Download transmission stability improvement by means of TCSC and SC

North – South 500 kV AC power interconnection:
transmission stability improvement by means of TCSC
and SC
Since spring of 1999, Eletronorte of Brazil has been operating a Thyristor-controlled Series Capacitor (TCSC) and five
fixed Series Capacitors supplied by ABB in Eletronorte´s 500 kV
interconnector between its northern and southern power
systems. All in all, about 1.100 Mvar of series capacitors have
been installed by ABB. The TCSC is located at Imperatriz at
the northern end of the power corridor connecting the two
systems which were previously not interconnected.
Feasibility studies had been performed regarding the interconnection of the two systems, and a decision was made
to go ahead and build the transmission corridor. Both AC
and DC alternatives were assessed, and decided in favour of
the AC option. It consists of a single 500 kV compact circuit
(subsequently doubled), more than 1.000 km long and series
compensated in several places along the line. Operation began
in 1998. The power transmission capability of the corridor is
1.300 MW.
Efficient exploiting of hydroelectric resources
The two power systems are mainly hydroelectric, comprising
more than 95% of the nation´s total volume of power generation and consumption. The “North-South Interconnection” has
the purpose of exploiting the hydrologic diversity between the
systems, and power flow occurs in both directions, depending
on current hydrologic conditions. As a consequence, the risk
of energy deficiency in conjunction with the rapidly growing
energy demand experienced by the country at present is
reduced.
North-South Interconnection
Marabá
348 Mvar SC
Imperatriz
107 Mvar TCSC
161 Mvar SC
Colinas
2x161 Mvar SC
Miracema
ABB 500 kV Series Capacitors
161 Mvar SC
Existing 500 kV systems
500 kV interconnector
The AC option is highly attractive as it facilitates the making
of inexpensive hydro energy available to a rapidly growing
federal economy as well as to future development over a vast
area having great economical potential. Several hydroelectric
plants are expected to be built along the same route in the
coming two decades, to be connected to 500 kV AC.
The integration of the national power system will also have
other related benefits, as for instance a reduction of the
required spinning reserve.
Power oscillation damping
The series capacitors installed in the North-South Interconnection have the task of raising the steady-state and dynamic
stability of the intertie. The TCSC at Imperatriz, the first of its
kind to be installed in Latin America, has the task of damping low-frequency inter-area power oscillations between the
power systems on either side of the interconnection. These
oscillations (0,2 Hz) would otherwise have constituted a hazard to power system stability and thereby to power transmission capability. The TCSC efficiently eliminates this obstacle
to power transmission.
Single-line diagrams
Technical data
500 kV
500 kV
Total series compensated system
Maximum system voltage
550 kV
Rated current 1500 A
Number of series capacitors:
fixed 5
TCSC 1
Totally installed reactive power 1100 Mvar
TCSC
Imperatriz
Fixed SC
Marabá
Imperatriz
Colinas
Miracena
Rating
107 Mvar
Rating
348 Mvar
161 Mvar
2x161 Mvar
161 Mvar
For power oscillation damping, the TCSC scheme introduces
a component of modulation of the effective reactance of the
power transmission corridor. By suitable system control, this
modulation of the reactance is made to counteract the oscillations of the active power transfer, in order to damp these out.
Maximum system voltage 550 kV
Nominal reactive power 107 Mvar
Rated current 1500 A
Rated continuous voltage 23,9 kV
Physical capacitor reactance 13,3 V
Nominal degree of compensation 5%
Boost level range 1-3
Nominal boost 1,20
A02-0171
TCSC
Power oscillation damping
1000
TCSC POD not active
1
900
The boost level can be varied continuously between 1 and 3.
Expressed in terms of degree of compensation, it can be
controlled over a range between 5% and 15%. At rated line
current, the nominal boost level has been set to 1,20.
800
Active power [MW]
The boost level, defined as the ratio between the virtual
reactance of the series capacitor and the physical capacitor
reactance is a key factor. It is a measure of the amount by
which the reactance of the series capacitor can be virtually
augmented in order to counteract system power oscillations.
700
600
500
400
300
200
100
0
0
300
1000
20
30
40
50
60
70
80
50
60
70
80
TCSC POD active
900
800
700
600
500
400
300
200
200
100
100
0
10
Time [s]
Active power [MW]
Thyristor valve
The thyristor valve is mounted at platform level. It is water
1000
cooled and utilizes indirect light triggered thyristors. The valve
900
is rated at 1500 A continuous current and at 3000 A for
800seconds. Furthermore, since the valve has to perform as
10
back-up
protection of the TCSC in extreme situations where
700
the
main ZnO overvoltage protection is reaching its thermal
600
limit, it needs to be able to withstand fault currents of up to
500
40 kA (peak) for about 60 ms, equal to the time it takes the
400
by-pass
breaker to close and take over the fault current.
0
0
10
20
30
40
50
60
70
80
0
10
20
30
40
Time [s]
For more information please contact:
ABB AB
FACTS
SE-721 64 Västerås
Sweden
Phone: +46 (0)21 32 50 00
Fax:
+46 (0)21 32 48 10
www.abb.com
Effectiveness of the TCSC for power oscillation damping as
shown in commissioning tests.