Month: December 2025

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-2 will maintain a constant base load or import/export level even with chang

ing utility frequencies. The MSLC-2 provides switch inputs to allow raising or lowering the internal digi

tal base load or import/export reference. The control also provides a remote analog signal input for ref

erence setting, if desired. (Signal variety: 0 to 20 mA, 4 to 20 mA, 0 to 5 V, 1 to 5 V and 0 to 10 V)

The MSLC-2 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-2 issues a breaker open command to separate the utility from the local bus. The ramp pause

switch can be used to stop the utility unload at any point. The maximum load that the MSLC-2 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.

The MSLC-2 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% load signal to the generators is reached.

Load Control

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The MSLC-2 has four load control modes available:

• Base load

• Import/export

• Process

• Utility unload

Load control begins with the breaker closure of the utility and another discrete input selecting the load

control mode wanted. If no load control mode is selected the MSLC-2 will be in the offline mode. The

system load immediately prior to breaker closure is used as the starting base load reference. On com

mand, 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.

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-2 will maintain a constant base load or import/export level even with chang

ing utility frequencies. The MSLC-2 provides switch inputs to allow raising or lowering the internal digi

tal base load or import/export reference. The control also provides a remote analog signal input for ref

erence setting, if desired. (Signal variety: 0 to 20 mA, 4 to 20 mA, 0 to 5 V, 1 to 5 V and 0 to 10 V)

Synchronizer

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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-2 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 volt

age 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.

The MSLC-2 control provides a safe automatic dead bus closure function. Deadbus closing permission

is granted to only one DSLC-2 or MSLC-2 control in the whole system through locking techniques done

over the communications network.

The MSLC-2. configured as tie-breaker control, allows selecting different closure modes or all modes:

• Alive bus A -> dead bus B

• Dead bus A -> dead bus B

• Alive bus B -> dead bus A

DSLC-2 equipped generators

Additional MSLC-2 functions include:

• Automatic dead bus closure capability for tie-breakers

• Multiple utility breaker and tie-breaker MSLC-2s on the same bus segment

• One dedicated Ethernet line for precise system communications between all DSLC-2s and

MSLC-2s on the system

• Ethernet Modbus/TCP for remote control and monitoring

• Serial Modbus RS-485 for remote control and monitoring

• Applications with up to 32 DSLC-2 and 16 MSLC-2

• Automatic segment control (self-recognizing of the segment)

• Full setup, metering and diagnostic capability through the PC program ToolKit

MSLC-2 function summary

Original 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-2 controls in isochronous load sharing

• Adjustable power factor control

• Built in diagnostics with relay output

• Multifunction adjustable high and low limit alarms and adjustable load switches with relay outputs

• Digital communications network to provide loading and power factor control of individual

Application

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The Woodward MSLC-2XT™ control is the direct successor of the former MSLC™ master synchro

nizer and load control. The MSLC-2XT™ is a microprocessor-based overall plant load control designed

for use in a system with Woodward DSLC-2XTTM, DSLC-2TM (“Digital Synchronizer and Load Control”)

controls on each generator to provide utility synchronizing, paralleling, loading and unloading of a

three-phase generating system.

Applications allow up to 32 generators to be paralleled and controlled in conjunction with up to 16

MSLC-2XT™, MSLC-2™. A dedicated Ethernet system provides seamless communications between

DSLC-2TM and MSLC-2TM units. A second Ethernet port is provided for customer remote control and

monitoring capability using Modbus TCP allowing DCS and PLC interfacing. Both together can be used

as a redundant Ethernet system. Modbus TCP is also available through additional Ethernet connection

(named C). Modbus RTU is available through a separate RS-485 port.

CB Aux Contact

Connect the utility breaker auxiliary (CB Aux) contact that opens and closes

when the utility tie breaker opens and closes. Wire the breaker auxiliary contact

in series between the +24 Vdc voltage source and terminal 47 of the MSLC. In

addition, it may be desirable to put an MSLC ON/OFF switch in series with this input.

Utility Unload Contact

Connect the utility unload switch to terminal 48.

Import/Export Control Contacts

The import/export mode of control is initiated by closing the CB Aux contact 47

and closing the import/export contact 49.

Process Control Mode Contact

If the MSLC will be used as a process control, connect a switch from +24 Vdc to

the Process Control discrete input, terminal 50. When this contact is closed, load

on the associated DSLC™ equipped generators in isochronous load sharing is

controlled at a level required to maintain the analog process input at a chosen reference.

Ramp Pause Contact

Connect the load ramp pause switch contact to terminal 51. When closed, this

contact will hold any load ramp in progress at its current setting until the contact is opened.

Raise and Lower Set Point Contacts

Connect a center off, double-pole double-throw switch to the Raise and Lower

Load inputs, terminals 52 and 53. If the remote reference will be used, install a

second double-pole double-throw switch to simultaneously select both the Raise and Lower inputs.

Local Bus Voltage Adjustment Contacts

The Local Bus voltage adjustment contact inputs allow manual voltage control of

the operating generator’s voltages for manual paralleling. Note, if the individual

generators are in VAR/PF control, they will return to VAR/PF control as soon as

the MSLC’s raise/lower switches are returned to OFF. The switches may also be

used to change the constant generator power factor reference if operating in that mode.

Discrete Inputs

The discrete inputs are the switch input commands to the MSLC. Discrete inputs

are optically isolated from the control and require 10 mA at 24 Vdc each to

activate. Discrete inputs may be powered by the same source as control power.

All contacts used in the discrete circuits should be the isolated dry contact type to

work properly with the low currents used in these circuits.

Connect the 24 Vdc supply common (–) to terminal 43. Route +24 Vdc through

the appropriate external contact to the discrete input.

Synchronizer Mode Switch

The synchronizer mode switch (single-pole, four-position) controls the operating

mode of the synchronizer. The switch must be wired to terminals 44. 45. and 46.

as shown in Figure 1-3. The four positions are Off, Check mode, Permissive

mode, and Run mode. When the switch is off, the synchronizer is out of operation.

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.

An adjustable ramp allows smooth entry and exit from the process control mode.

When the process control mode is selected, the load reference is ramped in a

direction to reduce the error between the process input and the process

reference. When the error is minimized or the reference first reaches either the

high or low specified pull-in limits, the process controller is activated. When the

load reference output reaches either 100% or 0%, the control will maintain that

load reference until process control is established. The MSLC is not capable of

overloading or reverse powering in order to attempt to meet the process

reference. The high and low limit switches mentioned above can be used to

indicate that either too many or too few generators are on-line to maintain the

process within its limits.