Systems Operation



SR4 Generator (Partial View)
(1) VR3 regulator. (2) Terminal box. (3) Droop rheostat location.

This manual covers the VR3 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.

VR3 regulator (1) is located in generator terminal box (2).


VR3 Regulator
(4) Terminal strip (for attachments). (5) Rheostat (voltage level). (6) Rheostat (voltage gain). (7) Fuses (PM stator fuses). (8) Fuses. (9) Fuses cover. (10) Terminal strip (for sensing and power).

The purpose of the VR3 regulator is to keep generator output voltage at a rated value. There are two controls on the VR3 that are standard.

* Voltage level rheostat (5) provides a no load voltage adjustment of approximately +10 to -25%.
* Voltage gain rheostat (6) provides an adjustment to compensate for engine RPM droop with load. Rheostat (6) can be adjusted to keep the same voltage at no load and full load, even when there is a small change in frequency (rpm).

Rheostats (5) and (6) are multiple turn. They do not have a fixed stop at the end of travel, but have an override ratchet.

SR4 Generator Schematic (Permanent Magnet Excited)
(1) VR3 regulator. (11) Lines (3-phase output voltage). (12) Lines (sensing voltage). (13) Lines (VDC excitation voltage). (14) Main stator. (15) Main rotor. (16) Exciter stator. (17) Exciter rotor. (18) PM stator. (19) Permanent magnet. (20) Lines [AC power to (1)].

VR3 regulator (1) uses all three phases to sense generator output voltage. Lines (12) function as sensing lines. Lines (12) connect generator output lines (11) to VR3 regulator (1) at terminals 20, 22 and 24 (AC input) on fuses (8) and terminal strip (10). Like other SR4 generator regulators, the VR3 regulates voltage based on volts per hertz.

Lines (20) are used to provide AC power for excitation to the VR3 regulator. Through permanent magnet (19) and stator (18), three phase 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 (12). The DC excitation voltage passes through lines (13) to exciter stator (16).

Fuse (7) limits the field current in the case of an internal short circuit or loss of sensing signal.

Fuses (8) are used to protect the VR3 from internal faults and exciter faults.

NOTE: To ensure proper generator operation, the VR3 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 VR3 regulator is connected differently on medium voltage generators. The only differences are:

* The regulator uses 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.

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