» Electrical Installations

Preparation of completion Reports

arjun — Mon, 22 Sep 2008 18:31:59 +0000

After completing the electrical installation works of a new HV/EHV installation or making additions to an existing HV/EHV installation, the electrical contractor who carried out the installation works shall conduct the necessary pre-commission checks and tests and prepare the completion report in the prescribed format. The completion report shall be signed by the electrical contractor and the owner of the installation and submitted to the Electrical Inspectorate and the supply authority. A model form ofthe completion report is given at the end of this chapter. The completion report shall necessarily contain the following details 1. Full name plate details of all electrical machines and equipments covered in the completion report. 2. Test results of main equipments and switch boards. 3. read more

Protective Relays

arjun — Mon, 22 Sep 2008 18:24:19 +0000

8.1 Introduction Relays are devices intended to protect electrical systems and equipements against damages caused due to abnormal operating conditions. In more technical terms, relays are devices designed to produce sudden pre-determined changes in one or more physical systems on the appearance of certain abnormal conditions in the physical systems controlled by them. Protective relays act as sensors of abnormalities and actuate control gears when required. Relays may be suitably set to operate with the required discrimination between sections in order to isolate only the faulty section /sections or equipment / equipments. A relay will have one or more energising quantities and one or more characteristic quantities in terms of which the relay is calibrated (eg. voltage for over voltage read more

7.Protective earthing

arjun — Mon, 22 Sep 2008 18:13:07 +0000

7.1 Introduction Earthing is a general term broadly representing grounding of power systems and bonding of equipment bodies to grounded electrodes. Earthing associated with current carrying power conductors, usually neutral conductor, is normally essential for the stability of the system and is generally known as system earthing. Earthing of non-current carrying metal works of equipment bodies is essential for the safety of life and property and is generally known as safety equipment earthing. The basic requirements of any earthing system are (i) It should consist of equipotential bonding conductors capable of carrying the prospective earth fault current and a group of pipe/rod/plate earth electrodes for dissipating the current to the general mass of the earth without exceeding the read more

6. Cables

arjun — Mon, 22 Sep 2008 18:00:25 +0000

6.1 Introduction Cables for power distribution are mainly characterised by the material of the conductor, voltage grade, type of insulation, type of sheathing, type of armouring etc. Cables are designed to safely carry the current it is required to carry under normal operating conditions as well as abnormal conditions. To carry a current safely means (1) the temperature rise and voltage drop should be within the prescribed limits and (2) the insulation of the cable should withstand the normal operating voltage as well as higher voltages that may arise under abnormal conditions. In some situations, the cable may encounter with severe mechanical stress or highly contaminated environment in addition to the electrical stress. Hence it is necessary to ensure by means of pre-test inspections read more

5. Switch Board Assemblies

arjun — Mon, 22 Sep 2008 17:48:17 +0000

5.1 Introduction Switching centres are the nerve centres of any electrical distribution system. These centres generally comprise of power control devices, bus chambers, switchgear chambers, cable alleys, control bus chamber, control wiring and protective relays and devices. The switching centres in industrial power distribution are usually classified as (i) Power Control Centres (PCC) (ii) Motor Control Centres (MCC) (iii)Power and Motor Control Centres(PMCC) (iv) Fuse Distribution Board (FDB) In small installations, the switching centres are designated as Main Switch Board (MSB), Sub Switch Boards (SSBs) and Fuse Distribution Boards (FDBs).High voltage switching centres are generally classified according to the level of voltage whereas medium voltage switching centres are classified on read more

4.Generators

arjun — Mon, 22 Sep 2008 17:35:19 +0000

4.1 Introduction Installation of generators involves coupling of rotating machines and hence requires high degree ofengineering skill and competence, both mechanical and electrical. In order to ensure long and satisfactory life, it is necessary that the machine foundations have adequate strength, there is perfect alignment between the prime mover and the alternator and that the vibration of the machines are within permissible limits. The generator shall be installed in a cool, well ventilated place devoid of moisture, oil, dust, grease, carbon and metallic dust. It shall not be mounted in an atmosphere containing inflammable gases, corrosive acid fumes or other injurious gases unless specially made for such applications. Installation of the generator and the prime mover calls for a wide read more

3. Motors

arjun — Mon, 22 Sep 2008 11:21:02 +0000

3.1 Introduction The reliability and trouble free service of a motor depend on the superiority of its electrical and mechanical design, the accuracy and care with which the components are manufactured and assembled and on the stringency with which the motor is tested at the manufacturer’s works and at the site of installation. The operational duty requirements of motors vary from application to application.For common applications like fans, pumps, small flour mills etc. the motors may have standard characteristics. But for special applications like cranes, hoists, lifts, power press, machine tools,power station auxilliary etc. and for industries like coal mining, oil refineries, paper plants, sugar industry, cement industry, lift irrigation etc. specially designed motors with read more

2.Power transformers

arjun — Sun, 21 Sep 2008 08:09:21 +0000

2.1 Introduction Transformer is the most important unit in an electrical distribution network. All transformers are subjected to thorough tests at the manufacturer’s works before despatch to the destination of erection.Due to limitations in transport, large capacity transformers are dis-assembled into various components before despatch. At site, the transformers are re-assembled with the various components like bushings, coolers, conservator etc. and then the internal body is dried out to remove the surface moisture sticking to the paper insulation during exposure at site. As erection of transformers involve assembly of various components, pre-test inspection of transformers have greater importance than other parts of an electrical system. The following paragraphs explain the pre-test read more

1.Introduction

arjun — Sun, 21 Sep 2008 07:44:53 +0000

An electrical installation work is complete only when the prescribed pre-commission tests are conducted on different components and the test results are found satisfactory. By carrying out the pre-commission tests, it is ensured that different components of the system have their declared specifications/characteristics and also the system is fit for safe and reliable operation. The precommission tests for different components of an electrical system are prescribed by the Bureau of Indian Standards and International Electrotechnical Commission. The manufacturers also recommend certain site tests before commissioning their equipments. The Electrical Inspector who is the authority to certify the safety of an electrical installation may insist on the owner of the installation to carry out read more