NEC Electrical System Design Criteria in Process Industry

This article is about the minimum requirements for the electrical system design and equipment.

Electrical System Design References

American National Standards Association / Institute for Electrical and Electronics Engineers (ANSI/IEEE)
C57.12.00 Standard General Requirements for Liquid Immersed Distribution and Power Transformer
C57.12.50 Requirement for Ventilated Dry Type Distribution Transformers, 15 to 500 kVA
C57.12.51 Requirements for Sealed Dry Type Power Transformers 500 kVA and Above
C37.2 Electrical Power System Device Function Numbers, Acronyms, and Contact Designations

American Petroleum Institute (API)
546 Form-wound Brushless Synchronous Motors
RP 2003 Recommended Practice for Protection Against Ignition Arising Out of Static, Lightning and Stray Currents
RP 500 Recommended Practice for classification of Locations for Electrical Installations at Petroleum Facilities Classified as Class I, Division 1 and Division 2
RP 505 Recommended Practice for classification of Locations for Electrical Installations at Petroleum Facilities Classified as Class I, Zone 0, Zone 1 and Zone 2

National Fire Protection Association (NFPA)
NFPA 70 National Electrical Code (NEC), 2008
NFPA 77 Static Electricity

NFPA 496 Purged and Pressurized Enclosures for Electrical Equipment
NFPA 780 Standard for the Installation of Lightning Protection Systems

National Electrical Testing Association (NETA)
ATS- Acceptance Testing Specifications for Electric Power Distribution Equipment and Systems

National Electrical Manufacturer’s Association (NEMA)
250 Enclosures for Electrical Equipment (1000 V Maximum)
VE 1 Metal Cable Tray Systems
FG 1 Fibre Glass Cable Tray Systems
MG 1 Motor Generator – 1

Utilization Voltages

Here in our case Electrical equipment and lighting shall be designed for 60 Hz operation at the system voltages listed below:

Design Calculations and Studies

  • The following power system studies and calculations shall be performed for proper design of electrical power systems and equipment in this article Power System and Equipment Design Calculations.
    a. load data calculation.
    b. transformer sizing and selection.
    c. cable derating.
    d. load flow.
    e. motor starting.
    f. short circuit capability.
    g. relay coordination.
    h. motor acceleration.
    i. harmonic analysis.
    j. load shedding (if required).
    k. insulation levels.
    l. lightning calculation.
    m. grounding calculation.
    n. power factor improvement.
    o. battery charger / UPS sizing calculation.
    p. dynamic and transient stability analysis (if required).
    q. 34.5 kV and above cable sheath voltage calculation (where applicable).
  • The power system studies and calculations shall be performed on  ETAP.
    a. If the design is an expansion of an existing facility, the existing database shall be checked to confirm it reflects the current state of the existing facilities, including protective relay settings. If the database does not exist it shall be created before the inputting of new system data.

Overcurrent Protection

Overcurrent devices shall be selected and applied to minimize damage to electrical  system components and to limit the extent and duration of service interruptions coincident with overload or fault conditions. Time vs. current coordination shall be performed using ETAP or EDSA PALADIN DESIGNBASE, computer studies program.
This time vs. current coordination curves shall be plotted on log-log graph paper. The graphical representation shall encompass protective devices from the source down to the largest 460 V motor or to any branch circuit device which may adversely affect selectivity and shall include the following:
a. System diagram.
b. Protective device time vs. current curves.
c. Available short circuit currents.
d. Cable maximum short circuit current.
e. Transformer data to include ANSI damage curve, inrush point and 4 x full  load current.
f. Motor data to include full load current, locked rotor current and permissible stall time.  Preliminary time vs. current curves shall be reviewed rior to equipment  purchases.

Power Factor Correction

  • Lighting fixtures shall be furnished with high power factor ballasts.
  • Main incoming power buses at each process units/ plants shall be power factor  corrected based on the normal operating load to 0.90 lagging or the value defined in the power purchase agreement with utility company, whichever is higher.  All power buses ( i.e. buses of switchgear connected to secondaries of distribution transformers) shall be power factor corrected to 0.90 lagging or higher based on the normal operating load.
  • The power factor correction shall be in conformance with Power System and Equipment Design Calculations and Power Factor Correction Capacitor Banks.
  • For power factor studies, power factors of motor loads shall be based on vendor data or typical motor data.
  • Capacitors for 480 V systems shall be dry metallized film units. Discharge resistors to automatically discharge the capacitor unit to less than 50 V in under one minute shall be provided. All internal conductors shall be copper. Capacitor unit shall be provided with internal protection to disconnect shorted capacitor elements from the circuit.
  • Capacitor installations on 4.16 kV systems shall have capacitors mounted in a metal enclosure with a door which has an interlocked grounding switch. The door is to be interlocked so it cannot be opened unless the switch is in the grounding position. The grounding switch is to be key interlocked with the upstream disconnect device so the grounding switch can only be closed when
    the circuit is opened or the switch is opened before the upstream device can be closed, or both.

Single Line Diagrams

  • The electrical system shall be fully described and defined by the use of single line diagrams.
  • System components for the electrical system, for example switchgear, transformers, motor control centers, and power panel shall be shown on single line diagrams. These system components shall be identified and their ratings indicated.
  • Individual loads shall be identified and presented on the single lines according to their physical location and function in the system.
  • Protective relaying shall be shown using the device numbering listed in ANSI/IEEE C37.2.

 

Hazardous Area Classification

Plant Facilities Designed in Accordance with NFPA 70

Plant facilities shall be designed using the following documents to determine the hazardous limits within the facility plot. For any new „Grass Roots‟ facilities, additions or modifications to facilities that have been previously designed to these documents, the latest versions shall continue to be used.
a. Articles 500 to 510 of the National Fire Protection Association No. 70, NFPA 70 (NEC).
b. The American Petroleum Institute „Recommended Practices for Classification of Locations for Electrical Installation at Petroleum Facilties Classified as Class 1, Division 1 and Division 2(API RP-500).
c. The American Petroleum Institute „Recommended Practices for Classification of Locations at Petroleum Facilities Clasiified as Class 1, Zone 0, Zone 1 and Zone 2.(API RP-505).
d.. The American Petroleum Institute Classification of Class I Hazardous Locations for Electrical Installations in Chemical Process Areas (API RP- 497A).
e.. The American Petroleum Institute Classification of Class II Hazardous Locations for Electrical installations in Chemical Process Areas (API RP- 497B).
f. The American Petroleum Institute Manual for Classification of Gases, Vapors, and Dusts for Electrical Equipment in Hazardous Locations (API RP-497M).

Air Purging

When purging or pressurization is to be utilized, equipment shall be in conformance with requirements of NFPA 496 in plants designed to NFPA 70 and classifications according to API RP-500 or 505.

Power Supply

Incoming Power

  • Incoming power voltage level will depend on techno-economic evaluation. It is subject to company approval and agreement with utility company. Refer to Basic Engineering Design Data (BEDD) for maximum variation of incoming power supply voltage and frequency.
  • Services shall be installed as required to meet the reliability requirements of the specific facility, by mutual agreement of the electrical utility and company. For any facility, the number of services shall be minimized and single point metering shall be utilized wherever possible.
  • The preferred arrangement would be for the utility to supply, own and maintain the incoming service transformers and switchgear outside the facility boundary. If this is not feasible, the main substation shall be strategically located in a preferably unclassified area between the utility‟s incoming service and close to the concentration of load to be served.
  • To develop the required power system calculations for the facility, the utility shall provide company with their system short circuit capacity, expressed in mega volt amperes (MVA) symmetrical and their system X/R ratio at the point of connection. In addition to this information the utility shall provide company with the type, size, rating and model number of the devices protecting the incoming
    service power cables.

Electrical Power Distribution System Design in Plants

Power Distribution System Design

The basic intention in the development of the power distribution system shall be to  develop a safe, flexible system, that will provide continuity of service in the event of a partial power outage or when equipment is taken out of service for maintenance. The design shall provide for convenient operation, ease of maintenance, future expansion and component interchangeability. The system shall be designed, and the protective relaying shall be coordinated, to provide minimum system disruption when isolating an electrical fault.

System shall be designed such that the necessary elements such as switchgear, cables, etc. are currently manufactured, and type tested. Equipment with a minimum of three years field proven experience shall be selected.

Bus and System Configurations

When selecting the  distribution system configuration, factors of reliability, application and investment cost
shall be considered. The three basic system arrangements to consider are:

Radial System

a. This system is the simplest and easiest to understand, operate and  diagnose. It is also the least expensive.
b. Radial systems are made up of single feeders, buses, transformers and power sources.
c. This type of system does not provide an alternate source of power, or  redundant components, so any major system component failures will result in loss of power and facility shutdown.

Primary-Selective System

a. This system offers a higher level of reliability and flexibility than the simple radial system.
b. Primary-selective systems have redundant feeders fed from two separate  power sources, so only half of the system transformers are on a single feeder. In the event of feeder failure, the affected load can be switched over to the alternate feeder for continued operation.
c. Since this system requires additional feeders, feeder protection and switching, the investment cost is higher than the radial system.

Secondary-Selective System

a. This system offers the highest level of reliability and flexibility of the three basic types.
b. Secondary-selective, also known as, double-ended systems are made up of double feeders fed from two separate power sources, double transformers and double buses. The buses are connected together by a circuit breaker, known as the tie breaker, that is normally left open.
c. In the event of a component failure or fault, power to half of the load would be lost, with the auto transfer scheme the system can be reestablished by Closing the tie breaker.
d. Due to the amount of duplication of major components in this type of system it also requires the greatest investment cost of the three types of system.
e. Where it has been determined that a loss of power could lead to a situation that is hazardous to human life, or where substantial loss of production could result, secondary-selective systems shall be used.

Classification of Electrical Loads

Normal Loads:

Loads where a single contingency failure could not lead to a situation that is hazardous to human life or cause a substantial loss of production. Normal loads can tolerate prolonged power failure without causing plant shut down
e.g. Secondary office buildings, Warehouses and Workshops. Radial or Primary-Selective System shall be considered to supply such loads.

Critical Loads:

Loads where a single contingency failure could lead to a situation that is hazardous to human life or cause a substantial loss of production and plant major shut down e.g. Major office buildings, Major computer or IT centers and
Process units. Secondary-Selective System shall be used to supply such loads.

Emergency Loads:

These loads are those whose operation involves the safeguard of an item of equipment/installation or the continuation of certain operations. In case of shutdown, emergency loads tolerate a short interruption of service, but it shall be automatically restarted and re-fed by emergency generator e.g. loads defined at Power System and Equipment Design Calculations . These loads shall be supplied from an emergency switchgear fed from a secondary-selective system and
emergency generator.

Vital Loads:

Loads whose operation affects personnel safety whether directly or indirectly. These loads do not allow the power supply interruption and shall be fed by UPS system e.g. DCS, Fire Alarm, Gas detection and Substation control systems.

Liquid Immersed Air Cooled Power, and Dry Type Transformers

  • In the power distribution system, liquid immersed air cooled power transformers shall be in accordance with Oil-Immersed Power Transformers Design Requirements.
  • Oil immersed power transformers rated below 2.5 MVA shall be “hermetically sealed” tank type equipped with off-load tap changer.
  • All LV/LV transformers shall be dry type unless otherwise specified.
  • Dry type transformers shall be rated in accordance with Dry Type Distribution and Power Transformers Design Notes and Transformers Dry Type above 500 kva.
  • For voltage tap and fan rating requirements see the data sheet specific to the transformer.
  • The transformer shall be derated to compensate for the extreme environment it is to be installed in, to provide continuous operation without a sacrifice in service life.

Power System Grounding Requirements

  • Three phase electrical systems shall be grounded at the neutral point of wye  connected windings for transformers and generators.
  • High resistance grounding systems may be approved by company if it is proved  that the following shall be provided:
    a. Full time operations or maintenance personnel familiar with ground fault  location procedures and equipment.
    b. Ground fault location equipment, provided as part of the high resistance  grounding system.
    c. A ground fault alarm system.
    d. A protective relaying system capable of isolating a second ground fault.

Automatic Transfer Switch

  • In situations where power is critical to life safety or continuous process operations a system shall be provided to automatically switch to an alternate or emergency source of power in the event of loss of the normal source. These automatic transfer switches and their related control systems shall be capable of sensing critical undervoltage and instantaneously transferring the critical load to the alternate source.
  • If the alternate source is a generator, the control system shall be equipped with provisions for generator starting.
  • The automatic transfer switch shall be of transferred back to the normal power supply manually, when normal system conditions have been restored.
  • The automatic transfer switch shall be a double throw type switch with no off or neutral positions provided. The most commonly used configurations shall be double throw, mechanically held, electrically operated or static transfer type.

Extra High and High Voltage Switchgear

  • High voltage switchgear, where required, shall be utilized for controlling and distributing power at voltages of 100 kV and above. It shall be of the metal enclosed SF6 gas insulated type.
  • 115 kV and 230 kV Gas insulated switchgear shall be in accordance with NEC High Voltage Gas Insulated Switchgear Design Requirement.
  • The switchgear shall be installed indoors. The arrangement shall be three phase or single phase enclosed, consisting of completely pressurized separate sections provided with rupture protection.
  • Busbar shall also be three phase or single phase enclosed.
  • The circuit breakers shall be of the SF6 gas, single pressure puffer type, with a  highly reliable hydraulic or pneumatic operating mechanism.

Medium Voltage Switchgear

  • Medium voltage switchgear shall be utilized in air-conditioned substations for controlling and distributing power at voltages above 1 kV to less than 100 kV.
  • Medium voltage switchgear shall be in accordance with  NEC Medium Voltage Switchgear Design Requirement . It shall be arranged in a single row, a back to back arrangement is unacceptable. The switchgear shall be designed to allow the installation of additional sections at a future date.
  • Each section shall be equipped with removable draw out vacuum or SF6 type switchgear assemblies that are identical in type and physical dimensions, for the purpose of interchangeability.

Low Voltage Switchgear

Low voltage switchgear shall be in accordance with NEC Low Voltage Switchgear Design Requirement . Low voltage  switchgear shall be utilized for controlling or distributing power at voltages of 1000 V or less. Generally this equipment shall be installed indoors. The switchgear shall be of the metal enclosed, freestanding, dead front steel structure type.

Station Batteries and Battery Charger

  • Station Batteries and Battery charger shall be in accordance with  Battery Racks and Battery Charger Installation.
  • The highly reliable 125 V dc redundant control power required for switchgear  shall be provided by stationary storage batteries.
  • Station batteries shall be lead calcium plates or nickel-cadmium type having a service life of not less than 20 years.
  • The batteries shall be located indoors, in racks, near the load to be served. The system shall be capable of delivering full rated output for the period of time stated in the data sheet.
  • The batteries shall be connected to a battery charger and to a load bus.
  • The battery charger shall be capable of supplying the required load current and the battery charging current.
  • The charger shall be the electronically controlled type, fully regulated and current limiting.
  • Circuit breaker protection shall be provided for both input and output. The dc output shall be isolated.

Energy Metering

Individual tariff precision metering of following sections are required for both active (kWh) and reactive (kVARh) energies and shall also be available at SCADA and DCS.
 Plant total
 S/Ss total (all substations)
 Each process section
 Utility
 Off Site
 EDG
 All main incomer feeders (normal and emergency) upto 480 Volt LV switchgear.

Electrical Reliability-

 All motors and critical equipment /systems for the process shall have a minimum voltage dip protection.
 Main and spare pump motors must be connected to different buses.
 Half of the fan motors of any air-cooled exchangers must be connected to the „A‟ bus and the other half to the „B‟ bus.

Motors

  • Induction Motors 200 HP and Smaller
    Induction motors 200 HP and smaller shall be in accordance with Induction Motors Design Requirements below 150 kW in Plants.
  • Induction Motors 250 HP and Larger
    • Induction Motors 250 HP and larger shall be in accordance with SES E06-S02.
    • For larger motors, one of the motor voltages 4000 V or 13200 V shall be selected to suit each specific application, considering technical evaluations and economic breakpoint.
  • Synchronous Motors
    • Synchronous motors shall be used in applications where low speed and high  horse power motors are required to drive large reciprocating compressors and pumps and similar equipment, and shall be in accordance with SYNCHRONOUS MOTOR ELECTRICAL DESIGN .
    • Where power factor correction is required, applications of synchronous motors shall be considered along with induction motors and capacitor banks in the development of a cost effective solution.
    • Synchronous motors shall be the brushless, salient pole type, larger than 185 kW and utilized at medium voltage. Single bearing engine type motors may be
      considered for driving large reciprocating compressors.
  • Adjustable Frequency Drives
    • Where process requirements dictate, squirrel cage induction motors shall be used with adjustable frequency drives, for variable speed operation.
    • Adjustable frequency drives shall be considered over traditional throttling  techniques and conventional methods of speed adjustment in applications where the load torque varies with speed, to minimize maintenance and take advantage of the inherently high efficiency of this kind of equipment.  Where available, the motor and adjustable frequency drive shall be specified as a package. If this is not possible, there shall be documented liaison between the motor and adjustable drive suppliers about the application of the equipment.
  • Single Phase Motors
    • Normally motors greater than 1/2 HP shall be three phase, 460 V.
    • Where required, motors below 1/2 HP, single phase, 230 V shall be used.
    • Single phase motors located in hazardous locations shall be of the totally enclosed explosion proof type as per NEMA 250.

Motor Control

Motor control circuit voltage shall be 230 V, single phase.

Medium Voltage Motor Control

  • Medium voltage motor controllers, for motors 200 HP and larger shall be 4000  V, three phase, 60 Hz, full voltage, across the line start, fused combination type with vacuum or SF6 contactor.
  • In addition to the current limiting fuses, the controllers shall be equipped with a solid state motor management system to provide a complete range of protection within the design capabilities of the motor.
  • Motors 1000 HP and larger, shall also be protected by bearing and winding RTD‟s.
  • Reduced voltage starting shall be used only when required by the electrical utility or when motor starting current causes an excessive voltage drop that affects the power system balance.
  • The controllers shall be installed indoors, grouped in factory assembled, metal enclosed, free standing, dead front assemblies. Busbars within the controller assemblies shall be insulated copper.

Low Voltage Motor Control

  • Low voltage motor controllers, for motors 200 HP and smaller shall be 480 V,  three phase, 60 Hz, full voltage, across the line start, magnetically operated, air break type.
  • The motor controllers shall be the combination type, comprised of an instantaneous motor circuit protector type circuit breaker for short circuit protection and as a disconnecting means; a magnetic contactor in conjunction with an overload relay to automatically disconnect the motor in the event of an overload or undervoltage condition; and an ambient temperature compensating thermal-overload relay in each ungrounded conductor of the motor power circuit.
  • Thermal magnetic circuit breakers shall be used for the protection of nonmotor loads controlled from the motor control center.
  • Motor controllers shall be mounted in factory assembled motor control centers.

Variable Frequency Drives

  • Variable frequency drives shall be used to control low voltage, three phase, 60 Hz squirrel cage induction motors, where variable speed output is required. This is accomplished by converting the three phase, 60 Hz input power to a variable ac frequency and voltage.
  • The drive unit shall be installed indoors near the motor control center or installed as an integral part of the motor control center line up.

Control Stations

Control stations for motors shall meet the following criteria:
a. Industrial type
b. Threaded through hubs
c. Factory sealed contacts, maintained or momentary, as required
d. Approved for the area classification in which they are installed
e. Push-button stations shall be provided with a lockout stop feature.

Control stations shall be mounted adjacent to, and within sight of the controlled motor.

Motor Re-acceleration

The restart criteria shall be established based on the process requirements (including  all package units). Sequential restart studies and calculations for all required equipments shall be performed.
The re-acceleration philosophy shall be as follows:
a. Inherent characteristics of motor contactors and control circuits shall  permit motors to remain connected to bus bars and ride through voltage falling from nominal to 80% of nominal and of a duration no longer than
0.4 seconds maximum.
b. For motors and associated control equipment “Voltage sag ride-through capability curves” shall be submitted to the COMPANY.
c. Motors shall trip on under voltage and require manual restarting in the event that the following conditions occur:
 Total loss of power supply
 Voltage falling below 80% of nominal at the bus or 75% of nominal  at Motor Terminal.
d. Motors required for continuous operation shall automatically and sequentially (at timed intervals) be re-accelerated individually or in groups, via Process Control DCS, when voltage reaches back 95% and above of
nominal and for a duration up to 2 seconds and above.
e. The selection of equipment to be re-accelerated and the sequence shall be as per process requirements.

Lighting

  • Equipment related to lighting systems, transformers, panel boards and fixtures shall be installed to not interfere with the normal clearances allotted for personnel and equipment.
  • Where possible, lighting circuits shall be arranged with the lighting distributed in a way that allows minimum evenly distributed lighting upon circuit de energization and for energy saving when higher levels of illumination are not required.
  • Lighting fixtures shall be listed and labeled by Underwriters Laboratories minimum.

Lighting Levels

  • Lighting levels shall be in accordance with Lighting Design Requirements in Process Industry and Building  Table I.
  • These are in-service values, after a maintenance factor of 0.65 has been applied, or a factor of up to 0.85 may be used indoors in air conditioned or pressurized areas. The Lux illumination levels are average vertical component values for the locations described at a horizontal plane 76 cm above the floor, ground or platform.

Lighting Transformers

  • Lighting transformers shall be in accordance with Lighting and Receptacle Circuit Wiring Requirements and approved for the area classification they are to be installed in.  Alternatively the primary voltage can be Medium Voltage if there is no 480V  available.
  • The transformers shall be provided with four 2.5 percent full capacity taps, two above and two below the rated primary voltage.
  • Transformer sizes shall be standardized at 15, 30, 45 and 75 kVA depending upon load requirements.
  • A lighting transformer shall be provided for every lighting panel board. The initial panel board load shall not exceed 70 percent of the transformer capacity.

Lighting Panel boards

  • Lighting panel boards shall be in accordance with Lighting and Receptacle Circuit Wiring Requirements .
  • The 400Y-230 V branch circuits shall be protected by 20 A air circuit breakers housed in lighting panel boards.
  • Panel boards shall be equipped with a main breaker.
  • Panel boards shall be; approved for the area classification; suitable for the corrosive atmosphere in which they may be installed; and located as close as practical to the load to be served.
  • Panel boards installed indoors or outdoors in hazardous areas shall be explosion proof NEMA 7.
  • Panel boards installed indoors in non-hazardous areas shall be NEMA 4.
  • Panel boards installed in corrosive atmospheres shall be NEMA 4X fiberglass reinforced polyester or equal.
  • Separate panel boards shall be provided for non-lighting load, for example single phase motors, receptacles, and instrument power circuits.
  • Panel boards installed outdoors shall be provided with breathers and drains.
  • Panel board load distribution shall be based on balanced loading of its transformer.

Branch Circuits

  • Branch circuit breakers for lighting, receptacles and single phase motors shall be single pole, rated at 20 A.
  • Single or two pole breakers with ratings higher than 20 A may be required for special load requirements.
  • Initial loading on branch circuits shall not exceed 70 percent.

Lighting Fixtures

  • General lighting where an outdoor industrial process or procedure takes place shall be provided by high pressure sodium or HID fixtures with high power factor ballasts. These fixtures shall be provided complete with globe, guard and reflectors.
  • The use of flood lighting shall be maximized, with supplemental local fixtures added as required. Flood lights and local fixtures shall have integral ballasts.
  • Offices, control rooms and similar indoor areas shall be illuminated with commercial and industrial type fluorescent fixtures provided with thermally protected rapid start ballasts.

Flood Lighting

  • Floodlighting fixtures shall be 230 V, single phase, high pressure sodium or mercury type. Power supply to flood lighting systems shall be fed from 3 phase 4 wire feeders. Adjacent flood lights shall be fed from alternate phases.
  • Three pole circuit breakers and contactors shall be provided for floodlighting circuits.
  • Floodlighting shall be photocell controlled with manual override.
  • Floodlights may be mounted on platforms, structures or poles. Poles shall be spun aluminum. Aluminum poles installed in corrosive areas shall be painted or coated with an anticorrosive.

Street Lighting

Plant street and roadway lighting shall be mounted on 10 m high light poles. Lighting shall be provided at street intersections.

Pipeway Lighting

Pipeway lighting shall be lighted to a minimum level, but shall still provide for safety. An  intensity of 20 lux shall be considered a reasonable minimum level.

Control Room and Indoor Lighting

  • Fluorescent lighting fixtures provided with rapid start ballasts and RFI filters shall be used for indoor lighting.
  • Manual switches located at the entrance of each office or equipment room shall control the lighting for that room.
  • The control room lighting shall be coordinated with the instrumentation equipment locations to minimize glare and reflection on panel mounted instruments and meters, CRT displays and annunciators.
  • Control room lighting shall incorporate multilevel switched fixtures or dimmers and special louvers over the fixtures to distribute light to reduce glare and reflection on CRT displays.

Local Instrument Lighting

  • Where required by the process, through vision gage glasses shall be  provided with special lighting fixtures designed for the purpose. Lamps for these fixtures shall be the long life type. Gage glass lights shall have a
    local control switch mounted adjacent to the unit for individual control.
  • Special lighting for individual field mounted instruments shall not be provided. Lighting fixtures for general illumination shall be mounted as close as possible to instruments to provide lighting.
  • The interior of walk in instrument shelters and under the weather protective hoods in front of local control panels shall be provided with lighting to permit the reading or maintenance of instruments at these locations.

Emergency Lighting

  • Emergency lighting shall be concentrated in areas critical to orderly plant shutdown and emergency services. Typically these locations are:
    a. control rooms, switchgear rooms and emergency generator locations.
    b. local control and instrument panels.
    c. essential process equipment and process control stations.
    d. safety showers and eye wash stations.
    e. fire control panels and areas around fire pumps.
  • Minimum of 20 percent lighting for outdoor process areas and buildings shall be on emergency power.
  • Self contained, rechargeable, nickel cadmium battery powered lighting units that can be switched on automatically in the event of loss of normal power are suitable for egress lighting.
  • Illuminated exit signs shall be on emergency power.
  • Light fixtures fed from emergency power shall be provided with instant or rapid restart ballasts.
  • Emergency lighting at plant buildings shall comply with requirements of SAF-03.

Lighting Control

  • The normal switching of outdoor lighting shall be by photocell control of an airbrake magnetic contactor. A manual override of the photo cell shall be provided. The photo cell, manual override switch and contactor shall be located adjacent to the lighting panelboard, in an enclosure suitable for the environment and approved for the area classification.
  • Rooms, for example individual offices, equipment rooms, washrooms, and instrument shelters shall be provided with local switches in enclosures suitable for the environment and approved for the area classification.
  • In industrial or process facilities where, for example, structures, columns, and towers have lighting on platforms above the grade level, a local switch shall be located at grade, at the base of the ladder or stairs leading up. This will permit turning off the lights on the upper elevation platforming when no longer required.

Convenience Receptacles

  • Convenience receptacles for 230 V, single phase non-process area shall be provided with 30 m extension cord to furnish a source of power for portable power tools and extension lighting, for maintenance and repairs.
    Maximum four receptacles shall be connected to a 20 ampere branch circuit.
  • The receptacles in the process area shall be positioned in a way that locations where portable power is required shall be within reach of a 15 m extension cord. Maximum four single receptacles shall be connected to a
    20 ampere branch circuit.
  • In process areas with vertical columns and towers, a receptacle shall be located at the base and on every platform providing access to a manway.
  • Receptacles shall be installed not more than 20 m apart, on all working platforms and tall structures so any location where portable power is expected shall be within reach of a 30 m extension cord.
  • Receptacles shall be suitable for the atmosphere and approved for the area classification they are installed in.
  • Receptacles shall have only bottom cable entries.
  • Receptacles shall be grounded through the ground core of the cable in addition to the requirements of NEC Article 250.130(A).

Welding Receptacles

  • A number of 480 V, three phase, 60 Hz, 60 ampere circuits shall be provided for supplying power to, for example, portable pumps and welding machines.
  • Welding receptacles shall be located so that 40 m ac power cords can cover all areas of the plot.
  • Plugs shall be provided with the welding receptacles, with one plug for every ten receptacles installed.
  • Branch circuit protection for the welding feeders shall be provided by remotely located thermal magnetic circuit breakers.
  • Overcurrent protection and a disconnecting means shall be provided as an integral part of the welding machine in accordance with NFPA 70 (NEC).
  • Welding receptacles shall be connected for a common phase rotation to match the existing rotation, when installed in existing facilities.

 Wiring Methods

  • Lighting circuits wiring shall be color coded, single conductor 90ºC, cross linked polyethylene (XLP), UL type XHHW or equal, in rigid conduit or metal clad (MC) 90ºC, XLPE, multi-conductor cable with overall PVC
    jacket, suitable for cable tray installation.
  • Buildings with finished walls, for example control centers or offices, wiring for lighting, receptacle power and other systems may be installed in Electrical Metallic Tubing (EMT). In addition to the single conductor branch
    circuit wiring a ground wire shall be included in the EMT.

Uninterruptable Power Supply (UPS)

  • UPS(s) shall be designed and manufactured in accordance with Uninterruptible Power Supply UPS Design Notes  and shall be sized as per Power System and Equipment Design Calculations .
  • UPS(s) shall have dedicated distribution panel(s).
  • UPS manufacturer shall be informed if UPS is to be used on High Resistance Grounded power system.
  • UPS shall be located in the building where control and instrumentation equipment is located.
  • For Security Systems UPS requirements refer to Section 32 of this standard.

Electrical Heat Tracing

Electrical heat tracing shall be specified for process design requirements and coordinated  with the process group.  When heat tracing is required, it shall be self-regulating, ribbon type approved for use in  the area classification in which it is installed.

Conduit and Fittings

Below Grade Conduit

  • Generally the installation of below grade conduit should be avoided, except in  buildings where conduit may be installed in concrete floors.
  • Below grade conduit shall be rigid hot dipped galvanized steel with a 40 mil (1.02 mm) PVC coating on the exteriorsurface and an epoxy coating on the interior surface.
  • Minimum size for below grade conduit shall be 1 inch. Below grade conduits shall be sized one size larger than required by Code maximum wire fill.
  • Reductions in conduit size shall be done above grade.
  • Below grade bends shall be of the large radius type.
  • Minimum depth for low voltage system conduit installation shall be 0.6 m below  grade and 0.9 m below grade for medium voltage systems.
  • There shall be no more than three 90º bends in a below grade conduit run.
  • Below grade conduits shall have a red tiles or concrete cover.
  • Spare conduits shall be provided with pull cords, terminated with plugged  couplings and installed flush with the finished floor in buildings, or 1 inch above the finished surface in other areas.

Above Grade Conduit

  •  Above grade conduit shall be rigid copper free aluminum or galvanized. In  locations where aluminum conduit may be subject to mechanical damage, for example compressor or skid mounted equipment bases, the conduit shall be rigid hot dipped galvanized steel with a 40 mil PVC coating on the exterior surface and epoxy coated on the interior surface.
  • Minimum conduit size shall be 3/4 inch unless otherwise noted. Conduit used behind control boards or other types of panels may be 1/2 inch.
  • Conduit shall be separated by a minimum of 150 mm from piping or equipment with surface temperatures in excess of 55ºC.
  • When conduit is terminated to equipment where vibration or movement is a concern a 0.6 m length of flexible liquid tight conduit shall be installed between the rigid conduit and the equipment.
  • Conduit fitting in the above grade conduit system shall be manufactured from copper free aluminum. Cover screws shall be stainless steel. Fittings shall be approved for the area classification and be suitable for the environment in which they are installed.
  •  When PVC coated rigid galvanized steel conduit is used, galvanized steel fitting with a 40 mil (1.02 mm) PVC exterior coating and epoxy interior coating shall be used. Cover screws shall be stainless steel. Fittings shall be approved for the area classification and be suitable for the environment in which they are installed.
  •  PVC coated clamps shall be used to fasten aluminum conduit to ungalvanized steel or concrete surfaces. Where aluminum conduit comes in direct contact with ungalvanized steel or concrete, the conduit shall be wrapped with insulating tape.
  • At transition points between aluminum and steel conduit an antioxidizing compound specially made for this application shall be applied to the threads.
  • Electrical metallic tubing (EMT) shall be restricted in use to installation in offices, control rooms and other similar buildings with finished interiors.
  • Straight runs of conduit in excess of 150 ft shall be provided with an approved expansion fitting.
    Where conduit runs exceeds equivalent of a 45 m run or more than the equivalent of four 90º bends, expansion joint fittings shall be installed. One 90º bend shall be considered the equivalent of 15 m of straight run conduit.
  • Conduit entry into enclosures or devices shall be side or bottom, top entry for outdoor installation is not allowed. If open-ended conduit installation is used then the cable entry shall be via appropriate cable glands as dictated by Hazardous Area Classification requirements.

Conduit Seals, Breathers, and Drains

  • Seal fittings shall be installed in conduit and cable runs where required by  NFPA 70, Article 501.
  • Breathers and drains shall be installed at all low points in conduit systems and  as required to prevent accumulation of moisture in the conduit and equipment enclosures.
  • Breathers and drains shall be approved for the area classification and be suitable for the environment in which they are installed.

Conduit Ells and Tees

  • Installation and construction of ell and tee fittings shall comply with 16.2.
  • No short radius ells or tees shall be used.

Cable Trays

  • Cable trays shall be aluminum or galvanized steel. Fiberglass trays shall be used for special applications, for example in areas where caustics or chlorine are present.  Aluminum cable trays shall be copper free, ladder type with construction and mechanical load in accordance with NEMA VE 1.
  • Fiberglass cable trays shall be the fiberglass reinforced polyester ladder type, ultraviolet radiation resistant and with construction and mechanical loading in accordance with NEMA FG 1.
  • Cable tray systems shall be continuous and complete, with system components rigidly attached together and to the tray system supports. Bends and offsets shall be kept to a minimum.
  • Cable trays in outdoor locations shall be covered. Covers for power trays shall be louver ventilated type secured to the tray with stainless steel banding. Trays used for instrumentation or communication cables require covers with ventilation provisions.
  • Vertical runs of outdoor cable tray shall be covered on both sides.
  • Cable installed in trays shall be approved for tray installation, approved for the area classification and suitable for the environment in which it is installed.
  • Cables in trays shall be grouped according to voltage level, insulation class and function.
  • Medium voltage cables shall be run in separate trays, with cables of each voltage level used run in dedicated trays.  Control cable and low voltage power cable may be run in the same tray provided that the
    cables are of the same insulation class.
  • Instrumentation cable shall be run in separate trays. Thermocouple cables in the same  tray shall be segregated by means of barriers. Critical shutdown and control system cables shall be run in separate trays or segregated from other cables by means of barriers in the tray.
  • Cable tray shall be grounded to the ground bus of the switchgear or motor control center  from which its cables originate.
  • Metallic tray systems shall be electrically continuous and grounded to the ground grid every 30 meters throughout the entire system using a 35 mm2 insulated single conductor copper cable.
  • Expansion joints and tray support points shall be as specified in the manufacturer‟s recommendations. Bonding jumpers shall be provided at expansion joints.
  • Cable trays shall be routed to avoid high fire risk areas, especially trays for fire alarm, communications or instrumentation systems. If cable tray has to be routed through areas of high fire risk, appropriate fireproofing and fire protection precautions shall be taken.

Direct Buried Cables in Underground Trenches and Duct Banks

Direct Buried Cables in Underground Trenches

  • Cables suitable for direct burial outdoors in underground trenches shall be metal clad with an overall PVC jacket and listed for direct burial application.
  • Cables routed under buildings and stubbing up into electrical equipment shall be installed in conduit sleeves extending 3 ft beyond building exterior buried edge of concrete foundation.
  • Cables passing through walls or other masonry structures shall be protected by conduit sleeves. These sleeves shall be packed and sealed after cable installation.
  • Cables passing under roadways shall be installed in steel pipe or concrete encased conduit. Spare conduit shall be sealed at both ends before trenches are back filled.
  • Below grade cable trenches should generally have earth side walls and bottoms unless otherwise noted.
  • Trenches shall be provided with space for 20 percent future cable additions. The future space shall be allocated in the top tier in trenches and conduit routed under roadways.

Trench Configuration for Low Voltage Cables

  • The bottom tier of cables in trenches shall be installed on a 75 mm minimum layer of sand or selected screened fill material. For multi-tier cable trenches a 150 mm minimum layer of fill shall be provided between cable tiers. The top tier of cables shall be 200 mm below the bottom of the protective red concrete covering slab. The space between the top tier of cable and the protective covering slab shall be completely filled with sand or selected screened fill.
  • The red concrete slabs installed over the cables shall be a minimum of 100 mm thick and fitted with lifting eyes. These protective slabs shall be laid end to end across the length of the trench at a depth of 230 mm from finished grade. Details of the slabs shall be provided by Civil Engineering.
  • After the red concrete slabs have been set in place across the trench, it shall be back filled to the level of finished grade.
  • Trench location shall be indicated by red concrete warning markers placed at 30 m intervals along the trench and at changes of direction.
  • Where trenches have concrete side walls, the top tier of cables shall be a minimum of 150 mm below the bottom of the trench cover. This space shall be completely filled with sand or selected screened fill.
  • In common trenches, low voltage branch circuits may be installed in up to a maximum 3 tier trench. Horizontal separation between cables shall be a minimum of 100 mm. Motor control cables shall be located in trenches with their associated power cables.

Trench Configuration for Medium Voltage Cables

  • 18.3.1 Only a single tier of medium voltage distribution cables shall be allowed in below grade trenches. These cables shall be installed on a 75 mm layer of sand or selected screened fill. The horizontal separation between cables shall be a minimum of 200 mm filled with sand or select screened fill.
  • Low voltage interlock and other control cables related to the switchgear or transformers associated with the medium voltage distribution cables may be run in the same trench screened. The control cables shall be separated horizontally from the power cable by a minimum of 200 mm of sand or select fill.

Cable Trenches Across Paved Areas other than Roadways

  • Below grade cable trenches across paved areas shall have load-bearing  concrete sidewalls and bottoms with removable covers.
  • Trench covers shall be of reinforced concrete, either precast or poured in  place, or steel checkered plate.
  • Trench covers shall be removable, fitted with a means of attachment for a  lifting device.
  • Trench covers shall be supported by the concrete trench sidewalls, the tops of  the trench covers shall be flush with the adjacent paving.

Below Grade Electrical Duct Banks

  • Duct banks shall be constructed of PVC conduit, encased in concrete.
  • Spacers to provide a minimum separation between conduits of 1 inch for  conduits 1.5 inches or smaller and 2 inches for conduits of 2 inches or larger. The spacers shall be placed at intervals of approximately 8 ft.
  • Conduit runs in duct banks shall be made continuous by the use of couplings.
  • Duct banks shall be provided with 20 percent spare capacity.
  • In duct banks constructed with PVC conduit under areas that are subjected  to light or infrequent vehicular traffic, unreinforced non-structural concrete shall be used.
  • In duct banks constructed with PVC conduit under areas that are subjected to heavy frequent vehicular traffic, for example under roadways, reinforced structural concrete shall be used.
  • The concrete encasement shall extend a minimum of 3 inches from any conduit in the bank to the outside surface.
  • The top layer of concrete on the duct bank shall be red concrete. From grade to the top of duct bank shall be a minimum of 18 inches.
  • Conduit stub ups in process areas shall be rigid steel. Where PVC conduit is used, a transition to rigid steel conduit shall be made below grade.
  • Manholes or handholes required for the duct bank system shall be located in non-hazardous classified areas. Manholes shall be provided with cable pulling irons embedded in the concrete side walls of the duct bank.
  • Below grade duct bank locations shall be indicated by red concrete warning markers placed at 64 ft intervals along the banks and at bends where no manhole is present.

Wire and Cable

Conductors shall be stranded copper except for thermocouple, telephone and special  instrument cable.

Conductor Sizes

Minimum size for conductors shall be selected from the current carrying capacity tables  of the latest version of the NEC. An ambient air temperature of 50ºC including derating factor shall be used in sizing of conductors.

Voltage Drop

Wire size shall be selected to limit maximum voltage drop for power and high intensity  discharge lighting circuits to 2.5 percent for feeder circuits and 2.5 percent for branch circuits. For incandescent lighting and instrumentation power circuits, the maximum voltage drop shall be 1 percent for feeder circuits and 2 percent for branch circuits or an overall of 3 percent.

Splices

  • Generally, power cables 8 AWG (10 mm2) and larger and control cables should be run continuously from origin to termination without splices or taps. Lighting circuits may be spliced or tapped.
  • Splices shall not be made underground. If required, splices shall be made in suitable fittings or junction boxes above ground.
  • Splices in low voltage stranded wire shall be made by compression type connections.
  • Splices in medium voltage cables require company approval and shall be made in accordance with the manufacturer‟s recommendations.
  • Splices in low voltage conductors shall be limited to branches circuit wiring or those required to permit installation.

Cable Terminations

  • Compression type connectors shall be used for terminating low voltage  stranded conductors.
  • Terminations of medium voltage cables shall be made in accordance with the  manufacturer‟s recommendations.
  • Medium and high voltage shielded cables shall be terminated with approved  stress relief devices.

5 to 35 kV Service

  • Medium voltage power cable shall be manufactured in accordance with the following, as applicable:
  • 5 kV cable shall be single or three conductor, copper, stranded and shielded, with cross-linked polyethylene (XLPE) or ethylene propylene rubber (EPR) insulation. The cable shall be rated at 90°C and shall have an overall outer PVC jacket.
  • 15 kV cable shall be single or three conductor, copper, stranded and shielded, with cross-linked polyethylene (XLPE) or ethylene propylene rubber (EPR) insulation. The cable shall be rated at 90°C and shall have an overall outer PVC jacket.
  • 35 kV cable shall be single conductor, copper, stranded, shielded with ethylene propylene rubber (EPR) insulation and an overall outer PVC jacket.
  • Medium voltage cables running through hazourdous areas shall be armoured.

600/1000 V Cable

Low voltage cable shall be jacketed copper conductor, stranded and complying with the NEC. It shall be rated for the proper voltage level and have a minimum temperature rating of 90ºC.
Low voltage cables running through classified hazardous areas shall be armoured.

Low Voltage Wire

Wire for building applications shall comply with requirements of NEC IEC Based Low Voltage Cables Selection Criteria .

Instrument Cable

Click Here for More Details.

Fire Alarm, Telecommunication, and Paging System Cable

Refer to relevant Click Here for Fire Alarm system. Refer to relevant Click Here for Telecommunication and Paging systems.

Fiber Optic Cable

Refer to Click Here for requirements of Fibre optic cables.

Grounding

Electrical equipment, metallic structures, vessels, conduit, manholes, cable trays and fencing shall be permanently and effectively grounded in compliance with NFPA 70- Article 250. The tallest columns, stacks, steel structures, cable trays and pipe supports shall be grounded for lightning protection. Process equipment, motors and control stations in hazardous classified  areas shall be grounded for the prevention of static discharge. For details see Bonding and Grounding & Installation of Grounding and Bonding Conductors and LIGHTNING PROTECTION SYSTEM INSTALLATION PROCEDURE.

  • Maximum resistance to ground shall not exceed 1 ohm for systems over 600 V and 5 ohms for systems below. Unless otherwise stipulated by the system supplier, computer systems shall be 1 ohm.
  • The system shall consist of grounding electrodes, ground loops, ground grids (where required) and connections to the equipment requiring grounding.
  • The main ground loop cables shall be a minimum 95 mm2, bare, stranded, tinned copper.
  • Cable size for outdoor equipment grounds shall be a minimum 16 mm2.
  • Minimum grounding cable size shall be 6 mm2.
  • Electrical equipment rated above 600 V shall have two connections to the ground system,  one at each end of the equipment.
  • Grounding system cable shall be stranded copper, with green or green with yellow striped PVC insulation.
  • Buried connections shall be the exothermic welded type. Approved compression type  connectors may be used above ground.
  • Ground electrodes shall be copper or copper clad steel, a minimum of 3048 mm (10 ft)  long with a minimum diameter of 3/4 inch.
  • Ground loop cable shall be buried a minimum of 450 mm (18 inches).
  • In non-metallic raceway systems a single insulated ground wire shall be pulled through  each section of the system to be used for equipment grounding.
  • Continuous cable tray systems shall have bonding jumpers installed across expansion joints and shall be connected to the grounding system at intervals not to exceed 30 m. If the tray system is not continuous from the source to utilization equipment, a separate grounding conductor is required.
  • System and equipment grounding electrodes shall be interconnected by means of the main ground loop.
  • A grounding grid consisting of 19 mm (3/4 in) by 3048 mm (10 ft) copper-clad steel ground rods and #3/0 AWG (95 mm2) copper cables forming a continuous loop or grid shall be used. The grid shall be installed in a uniform pattern.
  • Ground rods shall be installed through a single 914 mm (3 ft) length of 203 mm (8 in) diameter concrete pipe, with removable cover to permit periodic inspection and to provide access to the ground rod clamps. The cover of the concrete pipe shall be located flush with finished grade.

Cathodic Protection

Cathodic protection systems shall be in accordance with Topics written in PAKTECHPOINT. Rectifiers and Accessories for Cathodic Protection shall be as per Cathodic Protection Transformer Rectifier Stations.

Lightning Static and Stray Protection

  • Tall or isolated metallic structures, stacks, and columns shall be grounded for lightning protection.
  • The lightning protection system shall consist of lightning masts; structure mounted lightning rods of varying lengths and the lightning system conductors.
  • A direct connection to the plant main ground loop (grid) shall be provided for each lightning system conductor from lightning masts, lightning rods and above grade lightning protection interconnection conductors.
  • Lightning protection installations shall be in accordance with NFPA 780.
  • Tank trucks, tank cars, portable drums, storage tanks, and agitators shall be protected  against static electricity, lightening and stray currents. See API RP 2003 and NFPA 77 for details. Generally, all elevated or isolated, or both, metallic objects, for example columns, stacks, and structures shall be grounded for lightening protection.
  • When overhead high voltage power-lines runs in parallel with pipelines or crosses them, the clearances and precaution stated shall be taken, necessary studies, calculations shall be performed.

Substation 

Substations shall consist of power transformers, switchgear, motor control centers, power panels, alarm panel, station batteries and chargers, and other accessory equipment. Equipment, except large power transformers shall be installed externally on a substation building.

Heating, Ventilating and Air Conditioning Systems (HVAC) for Substation  Buildings

  • HVAC system design shall be as per ”HVAC System Design Criteria”. Substation buildings shall be provided with redundant HVAC systems- normally operating and standby unit(s). In the event of a failure of the normal unit an alarm shall sound in the control room.
  • If the HVAC systems are not powered from a secondary selective system, stand-by units shall be fed from an auxiliary power source.
  • The HVAC system shall provide positive pressure ventilation to the substation at all times. The system intakes shall be fitted with dust filters and shall alarm at the control room upon loss of positive pressure.
  • The battery room ventilation system and substation pressurization system shall be powered from emergency power supply system. In the event of a failure an alarm shall sound in the substation alarm panel and control room.

Doors, Windows and Wall Penetrations

  • Substation buildings shall not have windows.
  • Substation buildings shall have a minimum of two doors, placed to avoid dead end aisles. One door shall be suitably sized as an equipment door to accommodate entry and removal of the equipment installed in the substation.
  • Substation doors shall be double wall steel fitted with hydraulic door closures and stops. Doors shall be equipped with cylinder locks and inside panic bar door opening hardware.
  • Cables and conduits entering the building shall be via an approved fire stop.

Building Sizing and Equipment Arrangement

  • The substation building shall be sized, and the equipment arranged, to provide adequate space for:
    a. Removal of equipment from its enclosures.
    b. Equipment maintenance and testing.
    c. Provisions for a minimum of one additional section of equipment for switchgear and motor control centers. A site-specific review of future expansion requirements shall be made prior to allocation of substation
    floor space for future expansion.
    d. Clear working space in accordance with NFPA 70, Article(s) 110-32 to 110-34.

Warning Signs

Signs shall be posted at the entrances to the substation forbidding unqualified persons  to enter.

Station Batteries and Charger

Station batteries and battery charger used for 125 V dc switchgear control power shall be located in the substation building as per Electrical Engineering Substation Design.

Substation Lighting

Substation building lighting requirements are covered in Electrical Engineering Substation Design.

Alarms

Each substation shall have an audio-visual type annunciator panel and remote contact alarm. The annunciator panel shall have illuminated equipment nameplates and „test‟ and „acknowledge‟ pushbuttons.

Packaged Equipment Requirements

Electrical equipment that is fabricated as a unit package by an outside vendor shall meet the same requirements as the components and systems of the plant it is to be installed in.

Emergency Generation

The Emergency switchgear shall be normally powered through normal supply sourced from the switchgear line up through transformers. This shall be backed up by emergency power available from a  dedicated standby diesel generator. In case of failure of normal power, emergency power shall be available at the emergency switchgear through automatic starting of the diesel engine and an automatic transfer switch to change over to emergency power source. System shall automatically revert to the main utility power feed upon its restoration with no manual intervention required. Paralleling with utility is subject to utility approval. In addition to automatic transfer a manual transfer facility from normal to emergency and back is required.

  • The emergency generators shall be brushless type with solid state exciter.
  • Generator nameplate rating shall be suitably derated to meet actual ratings to be  expected at the site.
  • Generators shall be constructed to the requirements of Design Notes & Diesel Generator Working Principle and NEMA MG 1.
  • The Emergency Generator start philosophy shall be as below:
    a. If the Bus voltage falls below 70% for a period greater than 0.4 seconds, the Emergency Generator shall be started.
    b. If the voltage remains below 70% for a period greater than 10s then Automatic Transfer Switch (ATS) shall be switched to Emergency position to feed the Emergency loads only. Re-start shall then be inititiated for the motors under Emergency distribution.
    c. Equipment not connected to the emergency switchboard shall remain tripped and locked out.
  • Cables, fuel lines and other utilities to emergency power generation facilities shall be underground.

Equipment Identification (Name Plates)

Identification nameplates shall be located at all switchgear, motor starters, circuit breakers, push buttons stations, lighting panels and similar equipment. The nameplates shall be of laminated black and white plastic arranged to show black engraving on a white background. The nameplates shall be secured to the panels and equipment by stainless steel screws.

Inspection of Electrical Equipment and Systems

  • Inspections shall be performed upon completion of installation of new or modified electrical installations in SABIC facilities. These inspections shall include checking:
    a. proper support, routing and continuity of raceway systems.
    b. equipment is approved for the area classification in which it is installed.
    Conduit system drains and seals are correctly placed.
    c. enclosure and fitting covers have been correctly installed and sealed.
    d. equipment is free of physical damage.
    e. equipment and systems are properly grounded.
  • Electrical audit shall be made on systems related to life safety or where failures could result in substantial loss of production.
  • Consult equipment specific standards for inspection and test procedures unique to that equipment.

Maintenance of Electrical Equipment and Systems

  • Maintenance costs and convenience of maintenance shall be considered as factors in equipment selection.
  • Electrical equipment requiring adjustment or periodic calibration shall be supplied with required diagnostics and test points.
  • Maintenance manuals shall be required for all equipment.
  • Periodic maintenance schedules shall be established for all electrical systems and  equipment based on manufacturer‟s recommendations.
  • Electrical equipment and systems shall be built and installed to allow for replacement of  all parts critical to operation.

Testing of Electrical Equipment and Systems

  • Field checks and tests shall be according to NETA-ATS. Such tests shall include, but not be limited to the following:
    a. Visual check of wire and cable connections.
    b. Check ac and dc control circuits for short circuits and extraneous grounds.
    c. Check phase rotation of switchgear and motor control centers.
    d. Check equipment for proper mechanical adjustment and freedom of operation.
    e. Motor run-in.
    f. Function tests of power, control and lighting circuits.
    g. Function tests of electrical signal and alarm systems.
    h. Continuity check of low voltage power and control circuits.
    i. Insulation resistance, continuity, and dc high potential tests on medium and high voltage cable.
    j. Check resistance of grounding system.
    k. Check polarity of current transformers and potential transformers.
    l. Check current transformer ratios and continuity of the secondary circuit.
    m. Function tests shall be performed on the following major equipment:
    (i) power and distribution transformers
    (ii) medium voltage switchgear and circuit breakers
    (iii) medium voltage motor controllers
    (iv) low voltage switchgear and circuit breakers
    (v) low voltage motor control centers
    (vi) uninterruptible power supplies and other types of battery and charger systems
    (vii) motors
    n. Function tests, to determine proper operation, shall be performed on all components, for example switches, circuit breakers, relays, and starters including control interlocks and sequential control circuits.
    o. Special tests recommended by the manufacturer.

SCADA System, Metering, Monitoring and Control Philosophy

  • A Supervisory Control and Data Acquisition (SCADA) system may be used to monitor and control various remote functions of electrical equipment that may be located across a wide geographical area, by the use of a serial communications link between the master control and remote locations.
  • Various transmission media may be used for the SCADA communication link, for example telephone lines, microwave or UHF/VHF radio.
  • For specific requirements and details of SCADA systems see Electrical Power SCADA System Overview.
  • Metering and Monitoring Philosophy:
    The following measurements and status signals must be provided at the plant DCS and Electrical SCADA system:
    a. Status of all MV incoming, outgoing and bus-tie circuit breakers and emergency circuit breakers.
    b. Plant total kW, kVAR, kVA, kVAh, kWh, kVARh ( tariff class)
    c. Status of motors and heater breakers.
    d. Measurements of Voltage, Current, PF, kWh, kVA at all incomers feeders, and busses.
    e. Measurements PF, Coltage , Current , PF, kW, kWh, kVA for Induction Generators,  Standby Generators , and Heaters.
    f. Electrical fault signals for all drives , heaters, generators, etc.
    g. As per requirement of process/ instrumentation during engineering phase.
  • Control System Philosophy:
    a. All 4.16 kV and 480V motors shall be started direct on line, except those that are  equipped with VFD equipment.
    b. The starting and stopping of all motors shall be via DCS or from field control stations. Some motors can be started in Auto /and or in manual, as per process application requirement.
    c. In some instances additional emergency stop pushbuttons will be required near the machine at grade level. All such pushbuttons will be pull to trip and be shrouded.
    d. Control of all incomers, bus-tie and outgoing transformer feeder circuit breakers from 4.16kV down to 480V main switchgears shall be possible locally and from SCADA system.
    e. In addition to control commands , the following status signals shall be made available as a minimum at the DCS:
    i. Contactor/ breaker open/close status
    ii. Overload / breaker trip signal ( electrical fault)
    iii. Control supply (electrical ready signal for drives, regenerative heaters, generators , etc.)
    iv. Hand/Off/Auto
    v. Local / Remote
    vi. Running / not running
    vii. Motor current
    viii. Starter in place or withdrawn

 

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1 thought on “NEC Electrical System Design Criteria in Process Industry”

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