1. The document discusses power quality issues in smart grids, including various types of disturbances like voltage sags, transients, and harmonics. It defines several harmonic indices used to measure power quality. 2. Key power quality issues with smart grids are discussed, such as sustained interruptions, voltage regulation challenges, and harmonics from distributed generation sources. Operating conflicts from utility protection requirements, reclosing, interference with relaying, and other issues are also summarized. 3. Various power quality problems that can arise from interactions between distributed generation systems and the grid are described at a high level, including issues related to fault clearing, reclosing, voltage regulation, harmonics, islanding, ferroresonance, and sh

1. Dr. Unnikrishnan P.C.
Professor, EEE
EE403 Distributed
Generation & Smart Grids

2. Module VI
Cloud computing in smart grid: Private, public and Hybrid cloud.
Cloud architecture of smart grid.
Power quality: Introduction - Types of power quality disturbances -
Voltage sag (or dip), transients, short duration voltage variation,
Long duration voltage variation, voltage imbalance, waveform
distortion, and voltage flicker
Harmonic sources: SMPS, Three phase power converters, arcing
devices, saturable devices, fluorescent lamps, harmonic indices
(THD, TIF, DIN, C – message weights) Power quality aspects with
smart grids.

3. Harmonic Indices
Total Harmonic Distortion THD
Total Demand Distortion TDD
Telephone Interference Factor TIF
Distortion Index DIN
C-Message Weighted Index CMWI

4. THD is the ratio between the RMS values of the
harmonics and the RMS value of fundamental
THD for voltage:
Total Harmonic Distortion THD

6. TDD is the ratio between the RMS values of the
harmonics current and the RMS value of fundamental
current
Total Demand Distortion TDD
TDD for Current:

7. Telephone Interference Factor TIF
Telephone noise originating from harmonic currents and
voltages in power systems is generally quantified as a
telephone influence factor (TIF)

8. Telephone Interference Factor TIF
TIF factor at 60 Hz is close to zero, indicating that the phone circuits
and the ear are insensitive to power frequency noise
Even at the more common harmonic frequencies, such as the 5th
or the 7th, the TIF factor is still relatively low

9. Telephone Interference Factor TIF

10. Distortion Index DIN
The distortion index is defined in terms of the harmonic
power divided by the total power in the waveform itself

11. C-Message Weighted Index CMWI
 A noise spectral weighting used in a noise power
measuring set to measure noise power on a line that is
terminated by a 500-type (Musical) set or similar
instrument

12. Flicker Factor F
 Flicker is a frequency domain effect and can cause
discomfort in humans and animals

13. Power Quality Issues with Smart Grid
Sustained Interruptions: DGs are designed to provide
backup power to the load in case of power interruption
but increase the number of interruptions in some cases.
Voltage Regulation: Limiting factor for how much
Distributed Generation can be accommodated on a
distribution feeder
Harmonics: Harmonics from rotating machines are not
negligible in grid parallel operation
Voltage Sags: Most common PQ problem . The ability of
Distributed Generation to reduce sags is dependent on
the type of generation technology and the
interconnection location.

15. Operating Conflicts that can result in power quality
problems
1. Utility Fault Clearing requirements
2. Reclosing
3. Interference with Relaying
4.Voltage regulation issues
5.Harmonics
6.Islanding
7.Ferroresonance
8.Shunt Capacitor Interaction

16. 1. Utility Fault Clearing requirements
Figure shows the key components of the overcurrent protection
system of a radial feeder
There will frequently be two to four feeders off the substation bus.
This design is based mostly on economic concerns

17.  One essential characteristic is that only one device has
to operate to clear and isolate a short circuit, and local
intelligence can accomplish the task satisfactorily.
 Faults on the transmission system, which easily handles
generation, usually require at least two breakers to
operate and local intelligence is insufficient in some
cases.

18. 2. Reclosing
Most of the distribution lines are overhead, and it is common to
have temporary faults
Once the current is interrupted and the arc dispersed power is
restored by reclosing
DGs should be disconnected in the reclose interval to allow time for
the arc to dissipate or else it might damage DGs with rotating
machines

19. 3. Interference with Relaying

20. The desired sequence is for the recloser R to operate before the
lateral fuse has a chance to blow.
 If the fault is temporary, the arc will extinguish and service will be
restored upon the subsequent reclose within 1 or 2s.
This saves the cost of sending a line crew to change the fuse

21. 4. Voltage regulation issues
 When the fault occurs, the Distributed Generation disconnects
and may remain disconnected for up to 5 min.
 The breaker recloses within a few seconds, resulting in the
condition shown figure
 The load is now too great for the feeder and the present
settings of the voltage regulation devices.

22. 5. Harmonics
Harmonics from Distributed Generation come from inverters and
some synchronous machines. The PWM switching inverters produce
a much lower harmonic current content than earlier line-
commutated, thyristor-based inverters.

23. 6. Islanding
Distributed Generation protective relays will generally perform
their function independently of any outside knowledge of the
system to which they are connected.
Perhaps the greatest fear of the utility protection engineer is
that Distributed Generation relaying will fail to detect the fact that
the utility breaker has opened and will continue to energize a
portion of the feeder.

24. 7. Ferroresonance
Ferroresonance is a special kind of resonance in which the
inductive element is the nonlinear characteristic of an iron-core
device.
Ferroresonance occurs when the magnetizing reactance of a
transformer inadvertently is in series with cable or power factor
capacitance

25. Ferroresonance …….
Underground cable runs are normally fused at the point where
they are tapped off the overhead feeder line.
This is called the riser pole or dip pole.
Should something happen that causes one or two fuses to blow,
the relaying on the DG will detect an unbalanced condition and trip
the generator breaker.

26. Ferroresonance …….
This leaves the transformer isolated on the cable with one or two
open phases and no load.
This condition is conducive to ferroresonance because the cable
capacitance in an open phase now appears in series with the
transformer’s magnetizing impedance.

27. 8. Shunt Capacitor Interaction
Utilities use switched capacitors to help support the voltage during
high-load periods.
There can be several capacitor banks on the feeder. The capacitors
switch independently of the generator control
A 2 to 3 % increase in the voltage is common when a capacitor
bank is energized

28. Abbreviations
THD:Total Harmonic Distortion
TDD: Total Demand Distortion
TIF: Telephone Interference Factor
DIN: Distortion Index
CMWI: C-Message Weighted Index