to-hq-02-011 rev 00 philosophy for general electrical design.pdf

OMV Exploration & Production GmbH

00 Final Issue RAW 27/5/05 JEA 31/5/05 PZ 31/5/05 MF 3/6/05

A2 Client Comments Incorporated RAW 15/4/05

A1 Issued for Comment/Approval RAW 25/1/05

Issue Rev

Issue or Revision Description Origin By

Date Chkd By

Date Appd By

Date Appd By

Date

Philosophy for

Electrical Design Onshore

Document Number

TO-HQ-02-011-00


Document Number Rev Page Philosophy for Electrical Design

Onshore TQ-HQ-02-011 00 2 of 27

Revision Description of revisionA1 For Comment/Approval

A2 Client Comments Incorporated

00 Final Issue




Contents

1.0 PREFACE .......................................................................................................................5

2.0 DEFINITIONS .................................................................................................................5

3.0 ABBREVIATIONS...........................................................................................................5

4.0 INTRODUCTION.............................................................................................................5

5.0 APPLICABLE CODES, STANDARDS AND REGULATIONS........................................6 5.1 Codes and Standards List ........................................................................................................ 6 5.2 References ................................................................................................................................. 9

6.0 SYSTEM GOAL ..............................................................................................................9

7.0 SYSTEM BOUNDARIES ................................................................................................9

8.0 DESIGN PHILOSOPHY..................................................................................................9 8.1 General ....................................................................................................................................... 9 8.2 Flammable Gas/Vapour Hazards............................................................................................ 10 8.3 Standardisation of Equipment and Materials........................................................................ 11 8.4 Certificates, Declarations and Test Reports ......................................................................... 11 8.5 Quality Assurance and Control .............................................................................................. 11

9.0 DESIGN REQUIREMENTS...........................................................................................11 9.1 General ..................................................................................................................................... 11 9.2 Classification of Loads ........................................................................................................... 13 9.3 Load Assessment and Electricity Consumption .................................................................. 13 9.4 System Voltages and Frequency............................................................................................ 13 9.5 Supply Capacity....................................................................................................................... 13 9.6 Power Generation .................................................................................................................... 13 9.7 Transmission and Distribution Systems ............................................................................... 14 9.8 Switchgear................................................................................................................................ 14 9.9 Electric Motors......................................................................................................................... 16 9.10 General Lighting ...................................................................................................................... 16 9.11 Emergency and Escape Lighting ........................................................................................... 16 9.12 Short Circuit Ratings............................................................................................................... 17 9.13 Electrical Protection ................................................................................................................ 18 9.14 Earthing .................................................................................................................................... 19 9.15 Uninterruptible, Maintained Power Supplies ........................................................................ 21




9.16 Integrated Control Systems (ICS)........................................................................................... 22

10.0 DESIGN CONSIDERATIONS .......................................................................................22 10.1 General ..................................................................................................................................... 22

11.0 DESIGN CRITERIA.......................................................................................................23

12.0 MAINTENANCE IN DESIGN ........................................................................................23

13.0 DOCUMENTATION REQUIREMENTS.........................................................................24

14.0 CERTIFYING AUTHORITY REVIEW REQUIREMENTS..............................................27




1.0 PREFACE

This Philosophy defines the OMV Exploration & Production GmbH corporate policy on the design of Electrical Systems for onshore hydrocarbon production and processing facilities. The document specifies basic requirements and criteria, defines the appropriate codes and standards, and assists in the standardisation of facilities’ design across all onshore operations.

The design process needs to consider project specific factors such as the location, production composition, production rates and pressures, the process selected and the size of the plant. This philosophy aims to address a wide range of the above variables, however it is recognised that not all circumstances can be covered. In situations where project specific considerations may justify deviation from this philosophy, a document supporting the request for deviation shall be submitted to OMV E&P for approval.

Reference should be made to the parent of this philosophy, document number TO-HQ-02-001 for information on deviation procedures and Technical Authorities, general requirements and definitions and abbreviations not specific to this document

2.0 DEFINITIONS

The following definition is relevant to this document.

Variable Speed Drive System (VSDS)

A line fed a.c. to a.c. conversion system consisting of all facilities required to operate its electric motor at variable speeds.

3.0 ABBREVIATIONS

There are no abbreviations with particular relevance to this document.

4.0 INTRODUCTION

This document describes the philosophy to be used for the design, engineering and installation of electrical facilities, which comprise all fixed Electrical Installations for power and lighting up to and including main supply facilities for instrument and control equipment and safeguarding systems, cathodic protection




equipment, telecommunications equipment, fire fighting and alarm equipment, etc

5.0 APPLICABLE CODES, STANDARDS AND REGULATIONS

Codes, standards and regulations referred to in this philosophy shall be of the latest edition and shall be applied in the following order of precedence: -

• Local Regulations,

• The provision of this document,

• International standards (e.g. ISO, IEC etc),

• National standards. Design of the safety system shall comply with the standards listed within this philosophy, however, for instances where local standards are more onerous local standards shall apply.

5.1 Codes and Standards List

US Codes NFPA 70. National Electrical Code. (NEC) API RP 540 Electrical Installations in Petroleum processing Plants. Institute of Petroleum Model Code of Safe Practice, Part 1, Electrical Safety Code. NEMA MG1 Motors and generators. NEMA MG2 Safety Standard for Construction and Guide for Selection,

Installation and Use of Electric Motors and generators. International Electrotechnical Commission (IEC) IEC 60034 Rotating electrical machines. IEC 60038 Standard voltages. IEC 60050 International electrotechnical vocabulary. IEC 60056 High Voltage alternating current circuit-breakers. IEC 60071 Insulation co-ordination. IEC 60076 Power Transformers.




IEC 60083 Plugs and socket-outlets for domestic and similar general use. IEC 60099 Lightening arresters. IEC 60113 Diagrams, charts, tables. IEC 60120 Dimensions of ball & socket couplings of string insulator units. IEC 60227 Polyvinyl chloride insulated cables of rated voltages up to and

including 450/750V IEC 60255 Electrical relays. IEC 60298 A.C metal-enclosed switchgear and control gear for rated

voltages above 1kV and up to and including 52kV. IEC 60309 Plugs, socket-outlets and couplers for industrial proposes. IEC 60332 Tests on electric cables under fire conditions. IEC 60364 Electrical Installations of buildings. IEC 60383 Tests on insulators of ceramic material or glass for overhead lines

with a nominal voltage greater than 1000V. IEC 60433 Characteristics of string insulator units of the long rod type. IEC 60439 Low-voltage switchgear and control gear assemblies. IEC 60529 Ingress Protection Code. IEC 60536 Classification of electrical and electronic equipment with regard to

protection against electric shock. IEC 60549 High-voltage fuses for the external protection of shunt power

capacitors. IEC 60593 Internal fuses and internal overpressure disconnectors for shunt

capacitors. IEC 60617 Graphic symbols for diagrams. IEC 60623 Vented nickel-cadmium prismatic rechargeable single cells. IEC 60688 Electrical measuring transducers for converting a.c. electrical

quantities into d.c. electrical quantities IEC 60742 Isolating transformers and safety isolating transformers. IEC 60801 Electromagnetic compatibility for industrial-process measurement

and control equipment. IEC 60815 Guide for the selection of insulators in respect of polluted

conditions.




IEC 60831 Shunt power capacitors of the self heating type for a.c. systems having a rated voltage up to and including 1kV.

IEC 60871 Shunt capacitors for a.c. power systems having a rated voltage above 1kV.

IEC 60896 Stationary lead-acid batteries. General requirements and methods of testing.

IEC 60909 Short circuit current calculation in 3 phase a.c.systems. IEC 60947 Low Voltage switchgear and controlgear. IEC 61000 Electromagnetic compatibility. IEC 61089 Round wire concentric lay overhead electrical stranded

conductors. IEC 61241 Electrical apparatus for use in the presence of combustible dusts. IEC 61800 Adjustable speed electrical power drive systems

International Organisation for standardisation (ISO) ISO 9000 Quality management and quality assurance standards guidelines

for selection and use.

American Petroleum Institute (API) API – 14FZ Reccommended Practice for Design and Installation of Electrical

Systems for Fixed and Floating Offshore Petroleum Facilities for Unclassified and Class I, Zone 0, Zone 1 and Zone 2 Locations

API-505 Classification of Locations for Electrical Installations at Petroleum Facilities Classified as Class 1, Zone 0, Zone 1, and Zone 2

European Standards (CENELEC) Electrical apparatus for potentially explosive atmospheres. EN 50014 General requirements. EN 50015 Oil Immersion.’o’ EN 50016 Pressurised apparatus ‘p’ EN 50017 Powder filled ‘q’ EN 50018 Flameproof enclosure ‘d’ EN 50019 Increased safety ‘e’ EN 50020 Intrinsic safety ‘i’




EN 50021 Type of protection ‘n’ EN 50028 Encapsulation ‘m’ EN 50039 Intrinsically safe electrical systems ‘i’ EN50160 Voltage Characteristics of Electricity Supplied by Public

Distribution systems

5.2 References TO-HQ-02-012 Philosophy for Main Generators and Switchboard

Onshore. TO-HQ-02-013 Philosophy for Emergency Generator and Switchboard Onshore. TO-HQ-02-014 Philosophy for Electrical Cabling Design Onshore. TO-HQ-02-015 Philosophy for Uninterruptible Power Supplies Onshore. TO-HQ-02-016 Philosophy for Earthing, Bonding and Lightning Protection

Onshore. TO-HQ-02-017 Philosophy for Motors, Drives and Transformers Onshore. TO-HQ-02-018 Philosophy for Lighting and Trace Heating Onshore. TO-HQ-02-023 Philosophy for Safety Integrity Levels Onshore

6.0 SYSTEM GOAL

The Electrical Installation shall provide a safe and reliable supply of electricity at all times, under all operating conditions, including those associated with start-up and shutdown of plant and equipment, and throughout the intervening shutdown periods.

7.0 SYSTEM BOUNDARIES

The boundary of the electrical system is the interface with the public utility supply.

8.0 DESIGN PHILOSOPHY

8.1 General The design of the Electrical Installation shall be based on the provision of a safe and reliable supply of electricity at all times. Safe conditions shall be ensured under all operating conditions, including those associated with start-




up and shutdown of plant and equipment, and throughout the intervening shutdown periods.

The design of the Electrical Installation shall ensure that access is provided for all operational and maintenance purposes.

The design of electrical systems and equipment shall ensure that all operating and maintenance activities can be performed safely and conveniently and shall permit continuous operation for periods to be specified by OMV or specified during FEED in accordance with agreed standards and local operational requirements. To fulfil the above requirements, provisions may be required for alternative supply sources and supply routes, spare/standby capacity, load shedding and automatic restating schemes etc., details of which are given in Sections 8 and 9.

The simultaneous failure of two pieces of equipment shall not be catered for.

The insulating and dielectric materials used in all electrical equipment shall be non-toxic and shall not contain compounds that are persistent and/or hazardous environmental contaminants, e.g. polychlorinated biphenals (PCBs) etc.

Special attention shall be paid to provisional and temporary installations required for the erection of permanent installations to ensure compliance with basic rules for good working practice and safety, and to cope with increased hazards which are present in temporary installations.

8.2 Flammable Gas/Vapour Hazards To permit the proper selection of electrical apparatus for areas where flammable gas or vapour risks may arise, Hazardous Area classification drawings shall be prepared based on API-505. Electrical equipment shall, as far as is reasonably practicable, be located in safe areas. Control rooms and switch-houses should be situated in Non-Hazardous Areas. Where equipment is required to be installed in a hazardous area then API-14FZ shall be used. This standard highlights protection techniques required for electrical equipment to be located in Zone 0, Zone 1 or Zone 2. Techniques are also specified for equipment that are approved for Division 1 and Division 2 and are to be located in areas that are classed as zones.




8.3 Standardisation of Equipment and Materials Equipment of similar nature and incorporating similar or identical components and of similar or identical construction should be of the same manufacture. This applies to HV and LV switchgear with the same rated voltage, to power and convenience outlets, and to luminaries. Standardisation of materials and equipment shall be aimed for, as far as is compatible with rational design. Equipment which will become obsolete in the near future shall not be installed

8.4 Certificates, Declarations and Test Reports For all major equipment, the Contractor shall provide OMV with at least the manufacturers test reports in accordance with the specific design specifications, e.g. for generators, motors, VSDS, HV and LV switchgear, UPS equipment and transformers.

8.5 Quality Assurance and Control Contractors and suppliers shall demonstrate to OMV that they implement quality control and assurance systems which conform to the ISO 9000 series.

9.0 DESIGN REQUIREMENTS

9.1 General The design of the Electrical Installation shall be commensurate with any specific design criteria philosophy and/or objective that may be stated in the project definition phase, e.g. in a Basis of Design document and/or project specification, relating to a particular plant or facility. For instance, it may be defined by plant lifetime, skill of operating and maintenance personnel, operational flexibility, extension possibilities or noise limitations, etc. The philosophies to be employed will depend on the size and complexity of the installation; those approved for a specific project shall be set down clearly during the project definition phase. Any fundamental deviation thereafter shall be subject to the OMV’s approval. The conceptual designs and philosophies relating to the electrical system shall be adequately illustrated by the production of a system design specification, a key line diagram, basic layout drawings and functional /outline specifications. The electrical system and associated controls shall be designed on the basis of forming an integral part of the process plant facilities, as far as is practicable. For example, on-site electrical generation by the recovery of process heat energy




and integration of the electrical system controls with process control systems shall be considered. Furthermore, due regard should be given to the selection and utilisation of efficient electrical equipment in order to reduce energy consumption. The use of high efficiency / power factor electric drives, the use of VSDS for speed, flow or power control, the selection of low-loss transformers, etc, should be evaluated during the detail design and equipment procurement stages of a project. When designing electrical power systems, the following alternatives for the electricity supply shall be considered; own generation, public utility supply, or a combination of these within the limits and possibilities given by OMV. The design and selection of power sources shall ensure a degree of availability commensurate with the service required. Generating sets should normally be in an electrically centralised location and the distribution system arranged radially. Ring distribution systems shall be considered for residential/ industrial facilities located at relatively large distances from the power source or from each other. Power factor control and/or power transfer to alternative energy sources, mainly in connection with tariff characteristic of outside supplies, shall also be considered. A key line diagram of the Electrical Power System shall be prepared and kept up to date throughout the lifetime of the plant. System studies and protection reports, etc, shall be provided in support of the design. Depending on the type, size and complexity of the installation, such studies may comprise the following:

• Load flow studies.

• Fault level studies.

• Transient stability studies under three phase fault conditions.

• Dynamic performance studies under motor starting and/or loss of generation conditions.

• Protection grading studies, including relay setting schedules.

• Harmonic distortion studies.

The scope of the system studies shall be defined by OMV and agreed with the Contractor before the commencement. Where there is a public utility interconnection, the public utility’s study requirements should be considered within the scope of these studies.




9.2 Classification of Loads Electrical loads shall be classified as performing a service that is ‘vital’, ‘essential’, or non-essential as defined in Section 2.0.

9.3 Load Assessment and Electricity Consumption A schedule of the installed electrical loads, the maximum normal plant running load and the peak load, expressed in kilowatts and kilovars and based on plant design capacity when operating under the site conditions specified shall be prepared. This shall be updated regularly throughout the design stage of the project and shall form the basis of provision of the necessary electricity supply and distribution system capacity.

9.4 System Voltages and Frequency The system voltages shall be selected from IEC 60038, EN 50160 or equivalent, subject to compatibility with any existing installation with which interconnection is intended. The selection of system voltages shall be determined by OMV. The frequency shall be that used by the local public utility.

9.5 Supply Capacity The firm capacity of the electrical points of supply (generation, and associated power plant switchgear, and/or grid intake transformers and switchgear) shall be capable of supplying continuously 125% of the peak load, assessed in accordance with the applicable load data without exceeding specified voltage and frequency limits and equipment ratings. The spare capacity at plant substations shall be a minimum defined by OMV at the start of the construction phase, this spare capacity being retained for future plant debottlenecking and changes. The provision of stand-by capacity shall be considered in relation to safety, reliability and the requirement of continuity of plant operations. The reliability of distribution systems shall be at least comparable to their supply systems, each incorporating sufficient stand-by capacity to enable maintenance work, tests and inspection checks to be carried out. Electrical system maintenance requirements shall be considered in relation to plant shutdown for overhaul of process units.

9.6 Power Generation The number of generating sets to be installed and their individual ratings depend on many factors, e.g. maintenance requirements, economic size, future load development pattern, unit reliability etc. Sufficient stand-by capacity shall be




incorporated to fulfil the requirement of the peak load with the largest generating set out of service. The availability of further stand-by supply capacity to cater for generating set failures during such maintenance/repair periods shall be provided where the aggregate maintenance time warrants this. For plants with own generation capable of operating in island mode, an automatic load shedding system shall be provided.

9.7 Transmission and Distribution Systems

The economic consequences of electricity supply interruptions to essential services generally justify the provision of stand-by feeder capacity to facilitate the isolation of individual circuits for the purpose of equipment maintenance (e.g. on-load tap-changers, circuit breakers, etc), function testing (e.g. of protective relays and trip circuits) and possible repairs (e.g. cables and cable terminations) while maintaining electrical services operational. Therefore the stand-by feeder capacity shall enable the largest supply circuit to be withdrawn from service while satisfying the peak load requirements with the margins specified. The provision of stand-by capacity to non-essential service loads shall also be subject to an evaluation of the load requirements in conjunction with the relevant factors that may affect circuit reliability and circuit availability for carrying out maintenance, testing and inspection. Single overhead line circuits are not acceptable as a means of supplying vital or essential consumers. Duplication of circuits to non-essential consumers may also be required to improve reliability and to permit regular maintenance.

9.8 Switchgear

Currently available switchgear is considered to be sufficiently reliable to require no duplication in itself. Consequently, distribution and plant switchboards, including group motor control centres, shall have a single busbar system and a single switching device per circuit. HV switchboards at intake substations and power plant substations incorporating double busbar systems may be selected as an alternative to the above arrangement, but only if justifiable on the basis of facilitating system extension and operating flexibility which would otherwise involve significant disruption of electricity supply, or if facilitating a supply of differing priority/security from each busbar. An example of the latter would be where own generation and higher priority loads would be connected to one busbar, and a public utility supply (of poorer reliability) together with lower priority loads to the other busbar. The bus coupler circuit breaker would be utilised to effect disconnection in the case of grid supply interruptions.




Switchboards with double busbar systems shall incorporate one circuit breaker per circuit. HV and LV switchboards shall generally have a maximum of three sections and, consequently, a maximum of two bus section switches. LV switchboards with four sections in ‘H’ configuration are acceptable. Special arrangements, e.g. automatic changeover, may be required for switchboards supplying Vital Services, where an alternative supply is required. In the absence of quantitative analysis of circuit reliability data relating to a specific design that would support an alternative operating mode, and unless specific system design requirements dictate otherwise, the normal operating position of switchboard bus section switches shall be as follows:

• For LV switchboards the bus section switches shall be operated normally open, except on switchboards at the source of supply, i.e. at LV generator switchboards.

• For HV switchboards the bus section switches shall be operated normally closed on switchboards at intake substations, power plant substations and distribution substations. Bus section switches shall be operated normally open on switchboards at plant substations. N.B. In the above context ‘Normally Open’ and ‘Normally Closed’ refer to the bus section switch position when all the incoming switchboard circuits are available.

• When a switchboard panel serves a stand-by function to one or more main consumers, it shall be connected to a different busbar section from that which the main consumer or consumers are connected, provided that there is no possibility of a switchboard incoming circuit or busbar section becoming overloaded as a consequence of the selection of any main or stand-by consumers for operational use.

• Normally open bus section switches and/or interconnectors that may have to be operated simultaneously in the closed position shall be rated such as to permit the largest incoming circuit feeder to be withdrawn from service without the necessity to de-energise any switchboard busbar section or consumer circuit.

• The configurations of intake, power plant and distribution switchboards shall permit one switchboard section to be taken out of service while still maintaining normal downstream plant operations.




9.9 Electric Motors Currently available electric motors are considered sufficiently reliable for single essential drives. For Vital Services, stand-by units shall be installed, and supplied from a separate source of supply.

9.10 General Lighting Industrial lighting in ‘white’ colour shall in general be used for illumination. Where special requirements regarding colour distinction exist, these shall be met. Long life lamps in combination with electronic ballasts shall be used in new installations and for upgrading old installations, so as to take advantage of their increased efficiency and economic life. High pressure discharge lamps should be used in the case of lighting high buildings or large areas. In view of the restart time of this type of fitting after a Voltage Dip, sufficient fluorescent luminaries shall be installed for the basic lighting requirements of the area. The plant lighting system shall be based on the operational requirements and include as low as possible environmental influence. As far as practical, fluorescent lighting shall be used throughout the plant installations. Refer to Document Number TO-HQ-02-018 – Philosophy for Lighting and Trace Heating Onshore for further details.

9.11 Emergency and Escape Lighting Fixed emergency lighting shall be installed at strategic points in installations, including control rooms, switch-rooms, fire stations, first-aid rooms, watchmen’s offices, the main entrances and in all other buildings and areas where required for safety reasons. Locations and electrical arrangements shall be such that danger to personnel in the case of a power failure is prevented, and escape routes are lit. Emergency lighting shall be verified against the requirements of local authorities. The emergency lighting system shall consist of a number of standard luminaries of the normal lighting installation, which shall be fed via circuits having a stand-by supply from an emergency generator or from an Inverter having a battery with an autonomous time of at least 1 hour. In remote areas, where only a few fittings are required, self powered emergency luminaries may be used. Refer to Document No TO-HQ-02-018 - Philosophy for Lighting and Trace Heating Onshore for further details.




9.12 Short Circuit Ratings All equipment shall be capable of withstanding the effects of short circuit currents and consequential voltages arising in the event of equipment or circuit faults. N.B Damage occurring at the fault location is excluded from the above. The short circuit rating of equipment and cables, including the short circuit making and where relevant, breaking capacity of circuit switching devices, shall be based on the parallel operation of all supplies which can be operated in parallel, due regard being given to the distribution of short circuit current and to the limiting effect of system protective devices or control schemes, e.g. fuse links, Is-limiters, automatic supply changeover arrangements, etc N.B The short circuit current contributions from all supplies which can be operated in parallel shall include contributions via bus switches or inter-connectors which are capable of being operated simultaneously in the closed position. This includes bus section switches or inter-connectors etc, which are intended for normally open operation and on which no interlocking has been provided to prevent simultaneous closure. For new installations, including those forming part of plant extensions, the short circuit rating of the switchgear to be installed shall be based on the sum of the short circuit contributions of the following:

• The maximum short circuit level at the point of supply from which the new switchgear will be energised.

• An electrical loading of the new installation such that the firm capacity of the supply is fully utilised.

• Future planned increases in short circuit level due to the direct or indirect connection of machines, public utility supply or other sources of short circuit current.

• For a new switchboard at intake, power plant or distribution substations, a margin of not less then + 10% shall be allowed between the calculated fault level under the above mentioned conditions and the specified short circuit rating of the equipment. N.B. This margin is to allow for the tolerances permitted for machine characteristics and for increase in fault contributions arising from variations in system voltage.

• Mechanical Interlocks of switches shall be provided, where necessary, to ensure that equipment short circuit ratings are not exceeded, due regard being given to satisfy the above-mentioned operational requirements with respect to the provision of firm and stand-by capacity.

• Automatic break-before-make changeover arrangements of supply capacity shall not be introduced with the specific aim of justifying the use




of equipment having a lower short circuit rating than would otherwise be required when based on the parallel operation of all available supplies.

• The use of current-limiting reactors, Is-limiters and similar devices intended specifically as a means of limiting the magnitude of short circuit currents shall be permissible only when they form part of extensions or interconnections with existing installations. The application of the above mentioned current limiting equipment shall be considered only as a means of achieving system extensions or interconnections which could not otherwise be practical or economically realised without the use of such devices.

• When determining equipment short circuit ratings, the effects of contributions from asynchronous and synchronous machines on the switching duties of switchgear and on the dynamic and thermal loading of the Electrical Installations in general shall be taken into account. N.B. Short circuit current contributions from asynchronous machines need normally only be taken into account for determining the necessary dynamic withstand rating of equipment and the required making duty of circuit breakers tested in accordance with IEC 60056 and IEC 60947-2. However, where reliance is placed on circuit breakers having an enhanced making capacity, the effects of asynchronous machine contributions shall be taken into account in establishing the adequacy of the fault breaking duty of circuit breakers, taking into account the decay of the short circuit current contribution.

• Any restrictions imposed by the public utility with respect to short circuit current infeeds to their supply network shall not be exceeded.

9.13 Electrical Protection

The application and selection of protective systems and devices shall be based on the following premises: Electrical Installations connected to the public grid shall be protected in compliance with the requirements of the public utility.

A standardised protection method: The consideration to prescribe standardised protection methods shall be based on the requirement to control the total area of electrical protection. In the design phase attention should be paid at least to:

• Identification of fault sources.

• Analysis of fault sources.




• Possible elimination of the causes for the fault sources.

• Protection of the parts with possible fault sources.

• The safety of personnel and prevention of damage.

Standardised Protection Equipment: The consideration to apply standardised equipment is based on the requirements to control the reliability of the protection equipment. Standardised Calculation Methods: Standardised calculation methods based on acknowledged standards control the quality (reliability and repeatability) of the protection system The electrical system shall be equipped with automatic protection which shall provide safeguards in the event of electrical equipment failures or system maloperation. Automatic protective systems shall be designed to achieve selective isolation of faulted equipment with minimum delay. In any event this shall be within a time corresponding to the short circuit current withstand capability of equipment, system stability limits and the maximum fault clearance times.

9.14 Earthing AC system neutrals shall normally be earthed as detailed below. They shall not be designed for unearthed operation, except where forming an extension to an existing unearthed system

HV electrical systems shall be earthed by means of dedicated earth electrodes connected to the plant main earth grid.

HV system neutrals shall be earthed at each source of supply (transformer, direct-connected generator etc)

For grid infeed system the neutral point of transformers should be solidly earthed, unless otherwise stated by the public utility.

Transformer feeders to HV switchboards shall be resistance earthed. The rating of the resistors shall be such as to limit the earth fault current supplied by the equipment to which the resistor is connected to a magnitude approximately equal to the rated full load current of the supply equipment. (generator or transformer)




In situations where generators are to be connected directly to the main HV switchboard, (i.e. not via generator transformers) each generator should be earthed via it’s own earthing resistor. This however is subject to verification that the zero sequence, triple harmonic currents (3rd, 9th, 15th etc) that could circulate through the resistors under various loading conditions of the generators would not be damaging to the resistors. The rating of each resistor should be such as to limit the magnitude of the earth fault current to the rated load current of the generator to which it is connected. A resistor of higher Ohmic value than the aforementioned may be considered if such a resistor would limit the magnitude of circulating harmonic current to a harmless value, provided that with such a resistor, sufficient current would flow under each fault condition, which ensures positive operation of earth fault protection on all circuits. If the latter is not possible for any reason, other measures shall be adopted to limit such circulating currents, e.g. single point earthing at one of the supply sources or provision of controls to ensure that identical generators, each separately earthed, remain equally loaded and excited during normal operation.

In situations where generators of dissimilar ratings, characteristics or loadings are to be operated in parallel such as to give rise to circulating currents in the above mentioned earthing resistors that would exceed the thermal rating of the resistors, then the HV system shall be earthed via one resistor only. Each generator shall then be provided with a suitable switching device (i.e. remotely operated circuit breaker or latching contactor) to facilitate the connection of any machine to the single earthing resistor. During normal operations, only one generator shall be connected to the resistor. If the generator so connected is tripped for any reason, an alarm is required to prompt manual intervention to close the neutral-earth switching device on one of the other operating generators to facilitate the earthing of the system.

Where generators are connected to the main switchboard via individual step-up transformers, each generator neutral point shall be individually earthed through a single phase distribution transformer with a secondary resistor. The resistor shall be rated to limit the generator earth fault current to 10A or 3Ico where Ico is the per-phase capacitive charging current, whichever is the greater. N.B The per-phase capacitive current is that due to the generator stator windings, generator transformer LV winding, and generator main cable/connections.

Each earthing transformer and resistor shall be rated to withstand the respective earth fault currents for a duration of not less than 10s.

Resonant impedance earthing, e.g. Peterson Coil, may be considered for systems mainly comprising overhead lines, and thus subject to transient faults, e.g. lightning. It is advisable in this case to install a low value earthing resistor in




parallel with the normal high impedance device so that, if a fault on an outgoing circuit is not cleared within the allowed time, the resistor can be switched in to provide a higher fault current to allow clearance by back-up protection.

LV electrical system neutrals at each source of supply shall be solidly earthed by means of dedicated earth electrodes which have a direct, low impedance connection to the plant main earth grid.

For LV equipment, earth loop impedances shall be low enough to ensure that circuit disconnection is achieved under fault conditions within agreed parameters.

AC UPS systems shall have their neutrals solidly earthed. This applies equally to single phase and three phase systems. The Inverter (output) neutral shall be connected to the neutral of the bypass mains neutral, which shall be solidly earthed.

DC systems supplying instrumentation loads and switchgear control and protection loads shall be earthed down through a high resistance earth fault monitoring unit with a sensitivity to be defined during detailed design.

If buried cables are used for earthing purposes, only one side of the cable screen may be connected to the earthing rod.

9.15 Uninterruptible, Maintained Power Supplies AC and DC power supplies for critical/vital loads shall be derived from battery back-up UPS systems.

These may be single or duplicate systems depending on the level of reliability required.

The output capacity of vital UPS equipment shall be sufficient to clear distribution protection devices without the use of the mains or any by-pass system.

Systems or equipment requiring a duplicate supply shall derive each supply from separate UPS systems.

The batteries of UPS units shall be rated to energise the relevant loads for not less than a specified time e.g.:

• 0.5 hour for process plant shutdown.

• 1 hour for utility plants.

• 1 hour for emergency lighting.




• 10 minutes for non-process computer installations.

• 8 hours for fire fighting, fire alarm and telecommunications systems.

• 8 hours for HV and LV switchgear control. Where AC power supplies require to be maintained but may be interrupted by a failure of the main distribution system, back-up power supplies may be provided by automatically starting emergency diesel generators. The interruption of mains supply is typically 10 to 15 seconds.

Facilities should be provided to permit periodic on-load testing of emergency generators by enabling the generator to be synchronised with the mains supply. Each generator shall have sufficient fuel storage capacity for at least 8 hours full load operation.

9.16 Integrated Control Systems (ICS) Central monitoring and control of the electrical supply and distribution system should be integrated with the plant process Distributed Control System (DCS). A dedicated ICS for the Electrical Power System should be considered where centralised metering and overall electrical system supervision is required.

In addition, an ICS should provide additional features advantageous to plant operation and maintenance, e.g. alarm logging, fault recording, plant performance trends, self-diagnostic facilities, energy management and, if necessary, load shedding. The use of an ICS for remote control of switchgear should be subject to OMV’s approval.

Trip signals from the electrical protection shall be derived locally at the panel, and not form part of the external control system.

Consideration shall be given to the required interfaces between the ICS and ESD systems.

10.0 DESIGN CONSIDERATIONS

10.1 General The design of the electrical system should take account of the following:

• Life cycle costs as well as the capital cost, for example testing costs, false trip costs, commissioning and modification costs.




• Human factors.

• Selection and positioning of the correct field equipment suitable for the process and environmental conditions.

The electrical system shall provide protection for normal operation and for the conditions that may arise from an abnormal condition.

11.0 DESIGN CRITERIA

The electrical system shall be designed to take account of the environmental conditions of the site that it is to be located to ensure reliability is preserved.

Design of the electrical system should take account of the requirements covering the full lifecycle of the plant.

The controls of the electrical system shall not be affected by radio-frequency signals, from hand-held portable radio units.

All parts of the electrical system should be designed as a fail-safe system forcing all outputs to a de-energised/ open circuit state on a failure. An exception to this is for outputs where the failure of the output would create a hazard. Under these circumstances the output circuit should be line monitored and configured energised to trip.

Logic parts of the electrical system that cannot be designed as fail-safe, such as timers, shall be used in redundant arrangements. Any single failure within a redundant arrangement shall not prevent a demanded trip.

Digital and analogue signals shall be segregated from one another.

It should be noted that the CE Mark, or CE marking as it is officially named, is an obligatory product mark for the European market, which indicates compliance 'certification' according to the requirements formulated in the approximately 22 European 'CE Marking Directives' and subsequent European standards.

12.0 MAINTENANCE IN DESIGN

The electrical system shall be designed taking maintainability into consideration by simplifying maintenance and reducing maintenance costs where practical.




There should be sufficient maintenance overrides, redundancy and bypasses to enable parts of the electrical system to be maintained and tested minimising operational down time.

The electrical system should be designed to allow modifications and development to be implemented whilst minimising disruption to the process.

A separate engineer’s interface should be provided to the electrical system.

13.0 DOCUMENTATION REQUIREMENTS

All necessary drawings documents and reports relating to the design of the Electrical Installation and for it’s operation, and all necessary drawings required for the installation interconnection of equipment and cabling shall form part of the design package. The documents, reports and drawings shall be prepared and submitted for approval as required by the client. This shall generally be in two stages for document preparation and approval, namely ‘Project Specification’ and ‘ Design and Engineering’ which are typically required during the definition and implementation phases of a project. Fully detailed construction drawings shall be provided so that the site construction contractor can install all electrical equipment with no design effort. Vendor information and details shall be incorporated in the design package as soon as it becomes available. Such information shall be updated when alterations to the design are made and shall include additional information that is required during construction or may be required for future maintenance, troubleshooting and operation. As built drawings shall be prepared for the project covering all parts of the Electrical Installation and for its operation and all necessary related civil engineering, mechanical and instrumentation work. Documents shall include:

Key single line diagram. This shall show the complete a.c. electrical generation and distribution system of the plant including all HV feeds, main LV feeds and sub-distribution boards, together with:

• all sources of electrical power.

• The principal supply and distribution system interconnections at each voltage level.

• System capacities, equipment ratings and impedances, winding configurations and earthing arrangements.




• Block diagrams.

Block Diagram: This shall show the basic control and protection systems defining the protection, control, trip and alarm functions to be fulfilled at the different locations. It shall also indicate the reference signals and controls needed and all the auxiliary supplies required such as air, lube-oil, cooling water, electrical auxiliary supplies etc.

Single Line Diagram: This shall detail the main circuitry and it’s earthing systems. It shall also indicate the instrument transformers, relays, meters, etc, for the control, protection and operation of the equipment together with electrical data such as voltage, current and impedances.

A single line diagram of a.c. and d.c. interruptible and Uninterruptible, Maintained Electricity Supply systems shall be provided. The single line diagram shall detail for each system the system configuration, earthing arrangements, UPS and emergency generator ratings, the equipment number, function, location, nominal voltages, maximum load, number and type of battery cells and battery Autonomy Time.

Switchgear drawings: The following drawings shall be provided for each HV and LV switchboard:

• circuit/schematic or control diagrams, showing all circuit details in a schematic form to control a motor or other power device, and all information necessary for the identification and connection of the components and wiring.

• Interconnection/connection diagrams showing the external connection details of a switchgear panel, relay box or junction box, etc.

• Block diagrams showing the interconnection of the various items of equipment of a power system in a diagrammatic manner.

• Switchboard layouts showing the basic information needed for the construction, i.e. the switchboard outline dimensions, and the switchboard front outline layout.

Layout drawings: A substation/switchroom layout drawing shows the physical location and the civil provisions to be made for the installation of all transformers, switchgear and other electrical power, lighting, earthing and auxiliary equipment located in a substation. The cable runs and support systems shall also be shown. Space requirements for future switchgear, correct location and dimensions of transits in the substation floor for existing and future switchgear shall be shown.




Power, lighting, earthing, substation, and trench layout drawings shall identify:

• all major process equipment by their item numbers.

• All electrical equipment and cables by their equipment and cable numbers.

• Cathodic protection (CP) and ventilating systems (HVAC)

The power layouts shall show all power cabling, identified by cable numbers, lighting supply cables up to the main junction boxes, and the power and convenience outlet distribution board feeder cables.

Lighting and Small Power layouts shall show all luminaries, (normal and emergency), all level gauges, all power and convenience outlets distribution boards, and all boxes and cable routing, downstream of the main distribution boxes.

N.B. Luminaires etc, shall be identified by a support detail reference, circuit reference, and fitting/outlet reference. If required for clarity, separate or additional layouts should be prepared for different levels within a building or installation.

Earthing layouts shall show the main earthing grid, branch connections, earth electrodes, earth bars and conductor sizes for both the electrical earthing system and instrument clean earth system.

Cathodic protection layouts shall include all items to be protected, (such as: cables, rectifiers, anodes, reference cells, connection boxes, measuring posts, insulation joints.)

HVAC layouts shall include all items involved, such as ducts, heat exchangers, panels, heaters, fans, and cabling. As far as possible drawings shall be combined with the other electrical drawings.

The cable trench layouts shall show the physical location of all underground cable trenches, underground pipes and ducts.

Cross-sectional arrangement drawings shall be provided for all cable trenches, ducts and above ground cable routes showing the location and number of each cable along the routes.

Construction drawings (typical): Shall show typical construction and mounting details of the power, lighting and earthing installations which cannot otherwise be shown on the layouts. Each detail shall have a unique reference.




Area classification drawings: These shall show the classification of the areas with respect to the gas or vapour or dust explosion hazard, and shall include sectional elevations where needed for clarity.

Vendor drawings: Shall be provided to show as a minimum all the information specified in the relevant specification and requisition.

Equipment and Cable numbering: A logic system of numbering shall utilised. For plants having an existing numbering system, this system shall be followed.

14.0 CERTIFYING AUTHORITY REVIEW REQUIREMENTS

Some plants may require the design to be certified or validated by an independent certification authority due to local regulations or as instructed by OMV. Under these circumstances the certifying authority will require as a minimum the following documents for review:

• Basis of design document

• Functional design specification

• Key single line drawings.

• Cause and effect drawings

• Layout drawings

• Hazardous Area drawings.

• Electrical Protection Study

• Integrity Assessment (refer to Document No TO-HQ-02-023 - Philosophy for Safety Integrity Levels Onshore)

• Reliability assessment and calculations

These should be issued to the CA in a timely manner to obtain approval before commencing construction.

to-hq-02-011 rev 00 philosophy for general electrical design.pdf

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