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Installation of Twenty-four (24) Lines of 150kV XLPE Power Cables at 2.5 m Depth below Ground Level in the Tropical Urban City: Jakarta

John Yuddy STEVEN, PT. PLN (Persero), Indonesia, john.rembet@pln.co.id,

Yushan YUSUF, Ngapuli Irmea SINISUKA; Institut Teknologi Bandung, Indonesia, yushan@pln.co.id, ngapuli.sinisuka@stei.itb.ac.id

ABSTRACT Jakarta as the capital city of Indonesia, since 2010 has issued new rules about Network Utilities Placement Procedure, one of its contents about guidelines for the installation of high-voltage cables. This law stated that the high voltage cables should be buried at a depth of 2.5 m from the ground level to the top surface of the cable

In order to connect the substation (150 kV Tanah Tinggi Substation), required incomer transmission with double-phi configuration (4 circuit) with the number of cables per phase is two (2), so the total number of cable are twenty-four (24) cables. All the cables used XLPE insulation, the first and second circuit used 1000 sqmm copper conductor and for third and four circuits, used 800 sqmm copper conductor.

With the numbers of cables to install, and consider Jakarta as a crowded city in Indonesia, problems arise due to the rules above and also social and environmental issues. This makes some the limitations of the location, where only allows installing over the highway, crowded street and crossing the river.

We try to made calculation and simulation using COMSOL for the thermal resistance and ampacity of the circuit for this installation, but until the deadline it’s not finish. So this paper only covers the installation details.

Finally this transmission used two system of installation, there are open system with box-culvert construction, and boring system with concrete type and concrete pipe type. For box-culvert type, cable construction made by eight (8) rack support which each rack containing 3 cables, and for concrete type, cable construction made of six (6) cables in horizontal in four (4) stacking.

KEYWORDS

Power Cables, XLPE Cable, Power Cable Installation, Cable Ampacity, Ducts, Trench.

INTRODUCTION

Cable is one of the power transmission media on high voltage and low voltage, in addition to overhead line (OHL) conductor. Cables can be installed using duct, tunnel or pipes, we called closed type, and by direct buried method we called open type. In several big cities of developed countries, high-voltage cable transmission lines have been used through the tunnel. The tunnel is in addition to the power system; also used for other utilities such as telecommunications, water installation etc, while in developing countries such as Indonesia, high-voltage cables installation usually used direct buried.

There are different characteristic for each type of installation above. Open model have more problem then closed type, such as influence of ambient and limit for upgrade the system, but the benefits is more cheaper than closed type. So for developing countries, closed type

stills an option.

Jakarta as the capital city of Indonesia, since 2010 the government has issued new rules about Network Utilities Placement Procedure, one of its contents sets out about guidelines for the installation of high-voltage cables. This law stated that the high voltage cables should be buried at a depth of 2.5 m from the ground level to the top surface of the cable. It means that the depth of trench is more than 2.5 m depending on the number of cables. This is different from a common design that has been used in Indonesia, which high-voltage underground cables are usually buried with trench depth up to 2.5 m. With the new rules, it is necessary to re-design the method of high-voltage underground cables installation in Jakarta.

THEORY AND REVIEWS

Ampacity and Temperature

As the purpose of underground cables for power transmission, the first consideration is the current-carrying capacity of the cables or also called ampacity. In physical, in addition to electrical resistance of the conductor, ampacity also strongly influenced by the temperature, which by Neher and McGrath [1] described the relation of ampacity and other factors such as the equation (1).

� = ��� − (�� + ∆��) ��(1 + ��) ��′ (1)

In this formula, ampacity depends on the temperature of conductor (Tc), ambient temperature (Ta), temperature of conductor due to dielectric loss, electrical resistance (Rdc) and thermal resistance of the circuit (Rca’). With conductor temperature and ambient temperature are not controllable then the best way to manage the ampacity is to control the thermal resistance.

Thermal Resistance

Since Neher-McGrath equation developed, several researchers (as authors reviews) were applied and developed the equation then make the topic to found the best approach of ampacity calculation in the field.

M.A. Kellow [2] calculating the temperature rise and ampacity ampacity of underground cables by numerical procedure, with the point is to calculate the heat dissipation from a distribution duct bank. By numerical procedure, M. A. Kellow stated that the analytical procedure of Neher-McGrath is inaccurate especially in the case of a multi-cable duct bank installation.

M.A. El-Kady [3] also makes some calculation with objective to optimization of power cable and thermal backfill configurations. These calculations affirm about influence of backfill material to cable ampacity.

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M.A. Hanna and A.Y. Chikhani, M.M.A Salama [4, 5, 6] with 3 part of publication, make thermal analysis of power cables in multi-layered soil. This publication gives simulation of heat dissipation for several conditions of thermal resistance, which control by trench dimensions, distance between the cable and backfill material. They also extend the publication later, where with finite difference technique, they success to predict the heat dissipation and the temperature profiles from a system of three underground cables in a multi-layered soil [7].

J.A. Williams, D. Parmar and M.W. Conroy [8] also make some calculation for ampacity with soil thermal resistivity effect. This publication describes the controlled backfill optimization to achieve high ampacities on transmission cables.

F.de Leon, G.J. Anders [9], analyze with the Finite Element Method for the cable ampacity by effects of backfilling. They analyze the external thermal resistance (T4 as IEC 60287-2-1) by varying soil thermal resistivity and varying width and height of backfill. This publication show clearly simulation of ampacity result in relation with backfill dimension and effect of controlled backfill on top. The results show in Fig. 1 – Fig. 3.

In general, calculations of thermal resistance for calculate the current rating can use the IEC method by IEC 60287-2-1. From this standard, calculation of thermal resistance divided by internal thermal resistance compirising of 3 parts (T1, T2, T3) and external thermal resistance (T4). For external thermal resistance, calculation depends on the construction of the installation.

Fig. 1: Ampacity vs backfill width [9]

Fig. 2: Ampacity vs backfill heigt [9]

Fig. 3: Ampacity using a controlled backfill in top [9]

LOCATION AND CABLES

General Layout

These constructions have location on Cempaka Putih, Center of Jakarta, precisely located in the Pramuka highway road and Pramuka Sari I road, between GIS Tanah Tinggi 150 kV Substation and down-lead Gantry of OHL Transmission.

Surroundings of this location are public area like offices, schooling and army housing. Between median of Pramuka Sari I road, there are green area with small river and park (see Fig. 4), which all this area are protected.

Cables Route

With limited conditions, the cable are planned to install from GIS along Pramuka highway road and Pramuka Sari I road, passing under the river then to the Gantry. In general route as shown in Figure 4, with explanations in Table 1.

Table 1. Cables Route

SECTION DISTANCE REMARKS

1 40 meters GIS BUILDING

2 9 meters S/S AREA

3 27 meters CROSSING HIGHWAY

4 108 meters HIGHWAY

5 28.5 meters CROSSING HIGHWAY

6 222 meters CROWDED STREET

7 18 meters CROSSING RIVER

8 19.3 meters CROSSING STREET

9 78 meters PARK AREA

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Fig. 4: General Layout and Cables Route [10]

Cables

This project used 2 (two) kind of XLPE copper conductor cables with different dimension and structure from different manufactured for each direction. First is existing cable from warehouse which owned by PLN Indonesia with dimension of conductor 800 sqmm copper and second is new cable from manufacture with dimension of conductor is 1000 sqmm copper.

CABLES INSTALLATION

In Indonesia, especially in Jakarta, installation of underground cables generally using direct buried method. The first reason because it’s cheaper and second it’s easier for installation. So far with direct buried, maximum installation of power cables only 2 circuits with a number of cables only 1 for each phase, so in total only six cables. With the demand for electricity continues to grow and and for the needs of network reliability, then in this work as mentioned above, are needed 24 cables.

With the limitations of space for cable and with the new rules for buried cable must be 2.5 meters more from ground level, then the installation of these cables cannot use a common design - direct buried.

Based on cables route shown in Fig. 4, design made for each section according boundaries.

Substation Area

In this area, almost no difficult works on surface section, but due to existing GIS building, the problem is to synchronize the incoming cable route with the GIS basement or cable area. For this reason, in this section the construction design used box-culvert type as show in Fig. 5.

Crossing Highway

The next section is the path out of the S/S area, by considering bending the cable, the track should cross the highway. Its means needs to made 2 times crossing. With the traffic density cannot be compromised, the crossing section is used boring system. Then with consideration of the pressure, the construction is used concrete type as in Fig. 7.

Highway

As in the crossing highway section, in this section, boring system still used since the highway traffic could not be bothered. However, with the location being around the side road section, the surface pressure is not as big as crossing section, so the design used the type of concrete pipe as in Fig. 6.

Crowded Street

On this section, in general the construction used concrete pipe type like on the highway, but for ease installation, then also used box-culvert type in the middle of the section.

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Crossing River and

To cross the river, the same type used in highway crossing. But consider for the streamside, then the concrete type made with no boring system but by excavation and backfill arrangement with soil, gravel and aggregates.

Crossing Street

At this section also used concrete type as the highway type since the street is very crowded even not a highway road.

Park Area

For this section, with the surfaces is quiet, then the construction is used a box-culvert type, as well as the pulling location when the installation process.

200cm

30cm

30cm

200cm

50cm

230cm

box culvert

soil

aggregate

asphaltATB

Fig. 5: Box-culvert type

Fig. 6: Concrete type for river crossing

150cm

160cm

concrete type

soil200cm

50cmaggregate

asphaltATB

Fig. 7: Concrete type for highway crossing

A5.6 9th International Conference on Insulated Power Cables A5.6

Jicable'15 - Versailles 21-25 June, 2015 5/5

Fig. 8: Concrete pipe type

THERMAL RESISTANCE ESTIMATION

Based on IEC 60287-2-1, we try to made calculation and simulation using COMSOL for thermal resistance and ampacity of this circuit, but until the deadline it’s not finish. The following formulas are that we used in simulation.

Box-culvert type

Based on formula of external thermal resistance for cables laid in free air but protected from direct solar radiation;

�� = 1���ℎ(���)�/� ; ℎ = �(��)� + � (2)

Concrete type

This type is calculated based on formula of external thermal resistance for cables laid in ducts pr pipes with three parts of calculation.

Thermal resistance between cable and pipe:

��.� = !1 + 0.1(# + ��$)�% (3)

Thermal resistance of the pipe:

��.& = '(�.)2� ln-1 + �.�/0 (4)

External thermal resistance of the pipe:

��.) = 12� ('% − '2) ln 34 + 54& − 16 (5)

with the result as shown in Table 2.

Table 2.External Thermal Resistance of Concrete type

Parts Thermal Resistance (K m / W)

T4.1 0.384

T4.2 0.679

T4.3 1.893

CONCLUSION

We obtained three basic design for the installation of twenty-four (24) lines of 150kV XLPE power cables at 2.5 m depth below ground level, that are box-culvert type, concrete type and concrete pipe type.

Based on this project result, it’s open to discuss for better design for cables installation specifically in Indonesia, since the social issue and cost became the consideration.

REFERENCES

[1] J. H. Neher, 1964, “The Transient Temperature Rise of Buried Cable Systems”, IEEE Transactions on Power Apparatus and Systems, Vol. 83, No. 2.

[2] M. A. Kellow, 1981, “A Numerical Procedure for the Calculation of the Temperature Rise and Ampacity of Underground Cables”, IEEE Transactions on Power Apparatus and Systems, Vol. PAS-100, No. 7.

[3] M.A. El-Kady, 1984, “Calculation of the Sensitivity of Power Cable Ampacity to Variations of Design and Environmental Parameters”, IEEE Transaction on Power Apparatus and Systems, Vol. PAS-103, No. 8.

[4] M.A. Hanna, A.Y. Chikhani and M.M.A. Salama, M.M.A. Salama, 1993, “Thermal Analysis of Power Cables in Multi-Layered Soil, Part 1: Theoretical Model”, IEEE Transactions on Power Delivery, Vol. 8, No. 3.

[5] M.A. Hanna, A.Y. Chikhani and M.M.A. Salama, M.M.A. Salama, 1993, “Thermal Analysis of Power Cables in Multi-Layered Soil, Part 2: Practical Considerations”, IEEE Transactions on Power Delivery, Vol. 8, No. 3.

[6] M.A. Hanna, A.Y. Chikhani and M.M.A. Salama, M.M.A. Salama, 1994, “Thermal Analysis of Power Cables in Multi-Layered Soil, Part 3: Case of Two Cables in a Trench”, IEEE Transactions on Power Delivery, Vol. 9, No. 1.

[7] M.A. Hanna, A.Y. Chikhani and M.M.A. Salama, M.M.A. Salama, 1998, “Thermal Analysis of Power Cable Systems in a Trench in Multi-Layered Soil”, IEEE Transactions on Power Delivery, Vol. 13, No. 2.

[8] J.A. Williams, D. Parmar and M.W. Conroy [9] Francisco de León and George J. Anders, 2008,

“Effects of Backfilling on Cable Ampacity Analyzed with the Finite Element Method”, IEEE Transactions on Power Delivery, Vol. 23, No. 2.

[10] Google Maps, https://www.google.co.id/maps/.