Year: 2025

Process Control

A process controller is provided for cogeneration, fluid level maintenance,

pressure control, or other applications. An adjustable bandwidth signal input filter,

flexible PID controller adjustments, an adjustable deadband, and control

selectable for direct or indirect action, allow the process control to be used in a

wide variety of applications.

A 4–20 mA (1–5 Vdc or a 4–12–20 mA) process transmitter provides the process

signal to the MSLC. The MSLC includes an internal digital process reference

which may be controlled by the raise and lower switch contact inputs or by an

external 4–20 mA (1–5 Vdc) remote process reference. The output of the

process control, like the import/export control, is the percentage of rated load

setpoint to the individual generators in isochronous load sharing.

The maximum load that the MSLC can tell

the individual generators to carry is their rated loads. So, in the event that the

plant load is greater than the capacity of the operating generators, the utility

unload will stop when 100% rated load is reached on each of the operating

generators. This prevents accidental overloading of the local generators when a

reduced number are on line.

The MSLC also includes two adjustable load switches which can be used for

external functions or warnings when chosen system load levels are attained. The

high and low limit switches may also be activated when 100% or 0% base load

signal to the generators is reached.

The import/export control is an integrating control. It adjusts the percentage of

rated load carried by the individual generators, operating in isochronous load

sharing, in order to maintain a set import/export or base load level. The MSLC

will therefore maintain a constant base load or import/export level even with

changing utility frequencies. The MSLC provides switch inputs to allow raising or

lowering the internal digital base load or import/export reference.

The import/export control is an integrating control. It adjusts the percentage of

rated load carried by the individual generators, operating in isochronous load

sharing, in order to maintain a set import/export or base load level. The MSLC

will therefore maintain a constant base load or import/export level even with

changing utility frequencies. The MSLC provides switch inputs to allow raising or

lowering the internal digital base load or import/export reference. The control also

provides a 4–20 mA (1–5 Vdc) analog input for remote reference setting, if desired.

The MSLC is equipped with a Utility Unload switch, which provides an adjustable

time controlled ramp to lower the base load or import/export level. When the level

is below an adjustable threshold, the MSLC issues a breaker open command to

separate the utility from the local bus. Again, the ramp pause switch can be used

to stop the utility unload at any point. 

Load Control

The load control uses digital signal processing techniques to provide significantly

improved accuracy and speed of response over conventional analog

measurement techniques. Accuracy is improved because the instantaneous

measurement of the voltage and current signal wave forms allows true RMS

measurement. Measuring true RMS power allows optimal load control in parallel

applications even in the presence of power line distortions. This method provides

faster response time because it eliminates the long integration times required in

analog circuits. Measurement speed is particularly important in power control

applications where rapid response to load and speed changes is essential.

Load control begins at breaker closure when the MSLC takes control of the

system load. The system load immediately prior to breaker closure is used as the

starting base load. On command, the adjustable ramp allows smooth, time

controlled loading into a set import/export level. A ramp pause switch is provided

to stop the ramp at any point.

Synchronizer

The MSLC uses digital signal processing techniques to derive both true RMS

voltages and relative phase angles of the fundamental frequencies of the utility

and the local bus voltage wave forms. Digital signal processing techniques offer

significantly improved measurement accuracy in the presence of wave form

distortions, particularly since the phase measurement does not depend on zero

crossings of the voltage wave forms.

Either phase matching or slip frequency synchronizing may be selected. Phase

matching provides rapid synchronizing for critical standby power applications.

Slip frequency synchronizing ensures that the initial flow of power will be either

out of the local system (export) or into the local system (import), depending on

whether a positive or negative slip is chosen. For both synchronizing methods,

the MSLC uses actual slip frequency and breaker delay values to anticipate an

adjustable minimum phase difference between the utility and the local bus.

Additional synchronizer functions include voltage matching, time delayed

automatic multi-shot reclosing, auto-resynchronizing, and a synchronizer timeout

alarm. Each of these features may be enabled or disabled during setup.

Introduction 
This manual describes the Woodward MSLC Master Synchronizer and Load Control. 
Application
The MSLC is a microprocessor-based overall plant load control designed for use 
in a system with Woodward DSLC™ (Digital Synchronizer and Load Control) 
controls on each generator to provide utility synchronizing, paralleling, loading, 
and unloading of a three-phase generating system. 

MSLC functions include: 
 Selectable for phase matching or slip frequency synchronizing between the 
utility and a local bus with voltage matching; 
 Automatic system loading and unloading for bumpless load transfer; 
 Import/Export level control capability; 
 Process control for cogeneration, pressure, maintenance, or other process; 
 Proportional loading of associated DSLC controls in isochronous load sharing; 
 Adjustable Power Factor control; 
 Built in diagnostics with alarm relay driver output; 
 Multi-function adjustable high and low limit alarms and adjustable load 
switches with relay driver outputs; 
 Digital communications network to provide loading and power factor control 
of individual DSLC equipped generators; 
 Full setup, metering, and diagnostic capability through a hand held 
programmer terminal (Figure 1-2). 

MSLC functions include: 
 Selectable for phase matching or slip frequency synchronizing between the 
utility and a local bus with voltage matching; 
 Automatic system loading and unloading for bumpless load transfer; 
 Import/Export level control capability; 
 Process control for cogeneration, pressure, maintenance, or other process; 
 Proportional loading of associated DSLC controls in isochronous load sharing; 
 Adjustable Power Factor control; 
 Built in diagnostics with alarm relay driver output; 
 Multi-function adjustable high and low limit alarms and adjustable load 
switches with relay driver outputs; 
 Digital communications network to provide loading and power factor control 
of individual DSLC equipped generators; 
 Full setup, metering, and diagnostic capability through a hand held 
programmer terminal (Figure 1-2). 

ADJUSTMENTS

The Woodward Hand Held Programmer makes all

adjustments quickly and easily, through the control’s ten

convenient “menus”.  The control saves all set points in

permanent memory, which does not require batteries or

other power sources to retain data.  The Hand Held

Programmer prevents tampering with set points, yet allows

entries to be changed at any time.

• Menu 1 – Synchronizer Functions

• Menu 2 – Load Control Functions

• Menu 3 – Process Control Functions

• Menu 4 – VAR/Power Factor Control Functions

• Menu 5 – Configuration

• Menu 6 – Calibration

• Menu 7 – Generator Electric Parameters

• Menu 8 – Control Status Monitor

• Menu 9 – Discrete Inputs/Outputs Monitor

• Menu 0 – Diagnostics

OPERATING MODES

Isolated Bus — The DSLC talks over its LON to share

proportional real and reactive loads.  Real load (kW) is

controlled using percentages of full load for each machine,

and reactive loads (kVAR) are

shared by matching power factors.

The DSLC maintains a specified

bus voltage and frequency while

balancing loads.

Utility Parallel — The DSLC

measures real load (kW) on the

generator and adjusts the speed

control to match a set base load, to

control a process at a user-chosen,

externally adjustable setpoint.  Or it

can set a constant import/export

level using an MSLC ( Master

Synchronizer and Load Control).

The DSLC can also measure and

maintain a set reactive load (kVAR)

or can maintain a user-prescribed

power factor.

Transition Between Modes — The

DSLC will ramp at a user-chosen

rate from one mode to another

until the control is within 5% of its

target. It then shifts into dynamic

control, allowing bumpless

operating mode changes. In

addition, the DSLC automatically

changes its VAR/PF mode when

the real load mode is changed to or

from an isolated bus, load sharing

mode. Manual VAR/PF control

may also be selected.

ADVANTAGES

• Reduces wiring between synchronizer, load

control and automatic loading controls

• Having functions integrated into one box

eliminates the need for redundant sensors

(like PTs, CTs and MOPs) that connect to

individual modules such as the load sensor and synchronizer

• Hand Held Programmer reduces installation

and calibration time by allowing the user to

set up the control prior to starting the system

• Hand Held Programmer lets operator monitor generator

parameters, contact switches, and analog I/O for

installation and troubleshooting

• Reduces the amount of cabinet space needed

• Eliminates the need for additional relay logic or a PLC to

control dead bus closing

• Digital communications across the LAN reduce

susceptibility to noise on the load sharing lines

• Slip frequency paralleling, voltage matching, and speed

bias hand-off between the synchronizer and load control

result in smooth paralleling without the risk of reverse power trips

• Three-phase true rms power sensing makes the DSLC

accurate even with unbalanced phase loading and voltage fluctuations

• Can load share with Woodward analog controls when

used with the Load Sharing Interface Module. Refer to

Woodward Manual # 02031 for details.