MEO Orals on Marine Electro Technology Function 5- Part 5

What is synchroscope ?

• An instrument fitted at the main switchboard which indicates when two electrical supplies are in synchronism and can be paralleled.
• An instrument, which indicates that, voltages, frequencies and phase angle of two electrical supplies of running machine and incoming machine, are in synchronism and can be paralleled.
• Synchroscope should not be left in circuit for more than 20 minutes as it cannot continuously rotate.
• Synchroscope is a small motor with coils on the two poles connected across red and yellow phase of the incoming machine and the armature winding supplied from the red and yellow switchboard bus bars.

What is the synchronizing ?

• The process of bring the voltage, frequency and phase angle of electrical supplies into line in order to be paralleled and share the loads.

Explain Synchronising methods ?

• Synchroscope is the main method
• Back-up methods are: Lamp dark method
• Lamp bright method
• Rotating lamp method or Sequence methods (preferable)

Explain Rotating lamp method or Sequence method ?

1. One of the lamps known as key lamp is connected in one phase
2. Other two lamps are cross-connected
3. If two frequencies differ, lamps will bright up in rotation. Clockwise indicates incoming machine is fast, and counter-clockwise indicates it is slow
4. Synchronising moment is when key lamp is dark and other two lamps equally bright
5. If phase rotation is wrong, all lamps will become bright and dark together.
6. Remedy is to interchange any two phase connections

How to parallel the two generator with the aid of synchroscope  on ships ?

1. All meters and indicators must have in good working order.
2. Start the incoming generator with the correct staring procedure.
3. Check the working condition by readings pressure gauges, thermometer and audible and visual.
4. Watch for a minutes until prime mover come to stable.
5. Check the voltage of existing and incoming generator on the switchboard, check trip if have reset.
6. Move the selector switch to incoming generator. At that time, synchroscope pointer will rotate clockwise or counter clockwise direction.
7. Check the frequency and voltage of existing and incoming.
8. Carry out the adjustment by means of speed adjuster of prime mover to obtain the condition such that synchroscope pointer rotate in the clockwise direction at a speed of about 4sec/rev.
9. Close the circuit breaker of incoming generator when the pointer reaches just before 12’ O clock position.
10. Made off the selector switch.
11. Made load shearing the two generators by the speed adjuster of generator.

How do you parallel the two generators if synchroscope is out of order ?

1. If synchroscope is out of order, the two generators can be paralleled by emergency synchronizing lamps with sequence method.
2. The lamps are fitted as triangle forms, one on top and two on bottom.
3. To make parallel, reset if any trip
4. Move the selector switch to incoming generator. At that time, synchronizing lamps will give bright and dark sequence rotate clockwise or counter clockwise direction.
5. Check the frequency and voltage of existing and incoming.
6. Carry out the adjustment by means of speed adjuster of prime mover to obtain the required frequency.
7. Adjust the speed to meet the slow clockwise direction.
8. Incoming machine breaker is closed by hand when the top lamp (key lamp) dark and the both bottom lamps are equal brightness.
9. Off the selector switch and make load sharing the two generators by speed adjusting.

How do you monitor the correct instant for synchronizing without the aid of synchroscope or synchronizing lamps ?

1. It can be synchronized with 500V voltmeter as follow.
2. Connect a pair of 500V voltmeter probes across the one phase of the incoming machine circuit breaker and bus bar.
3. Adjust the generator speed until the voltmeter slowly fluctuates from zero to maximum.
4. Close the breaker when the voltmeter passes through zero.

Can you parallel the load of main G/E with emergency G/E and shore supply ?

• It cannot paralleled, circuit breaker interlocks are arranged in this system.

What are the generator safety devices ?

1. Over speed trip
2. L.O low pressure trip and alarm
3. F.O low pressure alarm
4. Jacket water high temperature alarm
5. Jacket water high temperature trip
6. Thermometer
7. Pressure gauge
8. L.O high temperature alarm
9. Dip stick
10. Crankcase relief valve

 Methods of armature reaction compensation ?

• By fitting inter poles between the main poles
• By fitting carbon brush rocker
• By fitting neutralizing winding

Reference:

Oral Guide by – MIN ZAR TAR

MEO Orals on Marine Electro Technology Function 5- Part 5