INTERVIEW QUESTION – PART – 49 What are the types of Sub-stations (SS)? Major equipment in SS and its function. SUBSTATION Substation may be defined as the equipment or an assembly of equipment, which changes one or more characteristics of the supply example power factor, frequency etc. CLASSIFICATION OF SUBSTATIONS BASED ON DESIGN Indoor substations: Apparatus are installed within the substations. Outdoor substations: These substations are erected for distribution of power in localities and are further classified as pole mounted substations and foundation mounted substations. BASED ON OPERATING VOLTAGES High Voltage substations – 11 kV and 66 kV Extra High Voltage substations – 132 kV and 400 kV Ultra-High Voltage substations – above 400kV TYPES OF SUBSTATIONS 01. SWITCHING SUBSTATIONS Switching substation means for switching operation of power lines without transforming voltage level to another level as per needs. 02. GRID SUBSTATIONS These are the substations from where bulk power is transmitted from one point to another point in the grid. These are important because any disturbance in these substations may cause the failure of grid. 03. CONVERTING SUBSTATIONS These substations converting AC to DC or vice-versa and converting frequency form higher to lower or vice-versa. 03. FREQUENCY CHANGING SUB-STATION There are many industrial applications for which frequencies lower or higher than the frequencies of normal supply are needed. High frequency heating and dielectric heating are examples. The substations which are installed for this particular purpose are called frequency changing substations. 05. POWER FACTOR CORRECTION SUBSTATION Substations which are used to correct or improve the power factor are known as power factor correction substation. Generally synchronous motors are used for this purpose. Therefore, they are also called synchronous sub-stations. 06. MOBILE SUBSTATIONS Mobile substations needed for temporary requirements such as for construction purposes. It requires special purpose and designs. 07. CINEMATOGRAPHY SUBSTATIONS The cinematography substations are special purpose substations and are required to meet the special requirements. 08. MINING SUBSTATIONS Mining substations as the name indicates are substations required for special purposes they need special design considerations, because of the extra for safety needed in the operation of the electric supply. 09. TOWN SUBSTATIONS These substations step – down the voltage at 33 / 11 KV for further distribution in the towns and any failure in such substations results in the failure of supply for whole of the town. MAJOR EQUIPMENT IN SS 1. TRANSFORMER Step up and step down the voltage. 2. BUS BAR A bus bar (sometimes pronounced "buzz bars") in electrical power distribution refers to thick strips of copper or aluminium that conduct electricity within a switchboard, distribution board, substation, or other electrical apparatus. The size of the bus bar is important in determining the maximum amount of current that can be safely carried. 3. ISOLATORS Isolators or disconnect switches operate under no load condition. They are not equipped with arc-quenching devices. 4. SWITCHES OIL SWITCH - The oil switch has both the blade and the contact mounted in a oil-filled tank. The switch is usually operated from a handle outside of the case. As the switch is opens, the arc formed between the blade and contact is quenched by the oil. 4. AIR-BREAK SWITCH: The air-break switch has both the blade and the contact equipped with arcing horns. [Arcing horns are piece of metal between which the arc resulting from opening a circuit carrying current is allowed to form] 5. CIRCUIT BREAKER The circuit breaker (CB) which normally gets signal from protective relays to operate, is an automatic switch which can interrupt the fault current. 6. FUSES & RELAYS FUSE A fuse is a short piece of metal, inserted in the circuit, which melts when excessive current flows through it and thus breaks the circuit. RELAY Relay is device which senses abnormal conditions on a power system by constantly monitoring electrical quantities of the system, which differ under normal and abnormal conditions. 7. CONTROL BOARDS AND 8. CONTROL ROOM