TNB Planning Guide LV

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Asset Management Department

Distribution Division

Tenaga Nasional Berhad

Low Voltage

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LOW VOLTAGE

PLANNING

GUIDELINES

November 2012

Asset Management Department Distribution Division,

Tenaga Nasional Berhad Wisma TNB

Jalan Timur, Petaling Jaya Selangor

Disclaimer

This guidebook does not confer legal rights or impose legal obligations upon any member of the public. While TNB has made every effort to ensure the accuracy of the discussion in this presentation, the obligations of the regulated community are determined by statues, regulations or other legally binding requirements. In the event of a conflict between the discussion in this presentation and any statute or regulation, this presentation would not be controlling.

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LV PLANNING GUIDELINES

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ACKNOWLEDGEMENT

We would like to express our deepest gratitude to the management of the Distribution Division, for the successful publication of this Low Voltage Planning Guidelines.

Our special thanks to Hj. Ismail Mohd Din, Senior General Manager, Asset Management Department for his full support and motivation to establish the revision of this guide book.

We would like to express our gratitude to the ever-committed LV Planning Guideline workgroup members, comprising Ir. Tan Siew Hwa, Mr. Kok Sheng Kheun, Mr Ideris Shamsudin, Mr Lim Chia Yih and Dr Rahman bin Khalid for their 2 years of hardwork in successfully completing this new edition of Low Voltage Planning Guidelines.

Our appreciation also goes to Assoc. Prof. Dr. Ir. Au Mau Teng, Ir. Lau Chee Chong, Ms Teo Siow Kim, Mr Ruslam Hussin, Mr Azmi bin Husin, Ir Rekha A/P Perumaloo, Ms Fadhlillah Adnan, Mr Fazely Haron and Ir Woo Chiew Chonng for their guidance and feedback in developing the guidelines. Special thanks to Dr. Marayati Marsadek for her untiring efforts in proof-reading this guide book.

Lastly, acknowledgement and thanks to all other distribution planning community members whose names are not listed above for their valuable contributions and ideas in preparing the contents of this handbook.

Thank you.

Dr. Abu Hanifah bin Azit Chief Engineer

System Planning & Development, Asset Management Department, Distribution Division, TNB

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FOREWORD

Objective of the power distribution system is to deliver electrical power to customers in a safe, reliable and most economical way. Several parameters of electricity supply such as frequency, continuity of supply, voltage level etc. should be within allowable limits to ensure that customers obtain satisfactory performance for their electrical equipment while ensuring that the demands of the customers are continuously met. The capital and

operating costs of doing so should be kept at the most optimum level, taking into account the total cost of ownership and losses in the system.

This document details out and standardizes planning methodology in TNB Distribution, which provides TNB Distribution Planners with a basic understanding of theory and practical application. This latest edition of Low Voltage Planning Guidelines also introduces additional requirement to adopt the changes in technology and expansion of network.

With this revised Low Voltage Planning Guidelines, I am confident that TNB Distribution Planners would be able to produce the most efficient LV network to meet customer’s service expectation.

Hj. Ismail bin Mohd Din Senior General Manager

Asset Management Department TNB Distribution

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C

HAPTER

1

GENERAL INTRODUCTION

1.0 INTRODUCTION

The design and development of supply system are critical in delivering quality supply to the customers. The quality of supply includes security, reliability and power quality.

To provide quality supply, the issue of cost needs to be considered. The optimized distribution system planning and development is introduced in order to achieve overall effective services to the customers.

The objective of this Low Voltage Planning Guidelines is to help the technical staffs at the district (kawasan) to plan and develop low voltage (LV) distribution system, so that TNB’s distribution systems:

i. Can fully meet customer expectations.

ii. Can achieve the corporate quality and reliability targets. iii. Is optimally planned at the most economic overall cost.

iv. Is capable of satisfying customer demand growth for the foreseeable future.

1.1 SCOPE

The scope of this document covers:

i. Definition of security, reliability and power quality for LV network. ii. Compliance with the Regulatory Requirements.

iii. LV Planning criteria.

iv. Typical LV network design.

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LV PLANNING GUIDELINES GENERAL INTRODUCTION

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1.2 DOCUMENT LAYOUT

This document comprises of 10 CHAPTERS, addressing separate topics for ease of use and future reference.

Each chapter is arranged in several sections, each of which addresses a specific aspect of the chapter topic. The chapter topic is summarized below:

Chapter 2 Refers to “Quality Of Supply” and TNB Corporate Standards

Chapter 3 Indicates the types and magnitudes of loads that can be fed from the LV network

Chapter 4 Describes the types and sizes of substations used by TNB and includes criteria to decide on the number of substations required to feed expected loads.

Chapter 5 Details the planning criteria and design for the LV distribution network, including services fed from the substations.

Chapter 6 Refers to the planning criteria for the LV network protection and earthing.

Chapter 7 Details out several main strategies to reduce LV technical losses

Chapter 8 Deals with the implications of “energy metering” on LV network planning.

Chapter 9 Redefine PQ phenomena in a simpler manner

and includes the possible mitigations.

Chapter 10 Details data that needs to be monitored and

managed for the LV distribution system

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C

HAPTER

2

QUALITY OF SUPPLY

2.0 OBJECTIVE

The objectives of this chapter are to: i. Define “quality of supply”.

ii. State the related LV system regulatory and engineering standards that need to be complied with.

2.1 DEFINITION OF QUALITY OF SUPPLY

The term “Quality of supply” means security, reliability and power quality of supply to the customers.

Security of supply means availability of supply to customers following the occurrence of a supply interruption. This aspect is measured by Security Level 1 – Level 4 as follows:

i. Security Level 1 - Less than 5 seconds. ii. Security Level 2 - Less than 15 minutes. iii. Security Level 3 - Less than 4 hours. iv. Security Level 4 - Less than 24 hours.

Reliability means ability of the distribution system to perform its required function under stated conditions for a specified period of time. This also describes the continuity of electricity supply to the customers. This aspect is measured by SAIDI.

Power quality refers to any power problem manifested in voltage, current or frequency deviations that result in failure or misoperation of customer equipment.

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LV PLANNING GUIDELINES QUALITY OF SUPPLY

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2.2 SYSTEM AVERAGE INTERRUPTION DURATION

INDEX (SAIDI)

Service reliability in TNB Distribution System is expressed by SAIDI. It is derived from the product of SAIFI (System Average Interruption Frequency Index) and CAIDI (Customer Average Interruption Duration Index).

In TNB system, only loss of supply exceeding 1 minute is termed as “outage” and will be counted in the computation of SAIDI.

The equation to compute SAIDI is as follow:

N d C n i i i

∑

= = 1 SAIDI (2.1)

The equation to compute SAIFI is given as:

N C n i i

∑

= = 1 SAIFI (2.2)

The equation to compute CAIDI is as follow:

∑

= = = _n i i n i i i C d C 1 1 CAIDI (2.3) where: i = interruption event

n = total number of interruptions

Ci = number of interrupted customers for each interruption event

di = duration of each interruption event

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2.3 SUPPLY SYSTEM STANDARDS

The supply system standard associated to voltage regulation and frequency variations for quality of supply adopted by TNB is shown in Tables 2.1and 2.2 respectively.

Table 2.1 Voltage regulation

Nominal 400V/230V

Tolerance Under Normal Condition

+ 10 % to – 6 % (MS IEC 60038) Tolerance Under

Contingencies Condition ± 10% Table 2.2 Frequency variations

Nominal 50Hz

Tolerance Under Normal

Condition ±1 %

Tolerance Under

Contingencies Condition 47 – 52Hz

The average restoration period is given as follow: i. Less than 5 seconds.

ii. Less than 15 minutes. iii. Less than 4 hours. iv. Less than 24 hours.

The acceptable permissible values for quality of supply at the point of common coupling are summarized in Table 2.3.

Table 2.3 Acceptable permissible values at point of common coupling Type Of

Disturbance Indices

Acceptable permissible values at point of common coupling

Reference Document Voltage Step Change ∆V % 1% - Frequent starting / switching and/or disconnection of load. UK’s Engineering Recommendation P28

3 % - Infrequent single starting/ switching or disconnection of Load – once in two (2) hours or more hours.

6 % - Starting/switching once or twice a year.

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Type Of

Disturbance Indices

Acceptable permissible values at point of common coupling

Reference Document Voltage Fluctuation and Flicker Absolute Short Term Flicker Severity (Pst)

1.0 (at 132kV and below)

UK’s Engineering Recommendation P28 0.8 (Above 132kV) Absolute Long Term Flicker Severity (Plt)

0.8 (at 132kV and below)

0.6 (Above 132kV) Harmonic Distortion2 Total Harmonic Distortion Voltage (THDV) % 5 % at ≤ 400 Volt Engineering Recommendation ER G5/4 4 % at 11kV to 22kV 3% at 33kV 3% at 132kV Voltage Unbalance Negative Phase Sequence Voltage %

2% for 1 minute UK’s Engineering

Recommendation P29

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C

HAPTER

3

LOADS

3.0 OBJECTIVE

The objective of this chapter is to:

i. Provide methodology for the estimation of maximum demand (MD) for the purpose of LV planning.

3.1 TYPES & CHARACTERISTICS OF LOAD

There are various types of loads such as lighting, electronic gear, heating and motor. Types and characteristics of these loads are tabulated in Appendix 1. It is important for distribution LV Planners to understand the characteristics of these loads in order for them to plan appropriately.

3.2 LOAD GROWTH

All loads supplied are subjected to growth over time. Load growth can be divided into:

i. Natural growth. ii. Step growth.

The respective growth rates depend on: i. Economic environment and growth. ii. Customer category.

iii. Customer affluence.

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LV PLANNING GUIDELINES LOADS

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v. Life styles.

vi. Presence of step loads.

LV systems need to be planned such that it can cater for credible load growth for the foreseeable future. The area load growth must be taken into consideration when designing supply infrastructure in a new development area. Normal load growth pattern in a certain area is represented by the graph shown in Figure 3.1.

Figure 3.1: Typical load growth pattern

3.3 LOAD DEMAND

The estimated load demand is based upon load declared by consumer and TNB’s own information on load profile characteristics for various consumer classes. Range of values is given as demand profile is known to vary according to geographical location of consumers around the TNB service areas in Peninsular Malaysia.

Fairly accurate assessment of individual and group demand of consumers is critical for correct dimensioning of network or facilities to meet the initial and future demand of consumers imposed on the network.

MD range in this section is meant for reference as the minimum value. MD declared by Consultants must be accompanied with the connected load and design calculations of the development.

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3.3.1 Typical Load Demand for Domestic Residential Premises

Table 3.1 indicates the range of typical individual domestic loads in urban, sub-urban and rural areas for different types of premises.

Table 3.1: Typical range of loads for domestic premises (kW per Unit)

No. Type Of Premises Rural

(kW)

Suburban (kW)

Urban (kW)

1 Low cost flats, single storey terrace, studio

apartment ( < 600 sq ft) 1.5 2.0 3.0

2 Double storey terrace or apartment 3.0 4.0 5.0

3 Single storey, semi-detached 3.0 5.0 7.0

4 Double storey, semi-detached 5 7.0 10

5 Single storey bungalow & three-room

condominium 5 7.0 10

6 Double storey bungalow & luxury

condominium 8.0 12 15

3.3.2 Typical Load Demand for Commercial Premises

Table 3.2 shows the range of commercial customer’s load density.

Table 3.2: Typical range of loads for commercial premises (KW per Unit) Type Of Commercial

Premises Min. Ave. High

Single storey shop house 5 10 15 Double storey shop house 15 20 25 Three storey shop house 20 30 35 Four storey shop house 25 35 45 Five storey shop house 30 40 55

3.3.3 Typical Load for Commercial Complex

For other commercial premises such as supermarkets, shopping complex, etc., the load demand is computed using the total floor area. The load density with respect to load environment is as shown in Table 3.3.

Table 3.3: Load density with respect to load environment for commercial complex

Load Environment Load Density

Low load density areas 6 watts / sq. ft. built up, Average load density areas 8 watts / sq. ft. built up, High load density areas 10 watts / sq. ft. built up.

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3.3.4 Typical Load Demand for Industries

Generally the demand for industries is declared by the

consultant/developers. However, as a guide, Planners can use an average of 20 watt / sq ft (215 watts / sq m) for Development Order Plan comment. Table 3.4 summarizes the load density associated to the load environment for industrial.

Table 3.4: Load density with respect to load environment for industries

Load Environment Load Density

Low load density areas 16 watts / sq. ft. built up Average load density areas 20 watts / sq. ft. built up High load density areas 24 watts / sq. ft. built up

3.4 COINCIDENT FACTORS

Multiple loads fed from a distribution network will experience diversity between different of occurrence in their peak demand. Hence the total demand fed will be less than the sum of the individual load demand. This factor is important in estimating the total maximum demand in a development.

Coincident factor (CF) is considered as the ratio of coincident maximum demand of 2 or more loads to the sum of their non-coincident maximum demand for a given period (the reciprocal of diversity factor). The CF depends on the number of customers of a group, as well as the different customer groups involved. CF is always less than or equal to 1.

3.4.1 Sample Calculation of Coincident Factor

Proposed coincident factors for different groups of customers are shown in Table 3.5.

Table 3.5: Group of coincident factors

Customer Groups Coincident Factors

Residential 0.90 Commercial 0.87 Industrial 0.79 Residential + Commercial 0.79 Residential + Industrial 0.87 Commercial + Industrial 0.79 Mixed Group 0.75

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Page | 11 If sufficient data is available, the following template can be used to compute coincident factor for any categories of customers:

unit kW 08:00 - 17:00 17:00 - 24:00 00:00 - 08:00 Domestic 200 5 10% 90% 50% Commercial 200 10 90% 30% 5% 08:00 - 17:00 17:00 - 24:00 00:00 - 08:00 Max CF Domestic 100 900 500 MD 1000 1000 1000 CF 0.10 0.90 0.50 0.90 08:00 - 17:00 17:00 - 24:00 00:00 - 08:00 Commercial 1800 600 100 MD 2000 2000 2000 CF 0.90 0.30 0.05 0.90 Group MD 1900 1500 600 Total MD 3000 3000 3000 Group CF 0.63 0.50 0.20 0.63

3.5 LOAD FACTOR

Load Factor (LF), is a ratio of average power consumption (kWh) to the peak demand over a period of time. It is reflected by the formula:

) ( ) ( ) ( period the for period specified Over L.F Hours kW MD kWh × = (3.1)

Load factors for different customer category vary according to the business type and operating cycle but generally are within recognizable values.

Table 3.6 summarized the typical values of load factors that can be used for planning purposes.

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Table 3.6: Typical load factors

CUSTOMER TYPE Typical Load Factor

Residential premises 0.35* Commercial 0.44* Industries Single shift 0.15-0.25 Double shift 0.40 – 0.60 Triple shift 0.60 – 0.95

*Source: Development of End User Load Model For Distribution Planning By TNBR

3.6 ALTERNATIVE SUPPLY

Customers having critical/essential loads such as lifts, operating theaters, dialysis machines etc. should have an alternative source of supply in case of utility power failure. The common sources of alternative power supply are:

i. Battery (connected directly, or through converters).

ii. Uninterrupted power supply (UPS) from dedicated battery and engine-generator set.

iii. Stand-by generating set.

This alternative supply is to be designed and installed by the customer / developer.

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C

HAPTER

4

DISTRIBUTION SUBSTATIONS

4.0 OBJECTIVE

The objectives of this chapter are:

i. To describe TNB's "standard" practices on the use of substations in LV distribution system.

ii. To describe the selection criteria for substation types.

4.1 DEFINITION

Distribution substation is defined as the substation that converts power from medium voltage to low voltage. Some typical distribution substations are as follows:

i. 33/0.4 kV ii. 22/0.4 kV iii. 11/0.4 kV

TNB's standard substation types include:

i. Indoor type – stand-alone buildings or attached to customer’s premise.

ii. Outdoor type – in fenced enclosures.

iii. Semi-indoor type – with transformer installed outdoor and switch gear indoors.

iv. Pad mounted switchgear H-Pole (PATOD) – with the transformer mounted on 2 pole, or 4 pole structures and pad mounted RMU Switchgear.

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LV PLANNING GUIDELINES DISTRIBUTION SUBSTATIONS

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In urban areas, substations are often equipped with more than one (1) transformer due to the high load density.

4.2 SUBSTATION SELECTION CRITERIA

The choice of substation type depends on several technical and non-technical factors. Amongst the factors that need to be considered are:

i. Physical location of the proposed substation.

ii. The control and other peripheral components to be installed, e.g. SCADA equipment, RTUs, power factor (p.f.) correction capacitors, etc.

iii. The system, and overall protection requirements for the substation, e.g., fully switched or RMU type, need for fire-fighting equipment, etc.

iv. The relationship of the substation to the overall distribution

development plan of the area. .

v. The magnitude and growth potential of the load to be fed.

4.2.1 Indoor Substation

Indoor type substation is the most favorable type of substation to TNB with the following advantages:

i. Public safety.

ii. Less chances of vandalism. iii. Enable VCB installations.

iv. Reduce exposure to environmental impact on equipment and operation maintenance personnel (eg: UV ray, rain & moisture etc).

Indoor substations may consist of single or double chambers. It can be either constructed as a standalone building or attached to customer premises.

Indoor type substations can be equipped with SCADA system (RTUs and other communication equipment), capacitor banks and load monitoring devices.

All substations in the industrial areas must be planned to use indoor type substations. For operation and public safety purposes, indoor substations must also be used in all strategic and critical substations.

4.2.1.1 Indoor Standalone Substation

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Page | 15 i. Easy transfer of land title from customer to TNB.

ii. Portable fire extinguisher is sufficient and it does not require extensive fire-fighting system.

iii. Easy access.

iv. Compliance to Uniform Building By-Laws 1984, By-Law 139: Separation of Fire Risk Area.

4.2.1.2 Indoor Attached Substation

Indoor attached substation has similar advantages to that of a stand-alone, except for:

i. The substation is part of customer’s building.

ii. Automatic and comprehensive firefighting equipment must be installed and maintained in order to meet the fire safety requirements.

iii. Land is leased to TNB for a limited period with the risk of lossing the substation site upon expiry of the tenure.

Due to these reasons, indoor attached substations are only allowed by TNB only if:

i. Domestic and commercial or industrial bulk supply customers with substation supply dedicated to them only.

ii. Customers must incorporate fire fighting facilities in their premises. iii. Customers without sufficient land to build indoor stand alone

substation.

4.2.2 Outdoor and Semi-Indoor Substation

Outdoor and semi-indoor substations are mainly used in rural areas due to their cost advantage. These types of substations require smaller land area, and easy installation. However, there are several disadvantages for these types of substations:

i. Installations are exposed to public access. ii. Higher chances of vandalism violation.

iii. Exposure to environmental effect on equipment and operation and maintenance personnel (eg: UV ray, rain & moisture etc).

4.2.3 Pad-Mounted Switchgear H-Pole

Pad-mounted switchgear H-Poles (PATOD) is normally used for system improvement in rural areas where substation land is difficult to be acquired.

The maximum capacity of pad-mounted switchgear H-Poles, limited by the physical load bearing capacity of the support structure is 300 KVA.

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There are several issues related to the conventional pole mounted substations (with link /drop out fuse as isolators) such as:

i. Difficulty in isolating supply. ii. Difficulty in fault finding.

iii. Safety of switching below a transformer. iv. 11kV drop out fuse is no more in stock.

In order to deal with the above mentioned issues, RMU switchgear is installed at the base of the H-pole to replace the traditional isolator link and drop out fuse design.

4.2.4 Compact Type Substation

Compact type substations are physically small and consequently require small sites. Therefore, it is unobstructive and can be erected quickly. Currently compact substations are available in 500 kVA and 1000 kVA capacities.

Compact substations are encouraged for domestic development (500kVA only) and commercial development (500kVA & 1000kVA) owing to the following advantages:

i. Require smaller substation land size hence can be placed closer to the customer loads.

ii. More efficient load distribution. iii. Shorter LV network.

Usage of compact substation is considered as ‘special features design schemes’ in which special features cost is charged to the consumer as per Clause 8.0 of Statement of Connection Charges 1994/1995.

Appropriate distribution network design is required to ensure security and restoration time to consumers will not be affected:

i. If the housing development is more than 5MVA, 11kV switching station shall be provided by the developer within the housing development to support 11kV network connection to the respective distribution substation.

ii. For housing development that is less than 5MVA, requirement of 11kV switching station depends on the existing network configuration and constraints.

iii. One unit of 11kV switching station is able to support a development of maximum 10MVA only.

Compact substation for non domestic and commercial development must obtain approval KJOW office (Surat Pekeliling PBK Perkhidmatan

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Page | 17 Kejuruteraan & Logistik, Perkhidmatan Dan Amalan Kejuruteraan A7/2004) and is to be strictly applied in selective situations under the following circumstances:

i. Genuinely limited space at site.

ii. Upgrading of load for existing customers.

Compact substation is also allowed to be used for system reinforcement projects for highly built-up areas where substation land is difficult to acquire.

4.2.5 Summary of Substation Characteristics and Usage

Table 4.1 summarizes the substation characteristics and their respective usage. Table 4.1: Substations Characteristics and Usage

No Type Characteristics Usage

1 Indoor Standalone Substation

Standalone building. Requires biggest footprint.

Suitable for any types of development, especially industrial customers. 2 Indoor Attached Substation Attached to customer’s building / premises. Substation land is leased to TNB for a limited period. Domestic, commercial or industrial bulk supply customers with substation supply dedicated to them only.

3 Outdoor & Semi Outdoor Substation

Small footprint with easy installations. Exposed to public access, easy vandalism & environmental effect.

Rural non domestic development. 4 Pad Mounted Switchgear H-Pole (PATOD) Smallest footprint. Limited physical load bearing capacity.

System improvement in rural areas.

5 Compact Substation Compact and requires small footprint.

Unobstructive & can be erected quickly.

Domestic & commercial developments are allowed to use compact substation. Appropriate distribution network design is required.

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4.3 SUBSTATION REQUIREMENT & TRANSFORMER SIZING

Every development area must have sufficient number of substations with appropriate transformers sizing (including PMU or PPU where necessary). To determine the number of sufficient substations and appropriate sizing of transformer, the following requirements have to be considered:

i. Maximum demand of the load to be supplied, including the estimated load growth in the foreseeable future of 15 years.

ii. Possible contribution to reinforce the LV network in the vicinity iii. TNB’s standard transformer ratings.

4.3.1 Domestic Development

For domestic development (tariff A), transformer size must be planned according to the load requirement with maximum of 1 transformer at each substation site. 500kVA compact substation is also allowed to be installed in domestic development.

The utilization of installed transformers capacity will reach 100% in 15 years assuming that the average growth rate as stated in Appendix 2. Hence, the planned transformer capacity is computed based on 85% of transformer loading. Table 4.2 provides the details on the number of substations required in residential development based on this principle.

Table 4.2: Computation on Number of Substation Required

(Domestic Development)

MD with GCF Transformer capacity at 85% loading

Up to 85 kVA 1 substation @ 100kVA (for rural supply) Up to 250 kVA 1 substation @ 300kVA

Up to 425 kVA 1 substation @ 500kVA Up to 638 kVA 1 substation @ 750kVA Up to 850 kVA 1 substation @ 1000kVA

> 850 kVA More than 1 substation is required

For MD >850 kVA, the number of substations required can be computed as below:-

Step 1: Calculate the minimum installed capacity (a) based on the principle of 85% transformer loading using the following relationship:

85 . 0 KVA) (in MD = a (4.1)

Step 2: Determine the number of 1000kVA transformer required to meet the capacity calculated in step 1 using the following formula:

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LV PLANNING GUIDELINES DISTRIBUTION SUBSTATIONS Page | 19 kVA 1000 a b = (4.2)

Number of substations = roundup (b) (4.3)

Step 3: Transformer capacity is selected based on the closest match of kVA to a, taking into account the possible MSVR in the area.

Example 1: Computation on Number of Substations Required (Domestic

Development)

Each terraced house in a housing scheme which consists of 250 terraced houses has an MD of 4 kW. The total MD by considering 0.9 group coincident factor is 900 kW (i.e (4 x 250)x 0.9 = 900kW). Assuming 0.85 p.f., the MD in kVA is 1059 kVA. The number of substations required is determined using the following procedures:

Step 1: 1246kVA 85 . 0 1059 85 . 0 KVA) (in MD = = = a Step 2: 1.25 kVA 1000 kVA 1246 kVA 1000 = = = a b

Number of substations = roundup (1.25)= 2 Step 3: Required transformer capacity

1 nos 1000kVA + 1 nos 300kVA Or

2 nos 750kVA

Example 2 : Computation on Number of Substations Required (Domestic

Development)

Each single-storey semi-detached house in a housing scheme which consists of 500 single-storey semi-detached houses has an MD of 5 kW. The total MD by considering 0.9 group coincident factor is 2,250 kW (i.e (5 x 500)x 0.9 = 2,250 kW). Assuming 0.85 p.f., the MD in kVA is 2647 kVA. The number of substations required is determined using the following procedures: Step 1: 3114kVA 85 . 0 2647 85 . 0 KVA) (in MD = = = a Step 2: 3.11 kVA 1000 kVA 3114 kVA 1000 = = = a b

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Number of substations = roundup (3.11)= 4 Step 3: Required transformer capacity

3 nos 1000kVA + 1 nos 300kVA

OR

3 nos 750kVA + 1 nos 1000kVA

4.3.2 Commercial Development

For commercial development (tariff B), transformer size must be planned according to the load requirement with maximum of 2 transformers at each substation site.

The utilization of installed transformer capacity will reach 100% in 15 years assuming that the average growth rate as stated in Appendix 2. The planned transformer capacity is computed based on 60% of transformer loading. Table 4.3 provides the detail of the number of substation required in commercial development based on this principle.

Table 4.3: Computation on the Number of Substation Required (Commercial Development)

MD Transformer capacity at 60% loading

Up to 180 kVA 1 substation @ 300kVA Up to 3000 kVA 1 substation @ 500kVA Up to 450 kVA 1 substation @ 750kVA Up to 600 kVA 1 substation @ 1000kVA

> 600 kVA Require > 1 substation with 1 substation or double chamber substation

For MD >600kVA, the number of substation can be computed as below:

Step 1: Calculate the minimum installed capacity (a) based on the principle of 60% transformer loading by using the following relationship:

60 . 0 KVA) (in MD = a (4.4)

Step 2: Determine the number of 1000kVA transformer required to meet the capacity calculated in step 1 by using the following formula:

kVA 1000

a

b = (4.5)

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Page | 21 Step 3: Transformer capacity is selected based on the closest match of kVA to

a, taking into account the possible MSVR in the area.

Example 1: Computation on Number of Substation Required (Commercial

Development)

Each single-storey shop house in a commercial development which consists of 80 units of single-storey shop houses has an MD of 10 kW. The total MD by considering 0.87 group coincident factor is 696 kW (i.e (10 x 80)x 0.87 = 696 kW). Assuming 0.85 p.f., the MD in kVA is 819 kVA. The number of substation required is determined using the following procedures: Step 1: 1365 kVA 60 . 0 819 60 . 0 KVA) (in MD = = = a Step 2: 1.365 kVA 1000 kVA 1365 kVA 1000 = = = a b

Number of substations = roundup (1.365)=2

Step 3: Required transformer capacity. 1 nos 1000kVA + 1 nos 500kVA

Table 4.4: Transformer Loading Computation (Individual Commercial Customer)

MD Transformer capacity base on customer’s maximum

demand

<180kVA Nearby substation (LV 4C Al cable <240m) or 1 substation @ 300kVA

180kVA up to 300kVA

1 substation @ 300kVA (1 circuit of LV 500mmp Al 1C PVC/PVC cable < 30m)

>300kVA up to 500kVA

1 substation @ 500kVA (2 circuits of 300mmp Al 1C PVC/PVC cable < 30m)

1 substation @ 750kVA (2 circuits of 500mmp Cu 1C PVC/PVC cable < 30m)

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For individual commercial customer where the substation is dedicated to individual customer the computation of transformer loading tabulated in Table 4.4 applies.

Example 2: Computation on Number of Substation Required (Individual

Commercial Customer)

An individual commercial application has an MD of 350 kW. Considering 0.85 p.f., the MD in kVA is 411 kVA.

Based from Table 4.4, supply has to be given through a new substation with 500kVA transformer capacity. 2 circuits of 300mmp Al 1C PVC/PVC cable is to be laid in concrete trench from transformer tail to customer MSB (<30m away).

4.3.3 Industrial Development

For industrial development area, the planning principle is similar to the commercial development area. The planned transformer capacity is computed based on 60% of transformer loading. The computation of required number of substations is as shown in Table 4.5.

Table 4.5: Computation on the Number of Substations Required (Industrial Development)

MD Transformer capacity at 60% loading

Up to 180kVA 1 substation @ 300kVA Up to 300kVA 1 substation @ 500kVA Up to 450kVA 1 substation @ 750kVA Up to 600kVA 1 substation @ 1000kVA

> 600kVA Require > 1 substation or double chamber substation Table 4.6: Computation on the Number of Substations Required

(Individual Industrial Customer)

MD Transformer capacity base on customer’s maximum

demand

<180kVA Nearby substation (LV 4C Al cable <240m) or 1 substation @ 300kVA

180kVA up to 300kVA

1 substation @ 300kVA (1 circuit of LV 500mmp Al 1C PVC/PVC cable < 30m)

1 substation @ 750kVA (2 circuits of 500mmp Cu 1C PVC/PVC cable < 30m)

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Page | 23 For single industrial customer, the transformer capacity is based on customer’s loading. The calculation of the number of required substations and transformer sizing shown in Table 4.6 applies.

Example 1: Computation on the Number of Substations Required (Individual Industrial Customer)

An individual industrial application has an MD of 200 kW. Considering 0.85 p.f, the MD in kVA is 235 kVA.

Based on Table 4.6, supply has to be given through a new substation with 300kVA transformer capacity. 1 circuit of LV 500mmp Al 1C PVC/PVC Cable is to be laid in concrete trench from transformer tail to customer MSB (<30m away).

Individual LV bulk customers are not allowed to take supply from substations with 2 or more transformersdue to the following reasons:

i. Paralleling of the LV sides of the transformers can create potential hazards due to high fault level on the system.

ii. Any bulk customer with MD>1000kVA is required to take 11kV bulk supply so as to reduce the technical losses (one of the initiatives to reduce technical losses in TNB system) .

Customers with high load factor can benefit from MV and HV supply as their electricity tariff would be lower. Furthermore, they would also have direct control over their incoming supply.

4.3.4 Multi-tenanted Buildings/ Development

For multi-tenanted buildings / development such as condominiums, apartments or shopping complexes, where the substation is dedicated to such development, the computation of transformer loading tabulated in Table 4.4 applies.

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C

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5

LOW VOLTAGE NETWORKS

5.0 OBJECTIVE

This chapter addresses the planning design requirements of TNB LV distribution network, such as:

i. Magnitude of the demand to be fed. ii. Types of network components.

iii. Types of LV network design.

iv. Technical and economic considerations and network suitability for an appropriate “life-time” operation.

This chapter also includes guidelines on public streetlighting which stipulates the relevant guidelines to help Engineers satisfy TNB’s stated standards of quality of supply to customers.

In this chapter, the guidelines are arranged according to the following groups:

i. Distribution network components. ii. Types of premises.

iii. LV reticulation design.

5.1 DISTRIBUTION NETWORK COMPONENTS

Distribution network components comprises of : i. Distribution Transformer.

ii. LV Feeder pillars.

iii. LV feeders, can be underground cables or overhead cables. iv. Five-foot-way mains.

v. Service cables. vi. Public Streetlighting.

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LV PLANNING GUIDELINES LOW VOLTAGE NETWORKS

Page | 25 The guidelines for each of the distribution network components mentioned above are explained in the following sections.

5.2 DISTRIBUTION TRANSFOMERS

Transformers used to step down medium voltages such as 33kV, 22kV, 11kV or 6.6kV to LV is known as distribution transformers.

5.2.1 Configuration

The LV tail from a distribution transformer can be connected to TNB Feeder Pillars or directly connected to customer’s Main Switch Board (MSB) depending on the connection schemes.

Feeder Pillars are used for distributing electricity to multiple customers as well as LV bulk supply to multi-tenanted buildings; whereas direct connection is for single customer with loads not more than 1000kVA.

Distribution transformer usage and size must adhere to the requirements as explained in section 4.3. It is mentioned that single commercial and industrial customer with MD>1000kVA shall take 11kV bulk supply. This is to eliminate multiple transformers connected to a common busbar at the customer’s side.

Separate MSB must be installed at the customer’s intake side for the owner and tenant supply when it involves multiple tenants and owner intake, such as condominiums, apartments or shopping complexes. Detailed design scheme is shown in Appendix 3: Multi Tenanted Building Design. However, multi-tenanted building customers are encouraged to take bulk supply with Independent Distributor license from Energy Commission. Independent Distributor is licensed to sell electricity to the tenants in a building / development.

In the case where multi-tenanted building requires supply through LV service connection from two transformers to customer MSB, interlocking facility must be provided at customer’s incomers to prevent parallel operation of two transformers.

5.2.2 Transformer Cable Tail

Table 5.1 indicates standard cable sizes used to connect the transformers to the TNB network.

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Page | 26

Table 5.1: "Transformer Tail" Cables Transformer kVA Rating HT Tail 11/.4 kV LV Tail Phase(sq mm) Neutral(sq mm) 100 70 mm2_{1C XLPE 1x300 AI 1C PVC/PVC 1x300 AI 1C} 300 70 mm2_{1C XLPE 1x500 AI 1C PVC/PVC 1x500 AI 1C} 500 70 mm2_{1C XLPE 2x300 Al 1C PVC/PVC 1x300 Al 1C} 750 70 mm2_{1C XLPE 2x500 AI 1C PVC/PVC 1x500 AI 1C} 1000 70 mm2_{1C XLPE 2x500 Cu 1C PVC/PVC 1x500 Cu 1C}

The recommended LV connections summarized in Table 5.1 are applicable to both connections to the feeder pillars or directly to the bulk customer's installations.

5.3 LV FEEDER PILLARS

LV feeder pillars are used to split the output from the secondary winding of the distribution transformers to several different circuits. LV feeder pillars provide fusing facilities for each circuit as protection where it can be used to disconnect or isolate supply to that particular circuit. The usage of LV feeder pillars are not restricted to after the secondary transformer tail but can also be used to further split the circuit from main feeder pillar.

The usage of LV Distribution Board has been discontinued since it does not comply with the Factory and Machinery (Fencing of Machinery and Safety) Regulation 1970, and Regulation 11 (Revised -1983), due to existence of exposed busbar. In the current substation design, LV Distribution Board has been replaced with Feeder Pillars. All new substation layouts have been designed to enable the Feeder Pillar usage.

5.3.1 Configuration

LV feeder pillars should accommodate a sufficient number of outgoing feeders in order to allow optimal distribution of LV system to meet the expected customer demand. The number of outgoing feeder pillars with respect to feeder pillar current carrying capacity is given in Table 5.2.

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Page | 27 Table 5.2: Typical Number Of Incoming & Outgoing Feeders In Feeder

Pillar Feeder Pillar Current

carrying capacity (A)

Typical Number of incoming feeders Typical Number of outgoing feeders 400A (Mini) 2 6

800A (Main / Sectional) 2 5

1600A (Main / Sectional) 2 8

At the planning stage (for commercial, industrial or mix development), it is recommended that spare feeders are made available at every substation, for customer upgrades in the future. The number of minimum spare feeders for each type of customer is listed in Table 5.3.

Table 5.3: Minimum Spare Feeders at the Planning Stage

Customer type Minimum Spare feeders

per substations

Group Commercial 2

Group Industrial 2

Mix Development 2

However, Planners should determine the necessity of spare feeders according to the needs of a particular development area. If the development area has the potential to become a busy commercial hub, then the Planner should plan for a higher spare capacity to cater the increase in the commercial customers like banks, eateries or convenient stores.

If a double chamber is planned, the number of minimum spares made available at the planning stage is required from one (1) of the transformers only. Appendix 4 shows typical outlook of different sizes Feeder Pillar.

A typical LV underground network design entails the following: i. Transformer tail to main feeder pillar.

ii. Main feeder pillar to sectional feeder pillar

• Incoming cable 2 x 300mmp 4T Al. XLPE (max fuse Amp = 250A) • J-slotted fuse / DIN type fuse

iii. Main/Sectional feeder pillar to mini feeder pillar

• Incoming cable 1 x 185mmp 4T Al. XLPE (max fuse Amp = 200A)

iv. From mini Feeder Pillar, lay LV service cable 70mmp or 25mmp XLPE Al 4C cable (depending on MD per unit) to individual unit.

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Page | 28

v. Loads connected must not exceed incoming feeder fusing rating. vi. Location of feeder pillar must comply with local authority

requirements and location agreed by developer.

Planners should take into account the extention of LV networks at the planning stage. To reduce the length of LV network, Planners should consider acquiring additional substation if high numbers of feeders or feeder pillars are needed. This requirement should be prompted during Ulasan Pembangunan stage.

5.4. LV FEEDERS

The outgoings from main feeder pillars which are used to distribute supply to customers are called LV feeders. LV feeders include underground and / or overhead cables.

5.4.1 Loading Limits

All LV conductors’ mains loading at planning stage must be at a maximum of 50% of their thermal capacity in order to achieve distribution technical losses at 4%,

To avoid having joints in the circuit, the length of LV underground cables must not exceed 240m. The length of LV underground and overhead cables are also limited by maximum voltage drop of 5% from reference voltage of 415V at the end of the circuit.

Effective and efficient planning of the LV distribution network is critical as:

i. It affects the cost of LV network, which forms a substantial portion of the project capital cost and is described in Section 5.9.

ii. It influences the magnitude of technical losses in the system. iii. It has an impact to the reliability of supply to customers.

5.4.2 Configuration

LV network is designed with security level 4. However, higher level of security can be designed based on consumer request at an additional cost and with special agreement from TNB.

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5.5 FIVE FOOT WAY MAINS

From the LV feeders, the circuit is further extended to LV services or Five Foot Way Mains, which is the last section of the circuit before terminating to the customers intake point.

“Mains” along terraced premises are often in the form of Five Foot Way Mains comprising of PVC single core insulated conductors or ABC insulated cables.

5.5.1 Configuration

Five Foot Way Mains configuration is currently standardised to three phase plus neutral in which it consists of four wire layout throughout its length using 7/.083 (25mm2) _{for PVC Al. or 3 x 16mm}2_{, 3 x 95mm}2_and

3x185mm2_{for ABC cables. Due to the increasing load demand by}

customers, it is necessary to use high capacity conductors. To facilitate the increasing load demand by customers, larger ABC cables are used instead of single core conductors. Five Foot Way Mains normally do not include feed back supply features.

5.6 SERVICE CABLES

Service cable includes all means of connection from TNB mains to customers’ installations. This consists of overhead cables, underground cables inclusive of direct connections from transformer terminals to the customer’s switch board.

5.7 STREET LIGHTING

Street lighting, given at a special tariff to local authorities, is part of the “local government’s” provision of public amenities. The intention is to encourage lighting up the public area, especially roads or streets at night.

TNB has recently extended the provision of street lighting to include such supply to domestic customers, also at a special tariff.

The lighting equipment used can be of standard TNB design, or of special design at the Local Authority’s cost.

5.7.1 Configuration

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Page | 30

i. Street Light for individual domestic customers and maintained by TNB

• The application of street lighting in this category is by individuals

and billed to the customer’s account at a determined flat rate per month.

• It is installed by TNB on the existing LV lines (i.e. 5-wire Aeriel Bundled Cables (ABC))

ii. Street Lighting for Local Authority but maintained by TNB

• This category of street lighting is installed by TNB upon request

by the Local Authority.

• It is installed on TNB poles and is maintained by TNB.

• It is metered and paid by Local Authority unlike the previous category which is paid by individual customer

iii. Street Light for Local Authority and maintained by Local Authority

• For this category of street lighting, a dedicated LV underground

cable is used to supply to the street lighting system

• It is metered and paid by Local Authority

• It can be supplied from TNB feeder pillars, existing or new

substation

Planners should plan for the street lighting supply at the initial stage so that the distance from the source to the street light meter panel can be optimized. The distance is restricted by voltage drop and technical loss of the service cable. Refer Appendix 5 for typical streetlight configuration.

5.8 DISTRIBUTION NETWORK TYPES

Network configurations with respect to types of premises and metering locations are designed to suit a particular development. Table 5.4 summarizes the network configuration associated with customer type, meter board location and design requirement.

Table 5.4: Network Configuration Associated with Customer Type, Meter Board Location and Design Requirement

Customer Type Meter Board

Location Design requirement

Residential Overhead Five Foot Way

Conductor PVC Al 1C 35mm2

(19/.064) as the five foot way mains

Residential Overhead Pole

Services drop Conductor PVC Al 1C 25mm2 _{(7/.083) into 3 houses} (max) with meters installed at the pole

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Page | 31

Customer Type Meter Board

Domestic Overhead

(with gate pillar) Gate Pillar

Use LV underground service cable from pole and junction box if looping of service cable is required (3 houses max). The bottom of meter must be >3 feet from floor level. Domestic Semi-Underground Five Foot Way UG Cable LV XLPE Al 4C 185mm2 terminated on the pole with service drop 35mm2 _Conductor PVC Al 1C 35mm2 _{(19/.064) as the} five foot way mains

Domestic Fully

Underground Gate Pillar

Fully underground design with junction box for looping of 3 houses max. The bottom of meter must be >3 feet from floor level.

Domestic Fully

Underground Meter Pillar

Fully underground design where developers prefer centralized metering scheme

Group Commercial

(U/G) Stair case

Ensure grill gate installations at staircase is after the centralized meter panel (by developer, before V.P. stage) Group Commercial (U/G) Upper front wall of the commercial premise

3 phase & 1 phase meters installed between 0.7m to 1.65m from floor level Group Commercial (U/G) Supporting vertical pillar of the building

Aesthetic design by the

developer’s architect. 3 phase & 1 phase meters installed between 0.7m to 1.65m from floor level Bulk Commercial

Meter Room in TNB Substation.

C.T. & voltage input to meter tapped from transformer tail

Group Industrial (U/G) Upper front wall of the industrial premise

3 phase & 1 phase meters installed between 0.7m to 1.65m range from floor level

Domestic Fully

Underground Gate Pillar

Fully underground design with junction box for looping of 3 houses max. The bottom of meter must be >3 feet from floor level.

Domestic Fully

Underground Meter Pillar

Fully underground design where developers prefer centralized metering scheme

Bulk Industrial

Meter Room in TNB Substation.

C.T. & voltage input to meter tapped from transformer tail

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Page | 32

Customer Type

Meter Board

Owner / tenant (LV) Owner’s main meter installed at TNB Metering Room, tenant’s meter installed at centralized meter room at ground floor (5 storey & below) or every floor (> 5 storey)

Splitting of owner and tenant feeders at TNB’s installations

Different types of premises need different types of network configurations. LV networks types can be grouped into:

i. Residential Overhead. ii. Residential Underground. iii. Commercial Overhead. iv. Commercial Underground. v. Industrial Overhead.

vi. Industrial Underground. vii. LV Multi Tenant and Owner. viii. LV Ring Circuit.

5.8.1 Domestic Overhead

LV reticulation using overhead lines to housing developments are the method preferred by TNB. Reticulation using this method is the most cost-effective when compared to other methods and also the easiest to maintain and repair. Ring system through overhead should be provided, wherever possible, as it can be easily incorporated into the system via jumper or connection at sectional poles.

Services can be distributed mainly using five foot way mains or directly from poles to individual premises.

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Page | 33 Detailed design is shown in Appendix 6 Standard Design O/H Dom A: Consists of 185mmp XLPE 4C from feeder pillar in substation to pole; 3x185+120+16mmp LV ABC as Overhead Mains;

7/.083 PVC/PVC as Five Foot Mains; Metered at five foot way.

Alternative Design O/H Dom B is shown in Appendix 7: Consists of LV ABC as Overhead Mains;

7/.083 PVC as Five Foot Mains; Metered at pole.

Alternative Design O/H Dom C is shown in Appendix 8: Consists of LV ABC as Overhead Mains;

25mmp 4C underground cable as service cables to the meters;

Metered at gate pillar (pipings are required and provided by developers. Loopings to 2 other units are allowed through junction box)

5.8.2 Domestic Underground

This method is used upon request by developers or as per the requirement of the Local Authority. Both would request for this method due to aesthetic reason of not having poles and overhead lines along the road. However, this method is expensive to construct due to extensive road excavation and involves erection of large numbers of feeder pillars to serve the customers. It is also difficult to maintain and repair. Hence, this method is treated as special features and the cost difference compared to overhead method (O/H Dom A) is chargeable to developer. The meter is required to be installed outside the premise and normally at the gate pillar or metering pillar.

Detailed design is shown in Appendix 9 Standard Design U/G Dom A: Consists of 2x300mmp XLPE Al 4C cable from main 1600A Feeder Pillar in a substation to 800A Feeder Pillar;

1x 185mmp XLPE Al 4C from 800A Feeder Pillar to 400A mini Feeder Pillar; LV service cable 25mmp XLPE Al 4C or 70mmp XLPE Al 4C from mini Feeder Pillar to customer meter panel;

Looping of 3 houses max is allowed through junction box.

5.8.3 Commercial Overhead

For shoplots at sub-urban area or rural area, supply can be distributed to commercial customers using overhead poles from the source to the shoplots. Overhead lines can be used for this situation if the load requirement is of low to medium density. The Planner must decide whether sufficient spare capacity is available to cater load growth for the shoplots.

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Page | 34

Five foot way mains for commercial lots will not pose a problem because meters and cut outs are accessible to TNB.

Detailed design is shown in Appendix 10 Standard Design O/H Com A (meter at individual lots).

5.8.4 Commercial Underground

This is the main method used to distribute electricity to shoplots in urban areas. The design fully utilizes underground cables with feeder pillars providing distribution outgoing to MSB of each lot.

Detailed design is shown in Standard Design U/G Com A of Appendix 11: Meters at individual lots.

5.8.5 Industrial Overhead

For industrial customers, it is seldom supplied through the overhead line unless it is small scale industries producing things like clay pots, ice plant, rubber products etc. Most of these factories are located sparsely and this is the reason supply is given through overhead system. The design is similar to commercial overhead network design.

5.8.6 Industrial Underground

The LV network design for this category is usually planned at early stage and it is found mostly in dedicated small and medium industrial area. Initially numbers and location of sub stations are determined during Ulasan Pembangunan stage and each factory is supplied with 100A 3 phase or 200A 3 phase.

Spare capacity for this category is important as growth potential is tremendous. Customers requiring loads beyond the available spare capacity shall be required to provide additional substation.

Detailed design is shown in Appendix 12 Standard Design U/G Ind A where meter pillar is located at customer’s front gate.

5.8.7 LV Supply for Premises with Separate Owner / Landlord

and Tenant Meters

This type of customer consists mostly of apartments, condominiums or shopping complexes. It is required to have separate MSB for landlord / owner and tenants for ease of disconnection.

Detailed design is shown in pin Appendix 3 Standard Multi-tenanted Buildings Design.

TNB Planning Guide LV

Asset Management Department

Distribution Division

Tenaga Nasional Berhad

Low Voltage

LOW VOLTAGE

PLANNING

GUIDELINES

ACKNOWLEDGEMENT

FOREWORD

TABLE OF CONTENTS

C

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1

GENERAL INTRODUCTION

1.0 INTRODUCTION

1.1 SCOPE

1.2 DOCUMENT LAYOUT

C

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2

QUALITY OF SUPPLY

2.0 OBJECTIVE

2.1 DEFINITION OF QUALITY OF SUPPLY

2.2 SYSTEM AVERAGE INTERRUPTION DURATION

INDEX (SAIDI)

∑

∑

∑

∑

2.3 SUPPLY SYSTEM STANDARDS

C

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3

LOADS

3.0 OBJECTIVE

3.1 TYPES & CHARACTERISTICS OF LOAD

3.2 LOAD GROWTH

3.3 LOAD DEMAND

3.3.1 Typical Load Demand for Domestic Residential Premises

3.3.2 Typical Load Demand for Commercial Premises

3.3.3 Typical Load for Commercial Complex

3.3.4 Typical Load Demand for Industries

3.4 COINCIDENT FACTORS

3.4.1 Sample Calculation of Coincident Factor

3.5 LOAD FACTOR

3.6 ALTERNATIVE SUPPLY

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4

DISTRIBUTION SUBSTATIONS

4.0 OBJECTIVE

4.1 DEFINITION

4.2 SUBSTATION SELECTION CRITERIA

4.2.1 Indoor Substation

4.2.2 Outdoor and Semi-Indoor Substation

4.2.3 Pad-Mounted Switchgear H-Pole

4.2.4 Compact Type Substation

4.2.5 Summary of Substation Characteristics and Usage

4.3 SUBSTATION REQUIREMENT & TRANSFORMER SIZING

4.3.1 Domestic Development

4.3.2 Commercial Development

4.3.3 Industrial Development

4.3.4 Multi-tenanted Buildings/ Development

C

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5

LOW VOLTAGE NETWORKS

5.0 OBJECTIVE

5.1 DISTRIBUTION NETWORK COMPONENTS

5.2 DISTRIBUTION TRANSFOMERS

5.2.1 Configuration

5.2.2 Transformer Cable Tail

5.3 LV FEEDER PILLARS

5.3.1 Configuration

5.4. LV FEEDERS

5.4.1 Loading Limits

5.4.2 Configuration

5.5 FIVE FOOT WAY MAINS

5.5.1 Configuration