MX321 AVR Voltage Regulator Guide

3. Analog input (A1, A2)

Used for connecting power factor controllers (such as Newage PFC3) or other external regulating devices. Input range ± 5V DC, input resistance 1k Ω. Important safety warning: Any device connected to this input must be completely floating (isolated from ground), with insulation withstand voltage not less than 500V AC. A1 is the internal 0V reference point of AVR, A2 increases excitation with positive polarity and decreases excitation with negative polarity. TRIM potentiometer adjusts input sensitivity (counterclockwise for zero gain, clockwise for maximum).

4. Current limit CT (I Limit)

Terminals S1 and S2 can also be configured with current limiting CT (appropriate transformer ratio needs to be selected). When the stator current exceeds the set threshold, the AVR automatically reduces excitation, limits short-circuit current, or assists in starting the motor. This function has an internal timer of 10 seconds, which will be turned off and self-locking when exceeded.

5. Overvoltage trip output

When the output voltage of the generator exceeds 300V AC and lasts for more than 1 second, the internal power devices of the AVR are turned off, and the external excitation circuit breaker tripping coil can be driven at the same time. Coil parameters: 10-30V DC, 20-60 Ω.

Panel control function and fine tuning

The MX321 printed circuit board is equipped with 9 adjustable potentiometers (partially factory sealed) and multiple jumper options. The adjustment direction for each function is shown in the table below:

Control Name Function Description Clockwise Effect

VOLTS regulates the output voltage of the generator to increase the output voltage

Stability prevents voltage oscillation (damping) and increases damping, resulting in a slower response

UFRO sets the underfrequency roll off inflection point frequency to decrease the inflection point frequency (seal preset)

DROOP setting increases the sag of parallel reactive power (5% typical)

TRIM analog input sensitivity increases external control signal effect

EXC overexcitation trip level increases trip threshold (sealed)

When DIP is under frequency, the additional voltage drop depth increases the slope of the drop

After DWELL under frequency recovery, the delay time for voltage recovery increases

I Limit: Increase the current limit threshold of the stator and raise the current limit point

OVER V overvoltage trip level (300V fixed) not adjustable (sealed)

Ramp no-load pressure building ramp time extends soft start time

Detailed adjustment steps:

1. Voltage regulation (VOLTS)

Rotate VOLTS counterclockwise to the bottom before starting.

If an external remote adjuster is connected, place it at the midpoint.

STABILITY should be placed at the midpoint first.

No load operation, frequency slightly higher than rated (recommended for 50Hz system 50-53Hz, 60Hz system 60-63Hz).

Be careful to rotate VOLTS clockwise until it reaches the rated voltage (e.g. 400V or 480V).

If there is voltage fluctuation, refer to the next step to adjust the stability and then fine tune again.

2. Stability adjustment and jumper selection

There are jumper wires on the MX321 board, and different response speeds are selected based on the generator power. Usually, select "LOW" for low-power units and "HIGH" for high-power units. Refer to PCB printing for specific location.

Slowly rotate the STAILLITY counterclockwise under no load until the voltage begins to become unstable (swing or drift).

Pull back a little further clockwise to find the "critical damping" point where the voltage is stable and closest to the unstable region.

This can balance response speed and stability.

3. Underfrequency Rolloff (UFRO) Adjustment

After the generator speed falls below the set threshold, the UFRO circuit reduces the voltage in a "V/Hz" ratio to prevent overload of the excitation system.

The factory has pre-set 50/60Hz and 4-pole/6-pole through jumper wires. The red LED lights up when the frequency is below the inflection point (such as 47Hz or 57Hz).

Users generally do not need to adjust; If optimization is needed, the LED can be monitored to light up just when the rated frequency drops by 1-3Hz.

4. Parallel droop (DROOP) adjustment

Only used when parallel operation is required. Need to connect the sagging CT.

Typical requirement: Voltage drop of 5% at full load with zero power factor.

Actual test: During single machine debugging, wiring can be temporarily omitted; Before merging, each machine adjusts DROOP to evenly distribute reactive power.

Clockwise increase droop (i.e. voltage drop is greater under the same reactive current), counterclockwise decrease droop.

5. Simulate input TRIM adjustment

After connecting the power factor controller, adjust the output of the controller to maximum (+5V), and turn TRIM clockwise to achieve the desired voltage change amplitude (usually ± 5% of the rated voltage).

If there are no external devices, TRIM can be set to the minimum (counterclockwise).

6. Overexcitation (EXC) and Overvoltage (OVER V) protection

Both are factory sealed settings and should generally not be adjusted on site.

Overexcitation detection: After the excitation voltage exceeds 75V DC and lasts for 8-15 seconds, turn off the power device; Overvoltage detection: Turn off after the main voltage exceeds 300V AC for 1 second.