GUIDELINES FOR SUBSTATION AND POWER DISTRIBUTION SYSTEM OF BUILDINGS
Introduction:
1.1 In India commercial use of electricity started in 1891 though it picked up after independence due to large number of thermal and hydro power stations set up in the public sector. The power generation capacity in India has increased from 1362 MW in 1947 to more than 4, 00,000 MW in 2018.
1.2 Electricity has become essential for modern life. Practically, like air and water, electricity has become a basic requirement. We require it to run our houses, water supply, lights, fans, domestic appliances, lifts, TV, internet, communication, transportation, hospitals, offices, schools, colleges, industries, infact everything connected with day to day life.
1.3 While, in advanced countries availability of quality and uninterrupted power supply is taken for granted, in our country, this is subject to frequent interruptions due to various factors i.e. inadequate supply, inefficient/overloaded power distribution, over loading, use of obsolete technology, inefficient maintenance etc. Often our offices are subject to power interruptions on account of inadequate planning and design and overlooking modern technology including inadequate attention to proper routine and preventive maintenance.
1.4 The parameters for quality electric supply are:
• Voltage: steady voltage, variation within permitted limits.
• Frequency
• Absence of harmful harmonics
• Protection against surge/lightning
1.5 CPWD for last several decades have been following modern practice for
substation and power distribution. While the whole nation has been following pole mounted transformers and overhead distribution, CPWD for last 50 years has been distributing power through indoor substations and underground cabling system. Now the central government wants to change the overhead system into underground system all over the country, responsible for power breakdowns and theft
1.6 Also, on account of digital and computerised working of our offices and institutions, it has become necessary to provide uninterrupted and quality electric supply.
2. Objective of modern power distribution system:
2.1 To provide quality and uninterrupted power supply to the building so that there is no disruption to the productive operation of various services operating in the building to ensure human comfort.
3. Design considerations.
3.1 Indoor Substations and Underground Cable power distribution:
3.1.1 CPWD substation specifications are based on Indoor substations with standby equipments and UG cabling for ensuring service with minimum breakdowns to overcome the disadvantages of outdoor substations as:
i) Outdoor substations are subject to dust, rain, storm, extreme heat and theft leading to breakdowns and higher maintenance. During winds, cyclones and storms, the entire distribution system including poles, and conductors collapse taking long time to restore the power supply.
ii) The indoor substations work at much lower ambient, say at 28 Degree C, when the outside temperature may be above 40 degree C. Similarly the UG cable of power distribution is far superior to overhead system.
3.1.2 Substation with DG Backup: Uninterrupted power supply is supplied by the substation to cater to various loads based on DG Backup and UPS backup. The decision on central vs. building wise UPS provisions are tobe taken after careful technical and economical consideration and user requirements. For meeting critical UPS loads which require high quality power input without harmonics/surges etc., suitable Isolating transformer needs to be provided after the UPS.
