4.5.1
Evaluating whether micro-generation can affect
neighbouring networks
This research examines one distribution network in isolation, assuming that the presence of micro-CHP on one network has no or minimal impacts on other networks. Specifically assuming that the presence of micro-CHP on a network does not have an impact on the voltage levels or power flows of neighbouring distribution networks. To test this assumption, a hypothetical setup was established consisting of two Maltby networks side by side. As with the original Maltby network, each of these two networks are fed by a single fixed tap transformer. Only now the two transformers are connected to a larger 35 to 11 kV transformer, which is in turn connected to the wider network. In real life neighbouring networks would not be identical, and a single 35 to 11 kV transformer will often serve several distribution networks, not just two. Despite this, the setup examined here should be sufficient to at least determine if there are impacts on other networks.
The two networks were labelled A and B. Micro-CHP was added to network A, but not to network B, and the parameters of both networks were monitored. This was done to see if the presence of micro-CHP on one distribution network affected the neighbouring distribution network. Five scenarios were examined, one with no micro-generation or heat pumps on either network, three with 100% of homes on
network A having micro-generation (Stirling engine micro-CHP, fuel cell micro- CHP and solar PV), and one with 100% of homes on network A having heat pumps.
Tables 4.3 to 4.7 detail the results of these tests. Table 4.3 examines the networks with no micro-generation deployment and confirms that the results from the two networks are identical. It also shows the baseline results for the main transformer. The remaining tables show the results for all the homes on the first network having different types of micro-generation. The first network is obviously affected. As for the second network, voltage levels and network losses are unaffected, the only slight change is that the maximum power flow through the transformer on the second network is slightly higher. As for the main transformer serving both networks, the only changes are that when micro-CHP is present on the network, the maximum power flowing through that transformer is reduced (due to electricity being generated locally), while when heat pumps are present the maximum power flow is increased (due to increased electricity demand on the network). Given the minimal impacts on the second network resulting from micro-generation being present on the first network, it was judged that it was valid to examine an individual distribution network in isolation.
Network A Network B
Main Transformer Minutes of Voltage over regulations 0 0
Minutes of Voltage under regulations 26 26 Max Power through transformer
(MVA) 1.33 1.33 2.97
Minutes of transformer overload 26 26 0
Max Voltage (PU) 1.05 1.05
Min Voltage (PU) 0.91 0.91
Total branch loss (MWh) 10.6 10.6
Total transformer loss (MWh) 15.2 15.2 62.4
Table 4.1 Examining two identical networks, each with no micro- generation. The first column looks at the impacts on the first network and its transformer, the second at the second network and its transformer and the third column looks at the impacts on the transformer serving both networks.
Net A 100% Stirling Network A Network B
Main Transformer Minutes of Voltage over regulations 567 0
Minutes of Voltage under regulations 13 26
Max Power through transformer (kVA) 1.16 1.33 2.74 Minutes of transformer overload 9 26 0
Max Voltage (PU) 1.06 1.05
Min Voltage (PU) 0.93 0.91
Total branch loss (MWh) 7.63 10.6
Total transformer loss (MWh) 10.7 15.2 51.5
Table 4.2 Examining two identical networks, on one (A) all homes have Stirling engine micro-CHP. The first column looks at the impacts on the first network and its transformer, the second at the second network and its transformer and the third column looks at the impacts on the transformer serving both networks.
Net A 100% FC Network A Network B
Main Transformer Minutes of Voltage over regulations 364000 0
Minutes of Voltage under regulations 2 26
Max Power through transformer (kW) 1.03 1.33 2.58 Minutes of transformer overload 2 26 0
Max Voltage (PU) 1.08 1.05
Min Voltage (PU) 0.93 0.91
Total branch loss (MWh) 7.57 10.6
Total transformer loss (MWh) 10.6 15.2 50.3
Table 4.3 Examining two identical networks, on one (A) all homes have fuel cell micro-CHP. The first column looks at the impacts on the first network and its transformer, the second at the second network and its transformer and the third column looks at the impacts on the transformer serving both networks.
Net A 100% Solar Network A Network B
Main Transformer Minutes of Voltage over regulations 124000 0
Minutes of Voltage under regulations 20 26
Max Power through transformer (kW) 1.33 1.33 2.97 Minutes of transformer overload 18 26 0
Max Voltage (PU) 1.14 1.05
Min Voltage (PU) 0.93 0.91
Total branch loss (MWh) 15.1 10.6
Total transformer loss (MWh) 20.8 15.2 55.7
Table 4.4 Examining two identical networks, on one (A) all homes have solar PV. The first column looks at the impacts on the first network and its transformer, the second at the second network and its transformer and the third column looks at the impacts on the transformer serving both networks.
Net A 100% HP Network A Network B
Main Transformer Minutes of Voltage over regulations 0 0
Minutes of Voltage under regulations 179 26
Max Power through transformer (kW) 1.57 1.33 3.39 Minutes of transformer overload 140 26 56
Max Voltage (PU) 1.05 1.05
Min Voltage (PU) 0.88 0.91
Total branch loss (MWh) 22.8 10.6
Total transformer loss (MWh) 31.6 15.2 97.6
Table 4.5 Examining two identical networks, on one (A) all homes have heat pumps. The first column looks at the impacts on the first network and its transformer, the second at the second network and its transformer and the third column looks at the impacts on the transformer serving both networks.
4.5.2
Other assumptions that need to be tested
One other assumption is that results from the Maltby network will also hold true for other networks. To test this, some of the scenarios were also tested on another network, the 'Darlington Melrose' network. This network model was also obtained from Northern Powergrid, and like the Maltby network is situated in a suburban area,
though it contains fewer homes than the Maltby network. The results from the two networks are examined and compared in the subsequent chapters (Section 5.4 and 6.4). It was found that as penetrations of micro-generation and/or heat pumps are increased, the results from the Darlington Melrose network follow the same trend as the Maltby network. This indicates that the implications from the Maltby network should hold true for other networks.
In a similar vein, while the Maltby network has a fixed tap transformer, it is possible (though uncommon) for other networks to have variable tap transformers, where the voltage output of the transformer can be raised or lowered to help regulate voltage levels on the network. As with the previous test, this is also examined in more detail in the results chapters (Section 5.3 and 6.4). The same trends in the results as micro- generation and/or heat pumps are increased is observed, though the variable tap network is better able to mitigate these trends. This would indicate that networks with variable tap transformers can accommodate more micro-generation and heat pumps before they start to cause problems.