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 .
WARNING: MAJOR CONTRACTOR ( LIKE l&t ML12,10
ML 8 ETC) ARE HAVING MOVING CONTACTS WHICH CAN BE EASILY REMOVED WITH SPECIAL
TOOLS . AT SITE THEFT OF MOVING CONTACT IS VERY COMMON THEREFORE YOU SHOULD BE VERY CAREFUL IN THIS ASPECT
OTHERWISE DURING CHARGING YOU WILL FIND INSPITE OF ALL REQUIRED CONDITIONS YOUR PANEL IS NOT GETTING
CHARGED. MOVING COST MORE THAN 60% OF THE MAIN CONTRACTOR COST.
CONTINUED TO PART-II
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