I am involved in upgrading a 30 year old analog DC drive to a Digital DC drive. This upgrade is often given a name like digital front end. It provides new up to date electronics, but keep existing contactors, bus work, power semiconductors, cabling and motors.
The only possible reason for this type of upgrade is economic. The cost of upgrading the drive must be less than the cost of a new drive, motor and cabling to the motor. This only applies to large powered motors. I submit 100 HP and larger. This week we are working on a 1500 HP drive. Two more will follow in future shut downs.
Keep in mind that the digital front end is not a standard product and needs custom engineering. Are the new electronics capable of gating existing Thyristors? Measurements should be taken. Are the existing dc shunts and AC current transformers compatible with the new controls? Control modifications will be required (PLC or drive master). Will the upgrade meet the local electrical codes? A full review of the entire drive may be required.
How long does a digital front end upgrade take? I have heard 24 hours, but have seen 72 to 178 hours for the first successful upgrade. The cost is one or two electricians and a drive engineer for that period. The electricians on this job should be the very best available. Wiring up water heaters is not good practice for upgrading drives. One drive engineer can support several drive upgrades at the same time. Expect to discover short shipped items such as connectors or powers supplies.
I will let you know how the commissioning goes in a future blog.