MX321 AVR Voltage Regulator Guide

After two types of protective actions, the red LED lights up and the generator must be stopped (completely stopped) in order to reset. This is an important safety feature that prevents automatic excitation recovery before the fault is eliminated.

7. Current Limit (I Limit)

Before use, make sure to connect a CT with the appropriate ratio. Adjust the I Limit potentiometer (increase the limiting current threshold clockwise).

After enabling this function, the AVR automatically limits excitation during a short circuit, and the amplitude of the short circuit current is controlled and can last for about 10 seconds. Afterwards, the internal timer cuts off the excitation.

If this function is not used, the CT terminal should be suspended.

8. DIP and DWELL (turbocharged engine adaptation)

When the generator is driven by a turbocharged diesel engine and sudden increase in load can easily cause the engine to smoke or experience a sudden drop in speed, DIP and DWELL can be used to improve the recovery process.

DIP (Drop Depth): Increase the slope of voltage drop when under frequency occurs. Counter clockwise is the standard V/Hz line; Clockwise decreases the voltage faster with frequency, thereby reducing the load torque and helping the engine recover speed.

DWELL (Recovery Delay): After frequency recovery, artificially delay the voltage rebound. This delay allows the engine to recover partial speed before bearing full magnetic load. Increase the delay time clockwise.

Typical start signal: The frequency drops below 45Hz at the moment of starting the unit with a large motor and the voltage cannot be restored for a long time.

9. RAMP (Soft Start)

Control the rise time of the no-load voltage building of the generator, which is about 3 seconds from the factory.

Adjust the RAMP potentiometer clockwise to increase the ramp time (up to approximately 4 seconds) and counterclockwise to decrease it (down to 0.4 seconds). A too short build-up time may result in excessive impact when closing the closed circuit.

Typical Fault Phenomena and Troubleshooting Strategies

Based on common on-site issues, the troubleshooting process is as follows:

Possible causes and solutions for the fault phenomenon

The generator does not build voltage, the red LED does not light up, there is no PMG input, or the AVR is damaged. ① Check whether the PMG wiring is open/short circuited; ② Measure PMG output (should be>100V AC); ③ Check the AVR fuse.

The voltage is too low and the VOLTS potentiometer is not adjustable, resulting in a failure or incorrect induction wiring. ① Check the induction terminal voltage (190-264V); ② Measure the resistance of the external micro adjuster or add a short jumper to terminals 1-2; ③ Try turning VOLTS clockwise to the maximum.

Voltage instability (swing), low stability setting, or generator speed fluctuation ① Adjust the station clockwise until stable; ② Check the performance of the engine governor; ③ Confirm that the jumper settings match the power.

Unequal distribution of reactive power in parallel, inconsistent droop CT transformation ratio or DROOP setting differences ① Check the CT transformation ratio of the two machines; ② Adjust DROOP separately to make the excitation current similar under the same load; ③ Check CT polarity (S1, S2 phase sequence).

After the load is put into operation, if the voltage does not recover for a long time and the DIP/DWELL setting is too large or the UFRO inflection point is too high, ① turn the DIP counterclockwise back to the minimum; ② Set DWELL counterclockwise to zero; ③ Check if the UFRO jumper is mistakenly set to a higher frequency (e.g. if a 60Hz unit misuses a 50Hz jumper).

The red LED is on and cannot reset the overexcitation or overvoltage protection action. ① Confirm that the generator has completely stopped; ② Check if the excitation circuit is short circuited; ③ Measure whether the main voltage exceeds 300V (due to regulator failure or external high voltage intrusion).

AVR overheating is severe, and the continuous excitation current exceeds the limit or the ambient temperature is too high. ① Measure whether the excitation current is greater than 3.7A; ② Check whether the rotor resistance of the excitation machine is lower than 15 Ω; ③ Improve ventilation or reduce usage.

Engineering maintenance and safety precautions

Regularly check the wiring: PMG and induction terminals are prone to loosening due to vibration and should be tightened every six months.

Cleaning and heat dissipation: Dust accumulation can lead to deterioration of heat dissipation, especially in high humidity or salt spray environments. Use compressed air to blow the surface of AVR.

Do not plug or unplug with power on: It is strictly prohibited to unplug the AVR plug when the generator is running, otherwise it may generate extremely high induced voltage and damage the circuit.

After replacing the AVR, it must be readjusted: the initial position of the VOLTS of the new AVR may be different, and it is necessary to start from the counterclockwise zero position according to the "voltage adjustment" steps.

Phase inspection of parallel units: Before parallel commissioning, use a phase sequence table to confirm that the induced voltage phase sequence of the two units is consistent; The polarity of the hanging CT wiring must be correct.