This feature is provided for voltage adjustment up to ±12% of rated voltage through a potentiometer. Turn the POT clockwise to increase voltage and vice versa, after reaching the nominal speed. Provision is made for connecting external potentiometer in the AVR for remote voltage adjustment.
This feature is provided to protect the AC generator from the sustained low speed operation through a potentiometer. AVR will reduce the voltage proportional to the speed below the set value. The procedure to set the FRO pot is as follows:
First run the generator at full speed (50Hz) turn FRO by few turns clockwise, ensure voltage does not increase. Now turn the FRO pot slowly anticlockwise. At a particular point Red LED glows and voltage will start to reduce, stop turning the pot at this point and turn the pot clockwise by two turns after nominal voltage is restored.
Factory default setting is 46Hz.
For 60Hz operation reset the FRO pot to 56Hz as per above procedure.
This feature is provided to arrest the voltage hunting through a potentiometer. Turn clockwise to increase stability (to arrest oscillation). Too far clockwise rotation will result in sluggish response and sometimes oscillations also.
Factory default setting is slightly more than critical damping (around mid way).
This feature is provided to protect the Exciter Field from over exciting through a potentiometer. Turn clockwise to increase the Excitation limit. This pot is initially set for 60% rating of the AVR. If the full load exc. requirement is less, then run & load the generator to its full load & rotate the pot ACW till the RED LED lights.
Factory default setting at 60%.
DROOP
A potentiometer is provided to adjust the droop for parallel operation of AC Generators. Follow the CT connections as per the AVR connection diagram.
Turn the QDC pot clockwise to increase droop and vice versa.
R 150 is provided with two accessory terminals A1 & A2 for injecting ±1.0 to ±4.5V DC. The variation in terminal voltage will be ±10% of the rated voltage.
Warning: a screw driver as the «vishay trimmer model 8» type should be used to set the potentiometer.
SI No | Control | Function | Direction |
V | VOLTS | To adjust the generator output voltage | Turn clockwise to increase the output voltage |
UF | UFRO | To set the Under frequency Knee point | Turn clockwise to reduce the knee point |
S | STAB | To arrest voltage hunting | Turn clockwise to increase the stability |
OE | OVER EXC | To set the over excitation limit | Turn clockwise to increase the limit |
DROOP | DROOP | To set voltage droop | Turn clockwise to increase the droop |
AC | ACC (DC i/p) | It is used for Auto synchronization | Turn clockwise to increase the gain |
Symptom | Cause | Action |
No voltage build up | Fuse blown | Check & replace |
Low residual across U and N terminal | If the residual voltage of the Generator at rated speed is less than 2.5V AC (L-N),then disconnect the Regulator and connect a 24V DC Battery keeping F1as positive and F2 as Negative. Connecting a free wheel Diode (BY 127) Right across the field with Diode Cathode to F1 & Anode to F2 during field flashing will help restoring the residual voltage. CAUTION: Remove the diode (BY-127) after field flash. 24V battery positive must be connected to F1 only and negative to F2. Reverse connection will Blow out Diode BY127 instantaneously. | |
Incorrect wiring | Check wiring | |
Rotating diodes and /or fuse failed | Check and replace | |
Panel voltmeter defective | Check and correct | |
AVR defective (repeated fuse blowing) | Replace after conducting static test | |
Grounded exciter field | Check and correct | |
High voltage build up | Loose, or no connection to ‘U’ terminal of the Regulator | Check and correct |
AVR defective | Conduct static test and replace if necessary | |
Low voltage build up | Low prime mover speed | Check and correct |
Sensloss is in circuit | Check and correct | |
AVR defective | Replace AVR | |
Voltage oscillation | Incorrect stab-pot sealing | Turn clockwise still Hunting is arrested |
Prime mover speed hunting | Check and adjust governor | |
Load hunting, fluctuates rapidly | Check and correct | |
High percentage of non linear load | Check and reduce the non linear load | |
High reactance in generator (during non linear loading) | Consult generator manufacturer | |
Poor regulation | The exciter field’s requirement is higher than 105V DC | Wrong selection or very low P.f load. Check and correct. |
Prime mover speed dips too much on load (kW load) | Adjust governor and reduce active load |
Equipment: Digital Multimeter.
Select Diode mode in digital multimeter.
Resistance between F1 & F2 (keeping common of multimeter jack to F1 of the AVR should give 0.4 to 0.6kW, and reverse keeping common of multimeter jack to F2 of the AVR should give INFINITY).
ZERO indicates power device failure in both the cases. No further tests (static test or dynamic tests) are allowed, and it will lead to rapture of fuse.
Resistance between F2 & U (both sides) should be 180kW.
Resistance between F2 & V (Keeping common of the multimeter to ‘V’ of the AVR should show about 2.2M ohms in 10MW range and reverse keeping common of the
Multimeter to F2 of the AVR should give 15 Mega ohms.
ZERO indicates power device failure in both the cases. No further tests (static test or dynamic tests) are allowed, and it will lead to rapture of fuse.
Resistance between U&V should give 300kW to 400kW. Open circuit indicates AVR failure. In static test lamp will not turn OFF or when connected to generator it will produce ceiling voltage (for 3Ø ONLY).
Resistance between U&N1 should give 200kW to 260kW. Open circuit indicates AVR failure.
In static test lamp will not turn OFF or when connected to generator it will produce ceiling voltage (for 1Ø ONLY).
Resistance between N&F1 should be very low or ZERO ohms. If it is open lamp will not glow when static test is conducted.
For 3-phase circuit
This should be attempted only after ascertaining that the regulator has passed all multimeter checks. Connect the regulator to three ph variable voltage source as shown in diagram 3 phase of this manual.
1. Keep ‘V-TRIM’ in minimum position.
2. Keep ‘FRO’ in fully maximum position.
3. Increase the applied voltage. The lamp should glow with increasing brightness. At a voltage around 360-380V the lamp should GO-OFF slowly. Further increase in voltage up to 415V should keep the lamp OFF. Decrease the voltage now to below 360 volts the lamp should glow bright again.
4. Turn ‘FRO’ pot anticlockwise the lamp should GO-OFF slowly. Now turn ‘FRO’ pot clock wise. The lamp should brighten up again.
5. It is difficult to prescribe a static test for checking the stability, as it is best found in closed loop test. However healthy regulator will behave as given below.
First keep the ‘STAB’ pot in fully anticlockwise. Conduct static test as in 1, 2 & 3, the lamp will GO-OFF rather swiftly at 360-380V and come again swiftly when the voltage is reduced below 360V.
Now keep ‘STAB’ pot fully clockwise, conduct static test as in 1, 2, & 3 the lamp should GO-OFF much slower and come again much slower. At end of this test keep pot mid-way.
If the regulator behaves as said above then the regulator is healthy.
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