06-02-2013, 03:24 PM
A Synchrophasor Assisted Frequency and Voltage Stability Based Load Shedding Scheme for Self-Healing of Power System
[attachment=49868]
INTRODUCTION
DESIGN OF A well-coordinated protection and control
scheme in present-day power systems, operating very
close to the stability limits, has become a challenging task. A
concept of preserving the overall power system stability was
developed under system integrity protection schemes (SIPS)
[1]. A few such schemes are under frequency load shedding
(UFLS), under voltage load shedding (UVLS), system separation,
etc. The control actions in the UFLS have been exercised
based on predefined design rules [2], which are deterministic
in nature.
Of late, protection and control solutions [3], utilizing synchrophasor
based wide area monitoring and control system
(WAMCS), are being proposed to avoid frequency, voltage,
and rotor angle instabilities. WAMCS gathers the system information
from multiple locations and sends wide area control
signals in response to the system disturbances. System data is
collected by the phasor measurement units (PMUs)
FREQUENCY AND VOLTAGE STABILITY ANALYSIS
The methodology used to analyze the system for frequency as
well as voltage stability, following a contingency, is described
below.
A. Frequency Stability Analysis
Frequency stability analysis has been carried out in the
present work based on a low-order system frequency response
(SFR) model [6], for estimating the magnitude and subsequent
classification of the disturbance.
PROPOSED ADAPTIVE LOAD SHEDDING ALGORITHM
The adaptive scheme, proposed in this paper, aims at
achieving frequency and voltage stability through load shedding,
assuming the availability of the PMU measurements. The
procedure is as follows.
1. Estimate the magnitude of the disturbance and classify it
as case-1 or case-2, as defined in Section II-A.
2. Calculate the load shedding requirement at the buses and
perform curtailment as given below.
COMMUNICATION REQUIREMENTS
All the real-time phasor measurements are assumed to be
available at the rate of 30 frames/s in 60 Hz systems and 25
frames/s in 50 Hz systems [19]. Data needed for estimating the
disturbance power is the frequency and from the generating
stations. Further, the scheme computes the VSRI, which
can be either calculated at the PMU [16] or at the PDC, based on
the positive sequence load bus voltage measurements. For a 12
channel PMU with the frame rate as specified above, the baud
rate is estimated to be 38 400 bps [22]. This study has considered
WAMS communication delay of 100 ms, in either direction, between
the PMUs and PDC, having the central processing unit.
[attachment=49868]
INTRODUCTION
DESIGN OF A well-coordinated protection and control
scheme in present-day power systems, operating very
close to the stability limits, has become a challenging task. A
concept of preserving the overall power system stability was
developed under system integrity protection schemes (SIPS)
[1]. A few such schemes are under frequency load shedding
(UFLS), under voltage load shedding (UVLS), system separation,
etc. The control actions in the UFLS have been exercised
based on predefined design rules [2], which are deterministic
in nature.
Of late, protection and control solutions [3], utilizing synchrophasor
based wide area monitoring and control system
(WAMCS), are being proposed to avoid frequency, voltage,
and rotor angle instabilities. WAMCS gathers the system information
from multiple locations and sends wide area control
signals in response to the system disturbances. System data is
collected by the phasor measurement units (PMUs)
FREQUENCY AND VOLTAGE STABILITY ANALYSIS
The methodology used to analyze the system for frequency as
well as voltage stability, following a contingency, is described
below.
A. Frequency Stability Analysis
Frequency stability analysis has been carried out in the
present work based on a low-order system frequency response
(SFR) model [6], for estimating the magnitude and subsequent
classification of the disturbance.
PROPOSED ADAPTIVE LOAD SHEDDING ALGORITHM
The adaptive scheme, proposed in this paper, aims at
achieving frequency and voltage stability through load shedding,
assuming the availability of the PMU measurements. The
procedure is as follows.
1. Estimate the magnitude of the disturbance and classify it
as case-1 or case-2, as defined in Section II-A.
2. Calculate the load shedding requirement at the buses and
perform curtailment as given below.
COMMUNICATION REQUIREMENTS
All the real-time phasor measurements are assumed to be
available at the rate of 30 frames/s in 60 Hz systems and 25
frames/s in 50 Hz systems [19]. Data needed for estimating the
disturbance power is the frequency and from the generating
stations. Further, the scheme computes the VSRI, which
can be either calculated at the PMU [16] or at the PDC, based on
the positive sequence load bus voltage measurements. For a 12
channel PMU with the frame rate as specified above, the baud
rate is estimated to be 38 400 bps [22]. This study has considered
WAMS communication delay of 100 ms, in either direction, between
the PMUs and PDC, having the central processing unit.