Electrical Power SCADA System Overview

This article is about the requirements for the Supervisory Control and Data Acquisition (SCADA) system for the electrical power system. The SCADA system is intended for electrical power system data acquisition and system condition monitoring, and will perform no control function or configuration of electrical devices. Main keywords for this article  are Electrical Power SCADA System Overview, SCADA System, Substation Circuit Monitoring and Alarm Systems, SCADA Architecture, SCADA Hardware.

SCADA References

Institute of Electrical Electronic Engineers (IEEE)
IEEE-730 Standard for Software Quality Assurance Plans
IEEE-802 Standards for Local Area Networks
National Fire Protection Association (NFPA)
70 National Electrical Code (NEC)
Underwriters’ Laboratories (UL)
1244 Electrical and Electronic Measuring and Testing Equipment

Electrical Power SCADA System Overview

SCADA System Arrangement

The SCADA system shall monitor the lineups of switchgear, and MCCs in the main and various unit substations located in process units throughout the facility. The various lineups contain microprocessor
type monitoring and protection devices that are wired together to communicate to a LAN within the substation. Substation LANs are networked together by the WAN.
System Function

  • Each substation shall be capable of functioning as a stand-alone system with independent local nodes. The local node at each substation compiles local device data which is communicated to the LAN.
    User consoles within each substation shall provide local monitoring capabilities.
  • LANs communicate system data with the SCADA summary node via the WAN. The WAN communicates with the summary node console and provides monitoring capabilities of all substation systems. The summary node in turn shall be capable of communicating information to the plant administrative, operating and engineering WAN(s).

    Electrical Power SCADA System Overview

SCADA Application Software

The SCADA Application shall provide software data display of data monitoring and setpoint configuration data for the metering and protective devices. The SCADA Application shall accommodate user customization of the system as well as be able to support third party tools for local data analysis.
a. The Monitoring of metering and setpoint parameters of metering and protective devices shall be represented in a consistent, modular format. Historical data logging, alarming, real time trending and historical trending shall be standard features within the SCADA package.
b. The basic SCADA graphical presentation shall be in the form of the power system single line diagrams utilizing standard ANSI/IEEE symbology. The system shall have the capability to display multiple layers of semi-detailed and detailed single line diagrams that dynamically display the magnitude of specified system parameters.
c. The graphic representation of metering and protective devices shall display all device data in tabular format. Graphic representations should be easily configurable by the end user, allowing for  the addition, deletion and changing of devices after installation. A data base display of selectable metering and protective device setpoints, operating parameters and stored information shall be provided.
d. The SCADA Application shall include event detection and logging from metering and protective devices. Time stamping rates shall be suitable for waveform capture. The SCADA application shall be
capable of displaying waveform capture and harmonic analysis graphics from the metering and protective devices supporting these features. As a minimum, waveform capture shall be selectable from 12, 24, 36, 48 or 60 cycles. Waveform capture shall be capable of being manually or automatically triggered.
e. The SCADA application shall be capable of exporting data in a format compatible with third party Power System Analysis software such as Electrical Transient Analysis Program (ETAP) by OTI. The SCADA application supplier shall confirm degree of compatibility with these third party analysis programs.
f. All software shall be configured by the vendor and delivered ready for use.
g. In addition to switchgear and MCC metering and protective devices, the SCADA system shall be capable of displaying information from other systems which communicate via standard interfaces and protocols.
h. Quality assurance – The software supplier shall confirm software development practices conform to IEEE-730.
i. All of the above mentioned capabilities shall be accessible through an intuitive graphical user interface designed as a native software application which provides a representation of the site or sites’ global location, building plan and floor plans, location of monitored equipment within those floor plans, equipment elevations and an easy to use navigation system within those representations.
j. The system shall have a true client/server architecture. The server retrieves real time data from the networked devices, supports an online database, and initiates automated data back up. The client/server provides a highly intuitive Graphical User Interface (GUI) with site and equipment views, data display, data analyzer, and alarm/message management system. The client(s)/server can monitor the entire infrastructure, including remote sites, from any network location or through telephone connection to the server(s).

SCADA Subsystems

The following sections address design considerations specific to configuration and operation of components and subsystems that comprise the SCADA system.

Substation Circuit Monitoring and Alarm Systems

  • The SCADA system shall be designed to continuously monitor all aspects of the power system and check for any condition which is outside user-defined limits. Any parameter found to exceed these limits will cause the SCADA system to generate an alarm at the summary node and local node workstations. In addition, a message indicating the date, time, and location of the alarm will be printed and logged into a system event log.
  • The system log shall provide a history of all alarm and upset events. All events shall be dated and time stamped at the sending device and propagated to the SCADA system. The system shall be capable of constructing a sequence of events from captured data. Time stamping rates must be capable of discriminating between high speed transient events. Alarm and event messages must be capable of being instantly sorted by sequence of events/alarms, source type, source name, date, micro second time stamp, device type or type of alarm.
  • The SCADA system shall have the following features:
    a. The system shall monitor the steady state and peak electrical system conditions of the designated circuits. Minimum monitored parameters are current, voltage, real power, apparent power, power factor, frequency, and power demand.
    b. Monitor the status of selected devices such as breakers and motor controllers for on, off, open, closed, or tripped conditions.
    c. Provide upon operator demand and/or periodically, a hard copy record of the electrical circuit abnormal occurrences and alarm conditions.
    d. Alarm abnormal electrical system conditions (e.g., low voltage, high current, breaker status, etc.), and malfunctions in the SCADA system (e.g., loss of power, communication error, etc.). Provide upon operator demand and/or periodically a visual display on a CRT screen, point-by-point, of the systems alarms. The alarm points shall be identified by an identification number. The alarm condition value, real time value and a description of the alarm point shall also be displayed on the CRT screen.
    e. Monitor essential equipment (generators, designated motors, etc.) running conditions using inputs from associated solid-state metering and protection devices provided on the switchgear, motor control centers or equipment control panels.
    f. Although, the SCADA system shall be designed to acquire stored data by polling monitoring devices on a set interval, monitoring system devices shall possess enough on-board storage capability to accumulate and store historical data for extended periods of time. The data retention time periods are to be defined by the user and shall not be less than 30 days. Manufacturers shall indicate data retention duration for each type of device provided.
    g. The system shall be provided with GPS (Global Positioning Satellite) clock time signal hardware and software to periodically time synchronize all data collection devices with internal time clocks.
    h. Equipment furnished for circuit monitoring duties shall be listed for intended application. Devices shall meet UL 1244 or equivalent. Devices shall be vibration and temperature tested.
    i. Equipment furnished shall be Federal Communications Commission compliant per FCC Part 15, for Class A devices.
    j. The system shall be able to trigger waveform captures, automatically upload waveforms from the networked devices, and view captured and recorded waveforms.
    k. The waveform module should be able to collect voltage and current waveform data and analyze  this data for presentation and fault analysis.
    l. The system should perform harmonic analysis to render values for the root mean square of the waveform, the peak harmonic value, the peak current and voltage, the total harmonic distortion (THD) and the crest factor (CF).

Local SCADA Node

  • Local nodes shall be located in the main and unit substations and shall be configured to retrieve data  from the designated switchgear, mcc(s) and other devices in the substation and monitor the electrical system in those locations. The type and quality of data shall be a user defined set of data, specific for the location.
  • SCADA system architecture shall be designed for optimum response to both normal data gathering and reporting and from manual requests for data from a local node workstation.
    a. The SCADA nodes shall have a maximum response time for data polling of less than 4 seconds.
    b. The SCADA nodes shall have a maximum response time for event polling of less than 6 seconds.
  • The local SCADA node shall be comprised of the following equipment.
    a. Local node computer
    b. One color CRT
    c. One operator interface device
    d. One logging/alarm and screen printer
    e. LAN and WAN communications interface hardware
    f. Power conditioning or backup equipment.
  • In addition to the SCADA system application, operator consoles shall permit use of other software programs.

Local Area Network (LAN)

  • A LAN for data acquisition shall be required in each substation location containing lineups of switchgear. The LAN network shall utilize TCP/IP. The LAN shall utilize TCP/IP protocol for communication to and from the PC. Other common protocols available on circuit monitoring and control devices, such as Modbus RTU, DMP 3.0, DeviceNet, etc., may be encapsulated on the LAN using gateway devices. The local node shall be connected with and control the acquisition of data at each substation.
    a. The LAN shall communicate with the WAN through an ATM host module. LAN and ATM host module shall reside in a common hub.
    b. Other devices, such as local printers, and Personal Computer Communication (PC COM) station, etc. shall be connected to the LAN.
    c. The LAN shall be used to communicate with microprocessor type circuit monitoring devices (meters and protective relays) motor starters and other designated substation devices.
    d. If a gateway is required, multiple devices should be able to be connected to a single communication port on the gateway per the requirements of the network.
    e. For the purposes of the initial system design, the maximum number of devices connected to a single highway shall allow 30% expansion while meeting all system performance criteria. The final number of devices shall be approved.
    f. The TCP/IP gateway shall communicate to the local node via a LAN. The local node shall store and retain all upset parameters in non-volatile memory (no battery back-up) in event of a control power failure.
    g. The local node shall retain the minimum and maximum values for each of the instantaneous values reported as well as the time and date of the highest peak for all the peak demand readings in non-volatile memory.
    h. On demand, the local node shall communicate data to the summary node via the WAN.                                                                                                                                                i. In case of a local node failure, all devices connected to the ethernet LAN shall communicate directly to the summary node via the WAN.
  • To reduce the network load, input devices shall be split up into multiple networks and the data shall be concentrated in a TCP/IP gateway module. As a minimum these modules should support 4 or more Modbus RTU networks.
  • The TCP/IP gateway module should support connectivity to ethernet networking.
  • The local node shall utilize a TCP/IP data collection driver to communicate TCP/IP encapsulated data to and from the TCP/IP gateway modules. This driver should be O.P.C. and DDE (Dynamic Data Exchange)/Net DDE compliant for integration with the ‘off the shelf’ SCADA software packages such as Enhanced Graphics/Wonderware.
  • A local SCADA node shall be able to display real-time data from all other nodes.
  • Quality assurance – The supplier shall confirm LAN design conforms to IEEE-802.

Wide Area Network (WAN)

  • The WAN network shall be installed between the remote substation locations and the summary node console room. The WAN network shall have tie-in capabilities to allow a possible future SCADA system for the existing electrical system. The network is to utilize a redundant FO network and support the ATM protocol as well as other protocols such as FDDI, Ethernet, Fast Ethernet, Token Ring and both types of ATM 25.6 and 155-OC3.
  • All WAN hardware should be modular and rack mounted with redundant backplanes, control modules, and power supplies.
  • The WAN networking cabling shall be two runs of multimode fiber optic cable to support a single cable failure without loss of network connectivity. The cabling shall be physically redundant, and run in separate ducts to prevent inadvertent cable cuts. This two fiber by two controller ATM switching mechanism will prevent the two most common failures from occurring simultaneously; cable cuts and network controller failure.

Network Interface Systems

  • TCP/IP Gateway
    A communication interface or gateway shall be provided to allow communication to other data systems. The system should be able to communicate to other third party systems including DCSs, PLC networks, and software systems.
  • Switch System
    Ethernet switching hardware shall be provided to provide services and management required by the switching hub. Ethernet switching hardware shall be cable of supporting ATM as well as other protocols to provide the most fault tolerant, highest throughput network available.

Summary SCADA Node

  • The summary node location shall be designated by SABIC (usually the main substation) and shall be a central source of data for the entire electrical system.
  • The summary node shall have three functions.
    a. Gather data from the main and unit substation local nodes.
    b. Communicate directly with the TCP/IP gateway at the unit substations in case of failure of the  local node.
    c. Output data to other plant WAN systems via DDE encapsulated within the TCP/IP.
  • SCADA system architecture shall be designed for optimum response to both normal data gathering and reporting and from manual requests for data from a summary node workstation. The SCADA nodes shall have a maximum response time for data polling of less than 4 seconds. The SCADA nodes shall have a maximum response time for event polling of less than 6 seconds.
  • The summary node shall be comprised of the following equipment :
    a. Workstation console
    b. Summary node computer
    c. Two color CRT’s
    d. One operator interface device
    e. Two logging/alarm and screen printers
    f. LAN and WAN communications interface hardware
    g. Power conditioning or backup equipment.
  • The router between the SCADA summary node and the plant WAN systems shall be provided by the SCADA vendor. This router shall be set up as a firewall to prioritize and to limit the random accesses from plant WAN systems to the SCADA system.

Summary SCADA Node Application

The summary node shall be capable of monitoring data and alarms from the remote locations (local nodes). This node shall also serve as backup to any local node in the remote locations over the WAN that is incapable of acquiring data from its LAN.
a. The summary data acquisition and alarm monitoring shall be accomplished by the summary node communicating directly to each remote local node for the information.
b. The summary node shall monitor a ‘health status’ parameter in each remote local node to determine if and when it should assume the responsibility for collecting the remote data. Upon availability of the remote local node for data acquisition, the summary node shall resume summary monitoring of that node.

SCADA Technical Requirements

SCADA Architecture

The SCADA system shall be engineered and designed as a complete system with an ‘open architecture’ (system communications shall be via RS-485, Modbus RTU, Ethernet TCP/IP or equal) approach to ensure that the system will be viable and can be modified and expanded as requirements dictate. System design shall ensure that the hardware and software are capable of being upgraded at site, without major system revamp.

Substation Circuit Monitoring and Alarm Systems

SCADA System Wiring Design

As an integrated networked information system, the overall SCADA system design and interconnecting wiring shall conform to applicable requirements of NFPA 70, Article 645 and Article 800. Other articles may also apply and are dependent on components and design of system.

SCADA System Reliability

The following reliability features shall be incorporated into the system:

  • The system design shall include two (2) isolated/independent FO cable paths from the local node to the summary node, such that a failure of one (1) cable does not incapacitate the rest of the system. The manufacturer shall recommend the configuration of the LAN to incorporate the necessary level of redundancy required.
  • A power backup system (UPS) shall be provided for the SCADA system. The main substation and unit substation building SCADA nodes shall be capable of allowing the system to hold data in memory and continue to monitor the system for up to twenty minutes.
  • Diagnostics and alarm functions for the power supply system shall be provided and tied into the SCADA system.
  • The SCADA system shall have self-diagnostic capabilities. The system shall be able to detect and alarm internal errors or malfunctions. It shall also be able to identify the following:
    a. Type of malfunctions
    b. Type of device and locations of the failure within the device
    c. The device location
    d. Errors made by the operator during command inputs

SCADA Hardware

Vendor Normally provide all hardware for the system as defined in this specification. The system shall include the following:

  • SCADA Computers – The SCADA node computers shall provide a minimum 100 MIPS processing power. They shall include all facilities to configure the operator console, support the keyboards, display alphanumeric and graphic information on the screens, drive printers, transmit and receive data and to communicate with the metering and protective relay devices and other SCADA node computers via the LAN and WAN. The computers shall be ‘hardened’, industrial grade. The local node computer system shall be rack mounted for installation in the workstation console. The computers shall have the following minimum features:
    a. CPU – Intel microprocessor of latest design with latest features and fastest available clock speed. (Ex. CPU shall be an, Pentium III, 1000 MHz clock speed, 512K Cache on motherboard, BIOS in flash EEPROM.)
    b. RAM: 256MB PC800 expandable to 1 GB
    c. Drive Storage: 40 GB, hard drive
    d. Graphics Adapter: AGP SVGA Graphics adapter with color monitor, dual monitor capable
    e. Video card: 32 MB VRAM AGP 4X interface
    f. 1.44 MB, 3.5″ floppy drive
    g. CD/DVD ROM Drive, Read/Write capable: Speed: 48xRead/ 24x Write
    h. 101 key Keyboard (shelf mounted)
    i. Microsoft compatible mouse or trackball
    j. Windows NT compatible LAN interface card
    k. Battery backed real time clock
    l. Internal Tape drive – 40 GB minimum
    m. Expansion slots – 2 PCI 64bit, 3 PCI 32 bit, 1 AGP
    n. MS Windows NT, latest version
    o. LAN software (vendor to specify) SCADA application software (vendor to specify)
  • Summary Node Computer
    The summary node computer shall have the following minimum features:
    a. CPU – Intel microprocessor of latest design with latest features and fastest available clock speed. (Ex. CPU shall be an Pentium III, 1000 MHz clock speed, 512K Cache on motherboard, BIOS in flash EEPROM).
    b. RAM: 256MB PC800 expandable to 1 GB
    c. Drive Storage: 40 GB, hard drive
    d. Graphics Adapter: AGP SVGA Graphics adapter with color monitor, dual monitor capable e. Video card: 32 MB VRAM AGP 4X interface
    f. 1.44 MB, 3.5″ floppy drive
    g. CD/DVD ROM Drive, Read/Write capable: Speed: 48xRead/ 24x Write
    h. 101 key Keyboard (shelf mounted)
    i. Microsoft compatible mouse or trackball
    j. Windows NT compatible LAN interface card
    k. Battery backed real time clock
    l. Internal Tape drive – 40 GB minimum
    m. Expansion slots – 2 PCI 64bit, 3 PCI 32 bit, 1 AGP
    n. MS Windows NT, latest version
    o. LAN software (vendor to specify) SCADA application software (vendor to specify)
  • CRT Monitors
    The color CRT monitor(s) shall be 20 in SVGA at Summary Node, 17 in SVGA at Local Node, high resolution, 0.28 dot pitch, 1280 x 1024 pixels, NI (non-interlaced) screen capable of displaying mixed alphanumeric/graphic information. The monitor(s) provided shall have self-convergence features to eliminate troublesome adjustments.
  • Computer Operator Interface Devices
    A Microsoft compatible trackball or mouse and light pen for point-to-select features shall be provided with each computer system.
  • System Mass Storage Medium
    The SCADA node computers shall be supplied with internal mass storage media as required. A fixed hard disk unit with a minimum storage capacity is the preferred primary media. For system backup storage a cartridge tape drive with a minimum of 40GB storage shall be provided.
  • Printers
    The summary node shall include a high-speed laser printer with full graphics capability. The printer shall have capability of printing on 8″x11″, 8″x14″ and 11″x17″ paper automatically as required. The local node shall include a rack mount Ink Jet color printer and enclosure slides. The manufacturer shall recommend the type of printer to be used to ensure the capture of all alarms from the SCADA system.
  • Local Node Workstation Console
    a. A free standing cabinet shall be provided with the following features:
    (i) Self supporting steel frame
    (ii) Removable panels and doors for quick, open access
    (iii) Front and rear access doors
    (iv) Key-locking doors provide a secure environment, sides accessible with slotted tool
    (v) 19″ racks and support pans
    (vi) Common power strip and termination
    (vii) Casters or leveling feet
    (viii) Fan cooling (if needed)
    (ix) Fluorescent light
    b. Cabinet shall be designed to house all local node equipment such as back plane, fiber patch panel, ethernet gateway and 17″ CRT/keyboard. c. A rack mounted UPS shall be located in the cabinet.
  • Summary Node Workstation Console
    a. A free standing electronic desk system shall be designed to house the computer, keyboard, monitor and mouse. CRT and printers shall be located on desk top. The desk shall include electronic bays offering standard 19″ rack. A built in storage bay to house miscellaneous items shall be furnished.
    b. A separate, free standing cabinet (see 11.2.8.1) shall be located beside the electronic desk system. A rack mounted UPS meeting requirements of 9.3.2, with MBB (make before break) isolation switch shall be located in the cabinet.

Definitions used in this article are 

For the purpose of understanding this specification, the following definitions apply.
ATM.
Asynchronous Transfer Mode.
Communications Protocol.
A formal set of conventions governing the control of Inputs and Outputs within the communicating process.
CPU.
Central Processing Unit.
DDE.
Dynamic Data Exchange.
Ethernet.
A high performance local area network standard providing the two lower levels of the ISO/OSI seven layer reference model, the physical layer and the data link layer.
Ethernet Gateway.
A physical device that translates information from the RS485 Modbus RTU communications protocol to Ethernet communications protocol.
FO.
Fiber Optic.
GBPS.
Gigabit per Second.
LAN.
Local Area Network.
Mbps.
Megabit per Second.
MCC.
Motor Control Center.
MIPS.
Million Instructions per Second.
Modbus RTU.
An industry standard, high performance network communications protocol developed by Modicon.
Open Protocol.
A protocol which is published and used by other manufacturers and is, therefore, non-proprietary.

PC.
Personal Computer.
PCI.
Personal Computer Interface.
RISC.
Reduced Instruction Set Computer.
RS 485 / EIA 485.
A physical wiring standard for high speed, noise tolerant network communication often used with the Modbus RTU protocol.
RTU.
Remote Terminal Unit.
TCP/IP.
Transmission Control Protocol / Internet Protocol.
WAN.
Wide Area Network.

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