Tuesday, September 25, 2018

Electrical Power Distribution Automation

Electrical power distribution is the last stage in the delivery of electric power. It carries electricity from the transmission system to the individual consumers. The primary distribution lines carry this medium voltage to distribution transformers.


The distribution networks of concern in this stage are 11KV lines or feeders downstream of the 33KV substations. Each 11KV feeder, which come from the 33KV substation branches further into several subsidiary 11KV feeders to carry power close to the load points, where it is further stepped down to either 230V or 414V.

Electrical Power Distribution Automation

Normally for fault detection, we have circuit breakers i.e. one circuit breaker for every main 11KV feeder at the 33KV substations, but these circuit breakers are provided as a means of protection to completely isolate the downstream network in the event of a fault. For quick fault detection, isolation of faulty region and restoration of supply to the maximum outage area, we need to have a system that can achieve a finer resolution.

In the event of a fault on any feeder section downstream, the circuit breaker at the 33KV substation trips, as a result, we have a blackout over a large section of the distribution network. If we can precisely identify the faulty segment, we can reduce the blackout area, by re-routing the power to the healthy feeder segments through the operation of sectionalizing switches, placed at strategic locations in various feeder segments.

The lack of information at the 33KV substations of the loading and health status of 11KV/415V distribution transformers and associated feeders is one of the main causes of inefficient power distribution.  When we have no monitoring, overloading occurs, which results in low voltage at the customer end, and this increases the risk of frequent breakdowns of the transformers and feeders.
To prevent the above problems from occurring in a power distribution network, we need to have an automated electrical power distribution system.


How Electrical Power Distribution Automated System work

To enhance the electrical power distribution reliability, sectionalizing switches are provided along the way of primary feeders. Thus, by adding fault detecting relays to the sectionalizing switches along with circuit breaker and protective relays at the distribution substations, the system is capable of determining fault sections. To reduce the service disruption area in the case of power failure, normally open (NO) sectionalizing switches called as route switches are used for supply restoration process. The operation of these switches is controlled from the control center through the Remote Terminal Units (RTU).

In a power distribution automation system, the various quantities e.g. current, voltage, switch status, temperature and oil level are recorded in the field at the distribution transformers and feeders, using a data acquisition device called Remote Terminal Unit. These quantities re transmitted on-line to the base station through a communication media. The acquired data is processed at the base station for display at multiple computers through a Graphic user interface (GUI).

In the event of a system quantity crossing a pre-defined threshold, an alarm is generated for operator intervention. Any control action, for opening or closing of the switch or circuit breaker is initiated by the operator and transmitted from the 33KV base stations through the communication channel to the remote terminal unit associated with the corresponding switch or CB. The desired switching takes place and the action is confirmed by the operator.

All these distribution automation functions of data collection, data transmission, data monitoring, data processing, man-machine interface etc. are realized using an integrated distribution SCADA (Supervisory Control and Data Acquisition) system.

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The implementation of SCADA system in any electric utility involves the installation of the following units:
  • Sectionalizing Switches
  • Remote Terminal Units
  • Data Acquisition System
  • Communication Interface
  • Control PC

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