Ship to shore power operation practice: phase sequence verification, negative sequence protection and switching SOP process

Mains, emergency and shore power switching practices

Ship Power Station Management Series: Power Conversion Logic and Shore Power Access Specification

I. Logical architecture of the electricity supply relationship

At present, the high-voltage power of large ships can be operated in parallel with the medium-voltage shore power for a short period of time, and the low-voltage power system still in use on ships is introduced here as an example. Through the simulator software, it is necessary to sort out the power supply relationship of main distribution board, emergency distribution board and shore power:

(1) When power is supplied to the main switchboard:
The contact switch closes to supply power to the emergency switchboard. Emergency generator stops and emergency generator main switch is disconnected. Shore power main switch disconnected.

(2) When the emergency generator is powered:
Contact switch disconnected. Shore power main switch disconnected.

(3) When shore power is supplied:
The contact switch closes to supply power to the main and emergency switchboards. Main and emergency generator circuit breakers are disconnected.

II. Operating instructions for connection to shore power

(i) Conditions for connection of ships to shore power

The main conditions that should be met when a ship is connected to shore power are: the shore power and ship's electricalSame electrical system, rated voltage, rated frequencyof shore power and ship powerphase sequence is identicalThe ship's generators should be disconnected from the power grid. It should also be confirmed that all generators on the ship have been disconnected from the grid.

(ii) Use and monitoring of shore power boxes

Shore power boxes generally have shore power indicators, switches, fuses, shore power terminals, and phase sequence indicators (or negative sequence relays).

1. Phase Sequence Detector (Indicator)

Phase sequence determiners are also called phase sequence indicators. The three phases of the circuit are loaded asymmetrically. When a phase connected to capacitor C is set to phase R, the brighter phase is phase S and the darker phase is phase T. When the relationship between the two lights is the same as the sign on the shore power box, it means that the shore power phase sequence is the same as the ship's power phase sequence. When the relationship between the two indicator lights is the same as the sign on the shore power box, it means that the shore power phase sequence is the same as the ship's power phase sequence.

2. Negative Sequence Relay

Negative sequence relay is also called reverse sequence relay. When the shore power phase sequence is correct and the three-phase voltage is symmetrical, the output voltage is 0 and the switch can be closed. When the phase sequence is inconsistent or broken, there is voltage output and the switch cannot be closed. It is used to prevent wrong phase sequence connection or single-phase operation.

(iii) Shore power connection and ship-to-ship power operation procedure (SOP)

Shore power access steps

- ① Notify the pilothouse and centralized control room; check the shore power voltage and frequency to ensure that it is consistent with the ship's power.
- ② Connect the power cable to the terminal block, close the shore switch, and the phase sequence indicator lights.
- ③ Adjust the phase sequence switch to ensure that the green light is on for the correct phase sequence (as shown in Figure 8-8).

Figure 8-8 Shore Power Box Phase Sequence Indicators

- ④ Press the shore power box closing button and the closing lamp lights up.
- ⑤ Disconnect the load, disconnect the main generator switch, and close the main switchboard shore power switch in turn (as shown in Figure 8-9).

Figure 8-9 Shore Power Switch

(vi) Discontinue operation of the generator set.

Shore power to ship power operation procedure

① Notify the relevant compartments; switch the control mode to manual and start the main generator set in readiness.
② Disconnect the shore power switch at the main switchboard.
③ Immediately close the main switch of the generator set to restore the power supply and start the critical load according to the procedure.
④ Press the break button on the shore power box.
⑤ Disconnect the shore switch and remove the shore power power cable.

C. Safety Checklist for Connecting to Shore Power

(1) When connecting to shore power, the shore power and ship power of theCurrent type, rated frequency, rated voltageThere must be consistency.

(2) When the shore power is a three-phase, four-wire system, the shore power shall beneutral conductorConnect to the terminal block on the shore power box that connects to the hull. Shore power can only be switched on when the hull is connected to the shore power neutral.

(3) Close the shore power box switch, and only when the shore power phase sequence is the same as the ship's power phase sequence can you go to the main switchboard to perform the transfer operation.

(4) Risk of prohibited parallel operation: When the ship is connected to shore power, the ship's generator is strictly prohibited from being switched on to supply power. Only after the shore power is removed can the generator be turned on to supply power, and it is impossible for both to be turned on at the same time (electrical interlocking protection).