Introduction
Maryland Port Administration’s Dundalk Terminal operates several dockside cranes for the loading and unloading of containers from ships. Cranes No.7 and 8 were originally installed in 1977 by IHL. In 1996 MPA replaced the obsolete GE equipment with Square D/Telemechanique controls. The upgrade included raise, boom extension, speed increase and control system upgrades. The electrical equipment supplied only a decade ago quickly became obsolete and began causing problems with the crane’s operation.
Downtime was increasing, components were failing and even the diagnostic capabilities were of little use. MPA also soon learned that technical support and parts were virtually impossible to obtain. MPA was at risk of losing one of these vital cranes for a large period of time if a major malfunction of the system should occur. MPA reviewed several different options for the upgrade. Their main objectives were:
1. Eliminate the Telemecanique Rectivar 4 electronic system
2. Replace the existing Telemecanique PLC
3. Eliminate the exposure of the port to downtime due to obsolete electrical parts
4. Complete the upgrade in a fourteen-day window
Bids were solicited for the electrical upgrade of both cranes No.7 and No.8. Each supplier was asked to present the most economical solution available. In many cases, vendors proposed the complete removal of both DC drives and associated hardware. Most proposed Installation schedules that were long and well in excess of 14 days. Avtron presented a solution that kept the large DC drive on the Hoist/Gantry section and replaced the smaller unit on the Trolley/Boom. By not replacing the Hoist drive, Avtron could save time during installation and provide a schedule that fit under 14 days. Avtron also demonstrated to the customer that its hardware could be used on any type of DC drive for retrofitting, and provided several successful references of similar projects.
To retrofit or replace
Many factors go into determining whether a section is a candidate for retrofitting the SCRs. A typical rule of thumb is that sections rated 250HP and above can be upgraded economically by keeping the original SCR power conversion system. Other key factors in this decision include:
1. Drive size and complexity
2. Whether or no the SCRs are still commercially available
3. SCR firing type
4. Drive Location and accessibility
5. Customer goals and objectives
Reviewing the customer’s cranes and analysing the key factors listed above, Avtron decided to propose a combination retrofit.
Key factors in the decision included:
1. The Hoist/Gantry drive was rated at 1,750 ADC which is a strong candidate for retrofits
2. Trolley/Boom drive was rated at 280 ADC which was small and could easily be replaced by a stand-alone drive
