20G11RD011AA0NNNNN — 755 Series AC Drive, 480V, 7.5 kW, Regenerative

The 20G11RD011AA0NNNNN is a 480V three-phase AC drive from the 755 series, configured for regenerative (RD) operation. Output current is 11A — approximately 7.5 kW / 10 HP under heavy duty conditions. The regenerative front-end replaces the standard passive diode rectifier with an active converter that can both draw power from the AC supply and return energy back to it, rather than routing braking energy to resistors as heat.

Regenerative drives are specified where the application regularly produces braking energy — hoist and crane drives decelerating heavy loads, winders managing web tension through speed transitions, test rigs cycling between acceleration and deceleration — and where that energy is significant enough that burning it in a resistor is either thermally problematic or economically wasteful. At 7.5 kW, the regenerative option starts making operational sense in high-cycle applications; at higher power levels, the energy recovery argument becomes more compelling with every cycle.

Specifications

Parameter	Value
Part Number	20G11RD011AA0NNNNN
Series	755 Series
Output Current (Heavy Duty)	11 A
Motor Power (approx.)	7.5 kW / 10 HP @ 480V
Input Voltage	380–480V AC, Three-Phase
Front End	Regenerative (active AFE — active front end)
Output Frequency Range	0–400 Hz
Control Modes	V/Hz, Sensorless Vector, Flux Vector (with encoder option)
Regenerative Power Return	Yes — energy returned to AC supply
Input Power Factor	Near unity (~0.98 with AFE active)
Input Current Harmonic Distortion	Low (AFE reduces input harmonics vs diode rectifier)
Braking Resistor	Not required for regenerative operation
Option Card Slots	Up to 5
Safe Torque Off	Category 3 / PLd (standard)
Enclosure	IP20 / Open Type
Operating Temperature	0°C to 50°C (derate above 40°C)
Standards	UL 508C, CE, RoHS

Commissioning Considerations

The regenerative front end requires commissioning steps beyond a standard drive. The AFE must be synchronized to the AC supply phase and frequency before it can return energy — an AFE that's not properly commissioned will fault on regenerative events rather than returning energy cleanly. Specific points to address in the drive parameters before first run:

AFE input voltage and frequency: configure accurately. An AFE synchronized to the wrong nominal voltage will not regulate the DC bus correctly during regeneration.
Input line reactor: the AFE typically requires an input line reactor (1–3% impedance) to limit the rate of current change during switching. Verify the reactor is installed and sized per the drive's installation guide — operating the AFE without the specified input reactor risks input current waveform distortion and potential supply tripping.
Precharge sequence: the AFE controls the DC bus precharge. Verify the precharge completes successfully before the first run command — an incomplete precharge fault on startup is usually a configuration or wiring issue with the AFE, not the output stage.
Regenerative test: after standard drive commissioning, perform a controlled deceleration test at reduced load and verify the AFE returns energy to the supply (check input power meter for negative power flow during deceleration). Confirm no DC overvoltage faults occur during the test.

FAQ

Q: Is a braking resistor still needed with this drive?

For normal regenerative operation, no. The AFE returns braking energy to the AC supply instead of routing it to a resistor. However, some installations include a small braking resistor as a backup for abnormal grid conditions — if the supply voltage rises above the AFE's regeneration ceiling (e.g., during a utility overvoltage event), a backup resistor can absorb the excess. Whether this backup is needed depends on the supply quality at the installation site.

Q: How much energy is actually saved compared to a non-regenerative drive?

This depends entirely on the application's duty cycle. For a crane or hoist that decelerates heavy loads many times per hour, regenerative recovery can offset 20–40% of total energy consumption. For a pump or fan that rarely brakes, there's almost nothing to recover. A calculation of the application's braking energy per cycle multiplied by the number of cycles per day gives a realistic estimate before committing to the regenerative option.

Q: Does the AFE require any special supply quality or a dedicated circuit?

The drive requires a stiff, balanced three-phase supply. Highly distorted supplies or supplies with significant voltage imbalance can interfere with the AFE's synchronization. An input line reactor (typically 1–3% impedance) is required between the supply and the drive — this is both a protection requirement and a waveform quality measure for the AFE's phase-locked loop.

Q: Can the regenerative drive be retrofitted into a system that previously used a braking resistor?

Yes, subject to the input line reactor and supply quality requirements. Physically, the drive replaces the existing non-regenerative unit; the braking resistor and DB transistor circuit become unnecessary. The input reactor typically needs to be added. Verify the existing supply circuit can accept the AFE's near-unity power factor draw and the briefly reversed power flow during regeneration — some older facilities have protection equipment configured to trip on reversed power flow.

20G11RD011AA0NNNNN New 20G11RD011AA0NNNNN 755 AC Servo Driver