtherNet/IP protocol. The interface on the PEC side is an Anybus module developed by HMS Industrial Networks. As the EtherNet/IP Anybus module‘s implementation allows only point to point communication, gateways were required for the swing units

S1 and S2, as they can be connected to any potline and therefore have to be able to communicate with all the potline controllers. The seamless integration of the PEC controllers of the rectifier units makes them appear as Allen-Bradley equipment to the rest of the world (SCADA, MES, potline controllers, etc.)

• Potline Controller PL3 PSR / AC 800 PEC rectifier controllers S1 and S2 communicate over an ABB proprietary PowerLink using an ABB PSR-PSR protocol.

• The four AC 800 PEC controllers communicate with each other through a dedicated redundant PowerLink.

In Conclusion

As demonstrated by the Rio TintoAlcan Isal Smelter Production Upgrade project, GIS can be integrated into existing facilities to support expansion and power supply for smelters with high energy and health and

safety requirements. SF6 insulated switchgear is an environmentally friendly and safe technology, with excellent operational capacities.

An upgrade can be fully tailored through engineering solutions to work with, and around, existing technologies, even where space restrictions may need to be considered.

Furthermore, the communication and control systems are designed to integrate seamlessly with existing ones, to provide flexibility and economical advantages, while securing optimal performance.

Authors: Bjarni Jonsson, RTA ISAL, Leader of Electrical Services, Haflidi Loftsson, Staki ehf, Chief Engineer and Max Wiestner, Head of the Aluminium business within ABB.

For more information Contact: ABB Switzerland Ltd.

Aluminium, BU- Industrial Solutions Max Wiestner,

Phone: +41 58 586 85 Email: max.wiestner@ch.abb.com

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