IEEE Power & Energy Magazine - September/October 2015 - 58

50.18

Bhadrawati
Solapur
Moga
Biharsharif

CGPL
Agra
Jeypore

Itarsi
Bassi
Durgapur

Kobra
Karcham Wangtoo
Sasaram

50.17

Frequency (Hz)

50.16
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50.11

0
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50.1

figure 11. Frequency of the various nodes in the western grid measured from PMUs during oscillation on
28 January 2014.

✔ fast rates of data communications
✔ new metering types including bus voltage angle mea-

surements and branch current angle measurements.
To take advantage of WAMS data for good visualization
and state estimation in SCADA, it is necessary to integrate
them. Until the complete SCADA is migrated to PMU measurements, these two technologies will mutually coexist.
There are various ways to integrate WAMS data to SCADA,
and some are as under the following:
✔ Inter Control center Communication Protocol (ICCP)
✔ IEC 60870-5-104
✔ FTP of the text/COMTRADE file
✔ integration at the database level.
Integration at the ICCP and IEC 60870-5-104 levels
would fall under standards, whereas FTP and DB integration are crude method nonstandards, compromising security
considerations. Integration through the latter method can be
considered for a temporary period.
Some of the important considerations related to the
integration over IEC 60870-5-101/104 with SCADA are the
following:
1) Down sampling phasor data to a level compatible to
SCADA, i.e., 2-10 s (Indian conditions, as per the
present specifications).
2) Normally, in SCADA, analog measurands are reported without time tag, but it can also report with time
tag; in such cases, time stamp mismatch problems can
be addressed.
3) Angle measurements from PMU are reported in -180˚
to +180˚ and need careful addressing while down sampling in PDC and using SCAD-based applications.
58

ieee power & energy magazine

4) SCADA applications such as SE should be capable for
phasor measurement input as initial conditions during
the solution.

Detection of Low-Frequency
Oscillations in the Indian Grid
The Indian grid has been experiencing low-frequency oscillations (LFOs) since its early days. In the western region, the
Vindhyachal and Korba region used to oscillate as the transmission link between the eastern and western part of the western grid were weak. The synchronization of the eastern and
western grid in 2003 was done using tie links having a thyristor controlled series capacitor (TCSC) for damping the LFO.
A similar case was while synchronizing the eastern region
grid with the northern region grid wherein the TCSC-installed
tie lines were used to damp out the interarea oscillations. Earlier, the SCADA data or the data from generators were used
for oscillation information, which were not accurate due to
low resolution. From PMUs, the operator is now able to visualize such oscillations in the system. Tools and techniques are
also in development to detect the source of such oscillations
and to analyze them in real time and take corrective action
before they create further complexities in the system. The
detection of LFOs and their history is of great help in planning
and implementing damping controllers of HVdc and TCSC.
With the introduction of synchrophasor measurements
units in the Indian grid, the oscillations are now monitored
at the NLDC and at each RLDC in real time. This has helped
the system operator in giving feedback to the planners for the
weak interconnection. For example, consider the frequency
plot as shown in Figure 11. It can be shown that system was
september/october 2015



Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - September/October 2015

IEEE Power & Energy Magazine - September/October 2015 - Cover1
IEEE Power & Energy Magazine - September/October 2015 - Cover2
IEEE Power & Energy Magazine - September/October 2015 - 1
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