Power Plant Control System Operation of Central Unit

Adjustable level detectors determine at which busbar load a generator shall start or stop. According to the starting sequence, selected with push-buttons at the front, start and stop orders are distributed to the basic units.

These orders are delayed one minute in order to prevent actions by temporary load variations. The delay will be bypassed when a fault occurs on a running set, overload is detected or a controlled load is required.

The unit also determines whether or not the number of connected sets is sufficient to cover the required load under normal conditions. In this case a signal to the units will permit a set with a non-critical fault to be disconnected and stopped. This signal will also permit a requested controlled load to be connected.

The unit provides the heavy load control function. When a controlled load is requested by an external closing contact, a simulated load will be added to the real load and this may result in the starting of a new set. When enough power is available, permission will be given to connect.

Eight loads can be controlled, programmable from 20% to 160% of a generator capacity. The connection order is given at 2 s intervals for each 1 pad. After black-out a delay of 30 s will prevent the connection of these loads from interfering with the connection of essential consumers.

At the request of a controlled load a corresponding lamp at the front starts flashing until the load is ordered to be connected and then it changes to steady light. The lamp remains lit and the control output activated until the request contact is opened.