coren project 2

March 22, 2018 | Author: Nwokolo Austine Chuks | Category: Insulator (Electricity), High Voltage, Electric Current, Transformer, Electrical Substation
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CHAPTER ONE 1.0 INTRODUCTION The project is about the reinforcement of Electricity Power Supply and Installation of 1 NO. 300KVA, 11KV/415V Transformer







Government Area of Delta State at the cost of five million nine hundred and forty-nine thousand twenty naira seventy kobo (N5,949,020.70k). My work as an Electrical Engineer attached to Onicha-Ugbo in Aniocha North Local Government Area is to go for survey on areas that have made request for reinforcement of electricity power supply or those areas that do not have electricity power supply. I visited the OnichaUgbo community on request for reinforcement of Electricity power supply by the indigenes. On getting to the areas concerned, feasibility studies which covers where the transformer can be installed suitably is put into consideration. The distance from the existing High Tension Overhead (OH) line is also considered. The case of installing a 300KVA, 11/.415KV transformer at Onicha-Ugbo covers a distance of five hundred (500) meters for the High Tension Overhead (OH) lines.

1.1 SCOPE OF WORK The scope of work for the project includes (i) construction of 11kv High Tension Overhead lines and low tension lines (ii)


Installation of 300KVA,11KV/415V transformer substation (iii) Inspection and testing.

1.2 DELIMITATION OF THE REPORT This report is restricted to Delta North Senatorial District of Delta State. While in some areas that are waterlogged, details cannot be given as Delta North Senatorial District is not known to be waterlogged. Onicha_Ugbo town is taken into consideration and the scope is limited to only a small part of Delta State.

1.3 OBJECTIVE OF THE TECHNICAL REPORT At the end of the exercise the technical report exposed the reader to the operation of various components used in the reinforcement of electricity power supply and installation of transformers. The technical report will also serve as a teaching aid on the basic principles of installation of transformers. The need for the report became necessary since one of the criteria for Chartership in the engineering profession is to give a small technical report on one’s experience within few years of practical application of engineering teachings, therefore, my work experience.







PROJECTS In carrying out the design for reinforcement of electricity power supply in Onicha-Ugbo, the following considerations, criteria and methods were put into use.

2.0 Survey / Drawing/Design 2.1 Survey Survey of the area is done by taking note of existing High tension/low tension lines. There may be need to extend the high tension only or with low tension lines running across it. Then I will find out the best option in taking electricity to that point that is in need. The mapping out of the area for the transformer substation is also covered in the survey. The distance of the high tension line is measured locally by taking each step as one metre and in every forty-five steps a span of low tension line is concluded while by taking a step of seventy a span of high tension line is concluded. Metre tape can be used if available and naming of street is made in the survey for better accuracy and if the distance is much, the car speedometer can be initialized while the distance is recorded at the point where the distance covers.



In drawing, we represent the low tension lines, high tension lines, transformer, streets, roads and necessary guide that can lead one to install as designed. The representation covers both existing and proposed lines as shown in the design figure I. The legend will surely show how/where the poles are to be placed and where the transformers are to be installed. The span for low tension line is forty-five metres while for high tension lines outside the town is seventy metres. At every ten spans, there exists an interpole or Hpole with four stay-wires with each pole having three pin insulators and four shackle insulators and steel galvanized cross arm. The conductor for high tension and low tension is 100mm2 AAC/ACSR Aluminium conductor wire. The height of the High tension pole is 10.4 m while … will be buried. The height of the low tension is 8.5m while will be buried. Concrete poles as support were used in the installation.

2.3 CONNECTIONS (SUBSTATION) The following connections were done at the substation. The H-pole must be mounted at the substation. The H-pole will bear the two or more channel iron, the lightening arrestor and J&P fuses. The 35mm2 x 3HT dropper cable runs from the 11KV over head (OH) High Tension line to the primary or high voltage side of the 300KVA, 11KV/415V transformer.


The 300mm2 x 1PVC/SWA/PVC (U/G) cable will run from the secondary or low voltage side of the transformer and linking up to the feeder pillar. The provision for the feeder pillar is 800A 4-way and the up-riser cable of 150mm2 x 4LT will now distribute to the 4-wire Low Tension (LT) lines. The schematic representation of this section

is as

shown in

fig.ii, fig.iii and fig.iv, The high tension overhead is made up of 10.4m concrete pole, steel galvanized cross arms, channel iron, tie straps, pin insulators, disc insulator and j-hooks, clamps, clevis. The high tension overhead pole has three pin insulators and for every ten (10) poles of HT line, two poles are mounted (Hpole) which will bear the steel galvanized channel iron. The tie straps support the steel galvanized cross arms. Eighteen number disc insulators are used for 33KV line where there is only one section while six number disc insulator will be adequate where there is only one section for 11KV line. Danger plates are mounted on every high tension overhead pole. Anti-climbers of 3 meter per pole is also placed around the pole. Every high tension pole should be earthed. The jhooks, clamps, clevis should be the anchor for the disc insulator.

2.5 TRANSFORMER PROTECTION The setting up of a high tension line that goes with a transformer involves huge amount of money. Therefore,


there is need to protect the transformer network. The provision made by the use of J&P fuses, lightening arrestors and aerial line isolator (especially for 33KV overhead line) go a long way in protecting the transformer network.

EARTHING Earthing is done to limit the potential (with respect to the general mass of the earth) of current-carrying conductors forming part of the system, and non-current carrying metal work associated with equipment, apparatus and appliances connected to the system. The sizes of earthing and bonding connections should be based on the following; High Voltage steel work earth lead or bonding – to be suitable for each fault currents of the H.V. system typical conductor requirements for 11KV are as follows: Since the project in question is ground mounted substations – earth leads 32mm2 (3/3.75mm2) copper conductor, bonding connections 25mm x 3mm copper strip or 25mm x 6mm aluminium strip. The MV neutral shall be connected to earth electrodes at or near the substation and to any metallic sheath and armouring of the MV distributors. The combined value for these electrodes should not exceed 10 ohms. The HV steel work earth electrodes provided for this purpose should be capable of passing a fault current of at least twice


the value required to operate the line protection equipment. The maximum resistance of these electrodes should not exceed 70 ohms. In general, earthing is done on the transformer, feeder pillar and the conductors. The trenches dug in order to bring the earth pole are of four / three holes measuring 5ft x 5ft for the transformer, 4ft x 4ft for the feeder pillar, conductors and lightening arrestors.


LINE CONDUCTORS – Material Sizes and Stranding The line conductors for new distribution systems shall preferably be aluminium or ACSR (Aluminium Copper Steel


Reinforced) of appropriate size as recommended below. Copper line conductors shall be used for maintenance purposes only where copper lines already exist. Copper conductors will, however, continue to be required for special purposes such as drop leads to equipment, earthing etc. The recommended conductors for the project are shown in the following table:


or To

copper equivalent


215 ACSR

part 1 1970 to

B.S. 125 1970 Metric


Curren Area t



Stranding AL (mm)




50mm2 181A











100mm 6/4.72


m2 150m



The neutral conductor shall be of the same size as the phase conductor. The normal arrangement of conductors for a three phase, 4-wire from top to bottom shall be as follows:


Red phase no. 1 Yellow phase no. 2 Blue phase no. 3 Neutral no. 4 3.1 MINIMUM HEIGHT OF CONDUCTORS The lowest conductor (neutral) on the pole shall not be less height above ground level at any point, after adjusting for the increased sag at 150oF (65 C), than Over roads and streets



Along roads or over other places accessible to vehicular traffic


Over places normally accessible to pedestrian traffic only -4.30m

3.2 LENGTH OF SPAN The standard span of 45 metres shall be regarded as normal for spans over 45 meters, the high tension overhead line span may be considered up to 70m outside town.



The approved poles are pre-stressed, reinforced concrete poles of 10.4m (34ft) for high tension pole and 8.6m (28ft) for low tension pole.

3.4 INSULATORS Insulators shall be of brown porcelain or of toughened glass 3.5 STAYS Stay wire shall be of 4/8 S.W.G and 7/8 S.W.G galvanized steel strand of 45 ton quality and shall comply with B.S 183 as applicable. Please see fig v.

3.6 RODS Stay rods shall be galvanized steel and comply with the requirement shown in

3.7 GROUND MOUNTED TRANSFORMER The substation shall be fenced using block and cement. The substation compound shall be surfaced with crushed stone, graded 1 ½ “ down and finished with a ¾ ” nominal size stone chippings. The transformer plinth and foundation of the feeder pillar shall be taken through the topsoil with a minimum (150mm) depth of mix concrete. This may be increased when necessary to good load bearing ground.


3.8 SUBSTATION EQUIPMENT – TRANSFORMER The transformer is oil-immersed, naturally cooled (typed On) suitable in all respects for outdoor operations, three phase 11000/415 volts, 300KVA. The schematic representation of this section is as shown in fig. vii, fig. viii and fig. ix. Transformer is a static electromagnetic apparatus which transforms one alternating current system into another with different voltage and current levels, but of the same frequency. Transformers are designed in various forms for different applications, some of these are: a. Power







distribution of electric power. b. Instrument





instruments for the measurement of current and voltage. c. Radio transformers – used in radio and electronic circuit. INSULATOR: A device that opposes the flow of current and does introduce resistance into the circuit e.g, sand, paper etc. CONDUCTOR: A device that allows the flow of current and does not introduce any resistance to it. E.g, copper, aluminium, steel etc. SPAN: The span is the horizontal distance between two adjacent supports.


INTERMEDIATE POLE: AN intermediate pole is a pole on which the conductors are supported on pin insulators. SECTION POLE: A section pole for the purpose of this specification is an ‘H’ pole inserted into the line where additional strengthening is required, stayed both ways in the direction of the line of route and with the conductors made off on tension insulation on each side. BONDING WIRE: The bonding wire is a conductor connecting together metal components. EARTHING WIRE: A conductor connecting components or a bonding wire to an earth electrode.


THE BILL OF ENGINEERING MEASUREMENT AND EVALUATION Herein referred to as BEME is a document showing the materials and quantity of materials with their local costing in one’s currency or international currency and at the back cover, the total cost for the execution of the Engineering job. Please see fig.x,xi,xii,xiii and fig.xiv for the enclosure of BEME for the reinforcement of electricity power supply at Onicha-Ugbo in Aniocha North of Delta State.


In the case of my area of work, the costing for survey, high tension line materials, high tension overheads labour, substation materials, substation labour, transportation of materials, contingency, amount allowed for Ministry of Mines, Power and steel and PHCN pre-commissioning testing fees and connection to PHCN National Grid and value added tax of 5%. This BEME is only restricted as a presentation from the Department of Electricity Power supply, Ministry of Energy, Asaba.

My job entails designing the high tension (HT) overhead lines, low tension (LT) overhead lines, township distribution network







(transformer substation).







substations are the responsibility of PHCN and Federal Ministry of Energy. My department carries out supervision and inspection of electrical projects. The following write-up describes some of the tests to be performed but the actual test figures may vary. Overall Requirements i.

High voltage test shall be conducted in accordance with PHCN safety rules (distribution).



The insulation level of the equipment under test shall be measured by means of a constant voltage insulation level set e.g, a “megger” before and after the application of a high voltage test


The application of a high voltage test to any item of equipment shall be recorded in a “Record of High Voltage Test” form. Please see fig. xv-xix for the enclosure of test results.

4.2 MATHEMATICS OF DERIVATION OF VALUE FOR BEME In below column is a little mathematics that will throw more light on the derivation for High Tension and Low Tension values for materials used in the design. Taking the case of the project into consideration that is the reinforcement of electricity power supply and installation of 2 no. 300 KVA 11KV/415V transformer S/S at Illah, we have: H.T Material The distance for high tension is 500 meters for the second transformer while the first is a direct dropping. The five hundred meter will cover about eleven (11) poles of high tension. Note that for every ten poles, there is a section of two poles. This will make a total of twelve (12) poles. In this case two extra poles are used to tie-off the high tension line for the first transformer dropping. The twelve poles plus the


two poles will make a total of fourteen (14) poles. To derive for cross arm, use the formula as: Cross arms = Total No. of poles – (section x 2). The total no. of poles here is 12 poles. Therefore, cross arm = 12 – (section x 2) = 12 – 2 = 10 Channel Iron = section x 2 Two section exist in this case, therefore, 2 x 2 = 4 Tie straps = Total no. of poles – no. of section = 12-2 = 10 Pin insulation = 3 x cross arm + 2 x no. of section = 3 x 10 + 2 x 2 = 34 Disc insulator length = No. of span x 3 x distance of one span = 10 x 3 x 50 = 1.5km = 1.6 km for sagging. Danger plate = no. of poles = 14 Anti-climber device (barbed wire) = 3meters x no. of poles = 3 x 14 = 42 meters. Stay assembly (complete) = no. of conductor stringing = 12 Earthing system complete with soil treatment = total no. of pole – ½ (no. of section) + 1 = 14 – ½ (4) = 12










accessories = no. of substation This is mostly used for 33KV overhead lines LT Earthing = No. of Poles (not applicable) 5 HT Earthing = No. of Poles – section = 14 – 2 = 12




PROBLEM ENCOUNTERED It must be stated here that a little problem was encountered in the course of the project. Solution was also proffered hence the installation work was a success. The problem was due to the earthing. From the test the earth resistance was very high (above 20 ohms) which was not acceptable Moreover, the earthing was improved by bringing the high resistance to an acceptable level with connection of more earth rod and earth mat at different nearby position properly linked with 70mm copper wire. Another problem that was experienced in the process of preparing the certificate for the payment of the project, is the delay in pre-commissioning test by PHCN and Federal Ministry of Energy.


Proper earthing network should be put in place especially at substation in order to protect the entire network


PHCN and Federal Ministry of Energy should respond quickly to pre-commissioning test

5.2 CONCLUSION The electrification

project of Onicha-Ugbo

village was

satisfactorily completed. I ensured the use of standard materials. For the installation, with earthing and protective devices put in place to achieve the maximum performance


of the installed transformers. The voltage level at the consumer end was between 220V – 230V at frequency of 50hz at the time of completion.

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