DECLARATION 2 PUBLICATION
5.5 Voltage variation results
Voltage variation analysis assesses the change in voltage at a busbar in the event of loss of generation. Two schools of thoughts define two approaches to the voltage variation test.
The first, aims to compare the pre-fault voltage to the post-fault voltage. Pre-fault load flows are executed with auto shunt and transformer tapping enabled. Post-fault voltages are determined by removing DG and locking all voltage compensation devices.
The second aims to record the change in busbar voltage at each ramp up of DG from 0MW to full load. This method has the advantage of monitoring the increase in busbar voltage (under locked transformer tap) to assess the continuous voltage change, resulting from increased DG injection.
Results of the second method are shown in 8.5.1.1 and 8.5.1.2. Tests were performed on the 132kV Diamond busbar and 33kV Basket busbar.
The test bus voltage rises as real power injected into the busbar reduces the upstream demand. The volt drop from the sending bus reduces, thereby raising the voltage at the receiving end. Voltage
“bending” can be seen at higher voltage busbars shown in Figure 5-7. This is associated with diminishing voltage rise due to the non-linear load flow solution of meshed impedance networks.
Voltage variation test results for the 11kV Earth busbar demonstrates the voltage increase.
5.5.1 11kV Earth busbar assessment for DG
5.5.1.1 Voltage variation results – Earth 11kV busbarThe fault level at the 11kV Earth busbar is 200 MVA therefore 8 MVA (8 MW Cos = 1) solar PV was applied. Voltage variation noted in section 5.4, shows an increase in voltage due to the injection of real power at 11kV basket busbar Figure 5-4. Small DG sizing causes a linear increase in voltage. A total increase in voltage of 1.4% is noted. Sudden loss of generation would result in a volt-drop of 1.4 %. This is allowable according to [3].
Consequently, the rise in bus voltage at the 66kV Earth bus exceeds the 1.05 p.u limit by 0.0015p.u. A smaller solar PV generator is therefore recommended. Alternatively, the operational voltage philosophy needs to endorse the lowering of set-point voltages at the 66kV Earth busbar.
Additional voltage variation results shown at Sapphire and Diamond 132kV busbars, Figure 5-6 and Figure 5-7, respectively. The 132kV Diamond busbar displays the diminishing voltage rise.
Figure 5-4 11kV Earth Busbar Voltage Variation Result
Figure 5-5 Voltage Variation Result of 66kV Earth Bus response to 8MW injection at 11kV Earth Busbar
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6.00 4.00
2.00
0.00 [-]
1.041
1.037
1.033
1.029
1.025
1.021
Earth 11kV BB: Voltage, Magnitude in p.u.
MSc P&E 7.11kV POC Brkr -Earth 11kV BB- PF Un Earth 11kV BB Graphs
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10.00 8.00
6.00 4.00
2.00
0.00 [-]
1.053
1.050
1.047
1.044
1.041
1.038
Earth 66kV BB: Voltage, Magnitude in p.u.
MSc P&E 7.11kV POC Brkr -Earth 11kV BB- PF Un Earth 66kV BB Graphs
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Figure 5-6 Voltage Variation Result of 66kV Sapphire Bus response to 8MW injection at 11kV Earth Busbar
Figure 5-7 Voltage Variation Result of 132kV Diamond Bus in response to 8MW injection at 11kV Earth Busbar
10.00 8.00
6.00 4.00
2.00
0.00 [-]
1.050
1.048
1.046
1.044
1.042
1.040
Sapphire 66kV BB: Voltage, Magnitude in p.u.
MSc P&E 7.11kV POC Brkr -Earth 11kV BB- PF Un Sapphire 66kV BB Graphs
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10.00 8.00
6.00 4.00
2.00
0.00 [-]
1.04571
1.04567
1.04563
1.04559
1.04555
1.04551
Diamond 132kV BB: Voltage, Magnitude in p.u.
MSc P&E 7.11kV POC Brkr -Earth 11kV BB- PF Un Diam ond 132kV BB Graphs
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5.5.1.2 Sub-transmission load flow – post DG 11kV Earth bus
The fault level at the 11kV Earth busbar is 200 MVA therefore 8 MVA (8 MW Cos = 1) solar PV was applied. Real and reactive power flows are shown in Figure 5-10. Prior to DG, Figure 5-8 and Figure 5-9, show two similar profile shapes at 11kV and 66kV busbars. Post-DG results are shown in Figure 5-10. Comparison of the pre- and post-DG at the 66kV Earth bus shows the deepening of midday profile as DG injection increases. The “commercial” Earth load profile has been altered to a “twin peak”, residential profile.
Figure 5-8 11kV Earth Busbar at 12PM – Pre–DG
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04:36:00 00:00:00
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21.00
16.00
11.00
6.00
1.00
Earth 11kV BB: Outgoing Flow , Ac tive Pow er in MW Earth 11kV BB: Outgoing Pow er, Reac tive Pow er in Mvar
MSc P&E QDS_Earth11KV
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Figure 5-9 66kV Earth Busbar at 12PM – Pre–DG
Figure 5-10 66kV Earth Busbar at 12PM – Post–DG
23:00:00 18:24:00
13:48:00 09:12:00
04:36:00 00:00:00
26.00
21.00
16.00
11.00
6.00
1.00
Earth 66kV BB: Outgoing Flow , Ac tive Pow er in MW Earth 66kV BB: Outgoing Pow er, Reac tive Pow er in Mvar
MSc P&E QDS_Earth66KV
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23:00:00 18:24:00
13:48:00 09:12:00
04:36:00 00:00:00
27.00
22.00
17.00
12.00
7.00
2.00
Earth 66kV BB: Outgoing Flow , Ac tive Pow er in MW Earth 66kV BB: Outgoing Pow er, Reac tive Pow er in Mvar
MSc P&E 7.11kV POC Brkr -Earth 11kV BB- PF Un QDS_Earth66KV
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5.5.1.3 Sub-transmission grid loss – post DG 11kV earth
The 11kV Earth busbar hosted a relatively small solar DG plant, due to its relatively low fault level. Introducing 8MWs of DG reduced grid losses by 9.5% for real power and 13% for reactive power. Loss reduction results from DG being consumed at the load. The 11kV Earth bus load profile makes it ideal for solar PV. Table 5-2 shows a summary of the post-DG grid loss reported extracted from DPF.
Table 5-2 Grid Loss Result after 8 MW of DG applied to 11kV Earth bus 2015/10/08 12:00:00 PM
Grid Summary Post DG on 11kV Earth 12pm Grid Losses = 7.03 MW 16.24 Mvar
Two additional post-DG assessments results are presented. In 5.5.1, solar DG was connected to a load centre busbar. In 8.5.1.1 and 8.5.1.2 solar DG was connected to network (non-load) busbars.
Analysis showed varying degrees of grid losses experienced based on load profile; load type; fault level.