Woodward MSLC Master Synchronizer and Load Control Load Control

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.