PROTASIS SA
Power System Consulting Services
for Industrial and Utility Networks
Prepared by: Vassilis Nikolaidis, Electrical & Computer Engineer, PhD
Ilias Milis,
Electrical & Mechanical Engineer, Technical Director
POWER SYSTEM STUDIES OFFERED
PROTASIS provides a wide range of studies:
•
Power-flow analysis
•
Short-circuit analysis
•
Protection coordination
•
Stability studies
•
Switching transient studies
•
Motor-starting studies
Intented to:
• Reduce operating costs
• Improve efficiency
• Increase reliability
• Improve system maintainability
PROTASIS GENERIC PROCEDURE FOR STUDIES
• Surveying the electrical network and the existing protection
equipment in an exhaustive manner.
• Gathering, tabulating and recording in electronic files:
 All the technical data of the power system elements.
 All the existing protection devices and their settings.
• Preparing the specifications for any new protective devices.
• Performing the necessary studies for the entire electrical
network by use of sophisticated software tools.
• Delivering professional documentation and providing a series
of prioritized recommendations for enhanced performance.
POWER-FLOW ANALYSIS
• Investigates the steady-state performance of a power
system under various operating conditions.
• The basic question in power-flow analysis is:
“Given the load power consumption at all buses of a known
electric power system configuration and the power production
at each generator, find the power flow in each line and
transformer of the network and the voltage magnitude and
phase angle at each bus.”
POWER-FLOW ANALYSIS
• Power-flow studies determine:
 Voltage (V)
Vi , θi
Pik , Qik
 Current (I)
Pjk , Qjk
Vk , θk
 Active (P) - Reactive (Q) power
 Phase angle (θ)
 Power factor (cosθ)
• The following are straightforward calculated:
 Loading of circuit components
 Transformer tap positions
 System losses
 Generators exciter/regulator voltage setpoint
Pk , Qk
Vj , θj
POWER-FLOW ANALYSIS BENEFITS
• The power-flow solution helps:
 Ensure that the power system is designed to satisfy operating and security
criteria
 Ensure that this is done for the most favorable investment and operation costs
 Decide new equipment additions or alternative solutions to:
 Solve present deficiencies (existing state)
 Meet future system requirements (planning stage)
• A number of operating procedures can be analyzed:
 Determining optimum capacitors size/location for power factor improvement
 Determining system voltages for large load connection or disconnection
 Contingency conditions (loss of equipment or load)
PROTASIS POWER-FLOW STUDY PROCEDURE
• The existent electrical network is mapped and its single-line
diagram is drawn.
• The whole network is modeled in a suitable software program.
• Determining all possible network configurations:
 Power production and load levels
 Topology schemes
 Scenarios with combination of the above conditions
• For all the aforementioned states:
 Power-flow analysis is performed
 The “N-1” security criterion is examined
• For power factor correction studies, the total and per substation
power factor is further computed.
PROTASIS POWER-FLOW REPORTING
• Tables with the electrical data of the network elements.
• Single-line diagrams of the network.
• Single-line diagrams depicting the power-flow study results
for each network configuration.
 The power-flow, in KW–KVAR or Amperes
 The bus operating voltages
 The loading percentage of each element, or of the CT associated
with the element, or of the overload protection setting
• Documentation of:
 The optimum positions for the transformer tap changers
 The power losses (total and per substation)
 The overloaded elements (transformers, lines, cables, CTs etc.)
SHORT-CIRCUITS
May lead to one of the following phenomena:
 Excessive overcurrents that could lead to equipment damage and
downtime
 Excessive transient or sustained overvoltages that compromise the
integrity and reliability of various insulated parts
 Voltage depressions in the vicinity of the fault that could adversely
affect the operation of rotating equipment
 Creation of system conditions that could prove hazardous to personnel
NEED FOR SHORT-CIRCUIT ANALYSIS
•
Short-circuit studies can be performed at the planning stage to:
 Finalize the system layout
 Assess the effect of short-circuits on the overall system voltage profile
 Determine the size of cables, transformers, and conductors
 Determine the size of interrupting devices
 Conceptualize and design neutral and substation grounding
•
For existing systems, fault studies are necessary in the cases of:
 Added generation or installation of extra rotating loads
 System layout modifications
 Rearrangement of protection equipment
 Verification of the adequacy of existing breakers
 Verification of the adequacy of the existing ground mat grid
 Relocation of existing switchgear to avoid unnecessary capital expenditures
 Post-Mortem Analysis
PROTASIS SHORT-CIRCUIT ANALYSIS PROCEDURE
•
The whole network is modeled in a suitable software program.
•
Various types of faults (3ph, 2ph, 2ph-g, ph-g)
on all system buses are simulated considering
all possible network configurations:
 Production and load levels
 Topology schemes
 Scenarios with combination of the above conditions
•
Fault analysis determines the magnitude of the prospective currents
flowing throughout the power system at various time intervals after a
fault occurs according to IEEE/IEC Stds.
•
The duty imposed on the protective system equipment is dependent
upon the magnitude of the current, which is dependent on the time
from fault inception.
•
The results are used to select fuses, breakers and switchgear ratings.
PROTASIS SHORT-CIRCUIT ANALYSIS REPORTING
• Tables with the fault currents at all the network buses
as per IEEE and IEC Stds.
• Direct comparison tables of the ratings of the ANSI or IEC
dimensioned breakers with the fault currents appearing at
the breakers’ locations.
• Recommendations for the existing switchgear and the new
one to be located in different substations within a network.
• Recommendations for minimizing short-circuit duties.
PROTECTION COORDINATION
• Definition:
The interruption of only the minimum amount of equipment
necessary to isolate the faulted portion of a power system. The
power supply to loads in the remainder of the system is maintained.
• Objective:
Minimize hazards to personnel and equipment while allowing the
least disruption of power service.
• Study:
The selection of protection schemes and relay settings that achieve
the objectives under abnormal system conditions.
 Selection and verification of the clearing characteristics
 Determination of the protective device settings
GRAPHICAL REPRESENTATION
•
The “coordination curves’’
show
graphically
the
protection
coordination
possible
with
the
available equipment.
•
They
permit
the
verification / confirmation
of
protective
device
characteristics, settings,
and ratings to provide a
properly coordinated and
protected system.
•
Sophisticated programs
provide
a
graphical
representation
of
the
device coordination as it
is developed.
PROTECTION COORDINATION BENEFITS
• Reliability:
Assurance that the protection will perform correctly.
• Selectivity:
Maximum continuity of service with minimum system
disconnection.
• Speed of operation:
Minimum fault duration avoiding equipment damage and
system instability.
• Safety:
Minimize hazards to personnel and equipment.
• Fault Location:
Coordination assures that fault is located on the isolated part.
PROTASIS PROTECTION COORDINATION PROCEDURE
• The whole network is modeled in a suitable software program.
• All the protective relays are modeled in the program.
• The settings of the existing relays are inserted in the program.
• The optimum set of relays settings is determined considering
all possible network configurations:
 Production and load levels
 Topology schemes
 Scenarios with combination of the above conditions
• Motor startups are simulated for all the aforementioned
scenarios to avoid undesirable operation of the overcurrent
protection.
PROTASIS PROTECTION COORDINATION REPORTING
• Records of the existing protection devices and their settings.
• Creation of protection setting sheets with information about:
 The hardware (substation, CT-VT, relay model and type)
 The software (relay operating elements/functions, settings to be applied
and ranges of their values)
 Editorial information (responsible engineer, setting sheet date and number)
• Full operating single-line diagram of the network showing:
 The installed protections
 The connected CTs and/or VTs
 The routing of the relays tripping signals
• Diagrams with:
 The operating characteristics of the relays for the suggested settings
 The short-circuit currents that activate them
 The corresponding operating times (prospective fault clearance time)
TRANSIENT STABILITY
•
Definition:
The ability of a power system, containing two or more
synchronous machines, to remain in synchronism after a large
change occurs on the system.
•
Common disturbances:
 Short circuits
 Loss of a tie circuit to a public utility
 Loss of a portion of on-site generation
 Loss of large amount of load
 Starting of a large motor
 Switching operations
•
Result:
 De-synchronization of synchronous generators
 Over/under voltage and frequency
 Undesired operation of protection equipment.
TRANSIENT STABILITY STUDY BENEFITS
•
Determine the “stability margin” of a system by checking:
 The damping of the power swings after a disturbance.
 The response of the protection scheme.
 The adequacy of any load-shedding scheme.
•
Improving system stability by adjusting:
 The settings of the generator control devices.
 The reactive power compensation devices.
 The settings of the installed protective relays.
 The settings of the load-shedding scheme.
 The instructions to the responsible engineers
concerning the available margin for stable operation.
PROTASIS TRANSIENT STABILITY STUDY PROCEDURE
•
Time-domain simulation is needed for the analysis of the
non-linear characteristics of power system stability.
•
Equipment involved in stability studies are accurately modeled:
 Generators
 Generators control devices
(excitation systems, governors, stabilizers)
 Synchronous and induction motors
 Dynamic self-restoring loads
 Power electronic devices
 Protective relays
•
All possible network configurations are determined.
•
The credible disturbances are determined and simulated.
•
Critical fault-clearing times are defined and proper settings
for the protective relays are selected.
PROTASIS TRANSIENT STABILITY STUDY REPORTING
•
Dynamical data of the non-linear equipment:
 Generators/turbine inertia, transient/subtransient reactances, time
constants, etc.
 Excitation/governing system parameters (exciter type, time constants,
dead-bands, gain, etc.)
 Dynamic motor/load data (equivalent motor circuit, time constants,
load coefficients etc.)
•
Simulated waveforms of:
 Voltage magnitudes of the system buses
 Rotor angles of generators
 System frequency (speed of generators)
 Excitation characteristics of generators
 Active and reactive power generation of generators
 Active and reactive power flow in critical lines
 Protective relay contacts state and tripping capacity
SWITCHING TRANSIENTS
•
Are of electromagnetic type:
 Oscillatory in nature, characterized by their transient period of oscillation.
 Very fast, compared with the power frequency of 50/60 Hz.
 Extremely important, because they stress electrical equipment to the
greatest extent.
•
Occur each time an abrupt circuit change happens:
 Breaker / Fuse opening or closing.
 Bus transfer operations.
 Other switching device operation.
•
Possible problems:
 Overvoltages => flashovers or insulation breakdown.
 Flashovers usually cause temporary power outages due to tripping
of the protective devices.
 Insulation breakdown usually leads to permanent equipment damage.
 Overcurrents => electromagnetic forces-excessive heat generation.
SWITCHING TRANSIENTS
Switching studies in industrial and utility systems involve:
 Capacitor bank / Harmonic filter switching (common)
 Transformer energizing / de-energizing (common)
 Cables / Lines switching including reclosing (common)
 Malfunctioning of breakers or switches (abnormal)
 Restrike phenomena (line dropping and capacitor de-energization)
 Switching surge reduction by CB controlled closing
 Optimum surge arrester sizing and location
 Transient recovery voltage on distribution and transmission systems
 Ferroresonance
PROTASIS SWITCHING TRANSIENTS STUDY
• Objectives:
 Identify the nature of transient duties
(magnitude, duration, frequency of oscillations):
 For any realistic switching operation
 For abnormal conditions (inception/removal of faults)
 Recommend corrective measures to mitigate transient overvoltages
and overcurrents.
• Three basic approaches:
 Direct transient measurements (e.g. BMI DRANETZ devices)
 Computer simulation (Electromagnetic Transients Program – EMTP).
 Circuit breakers
 Single-phase fuses
 Transformers
 Shunt reactors/capacitors
 Surge arresters
 Combination of the previous ones
PROTASIS TRANSIENTS STUDY REPORTING
•
All the data needed for the accurate simulation of the
equipment under investigation:
 Capacitor bank parameters (R, C, ωο)
 Lines and cables lumped/distributed parameters (R, L, B)
 Transformer winding data (R, L ,C)
 Transformer and reactor saturation curves
 Surge arresters V-I characteristics
 Circuit breaker internal configuration etc.
•
Simulated waveforms of:
 Voltage transient responses
 Inrush currents
 Surge arrester energy absorptions
 Transient recovery voltages on circuit breakers
 Restrike phenomena
•
Recommendations and conclusions for every particular study.
MOTOR STARTING COMMON PROBLEMS
• Large terminal voltage drop =>
 Low starting torque to accelerate up to running speed
 Extension of the starting time
• Large area voltage drop =>
 Running motors may stall
 Undervoltage / overcurrent relays may operate
• Frequent voltage drop =>
 Flicker in the lighting system
TYPES OF MOTOR STARTING STUDIES
• The voltage drop snapshot.
System currents and voltages just after the motor-starting are
examined
• The time-domain simulation analysis.
 Provides detailed information for the motor-starting period:
 Motor slip-torque characteristic
 Terminal voltage magnitude and angle
 Complex motor current
 System bus voltages and currents
 Appropriate for sequential motor starting simulation
 Currents and voltages monitoring at important locations throughout the
system
MOTOR STARTING STUDY BENEFITS
The study can help:
• Select
 The best starting method
 The proper motor design
 The required system design
• Determine the proper transformer tap changer positions.
• Determine additional precautions that should be taken if
extreme voltage dips are presented during motor startups.
• Eliminate the possibility of an undesirable operation of the
overcurrent protection during motor startups.
PROTASIS MOTOR STARTING STUDY PROCEDURE
•
The weakest network configuration is considered.
•
Individual motor starting analysis
 The effect of a particular motor starting is investigated.

Static approach: a load-flow solution is derived just after the motor
starting => Voltage on every system bus (usually voltages should be
> 0.8 pu) and initial starting currents are checked (overcurrent
protection settings evaluation).

Dynamic approach: a time-domain simulation is performed =>
Voltage and current responses are monitored during all the examined
time period including reacceleration procedures.
•
Sequential motor starting analysis
 A motor starting priority list is determined and simulated.

Dynamic approach: a time-domain simulation is performed.

System current and voltage response is checked for all
the examined time period of successive motor starts.
PROTASIS MOTOR STARTING STUDY REPORTING
•
Data of motors under investigation:
 Starting power factor and starting current
 Speed-torque characteristics of both motor and load.
 Equivalent motors and generators circuit parameters for dynamic analysis.
 Synchronous generators/motors excitation parameters for dynamic analysis.
 Starting method: DOL, Autotransformer, Delta/Wye switches, Soft starters
•
System voltage profile indicating unacceptable bus voltage
magnitudes.
•
Single-line diagrams depicting load-flow results before and
after motor starting.
•
Single-line diagrams depicting operating times of the relays.
•
Simulated waveforms of voltage/current responses during
sequential motor starting.
PROTASIS SOFTWARE LIBRARY
PROTASIS SA uses industry standard programs.
POWER-FLOW STUDIES
SHORT-CIRCUIT STUDIES
• SIEMENS PSS®E
• SIEMENS PSS®E
• ASPEN One Liner / Power Flow
• ASPEN One Liner / Power Flow
• ELECTROCON CAPE
• ELECTROCON CAPE
• CYME 5.0 / CYMFLOW
• CYME 5.0 / CYMFAULT
STABILITY STUDIES
• SIEMENS PSS®E
TRANSIENT STUDIES
• CYME EMTP-RV
• CYME EMTP-RV
• CYME 5.0 / CYMSTAB
COORDINATION STUDIES
MOTOR STARTING STUDIES
• SIEMENS PSS®E
• SIEMENS PSS®E
• ASPEN One Liner / Power Flow
• ASPEN One Liner / Power Flow
• ELECTROCON CAPE
• CYME EMTP-RV
• CYME 5.0 / CYMDIST
• CYME 5.0/Dynamic Motor start