The document proposes a differential power-based technique to detect symmetrical faults during power swings. It uses an auto-regression method to predict voltage and current samples during swings. The difference between predicted and actual samples is used to calculate differential power, which is high for faults and low for swings. The method was tested on different systems and fault scenarios and could accurately identify faults during slow and fast swings.

1. WELCOME

2. SYMMETRICAL FAULT DETECTION DURING
POWER SWING

3. ABSTRACT
• If a fault occurs during a power swing, it should be detected
and the unblocking function should be invoked to clear the
fault as soon as possible.
• Distance relays are getting blocked during power swing to
ensure reliability of the power system.
• Due to the symmetric nature of signals during the power
swing, symmetrical faults are difficult to be detected.
• In this paper, a differential power-based fault detection
technique is proposed for the detection of symmetrical faults
during power swings.

4. Cont…
• The differential power is calculated from the difference in
predicted and actual samples of voltage and current.
• The predicted voltage and current samples are obtained
using the auto regression technique.
• The proposed method is tested for different fault conditions
and the results are compared with the available method.
• The proposed method is found to identify symmetrical faults
accurately during slow and fast power swings for different
power systems.

5. Literature survey
• Power Swing which is basically caused by the large disturbances in
the power system which if not blocked could cause wrong operation
of the distance relay and can generates wrong or undesired tripping
of the transmission line circuit breaker.
• To prevent unwanted distance or other relay operation during a
Power Swing, we did fundamental studies of traditional and
advanced detection and prevention methods.
• However, many studies have shown that undesirable zone 3
distance relay operations have initiated tripping which lead to
cascading events and finally wide-area voltage collapse (Jonsson
and Daadler, 2003; Kim et al, 2005; Jin and Sindhu, 2008 ; Lim et al,
2008).

6. Cont…
• To improve reliability of relay operation, adaptive scheme for
distance protection has been introduced by many researches
(Horowitz, Phadke and Thorpe, 1988, Thorpe et al, 1988: Jonsson
and Daadler, 2003; Kim, Heo and Aggarwal, 2005; Lim et al, 2008).
• In adaptive distance protection relaying, an important aspect to be
considered is developing an indicator that can differentiate between
faults and power swings.
• The objective is to permit the trip signals during faults and block the
trip signals during other events.
• My enhancement to the topic is to clear or rectify the condition using
The Fault Mitigation Technique.

7. LITERATURE REVIEW PAPERS
Detection of Symmetrical Faults by Distance Relays During Power
Swings.
(IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 25, NO. 1, JANUARY 2010)
• To maintain security of distance relays, power swing blocking is
necessary to prevent unintended operation under power swings.
• This paper presents a new method for detecting a symmetrical fault during
a power swing, based on extracting components of the current waveform
using the Prony method.
• The merit of the proposed method was demonstrated by simulating
various cases including solid faults and arc fault on a typical power
system.
• The ease of implementation as well as accuracy and high speed of fault
detection are important advantages of the proposed method.

8. A Novel Approach to Detect Symmetrical
Faults Occurring During Power Swings by
Using Frequency Components of Instantaneous
Three-Phase Active Power
(IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 27, NO. 3, JULY 2012)
• Based on the damping frequency component of 50 (or 60) Hz created on
instantaneous three-phase active power profile after inception of a
symmetrical fault, the proposed method will be able to detect the fault in
less than one power cycle.
• This detection method can be readily implemented, and is immune to the
power swing slip frequency, fault inception time, and fault location.
• The proposed method has several advantages that are superior to the
existing methods. First, since it requires only three-phase active power,
which can be simply calculated by production of instantaneous voltage
and current, and FFT, which is coded in all digital relays, the new method
can be readily implemented. Second, the new method is very fast.

9. Fast Distance Relay Scheme for Detecting
Symmetrical Fault During Power Swing
(IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 25, NO. 4, OCTOBER 2010)
• The paper provides a fast detection scheme for symmetrical fault during
power swing for distance relay, which is based on extracting the high-
frequency component energy of forward and backward traveling waves
induced by faults.
• The multi resolution analysis based on wavelet transform has the ability to
decompose the analyzed signals into different frequency bands. The
selection of mother wavelet and the number of levels of wavelet transform
are carefully studied.
• The fault can be identified by feature extracting from the d1 component of
Daubechies-8 (Db8) wavelet transform.
• This proposed method can be used for distance relay operation blocking
or monitoring.

10. A Classification Approach Using Support Vector
Machines to Prevent Distance Relay Mal-operation
Under Power Swing and Voltage Instability
(IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 27, NO. 3, JULY 2012)
• Distance relays, in the power transmission systems, are susceptible to the mal-
operation under certain system events, such as power swings and voltage
instability
• The proposed scheme segregates the power system events into faults, power
swings, and voltage instability.
• This paper also proposes a new index, called the relay ranking index, for
identifying the relays most vulnerable to the mal-operation due to power
swings and voltage instability.
• The scheme effectively discriminates the dynamic encroachment events and
differentiates the system events into power swings and voltage instability by
utilizing the transmission- line reactive power loss as a key indicator for the
voltage-unstable situation.

11. Mitigating the Impacts of CCVT Subsidence
Transients on the Distance Relay
(IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 27, NO. 2, APRIL 2012)
• The paper presents a comprehensive time-domain model of the
coupling capacitor voltage transformer (CCVT) to investigate the effect
of CCVT subsidence transients on the distance relay.
• The studies show that voltage-zero subsidence transients can
adversely impact the performance of the distance relay and result in
the overreach problem.
• The method is based on improving the degree of accuracy of the
voltage Phasor estimation during the CCVT subsidence transients.
• The proposed method is not affected by harmonics and high-
frequency transient distortions of the voltage, and prevents the relay
overreach problem.

12. Review of existing methods
• In a power system disturbance-like faults, generator
disconnection and change in the large block of
loads are the main reasons for power swing.
• Large variations in voltage and current causes
undesired tripping of distance relay which may lead
to subsequent line outages.
• The power swing blocking (PSB) function is used to
prevent mis-operation of distance relays during
swing.

13. • If a fault occurs during the power swing, it should
be detected and suppressed.
• Conventional fault detection techniques may fail to
distinguish fault during the power swing.
• Symmetric nature of phase voltages and currents
during the swing makes this task tedious.

14. PROPOSED METHOD
• Full-cycle sample points of voltage and current
are predicted using auto regression technique
for any phase.
• It models the nth value of a variable as a
function of previous values, where k is the order
of the model.
• The accuracy of the prediction technique
improves with a higher value of k.

15. PHASE 1 - CASE STUDY
• The method is tested for various fault conditions
during the power swing for a 400-kV double-
circuit transmission system (i)
• A 230-kV WSCC 3-machine, a nine-bus system
(ii)
• Simulation and analysis are going to be done
through PSCAD/EMTDC

16. • i)
• ii)

17. ANALYSIS WITH AUTO REGRESSION
PROGRAMME
• Auto regression is a special technique for
regression analysis.
• The technique models nth values of the system
as a function of K previous values.
• Higher values of K improves the system
prediction accuracy.

18. Cont…
• The expression for the Kth order auto regression model
is
• where a1,a2….aK are the auto regression coefficients
and i’s are the samples of the variable.
• The calculation of coefficients are done by considering
the P available samples of the system.

19. Cont…
• matrix form of the system can be written as
• It can be further written as
• The future sample points are calculated using
available samples and [A]

20. Cont…
• The expression for obtaining future samples
(next q samples) is
• The accuracy of prediction decreases with
length of q.
• The accuracy of the technique depends on the
selection of k, p, q.

21. Cont…
• The coefficients of the auto regression technique are
calculated using previous samples of a variable and
these samples gives a clear picture of the future
disturbances and system oscillations.
• The difference between the predicted and actual values
of the variable is found to be negligible when there is no
external disturbance with the selected system.

22. Cont…
• The differential components of voltage and
current at any sampling instant of time are
calculated as follows:

23. Cont…
• The rms values of differential voltage and
current are calculated over a period of one cycle
Where N is the number of samples per cycle

24. Cont…
• The differential power ΔP is calculated
from the rms voltage and current as

25. RESULTS FOR THE DOUBLE-CIRCUIT LINE
• The system is simulated using PSCAD/EMTDC
software with a distributed transmission-line model.
• A three-phase fault is created in Line-2 at point F at
0.5 s, which is cleared after 0.1 s by the opening of
breakers B3 and B4. As a result, the distance relay R1
in line-1 experiences a power swing.
• Any fault in line-1 during the swing has to be detected
by relay R1.

26. FLOW DIAGRAM FOR THE PROPOSED
DOUBLE CIRCUIT LINE

27. Results
Differential component of voltage

28. Differential component of current

29. • Differential power for the 3Phase fault at 3.65s
during power swing.

30. Inference
• The difference in the actual and predicted samples of the
voltage and current during the power swing followed by a
three-phase fault at 3.65 s are shown.
• The wave forms obtained are clearly showing the
predicted and actual samples of voltage, current and
power during the swing and fault.
• Difference in predicted and actual samples of voltage
and current is less during the power swing and high for
the fault period.

31. • The differential power can be obtained directly from the
current – voltage waveforms.
• The magnitude of ΔP is negligible for the power swing
and high for the fault period.
• The algorithm identifies the fault if the magnitude
exceeds the threshold value of ΔP.
• The selection of threshold value is much important to get
a more accurate fault detection.
• The threshold value should be greater than the
maximum differential power during the swing condition.

32. CONCLUSION
• Detection of symmetrical fault during power swing is actually a
threat to power system protection.
• The base paper is hereby proposing an auto-regression based
study of symmetrical fault components during the swing period.
• But mitigating a fault is much beneficial than making a tripping with
the CBs.
• The thesis is thus proposing a fault mitigation scheme to assure an
improved reliability with the power system.