COMPACT SUBSTATION WITH 34.5kV GIS (GAS-INSULATED SWITCHGEAR. Cleverson Shindi Takiguchi S&C Electric Europe LTd. Cape Town/WC South Africa

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1 COMPACT SUBSTATION WITH 34.5kV GIS (GAS-INSULATED SWITCHGEAR Cleverson Shindi Takiguchi S&C Electric Europe LTd. Cape Town/WC South Africa Alexandre Taijun Ohara S&C Electric Company Curitiba/PR Brazil

2 ABSTRACT Conventional 34.5kV substations with exposed busbars: occupy a significant portion of land, are quite unsafe for being tipically in the middle of the towns and have a very negative visual impact. This paper describes a different alternative utilizing SF6 insulated switchgear on a very compact arrangement utilizing insulated cables that are routed thru underground cable trenches. This solution has a much shorter field work since the switchgear comes fully assembled and tested from the factory including the protection and control part. The solution also allows remote control from the Scada system. As a key differentiator compared to other gas-insulated solutions this counts on viewing windows so that contact position can be easily seen by the operators so this feature from the conventional substations is not lost. Another important feature is that the switchgears are free of maintenance. This paper will show real field applications and the business case that justify its deployment. 1. Introduction Technically the utility industry defines only two systems: transmission and distribution. In practice, however, a third system exists. It is considered a distribution system, but operates similarly to a transmission system by delivering power to distribution substations. This system is identified as the sub-transmission system. The sub-transmission system is used to supply power and energy to electric substations, but is not planned, designed, and constructed to the same utility industry standards as the transmission system. While the sub-transmission system may operate at voltages from approximately 15 kv through 138 kv, the subtransmission systems in some utilities operat at 34.5 kv, with some 23 kv and 46 kv systems. Figure 1 shows a pair of 34.5 kv sub-transmission lines. The 34.5 kv circuit on the left consists of single wood poles, three current-carrying conductors attached to cross arms, and a grounded neutral wire attached to the pole below the cross arm. Note that tipically the construction of the sub-transmission lines is not as robust as the transmission lines and, in this case, consists of wood poles and cross-arms that take on a similar appearance to the distribution system described below.

3 Figure 1: Two 34.5kV sub-transmission lines Electric distribution substations are used to reduce voltage levels from transmission and subtransmission to distribution level. This allows power to be delivered by distribution lines to distribution transformers that further reduce the voltage to a level useable by the customer. Figure 2 shows a relatively small electric distribution substation that reduces 34.5 kv subtransmission voltage to 13.8 kv, which is then distributed to industrial, commercial, and residential customers. A typical electric distribution substation will have the following equipment: Incoming transmission or sub-transmission line Distribution transformer Transformer protection including such things as fuses, circuit breakers and lightning arresters Voltage regulators to raise or lower the distribution voltage as required Electric outgoing distribution circuits complete with metering and circuit protection as circuit breakers or reclosers A substation fence for safety and security purposes Figure 2: 34.5kV to 13.8kV Unitil electric distribution substation

4 Some utilities (tipically those with lower density of loads) opt for distribution using 34.5kV which has proven to be a highly economical way to serve the more remote locations within their concession areas. The design for 34.5kV substation has been tipically followed a traditional construction design with overhead busbars, conventional equipments (circuit-breakers, disconnects, surge arresters, instrument transformers and so on) which has some drawbacks: Take a considerable amount of land; In most of cases given the construction involved these can take almost the same time to erect compared to substation of higher voltages (69kV, 138kV and above); Since these are tipically installed in the middle of small/medium cities the visual impact is often a problem that utilities have to deal with since living nearby a conventional substation can at times make the real estate value of the properties to go down; Also for these being in the middle of the cities another potential problems rises in terms of safety. It has been reported by some utilities some accidents with personal injury when people broke into these substations for stealing material or other purposes; Operation and maintenance costs can be quite high since these designs with exposed busbars and conventional equipment would often require intervention. These interventions also can cause downtime with planned outages which decrease the reliability indexes. 2. Copel (Distribution Utility) Existing System The origin of Copel s 34.5 kv system is the substations of 138 or 69 kv (called source substations), with the installation of three phase transformers, where the high voltage is transformed to two medium voltage levels: 34.5 and 13.8 kv. Figure 3 illustrates this process. Figure 3 Origin of Copel s 34.5 kv System

5 Copel s 34.5 kv system has the power distribution and subtransmission function. The MRT configuration (single phase with ground return) is highlighted in the distribution system, especially to provide to rural consumers where there are circuits of over 6,000 km, totaling approximately 120,000 medium to low voltage transformers in the entire 34.5 kv system. In the subtransmission segment, lines that supply small substations of 34/13 kv are used, and they normally provide for small cities, maintaining the voltage regulation, control, protection, segmentation of circuits and the possibility of tele-operation by the regional operation centers. Figure 4 shows the described characteristics. 13,8 kv 13,8 kv SE 138/34,5/13,8 kv 34,5 kv 4 CAA (ou 2/0 CAA) T A 34,5 kv 13,8 kv 13,8 kv 34,5 kv SE 34,5/13,8 kv Figure 4 Functions of the 34.5 kv System There is a total of 265 substations of 34.5/13.8 kv, which normally consist of two transformers, totaling up to 14 MVA, capacitor bank of up to 3x1200 kvar, voltage regulator bank of 12 MVA, busbar with possible reversible power flow, in a maximum of four circuits of 34.5 kv and four circuits of 13.8 kv. It must also be emphasized that the substations normally have one or more alternative sources of supply through a radial system, but there may be restriction to the supply of the substation in case of a non-primary source. Figure 5 shows the reversible busbar concept, where the load supply can be performed through the primary or secondary (alternative) source with voltage regulation and protection selectivity. The secondary source in this configuration can be supplied by a primary source and vice versa. The busbar configuration has four sets of single pole switches (29-01, 29-02, and 29-04) where two operating switches under automated load are added to automate the transfer between sources. This configuration with reversible busbar was initially executed in the conditions where the voltage regulators and automatic reclosers cannot operate with inverted flow.

6 Figure 5 Reversible Busbar of 34/13 kv Substations The Figure 6 shows an overview of the sectors of an SE of 34/13 kv. Figure 6 Sectors of an SE 34/13 kv 3. The proposed alternative system The GIS switchgears were specified to the following criteria: a. Three three-phase terminals, for the incoming feeders, outgoing feeders and transformer protection; b. Grounding terminal and window for visualization of the internal contacts (visible gap), in accordance with the safety; c. Rugged contruction with stainless steel enclosure in order to withstand the environmental harsh conditions since these are installed outdoors; d. SF 6 or vacuum insulation; e. Supervision, control and automation system integration with the equipment in the control panels, with electric quantity measurement (voltage, current, power), switchgear status (open, closed, grounded), remote opening and closing commands;

7 f. Compact dimensions in order to allow the saving of costs with land; g. Minimum (or low) maintenance; Below is a comparison between the conventional design and the compact design with GIS switchgear: Conventional Design Compact Design with GIS Land: 1,600m2 Land: 600m2 Busbar: exposed Busbar: protected Higher Civil work Lower Civil work costs costs Execution time: 300 Execution time: 120 days days Table 1: Comparison between the two alternatives Below are some details of the design of the compact substation with GIS switchgear: Figure 7: Overall lay-out of the compact substation

8 Figure 8: Single-line diagram (Blocks A thru E indicate the compact GIS that were deployed) Blocks: Block A represents the incoming 34.5kV lines switching scheme. This allows the flexibility to switch between the two sources in order to improve the reliability of the system; Block B represents the switching to isolate/bypass the Voltage regulator that is widely used on the 34.5kV system of COPEL given the long distribution lines that are part of the system; Block C represents the protection for the 34.5/13.8kV step-down transformers; Block D represents the switching between the secondary side of the 34.5/13.8kV transformers as well as the connection/isolation of the capacitor banks and grounding transformers Block E represents the outgoing 13.8kV feeder (in this example two outgoing feeders are shown but the solution can accommodate more feeders to provide future expansion)

9 Figure 9: Side-view showing the cable trenches underneath the GIS Switchgear Figure 10: 3D view of the complete solution with Compact GIS Switchgear 4. Conclusion The presented solution becomes a very interesting cost-effective alternative for the 34.5kV systems of COPEL as well as of other utilities that have similar system and similar challenges. The utilization of unique-featured GIS Switchgear as the core of the solution was key in order to facilitate the acceptance of the solution by the COPEL lineman and that was mainly due to the fact that the GIS Switchgear has large viewing windows that can allow them to see the visible-break which was one safety feature that the conventional substation. Other key feature of this solution is that with the exception of the Power Transformer and Voltage Regulator all the switchgear is free of maintenance which require less downtime which is critical to improve the reliability of the 34.5kV system. The reduction of land required is also a plus

10 given the fact that especially in the small townships where these are tipically installed the space constraint has become such a big problem both on the availability as well as in terms of cost. In terms of the business case even though this solution has a higher Capital Investment the total cost of ownership is much lower compared to the conventional substations and adding to that it is much safer for the lineman as well as for the public in general making of this a very interesting alternative for the future construction of substations at COPEL. 5. Bibliographical Reference [1] Automation of 34/15kV Substations and Integration with the Distribution Network, J. S. Omori, R.P. Siqueira, V. Zarnicinski, M.F. Wadeck, SIMPASE - Symposium of Automation and Electric Systems, 2011 Author: Cleverson Takiguchi has extensive knowledge in the energy sector. With almost 20 years of global industry experience, and over 30 published papers, Cleverson Takiguchi has become a thought leader in the area of Smart Grid applications and Power Systems. Cleverson has worked in the Brazilian operation of S&C for 14 years, 7 years of which were spent in leadership roles. Cleverson has now taken his skills and experience to Cape Town, with the aim to develop business across Sub-Saharan Africa. In his current position, Cleverson will cover the full range of S&C products and services and also provide sales and engineering support. Furthermore, Cleverson will take an active approach to engaging new target markets and enhancing S&C s brand in the region. Cleverson is heavily involved with several trade associations including: South African Wind Association, as well as being on the advisory board for both the African Utility Week and Distributech Africa conferences. Cleverson regularly engages with media and often speaks on the opportunities facing the African Grid, as well as: transmission and distribution, energy security, energy storage, energy supply, Smart Grid and automated communications.

11 Co-Author: Alexandre Taijun Ohara is a specialist in Distribution Automation. With 15 years of experience in the energy sector, Alexandre is the Manager of Power System Solutions of S&C Electric South America Business Unit. Alexandre started in the Energy Sector working as a SCADA Developer in Copel, one of the biggest utility in Brazil. In 2002, he moved to S&C Electric Co. starting as Project Manager for EPC Projects in Substations. With his technical background, he become specialist in Distribution Automation products and solutions from S&C Electric for South America Market. In 2011, he was promoted to Supervisor of Application Engineer, leading the group responsible to develop customized solutions using S&C products. In his current position since 2013, Alexandre is responsible to lead his group to deliver comprehensive services and solutions for electric utilities, renewable energy plants and critical power users like hospitals, factories and data centers. Co-Author: Presenter: The paper is presented by Cleverson Shindi Takiguchi.