Usage:
Operation Of Generator
SRCR Generator Wiring Diagram
A1 REGULATOR ASSEMBLY
A2, 3 SUPPRESSION ASSEMBLY
C1 SURGE CAPACITOR
C2, 3, 7 SUPPRESSION CAPACITOR
C4, 5, 6 RF1 SUPPRESSION CAPACITOR
CR1 CONTROLLED RECTIFIER
CR3, 4 POWER RECTIFIER
CR5 FIELD RECTIFIER
CR7, 8, 10 SURGE SUPPRESSION DIODE
CR9 BLOCKING DIODE
E1 MAIN HEAT SINK
E3 AUX. HEAT SINK
E4 SCR HEAT SINK
F1, 2, 3 FUSE
K1 BUILD UP RELAY
L1 FILTER REACTOR
L2 SENSING REACTOR
L3 REVOLVING FIELD
L4 STATOR
L5 SUPPRESSION REACTOR
L6 SCR REACTOR
L8 DIODE REACTOR
R1 REGULATOR GAIN RESISTOR
R2 REGULATOR GAIN POT
R3 VOLTAGE DROOP POT
R4 VOLTAGE LEVEL POT
R5 RESISTANCE WIRE
R6 SURGE RESISTOR
T1 ISOLATION TRANSFORMER
T2 VOLTAGE DROOP TRANSFORMER
TB1, 2 TERMINAL BLOCK
FOR GENERATORS 8L50 & 8L78
A1 REGULATOR ASSEMBLY
A2 SUPPRESSION ASSEMBLY
C1 SURGE CAPACITOR
C2, 7 SUPPRESSION CAPACITOR
C4, 5, 6 RF1 SUPPRESSION CAPACITOR
CR1 CONTROLLED RECTIFIER
CR3, 4 POWER RECTIFIER
CR5 FIELD RECTIFIER
CR7, 8, 10 SURGE SUPPRESSION DIODE
CR9 BLOCKING DIODE
E1 MAIN HEAT SINK
E3 AUX. HEAT SINK
E4 SCR HEAT SINK
F1, 2, 3 FUSE
K1 BUILD UP RELAY
L1 FILTER REACTOR
L2 SENSING REACTOR
L3 REVOLVING FIELD
L4 STATOR
L5 SUPPRESSION REACTOR
L6 SCR REACTOR
R1 REGULATOR GAIN RESISTOR
R2 REGULATOR GAIN POT
R3 VOLTAGE DROOP POT
R4 VOLTAGE LEVEL POT
R5 RESISTANCE WIRE
R6 SURGE RESISTOR
T1 ISOLATION TRANSFORMER
T2 VOLTAGE DROOP TRANSFORMER
TB1, 2 TERMINAL BLOCK
FOR GENERATORS 8L51, 8L52, 8L69, & 8L84
A1 REGULATOR ASSEMBLY
A2, 3 SUPPRESSION ASSEMBLY
C1 SURGE CAPACITOR
C2, 3, 7 SUPPRESSION CAPACITOR
C4, 5 6 RF1 SUPPRESSION CAPACITOR
CR1 CONTROLLED RECTIFIER
CR3, 4 POWER RECTIFIER
CR5 FIELD RECTIFIER
CR7, 8, 10 SURGE SUPPRESSION DIODE
CR9 BLOCKING DIODE
E1 MAIN HEAT SINK
E3 AUX. HEAT SINK
E4 SCR HEAT SINK
F1, 2, 3 FUSE
K1 BUILD UP RELAY
L1 FILTER REACTOR
L2 SENSING REACTOR
L3 REVOLVING FIELD
L4 STATOR
L5 SUPPRESSION REACTOR
L6 SCR REACTOR
L8 DIODE REACTOR
R1 REGULATOR GAIN RESISTOR
R2 REGULATOR GAIN POT
R3 VOLTAGE DROOP POT
R4 VOLTAGE LEVEL POT
R5 RESISTANCE WIRE
R6 SURGE RESISTOR
T1 ISOLATION TRANSFORMER
T2 VOLTAGE DROOP TRANSFORMER
TB1, 2 TERMINAL BLOCK
FOR ALL OTHER GENERATORS
Introduction
The Statically Regulated Controlled Rectifier Generator gives improved performance and longer service life by applying a method of excitation controlled by an automatic voltage regulation system that contains no moving parts. The generator voltage build-up 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 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 (22 and 24) to terminals (TB2-4 and TB2-3), through wires (35 and 36), fuses (F1 and F2), wires (11 and 12), suppression reactor (L5), wires (56 and 57), to the power rectifiers (CR3 and CR4) mounted on heat sink (E1) which rectifies the AC power to provide halfwave DC power. If controlled rectifier (CR1) has not received a gate signal to allow current to flow the AC voltage will alternately charge capacitor (C7) and paralleled capacitors (C2 and C3). [NOTE: Capacitor (C3) not required on generators 8L51 and 8L52]. When a gate signal is applied to controlled rectifier (CR1), DC current will flow from heat sink (E1) through the SCR reactor (L6), heat sink (E4) and controlled rectifier (CR1) to heat sink (E3).
The current flows from heat sink (E3) through regulator gain resistor (R1), wire (30) to terminal (TB2-1); through wire (C1) to positive "+" end of revolving field (L3). The current flows through the revolving field (L3), wire (C2) to terminal (TB2-2), through wire (45), fuse (F3), wire (26) to terminal (TB2-5). The current continues through wire (26) to the neutral (T0) of the stator winding (L4).
To sustain current flow in the revolving field (L3) when controlled rectifier (CR1) is not conducting, because of no circuit from stator (L4) phase 3 or before the gate signal is received at (CR1), there is a circuit from the negative "-" end to the positive "+" end of revolving field (L3). This circuit starts at wire (C2) and terminal (TB2-2), through wire (45), diode reactor (L8) or wire (27) (NOTE: Diode reactor (L8) is not required on generators 8L51 or 8L52; wire (27) is used to complete the circuit), 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 diodes (CR7 and CR8) connected across power rectifiers (CR3 and CR4) limit abnormal transient peak voltages on the power rectifiers. Suppression assembly (A3) limits abnormal transient peak voltages on controlled rectifier (CR1). Fuses (F1, F2 and F3) are the "fast-blow" type and provide protection against secondary damage of the excitation circuit if any component should fail or malfunction. Surge suppression diode (CR8), surge resistor (R6) and surge capacitor (C1), and suppression assembly (A2) minimize the effects of voltage surges (spikes) in the excitation circuit and protect field rectifier (CR5) against abnormal transient peak voltages.
CONTROL RECTIFIER SYMBOL
1. Anode. 2. Cathode. 3. Third terminal (gate).
Control rectifier (CR1) is, in effect, an "on-off" valve that can either allow current to flow or can stop the flow of current through the excitation circuit. A control rectifier has the usual diode 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 three 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 rectifier (CR1) is "off" once each cycle and "gate" must receive a signal to "turn on" the controlled rectifier some time during the next cycle.
The timing of the signal to the gate of the control rectifier (CR1) is a function of regulator assembly (A1). As generator load increases, regulator assembly (A1) signals the "gate" of the control rectifier 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 "gate" later in the cycle and excitation time is less. Even when control rectifier (CR1) is "off" and current form 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 build-up relay (K1) are connected, in effect, from phases 1 and 2 to the "gate" of control rectifier (CR1) and through resistance wire (R5) to the cathode of control rectifier (CR1). The build-up relay coil is connected in the excitation circuit by wire (26), fuse (F3), wire (44), wire (49), or wire (40) and wire (18) between terminals (TB2-5 and TB1-5), and wire (17) between terminal (TB2-5) and pin terminal (B) of the build-up relay (K1). The other side of the coil is connected to phases 1 and 2 through wire (21) to heat sink (E1). When generator output voltage is low the "gate" of control rectifier (CR1) receives a continuous signal during the positive half cycle of phases 1 and 2. The signal from phases 1 and 2 reach heat sink (E1) through power rectifiers (CR3 and CR4). From the heat sink it goes through wire (21) to pin terminals (A) and (1) of build-up relay (K1), them through the closed contacts of the 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 (CR1) and through resistance wire (R5) and wire (22) to the cathode of the control rectifier (CR1). A small voltage drop across resistance wire (R5) causes the "gate" of control rectifier (CR1) 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 (CR1). 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 the "gate" of (CR1). 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 regulator 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.
GENERATOR VOLTAGE ADJUSTMENT CONTROLS
4. Voltage droop control. 5. Voltage level control. 6. Regulator gain control.
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 can be obtained by adjusting voltage droop control (4) from counterclockwise for no voltage droop toward clockwise for increased percentage of voltage droop. 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.
It was previously stated that control rectifiers "turn on" in approximately three micro-seconds. This extremely fast "turn on" causes shocks loading on stator (L4). AC voltage shocks will generate harmonics at radio frequencies. For many applications, these harmonics would be very undesirable.
The shock loading of the stator (L4) is considerably reduced by the suppression capacitors (C2, C3, and C7) and the SCR reactor (L6). As mentioned earlier, the suppression capacitor (C7) and the paralleled suppression capacitors (C2 and C3) alternately accept a voltage charge during the time that controlled rectifier (CR1) is not in a conducting state. When a gate signal is applied to controlled rectifier (CR1), the initial surge of power (current flow) is supplied by the voltage charge on either suppression capacitor (C7) or the paralleled suppression capacitors (C2 and C3). [NOTE: Capacitor (C3) not required on generators 8L51 and 8L52]. The current rise time is impeded by SCR reactor (L6). 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 two-phase half-wave DC 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 neutural to generator frame ground. To gain the 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 the control rectifier "gate" with electric impulses.
The regulator assembly contains resistors, rectifiers, capacitors and transistors in circuits connected to terminals (1 through 10A) on the side of the regulator assembly. Because of the many components and the complexity of the circuits, the complete assembly is sealed in non-conductive synthetic resin and is serviced as a unit.
From stator (L4) of the generator, a circuit (connected from both phase 2 and the stator neutral) including sensing rector (L2) and voltage level potentiometer (R4) leads to terminals (9 and 10) 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 the 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 terminal (8), supply the "gate" of control rectifier (CR1) with electric impulses which cause the control rectifier to "turn on" the excitation circuit to revolving field (L3) [as required] to maintain constant generator output voltage.
REGULATOR ASSEMBLY
REGULATOR ASSEMBLY