QnA: MSBD (MAIN SWITCHBOARD)

Q. What is the IP(Ingress Protection) degree provided for MSBD?

A. IP21

Q. What are the safeties protection provided by ACB?

A. In above list, Some are optional It may have or may not

• Adjustable Long Time Delay Trip -LTD (Normally 105 to 120% of Full Load Current, Trip time from 20 to 120 seconds)
• Adjustable Short Time Delay Trip -STD (Normally 200 to 600% of Full Load Current, Trip time from 0.1 to 1 seconds)
• Adjustable Instantaneous Trip -INST (1000% of Full Load Current, Instant Trip)
• Adjustable Pre Trip Alarm -PTA
• Adjustable Ground Fault Trip -GFT
• Under Voltage Trip -UVT (set at 50% of rated voltage)
• Arc Contacts, Arc Runner, Arc Chutes

Q. What are the safeties provided for MSBD?

A. Following safeties are provided

• Overload protection
• Under frequency protection(58Hz trip,59Hz alarm)
• Over frequency(62Hz trip,61Hz alarm)
• Under Voltage protection(80% of rated voltage,120% of rated voltage)
• Over Voltage Protection
• Reverse Power protection
• Preferential trip protection.
• Continuos Insulation Monitoring is also provided.
• No liquid line over MSB
• Ebonite Handrail
• Approved insulation rubber and Gloves ( It should sustain 15KVA for at least 1 minutes)
• 0.6 meter clearance area all around MSB(For High Voltage its 1 meter)
• Danger, High Voltage, Precaution against electric shock, Burn Playcards
• Circuit diagram of MSB should be near MSB
• MSB is installed in less vibration area of ship
• 1 portable CO2 extinguisher near MSB

Q. How the reverse power is detected?

A. It is difficult to determine the direction of AC to make tripping of generator during motoring. For this purpose the reverse power relay utilizes technique of monitoring current lagging direction to voltage. During sourcing (Generating)the current will lag the voltage by some angle positive way. During motoring of generator this positive lagging to voltage will change to negative lagging to voltage. This change in phasor angle will cause the aluminium disc inside the relay to rotate in opposite direction causing to trip the ACB

Q. What are setting values for reverse power relay?

A. 15% of KW for 4 stroke engine, 25% for 2 stroke engine at synchronous speed. For steam turbine 3% of KW.

Q. What is preferential tripping?

A. When Generator load reaches 110% trip operates after a fixed time delay causing non-essential loads to be shed in order to avoid overload on generators. The tripping sequence is as follows:

First tripping at 5 sec:
Shut down non-essential loads [air condition, entertainment, accommodation fans, cargo hold fans, amplifiers, etc.] to reduce the generator load.
Second tripping at 10 sec:
Shut down essential loads [services required for running the ship properly, leaving the loads of top priority services to maintain Propulsion and Navigation.
if generator load is still high.
Third tripping at 15 sec:
Shut down the main generator as last action, if the load is still too high, it may be due to short circuit or insulation breaking.

Q. What is mechanism of Preferential tripping?

A. Now PLC or Embedded system based PMS(Power Management System). Earlier Dashpot & Timers was used.

Q. What are the methods of synchronization?

A. Synchroscope, Bright Lamp Method, Dark lamp method, Voltmeter method.

SYNCHROSCOPE METHOD: When the incoming generator frequency is same as bus bar frequency say 60Hz and indicator in synchroscope rotates slowly clockwise(about 5 to 7 seconds per revolution). The incoming generator breaker is closed when indicater indicates 12 o clock position in Synchroscope Usually at 11 o clock closing action is taken by personnel because of human response time.

DARK LAMP METHOD: Two lamps are connected to same phase of incoming generator and busbar. Flickering of lamps are monitored. Flickering must be slow and when both lamps are dark ACB is closed.

BRIGHT LAMP METHOD: Two lamps are connected to different phase of incoming generator and bus bar. In phase condition is shown when both lamps are equally bright.

VOLTMETER METHOD: Connect Analog voltmeter(except up to 500V on a 440V system). This procedure is done safely behind synchroscope terminals. Check circuit diagram of synchroscope before doing it. Adjust generator speed until voltmeter move very slowly from zero to maximum and close the breaker when the voltmeter indication passes through zero.

Q. What is Dead-Front Switchboard & Dead Switchboard?

A. Dead-Front switchboard is one with insulated switches and no exposed terminals on front.

Dead-SwitchBoard is one in which there is no supply available

Q. What is Sequential starting?

A. The Automatic starting of Essential machineries after power is restored from Blackout condition. Following is the general sequence starting of machineries.

Immediate starting machineries after power restored without any delay: 1)Steering gear 2)Fuel Oil Feed & Booster pump 3)Radio & Navigation Equipment 4)Engine Room & Accommodation Lighting
05 Secs after main power is restored: 1) Stern Tube Lube oil pump 2) Main LO Pump
10 Secs after main power is restored: 1) MCSW P/P 2) LT CW P/P 3) M/E JCW p/p
15 Secs after main power is restored: 1) Deck seal water p/p 2) Aux.Boiler & Comp.Boiler Feed p/p
20 Secs after main power is restored: 1) All E/R fans 2) Fire & GS Pump

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