- 1 - 2001-04-19
© ABB Power Technology Products AB / HVC
Johan Karlstrand
ABB AB – High Voltage Cables
WETS-07
Reactive Compensation
© ABB Power Technology Products AB / HVC - 2
Agenda
„
What is reactive power?
„
Uncompensated cable links – critical length
„
Tuned compensation – perfect balance
„
The Icelandic story – an example from a pre-study done by ABB
„
Some conclusions
WETS’07 - Paris 28/6
What, in fact, is reactive power….
„
© ABB Power Technology Products AB / HVC - 3
„
„
Basic truths:
1.
No macroscopic change in energy can be instantanous
2.
Electrical power can only be transmitted with interacting electric and magnetic fields (EM-fields)
3.
Electrical active power is created with voltage (electrical field) and current (magneteic field) in phase
with each other
If U and I not in phase, we introduce:
1.
Inductance (L) → a constant related to magnetic energy
2.
Capacitance (C) → a constant related to electrical energy
The reactive power is a mathematical (engineering) way to take into account the
time lags between voltage and current in a transmission system !
„
If U and I in phase:
Active Power
„
If U and I not in phase:
Reactive Power
WETS’07 - Paris 28/6
© ABB Power Technology Products AB / HVC - 4
… and which are the consequences for the network, using cables?
„
Voltage support during high load conditions
„
Too high voltage during low load conditions
„
Normally lower losses but for long uncompensated links, higher losses
„
Higher short circuit power in the network
„
May improve transient stability
„
May prevent voltage collapse
WETS’07 - Paris 28/6
© ABB Power Technology Products AB / HVC - 5
Agenda
„
What is reactive power?
„
Uncompensated cable links – critical length
„
Tuned compensation – perfect balance
„
The Icelandic story – an example from a pre-study done by ABB
„
Some conclusions
WETS’07 - Paris 28/6
Uncompensated Cable Links – Critical lengths (1)
„
Typically, the capacitance increases with the rating, i.e. the larger conductor
cross-section the higher capacitance (C’):
„
132 kV:
0,13 to 0,34 μF
„
220 kV:
0,13 to 0,27 μF
„
400 kV:
0,13 to 0,23 μF
160
Ptot
L≈
nω ⋅ C 'U o2
(Simplified formula)
300 mm2 Cu 2000 mm2 Cu
Critical Length [km]
© ABB Power Technology Products AB / HVC - 6
140
500 mm2 Cu
120
2500 mm2 Cu
100
132 kV
80
220 kV
630 mm2 Cu
400 kV
60
2
2500 mm Cu
40
20
0
0
100
200
300
400
500
600
Power Rating [MVA]
WETS’07 - Paris 28/6
700
800
Uncompensated Cable Links – Critical lengths (2)
U [kV]
132 kV
220 kV
400 kV
Q [MVAr/km, and phase]
0,2 – 0,7
0,7 – 1,4
2,2 – 4,2
U [kV]
132 kV
220 kV
400 kV
Critical length [km]
130-150
120-140
60-90
1
There may be either
technical or economical
reasons for compensation
with 10-20% reduction in
current or 40-60% of Lc!
I L /I
© ABB Power Technology Products AB / HVC - 7
0,8
0,6
0,4
0,2
0
0
0,2
0,4
0,6
0,8
1
L/Lc
WETS’07 - Paris 28/6
© ABB Power Technology Products AB / HVC - 8
Agenda
„
What is reactive power?
„
Uncompensated cable links – critical length
„
Tuned compensation – perfect balance
„
The Icelandic story – an example from a pre-study done by ABB
„
Some conclusions
WETS’07 - Paris 28/6
Power[MW]
Tuned Shunt Compensated Cable Links
At 75 km:
P=1020 MW (-5%)
Q=335 MVAr in
each end
1100
1000
900
800
700
600
500
400
300
200
100
0
400 kV
220 kV
132 kV
66 kV
© ABB Power Technology Products AB / HVC - 9
0
Voltage limitation at
66 kV/100 km
25
50
75
100 125 150 175 200 225 250
At 220 kV/120 km:
P=300 MW (-11%)
Q=180 MVAr in
each end
Length [km]
Indicates normal range of critical length
Indicates possible approximate border between AC and DC
WETS’07 - Paris 28/6
Cost example for fixed inductive compensation 220 kV/400 MW
„
Needed power consumption for 120 km:
2x180=360 MVAr
„
Cost for the cable for 60 km (0,5 Lc) :
1 curr/MVA
„
Cost for fixed shunt compensation:
0,15 curr/MVAr
„
10% (=40 MW) decrease in rating:
40 curr
„
© ABB Power Technology Products AB / HVC - 10
„
⇒ Available MVAr’s is 40/0,15=267 MVAr < 360 MVAr
20% (=80 MW) decrease in rating:
80 curr
„
⇒ Available MVAr’s is 80/0,15=533 MVAr > 360 MVAr
„
Conclusion: It may be economical justified with fixed inductive shunt compensation
when the derating is between 10-20%.
WETS’07 - Paris 28/6
Typical voltage and current profiles for a tuned system
Sending End
Receiving End
Relative change [%]
110
100
90
80
Δι
Current profile
Δν
Voltage profile
70
60
50
0
20
40
60
80
Cable Length [km]
Relative change [%]
© ABB Power Technology Products AB / HVC - 11
Sending End
Receiving End
120
115
110
105
100
95
90
85
80
0
20
40
60
80
Cable Length [km]
WETS’07 - Paris 28/6
© ABB Power Technology Products AB / HVC - 12
Agenda
„
What is reactive power?
„
Uncompensated cable links – critical length
„
Tuned compensation – perfect balance
„
The Icelandic story – an example from a pre-study done by ABB
„
Some conclusions
WETS’07 - Paris 28/6
The Icelandic story – (not a realized project)
Ref. – Cigre’ Paper 21-201, 2002
Laxárvatn
LV1
Rangárvellir
BL1
BL2 Varmahlíð
Blanda 150 MW
Laxá 28 MW
Krafla 60 MW
KR1
This implied problems with
transient stability in the system.
KR2
Reyðarfjörður
200 km
TE1
Teigarhorn
Vatnshamrar
VA1
„
HO1
Sultartangi 120 MW
Nesjavellir 60 MW
Sog 90 MW
© ABB Power Technology Products AB / HVC - 13
„
Hryggstekkur
HT1
Svartsengi 45 MW
Severe weather conditions
implied a lot of faults on the
OH-line ring.
RA1
Hrútatunga
Brennimelur
„
Hólar
Hrauneyjafoss 210 MW
Vatnsfell 90 MW
Sigalda 150 MW
Búrfell
270 MW
Hydropower
SI4
Prestbakki
Geothermal
PB1
Substation
Power Intensive Industry
Transmission line
WETS’07 - Paris 28/6
Solution: A purpose-built 200 km
long XLPE cable crossing the
island.
© ABB Power Technology Products AB / HVC - 14
The solution…
1x300, Al
Ins. thickness: 12 mm
Cu-wires/Al-laminate
HDPE-sheath
WETS’07 - Paris 28/6
© ABB Power Technology Products AB / HVC - 15
… and the benefits of using the cable here
„
The cable links is preventing post fault voltage collapse and improves transient
stability for the whole network!
WETS’07 - Paris 28/6
© ABB Power Technology Products AB / HVC - 16
Agenda
„
What is reactive power?
„
Uncompensated cable links – critical length
„
Tuned compensation – perfect balance
„
The Icelandic story – an example from a pre-study done by ABB
„
Some conclusions
WETS’07 - Paris 28/6
© ABB Power Technology Products AB / HVC - 17
Optimum reactive power control - Conclusion
„
Degree of compensation changes with the characteristics of the network and the reactive power
loads
„
If the cable link is operating ”far from” the loads (inductive machines etc), the higher degree of
compensation you need. Remote syncrounuous generators has a cos(φ) close to 1.
„
In EHV networks it may be sufficient with fixed compensation with a high degree of compensation.
For long lengths, a huge amount of reactive power is needed, though.
„
In HV networks (which are closer to the loads) a lower degree of compensation may be needed.
Additionally, SVC-Classic or SVC-Light control may be needed.
„
Voltage limitations (5-10%) are mainly present in HV networks below (100 kV/50-100 km) for tuned
systems. For higher voltages/lengths, the charging current, losses etc set the limitations.
„
40-60 % of the critical length (10-20% decrease in rating)– take a look if inductive shunt
compensation may be cost efficient!
„
There is no extra ”MW-loss” for HVDC-Light systems. It is always interesting to look at the extra
advantages, which are offered with DC-control as well as the other known benefits from extruded
cable systems in general.
WETS’07 - Paris 28/6
© ABB Power Technology Products AB / HVC - 18
WETS’07 - Paris 28/6