Power System Control Centers and Their Role in the Restoration

Process after a Major Blackout

GEORGIOS FOTIS, CHRISTOS PAVLATOS, VASILIKI VITA

Department of Electrical and Electronics Engineering Educators, ASPETE,

School of Pedagogical and Technological Education of Athens,

N. Heraklion, 14121,

GREECE

Abstract: - Power control centers have evolved since their ground-breaking inception in the 1960s, and they

are extremely important for the operation of the power system, ensuring maximum reliability. There has been

much discussion about mandating reliability requirements, but for the most part, reliability standards are

already in place for electricity grid design and operation. Unfortunately, these standards do not examine in

detail monitoring and control, possibly due to the false belief that reliability primarily comes from redundancies

in transmission and generation. The grid can operate even more closely to its limits thanks to improved grid

control and monitoring, which also increase reliability. In this paper, the significant role of the power system

control centers in the event of a major blackout is discussed, proving their significance in the restoration

process.

Key-Words: - Blackout, Power Energy Control Centers, Transmission System Operators, Restoration plan,

Stability

Received: July 14, 2022. Revised: January 17, 2023. Accepted: February 22, 2023. Published: March 28, 2023.

1 Introduction

A practical dispatching automation system has been

steadily developed over the years and is crucial to

ensure the reliable operation of the power grid.

However, there is a significant disconnection

between the current standards and the ongoing

growth of the power system, particularly in the

following areas: (1) As the electricity grid's

operating characteristics become more complex, the

difficulty of security control follows as well; (2) in

an economic dispatch, the need of energy saving is

increasing; and (3) the optimization level of power

system operation needs improvement, [1], [2], [3].

Worldwide, blackouts occur regularly every day,

[4]. Most are brief and have minimal bearing on

consumers without access to power, [5]. However

large blackouts that had a big impact have happened

all around the world over the past 20 years, [6], [7].

In recent decades there is a turn in renewable energy

sources such as solar and wind energy to reduce the

CO2 emissions that affect the world’s climate, [8].

Recent research works have shown the necessity of

renewable energy sources in a power system for the

reduction of CO2 emissions, [9], [10]. Using other

energy sources different than fossil fuels may have

risks but their use is preferable in techno-economic

terms, [11]. The penetration of renewable energy

sources must follow certain rules ensuring

scalability and replicability, [12]. However,

Variable Renewable Energy Sources (VRES)

intrinsic variability decreases the power system’s

reliability, in severe weather conditions, [13]

proving the need for energy storage and flexibility

of the power system, [14]. From this fact is clear

that in a power system, a blackout risk is always

present with an unpredictable impact on the society

and the economy, [15], [16]. It must be mentioned

here that this high penetration of VRES also affects

the power quality of the grid as the voltage levels,

[17], [18], that may cause voltage collapse and a

possible blackout, [15].

There isn't a single solution to the question of

figuring out the ideal VRES penetration, [19], and

quantity of storage, [20], but various standards

might apply in each instance, [21]. Also, despite the

fact that almost every country in Europe has a

connected power system and that the European

Network of Transmission System Operators for

Electricity (ENTSO-E) has provided guidelines for

the European grid, [22], [23], [24], [25], [26], [27],

[28], [26], there is always a chance of a significant

disruption or, even worse, a complete blackout.

Reduction of losses and restoration time,

minimization of adverse social effects, and quick

and safe return of the power system to regular

operation are the goals of restoration. The

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Georgios Fotis, Christos Pavlatos, Vasiliki Vita

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Volume 18, 2023

development of restoration methods has made

extensive use of non-structured approaches,

technologies, and object-oriented expert systems to

accomplish the goals, [30]. As computational

intelligence has advanced, some intuitive

algorithms, including genetic algorithms, [31],

artificial neural networks, [32], and fuzzy logic,

[33], are used to restore systems. Based on the

regional distribution features in space, multi-agent

technologies, [34], [35], [36], [37], have been

created with promise. Expert systems and heuristic

rules are effectively extended by decision support

systems, [38].

For the efficient use of a power system, the

loadability limits must be calculated online.

Maximum loadability limits were formerly

calculated in power system control centers using

time-consuming simulations and off-line studies,

which were particularly difficult to be done when

stability considerations were included. There are

now straightforward applications that can determine

very fast how unstable is a certain operating state.

The goal after a blackout is to restore the power

system. In this process, the power system control

centers (PSCC) have a significant role. In the

current work the main principles of the power grid’s

stability, the role of the PSCCs, and basic guidelines

after a blackout are presented. This paper also

emphasizes the dispatcher's significance in the event

of a major blackout. If a dispatcher is not competent

and well-trained, the restoration plan as it will be

described in section 6 will not be possible to be

carried out. This work also examines and shows that

a power system cannot be operated just by fast and

intelligent software tools, but it also heavily relies

on human skills and abilities. The restoration

requires dispatchers who can adapt it to the current

state of the transmission system.

The structure of this work is as follows. The

significance of the PSCC and its role in the

electricity system is discussed in section 2. The

dispatchers, who work in these centers, are familiar

with the monitoring importance and a thorough

examination of the hardware and software systems

that the PSCCs are based on, so they are prepared to

handle any issue that might arise in the transmission

system. Section 3 presents the evaluation of the

power system state, and Section 4 analyzes the

assessment of steady-state stability. The design of

the dynamic security evaluation in a PSCC is

provided in section 5, and the restoration plan and

the steps that must be taken after a significant

blackout are thoroughly examined in section 6. The

two final sections, 7 and 8, provide the concluding

notes.

2 Power System Control Centers

(PSCC)

2.1 The Main Scope of a PSCC

A fundamental design feature of PSCC is that it

increases system reliability and economic feasibility

by performing Energy Management (EM), [39],

[40], [41], [42]. The PSCC has existed for decades

as the interconnected system's central decision-

making body for electric transmission and

production has been extended as well. It performs

the tasks required for supervising and organizing the

electricity system's economic and physical

operations on a minute-by-minute basis. An

interconnected electricity system needs carefully

coordinated decision-making to maintain its

integrity and economy. As a result, one of the

PSCC's main responsibilities is to regulate and

monitor the physical functioning of the connected

grid. A high-level view of the PSCC is illustrated in

Figure 1, where we can identify the SCADA system

with the related telemetry and communications

equipment with all the elements of the power system

(circuit breakers, disconnectors, etc.) and how the

software applications of the Automatic Generation

Control (AGC) are implemented in it.

Figure 1 is a schematic diagram illustrating the

information flow between various computer-based

tasks to be carried out in a PSCC. Remote terminal

units (RTUs), which encode measuring transducer

outputs and opened/closed status information into

digital signals and transfer them to the operations

center across communication circuits, provide the

system with information on the power system. The

PSCC can communicate control data, such as set

points to raise or lower the speed of generators, and

commands to open or close circuit breakers (CBs).

Analog measurements and breaker/switch status

indications are also data entering the control center.

The Automatic Generation Control (AGC) program

must use the analog measurements of generator

outputs directly, but all other data must first go

through the state estimator before being used by the

other programs.

The control in PSCC consists of the three

following levels:

 Level 1: Instantaneous control of the turbine

governor, which adjusts generation to balance

changing load.

 Level 2: The ACG, also known as load

frequency control (LFC), repeats the process

every 2 to 6 seconds to keep frequency and net

power interchange.

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Georgios Fotis, Christos Pavlatos, Vasiliki Vita

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Volume 18, 2023

 Level 3: Economic Dispatch divides the load

amongst the units such that the fuel cost is

minimized at intervals of 5 to 10 minutes.

The PSCCs are also in charge of the main

voltage control in the power system for:

• The generator bus voltage, regulated by

excitation controls.

• The Static VAR Controllers (SVC), shunt

capacitors, transformer taps, and other

transmission voltage control devices.

Fig. 1: Schematic diagram of the information flow between various computer-based tasks carried out in a

PSCC.

2.2 Automatic Generation Control (AGC)

To adjust the generation against the load at the

lowest possible cost, AGC consists of two main and

a number of minor functions that run in real-time

online. Load frequency control and economic

dispatch are the two main tasks, and each is

explained in detail below. Interchange scheduling,

which starts and finishes scheduled interchanges,

reserve monitoring, which ensures there is enough

reserve on the system, and other comparable

monitoring and recording operations are the minor

functions.

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Georgios Fotis, Christos Pavlatos, Vasiliki Vita

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Volume 18, 2023

2.3 Monitoring

An energy control center performs the task of

coordinating the system components' responses

during both routine operations and emergency

situations. In typical circumstances, the digital

computer is given the responsibility of repetitive

control, while human operators do selected

monitoring. The incoming stream of data is

processed by the digital computer to look for

anomalies, and the human operator is alerted by

lights, buzzers, and monitor presentations. Digital

computers frequently handle much lower-level or

less serious incidents of exceeding normal

boundaries. Normal control operations might be

suspended if the digital computer detects a more

serious problem. Many alerts may be found in

emergency situations, such as the failure of a

significant generator or excessive power demands

placed on tie lines by a nearby utility. In these

situations, the system may enter an emergency

status.

2.4 Data Acquisition and Control

Data acquisition supplies the status and

measurement data required to oversee the overall

operations of computer control systems. The

purpose of security control is to establish operating

conditions by analyzing the effects of errors

between the master station and remote terminal unit

(RTU) of a Supervisory Control and Data

Acquisition system (SCADA). To observe and

manage power plants, the master station sends data

to the RTU. At generating stations, transmission

substations, and distribution substations, RTUs are

placed. RTUs broadcast measurements and device

status to the master station, and they also receive

control instructions from the master station.

The steady-state reading can be simultaneously

gathered from numerous instrument sites and

preserved for later analysis using a computer-aided

data-collecting technique. Voltage or current

variations could be the outcome of the transient. It

can be challenging to pinpoint the transient's origin

in a real power system, where it may cause

component failure. The transients can be lowered

and analyzed using a data acquisition system.

2.5 Phasor Measurement Units (PMU) for

Power Systems

A PMU is a device that determines the phase angle

and magnitude of an electrical phasor quantity (such

as current or voltage) in the electrical grid using a

shared time source for synchronization. PMUs can

rapidly reconstruct the phasor quantity—which

consists of measurements of both an angle and a

magnitude—using samples from a waveform. These

time-synchronized data are essential because

frequency imbalances can strain the grid's supply

and demand, which could result in power outages.

PMUs can gauge the electrical frequency of the

power grid. A typical PMU may report

measurements up to 120 times per second with a

very high temporal resolution.

Unlike traditional SCADA measurements, which

generate a measurement every two to four seconds,

engineers can now analyze dynamic grid events. As

a result, PMUs give utilities improved monitoring

and control capabilities, making them one of the

most crucial measuring tools for the development of

power systems. A PMU can be a separate device, or

it can be integrated with another device, such as a

protective relay, to perform the PMU function.

EMS and SCADA are examples of existing

power grid technologies that can only provide a

steady state picture of the power system with a high

data flow delay. Due to technical issues

synchronizing measurements from various

locations, it is not possible to use SCADA to

measure the phase angles of bus voltages of the

power system network in real-time.

Measurements were made more slowly, and the

operator only received a limited amount of

information on the power system's dynamic

behavior. By synchronizing voltage and current

waveforms at separated places, PMUs helped to

solve this issue. PMU outperforms SCADA in terms

of performance, reliability, and speed.

A PMU is a device that uses voltage, current,

and/or time synchronizing signals to estimate

frequency, rate of change of frequency, and phasor.

PMUs use Global Positioning System (GPS) signals

to give real-time synchronized measurements in the

power system with better than 1 ms synchronization

precision. In power system substations, PMUs

measure the time-stamped positive sequence

voltages and currents of all the tracked buses and

feeders. A suitable location is chosen for the

collection of data from several substations, and a

coherent image of the state power system is

produced by lining up the time stamps of

measurements.

The major applications of the PMUs are:

 Monitoring thermal overloads

 Analysis of disturbances

 Stability monitoring

 Restoration of the power system after a

blackout

 State estimation

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 Control in real time

 Adaptive protection

2.6 System Hardware Configuration

A small number of operators can keep an eye on the

generating and high voltage transmission system

thanks to the supervisory control and data

acquisition systems. Electric utilities almost always

use a redundant set of dual digital computers for the

purposes of remote data acquisition control, energy

management, and system security in accordance

with the concepts of high reliability and fail-safe

failures.

The online units, which are typically one

computer, monitor and manage the power system.

Off-line batch applications like load forecasting or

hydro-thermal allocation might be running on the

backup computer. A shared disk memory between

the two computers is frequently updated by the

online computer. The common disk's stored data is

loaded into the online computer's memory in

response to a failure over or switch-in status

instruction.

The online computer's information has a

maximum age of updating cycle. Using input-output

microprocessors that have been configured to

interact, as well as pre-process the analog

information, check for limits, convert to another

system of units, and other tasks, all peripheral

equipment is connected to the computer. The central

processing unit is not hampered by the

microprocessors' ability to move data in and out of

computer memory. These safeguards frequently

result in a 99.8% or higher availability guarantee for

all crucial hardware operations.

In addition to hardware, fresh digital code for the

system's control can be created, tested, and put

online on the backup computer. Most of the time,

digital computers are used in fixed cycle operating

mode with priority interrupts, which causes them to

run a series of tasks on a recurring basis. The scan

cycle for the most important functions is the

quickest. The following categories are typically

scanned every two seconds:

 Every status point, including the location of the

switchgear, the loads and voltages in the

substation, the tap positions of the transformers,

and the capacitor banks.

 Schedules for interchanges and tie-line flow.

 Lines’ capacity, operational restrictions, and

generator loads and voltage.

 Telemetry verification to find errors and failures

in the distant bidirectional communication links

between the digital computer and remote

equipment.

Every 4 seconds, the turbine generators are

frequently instructed to operate at higher power

levels, with load adjustments dependent on each

unit's response capacity in MW/min. The computer,

while running an economic dispatch program,

adjusts the base power settings for each unit's

reaction capabilities every 5 minutes on average.

3 Power System State Estimation

The system states produced from unsophisticated

measurements in power systems are not precise

enough to be used for complex system operations

and online control due to the inherent flaws in

metering devices and communication networks.

This is why correct state estimation is a crucial

feature in power systems. Based on a collection of

real-time measurements, a state estimator (SE)

establishes the state of the system. There are three

kinds of real-time measurements that can be made

within the framework of a PSCC:

 Examples of analog metrics are real and

reactive power flows over transmission

lines, real and reactive power injections, and

bus voltage magnitudes.

 Switch and breaker state, as well as

transformer LTC positions, are measured

using logic.

 Predicted bus loads and production are

examples of pseudo-measurements.

Telemetered readings of analog and logic are

sent to the PSCC. The statistics may contain noise

and errors. Data errors can be brought on by noisy

communication systems, malfunctioning measuring

and telemetry equipment, and delays in data

transmission. A system's state is described by a set

of variables that, at any given moment, contain all

the data necessary for us to fully predict how the

system will behave at time t. A practical decision is

to choose a small number of variables, designating a

small number of state variables that are adequate. It

should be noted that the state variables may not

always be easily available, quantifiable, or

observable. The system model used is built on a

nodal depiction, making the choice of the state

variables simple.

The voltage magnitudes and angles are the state

variables, while line impedances are assumed as

known. This follows because, once the state values

are known, all other values can be specified

uniquely. State estimation is a mathematical

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DOI: 10.37394/232016.2023.18.7

Georgios Fotis, Christos Pavlatos, Vasiliki Vita

E-ISSN: 2224-350X

Volume 18, 2023

procedure that generates a description of the power

system by computing the best estimation of the state

variables (bus voltages and angles) of the power

system based on the incorrect data that was

received.

Secondary quantities (like line flows) are easily

derivable once state variables are approximated. The

network configuration is established by the network

topology module after processing the logic data. In

addition to using data from the network parameters,

the configuration of the network provided by the

topology of the network, and occasionally pseudo

measurements, the state estimator processes the

collection of analog measurements to determine the

system state. Since it is not feasible to measure all

network parameters in-depth in the field, one-line

diagrams and manufacturer data are used to

calculate parameter values. This could then add

another potential error source.

The fundamental power system state estimator's

mathematical formulation assumes that the power

system has static behavior. Assume a system with n

state variables, represented by xi where i=1,...,n.

Suppose there are m measurements accessible. The

state vector is x, and the measurement vector is

indicated by the letter z. If the noise is v, then the

relation between measurements and states denoted

by h is given by:

 󰇛󰇜  (1a)

or:

  󰇛󰇜  (1b)

If h(x) is linearized, then:

     (2)

The measurement matrix, or H, is unaffected by

the state factors.

The goal is to find the best estimation of x,

denoted by . The weighted least squares (WLS)

idea is the foundation of the most widely used

method. The technique seeks to reduce the

differences between the related equations and the

measurements. To achieve this, the next

optimization function must be minimized:

 󰇛󰇜

  󰇛󰇜  󰇛󰇜 (3a)

Where R is a diagonal matrix that has the

variances of the measurement error. (3a) can be

rewritten as:

󰇛󰇜󰇛 󰇛󰇜󰇜



 (3b)

To have a minimum the following equation must be

fulfilled:

󰇛󰇜

  󰇛󰇜󰇟  󰇛󰇜󰇠  (4)

Where H(x) is the Jacobean measurement matrix

with m x n dimensions:

󰇛󰇜󰇛󰇜

 (5)

After h(x) is linearized:

󰇛  󰇜 󰇛󰇜  (6)

The following obtained:

󰇛󰇜  󰇟  󰇛󰇜󰇠 (7)

    (8)

The best estimations are found by applying the

equation below:

  



󰇟  󰇛󰇜󰇠 (9)

This means that a criterion of convergence

decides when the iteration is halted, and the state

variables are incrementally approximated to a value.

The measurements are related to one another

separately by the matrix W, also known as the

weighting matrix. The selection of W components

affects the outcomes. All measurements are of

identical quality if W=I is chosen.

4 Assessment of Steady State Stability

The analysis of steady-state stability goes far

beyond merely estimating the probability of

instability as small, gradual changes in load near the

maximal loadability limit. The steady-state stability

analysis calculates the separation from a system

state where voltages may collapse and units may

lose synchronism, regardless of the underlying

solution technique. This distance is measured using

a straightforward indicator called the steady-state

stability reserve. System-wide and for transmission

corridors with stability restrictions, the evaluation is

conducted.

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DOI: 10.37394/232016.2023.18.7

Georgios Fotis, Christos Pavlatos, Vasiliki Vita

E-ISSN: 2224-350X

Volume 18, 2023

4.1 Steady-State Stability (Power and

Voltage Reserve Indicators)

The idea of steady-state stability reserve provides a

very simple way to express "how far" the present, or

actual, system state is from the "critical" state where

even a small change in the operating parameters

may result in steady-state instability. These are the

two categories of stable reserve indicators:

 

 󰇟󰇠 (10)

 

 󰇟󰇠 (11)

where:

: determines the stable

reserve's power capacity (in MW).

: determines the voltage

values for the stable reserve.

: is the total power (in MW) of the system’s

utilization, including generation and imports.

: is the power (in MW) in the actual (base)

case.

: is the average system voltage in the critical

case.

: is the voltage in the base case.

Maximum MW network utilization, also known

as maximum MW loadability, or the system

operating conditions just before the state of voltage

collapse is achieved by alternating steady-state

stability calculations that determine whether the

system is stable or unstable.

5 Dynamic Security Assessment (DSA)

The design of a DSA system enables the selection of

various load-flow situations and the construction of

individual contingencies for automatic evaluation.

User-defined parameters are used to evaluate the

contingencies. Figure 2 shows the procedure

graphically. Several user-selectable load-flow

scenarios are offered at the simulation level. The

most serious scenarios can be chosen and calculated

using the contingency builder. The software defines

the security criteria that can be combined to create

sets of standards characterizing the constraints of

the system and are appropriate for each user's

requirements. The DSA notifies and records the

events that result in system limit breaches, such as

unstable generators, voltages below 80%, angles

between nodes greater than 40°, and so on.

Fig. 2: The structure of the DSA system.

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DOI: 10.37394/232016.2023.18.7

Georgios Fotis, Christos Pavlatos, Vasiliki Vita

E-ISSN: 2224-350X

Volume 18, 2023

These scenarios are very simple to recalculate,

and the analyst can see all the usual characteristics

to get a clearer understanding. The operator can also

keep track of the key contingencies concurrently.

One of a DSA system's primary design criteria

should be its capacity to:

 Simulate key elements of active switching or

control equipment, such as capacitor banks and

FACTS devices, along with their control

mechanisms. These elements include lines,

cables, transformers, and other inactive grid

equipment.

 When simulating cascading faults, depict the

essential protection's action.

 When simulating contingencies, use a

straightforward method for building

contingencies.

6 Restoration Plan

6.1 General Guides after a Blackout

The ability to restore an Electric Power System after

any fault is critical to its operation. Many European

Transmission System Operators (TSOs) have

available online their restoration plans as the

Belgian TSO (ELIA), [43], or the Irish TSO

(EIRGRID), [44]. There have been plenty of

research works on the restoration process after a

blackout, [45], [46], [47]. The restoration process

can be divided into three stages: start-up of

generators, restoration of the transmission system,

and restoration of supply to consumers (loads).

After the start-up sequence of the generating units is

determined, it is very important to find the shortest

"path" to transfer the energy to the transmission

network, so that we have an immediate energy

supply to the network. In Table 1 the general guides

for restoration after a blackout are shown.

Table 1. General guides for restoration after a blackout for the dispatchers of a PSCC

Actions

Tools

Communication

Wind farm shutdown signal

Communication of the National Control Center with all the Regional

Control Centers, the Distribution System Operator (DSO), and TSOs

of neighboring countries

Landlines, Mobiles Phones, or other

communication systems each TSO has (e.g.,

power line carrier)

Status determination of Black Start (BS) and Non-Black (NBS) Start production units

Communication with Black Start units – setting time for black start

Relevant information must be referred to the

restoration plan of each regional control

center

Communicating with non-Black Start units, determining their status and

the critical time to restore power and restart time after power is

restored.

Priority of non- Black Start units for power supply

Division of the transmission system into subsystems

Use of the restoration plan as a guide and designing

dividing lines in the network plan.

Clear demarcation of the subsystems

Route selection from BS units to NBS units with priority

Estimation of the transmission system status

Studies, reports, and information from the Energy

Management System (EMS) that the TSO

uses

Collaboration with the TSOs to ensure that the route has the required

technical staff

Subsystem electrification and load supply

Subsystem electrification either using the bottom-up or the top-down

method

During the load supply, ensure that the frequency is high enough and the

voltage drop that will occur with the connection will not create very

low voltages

Priority of loads for reconnection in consultation

with the DSO

Synchronization of subsystems

Use synchronization points as defined in the restoration plan if possible.

Use of the restoration plan that each TSO has

issued

Providing instructions to the operators during the synchronization process

Completion of the restoration process

Gradual System’s restoration

EMS contingency analysis

WSEAS TRANSACTIONS on POWER SYSTEMS

DOI: 10.37394/232016.2023.18.7

Georgios Fotis, Christos Pavlatos, Vasiliki Vita

E-ISSN: 2224-350X

Volume 18, 2023

Some important issues during a blackout are the

following:

 The operators of black start power stations and

the substations must be authorized so that, if no

voltage is present, they will open all (external to

the station) breakers.

 In thermal power plants, power to the auxiliary

machinery must be restored within a short

critical time to achieve a "warm restart".

 The TSO must declare its status (Normal, Alert,

Emergency, or Blackout) to the EAS System,

informing this way all the other TSOs of

ENTSO-E.

The cooperation of TSOs, particularly those in

proximity, is a crucial factor during the repair

process. Typically, nearby TSOs must energize the

interconnection power lines after a blackout during

the top-down restoration process. The European

Awareness System (EAS) is also a helpful

instrument for communication between TSOs,

signalizing the rise of emergency situations and also

helping with system restoration. Distribution System

Operators (DSOs) are typically encouraged to

reduce loads before a major blackout and during the

TSOs' attempt to prevent it. The DSO's "strategy"

up to this point in the event of a blackout is to wait

for TSO restoration and increase loads while it is

happening. Cooperation between TSO, DSO, and

governmental organizations like the Police and the

Fire Brigade, should be guaranteed to reduce the

restoration time in a blackout, particularly if it has

been brought on by a natural catastrophe like flood,

earthquake, fire, etc.

6.2 Activation Strategies after a Blackout

There are two central principles that guide the

process of restoring the electricity system after a

blackout:

Bottom-up: Using Black Start units and/or house

load units with islanding capabilities, the affected

areas are recovered by self-reactivating the area in

chunks ready for resynchronization with another

area.

Top-down: Using interconnection links to

transfer energy from a safe system, a normally

isolated system with a serious disruption is revived

using external voltage sources. The interrupted TSO

must vouch for its commitment to adhering to the

limits of active and reactive power flows on the

interconnection lines set forth in bilateral

agreements.

The current practices across Europe are:

a. In the Baltic region, restoration plans are based

on the top-down principle.

b. In continental Europe and the Nordic regions,

both methodologies are used, considering the

existing situation (availability of Black Start

units and units in auxiliary feed mode within the

TSO's area of responsibility, duration of the two

principles, and the state of the voltage in the

neighboring network).

c. In Great Britain, the restoration plans are based

on the bottom-up principle.

d. In the Ireland / Northern Ireland region, once

the Black Start units start-up, the non-Black

Start target unit supply restoration routes will be

activated and initial load restoration will be

required to stabilize the restoration routes

(balancing the production with the demand).

The TSO determines the load restoration steps

required in terms of size and location and the

relevant DSO load coordinator will implement

them. Very good coordination between TSO and

DSO is required, especially in the early stages of

restoring stable operation and minimizing frequency

and voltage deviations.

For example, in Figure 3 the geographical

distribution of three separate subsystems (NW, NE,

S), during restoration in the Belgian TSO (ELIA),

using the bottom-up strategy is depicted, [43]. The

restoration plan defines that in case of a blackout, 4

black start units will be used for the formation of

these three separate regions.

WSEAS TRANSACTIONS on POWER SYSTEMS

DOI: 10.37394/232016.2023.18.7

Georgios Fotis, Christos Pavlatos, Vasiliki Vita

E-ISSN: 2224-350X

Volume 18, 2023

Fig. 3: Geographical distribution of 3 separate subsystems (NW, NE, S), during restoration in the Belgian TSO

using the bottom-up strategy.

6.3 Factors that May Affect the Restoration

Process

Although there is a restoration plan from every

TSO, very often there are some unpredictable

situations that may cause its modification during

restoration, [46]. In [47], an estimation method of

the probability of restoration or recovery time for

electric power systems is proposed. Common

problems that occur during a restoration process are:

 Generators that lose their auxiliary loads may

not be able to remain in this state for long. In

many stations, it is not possible to close the high

voltage (HV) switch with a "dead busbar" so

that a subsystem cannot be formed from a single

generator.

 According to restoration guidelines, all

substations must be isolated, which means that

all circuit breakers must be opened. However,

some high-voltage circuit breakers may not

have opened in time.

 The mobile phone network will almost certainly

be congested and may even collapse due to a

national outage. A complete failure of all

communication systems is extremely unlikely.

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DOI: 10.37394/232016.2023.18.7

Georgios Fotis, Christos Pavlatos, Vasiliki Vita

E-ISSN: 2224-350X

Volume 18, 2023

Satellite phones must be installed at multiple

key locations, including all Black Start power

units and all Control Centers. If these phones

are the only available methods of

communication, recovery time will be

significantly longer.

 Some electrical components of the Transmission

System (substations, power lines, etc.) may be

unavailable as planned in the restoration plan.

Uncontrollable parameters such as traffic chaos

and extreme weather conditions can

significantly delay the access of personnel to the

substations or the control centers on the day of

the incident.

7 Discussion

In this work, the role of a PSCC has been

analytically presented. The monitoring and control

of the grid through the PSCCs provide reliability

because it enables the operation of the grid even

closer to its limits. The PSCC is the “brain” of a

power system. It detects the power system's

condition, finds its state, plans its movement, and

offers protection from exogenous events. However,

the final decisions are taken by the personnel of the

PSCC known as dispatchers. Dispatchers are

electrical engineers, working in shifts to provide the

system’s balance and are the ones who will face the

great difficulty of a blackout. They should be

technically educated, and well-trained because the

importance of their job demands it.

This research work focuses also on the

importance of the dispatcher in a possible blackout.

The restoration plan as it was presented in section 6

will not be possible to be followed unless capable

and well-trained dispatchers know what to do in

such an event. Sometimes they have to unjust the

restoration plan, something that requires skills. The

software systems that a PSCC has are extremely

important for the operation of a power system and

cannot be done by humans. However, the restoration

process following the bottom-up or top-down

procedures needs dispatchers who will be able to

adjust it to the current power system’s conditions.

8 Conclusions

The crucial role of PSCCs in the optimum operation

of power systems and their significant role in power

system restoration have been discussed in this work.

However, they need improvements in their design

and operation. Here are a few things to think about

when designing control centers:

 Many control centers that are unable to

communicate with one another cannot control a

single interconnected grid. It must be simple to

store and exchange data automatically and

continuously without relying on operator-to-

operator phone calls.

 The monitoring systems must be standardized,

including the frequency of data collection, time

stamping, alarming, visualization, etc., to allow

dispatchers at various control centers located

throughout the grid to interact effectively.

 More specificity is required in the control

reliability requirements. The same ones, like

voltage control, are less common even though

this has been done for frequency control.

 The real-time data made accessible to operators

and control centers across the grid should be

chosen based on reliability requirements. The

current argument over whether certain data

belongs to generating firms as proprietary must

end when the grid's dependability is harmed.

If the above suggestions are adopted the operation

of the power systems via the control centers will be

significantly improved and the very known effects

of possible back out to the society and the economy

will be minimized.

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E-ISSN: 2224-350X

Volume 18, 2023

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Georgios Fotis, Christos Pavlatos, Vasiliki Vita

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Contribution of Individual Authors to the

Creation of a Scientific Article (Ghostwriting

Policy)

The authors equally contributed in the present

research, at all stages from the formulation of the

problem to the final findings and solution.

Sources of Funding for Research Presented in a

Scientific Article or Scientific Article Itself

No funding was received for conducting this study.

Conflict of Interest

The authors have no conflict of interest to declare

that is relevant to the content of this article.

Creative Commons Attribution License 4.0

(Attribution 4.0 International, CC BY 4.0)

This article is published under the terms of the

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DOI: 10.37394/232016.2023.18.7

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Volume 18, 2023