Besides HT cubicles other common electrical items are transformer , LTMCC ( Low tension Motor eontrol center ) , Different Power distribution board coming under lighting packages etc. In this dispatch we will discuss only about LTMCC. There are numbers of LTMCC in a power station which can be classified as LTMCC or the name of the system like soot Blower MCC, Valves MCC etc. LTMCC is having operating voltage of 415 V.
To appreciate the construction feature of LTMCC one must study the IS ( Indian standard ) codes for items . Few of them is listed below for ready reference.
375 Specification for Marking & Gen Arrangement of Swgr, Busbars, Main Connection & Aux. Wiring
513 Cold Rolled Low Carbon Steel Sheet & Strips
722 Specification for A. C. Electricity Meters. (Integrity Meters)
1248 Specification for Direct Acting Electrical Instruments.
1822 AC Motor Starters of Voltages not exceeding 1000
1841 Specification for EC grade Aluminium Rod Produced By Rolling
1897 Specification for Copper Strips for Electrical Purposes
1901 Visual Indicator Lamps.
2147 Degree of Protection provided by Enclosure for Low Voltage Switchgear
2208 Specification for HRC Fuse Links up to 650 Volts
2516 A.C. Ckt Breaker Requirement for Voltages not Exceeding 1000 V (Part - I, Sec - I + Part - II, Sec-II)
2705 Specification for Current Transformers.
3231 Electrical Relays for Power System Protection.
3247 Switchgear General Requirements
3427 Metal Enclosed Switchgear & Control gear
4064 Specs for Heavy Duty Air Break Switches Fuses for Voltages not exceeding 1000 V.
4237 General Requirement for Switchgears & Control gear for Voltage not exceeding 1000 V
6875 Control Switches / Push Buttons
8623 Factory Built Assemblies of Switchgears & Control Gear.
8828 Miniature Circuit Breaker
13947 LV Switchgear and Control Gear.
General Information on LT MCC ( only a few ones to understand the construction features.)
-the enclosure shall provide a degree of protection of not less than IP-52. The height of all the panels shall not exceed more than 2200 mm & depth shall not be more than 500 mm for Single Front & 800 mm for Double Front, except for the Circuit Breaker panel, where the depth could be 1000 mm.
- CRSP (t=1.4mm and above) , angle , channels are used for cubicle construction.
-The Panel shall be fully compartmentalized with all doors on the front only.
The panel should have cable entry point , Bus bar mounting system , shrouding of bus bar etc
- There will three live bus bar and one neutral bus bar running horizontally and vertically .
-Earth bus bar will run all around the panel . The size will be same as neutral . Earth will be ultimately connected with station earth at the end of the panel.
-Bus bars shall be of high conductivity Aluminum with current density of 800 A Inch² .
- As per requirement and to facilitate easy transportation panels are sent as per transportation size which are then assembled at site .