control of power systems (1)

8/13/2019 Control of Power Systems (1)

1/43

Control ofPower Systems

Prepared ByA K K Tahira Tasneem

Assistant Professor - EEE


2/43

Outline Review of AGC and reactive power control System operating states by security control

functions Monitoring, evaluation of system state by

contingency analysis Corrective controls (Preventive, emergency and

restorative) Energy control center SCADA system Functions monitoring , Dataacquisition and controls EMS system .


3/43

Review of AGC and reactive

power control Modern implementation of automaticgeneration control (AGC) schemes usuallyconsists of a central location whereinformation pertaining to the system istelemetered.

Control actions are determined in a digital

computer and then transmitted to thegeneration units via the same telemetrychannels.


4/43

To implement an AGC system1. Unit megawatt output for each committed

unit.

2. Megawatt flow over each tie line toneighboring systems.3. System frequency.


5/43

The use of digital telemetry is becomingcommonplace in modern systems whereinsupervisory control.

That is opening and closing substationbreakers, telemetry information and controlinformation (i.e) unit raise/lower is all sent viathe same channels.


6/43

The basic reset control loop for a unit consistsof an integrator with gain K

Basic generation control loop.


7/43


8/43ACE calculation.


9/43Overview of AGC logic.


10/43

AGC Features

Assist action Filtering of ACE Telemetry failure logic Unit control detection Ramp control Rate limiting Unit control modes


11/43


12/43

Normal

EmergencyExtremis

AlertRestorative

Restart

Resynchronisation

Preventive Control

Emergency Control

E,I

,I E,I

E , ,

E Equality Constraint: I Inequality Constraints and - Negation


13/43

Normal State The system is, for most of the time, in its

normal state. Frequency and Voltages are kept at rated or

prescribed values.

Real and Reactive power demanded by theloads match with the output of sources. E Equality

I

Inequality

Loading of generators,transformers or transmission line is with intheir rating or capacity limits.


14/43

Alert State

If the capacity margin below the thresholdvalue or if a disturbance occurs, the securitylevel is reduced and the system enters alertstate.

All equalities and inequalities aremaintained.

The system operates fully synchronized. Preventive control actions need to be

initiated to restore reserve margin.


15/43

Emergency State Second contingency occurs before

preventive action is effected. It may reached directly from normal state,

if the original disturbance is more severe. The generation still tracks the load and the

system remains synchronized. It is most urgent that the system be

returned to a normal or at least alert state.


16/43


17/43

Contingency Analysis To predict the effect of outages, contingency

analysis techniques are used.

Single line failure, multiple equipmentfailure and all possible outages are studied.


18/43


19/43

Energy Control Centers

The energy control center (ECC) hastraditionally been the decision-center for the

electric transmission and generationinterconnected system. Minute-by-minute physical and economic

operation of the power system.


20/43

In the continental U.S., there are only three

interconnected regions:1. Eastern,2. Western, and

3. Texas, But there are many control areas , with each

control area having its own ECC.


21/43

Maintaining integrity and economy of aninter-connected power system requiressignificant coordinated decision-making.

So one of the primary functions of the ECCis to monitor and regulate the physicaloperation of the interconnected grid.

Two-level hierarchy of ECCs Independent System Operator (ISO) - high-

level decision-making. The transmission owner ECC - lower-level

decision-making.


22/43

High-level view of the ECC

27

Substation

Remoteterminalunit

SCADA Master Station

C o m m u n i c a t

i o n

l i n

k

Energy control center with EMS

EMS alarm displayEMS 1-line diagram

ECC C t


23/43

ECC Components

SCADA

Overloads &Voltage Problems

PotentialOverloads &

Voltage Problems

Breaker/Switch StatusIndications

System Model Description

Telemetry &Communications equipment

StateEstimator

NetworkTopology

program

AGC

EconomicDispatch

Calculation

OPF

ContingencySelection

Contingency AnalysisSecurityConstrained OPF

Display Alarms

Updated SystemElectrical Model

Analog Measurements

Display to Operator

Power flows,Voltages etc.,

Display to Operator

Bad MeasurementAlarms

Generator OutputsGenerationRaise/Lower Signals

State EstimatorOutput

SubstationRTUs


24/43

The system control function traditionally used inelectric utility operation consists of three mainintegrated subsystems:

The energy management system (EMS)

The supervisory control and data acquisition(SCADA), and

The communications interconnecting the EMSand the SCADA.


25/43

SCADA system

Supervisory control indicates that theoperator, residing in the energy controlcenter (ECC), has the ability to controlremote equipment.

Data acquisi tion indicates that informationis gathered characterizing the state of the

remote equipment and sent to the ECC formonitoring purposes.


26/43

A SCADA system performs four functions:1. Data acquisition

2. Networked data communication3. Data presentation4. Control


27/43

These functions are performed by four kinds of SCADAcomponents:

1. Sensors (either digital or analogue) and control relays thatdirectly interface with the managed system.

2. Remote telemetry units (RTUs). These are smallcomputerized units deployed in the field at specific sites andlocations. RTUs serve as local collection points for gatheringreports from sensors and delivering commands to controlrelays.

3. SCADA master units. These are larger computer consolesthat serve as the central processor for the SCADA system.Master units provide a human interface to the system andautomatically regulate the managed system in response tosensor inputs.

4. The communications network that connects the SCADAmaster unit to the RTUs in the field.


28/43

The monitoring equipment is normally locatedin the substations and is consolidated in theremote terminal unit (RTU).

The RTUs are equipped with microprocessorshaving memory and logic capability.

Newer RTUs generally have intranet orinternet capability.

Relays located within the RTU, on command

from the ECC, open or close selected controlcircuits to perform a supervisory action.


29/43


30/43

Such supervisory actions are Opening or closing of a circuit breaker or

switch Modifying a transformer tap setting Raising or lowering generator MW output

or terminal voltage Switching in or out a shunt capacitor or

inductor The starting or stopping of a synchronous

condenser.


31/43

Information gathered by the RTU andcommunicated to the ECC includes both analoginformation and status indicators.

Analog information includes Frequency, Voltages, Currents, and Real and Reactive power flows.

Status indicators include Alarm signals (over-temperature, low relay battery

voltage, illegal entry) Whether switches and circuit breakers are open or

closed. Information is provided to the ECC through a

periodic scan of all RTUs.


32/43

Communication technologies

The form of communication required for SCADAis telemetry .

Telemetry may be analog or digital.

In analog telemetry, a voltage, current, orfrequency proportional to the quantity beingmeasured.

In digital telemetry, the quantity being measured

is converted to a code in which the sequence ofpulses transmitted indicates the quantity.


33/43

Block Diagram of Telemetering System

Quantity to be

telemetered

Transducer A/Dconverter

Telemetertransmitter

Telemeterreceiver

Computer

D/Aconverter

Indicatingmeter

Recordingmeter

Signal circuit (wire line,PLC, microwave, etc.)


34/43

Energy Management System (EMS)

The EMS is a software system. Most utility companies purchase their EMS

from one or more EMS vendors.

These EMS vendors are companies specializingin design, development, installation, andmaintenance of EMS within ECCs.


35/43

Industrial for Power EMSElectrical ProcessSystem configurationFunctionality Power EMSReferencesBenefits


36/43

Critical LoadsLimited In-plant GenerationInsufficient reliability of Public Grid

Why Power EMS?

Load Shedding} Several GeneratorsContracted Power Importation Power Control} Different Electrical OperationalConfigurations possible Mode Control} Complex Distribution Networks

Local only Control facilities SCADA

} P EMS S O i


37/43

Fast Functions are performed by Controllers:

Load Shedding / Re-Acceleration / Re-StartingPower Control

Mode Control

MCC

A B B T r a n s m i t OyN e tw o r k P a r tn e r

FEEDER TERMINAL REF541A B B N e t w o r k P a r t n e r

Uaux =80. .. 265Vdc/ acfn =50HzIn =1/ 5A ( I)

1MRS xxxxxx98150Un= 100/ 110V (U)

Uon= 100/ 110V ( Uo)

Ion= 1/ 5A (I o)

9509

A B B T r a n s m i t O yN e tw o r k P a r tn e r


Uaux =80. .. 265Vdc/ ac

fn =50HzIn =1/ 5A ( I)

1MRS xxxxxx

98150Un= 100/ 110V (U)Uon= 100/ 110V ( Uo)

Ion= 1/ 5A (I o)

9509

Substation N

S800 I/O

Serial links to AVR

Serial Links to Emergency Diesel GeneratorSerial links to Governor



Uaux = 80. . .265Vdc/ acf n=50HzI n= 1/ 5 A( I )

1MRS xxxxxx98150Un = 100/ 110V ( U)

Uon =100/ 110 V( Uo)

Ion =1/ 5A ( Io)

9509



Uaux = 80. . .265Vdc/ ac

f n=50HzI n= 1/ 5 A( I )

1MRS xxxxxx

98150Un = 100/ 110V ( U)Uon =100/ 110 V( Uo)

Ion =1/ 5A ( Io)

9509

ACS 601

TCP/IP Network

X-terminals(Process DCS)

Power EMS System Overview

Control IT

Substation 2Substation 1 Substation Z

Operate IT Engineering IT


38/43

Functionality Power EMS

Load Shedding Active and Reactive Power Control Supervision, Control and Data Acquisition

(SCADA) Mode Control

Re-Acceleration / Re-Starting Synchronisation


39/43

Load Shedding

Functionality Power EMS

?

Without Load SheddingWith Load Shedding


40/43

Load Shedding: The types

Fast Load Shedding on Loss of PowerResources

Load Shedding on Frequency Drop Slow Load Shedding on Overload Slow Load Shedding for Peak Shaving

Manual Load Shedding


41/43


42/43


43/43

Thank You

control of power systems (1)

Documents