Exercise 1. Put the words in the correct order

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A substation is a high-voltage electric system facility. It is used to

switch on and off generators, equipment and circuits or lines in a system. It is also used to change AC voltages from one level to another or change al- ternating current to direct current or vice versa. Some substations are small; they have a transformer and switches. Other substations are very large with several transformers and dozens of switches and other equip- ment.

The substation control house contains switchboard panels, batteries, battery chargers, supervisory control, power-line carrier, meters and relays. The control house provides all weather protection and security for the con- trol equipment.

Batteries are used in the substation control house to power the con- trol systems in case of a power blackout. Control panels contain meters, control switches and recorders located in the control building, also called a doghouse. These are used to control the substation equipment, to send power from one circuit to another or to open or to shut down circuits when needed.

There are three main types of substations.

A step-up transmission substation receives electric power from a nearby power plant and uses a large power transformer to increase the voltage for transmission to distant places. A transmission bus is used to distribute electric power to one or more transmission lines.

A substation can have circuit breakers that are used to switch genera- tion and transmission circuits in and out of service. This is made in case of emergencies requiring shut-down of power to a circuit or redirection of power.

The voltages from a step-up transmission substation are determined by the customer needs in regional grids. Direct current voltage is either positive or negative. A DC line has two conductors, so one would be posi- tive and the other negative.

Step-down transmission substations are located at switching points in an electrical grid. They connect different parts of a grid and are a source for subtransmission lines or distribution lines. The step-down substation can change the transmission voltage to a subtransmission voltage, usually 69 kV. The subtransmission voltage lines can then serve as a source to dis- tribution substations. The power goes to a distribution substation.

Distribution substations are located near the end-users. Distribution substation transformers change the transmission voltage to lower levels for end-user consumption. Typical distribution voltages vary from 34,500Y/19,920 volts to 4,160Y/2,400 volts.

34,500Y/19,920 volts means a three-phase circuit with a grounded neutral source. This would have three high-voltage conductors or wires and one grounded neutral conductor, a total of four wires. The voltage between the three-phase conductors would be 34,500 volts and the voltage between one-phase conductor and the neutral ground would be 19,920 volts.

From distribution substation the power is distributed to industrial, commercial and residential customers.

Exercise 1. Put the words in the correct order

1. A step-up transformer, places, is, to increase, for, to, transmission, the voltage, distant, used.

2. Are, of, three, there, types, substations, main.

3. A source, step-down transmission substations, distribution lines, are, for.

4. Determined, the voltage, needs, by, is, the customer.