Usage:
Operation Of Generator
A1 Regulator Assembly
A2,3,4 Suppression Assemblies
C1 Surge Capacitor
C2,3 Suppression Capacitor
C4,5,6 RFI Suppression Capacitors
CR1,2 Control Rectifiers
CR3,4 Power Rectifiers
CR5 Field Rectifier
CR6 Build-up Diode
CR7,8 Surge Suppression Diodes
CR9 Blocking Diode
E1,3 SCR Heat Sink
E2,4 Rectifier Heat Sink
E5 Field Rectifier Heat Sink
F1,2 Fuses
K1 Build-up Relay
L1 Filter Reactor
L2 Sensing Reactor
L3 Revolving Field
L4 Stator
L5 Suppression Reactor
L6,7 SCR Reactor
L8 Diode Reactor
R1 Regulator Gain Resistor
R2 Regulator Gain Potentiometer
R3 Voltage Droop Potentiometer
R4 Voltage Level Potentiometer
R5 Resistance Wire
R6 Surge Resistor
R7 Damping Resistor
T1 Isolation Transformer
T2 Voltage Droop Transformer
T3 Regulator Transformer
TB1,2 Terminal Block
SRCR GENERATOR WIRING DIAGRAM
Introduction
The Statically Regulated Controlled Rectifier Generator gives improved performance and longer service life by applying a method of excitation which is controlled by an automatic voltage regulation system that contains no moving parts. The generator voltage buildup system uses only one moving part: a relay, which operates only when the generator is started or shut down.
Generation Of Voltage
The generator is constructed with the armature coils wound on stator (L4) and the field coils wound on the rotor, designated in the wiring diagram as revolving field (L3). The field coils are wound on magnetic steel that will retain a small amount of residual magnetism. The revolving field is connected directly to the engine flywheel through the generator shaft and coupling.
As the engine turns revolving field (L3), a small amount of alternating current voltage is generated in stator (L4) by the influence of residual magnetism in the revolving field. A portion of this alternating current (AC) is rectified to direct current (DC) and this portion is directed back to the revolving field to increase its magnetism. The procedure of excitation can be traced on the SRCR Generator Wiring Diagram by following the path of AC power from stator (L4).
The AC current from phases 1 and 2 flows through wires (3 and 22) to terminals (TB2-3 and TB2-4), through wires (35 and 36), fuses (F1 and F2), wires (61 and 59), suppression reactor (L5), wires (62 and 60) to heat sinks (E2 and E4). If controlled rectifiers (CR1 or CR2) have not received a gate signal to allow current to flow, the AC voltage charges the paralleled capacitors (C2 and C3). When a gate signal is received at either controlled rectifier (CR1 or CR2), current will flow from heat sink (E2 or E4) through the SCR reactor (L6 or L7) and the associated controlled rectifier to heat sink (E5).
The current flows from heat sink (E5) through regulator gain resistor (R1), wire (30) to terminal (TB2-1); through wire (C1) to the positive "+" end of revolving field (L3). The current flows from here through the revolving field (L3), wire (C2) to terminal (TB2-2), through wire (29) and either power rectifier (CR3 or CR4) to the other side of the power source.
To sustain current flow in the revolving field (L3) when controlled rectifiers (CR1 or CR2) are not conducting (because of no circuit from stator (L4) phase 3 or before the gate signal is received at (CR1 or CR2), there is a circuit from the negative "-" end to the positive "+" end of revolving field (L3). The circuit starts at wire (C2) and terminal (TB2-2), through wire (29), diode reactor (L8), field rectifier (CR5), regulator gain resistor (R1), wire (30), terminal (TB2-1), wire (C1) to the positive "+" end of revolving field (L3).
This circuit maintains a flow of current due to self induced voltage of the magnetic field. A mechanical analogy of this circuit is: an engine flywheel as it maintains crankshaft rotation between the power strokes of the individual pistons.
Voltage surge suppression diode (CR7), connected across power rectifiers (CR3 and CR4), limits abnormal transient peak voltages on the power rectifiers. Suppression assemblies (A2 and A4) limit abnormal transient peak voltages on controlled rectifiers (CR1 and CR2). Fuses (F1 and F2) are the "fast-blow" type and provide protection against secondary damage of the excitation circuit if any component should fail or malfunction. Damping resistor (R7) smooths out the oscillations that are caused by the reversal of current flow in suppression reactor (L5). Surge suppression diode (CR8), surge resistor (R6) and surge capacitor (C1) between terminals (TB2-1) and (TB2-2) and suppression assembly (A3) minimize the effects of voltage surges (spikes) in the excitation circuit and protect field rectifier (CR5).
CONTROL RECTIFIER SYMBOL
1. Anode. 2. Cathode. 3. Third terminal (gate).
Control rectifiers (CR1 and CR2) are in effect, "on-off" valves that can either allow current to flow or can stop the flow of current through the excitation circuit. A control rectifier has the usual rectifier terminals, anode (1) and cathode (2), and a third terminal (3) that, for explanation purposes, will be referred to as the "gate". When gate (3) receives an electric impulse, it takes approximately 3 micro-seconds (.000003 second) for a control rectifier to "turn on" and allow current to flow. The control rectifier stays "on" until no current is flowing; then it turns "off". Because of no circuit from phase 3, current does not flow once during each complete cycle. Therefore, control rectifiers (CR1 and CR2) are "off" once each cycle and each gate must receive a signal to "turn on" the controlled rectifiers some time during the next cycle.
The timing of the signal to the gate of each control rectifier (CR1 and CR2) is a function of regulator assembly (A1). As generator load increases, regulator assembly (A1) signals the "gates" of the control rectifiers earlier in the cycle, permitting a longer excitation time to the revolving field thereby providing the required additional excitation to maintain rated voltage with increased load. When generator load decreases, regulator assembly (A1) signals the "gates" later in the cycle and excitation time is less. Even when control rectifiers (CR1 and CR2) are "off" and current from phase 1 and phase 2 is blocked, revolving field excitation current is sustained for a complete cycle by the circuit that includes field rectifier (CR5). (Remember the flywheel analogy.)
Build-up relay (K1) has the only moving part (except for the rotating field) in the entire exciting and regulating system. The relay has contact points that operate only when the generator is being started or stopped. The normally closed contact points in the build-up relay (K1) are connected, in effect, from phase 2 to the "gate" of control rectifier (CR2) and through resistance wire (R5) to the cathode of control rectifier (CR2) at auxiliary heat sink (E5). The relay coil is connected in the excitation circuit by wire (63), between terminal (TB2-2) and pin terminal (A) on the buld-up relay (K1). The other end of the build-up relay coil connects to stator (L4) neutral, by wire (17), between relay pin terminal (B) and terminal (TB2-5). When generator output voltage is low, the "gate" of control rectifier (CR2) receives a continuous signal during the positive half cycle of phase 2. The signal from phase 2 passes through wire (60), heat sink (E4), build-up diode (CR6), wires (39 and 21), through the closed contacts of build-up relay (K1). The signal continues from build-up relay pin terminal (9) through blocking diode (CR9), through wire (23) to the "gate" of control rectifier (CR2) and through resistance wire (R5) and wire (38) to the cathode of the control rectifier (CR2). A small voltage drop across resistance wire (R5) causes the "gate" of control rectifier (CR2) to have a positive voltage in respect to the cathode of the control rectifier. This voltage is enough to "turn on" the control rectifier. Blocking diode (CR9) prevents the gate signal from the regulator (wire 8) from being shunted to the cathode of (CR2). As soon as the generator voltage in the relay coil circuit reaches pick-up voltage, the coil causes the contact points to open and regulator assembly (A1) now supplies the signals to both (CR1 and CR2) "gates". When the engine is stopped, pick-up voltage to the coil stops and the contact points close. Pick-up voltage is generated at a speed somewhat less than engine low idle speed.
Voltage level control (5) is a manual control to adjust voltage level potentiometer (R4) when it is necessary to adjust generator voltage to obtain correct line voltage.
Regulator gain control (6) is a manual control to adjust gain potentiometer (R2). Regulator gain control (6) and voltage level control (5) are adjusted in sequence to obtain precise generator voltage regulation when the engine is equipped with either a 3% mechanical speed droop or an isochronous (0% speed droop) engine governor. See OPERATION AND MAINTENANCE INSTRUCTIONS or OPERATION GUIDE for the engine.
When two or more generators are to be operated in parallel, it will be necessary for the voltage of each generator to decrease a specified amount as the generators are loaded. This decrease in voltage, as a generator is loaded, is called voltage droop. Voltage droop control (4) is a manual control to adjust voltage droop potentiometer (R3). Correct generator voltage droop toward clockwise for increased percentage of voltage droop. Voltage droop can be obtained by adjusting voltage droop control (4) from counterclockwise for no voltage droop control (4) must be adjusted in sequence with voltage level control (5) and regulator gain control (6). See, OPERATION AND MAINTENANCE INSTRUCTIONS or OPERATION GUIDE for the engine.
GENERATOR VOLTAGE ADJUSTMENT CONTROLS
4. Voltage droop control. 5. Voltage level control. 6. Regulator gain control.
It was previously stated that control rectifiers "turn on" in approximately three micro-seconds. This extremely fast "turn on" causes shock loading on stator (L4). AC voltage shocks will generate harmonics at radio frequencies. For many applications, these harmonics would be very undesireable.
The shock loading of the stator (L4) is considerably reduced by the paralleled suppression capacitors (C2 and C3) and the SCR reactors (L6 and L7). As mentioned earlier, the suppression capacitors (C2 and C3) accept a voltage charge during the time that controlled rectifiers (CR1 or CR2) are not in the conducting state. When a gate signal is applied to either controlled rectifier (CR1 or CR2) the initial surge of power (current flow) is supplied by the voltage charge on the suppression capacitors (C2 and C3). The current rise time is impeded by SCR reactors (L6 or L7). Interference from radio frequencies is further reduced by suppression reactor (L5) and RFI suppression capacitors (C4, C5 and C6). The suppression reactor (L5) is connected in series with the exciter AC voltage supply. The RFI suppression capacitors (C5 and C4) are connected from phase 1 and phase 2 to neutral and capacitor (C6) is connected from neutral to generator frame ground. To gain maximum effect from the RFI suppression capacitors, the generator frame should be connected to an earth or building (station) ground.
Regulator Assembly
After the generator voltage builds up enough to open the contact points of build-up relay (K1), the relay has accomplished its function. When the build-up relay contact points are open, regulator assembly (A1) supplies both control rectifier "gates" with electric impulses.
The regulator assembly contains resistors, rectifiers, capacitors and transistors in circuits connected to terminals (1 through 12) on the side of the regulator assembly. Because of the many components and the complexity of the circuits, the complete assembly is sealed in a non-conductive synthetic resin and is serviced as a unit.
A1 Regulator Assembly
A2,3,4 Suppression Assemblies
C1 Surge Capacitor
C2,3 Suppression Capacitor
C4,5,6 RFI Suppression Capacitors
CR1,2 Control Rectifiers
CR3 Power Rectifiers
CR6 Build-up Diode
CR7,8 Surge Suppression Diodes
CR9 Blocking Diode
E1,3 SCR Heat Sink
E2,4 Rectifier Heat Sink
E5 Field Rectifier Heat Sink
F1,2 Fuses
K1 Build-up Relay
L1 Filter Reactor
L2 Sensing Reactor
L5 Suppression Reactor
L6,7 SCR Reactor
L8 Diode Reactor
R1 Regulator Gain Resistor
R2 Regulator Gain Potentiometer
R3 Voltage Droop Potentiometer
R4 Voltage Level Potentiometer
R5 Resistance Wire
R6 Surge Resistor
R7 Damping Resistor
T1 Isolation Transformer
T3 Regulator Transformer
TB1,2 Terminal Block
REGULATOR ASSEMBLY
From stator (L4) of the generator, a circuit (connected from both phase 2 and the stator neutral) including sensing reactor (12) and voltage level potentiometer (R4) leads to terminals (12 and 11) on the regulator assembly (A1). This circuit from the generator stator will establish an alternating current voltage reference. Here the AC voltage is divided in direct proportion to the reactance of the sensing reactor and the combined resistance in he regulator assembly and the potentiometer. Because frequency varies the reactance of the sensing reactor, the voltage applied to the arm of the potentiometer is independent of engine speed or frequency change. This AC voltage reference also connects to isolation transformer (T1) primary winding. The transformer isolates the regulating circuit and also prevents the voltage divider sensing circuit and the regulator circuit from becoming parallel circuits.
The AC voltage from the secondary winding of the isolation transformer enters the regulator assembly through terminals (1 and 2). Terminals (1 and 2) lead to four diodes that make up a full wave rectifier which changes AC voltage to DC. This DC voltage is filtered by filter choke (L1) connected to terminals (3 and 5). The filtered DC voltage supplies a network of transistors, resistors, capacitors and diodes. The transistors in this network amplify any voltage variations in the input from the isolation transformer. This amplified voltage controls a timing circuit in the regulator assembly. Signals from the timing circuit, through terminals (7 and 8), supply the "gates" of control rectifiers (CR1 and CR2) with electric impulses which cause the control rectifiers to "turn on" the excitation circuit to revolving field (L3) [as required] to maintain constant generator output voltage.