Ask an electrical contractor what a medium-voltage drive project involves and the drive itself is only the first item.
There is the phase-shifting transformer, usually a separate piece of equipment with its own footprint, its own foundation, its own cabling and its own commissioning. There may be harmonic filtering to satisfy the utility. There is often an output filter, because long cable runs and steep switching edges are hard on motor insulation.
Four line items, four sets of interfaces, four things to coordinate.
Let’s be precise about the claim in the headline, because it matters technically. The transformer has not been eliminated.
A multi-level cascade drive needs a multi-winding phase-shifting transformer to feed its power cells, and the AT27 has one. What changed is that it is a dry, multi-winding transformer inside the drive cabinet, engineered as part of the machine rather than procured, sited and connected as a separate asset.
Figure 1. What an AT27 replaces on the single-line diagram.
The phase shift across the transformer’s secondary windings is what cancels the low-order harmonics. Because the cell count sets the number of secondaries, the AT27 operates at 18 to 66 pulse depending on how many cells sit in each phase.
The result is THD of input current below 5%, and an input power factor of 0.96.
That figure is what allows full IEEE 519 compliance without external filters or add-ons. Not a filter bolted on to meet a limit, but a topology that does not create the problem in the first place.
| Parameter | Value |
|---|
| THD input current | Below 5% |
| Input power factor | 0.96 |
| Rectifier pulses | 18 to 66, depending on the number of cells per phase |
| THD output voltage / current | Below 5% / below 2% |
| Transformer type | Dry, multi-winding phase-shifting |
| Winding material | Aluminium (RD); copper with aluminium optional (ED RG) |
| Insulation class | Class H, maximum winding temperature 180°C |
| Efficiency | Not less than 96.5% (RD); not less than 97% (ED RG) |
| Overcurrent | 110% for 120 s; 140% for 3 s |
| Motor types | Induction and permanent magnet synchronous |
The output side matters just as much
The multi-level output waveform gives THD of output voltage below 5% and output current below 2%.
In practice, that removes the argument for a dv/dt or sine filter on the motor side, which is why the AT27 RD is specified with no output filters.
For a retrofit, that is the difference between reusing the existing motor and cable run and rewriting the scope to include both.
The AT27 line splits by what the application does with its energy.
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AT27 RD is the two-quadrant drive for standard industrial duty, where simplicity and clean power matter more than complexity. Single or double cabinet depending on power, single-side service access so it can sit against a wall, forced-air cooling with roof-mounted fans whose speed follows the real-time temperature of the transformer and IGBT modules. Door filters can be replaced without shutting the drive down.
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AT27 ED RG is the four-quadrant regenerative version, for applications that need vector control and want the braking energy recovered into the grid rather than burned in a resistor.
| Input voltage | AT27 RD active power | AT27 ED RG active power |
|---|
| 3.3 kV | 160 to 2500 kW | 160 to 800 kW |
| 4.16 kV | 200 to 3200 kW | 200 to 1120 kW |
| 6 and 6.6 kV | 200 to 5000 kW | 200 to 1600 kW (6.6 kV) |
| 10 kV | 320 to 6300 kW | Not applicable |
| 11 kV | 320 to 8000 kW | Not applicable |
| 13.8 kV | 320 to 9100 kW | Not applicable |
Both share the UMKA37 controller: a 10-inch touchscreen, a built-in Wi-Fi module for configuration and diagnostics, local control at the cabinet or remote control over digital input, RS-485 or Ethernet, with the control channel switchable on the fly.
What to check before assuming it fits
Two conditions are worth confirming early, because they are the ones that catch projects out.
The AT27 RD is specified for indoor operation, +1 to +40°C.
Rated power holds up to 1000 m above sea level, with a reduction of 1.5% per 100 m above that. High-altitude mining sites need that calculation done at the quotation stage, not at commissioning.
Planning a medium-voltage drive project? Send us the motor rating, the supply voltage, whether you need regeneration, and the site altitude.
We will tell you which AT27 configuration fits and what drops off your single-line diagram.
Request a configuration proposal for the AT27.
