Distribution reliability

In this case study, reliability indicators SAIDI and MAIFI are taken into account by using “supply criterion” in different residential areas. (SER; 2010) The method has been developed in Finland by the industry itself in order to increase distribution reliability by taking into account customer needs as well as needs of the society and different residen-tial areas. In Finland, VFV increases and has increased distribution reliability by build-ing new primary substations, which shortens the average cable length. Also urban and rural area distribution becomes differentiated from each other, so that urban areas are not affected by faults in rural areas and the amount of voltage dips decreases as feeders divide into multiple substations. The distribution reliability has also been increased by investing on substation and network automation and by carrying out enhanced mainte-nance and animal protection. Today, also many maintemainte-nance related works are planned to be performed without causing an interruption to electricity delivery whenever it is possible. The share of these “voltage works” is increasing all the time as new techniques are being developed. At the same time, VFV has developed a construction method for weatherproof networks. This means that all pole mounted distribution transformers, which are sensitive to weather conditions, are replaced with kiosk -type transformers in future. All low-voltage wires from secondary substations to properties are built with underground cables and also medium-voltage network is built with cabling, even in ru-ral areas. The strategy is concerning construction works related to renovation and build-ing of new network. Below there is a Table 6.2 that shows the impact of investments and operational activities on reliability and operational costs.

Table 6.2, Customer level impacts of investments on reliability and OPEX, where an arrow up means increase and arrow down means decrease. (Honkapuro, 2008)

At the moment, the level of cabling in VFV’s medium voltage network (20kV) is around 8 % and in low voltage network around 31 %. A long term target for reliability indicator SAIDI is under 100 𝑚𝑖𝑛/𝑎. Powerful storms in year 2010 as well as snowy

winters have distorted the statistics quite strongly. At the moment within VFV’s net-work in Finland SAIDI can be evaluated to be 150 𝑚𝑖𝑛/𝑎 when excluding recent ex-traordinary natural phenomenon. According to supply criterion, the current development level can be estimated to be quite good when the effects of resent natural phenomenon are limited of from the review and the different residential areas are taken into account.

Statistics show that during year 2011, about 86 % of the total network meet well the requirements according to “supply criterion”. On the other hand, year 2010 was much more challenging because of the great storms and just 40 % of the network could reach the requirements. VFV also uses high impedance grounded (compensated) networks in MV level distribution grid. Today, many parts of the networks have been changed to use compensated grounding and the objective is to achieve fully compensated MV network in the future. At the moment, the share of compensated MV network is approximately 70 %. The share of compensated overhead lines is currently 67 % and the share of com-pensated cables is68 %. There is a Figure 6.14 below that presents the results.

Figure 6.14, Results for Vattenfall’s distribution business in Finland based on the au-thor’s analysis and knowledge.

In Sweden, VFS has invested a lot to large scale cabling. In year 2003 VFS started a program as an objective to isolate and change to underground cables 60 % of the com-pany’s MV networks in heavily forested terrains. There is a plan to introduce a new target for the program in year 2015. (Fritz, 2011) Over the past few years, totally over 11 000 kilometers of cable has been installed by Vattenfall AB in Sweden.

VFS has increased the level of cabling in the network and currently there are plans concerning network automation in order to improve the reliability of the network. At the moment, VFS has a target: SAIDI 165 𝑚𝑖𝑛/𝑎 for year 2011. A long term target for reli-ability indicator SAIDI is under 100 𝑚𝑖𝑛/𝑎, which is the same target as VFV has. The long term target will be achieved by continuing the program with cabling which has

already advanced quite remarkably and by introducing new network automation, re-motely controlled disconnectors and reclosers, for example. (Fritz, 2011) VFS has quite different network structure, especially concerning MV networks, when compared with the network of VFV in Finland. One great difference is that there are much more differ-ent voltage levels in the MV network. In Sweden, all the lines from 70 kV to lower voltages are high impedance grounded networks. (Eng, 2011) There is a Figure 6.15 below that presents the results.

Figure 6.15, Results for Vattenfall’s distribution business in Sweden based on the au-thor’s analysis and knowledge.

6.3.8 Power quality

In Finland, within VFV it is not possible to make a contract for a certain power (volt-age) quality at the moment. Naturally, legislation (standard EN-50160) determines the minimum requirements for voltage quality performance. In case a customer has very sensitive loads and equipment (for example in a hospital etc.), it is possible to discuss and make a contract concerning improved voltage quality. This means that the contracts can be made only case by case, because there is no selection of different voltage quali-ties offered at the service agreement.

Within VFV’s network, Iskraemeco MT372 meters measure 𝑈𝑟𝑚𝑠 values in every three phases. Voltage dips are represented as percentages of 𝑈_𝑟𝑚𝑠 nominal value. The daily peak and minimum values of phase voltages are also measured and recorded.

Voltage asymmetry is monitored by comparing measured voltages and the average volt-ages of all three phases. If the difference gets too high (limit value crosses), the meter sends an alarm signal. It is important to define two threshold levels to the meter correct-ly. It means when the voltage on one-phase rises, the upper threshold level must be set up high enough so that it is only exceeded in zero faults and an alarm is sent. If the

up-per and lower threshold limit is exceeded at the same time, the system sends an alarm about asymmetrical voltage situation. These monitoring features are significant from power quality perspective.

The voltage quality performance of the VFV’s distribution network is advanced.

VFV has increased the amount of primary substations and the share of high impedance grounded networks. This has decreased the amount of voltage dips and flickering re-markably. As a consequence, voltage quality complaints are therefore relatively rare and customers are mainly satisfied to the quality they receive. Nevertheless, if a customer complaint is made related to quality issues, there is a systematic method how the quality is being improved within a reasonable period of time, effectively. VFV realizes also proactive voltage quality improvements by utilizing the continuous power quality meas-urements at the customer connection points. Based on the measmeas-urements, critical parts of the network from voltage quality perspective can be identified. This creates an oppor-tunity for VFV to accomplish power quality improvements, even before a network cus-tomer recognizes voltage deviations and makes a complaint. This type of activity is very important from customer service as well as service quality point of view. There is a Fig-ure 6.16 below that presents the results.

Figure 6.16, Results for Vattenfall’s distribution business in Finland based on the au-thor’s analysis and knowledge.

In Sweden, within VFS the situation concerning different voltage quality contracts is similar to that in Finland. There is no ready selection of different voltages, but in indi-vidual cases a contract can be made for better voltage quality that the standard EN-50160 requires based on customer’s needs (very sensitive loads). In these cases, the contract is made by having direct contact and negotiations with the customer about the

different requirements for voltage quality. These individual contracts are mainly done with bigger customers at HV level. (Eng, 2011)

Within VFS, there are three types of AMR meters installed. Only the latest, third generation is able to monitor voltage deviations in three phases like over/under voltages, voltage asymmetry, zero faults, daily peak and minimum voltages etc. 70 % of meters installed are capable to do this, so the quality monitoring is not fully comprehensive in LV network at the moment. (Garpetun, 2011) The power quality performance is in gen-eral advanced both in high and low voltage levels. In some network areas, especially in the northern Sweden, there still are some problems with the power quality because of long distances and sparsely populated area in combination with relatively old network structure. (Lehtonen, 2011)

Customer complaints related to quality issues are relatively rare also in Sweden. All the lines from 70kV down are high impedance grounded. At the low voltage level, where the complaints are more common, there is a standard process to handle the quali-ty improvements. Customer service takes the complaint and sends the information to power quality department where analyzes are carried out and the decision concerning the follow-up procedure is chosen. This makes the process effective and comprehensive.

At high voltage level the complaints are rare, approximately 15 to 20 pieces per year.

Therefore there is no standard process; instead there is a straight customer contact and discussion about the voltage quality. Within VFS, the level of proactive quality im-provements is currently quite low. There are some cases where imim-provements are car-ried out based on the AMR quality monitoring, but mainly the quality improvements are carried out based on customer complaints. (Eng, 2011; Lehtonen, 2011) There is a Fig-ure 6.17 below that presents the results.

Figure 6.17, Results for Vattenfall’s distribution business in Sweden based on the au-thor’s analysis and knowledge.