Introduction

SR4 Generator (Partial View)
(1) VR3F regulator. (2) Terminal box. (3) Droop rheostat location. (4) Power transformer PT2 (if required).

This manual covers the VR3F voltage regulator as it is used on 4/6 and 10/12 lead, self-excited SR4 generators. 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
(5) Terminal strip (for attachments). (6) Rheostat (voltage level). (7) Fuse holder. (8) Terminal strip (for sensing and power). (9) Fuse cover. (10) Fuses. (11) Jumper (for selecting 1x1 or 2x1 slope). (12) Jumper (for selecting 50 Hz or 60 Hz operation).

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 (6) provides a no load voltage adjustment of approximately +10 to -25%.

Additional features built into the VR3F are:

* Jumper (11) 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 (11).

* Jumper (12) provides a means of selecting a 50 Hz or 60 Hz operating frequency. Remove jumper (12) for 50 Hz frequency operation.

Rheostat (6) is multiple turn. It does not have a fixed stop at the end of travel, but has an override ratchet.

SR4 Generator Schematic (Self-excited 4/6 lead)
(1) VR3F regulator. (4) Power transformer PT2. (13) Lines - 3 phase output voltage. (14) Lines - sensing voltage and AC power. (15) Main stator. (16) Main rotor. (17) Exciter stator. (18) Exciter rotor. (19) Lines - VDC excitation voltage.

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

Wires 20 and 24, of lines (14), are used to provide AC power to VR3F on 10/12 lead generators and to step-down power transformer PT2 (4) on 4/6 lead generators. PT2 will step-down the AC voltage to 240 VAC for excitation to the VR3F regulator. The regulator rectifies the AC voltage and controls the excitation current to exciter stator (17).

Two fuses, in secondary output wires 30 and 31 of PT2 and two fuses (10) in lines 20 and 24 of the regulator, limit the field current in the case of an internal short circuit or loss of sensing signal.

NOTE: VR3F regulators include an overcurrent shutoff to protect generator components. If the unit operates for an extended period of time at low rpm, the overcurrent shutoff may trip. It will reset automatically when the generator is completely shutoff. For 60 Hz generator operation, the recommended minimum operating speed is:

Four pole ... 1200 rpm

Six pole ... 800 rpm

NOTE: VR3F regulators are sensitive to A-B-C phase rotation. Connections must be as shown in this manual; T1 to 22, T2 to 24, and T3 to 20.

NOTE: If it is required to provide a shutoff for the VR3F regulator, connect a SPDT switch (rated 20 amp, 240 volt) in:

Line 30 - for generator sets with a power transformer only.

Line 24 - for generator sets with sensing and power transformers.

Line 24 - for generator sets with no power or sensing transformers.