AUTOMATIC SUBSTATION CONTROL

   The electrical energy is transferred from large g enerating stations to distant load centres via various sub-stations. In every sub-station certain supervision, control and protection functions are necessary. Every substation has a control room. The relay and protection panels and control panels are installed in the control room. The various circuit breakers, tap changers and other devices are controlled by corresponding control-relay panels. In a small independent sub-station, the

supervision and operation for normal service can be carried out by the oper ator with the aid of analogue and digital control systems in the plant. The breakers can be operated by remote control from the control room. During faults and abnormal conditions, the breakers are operated by Protective relays automatically. Thus, the primary control in sub-station is of two categories.

1. Normal routine operation by operators command.

2. Automatic operation by action of protective relays and control systems.

SUB STATION CONTROL FUNCTION ARRANGED THROUGH SCADA SYSTEM:

1. Alarm Functions

    To sound alarm/annunciation regarding dangerous, uncommon events such as abnormal values of process parameters, fire, illegal entry in premises, over temperatures, low voltage of auxiliary supply, unusual happening etc. Alarms are obtained from data logger and are for alerting this operator in the control room.

2. Control and Indication

Control of two position devices such as circuit -breakers, isolators, earthing-switches,starters. Indication of ON/OFF state of the devices on control board/mimic diagrams.

Control of position of devices having positions (closed, middle open) e.g. values, input settings, indication of position on control panels.

Control positions of multi-position device e.g. tap changer, indication of position on control panels.

Indication without control.

Control without indication : e.g. raise or lower control of generator load by automatic load frequency control.

Set-point control to provide set point to a controller located at remote sub -station.

3. Data collection, recording, display.

4. Sequential operation of devices with predetermined time and conditions for operation of various devices e.g.

Auto-reclosing of circuit-breakers operation O-CO-Time-CO Operation of circuit-breaker, isolator and earthing switch in a particular sequence during opening of circuit and another sequence during closing of circuit.

5. By means of SCADA system, the operator in control centre can cause operations in a remote sub-station. The possible remote operations include :

Opening and closing of switching devices I

Tap-changing of transformers (voltage control)

 Switching of capacitor banks (voltage control)

 Load shedding (load frequency control)

6. Some of the remote operations are made automatic by one -line computer based system without human intervention e.g. Net work islanding, Backup protection. The automatic control function are segregated into :

 Interconnection functions

 Transmission line automatic function

 Distribution system automatic functions