Introduction

SR4 Generator (Partial View)
(1) VR3F regulator. (2) Terminal box. (3) Droop rheostat location.

This manual covers the VR3F regulator used on the permanent magnet (PM) excited SR4 generator. This manual must be used in conjunction with service manual Electric Set Generators SENR7958 and Operation And Maintenance Manual SEBU6150. Follow all safety procedures and warnings in the above generator manuals.

VR3F regulator (1) is located in generator terminal box (2).

Operation

VR3F Regulator
(4) Terminal strip (for attachments). (5) Rheostat (voltage level). (6) Fuse holder. (7) Terminal strip (for sensing and power). (8) Fuse cover. (9) Fuses. (10) Jumper (for selecting 1x1 or 2x1 slope). (11) Jumper (for selecting 50 Hz or 60 Hz operation). (12) Fuses (PM stator fuses).

The purpose of the VR3F regulator is to keep generator output voltage at a rated value. There is one control on the VR3F that is standard.

* Voltage level rheostat (5) provides a no load voltage adjustment of approximately +10 to -25%.

Additional features built into the VR3F are:

* Jumper (10) provides a means of selecting a 1x V/Hz or a 2x V/Hz slope. The 2x V/Hz slope will help the generator set pick up a full block load. 2x V/Hz operation is selected by removing jumper (10).

* Jumper (11) provides a means of selecting a 50 Hz or 60 Hz operating frequency. Remove jumper (11) for 50 Hz frequency operation.

Rheostat (5) is multiple turn. It does not have a fixed stop at the end of travel, but has an override ratchet.

SR4 Generator Schematic (Permanent Magnet Excited)
(1) VR3F regulator. (13) Lines (3-phase output voltage). (14) Lines (sensing voltage). (15) Lines (VDC excitation voltage). (16) Main stator. (17) Main rotor. (18) Exciter stator. (19) Exciter rotor. (20) PM stator. (21) Permanent magnet. (22) Lines [AC power to (1)].

VR3F regulator (1) uses all three phases to sense generator output voltage. Lines (14) function as sensing lines. Lines (14) connect generator output lines (13) to VR3F regulator (1) at terminals 20, 22 and 24 (AC input) on fuses (9) and terminal strip (7). The VR3F regulates voltage based on 1x volts per hertz or 2x volts per hertz. The VR3F offers an approximate 8 volts per hertz (1x) or 16 volts per hertz (2x) characteristic on 480V generators.

Lines (22) are used to provide three phase AC power for excitation to the VR3F regulator. Through permanent magnet (21) and stator (20), three phase AC power for excitation voltage is generated. Regulator (1) rectifies the three phase AC voltage to DC voltage. Regulator (1) controls the DC excitation voltage based on the level of the sensing voltage on lines (14). The DC excitation voltage passes through lines (15) to exciter stator (18).

In-line fuses (12) limit the field current in the case of an internal short circuit or loss of sensing signal.

Fuses (9) are used to protect the VR3F from internal faults and exciter faults.

NOTE: To ensure proper generator operation, the VR3F regulator must be connected as shown in this manual; T1 or T7 to 22, T2 or T8 to 24, and T3 or T9 to 20.

Medium Voltage Generators (Voltages above 600 VAC)

The VR3F regulator is connected differently on medium voltage generators. The only differences are:

* The regulator uses 100/120 VAC three phase (delta or open delta) sensing through a transformer.

* The transformer is supplied by the customer.

* The regulator is located with the switch gear, instead of being mounted in the generator terminal box.

NOTE: The VR3F PM regulator has an over excitation circuit which will allow the VR3F regulator to provide forcing for 10 to 30 seconds. The amount of forcing time depends on the continuous excitation level before the VR3F regulator goes into a forcing condition. The higher the continuous excitation level, the faster the VR3F regulator over excitation circuit will trip. Once the over the excitation circuit trips, the regulator will be disabled and the generator output voltage will fall to residual voltage. To reset the regulator, the generator set has to be turned OFF for at least one minute.

NOTE: When operating the VR3F regulator at speeds below 1200 rpm on four pole generators and 900 rpm on six pole generators, the VR3F regulator should be disabled. Otherwise the regulator could go to high voltage.

NOTE: If it is required to provide a shutoff for the VR3F regulator, connect a three pole double throw switch (rated 15 A, 120 VAC) in lines 26, 28 and 30 (11 GEN, 12 GEN and 30 GEN).