MSLC Master Synchronizer and Load Control

9907-004 (4-Wire Wye) 

9907-005 (3-Wire Delta, 120 V) 

9907-006 (3-Wire Delta, 240 V)

General Information

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).

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.

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.

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. 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.

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.

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.

VAR/PF Control

The VAR/PF function controls the power factor on all of the DSLC equipped machines operating in isochronous load sharing. The PF control begins on breaker closure. The MSLC has three modes of VAR/PF control (which are selected in Menu 4):

• Constant Generator Power Factor—sets the power factor reference on all of the DSLC controls to the internal reference chosen in the MSLC. The power factor can then be adjusted using the voltage raise and lower inputs. The voltage raise command will make the power factor more lagging. Conversely, the voltage lower command will make the power factor more leading. 

• Utility Tie Power Factor Control—adjusts the power factor reference on all of the DSLC controls in isochronous load sharing in order to maintain the power factor across the utility tie. 

• Utility Tie VAR Control—adjusts the power factor reference on all of the DSLC controls in isochronous load sharing in order to maintain the level of reactive load being imported or exported from the utility.

Manual Organization

• Chapter 2 covers electrostatic discharge awareness. The MSLC is an electronic device containing sensitive components. While the control is designed for safe handling in the industrial environment, certain cautions must be observed during handling and shipping or when removing the cover. 

• Chapter 3 covers MSLC installation and wiring, including each major group of connections, along with any special instructions. 

• Chapter 4 covers MSLC configuration, setup, and adjustment. The chapter explains the purpose of each set point and recommended initial value. 

• Chapters 5 through 8 explain the major functions of the synchronizer, import/export control, process control, and PF control. 

• Chapter 9 describes the Echelon Local Operating Network (LON) used by the MSLC to communicate to the individual DSLC controls. 

• Chapter 10 provides a troubleshooting guide. Due to the extensive built-in diagnostics, MSLC installation may be tested and verified quickly. 

• Chapter 11 describes how to return the control to Woodward in the event of damage or failure of an internal component. 

• Appendix A contains a work sheet to aid in setup and to provide a place to record setup values for future reference. 

• Appendix B lists the MSLCs physical and electric specifications.