internship report tnb distribution selangor


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A report required to be submitted in for Internship Training in UNITEN


















This industrial training report is done as per requirement set by University academic regulation for the completion of industrial training and to present the knowledge gained in the 3 months we are in the training. We were required to complete 3 months/12 weeks of training at the company or organization we have chosen.The company that I have joined for my internship is Tenaga Nasional Berhad, or better known as TNB. TNB is the largest power utility company in Malaysia and South East Asia, with MYR 99.03 billion worth of assets. Tenaga Nasional Berhad is divided to several main divisions, mainly TNB Generation, TNB Transmission and finally TNB Distribution;which serves the end user customers. I applied to undergo training at TNB Distribution office for the state of Selangor. I was posted to the 33kV division of TNB Distribution. TNB Distribution of also known as TNBD is divided to 2 main division, 33kV and 11kV. TNBD 33kV deals with 33kV voltage which is stepped down from 132kV supplied from TNB Transmission network. Therefore, 33kV division is the first division to handle incoming voltages from the Generation and Transmission. TNB D 11kV deals with voltages from 11kV until 415V which is supplied to light industries and home users.TNBD Selangor main office is situated at ARAS 9, MENARA MRCB, NO. 2, JALAN MAJLIS 14/10, SEKSYEN 14, 40000 SHAH ALAM, SELANGOR and the Yard is situated at Seksyen 15, Shah Alam. The TNB Yard operates as the store for equipments,vehicles and for technical staff offices. These two places are the place where I spent my 3 months of training , with most of the time, I would follow the technical team to site projects or some days where I will drive myself to the site if it is nearby or late at night.Safety is the main priority in TNB and in the first day of site visitation, I was given a new safety helmet and TNB safety vest to be wore at every site that I go. During the training, I was joined by another trainee from UNITEN, named Nurul who is also posted to TNBD Selangor. We both would go to the same site visit and projects.

Figure 1 Technician and myself in cable pit. Example of safety helmet and safety vest

The training schedule provided to me was comprehensive and complete, as I was posted to all the department in 33kV division. There are 5 department and 3 sub-department as shown below; The departments in TNBD 33kV are depended on each other to ensure a smooth and safe operations of electricity supply to customers and reduce downtime and complains rate. Tagging along the technical team showed me the tough job in providing uninterrupted power supply to our customers. We had to go through jungles, mud, heavy traffic and late nights to ensure TNB customers can enjoy the ease of life electricity has given us. During this time, I have learned good work ethics and team work among the staffs.



The name of the company is Tenaga Nasional Berhad or better known as TNB. There are several sub companies under TNB and the subcompany I am interning is the TNB Distribution 33kV Selangor.


On 22 June 1965, Central Electricity Board (CEB) of the Federation of Malaya was renamed as the National Electricity Board of the States of Malaya (NEB). Committed to long term programme of growth and expansion backed by plans carefully crafted and laid down in the period of CEB, NEB is now firmly led by a Malaysian as the CEO.The National Grid was one of the plans in full motion. The National Grid or Grid Nasional in Malay is the primary electricity transmission network linking the electricity generation, transmission, distribution and consumption in Malaysia. Electricity generating plants are strategically located at Paka in Terengganu, Temengor, Kenering, Bersia and Batang Padang in Perak, Connaught Bridge, Kapar and Serdang in Selangor, Cameron Highlands in Pahang, Prai in Penang, Port Dickson in Negeri Sembilan, Pergau in Kelantan, Pasir Gudang in Johor and in Malacca.The central area network with Connaught Bridge Power Station in Klang was the precursor of the energy grid; it also tapped into the Cameron Highlands Hydro scheme from the Sultan Yussuf Power Station, and was extended into a western network.Later in the 1980s, the loop was finally complete; it prevailed over some of the most formidable terrain in the northern Peninsula, and Kota Bahru was successfully placed within the grid.The National Grid is also interconnected to the transmission network of the Electricity Generating Authority of Thailand (EGAT) through a 117 MVA, 132 kV Single Circuit Line, which has since been upgraded to a HVCD line. The Grid is connected to Singapore Power Limited (SP) through a capacity of 250 MVA 230 kV transmission lines and submarine cables. These significant connections provided us the first evidence of rudimentary ASEAN grid on the map.Plants within the Grid form a power bloc governed by technological alliances and careful arrangements to further the common good for all. The National Load Despatch Centre made active communications possible in order to identify the needs of the community we serve.

Keeping the nation's interest in mind, the government relentlessly pursued its ultimate objective and two pieces of legislation were passed to replace the existing Electricity Act, and to provide for the establishment of a new corporation TENAGA NASIONAL BERHAD (TNB), purposefully replacing the NEB (Successor Company Act). Datuk Hj. Ibak bin Abu Hussein became the last Deputy Chairman and General Manager of the NEB and the first Managing Director of TNB.

On 1 September 1990, Prime Minister Dato Seri Dr. Mahathir bin Mohamad officially proclaimed TNB as the heir and successor to NEB. TNB became a private company wholly-owned by the government; on the same day, Tan Sri Dato Haji (Dr) Ani bin Arope was appointed Chairman.1.3 COMPANY PROFILETenaga Nasional Berhad (TNB) is the largest electricity utility in Malaysia and a leading utility company in Asia. Listed on the Main Board of Bursa Malaysia with almost RM87 billion in assets, the Companys more than 33,500 employees serve an estimated 8.3 million customers in Peninsular Malaysia, Sabah and Labuan. TNB has been Keeping the Lights On in Malaysia ever since it was set up as the Central Electricity Board in 1949, powering national development via the provision of reliable and efficient electricity.TNBs core businesses are in the generation, transmission and distribution of electricity. In Peninsular Malaysia, the Company supplies households and industry with electricity generated from six thermal stations and three major hydroelectric schemes. It also manages and operates the National Grid which links TNB power stations and IPPs to the distribution network. The grid is connected to Thailands transmission system in the north and Singapores transmission system in the south. In East Malaysia, TNB has an 80% equity in Sabah Electricity Sdn. Bhd. (SESB), which manages the Sabah Grid.Other than its core business, TNB has diversified into the manufacture of transformers, high voltage switchgears and cables; the provision of professional consultancy services; and architectural, civil, electrical engineering works and services, repair and maintenance. The Company also engages in research and development, property development and management services. Tapping into opportunities available overseas, TNB is making inroads into emerging markets, focusing on the Asia-Pacific, Middle East and North Africa regions.In 2005, the Company embarked on a 20-Year Strategic Plan with the ultimate objective of transforming into a world-class player by the year 2025. To support this vision, TNB invests significantly in the continuous professional development of its employees through structured programmes. There is also renewed emphasis on sustainability, both of the organisation and of the Malaysian environment. The Strategic Plan entails greater focus on green initiatives such as the development of renewable sources of fuel, and more effective demand side management via energy efficiency, thus complementing the Governments carbon reduction agenda.As a leading Government-linked company, TNB also places strong emphasis on its social responsibilities. Through its foundation Yayasan Tenaga Nasional (YTN), established in 1993, the Company runs numerous CSR programmes that benefit the underprivileged. Among its many successful social outreach programmes are those that education via scholarships and better health for all.1.4 COMPANY VISION"To Be Among the Leading Corporations in Energy and Related Businesses Globally"1.5 COMPANY MISSION"We Are Committed to Excellence in Our Products and Services"


Figure 2 General view of TNB Electrical System2.1 TNB GENERATIONGeneration station is the main source in TNB for generate electricity. The Generation division owns and operatesthermalassets and hydroelectric generation schemes in Peninsular Malaysia and it has a generation capacity of 11,296 MW.2.1.1 TNB GENERATION POWER STATIONS2.1.1.1 HYDROPOWERED POWER PLANTSSungai Perak hydroelectric schemes, with 649 MW installed capacity: Sultan Azlan Shah Bersia Power Station72 MW Chenderoh Power Station40.5 MW Sultan Azlan Shah Kenering Power Station120 MW Sungai Piah Upper Power Station14.6 MW Sungai Piah Lower Power Station54 MW Temenggor Power Station348 MWSungai Terengganu hydroelectric scheme, with 400 MW installed capacity: Sultan Mahmud Power Station400 MWSungai Pergau hydroelectric scheme, with 600MW installed capacity: Sultan Ismail Petra Power StationPergau Dam600MWCameron Highlands hydroelectric scheme, with 262 MW installed capacity: Sultan Yusof Jor Power Station100 MW Sultan idris Woh Power Station150 MW Odak Power Station4.2 MW Habu Power Station5.5 MW Kampong Raja Power Station0.8 MW Kampong Terla Power Station0.5 MW Robinson Falls Power Station0.9 MWIndependent hydroelectric schemes Sg Kenerong Small Hydro Power Station inKelantanat Sungai Kenerong, 20 MW owned by Musteq Hydro Sdn Bhd, a subsidiary ofEden Inc Berhad GAS FIRED POWER PLANTS Connaught Bridge Power Station Genting Sanyen Kuala Langat Power Plant Karambunai Power Station Lumut GB3 Power Station Lumut Power Station Nur Generation Plants Paka power station Pasir Gudang power station Petronas Gas Centralized Utilities Facilities (CUF) Port Dickson Power Station Prai power station Putrajaya Power Station Sarawak Power Generation Plant Sepanggar Bay Power Plant Sultan Iskandar Power Station Sultan Ismail Power Station Tanjung Kling Power Station Telok Gong Power Station 1 Telok Gong Power Station 2 Teknologi Tenaga Perlis Consortium Tuanku Jaafar Power Station2.1.1.3 COAL FIRED POWER PLANTS Jimah Power Station Manjung Power Station PPLS Power Generation Plant Sejingkat Power Corporation Plant Sultan Salahuddin Abdul Aziz Shah Power Station Tanjung Bin Power Station OIL FIRED POWER PLANTS Gelugor Power StationPenang at Teluk Ewa Melawa Power StationSabah in Melawa Sandakan Power Corporation PlantSabah at Sandakan Stratavest Power StationSabah at Sandakan Tawau Power PlantSabah at Tawau


TNB has transmission including theNational Gridwhich is energized at 132, 275 and 500kilovolt(kV), with its tallestelectricity pylonin Malaysia and the National Grid is linked via 132 kV HVAC and 300 kV HVDC interconnection to Thailand and 230 kV cables to Singapore. More than 420[4]transmission substationsin the Peninsular are linked together by approximately 11,000km[5]of transmission lines operating at 132, 275 and 500kilovolts(kV). The 500 kV transmission system is the single largest transmission system to be ever developed in Malaysia. Begun in 1995, Phase 1 involved the design and construction of the 500kV overhead transmission lines fromGurun,Kedahin the North along the west coast toKapar, in the central region and fromPasir GudangtoYong Pengin the south of Peninsular Malaysia.The total distance covered for the 500 kV transmission lines is 522km and the 275 kV portion is 73km. Of the lines constructed, only the Bukit Tarek to Kapar sections had been energized at 500 kV. The remaining lines are presently energized at 275 kV. Later, in order to cater for the additional power transmission requirements from the 2,100megawatt(MW)Manjung Power Station, the 500 kV system was extended fromBukit TarektoAir Tawarand from Air Tawar to Manjung Power Station. In 2006, the 500 kV lines betweenBukit BatuandTanjung Binwere commissioned to carry the power generated by the 2,100 MWTanjung Bin Power Station.

2.3 TNB DISTRIBUTIONThe Distribution division conducts the distribution network operations and electricity retail operations of TNB. The division plans, constructs, operates, performs repairs and maintenance and manages the assets of the 33 kV, 22 kV, 11 kV, 6.6 kV and 415/240 volt in the Peninsular Malaysia distribution network. To conduct itselectricity retailingbusiness, it operates a network of state and area offices to purchase electricity from embedded generators, market and sell electricity, connect new supply, provide counter services, collectrevenues, operate call management centers, provide supply restoration services, and implements customer and government relationshipsThe substations under the governance of TNB Distribution is the PMU-Pencawang Masuk Utama , PPU- Pencawang Pembahagian Utama, SSU-Stesen Suis Utama, PE-Pencawang Eletrik and feeder pillars.

2.3.1 PENCAWANG MASUK UTAMAPencawang Masuk Utama is the interconnection point of 132kV or 275kV to the distribution network. The standard transmission capacity and voltage transformation provided at the PMU are as follows:-

- 132/33kV, 2 x 90 MVA- 132 /11 kV, 2 x 30 MVA

Figure 3 90MVA Step Down TX

Figure 4 30MVA Step Down TX

2.3.2 PENCAWANG PEMBAHAGIAN UTAMAMain Distribution Sub-station is normally applicable to 33kV for interconnecting 33kV networks with 11 kV networks. It provides capacity injection into 11 kV network through a standardized transformation of 33/11 kV.

2.3.3 STESEN SUIS UTAMASSU at 33kV, 22kV and 11 kV are established to serve the following function:-1. To supply a dedicated bulk consumer ( 33kV, 22kV, 11 kV)2. To provide bulk capacity injection or transfer from a PMU/PPU to a load center for further localized distribution.

2.3.4 PENCAWANG ELEKTRIKDistribution sub-stations are capacity injection points from 11 kV, 22kV and sometimes 33kV systems to the low voltage network (415V, 240V). Typical capacity ratings are 1000kVA, 750kVA, 500kVA and 300kVA.

Conventional substation designs are of indoor type (equipment housed in a permanent building) and out-door type (ground-mounted or pole-mounted). Standardized M & E design of 11/. 433kV sub-station is available at TNB offices. Compact substation (11 /. 415kV) has limited application and is to be strictly applied in selective situations under the following circumstances:-

System reinforcement projects for highly built-up areas where substation land is difficult to acquire. Any request to use compact substation for dedicated supply to a single or limited group of low voltage consumers is subject to TNB approval in accordance to site constraints situation, and to be considered as special feature design schemes.

Figure 5 Standalone Substation

Figure 6 Pole Mounted Substation CHAPTER 3


3.1 PLANNING DEPARTMENTPlanning department is the first department I was posted to during the training period. The planning department is responsible in planning out the entire TNB system in the region they are in control. Application for new power supply to new housing or industrial projects are forwarded to this department for consideration and feasibility. Ms.Kumutha is one of the engineer in Planning Department. She taught me and my intern partner, Nurul valuable lesson of Planning Guidelines and Distribution Code for TNB system planning. This department handles a lot of guidelines and law in creating the perfect and stable system for the applicants before approval is given. Many meetings will be held before a project approval is given. Other than planning system for new applications, Planning Department also does Planning Cycle study at 33kV system. It is done to accommodate changes to the 33kV system.3.1.1 SINGLE LINE DIAGRAM Single line diagram are mostly used to visualize the complex detailed drawing of TNB system map. It simplifies the map to a manageable size to see where and which substation are connected to each other. Planning engineers should be good in reading and making a single line diagram to assess the stability of the system. I was tasked to do a single line diagram based on a system map given by my engineer on the Puchong area. I was given the detailed plan of the Puchong area system map and asked to convert it into SLD.

Figure 7 Detailed System Map of Puchong

The blue lines represents the existing cables that are between these substations and the green lines represents the cables that are planned to be connected between these stations. The reason of using multiple cables are to carry more load between stations and ensure less fault time.3.1.2 NTL (NON TRANSFERABLE LOAD) AND BOTTLENECKBottleneck are a situation where required amount of power ie.MW could not be supplied to a substation during outage. The causes of bottleneck is mainly due to cables used are not in the same type or the load is more than what the cable could carry. TNB uses XLPE,630mmp , Aluminium 1 core cable. The maximum load carrying capacity of this XLPE cable is 30MVA,equivalent to 27MW at 0.9power factor. In some area in other states, there are cables which are the Copper core cables. Copper core cables are the cables laid during the 1970s and now discontinued. Bottleneck can occurs in circuits utilizing this 2 type of cables in the same circuit because Copper core cables can carry 42.5MVA,a significantly higher load then Aluminium XLPE cable.

In the figure above we can see a simple Single Line Diagram representing an electrical circuit. 2 PMUs and 2 PPU are connected together with Aluminium cables with one NOP( normally off point ) between the 2 PPU. NOP are switch point which are usually in open position during normal operation. In the event of shutdown or breakdown in either PPU, this NOP will be closed to join PMU A and PPU 1 to take care of loads in PPU 2.CASE STUDY

PMU A is connected to PPU 1 which has a load of 20MW with a single Aluminum cable.PMU B is connected to PPU 2 which has load of 20MW with a single Copper cable.CASE 1

Cable connecting PMU A and PPU 1 has been broken. NOP must be closed to bring supply from PPU 2. PPU 2 is connected to the PMU B via a Copper cable which can carry 42.5MVA load which is far higher than the combined load of 40MW. Therefore bottleneck does not occur.


Cable connecting PMU B and PPU2 has been broken and NOP has been closed to ensure continuous supply. However PMU A and PPU 2 cannot handle the total load of 40MW because this circuit is using an Aluminum cable which is only rated until 27MW load. Therefore 13MW of load cannot be supported by the PPU 2.This kind of bottleneck will increase fault and tripping in the circuit as many PPU might not be able to support the increase of load above its rated usage. If similar type of cables are used in the circuit, the Planning Department can accurately find out high load area and approved the installation of more cables to connect the substations together to ensure system stability.Most of the PPU and PMU are connected via 2 cables running parrallel carrying 50% of load each to reduce this bottleneck and downtime problem. In the case of one cable going faulty, the 2nd cable can automatically carry full load of 27MW to continue supplying power.

3.1.3 PLANNING CYCLEPlanning cycle is an annual exercise carried out by the Planning Department to foresee and forecast the load requirement of the existing system and making adjustments to accommodate any changes that might occur. STEP 1-LOAD FORECASTINGUsing historical data of Electrical Sales in Selangor since 1994, we come up a trend line to see how the electrical growth is going to be and we will forecast for 20 years of development. A software called Forecast Pro is used to find out the percentage of growth in the area the forecasting is carried out. STEP 2 LOAD DISAGGREGATIONAfter finding out the percentage of load growth, we model it into the current load of the area. Example : Petaling Jaya. In 2014 , Petaling Jaya requires 1000MW of load for a stable system. In Petaling Jaya alone ,we have 7 PMU with 2 x 90MVA transformers each. Lets take PMU A with 2 x 90MVA transformers. PMU A 2014 --------------------70 MW 2015 ---------------------72MW 2016 ---------------------74MW YEARLY GROWTH


Every transformer in every TNB substations are loaded up to 50% capacity only as standard practice. The reason for this practice is that in an event of fault in one transformer, the 2nd transformer can carry the full load and the station can continue supplying power as usual. In this case, this PMU A can carry the load for several years without needing any modification and staying at the 50% loading capacity limit.

3.1.4 33KV NETWORK

TNB Selangor employs n-1 network for most of its electrical network. N-1 source network means if the is any fault in one source,which is the PMU , the PPU can be supplied from another PMU, ensuring a steady supply. N-1 feeder element means 2 cable connecting the PPU and PMU. This n-1 network system is used to reduce downtime caused by fault and for steady supply. In high risk areas such as Putrajaya and KLIA, n-2 feeder element is used. N-2 feeder element has 2 cables carrying load parallel,ie if the load is 10MW, each cable carries 5MW each so if there is any fault in any cable, the second cable can start carrying the full load automatically whereas in n-1 feeder element, an Authorised Personnel has to go the substation to turn on the NOP and connect the two PPUs together.A 33kV PPU usually has 2 transformers rated at 30MVA each. Each transformers are loaded at 50 % capacity which is known as firm capacity. Any loading above 50% is known as above firm capacity and load desegregation exercise has to be carried out by Planning Department to move the extra load to either a low loading PPU or build a new PPU nearby to accommodate the extra loading.33kv Network in Selangor utilizes 2-1-2 network which complies to n-1 feeder element-cable backup and n-1 source-PMU backup. All this system and exercise is in place to make sure the customers receives uninterrupted power supply all day long.3.1.5 DC SYSTEMIn a substation, DC system is used to supply DC voltages to protection devices and support system in Switchgears, Control Panel and Relay activation. 11kV substation uses 30V of DC voltage whereas in 33kV substation uses 110V DC. The DC system is supplied via a battery bank located inside the substation building to support the DC system during power outage. A PPU has a battery bank of 88 cells@ 1.25V each. The batteries are usually made off Lead Acid or Nickel Cadmium cells.


PMU 275/33/11KV , 132/33/11KV , 132/11KVPPU - 33/11KVPE 33KV/415V , 33KV/0.433V ,

3.2 PROJECT DEPARTMENTProject and Construction Department is the department where new approved substations, underground cable projects are carried out after approval from Planning Department is given. These department are responsible for every new project TNB carries out and must ensure all projects are down up to TNBs standards. These department also deals with a lot of procedures and laws to ensure a quality station is built and commissioned.3.2.1 PROCEDURES INVOLVED1. Project Implementation Report2. Prosidur Proses Tender Projek 33kV3. Prosidur Proses Mesyuarat Kick-off4. Prosidur Mendapatkan Kelulusan Lukisan dan Permit Mula Kerja5. Prosidur Proses Factory Acceptance Test6. Prosidur Proses Kerja di Tapak Bangunan7. Prosidur Proses Kerja di Tapak Pepasangan 33kV8. Prosidur Sijil Pelepasan Pepasangan (Clearance Certificate)9. Prosidur Pengeluaran Take Over Certificate ( TOC)10. Prosidur Proses Completion Cert dan Pembayaran Wang Tahanan Akhir11. Prosidur Mendapatkan Kelulusan Perubahan Harga12. Prosidur Proses Pembayaran untuk Perkhidmatan dan Bekalan13. Prosidur Mendapatkan Kelulusan Tambahan Masa14. Prosidur Proses Dokumen Tender Bahagian Pentadbiran, Jabatan Perancangan dan Pembangunan Aset15. Prosidur Proses Mesyuarat Pemantauan3.2.2 HOW PROJECT DEPARTMENT WORKS

In the work done by Project Department can be divided into 2 main jobs. One is cabling works and also substation works. Cabling works is about laying new cables between an existing station to a new one or adding new cables between 2 old stations to improve bottlenecks. TNB utilizes 33kv XLPE Aluminum single core cables in its system. The cables are laid in bundles of 3, the red phase, blue phase and yellow phase. Pilot cables are also laid parallel to the power cables. Pilot cables are communication cables that connects 2 substations protection equipment to carry fault data. Each cable drum has 500metres of XLPE cable. Pilot cable

For substation works, Project Department are tasked to build and commission new PPU and P/E. PMU building and commissioning comes under TNB Transmission therefore 33kV Project Planning is not involved in PMU building. Project Department must install new transformers, Switchgears, Low Voltage Distribution Box, Battery Equipment for DC System and Control Panel Relay. Project Department also has to carry out Installation and Commissioning Test with the Substation Maintenance Department and building contractor to ensure all equipment is installed and working as it should.3.2.3 MAJOR EQUIPMENTS IN A SUBSTATION3.2.3.1 SWITCHGEARSwitchgear is a common term used to describe a switching device and their combination with associated control, measuring, protective and regulating equipment with is accessories, enclosure and supporting structures. Switchgear is a combination of two units of switches for the incoming and outgoing feeders and also as circuit breaker for the transformer feeders. Operations of the breakers are done via a control panel remotely, or by operating handle manually. Current switchgears fitted in TNB substation are SF6 gas insulated switchgears or commonly known as GIS. There are also Vacuum Circuit Breakers or known as VCB, Oil Circuit Breaker and also Gas circuit breaker. Gas Insulated Switchgear can reduce the risk of arcing and flashovers during switching as the process is done within the confines of the switchgear enclosure. The same goes to the VCB switchgear.

Figure 8 VCB Switchgears at PPU Setiawalk

Figure 9 Inside GIS Switchgear

Figure 10 Back of the SwitchgearCOMPONENTS IN SWITCHGEARI. Fuse in transformer feederSwitch is capable to trip and isolate the supply automatically during overload and fault conditions. In order to trip and isolate, a medium voltage fuse is used to trigger the tripping mechanism. The size of fuse depends on the ability of transformer and incomer feeder voltage.II. InterlocksIt is is prepared with mechanical interlocking facilities to ensure safety.

III. IndicatorsEvery feeder to give indication if the every phase of the feeder is live or not.IV. Gas GaugeThe level of gas in gauge indicates whether enough level of SF6 is presentinside the tank especially prior to operation of the switches.


1. Pedestal11. Mechanism Front Cover2. Cable Clamp12. Ledge for Voltage Indicator3. High Voltage Compartment13. HRC Fuse Tripping Linkage(gas tight tank)14. Plug Fixing Bracket4. Cable Connection Adapter15. Upper Fuse Plug 5. Bushing16. Fuse Cover6. Operating Shaft Socket17. Lower Fuse Plug7. Position Indicator18. Interlocked Front Cover8. Voltage Indicator9. Gas Pressure Gauge10. Lifting Lug3.2.3.2 TRANSFORMERTransformer is a static piece of equipment with two or more windings which by electromagnetic induction, transfers alternating voltage (AC Voltage) from a primary coil winding to a secondary coil winding. A transformer may be used as a safe and efficientvoltage converter to change the AC voltage at its input to a higher or lower voltage at its output without changing the frequency. Other uses include current conversion, isolation with or without changing voltage andimpedance conversion. An alternatingelectric currentflowing through the primary winding (coil) of a transformer generates a varying electromagnetic field in its surroundings which induces a varyingmagnetic fluxin the core of the transformer. The varying electromagnetic field in the vicinity of the secondary winding induces anelectromotive forcein the secondary winding, which appears as a voltageacross the output terminals. If a load is connected across the secondary winding, a current flows through the secondary winding drawing power from the primary winding and its power source. Rated power is a conventional value of apparent power indicating the capacity of the transformer in kVA or MVA. In normal TNB Distribution substations, 2 transformers are usually utilised and rated at 7.5MVA , 15MVA, 30MVA, and 90MVA.


1. High Voltage Bushing 10. Low Voltage Bimetal Lug2. Sampling/Drain Valve11. Low Voltage Bushing3. Jacking Pad12. Top-Mounted Thermometer4. Corrugated Fin Wall5. Off Circuit Tap Changer6. High Voltage Bimetal Lug7. Pressure Relief Device (PRD)8. Oil Level Gauge9. Low Voltage Bushing Flag

Hermetically sealed type is more advantageous compared with the conservator type transformer. The main advantage is that the oil is not in contact with the atmosphere, thus avoiding absorption of moisture and oxygen from the environment that can speed up the degradation process of the insulation.II. Conservative Tank Transformer

1. Cooling Radiator12.Main Conservator2. Main Tank13.OLTC Conservator3. Motor Drive Unit (MDU)14.Pressure Relief Device (PRD)4. Lifting Lug for Complete Unit15.CT Terminal Box5. High Voltage Cable Box16.Local Control Panel (LCP)6. Oil Level Indicator17.Inspection Vent7. Cable Box Breather18.Low Voltage Cable Box8. Buchholz Relay19.Lifting Lug for Cover9. Cooling Fan20.On Load Tap Changer (OLTC)10. Core Earth Box21.Top Cover11. Air Leak Detector

Figure 11 30MVA Conservative Tank Transformer

Inside of the transformer, the coils are kept cool using insulating fluid which is a mineral oil, called Hyrax oil. This oil keeps the coils in normal operating temperature and reduces electrical flashovers. The transformer also has to water and moisture proof so silica gel is used to remove moisture from the air that goes into the transformers and into the oil. New Silica GelOld Silica Gel


Usually in the substation, ONAN cooling system are used in transformers. It indicates oil natural air natural. The heated oil circulates in the transformer tank by the principle of natural convection and it is cooled by the natural air. Cooling fins and radiators provide the means of increasing the area for heat dissipation.

3.3 MAINTAINANCE UNIT SUBSTATIONAs the name suggests, TNB Distribution 33kV has a maintenance unit that comprises maintains its assets and equipment in proper working condition. This unit ensures all switchgears and transformers are working in proper condition. This substation maintenance unit is responsible in making sure a substation is operating well. There are several maintenance procedures such as Preventive Maintenance, Condition Based Maintenance, Scheduled Shutdown and also Breakdown Shutdown. Scheduled shutdown are usually half substation shutdown or one transformer shutdown to do periodical maintenance whereas breakdown shutdown are usually if there are any catastrophic failure to the equipment such as fire or transformer fault which requires the substation to go offline. Authorized Personnel or known as AP is the main man in the technical part of this unit as he is the only person who has the license or the rights to do switching to the switchgears. AP has to do the switching in order for maintenance work to be carried out in an orderly and safe manner. He has to issue a Work Permit and carry out safety checks before handing over to the technicians.

3.3.1 SWITCHING Every step of switching is very important and must take it seriously. The switching steps are shown as below:1. Before we do anything, we must write down all the switching procedure clearly and explain to competent person (CP).2. Every switching, authorize person (AP) must accompany by a CP because CP will observe whether AP is doing the right procedure for switching. 3. AP must make sure inside the substation has enough lighting to do switching.4. AP must ensure in front of switching panel has a rubber map on floor for safety purpose.5. AP must wear personal protective equipment (PPE) fully such as fire redundant suit, glove, safety helmet with vessel and safety boots.6. AP have to make sure and check all the tools are in good condition and fulfill TNB standard and record down in a check list.7. AP must record down every load reading before and after inside a log book for their reference.8. Before switching, AP must check whether switch gear is in good condition to do switching. Standard checking can be done with checking SF6 gas gauge at the switch gear or checking whether get ozone smells from the switch gear.9. Every switching activities must come out with four important steps which are switch off, rank out, prove dead and earth on.10. Phasing stick is used to prove the system is dead. There are two types of phasing stick: Subtraction phasing stick in phase will show 0V. Addition phasing stick in phase will show 12.6V.11. Non-standard lock is need to lock at the switch gear handle termination partial discharge spout (PDS) to prevent anonymous people go and do dangerous switching. 12. Precaution notice need to put on the non standard lock and written person in charge and contact number.13. Dangerous notice needed to put in front of work space to aware public on safety.14. Permit to work (PTW) can be issued to contractor when the system is proven dead and earth on.





3.3.2 OLTC (ON LOAD TAP CHANGER) MAINTENANCEAtap changeris a connection point selection mechanism along a powertransformerwinding that allows a variable number of turns to be selected in discrete steps. A transformer with a variable turns ratio is produced, enabling steppedvoltageregulation of the output. The tap selection may be made via an automatic or manualtap changer mechanism. For many power transformer applications, a supply interruption during a tap change is unacceptable, and the transformer is often fitted with a more expensive and complex on-load tap-changing (OLTC, sometimes LTC) mechanism. On-load tap changers may be generally classified as either mechanical, electronically assisted, or fully electronic. OLTC MAINTENANCEOLTC maintenance is done in this following steps : Transformer tap has to be changed manually to tap 9B or MR branded tap changer or tap 9 for other brand of tap changer. These tap are d maintenance tap and the diverter switch can be lifted out. Draining the on-load tap changer oil from the diverter switch oil compartment. Old mineral oil is removed from the tank and stored in empty barrel Removing the diverter switch insert using the lifting device. Performing maintenance on the diverter switch insert and cleaning the diverter switch oil compartment. Diverter switch is wiped clean off carbon and dirt. Installing the diverter insert with the lifting device. Filling the diverter switch oil compartment and the oil conservator with fresh oil. Hyrax oil is used as the insulating oil Performing maintenance on the motor drive, protective relay and drive shafts. Performing operational checks and recommissioning.ON TOP OF TRANFORMER. DIVERTER SWITCH CAN BE SEEN. MINERAL OIL HAS BEEN REMOVED



3.3.3 PREVENTIVE MAINTENANCEAs we have known earlier, preventive maintenance is done to avoid major preventable fault from occurring and ensure the system is stable and functioning well. Preventive maintenance is done is a scheduled way where half busbar will be shutdown to allow preventive maintenance to be carried out. Half bus bar shutdown means one transformer is shut down and the load is carried by the 2nd transformer, in line with the 50% load requirement set by the Substation guidelines. CIRCUIT BREAKER MAINTENANCECircuit breaker maintenance is done to remove dusts and ensure all moving parts are moving freely. Switching is done to isolate the breakers and circuit breakers are racked out. WD40 lubricant is used prevalently and a cleaning solution is used to wipe the dirt as water may cause moisture condensation in the breaker and cause flashover.Cleaning the inside of the busbarOpening the front over of 11kV Circuit Breaker truck

33kV Vacuum Circuit Breaker racked out

11kV circuit breaker with front cover removed


3.3.4 CONDITION BASED MAINTENANCE (CBM)Condition-based maintenance(CBM), shortly described, is maintenancewhen need arises. This maintenance is performed after one or more indicators show that equipment is going to fail or that equipment performance is deteriorating.This concept is applicable to mission critical systems that incorporateactive redundancyandfault reporting. It is also applicable to non-mission critical systems that lack redundancy and fault reporting.Condition-based maintenance was introduced to try to maintain the correct equipment at the right time. CBM is based on using real-time data to prioritize and optimize maintenance resources. Observing the state of the system is known ascondition monitoring. Such a system will determine the equipment's health, and act only when maintenance is actually necessary. Ideally condition-based maintenance will allow the maintenance personnel to do only the right things, minimizing spare parts cost, system downtime and time spent on maintenance. TECHNIQUES USED IN CBMTransformersThermography HotspotsOil analysis -Oil condition & contentFrequency response analysis -Frequency responseSurface conductivity measurement -Pollution levelCircuit breakersThermography -HotspotsCoil current analysis (CCA) Coil currentDynamic resistance measurement Dynamic resistanceSurface conductivity measurement -Pollution level

Partial Discharge detection toolCircuit Breaker Timing Test

3.4 MAINTENANCE UNIT CABLE As the name suggests, Cable maintenance unit deals with medium voltage underground cable maintenance. Medium voltage underground cables are cables that carries 33kV load from PMU to PPU and henceforth. This unit also deals with breakdowns and repair works as cables are the main lifeline in power transmission.3.4.1 TYPES OF CABLESTNB utilized several types of underground cables in the past but currently in the process of standardizing all cables to the same type to reduce bottleneck in the power system. 33 kV, XLPE, single core, 630 mm2 Aluminium 11 kV, XLPE, single core, 500 mm2 Aluminium, with M16 bolts 11 kV, XLPE, three core, 240 mm2 Aluminium, with M12 boltsXLPE, is a form ofpolyethylenewithcross-links. It is formed into tubing, and is used predominantly inbuilding services pipework systems, hydronic radiant heating and cooling systems, domestic water piping, andinsulationfor high tension (high voltage) electrical cables.


3.4.2 CABLE LAYINGTNB underground cables are laid in trenches or through HDD technique. 2 set of cables with red, yellow and blue phase are laid together with pilot cable between them. The depth of the cable pit are usually 6 feets.Pilot cable33kV cable

Concrete slabPower cable and pilot cable

Concrete slab indicating the cables are laid on top of the power cables. The purpose of this slab is to avoid accidental damage during excavation. Below the concrete slab, the cable pit is filled with fine sand and on top of the slab with more fine sand and rocks and finally sealed with premix tar.

3.4.3 JOINTS

Connector: Aluminum or Copper depending on conductor type. For crimped type the size depends on conductor size whereas mechanical type has range taking capability. Semi-conducting conductor shield: Same function as conductor shield of cable. Insulation: Usually EPDM (Ethylene Propylene Diene Monomer) rubber material and silicone. Semi-conducting insulation shield: Same function as insulation shield of cable. Metallic Shield: Breaded Copper Strip or Copper stocking bonded with the main cable copper tape at both ends. Outer Protection: Resin to protect joint body from mechanical damage.3.4.4 CABLE FAULT DETECTIONCable fault are fault that occurs at joints or on the cable itself. This type of faults required that section of cable to be dug up and replaced. Joint fault requires new joints to be done.Medium Voltage Cable joints dominant failure modes identified by TNB Distribution Division are localized defect caused by assembly error, localized defect caused by material defect and insulation ageing. For terminations additional dominant failure modes identifiedbyTNBDistributionDivisionarelocalizeddefectcausedbyenvironmentalstresses, localized defect caused by insulator tracking and insulation ageing due to water penetration. Most of the above failure modes progress slowly to deteriorate the condition of the joints and terminations over time. DEVICES USED IN FAULT DETECTIONThe steps in a correct approach for cable fault location are in the proper sequence as follows: Analysis of fault Pre location Pin Pointing Confirmation and re-test

The exact location of cables and conductors is an essential aspect of modern cable fault finding and helps to save existing cable networks from damage. Pin-pointing is the application of a test that positively confirms the exact position of the fault. Before the commencement of pin-pointing, the pre located fault distance should be marked on the cable route which is measured by means of a trumeter. The fault can be detected by the use of a semisphone. This method is also known as thumping method as a thumping sound can be heard at the fault location.

Fault detected

Fault marked

Fault found

Cable has been replaced and joint

3.5 MAINTENANCE UNIT OVERHEAD LINES Overhead maintenance unit is responsible for medium voltage overhead lines that runs in the interior parts of Selangor. Overhead lines are used in long lines where underground cables are not feasible and too costly to install. Places such as Kuala Selangor and Rawang has a lot of overhead lines to carry supply to those areas. In some areas, 33kV overhead lines run in parallel with 132kV TNB Transmission lines. Cables used in overhead lines are bare aluminium 150mmp Silmalec cables.

3.5.1 MAIN COMPONENTS OF OVERHEAD LINES Conductor which carries electrical power from substations to another Supports which maybe the poles or tower to keep the conductors in a suitable height. In this case its poles. Insulators which are attached to support and insulate the conductor from ground.

H-PoleLine Tensioner pole

These two type of poles are predominately used in TNB overhead system. Conductor cables hangs from insulating dish and kept in tension. These insulating dish are usually made of glass or ceramic for its insulating properties.

3.5.2 AUTO RECLOSERAutorecloser, is acircuit breakerequipped with a mechanism that can automatically close the breaker after it has been opened due to afault.Reclosers are used on overhead distribution systems to detect and interrupt momentary faults. Since many short-circuits onoverhead linesclear themselves, a recloser improves service continuity by automatically restoring power to the line after a momentary fault. Two main brands used in TNB is NuLec and Entec. Autorecloser comes with its own control panel which can be operated remotely via SCADA.Auto Recloser

The control system for a recloser allows a selected number of attempts to restore service after adjustable time delays. For example a recloser may have 2 or 3 "fast" reclose operations with a few seconds delay, then a longer delay and one reclose; if the last attempt is not successful, the recloser will lock out and require human intervention to reset. If the fault is a permanent fault (downed wires, tree branches lying on the wires, etc.) the autorecloser will exhaust its pre-programmed attempts to re-energize the line and remain tripped off until manually commanded to try again. About 80-90% of faults on overhead power lines are transient and can be cured by autoreclosing.NuLec Control Panel

Fault data is being downloaded to be analysed

3.6 PROTECTION UNITProtection unit is the unit responsible for maintenance of control panels, relays, battery banks and other power protection equipment inside of a substation. Protection systems usually comprise five components: Currentandvoltage transformersto step down the high voltages and currents of the electrical power system to convenient levels for the relays to deal with; Protective relaysto sense the fault and initiate a trip, or disconnection, order; Circuit breakersto open/close the system based on relay and autorecloser commands; Batteriesto provide power in case of power disconnection in the system. Communication channels to allow analysis of current and voltage at remote terminals of a line and to allow remote tripping of equipment.TNB utilizes a combination of analogue and digital relays for its tripping circuit such as Over current earth fault, alarms and earth faults. Protection Unit also carries out transformer ratio test to ensure the tap changer is attached back properly after an OLTC maintenance is done.

3.6.1 CONTROL PANELControl panels are essentially an enclosure to mount relays and meter to monitor and remotely trip the switchgears in cases of shut down or automatically due to fault. Control panels also will indicate the source and type of fault that has occurred so proper actions can be taken.

3.6.2 RELAYSProtective relayis a device designed to trip acircuit breakerwhen a fault is detected. The first protective relays were electromagnetic devices, relying on coils operating on moving parts to provide detection of abnormal operating conditions such as over-current, over-voltage, over- and under- frequency. Microprocessor-based digital protection relays now emulate the original devices, as well as providing types of protection and supervision impractical with electromechanical relays.Over current relayA digital over current relay is a type of protective relay which operates when the load current exceeds a preset value. In a typical application the over current relay is connected to a current transformer and calibrated to operate at or above a specific current level. When the relay operates, one or more contacts will operate and energize to trip (open) a circuit breaker. An analogue relay uses electromagnetic to activate the coils to trip the circuit.

Analogue Relay

An overcurrent and earth fault relay test to ensure the required tripping time is achieved

3.6.3 SCADAThe full form of SCADA system is Supervisory Control and Data Acquisition. It is a concept used to describe a system that enables control and monitoring of devices or equipment remotely. SCADA system is used to assist the operation and management of transmission and distribution of electricity. The advantages of using SCADA system are optimization of plant processes and provide operations that are more efficient, reliable and safer. There are three main mechanism in SCADA system, master system, communication system and remote terminal unit (RTU). The flow of communication is like this, remote terminal unit is collecting field data and sending data back to a master system via a communication system. The master system is located in Regional Control Centres (RCC). RCCs are located at Kuala Lumpur for southern areas and Seberang Jaya for northern areas.

Master SystemMaster System is fundamentally a network of computer subsystems with many functions to support the operation of the SCADA based control centre. Master system consists of three main subsystems, front-end subsystem, back-end subsystem and Human Machine Interface (HMI) subsystem.

Function of Subsystems:I. Front-End Subsystem Receive data from RTU then send it to back-end system Receive control requests from back-end system and send it to RTUII. Back-End Subsysten processes control commands received from (HMI), packages it and sends to front-end subsystem processes data received from front-end subsystem and sends to HMIIII. Human Machine Interface Subsystem (HMI) processes controller commands and send to back-end subsystem receives information from back-end subsystem and presents it visually on monitorsCommunication SystemThe main function of communication system is to transfer data between RCC and RTU. The communication mediums as shown below:I. Fibre OpticsIV. GPRSII. Pilot Cable V. RadioIII. Leased LinesVI. MicrowaveRemote Terminal Unit (RTU)Generally the RTU is installed in a substation. The function of RTU is to collect data from the remote station, processes and executes control commands from the master system. RTU can be classified into 2 types as shown below:I. RTU for SSU 33kV RTU cubicle is Floor-Standing type DC supply is 110 VDC Generally located in Control Room beside Supervisory Interface Panel

3.6.4 BATTERY BANK AND DC SYSTEMBattery is used as support to supply station auxiliaries whenever station AC supply fails. It is intended to supply for 5 hours during any station AC supply blackout. It also serves as an extra DC source whenever the station DC load requires supply more than what can be delivered by the charger. While the charger is a tool that rectifies AC supply into DC. It is to charge the standby battery bank during usual operation. Battery banks and battery chargers should be well maintained to make sure that the protection system functions properly. DC system is required as the tools in the switchgears and control relay panels run on 110V DC voltage. For a PMU, it needs 86 batteries and total 110V.

Battery charger

CHAPTER 4DISCUSSION AND CONCLUSIONInterning with TNB 33kV Selangor, Ive learned the inner working of TNB and its systems, how each and every unit works together to keep a stable power system. As the largest power utility company in Malaysia, there is a lot of stakes and consideration has to be taken when each actions are done. Each unit has its own procedure on how the work is done so consumers will not be affected by the works carried out. While in TNB, Ive learnt as much as possible by tagging along the team and also helping in some works as hands-on learning is the best teacher.While in Substation Maintenance unit, I help out in OLTC maintenance job, to clean the diverter switch, unscrew the cable box and sorting out tools from the truck. I did help too in Preventive Maintenance by opening up the front cover of the VCB truck.While in Cable Maintenance unit, the biggest project or task Ive been involved is fault tracing and replacement of cable at Sunway Mentari. This job is carried out at night, approximately 10.00pm onwards and we walked the whole length of the cable to find the fault location and also to dig out the faulty cable. Several problem arose during this project where cable fault was misjudged as one cable fault whereas the actual fault was on 3 cables. Therefore my supervisor and I had to drive to TNB Main Store at Rawang to get extra 40m of cables for replacement. While in Overhead Maintenance unit, there was a major breakdown which lasted 1 week to recover. It was due to severe rain storm which caused nearly 7 overhead poles to fall and power outage to occur. This event took 1 week for the teams to rectify. They had to replace the stay cables which are responsible in keeping the poles upright but faced problems as groundwater fills up the dug pit. I liked Overhead Maintenance as most of the job task is far as also in the wilderness. Meanwhile in Protection Unit, my supervisor taught me on how to reset a battery charger and change the battery charger card. The battery charger was not supplying enough DC voltage to the battery bank, therefore battery bank did not have enough power to sustain and battery water is drying up too fast. Being in TNB has taught me on how to be a good and diplomatic person as well as an engineer. We have to be diplomatic with our staffs so they will not feel pressured or feel hatred towards myself if I were to ask them to do a job. Safety is also paramount in TNB as we deal with deadly voltages that can kill. Therefore safety must be observed at all time to avoid such disaster.

REFERENCES1. Buku Panduan Piawai Baru Rekabentuk Pencawang Elektrik (Jenis Bangunan),Bahagian Pembahagian, TNB

2. Substation Design Manual, TNB Distribution

3. Electricity Supply Handbook, TNB


5. XLPE Insulated Cables, Tenaga Cable Industries.

6. Mechanical Design of Overhead Lines