Many words such as Transformers, Receiving Stations and Substations have found their way into the vocabulary of the common man though relatively few understand what these words actually mean and what role these equipment and facilities play in supplying power for daily use.

Reliance Energy Limited receives power in bulk from its 2x250 MW coal based thermal power plant at Dahanu and Tata Power Companies (TPC). The Power generated at the Dahanu Thermal Power Station (DTPS) is stepped up to 220 kV and transmitted through four circuits to our main 220/ 33kV Receiving Stations at Ghodbhunder, Versova and Aarey.

Dahanu Thermal Power Station

At these Main Receiving Stations, Power is stepped down to 33 KV for sub-transmission through underground cables.

Power from the Dahanu TPC is supplied through underground cables to the REL Receiving Stations at 33/ 22 kV at 8 supply points.

Presently, there are 54 Receiving Stations that receive power at 33 kV from the 3 main receiving stations of REL. Similarly power from TPC is received at 33/ 22 kV. These 54 Receiving Stations, further step down power to 11kV. Power is then distributed from the Receiving Stations through 11 kV underground cables and in few cases, through overhead lines.

However, the end user or the consumer requires supply of three phase 433 volts for motive power and single phase 230 volts for lights, fans and other domestic appliances. The stepping down of electric power from 11 KV to 433 volts is accomplished in the substation by means of distribution transformers.

Power Transformer

Most of the substations in the Reliance Energy Ltd's system are of the indoor type, with all equipment housed within the substation. Nowadays, substations house the switchgear inside and distribution transformers outside the substation room. The advantage of this type of substation is enhanced ventilation and cooling of the transformer.

The Equipments at a typical REL substation are:

1. High tension (11 kV) Switchgear

2. Distribution transformers

3. L.T. Distribution panels.

A Typical REL Substation

11 kV Switchgear

This switchgear is used to connect or isolate the distribution transformers and also protect it during fault conditions. Fig. Shown is a Ring Main Unit (RMU) switchgear. It comprises of two Isolators and one Circuit Breaker/ Oil Fuse Switch. The Isolators when switched 'ON' enable electric power to flow from one substation to other substation. When breaker or oil fuse switch is switched 'ON' the transformer is fed with electric power of 11000 volts and when switched 'OFF' it is disconnected from the 11000 volts supply. In the event of a fault or excessive overloading of the transformer, the breaker or oil fuse switch senses this condition and switches 'OFF' automatically, thus isolating the Transformer and preventing any further damage to it.

11KV Ring Main Unit

Distribution Transformer

Transformers are used to step up or step down electric power from a given voltage to another. For this purpose, the transformer has two windings known as primary and secondary windings. The Transformers in the Reliance Energy Ltd's system are of the step down type. Thus, the input to the primary winding of the distribution transformer is 11000 volts and the output on the secondary winding is 400 volts. The size or capacity of the distribution transformer depends upon the quantity of electric power handled by the transformer. The different sizes of transformers in our system are 100, 250, 315, 400, 500, 630, 990, 1500 and 2000 kVA where kVA is the unit of power.

11/0.433 kV Transformer

Low Tension Distribution Panel/LT Circuit Breaker Panel

The distribution panel inside a substation is similar to the roadside L.T. pillars. A typical distribution panel is of 6 ways or 8 ways i.e. either 6 cables or 8 cables can be connected to these panels. Low-tension cables can be connected to these panels. Low-tension cables are connected between the L.T. side of the transformer and panel or Air circuit breaker. The number and size of these cables would depend on the size of the distribution transformer.

Two ways of the distribution panel are specially made for connecting incoming cables. The balance ways of the distribution panel are connected to outgoing L.T. cables also known as distributors. These cables run across the adjacent streets and supply power to the area around the substation. The protection of these cables is provided by means of HRC fuses.

8 Way L.T. Panel

The 11kV Distribution Substations in the Reliance Energy Ltd's system are interconnected to form a 11 kV Ring Main System.

The Reliance Energy Limited All India Network.

Reliance Energy Limited's network covers a total area of 1, 24, 300 sq. kms. The company has a national customer base of 5 million with an annual consumption of 15,600 million units!

Distribution Companies:

Reliance Energy has been actively participating in the recent Privatization efforts of the Govt of India. For details of the distribution facilities of Reliance Energy Limited in other areas of the country, click on the links featured below