Usage:
Wiring Diagrams
Introduction
The 3100 Series Generator is a complete electrical power system consisting of three basic components; the AC generator, a brushless exciter and a magnetic amplifier type voltage regulator. The brushless exciter and the generator field rotate and are mounted on a common shaft. The voltage regulator consists of four basic circuits:
- 1. Sensing and differential detector
- 2. Differential pre-amplifier
- 3. Saturable transformer (magnetic amplifier)
- 4. Output rectifier bridge
- 2. Differential pre-amplifier
All of the regulator components are mounted within the control console at the rear of the generator.
Operation
The closed loop control block diagram illustrates the generator regulator system divided into basic functions. To increase the performance of the generator, a voltage regulator is used as a generator field exciter. With external constant field excitation, the generator output terminal voltage would be the same as normal, ranging from 10 to 50% regulation. The regulator on the 3100 series generators insures an output voltage that is constant within ± 2% under rated full load conditions. The regulator obtains its power from the generator output voltage and current.
The voltage and current are combined magnetically in a saturable transformer (TS-1). The transformer is specially designed with a control winding that reduces the output as the control signal increases. Winding (H), the transformer primary, provides the power to the transformer from the generator output voltage under no load current conditions. L1 is a series current limiting reactor that provides a reasonably constant supply current to the transformer. Winding (X) is the output AC which is rectified by the bridge circuit (BR-1) to provide direct current for field excitation. Winding (I) is the load current boost. Since generator field excitation is nearly proportional to load current, an increasing load will provide additional current to transformer (TS-1) resulting in a nearly exact increase in field excitation.
The generator output voltage is decreased through transformer action, rectified by diodes (D5, D6, D7, D8) and filtered to a smooth, low ripple, direct current by (L2, R17 and C2). A small portion of this DC voltage, at voltage divider (R12, R13, R14) is compared to a reference zener (Z1) voltage. The difference voltage is amplified by transistors (Q3) and (Q4). The output of (Q3) and (Q4) drives (Q1) and (Q2) to furnish a value of control current necessary to maintain desired field excitation.
To provide a means for voltage adjustment, compensation for circuit tolerance and increases in field power due to thermal effects, a control winding (C), connected to C- and C+, is powered by a transistorized pre-amplifier.
Parallel Operation
The 3100 Series voltage regulator can be modified for parallel operation. With the paralleling option, two or more generators may be operated in parallel, regardless of rating, provided each generator has the same phase, voltage and frequency. Each generator should supply no more than its full KW load rating. Do not attempt to operate the 3100 Series Generator in parallel, when not equipped with the paralleling option.
NOTE: Never attempt to parallel the 3100 Series Generator with commercial sources.
Do not close the load circuit breakers until the generators have been checked for correct PHASE ROTATION and adjusted for SYNCHRONIZATION. |
Phase Rotation
Before placing two or more three-phase generators in parallel, make certain the generators have the same phase rotation. This can be accomplished by connecting a three-phase induction motor to each of the generators and checking the rotation of the motor. Make certain the motor terminals are connected to the corresponding generator or bus terminals for each test. Phase rotation will be the same if the motor rotates in the same direction when connected to either generator.
If the motor rotates in the wrong direction when connected to one of the generators, reverse any two of the three generator leads (except neutral when used). Recheck motor rotation and continue checks until the motor rotates in the same direction when connected to either machine.
If motors are not readily available for the procedure outlined, lamps may be substituted as indicated in Figs. 1 and 2.
FIG. 1. Lamp connections across circuit breaker poles to check phase rotation.
FIG. 2. Lamp connections across circuit breaker poles to check phase rotation.
Synchronizing Generators
Do not attempt to parallel generators until each has been checked for correct phase rotation and adjusted for the required system voltage with the line switch open.
If a synchroscope is not available, generators can be synchronized by using incandescent lamps connected across the load circuit. Make certain that the voltage rating of the series lamps equals the voltage rating of the generator.
Lamp Connections for Sychronizing Generators
Synchronize the generators by varying the speed of the generator to be paralleled until fluctuation of the lamps is very slow. When the lamps are dark, close the load (line) switch or circuit breaker. Extreme care must be exercised to ensure that the switch is closed at the exact instant the lamps become dark.
Exercise extreme caution when using this method of synchronization to avoid exposure to dangerous voltages. |
Power Load Division
Adjust the engine governors in accordance with instructions in the Engine Service Manual. Division of kilowatt or actual power load between generators operating in parallel is practically independent of generator excitation. Do not attempt to vary the amount of KW load between paralleled generators by making adjustments to the voltage regulator.
Reactive KVA Division
The division of reactive KVA between paralleled generators depends upon generator excitation. Methods of correcting the excitation of individual generators, should they take more or less than their share of the reactive KVA, are the addition of cross-current compensation or voltage-droop controls to the voltage regulator circuit.
Adjustment of the cross-current or voltage droop rheostat would usually be set so there is just enough resistance in the circuit to give stable operation of the generators under reactive KVA load conditions.
Place the generator in operation and apply a lagging power factor load (induction type load). Check the voltage droop. Maximum voltage droop from no load to full load is obtained with full voltage-droop resistance. A droop of 3% to 4% is frequently employed. Adjust each generator to be paralleled for identical droop characteristics.
Bring all generators up to correct speed and adjust all output voltages to identical values. Synchronize and parallel the generators. Load the paralleled generators and check for satisfactory division of load currents. Make any corrections necessary by adjusting the voltage - adjust rheostat and the droop control resistors.