MEASUREMENTS OF GEOMAGNETICALLY INDUCED CURRENTS, GICs, IN THE
NORWEGIAN POWER GRID.
Evald A. Sæthre
P.O. Box 5192 Maj.
Statnett SF
N-0302 Oslo
evald.sathre@statnett.no
Trond M. Ohnstad
P.O. Box 5192 Maj.
Statnett SF
N-0302 Oslo
trond.ohnstad@statnett.no
Abstract:
The paper presents results of observations and measurements of geomagnetically induced currents, GICs, in the
Norwegian Power Grid during February 1999 – June 2002. Statnett wanted to find out how GICs affected the power
Grid. In addition to the GIC currents we measured the phase currents and voltages at 300 and 420 kV level at different
places in Norway. Small GIC’s occurred rather often. Approximately twice a year we measured incidents of larger
GIC’s with durations of 6 minutes. During the large storms we could see how the harmonic distortion in voltage (THD)
at 300 and 420 kV level increased up to the maximum planning level and how the voltage decreased. However so far
we have not detected that the GICs have created any problems in the Grid.
1. INTRODUCTION
It has been known for a long time that geomagnetically induced currents, GICs, have created trouble for the grid
companies. The geomagnetically activity are expected to have a peak in 2002 (Solar cycle 23). Therefore Statnett, the
Norwegian Power Grid Company, wanted to measure the size of the GIC’s and to find out how they affected the
operation of the Grid.
The Norwegian Power Grid consists of 420kV ( 1645 km ) and 300kV (3800 km ) solid earthed system and a 132kV (
2635 km ) of resonant earthed neutral system. The long transmission lines runs both West – East and North – South.
The GICs in the transmission lines flows to earth through the earthed transformer-neutrals. The GICs are very low
frequency currents (DC currents ) with a duration of 1-6 minutes. They could result in saturation of the transformers and
generate distortion (harmonics) in currents and voltage.
THD or Total Harmonic Distortion are a measure of how much the voltage or current are distorted in % of the normal
voltage/current. Large contents of THD can lead to lack of reactive power and voltage drop or in the worst-case voltage
breakdown. High level of harmonics can also lead to tripping of capacitors and give more voltage problems. GICs also
could trip protection systems. The planning level of maximum THD in the Norwegian power Grid are 3.0 %.
2. MEASUREMENTS
The zero-sequence current of a 420 /300 kV, 1000 MVA transformer at the transformer station of Sylling was
measured. Fig.1 shows the measuring system. A Hioki 8840 transient recorder was used to measure the current, Io,
through a series shunt. The recorder was set to trigger level of 20 Amp. In addition a PQNode 8020 (BMI), Power
Quality Instrument, was used to measure harmonics in currents and voltages continuously at 300 and 420 kV level at
Sylling and at several places in Norway (Kristiansand and Kvilldal ). We used a sampling rate of 2 kHz and could thus
measure up to 40 th harmonic in current and voltage.
3 0 0 A /6 0 m V sh u n t
300kV
420kV
Io
U
T r a n sie n t
R ecord er
P o w e r Q u a lity
In st r u m e n t
SVC
P Q N od e:
m in /a v /m a x
SSW ave
F lu k e S c o o p e m e te r :
THD
.
Fig.1 GIC measuring system at Sylling transformer station.
3. RESULTS
Fig 2. shows as an example of the measured transformer zero-sequence current at Sylling without geomagnetically
induced currents, GIC, current (Fig 2A) and with GIC current (Fig. 2B).
Normally, without GIC current, the current to earth through the transformer at Sylling are a small 3.harmonic current ( 3
Amps) with no DC component (Fig. 2A). The figure on the right shows the transformer current Io during the GIC storm
1.3.99. The current now have a DC component of 15 A and a AC component with peak value up to 30 A and a large
5.harmonic component.
Fig 2 A
Fig. 2 B
Transformer Current , Io.
During the storm 1.3.99. Kl.01:40
40
40
30
30
20
20
Io (A)
Io (A)
Transformer Current , Io.
Normal level
01.03.99
10
10
0
0
-10
-10
1,99
2,00
2,01
2,02
Time (s)
2,03
2,04
1,99
2,00
2,01
2,02
2,03
2,04
Time (s)
Fig.2 Measured transformer current at Sylling without GIC ( Fig.2A) and with GIC (Fig.2B).
Table 1. shows a overview of measured GICs in Sylling. The table shows time, duration (when Io > 20 Amp) and size
of the current (peak value and DC component).
The duration of the GIC was from 1- 6 minutes.
Table 1. Overview of measured GICs in Sylling.
Date
18.02.99
18.02.99
18.02.99
19.02.99
01.03.99
01.03.99
01.03.99
10.03.99
17.04.99
17.04.99
17.04.99
15.07.00
12.08.00
17.09.00
13.10.00
7.11.00
27.11.00
29.11.00
31.03.01
at 15:52
at 19:29
at 19:33
at 00:44
at 01:24
at 01:40
at 02:25
at 04:49
at 05:48
at 06:06
at 06:15
at 22:24
at 05:06
at 00:36
at
at
at 00:00
at 02:00
at 08:53
Current Io ( A )
Duration
(minutes)
max./min. DC
value
component
- 22.0
-4 1.5 min
27.1
5 2.5 min
27.1
5 3.0 min
-21.2
-4 4.0 min
-21.9
-4 1.5 min
30.0
15 4.0 min
-21.0
-3 1.0 min
22.0
5 2.0 min
25.0
7 6.5 min
24.0
4 1.5 min
-22.0
-5 1.0 min
40.0
25 5.0 min
35.0
22 4.5 min
35.0
23 4.0 min
24.0
18 3.0 min
25.0
16 3.5 min
30.0
18 4.0 min
35.0
20 5.0 min
40.0
25 5.5 min
The distortion (THD) of currents and voltages was measured continuously with the PQNodes. Fig.3 shows trend curve
of THD of the voltage (phase A) at 420 kV level at Kvilldal during the GIC storm 31.3.01. Normally the THD level at
Kvilldal are 1.3 %. At 08:53 AM the GIC storm starts and the THD level increases to 2.4 %.
The GIC storm lasted for 4 minutes. During the GIC the 420 kV voltage decreased 1-2 kV.
3,00
GIC
08:53am
2,50
THD ( % )
2,00
1,50
1,00
0,50
0,00
00:02
01:02
02:02
03:02
04:02
05:02
06:02
07:02
08:02
09:02
10:02
11:02
12:02
13:02
14:02
Time ( min: sek)
Fig.3 Trend curve of THD of the voltage at 420 kV level at Kvilldal 31.3.01
15:02
16:02
17:02
It is the change in the magnetic field created by sunspots that produces GICs. Daily data from measurements showing
curves of the geomagnetic field are collected from the University of Tromsø (via internet). In this way we could see if
and when there have been a GIC.
5. CONCLUSIONS
Results of observations and measurements of geomagnetically induced currents, GICs, in the Norwegian Power Grid
during february 1999 – june 2002 are presented.
Small GIC’s occurred rather often. Approximately twice a year we measured incidents of larger GIC’s with durations of
6 minutes. During a large storm 31.3.01 we could see how the harmonic distortion in voltage (THD) at 420 kV level in
Kvilldal increased from a normal level of 1.3 % to 2.4 % and how the voltage decreased 1-2 kV. This is below the
maximum planning level of 3 %. However so far we have not detected that the GICs have created any problems in the
Grid.