Type F Systems Operation

Usage:

Operation Of Generator

EARLIER SRCR GENERATOR WIRING DIAGRAM FIG. 1

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 Diodes

CR7,8 Surge Suppression Diodes

CR9,11 Blocking Diodes

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

EARLIER SRCR GENERATOR WIRING DIAGRAM FIG. 2

A4 Suppression Assembly

C2,3 Suppression Capacitor

CR1,2 Control Rectifiers

CR3,4 Power Rectifiers

CR6 Build-up Diodes

CR7 Surge Suppression Diode

CR9,11 Blocking Diodes

E3 SCR Heat Sink

E2,4 Rectifier Heat Sink

E5 Field Rectifier Heat Sink

K1 Build-up Relay

L7 SCR Reactor

R2 Regulator Gain Potentiometer

R5 Resistance Wire

TB1 Terminal Block

EARLIER SRCR GENERATOR WIRING DIAGRAM FIG. 3

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 Diodes

CR7,8 Surge Suppression Diodes

CR9,11 Blocking Diodes

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

EARLIER SRCR GENERATOR WIRING DIAGRAM FIG. 4

A4 Suppression Assembly

C2,3 Suppression Capacitor

CR1,2 Control Rectifiers

CR3,4 Power Rectifiers

CR6 Build-up Diodes

CR7 Surge Suppression Diode

CR9,11 Blocking Diodes

E3 SCR Heat Sink

E2,4 Rectifier Heat Sink

E5 Field Rectifier Heat Sink

K1 Build-up Relay

L7 SCR Reactor

R2 Regulator Gain Potentiometer

R5 Resistance Wire

TB1,2 Terminal Block

LATER SRCR GENERATOR WIRING DIAGRAM FIG. 5

A4 Suppression Assembly

C2,3 Suppression Capacitor

CR1,2 Control Rectifiers

CR3,4 Power Rectifiers

CR6,10 Build-up Diodes

CR7 Surge Suppression Diode

CR9,11 Blocking Diodes

E3 SCR Heat Sink

E2,4 Rectifier Heat Sink

E5 Field Rectifier Heat Sink

K1 Build-up Relay

L7 SCR Reactor

R2 Regulator Gain Potentiometer

R5,8 Resistance Wire

TB1 Terminal Block

LATER SRCR GENERATOR WIRING DIAGRAM FIG. 6

A4 Suppression Assembly

C2,3 Suppression Capacitor

CR1,2 Control Rectifiers

CR3,4 Power Rectifiers

Cu6,10 Build-up Diodes

CR7 Surge Suppression Diode

CR9,11 Blocking Diodes

E3 SCR Heat Sink

E2,4 Rectifier Heat Sink

E5 Field Rectifier Heat Sink

K1 Build-up Relay

L7 SCR Reactor

R2 Regulator Gain Potentiometer

R5,8 Resistance Wire

TB1 Terminal Block

SRCR GENERATOR WIRING DIAGRAM FIG. 7

A1 Regulator Assembly

F2 Fuse

L1 Filter Reactor

L2 Sensing Reactor

L4 Stator

R3 Voltage Droop Potentiometer

R4 Voltage Level Potentiometer

T1 Isolation Transformer

T2 Voltage Droop Transformer

T3 Regulator Transformer

TB1,2 Terminal Block

Introduction

The Statically Regulated Controlled Rectifier (SRCR) generator uses a method of excitation controlled by an automatic voltage regulation system that has no parts that move. The voltage build-up system has one relay.

The generator is made with the armature coils wound on stator (L4) and the field coils are wound on revolving field (L3). The field coils are wound on magnetic steel that will retain a small amount of magnetism even when there is no current to the field. The generator shaft is connected to the engine flywheel by a flexible coupling.

NOTE: The difference between earlier and later SRCR voltage build-up systems is in the wiring of build-up relay (K1).

Voltage Build-Up (Earlier)

Build-up relay (K1) has the only part that moves [except for revolving field (L3)] in the excitation/regulation system. The build-up relay contacts are normally closed. When the generator set is started residual magnetism in revolving field (L3) induces a low voltage in stator (L4).

When phase 1 is positive in relation to phase 2, current wants to follow the path illustrated on Fig. 1. Control rectifier (CR1) will not let current flow unless it gets a gate signal from wire 7. The gate signal is given through build-up relay (K1). The path of current flow is illustrated on Fig. 2.

The small voltage drop across resistance wire (R5) causes a potential difference between the gate lead and the cathode of (CR1). Control rectifier (CR1) "turns on" and current flows through the excitation circuit. This increases the voltage induced in stator (L4).

When phase 2 becomes positive in relation to phase 1, current wants to follow the path illustrated in Fig. 3. Control rectifier (CR2) will not let current flow unless it gets a gate signal from wire 8. The gate signal is given through build-up relay (K1). The path of current flow is illustrated on Fig. 4.

The small voltage drop across resistance wire (R5) causes a potential difference between the gate lead and the cathode of (CR2). Control rectifier (CR2) "turns on" and current flows through the excitation circuit. This increases the voltage induced in stator (L4).

The voltage increases caused by current flow through (CR1 and CR2) compound. That is, more current through the field means more stator output to the excitation circuit. This is known as voltage build-up.

At a speed a little less than low idle, generator voltage is enough to activate the coil in build-up relay (K1). The relay contacts open and regulator assembly (A1) begins to give the gate signals to (CR1 and CR2).

When the engine is stopped, voltage to the relay coil stops and the contacts close.

Voltage Build-Up (Later)

Operation of the voltage build-up system on later generators is similar to the earlier generators except, there is a separate resistance wire across each controlled rectifier. (R8) gives the potential difference necessary to gate (CR1). See Fig. 5. (R5) gives the potential difference necessary to gate (CR2). See Fig. 6.

Normal Operation

Regulator Assembly

Regulator assembly (A1) contains resistors, rectifiers, capacitors and transistors in circuits connected to terminals 1 through 12 on the side of the regulator assembly. The regulator assembly is sealed in a non-conductive synthetic resin. This gives protection to the many components and complex circuits. The regulator assembly is serviced as a unit.

The circuit illustrated on Fig. 7 is the AC voltage reference for regulator assembly (A1).

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 of frequency change. This AC voltage reference also connects to isolation transformer (T1) priamry 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 and 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.

Blocking diode (CR11) prevents the gate signal from wire 7 from being shunted to the cathode of (CR1). Blocking diode (CR9) prevents the gate signal from wire 8 from being shunted to the cathode of (CR2).

Control Rectifiers

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 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 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 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).

Flyback Circuit

FLYBACK CIRCUIT

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 form 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 like the action of an engine flywheel as it maintains crankshaft rotation between the power strokes of the individual pistons.

Protection Components

Voltage surge suppression diode (CR7) connected across power rectifiers (CR3 and CR4) limits abnormal transient peak voltages on the power rectifiers. Suppession 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 again 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).

Radio Suppression

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 undesirable.

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 (16 or L7). Interference from radio frequencies is further reduced by suppression reactor (L5) and RFI suppression capacitor (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 the maximum effect from the RFI suppression capacitors, the generator frame should be connected to an earth or building (station) ground.

Regulator Adjustments

GENERATOR VOLTAGE ADJUSTMENT CONTROLS
4. Voltage droop control. 5. Voltage level control. 6. Regulator gain control.

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.

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.

COMPONENT LOCATION