1. Smart Power Grid
Monitoring System
Case Study
Talk by
Isma Hadji
Imane Hafnaoui
University of M’Hamed Bouguara - IGEE

2. Outlines
• Introduction
• Smart grids
• Phasor Measurment Units (PMUs)
• Monitoring
• Power system stability monitoring
• Out-of-step stability
• Conclusion

3. Introduction
• Traditionally, electrical grids mainly consisted of
power stations, transmission lines and transformers.
• Nowadays, grids are growing bigger and they are
becoming smart grids, implementing virtually all the
processing and management needed by a power
system from monitoring, through control to
protection.
• One of the most important elements of modern
energy management systems is monitoring of the
state of the power system from real-time
measurements.
• This is today done using PMUs and WAMS

4. Smart Grids
• A Smart Grid is an electric network that can
intelligently integrate the actions of all users
connected to it – generators, consumers and those
that do both – in order to efficiently deliver
sustainable, economic and secure electricity
supplies.

5. Phasor Measurement Units
• Phasor Measurement Units (PMU) provide real-time
measurement of positive sequence voltages and
currents at power system substations in real time.
• Electrical Quantities recorded by PMUs
– Bus voltages
– Three-phase line currents for every critical line.
– Frequency
– Megawatts and Mega-vars

6. Phasor Measurement Units
Disturbance Recording
– PMUs are placed at key locations on the system
– Depending on the type of trigger, a PMU will
record when a power system fault is observed at
its location.
– The captured phasors are time tagged based on
the time of the UTC Time Reference.

7. Phasor Measurement Units
Applications
– Power system real-time monitoring
– Advanced network protection
– Advanced control schemes

8. Monitoring
• Energy monitoring is primarily a management
technique that gathers energy information that will
be used as a basis to eliminate losses, reduce and
control current levels of energy use and improve
the existing operating procedures. It builds on the
principle “you can’t manage what you don’t
measure”.
• In today’s large scale systems there are plenty
phenomena that need to be detected and
monitored to keep them working at their best.
• Monitoring represents the first line of protection for
any power system.

9. Monitoring
The Imperatives of Monitoring
• Power assurance
• Visibility into power conditions
• Energy efficiency
• Energy cost allocations
• Proactive planning

10. Monitored Phenomena
Islanding Detection
Islanding refers to the condition in which a
distributed generator (DG) continues to power a
location even though electrical grid power from the
electric utility is no longer present.
Example: a solar panel in a blackout scenario.
Detection: At the substation, voltage and angle are
measured and time stamped before being sent to
the receiver at the DER-plant. It can there easily be
determined if the DER-plant is synchronized with the
grid or not.

11. Monitored Phenomena
Line Thermal Monitoring
Loose connections or deterioration of contact surfaces result in local
temperature rise which may result in possible forced outages. It is wise
to say that temperature monitoring is necessary.
This type of monitoring plays as a congestion manager as it
improves power flow control.
Detection
•The voltage and current phasors measured at both ends of a line
are collected using PMUs
•Actual impedance and shunt admittance of a line are computed.
•Resistance of the line/cable is extracted.
•Based on the known properties of the conductor material, the
actual average temperature of the line is determined.

12. Power System Stability Monitoring
• Power systems are subjected to a wide range of
small or larger disturbances during operating
conditions.
• The power system must adjust to these changing
conditions and continue to operate satisfactorily
and within the desired bounds of voltage and
frequency.
• For this reason monitoring power system stability is of
paramount importance in any power system.

13. Power System Stability Monitoring

14. Power System Stability Monitoring
Voltage stability monitoring
• The problem of voltage stability may be simply
explained as inability of the power system to
provide the reactive power needed by the system.
• In general, the analysis of voltage stability problem
of a given power system should cover the
examination of these aspects:
– How close is the system to voltage instability or collapse?
– When does the voltage instability occur?
– Where are the vulnerable spots of the system?
– What are the key contributing factors?
– What areas are involved?

15. Power System Stability Monitoring
Angle stability monitoring
• When the system is operating under
unforeseen conditions or under unusually
high stress, the system can experience angle
instability. In that case, the system breaks up
into many islands, resulting in large loss of
loads and generations and a potential
blackout scenario.

16. Power System Stability Monitoring
Power oscillation monitoring
Power oscillation monitoring is concerned with the detection of
power swings in a high voltage power system.
Low-frequency oscillations occur when an individual or group of
generators swing against other generators operating
synchronously on the same system, caused by controls
attempting to maintain an exact frequency.
• Synchrophasor data are critical to detect potential and
actual oscillations; which require the high-speed PMUs.
– Examining bus voltages and frequencies will allow
observation of inter-area oscillations.
– The energy of power oscillations indicates whether
oscillations are growing or dissipating.

17. Out-of-Step Stability
Out-of-Step Analysis
Power Transmission
Power-Angle Curve Capability of the Normal
System with Different Types of
Faults

18. Out-of-Step Stability
Equal Area Criterion
• After a fault, the power output is
reduced to PF, the generator rotor
therefore starts to accelerate, and
δ starts to increase. At the time that
the fault is cleared (δC), there is
decelerating torque acting on the
rotor.
Because of the inertia of the rotor
system, the angle continues to
increase to δF when Area-2 = Area-
1.
 If δF is smaller than δL, then the
system is transiently stable. With
sufficient damping, the angle
difference eventually goes back to
the original balance point δ0 .

19. Out-of-Step Stability
Equal Area Criterion
 if Area-2 is smaller than Area-1 at
the time the angle reaches δL,
then further increase in angle δ
will result in an electric power
output that is smaller than the
mechanical power input.
Therefore, the rotor will
accelerate again and δ will
increase beyond recovery.
This is a transiently unstable
scenario.
To watch out for these cases and be able to take the
right measures, real-time measurements and
computations of the two areas is necessary.
This is now easily achieved thanks to PMUs.

20. Conclusion
• The concept of modern smart power grids was
introduced. Power monitoring and management deliver
confidence that power systems are doing what they
should, that personnel will be immediately notified of
alert conditions in time to resolve, not just react, and the
confidence of being able to predict and prevent
problems before they occur.
• Placement of PMUs in power systems to easily support
wide area recording with synchronized data, and that
for enhancement of power system stability such as rotor
angle stability, power system oscillations, and voltage
stability in an integrated power system network.

21. THANK YOU