IEEE Power & Energy Magazine - May/June 2019 - 44

tap ratios. Measurements and status signals at the HVdc stations are communicated to the control centers via DNP3.
The communication between the two HVdc stations may be,
for example, by fiber synchronous optical networking rings.
The control center for each ac system has visibility of the
status of the HVdc converter stations at both ends. As shown
in Figure 3, the control center receives measurements of ac
and dc voltage, current, and power; the firing angle of the
converter; the firing angle limits; the status of the ac and dc
CBs; and the tap setting of the commutating transformer.
Along with these measurements from the HVdc converter
stations, the control center receives measurements of line
flows and bus voltages from the rest of the ac system.
Power injection is typically ramped slowly, at a rate on
the order of tens of minutes. This rate is necessary to achieve
an increase from nearly no flow to maximum-rated line
capacity, with a maximum ramp rate of nearly 1,000 MW/
min. Detection of suspicious activity may be performed for
the duration of this ramp to ensure proper system behavior.

Threat Analysis and Detection
Potential hazards that threaten to negatively impact the grid
are primarily associated with data communication interfaces between technology, such as SCADA, or synchrophasor schemes in power transmission and distribution.

Industrial control system devices that exchange information between HVdc substations and control centers provide
an interface, which may introduce incorrect or malicious
commands. The scenario of an erroneous or spoofed power
dispatch control command from the ac control center will
impact the HVdc system and, more generally, the larger ac
grid. Influences based on erroneous sensor measurements
are of concern as well.
Detection of an incorrect power-order command on the
HVdc system from the dispatch center or system control
center may be seen in the general architecture illustrated in
Figure 3. The sensors in the power system send the measurements from different locations, such as substation buses,
transmission lines, transformers, and so on, to the system
control center using the SCADA system. The control center utilizes these measurements to determine the state of the
power system and generate new control commands to be
issued, if needed, to reach the desired state. The commands
from the control center are issued again over the SCADA
system to relevant components.
Detection relies on fast state estimation using the uncompromised measurements from the wide-area ac power system, as shown in Figure 4. If the estimate is computed rapidly enough to mitigate a destabilization on the part of the dc
system, action may be taken to avoid the problem. A highly

ac and dc System Model Control
ICCP Protocol

Export/Import
Agreement Signal

Power
Po
Pow
ow
wer
er System
Sy
Sys
ystem
em
m1
Control
Con
Co
Con
ntro
rro
ol Center
Ce
en
ent
n
nter
er
SCADA/EMS
SCA
SCA
SC
CADA/EMS
DA
D
DA/
A/E
A/
EM
EMS
MS

Power
Po
Pow
P
o
ow
we
err System
Sy
Sys
S
y tem
te
em 2
e
Control
Co
C
Con
on
o
ontro
ntro
ttrro
rol Center
Cent
en
ntter
n
er
SCADA/EMS
SCA
SC
CA
ADA
DA/
A//EMS
A
MS
MS

Measurements Using
U ing DNP3
Us

Measurements Using DNP3

Vac, Iac, Pdc, Vdc Idc,
ac Line Breaker Status
Firing Angle
Commutating Xmer Ratio
Minimum Firing Angle
Maximum Firing Angle

ac
Power
System 1

Secure
S ure Telephone Line
Sec

Secure Telephone Line

Export/Import
Dispatch Signal

Sending End

Receiving End
DCCB
B

ACCB
A B
ACC

Vac, Iac, Pdc, Vdc Idc,
ac Line Breaker Status
Firing Angle
Commutating Xmer Ratio
Minimum Firing Angle
Maximum Firing Angle

Converter

DCCB
D B
DCC
Cable

ACCB

ac
Power
System 2

Converter
HVdc Station

HVdc Station
Two Fiber SONET Rings

figure 3. The basic HVdc system operation. EMS: energy management system; ICCP: intercontrol center protocol;
SONET: synchronous optical networking.
44

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may/june 2019

IEEE Power & Energy Magazine - May/June 2019

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