ApplicationSolution

Summary

The Invensys industrial

Power Management

System consists of a set of

modules to support your

plant when problems occur

on the grid or within the

power system inside the

fence line. For large and

small plants, the solutions

are bundled together or

broken into component

parts depending on

the plant’s needs.

Business Value

The strategy with

the Invensys Power

Management System

is simple - Provide the

applications that will extract

the correct information

from your substations and

deliver fast, intelligent

and robust breaker

and power control. The

second strategy is to

provide customers with

the advantage of the same

environment for the DCS

and Safety systems for

lifecycle cost protection

and integration integrity.

INTRODUCTIONPlants incorporate automation control, safety systems and SCADA (for power) to manage plant processes. These disparate systems can operate in a unified way to gain the greatest value for operators and lowest lifecycle costs. By utilizing the same HMI and same tools for engineering, these systems become a combined system solution which minimizes engineering and long term maintenance costs.

Industrial plants should always look to the process control manufacturer when managing power, as control of the power system it is critical to the operation of the plant. The SCADA system is the front line for power measurement and operator control.

Some industrial plants may use smaller amounts of power and may source power almost exclusively from the public grid. Power management is just as critical for these plants. In fact, it may be even more critical since these plants have no back-up or very minimal back-up to protect important safety systems.

Larger plants pose a more complicated set of issues in addition to the fundamental power management requirements in smaller plants. These issues include: (a) matching generated power with the grid power; (b) deciding how to balance power between multiple generating sources inside the plant; (c) managing a much larger distribution network around the plants containing multiple busses at multiple voltage levels; and (d) substation monitoring control, each becomes critical and complex applications.

In order to maintain adequate amounts of quality power and to protect industrial plants from power outages, Invensys offers the following application modules as part of our complete industrial Power Management System (PMS) for small to large plants.

Invensys Industrial Power Management Systems

SMALL PLANT POWER MANAGEMENTWe describe small plants as those that rely primarily on the electrical grid to supply power to their plant’s industrial and non-industrial needs. However, most plants will have one or more small diesel generators or gas fired generators to kick-in immediately after a global power outage. These generators can supply enough power to manage critical emergency and back-up functions that will allow the plant to operate at a safe level until the grid power is restored. The SCADA system provides the functions of monitoring substations, including: (a) monitoring the quality of the incoming electricity from the grid; (b) monitoring the quality of the power from the small turbines when asked to spin up power quickly; (c) monitoring quality of the electricity on the plant’s busses; and (d) collecting data from all of the metering devices inside the substation.

Intelligent Electrical Devices and Substation Device Monitoring:

Intelligent Electrical Devices (IEDs) and older electrical devices are located in substations to manage and read power quality, set interlocks, identify breaker positions, and collect time stamped information among other things. Each substation requires this information to accurately manage the breakers protecting the plant from the grid. For instance, if there is a problem with incoming power to the plant such as a voltage or frequency anomaly, plant breakers will trip to protect vital assets. After the power from the grid has been restored the breakers need to be closed and other equipment powered up. The SCADA system continues to monitor the IEDs to evaluate the grid sources or back-up generating sources and makes decisions based on the quality of power. Automating this feature with the Invensys SCADA system can save valuable time and can make sure that the power quality is truly ready for distribution to the plant.

Total Grid Failure and Restoration:

In smaller plants, grid failure will probably be due to voltage or frequency anomalies detected at the substation. Metering units will be monitored by the SCADA system and when the meters sense the anomalies, the IEDs or substation devices trip the breakers and notify the SCADA system. The SCADA system collects the information and stores it in Sequence of Event (SOE) files for later analysis.

Following total power failure, the Total Grid Failure and Restoration module ensures that nominated breakers are reclosed following startup of the emergency back-up power source(s). The Automation system can start the motors associated with the critical processes.

Plants are usually equipped with small power generators that may supply 10 MW or less to preserve minimal safety levels. In many cases, processes are still running and allowing them to run to completion is critical to avoid costly re-starts when processes are halted. In many cases, a restart could turn into days and cost hundreds of thousands of dollars to clean up if the process is not run to completion. These engines are also designed to supply enough power to keep electricity flowing to office buildings and other critical loads. These ancillary systems need start-up control and the SCADA system supports the management of the electricity on the plant grid during the start-up. This ‘black-start’ management monitors the quality of the power from the turbines and makes decisions on breaker control to various parts of the plant.

Total Global Power Failure Module

Event Disturbance and Reporting:

The Event Disturbance Record (EDR) module is designed to record and acknowledge alarms and trips, transient voltage and frequency excursions, status changes of breakers and trip units, and to record data before, during and after these events. The EDR module continuously monitors all protective relays and other devices for faults.

A very critical element of the EDR module is time synchronization. Time synchronization can be done directly by the Invensys SCADA Data Concentrator. Having the data concentrator perform this function as part of the communications protocol to the IEDs significantly minimizes costs from GPS clocks and wiring. Since the local SCADA Data Concentrator holds the time synchronized data it is also available at the Master SCADA Station.

The Post Event Report (PER) module is a decision support tool which aids in the analysis of system operations before and after an event. An event can be defined for an action at any data point monitored by the system. Examples of the types of data which are monitored include equipment going offline, voltage or frequency excursions, a unit trip, or a breaker trip. The PER package will generate a report based on the historical data related to the event from the historian database.

Economic-Supply Tie Line Control:

Industrial power users are subject to changing rates depending on their usage. In many contractual agreements, plants are charged at the rate of their highest usage, also known as “ratchet” charges. This is because the power plants must make enough electricity to meet the demand required by the plant. Even if the demand is short-lived the power generators must size their delivery to meet that demand or the generators will be subject to penalties.

The power management system at a facility monitors incoming power through power meters and those values are captured by the SCADA system. The Invensys Economic-Supply Tie Line Control module works to collect power usage in the plant and it then creates a simple model of anticipated demand. If the anticipated demand exceeds a certain operator specified end of billing period amount, then the system notifies the operator to shed load to avoid increased demand (i.e. ratchet) charges.

The Economic-Supply Tie Line Control module works by monitoring the actual tie line MW coming into the plant against the operating limits of the contract. The module calculates the deviation of tie line MW versus the scheduled/contracted value, calculates the energy (hourly, daily or monthly MWH) and calculates the cost associated with the deviation MWH. The module controls the power consumption of the plant to maintain the tie line MW within the scheduled or contracted MW. The control could be for circuit breakers of the feeders, heaters, ACs, steam volume, etc. They could be either digital or analog controls. The module also provides supporting functions such as reports, alarms, and displays.

LARGE PLANT POWER MANAGEMENTWe define large plants as those that are generating their own power to run the plant. These plants may also have a tie to the grid for emergency power or the tie would be used as a source of additional power in case of limited production from the plant’s generation assets. These plants may have anywhere from one to a dozen generators that can supply 100MW or more. Invensys has worked on projects with up to 11 generators and power demand near 1,000MW.

The combination of plant production of electricity and absorption of grid power creates multiple problems that require a sophisticated power management system. Our world-class Invensys SCADA system has been used to manage power at some of the world’s largest natural gas liquefaction plants, mines, and refineries as well as major utilities.

Load Shedding Control:

A critical component of any process plant is the amount of quality power available. Quality power is just as much a raw material as crude oil, pulp, sugar and water. Without any of these in the correct proportions and quality the process will shut down or deliver poor quality product. When power quality goes down for a variety of reasons such as a frequency drop or voltage sag, equipment can be damaged or areas of the plant can be affected.

Load shedding is designed to proactively shut down power to parts of the plant that are less important than others. There are two kinds of load shedding methods that our PMS Load Shedding module handles. Each form is designed to shut down parts of the plant but each does it based on separate power conditions. One very critical element of a good load shedding system is the ability to avoid shedding power when it is unnecessary. This is a major problem that plants with older shedding systems experience because of frequency and tie-line breakers which act in all-or-nothing modes.

Slow load shedding is typically performed when there is a slow degradation in frequency, also known as a sinking island scenario. A decay rate is defined so that if the plant frequency decays by more than the operator entered amount, non-critical load is shed to restore frequency.

Fast load shedding is typically performed when there is a significant loss of voltage from the external grid or the internal power lines. This catastrophic failure requires the shutdown of the non-critical processes to be performed within 100 msec in advance of the plant power protection system. In this scenario, appropriate number of breakers around the plant, which are equivalent to the lost generation, are immediately tripped.

Load Shed Overview Module

To perform either of these processes requires a load shedding algorithm. Various algorithms based on critical processes or based on daily plant production schedules are created and downloaded to the load shed controllers. From the control room, operators can determine the appropriate daily matrix, then download it to the load shed controller.

Invensys manufactures the world class SCD5200 Station Control Device which maintains the load shedding program for the substations. The SCD5200 reads critical IEDs and older electrical devices in the substation. Based on readings from the sophisticated SCD5200’s Transducer Card those measurements are made and instantly transferred back to breaker controls that open up breakers in under 100 msec.

Automatic Generation Control (AGC):

As the power load in the plant goes up the turbines need to keep up with the demand and that means increasing the rotational frequency which drops voltage across the power network. This is not a catastrophic thing from a short term standpoint, but it does need to be managed by a SCADA system for the fleet of generation until the power network stabilizes. The Invensys Automatic Generation Control module constantly looks at the frequency and net interchange, and adjusts the generator outputs by sending set-points or raise/lower pulses to raise or lower the MW outputs of the generators.

In order to maintain a steady state frequency as closely as possible, generating units are automatically adjusted every 2-4 seconds by the AGC module. AGC also maintains scheduled interchange with the grid through tie line bias control.

Automatic Generation Control Module

SCD5200 Station Computing Device

Elecsolve Electrical Modeling

Understanding a plant’s power curves, responses to deviations, and the integration of multiple units on the plant’s grid is the cornerstone of managing a plant’s power system. In many cases, initial estimates of responses and interactions consist of intelligent guesses. Invensys has created a hi-fidelity modeling system for electrical systems. Elecsolve takes the guessing out of the equation. It allows power and electrical engineers to test applications before putting electrical systems in place. It also allows engineers to design their plant to balance loads and the associated power required to run those loads. Elecsolve manages applications such as load shedding, load sharing, and load response to name a few. The system works by using numerous theoretical and actual data inputs from the plant load and power flow into and around the plant. Coupled machine dynamics equations produce response of each machine around the plant and the frequency of the inertial center of the network to accurately monitor and calculate responses.

Economic Dispatch:

The Invensys Economic Dispatch module provides the best operating mix and conditions for the generating units within the plant. As mentioned before, generators are ramped up and down depending on the demand. As part of the power ramping function across generators in the plant, decisions can be made as to which generators will be ramped up or down to meet increasing or decreasing need. If there are multiple energy sources for the generators then the decision is usually based on economic conditions. However, the decision could also be a function of the demand rate for power across the plant. Steam generators sometimes cannot react quickly enough to meet instantaneous demand and in that case our Economic Dispatch module may choose a gas turbine as the unit to ramp. As part of the module, costs will have to be a component of the algorithms and matrix within the SCADA system.

The Invensys Economic Dispatch module uses the following data in the calculations:

• System area fuel costs

• Incremental cost of generation

• Incremental cost of reserve

The Invensys Economic Dispatch module delivers the following data:

• Base point for the generation units in MW

• Participation factors for AGC to update control set points between generators

• Regulating reserve (spinning reserve) for emergency power demand conditions

Islanding:

In some cases, management of islanding conditions at a plant adds another element of complexity if the plant generation breaks from the grid. Each bus will have generation and load associated with it. When a bus separates from the grid, the island mode frequency and voltage control scheme will take place and the Invensys industrial PMS will come into effect. The PMS will support the load/frequency control and load sharing, as well as the voltage/reactive power control in conjunction with the generator’s Automatic Voltage Regulator (AVR) when the plant is operating in the island mode.

Scheduling:

Some plants with more generating units may take advantage of scheduling applications. In scheduling applications for deregulated parts of the country, plants can purchase power based on fee schedules. The Scheduling module allows plants to buy power in the network of the available generation sources across the local grid. The SCADA system can actually decide how to make-up power for any additional plant needs. If the system needs 10MW, the SCADA system can make decisions to buy from the grid or make additional power with on-site generation.

Conclusion:

Power Management Systems are critical to all kinds of process industries. Onshore process plants, drilling platforms, FPSOs, commercial buildings, and any facility where providing quality power to critical parts of the facility’s assets requires systems like the Invensys Power Management Systems.

The Invensys industrial PMS family of modules provides any large or small industrial plant, facility, ship, or platform with tools necessary to manage incoming power and maintain quality power so the plant can stay up and running. When running Invensys control and safety systems the decision to integrate the industrial PMS becomes a logical decision because of the lifecycle costs associated with working with one vendor.

Offshore Platform

LNG Tanker

Crude Oil Refinery

LNG Liquefaction

Crude Oil Tanker

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Rel. 07/13 PN FX-0234