VFD Challenges for Shipboard Electrical Power System Design

5Shipboard VFD Application and System Grounding

The shipboard power system is different from the shore‐based power distribution with neutral line and ground line. The shipboard power system is ungrounded. The shore‐based power distribution is with neutral line and ground line. However, there are special cases on ships where the grounded distribution is used in a controlled manner, such as shipboard workshop equipment.

In some installations the shipboard power system, particularly the low voltage grounded distribution system is used along with the 450 V ungrounded system. This feature of ungrounded ship service power system distribution and low voltage grounded distribution system is presented in view of the VFD installation (See Figure 5.1).

5.1 VFD Motor Controller and Grounding

Shipboard VFD motor controller installation in an ungrounded power system EMC/EMI noise played a vital role. To mitigate VFD‐generated EMI noise and to prevent high frequency current affecting other equipment, the understanding of equipment grounding, drain wire requirements, and cable shielding, as well as termination of the main conductors, drain wires, and shielding is very important.

The following termination guidelines are recommended:

1. VFD drain wire (ground wire) should have a positive ground connection at the VFD enclosure as well as the motor enclosure, ensuring low resistance path.
2. The ground wire should of the same size as the power cable to maintain the same current level protection. ...