Procedure for the Operation of Shore Power | Questions & Answers

 

Shore Power

Shore supply is used mainly during dry dock when alternator have to overhaul

Nowadays shore power is used for emission control in ports

Introduction

Generally, shore connection box is provided in the emergency generator room. The shore connection box connects, via a moulded case circuit breaker (MCCB) on the emergency switchboard, to the main switchboard disconnecting switch panel, where an air circuit-breaker (ACB) connects it to the main switchboard bus bar.

When onshore power, the emergency switchboard can be supplied as normal through the main/emergency switchboard bus tie circuit-breakers.

Monitoring lamps for SHORE ALIVE and SHORE MCCB CLOSED are located on the main switchboard synchronizing panel, and a voltmeter and ammeter with the facility to monitor the shore voltage and current is located on the main switchboard.

A frequency meter, ammeter, and voltmeter are located on the emergency switchboard, emergency generator panel with the facility to monitor the shore supply frequency, current, and voltage.

A phase sequence monitoring system, watt-hour meter, and SHORE ALIVE, SHORE MCCB CLOSED, and SHORE MCCB OPEN indicators are fitted at the shore connection box on the emergency switchboard.

The phase sequence should be checked before connecting shore power to the switchboards. When the shore supply has been connected at the box, it should be switched on ashore and the PHASE SEQUENCE TEST push-button pressed. If the phase sequence is incorrect the shore supply must be isolated and two supply phases changed over. The supply should then be reinstated and the phase sequence checked again.

The watt-hour meter is provided to measure and record the power consumed by the vessel when onshore supply.

Interlocking is provided between the ship’s main generator ACBs and the shore supply breaker. The shore supply breaker cannot be closed if any generator ACB is closed. Conversely, none of the ship’s generator ACBs can be closed if the shore supply breaker is closed. This arrangement prevents the shore supply from being paralleled with any other supply.

Components of shore connection box

Data plate- it contains ship’s working voltage, frequency, and instruction for shore connection.

Voltmeter

Frequency meter

Phase sequence indicator

Wattmeter

Indication lamps

Circuit breaker and fuses

Pre checks before connection of shore power

Check the shore connection root hatch cover for freeness and obstructed with any object.

Make sure the receiving terminals are good in order.

Check the indication lamps

Make sure the ship’s batteries are fully charged.

Checks during shore connection

Check the shore power cable condition

Carry out megger test for shore power cable.

Connect the shore power cables into the shore power box in the emergency generator room via the given way.

Make sure the earthing cable arranged to shore earthing to the ship’s hull.

Note down and take the pictures of shoreside wattmeter readings and ship wattmeter readings.

Switch on the shoreside power. Confirm the SHORE ALIVE indicator lamp is illuminated at the shore connection box.

Ensure the voltage, and frequency of the shore supply with ship rated voltage, and frequency.

Check the phase sequence is correct.

Procedure for the Operation of Shore Power Reception

Isolate the emergency generator to ensure that it does not start.

Isolate all non-essential services. Reduce load at the main switchboard to the absolute minimum.

Turn the GEN CONTROL selection switches on the main switchboard generator panels to the MANUAL position. This is to ensure that no main generators start when the vessel blacks out.

At the main switchboard, open all the generator ACBs. The vessel blacks out.

Close the breaker for shore power at the shore connection box.

The bus tie at the main switchboard disconnecting switch panel is not fitted with an Undervoltage trip and will therefore remain closed upon the loss of power. The shore power will therefore now be supplying the main switchboard.

Proceed to supply essential services as necessary.

If no maintenance is scheduled for the emergency generator, it may be left on automatic standby. The emergency generator will then feed emergency lighting, etc, in the case of failure of the shore supply.

The shore supply should be closely monitored to ensure the rated current limit is not exceeded.

Procedure for Transfer from Shore Supply to Main Diesel Generator

Isolate all non-essential services. Reduce the load at the main switchboard to the absolute minimum.

Ensure the main switchboard GEN CONTROL selection switches are still set to the MANUAL position. This is to ensure that no main generators start when the vessel blackout.

Set the emergency generator MODE switch at the emergency generator engine local control panel to MANUAL.

Run up the selected main generator on local control.

Open the shore power breaker at the emergency switchboard shore connection panel. The main and emergency switchboards blackout.

Turn the relevant ACB CONTROL switch at the main switchboard synchronizing panel to the CLOSE position.

The ACB will receive a close command and will close. The main diesel generator is now supplying the main switchboard. The bus tie receives a close command and closes, the BUS TIE CLOSED indicator on the emergency switchboard is illuminated, the emergency switchboard is now being supplied from the main switchboard.

Check the voltage and adjust the frequency to 60Hz. Supply main lighting and other required consumers.

Set the emergency generator for its normal automatic start condition.

Isolate the shore supply from ashore and remove cables.

Note down and take the pictures of shoreside wattmeter readings and ship wattmeter readings.

What happens if the shore supply voltage is lower than the rated voltage?

The induction motor will draw more than the rated current, and it leads to overheating of the windings.

Reduce the starting ability.

Reduce the motor's life.

Magnetic flux is reduced, and it reduce the torque capability.

Affect the motor to handle the load.

What happens if the shore supply voltage is higher than the rated voltage?

High voltage on a motor tends to push the magnetic potion of the motor into saturation. The overvoltage can cause excessive current to flow as well as creating excessive voltage stresses. In both cases, the electrical insulation system inside the motor or equipment can be degraded reducing life or causing damage.

Effects of frequency variations

For induction motor:

RPM is directly proportional to the frequency.

So, it will affect the speed of motor.

Example:

When a 50 Hz motor is made to run on 60 Hz supply:

 [(60 – 50)/ 50]  X 100 = 20 %.

The motor runs 20 % faster than its normal rated speed. This is not safe for the equipment as the insulations may be rated for lesser capacity and windings may burn out.

If your ship is designed for 60 Hz at 440 V – what value should supply voltage be if operating the shore at 50 Hz?

The ratio voltage/frequency in the case of motors and transformers.

The ratio for 440V and 60 Hz would be 7.33 V/Hz.

So, 7.33 X 50 = 366

Which is closer to the standard 380 volts 50Hz.

By doing this the efficiency of pumps will be reduced, and we definitely have to keep an eye on the temperatures of the motor windings.

In this case, may not be able to load the machines up to their rated power, but for lower power requirements supplying them at 380V/50Hz will work. Definitely, other stated parameters (efficiency, power factor, etc) will not be met.

With regard to electronic equipment, this type of equipment uses AC/DC converters anyway, so they should not be affected.