Main Switchboard (MSB)


The main switch board shall consists of switch gears, neutral switches, protective device instruments, power factor regulator device,

Main Switchboard

Main Switchboard

and synchronizer, mounted in sheet steel, floor mounting cubicles type, electrically and mechanically connected to form a composite switchboard.

The switch board and the component shall be fully protected against tropicalized ad climate condition and shall be dust and splash proof.

Rubber gasket plates shall be provided for mounting equipment and insulating panels between compartments shall be of high quality Bakelite.

The switch board shall be designed to serve two (2) units’ turbo alternator, three (3) units’ diesel genset, out-going panel and blank space to future extension of the mill capacity to 60 tons ffb/hour.

All steel used for the switch board construction shall be thoroughly cleaned of

all rust, oil and grease with dioxide or equal before painting. Painting shall be

two (2) coats of zinc chromate primer followed by two (2) coats of semi gloss

finishing synthetic enamel.

Bus Bar

The bus bar shall be tinned, air insulator and capable of carrying continuous load per phase at 3.600 amperes without exceeding the maximum permissible temperature in an ambient temperature of 47 degree C. The cross section for phases of each bar not less than 2.400 sq. mm, and for the neutral not less than 1.200 The bus bar shall be of unit length, of high conductivity hard drawn copper, rectangular bar. Color coding of the bar shall be in accordance with PUIL 1987.

Switch Gear

Five (5) units’ switch gear for turbo alternator and diesel generating sets shall be installed in the main switch board.

Switch board Gear for turbo alternator shall be of horizontally draw out type, airbreak metal clad cubicle type at suitable rating, isolating plugs and socket with

automatic safety shutters and having provision for pad locking. The rupturing capacity shall be minimum 31 MVA at 380 volts. Test certificate proving this rating from “Lembaga Masalah Ketenagaan” (LMK) PLN or other internationally recognized body shall be submitted to the Engineer. The switch gear shall be triple pole, manually operated single air break trip face integrated isolator.

Switch gear for diesel gensets could be of fixed type, there fore 3P-N Isolator or disconnector shall be installed between the bus bar and the switch gear for isolating during maintenance.

Neutral Switch

For neutral switch purpose, single pole knife switch shall be used. Earthing provision for the neutral shall be done at load side of the switch.

Power Factor Corrector

Power factor corrector computerized system as made by Nokia of Finland or equivalent shall be installed the system shall capable to improve power factor from 0.65 to about 0.95.

The power factor corrector in general comprises of reactive computerized power regulator and capacitor bank. The regulator shall be 12 steps, digital display, manual and automatic operations, fast response, panel mounting with minimum face 144 x 144 mm.

The capacitor bank shall include 8 step of capacitor, expandable to 12 steps; capacitor element shall of self healing and dry materials. Insulation level 3 Kv Rms/15 Kv Crest.


All the six generating sets can be paralleled to the common bus bar at the main switch board. Each of generating set own synchronizing switch and key, Generally the synchronizer comprise of synchronoscope, double volt meter, double frequency meter synchronizing lamp and fuses, that installed in a particularly swing type panel. The panel shall be positioned that easily in monitoring during synchronizing operation.

Protective Device, Instruments and Others

The main switch board also provided with followings:

Protective devices to protect generating sets from reverse power, earth fault, overload and under voltage conditions. If such condition happens, protective device will actuate the switch gear to trip.

Instruments for reading electrical units such ampere meters, volt meters, frequency meters KWH meter, hour counter, KW meters power factor meter and others as necessary. The instruments shall have a minimum 144 mm x 144 mm face of suitable range and rating.

A panel heater, switch and indicator shall be installed in the base of each cubicle to prevent condensation. The heaters’ power not less than 80 watt.

Main switch boards’ lighting shall be installed in the canopy of board. Lighting system shall be arranged that in power interruption condition, some of lighting continuously lit by the Uninterruptible Power System (UPS) that provided for such conditions.

Out Going Feeder Cubicles

Out going panels shall be mechanically and electrically in one composite with the main switch board. The panels shall be provided with appropriate circuit breakers, ampere meters, volt meters, selector switch etc, to serve the following distribution board and motor control centres in and out of the mills:

01. Effluent treatment plant.

02. Office.

03. Oil storage tank.

04. Fruit reception.

05. Boiler demineraliser plant.

06. Studge recovery.

07. Workshop distribution board.

08. Domestic.

09. Water treatment plant.

10. Boiler no.1

11. Boiler no.2

12. Clarification station.

13. Kernel recovery station.

14. Threshing, pressing and depericarping station.

15. Compound lighting.

16. Lighting.

The circuit breaker shall have height breaking capacity, quick make and brake, thermal and magnetic setting adjustable, on and off trip states shall clearly indicated in different colours. The circuit breakers shall be of Merlin Gerin, Mitsubishi.

Out going to compound lighting shall be controlled manually and automatically by time switch.


Related Post :

Motor Control Centre (MCC) and Distribution Boards (DB)

Power and Lighting Circuits

Lightning Protection and Earthing


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