The major components of a typical substation include air circuit breakers, buses, capacitors, circuit switchers, conduits, control houses, converter stations, current transformers, disconnect switches, distribution buses, duct runs, frequency changers, grounding equipment, high-voltage cables, fuses, lightning arresters, manholes, metal-clad switchgear, meters, microwave systems, oil circuit breakers, potheads, and voltage transformers. Capacitor voltage transformers are used to transform high voltages to low voltages suitable for meters, relays and other equipment and provide insulation between high voltage and low voltage circuits.

2. SUBSTATION EQUIPMENTS
The major components of a typical substation are:
Air Circuit Breaker Distribution Bus Potheads
Batteries Duct Runs Power-line Carrier
Bus Support Insulators Frequency Changers Power Transformers
Capacitor Bank Grounding Resistors Rectifiers
Circuit Switchers Grounding Transformers Relays
Concrete Foundation High-Voltage Underground Cables SF6 Circuit Breakers
Conduits High-Voltage Fuses Shunt Reactors
Control House Lightning Arresters Steel Superstructures
Control Panels Manholes Supervisory Control
Control Wires Metal-clad Switchgear Suspension Insulators
Converter Stations Meters Synchronous Condensers
Coupling Capacitors Microwave Transmission Bus
Current Transformers Oil Circuit Breakers Vacuum Circuit Breakers
Disconnect Switches Potential Transformers
Air circuit breakers are used to interrupt circuits while current flows through them. Compressed air is used to
quench the arc when the connection is broken.
Bus support insulators are porcelain or fiberglass insulators that serve to isolate the bus bar switches and other
support structures and to prevent leakage current from flowing through the structure or to ground. These
insulators are similar in function to other insulators used in substations and transmission poles and towers.

3. Capacitors are used to control the level of the voltage supplied to the customer by reducing or eliminating the
voltage drop in the system caused by inductive reactive loads.
Circuitswitchers provide equipment protection for transformers, lines, cables, and capacitor banks. They also
are used to energize and deenergize capacitor banks and other circuits.
Conduits are hollow tubes running from manhole to manhole in an underground transmission or distribution
system. They can contain one or more ducts (See Duct Runs). They can be made of plastic (PVC), fiberglass,
fiber, tile, concrete, or steel. PVC and fiberglass are most commonly used.
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
control equipment. It is also called a doghouse.

4. Converter stations are located at the terminals of a DC transmission line. Converter stations can change
alternating current into direct current or change direct current to alternating current. Sometimes converter
stations are located at a generation power plant or at transmission substations. Two unsynchronized AC
transmission systems can be connected together with converter stations.
Converter stations are also found in most substations for converting the emergency battery back-up system to
AC power for use in an emergency.
Couplingcapacitors are used to transmit communication signals to transmission lines. Some are used to
measure the voltage in transmission lines. In signal transmission the coupling capacitor is part of a power line
carrier circuit as shown in the schematic below. A coupling capacitor is used in this circuit in conjunction with a
line trap. Line traps can be installed at the substation or on a transmission line tower.
Primarycouplingcapacitor
Currenttransformers can be used to supply information for measuring power flows and the electrical inputs for
the operation of protective relays associated with the transmission and distribution circuits or for power
transformers. These current transformers have the primary winding connected in series with the conductor
carrying the current to be measured or controlled. The secondary winding is thus insulated from the high
voltage and can then be connected to low-voltage metering circuits.
Current transformers are also used for street lighting circuits. Street lighting requires a constant current to
prevent flickering lights and a current transformer is used to provide that constant current. In this case the
current transformer utilizes a moving secondary coil to vary the output so that a constant current is obtained.

5. 400 kVcurrent transformer
Pole type constant currenttransformer
Disconnect switches or circuit breakers are used to isolate equipment or to redirect current in a substation.
Many different types of disconnect switches are shown below.
Disconnect switcheson an outgoing
distribution circuit

6. A distribution bus is a steel structure array of switches used to route power out of a substation. The power
goes from the transformer to the distribution bus.
Ductruns are hollow tubes running from manhole to manhole inside a conduit (see conduits) in an underground
system. They are of various sizes usually from 2 to 6 inches in diameter. Electrical cables are run through ducts
and the ducts are sized accordingly. The diameter of a duct should be at least 1/2 to 3/4 inch greater than the
diameter of the cable(s) installed in the duct. They can be made of plastic (PVC), fiberglass, fiber, tile,
concrete, or steel. PVC and fiberglass are most commonly used.
A frequency changer is a motor-generator set that changes power of an alternating current system from one
frequency to one or more different frequencies, with or without a change in the number of phases, or in
voltage. Sometimes a converter is used to accomplish this.

7. Grounding Resistors are designed to provide added safety to industrial distribution systems by limiting ground
fault current to reasonable levels. They are usually connected between earth ground and the neutral of power
transformers, power generators or artificial neutral transformers. Their main purpose is to limit the maximum
fault current to a value which will not damage generating, distribution or other associated equipment in the
power system, yet allow sufficient flow of fault current to operate protective relays to clear the fault.
A groundingtransformer is intended primarily to provide a neutral point for grounding purposes. It may be
provided with a delta winding in which resistors or reactors are connected.

8. High-Voltage underground cables are constructed in many different ways, but are usually shielded cables. They
are made with a conductor, conductor-strand shielding, insulation, semi-conducting insulation shielding,
metallic insulation shielding, and a sheath. The sheath can be metallic and may then serve as the metallic
insulation shielding and be covered with a nonmetallic jacket to protect the sheath. This sheath helps to reduce
or eliminate inductive reactance. Such cables are commonly used in circuits operating at 2400 volts or higher.
High voltagefuses are used to protect the electrical system in a substation from power transformer faults. They
are switched for maintenance and safety.

9. Lightning arresters are protective devices for limiting surge voltages due to lightning strikes or equipment
faults or other events, to prevent damage to equipment and disruption of service. Also called surge arresters.
Lightning arresters are installed on many different pieces of equipment such as power poles and towers, power
transformers, circuit breakers, bus structures, and steel superstructures in substations.

10. A manhole is the opening in the underground duct system which houses cables splices and which cablemen
enter to pull in cable and to make splices and tests. Also called a splicing chamber or cable vault.
Switchgear can be either for outdoor use or indoor use. An outdoor metal-cladswitchgear is a weatherproof
housing for circuit breakers, protective relays, meters, current transformers, potential transformers, bus
conductors, and other equipment. An indoor switchgear must be protected from the environment and contains
the same types of equipment as the outdoor type.

11. Various types of meters are found in substation control houses. They all are measuring devices and can be an
indicating meter or a recording meter. An indicating meter shows on a dial the quantity being measured. A
recording meter makes a permanent record of the quantity being measured, usually by tracing a line on a
chart or graph.
Substations commonly use microwave communication equipment for communication with local and regional
electric power system control centers. This system allows for rapid communication and signaling for controlling
the routing of power.
Electric power for microwave transmission comes from special transformers that reduce incoming transmission
voltage to that required for the microwave system.
Oil circuitbreakers are used to switch circuits and equipment in and out of a system in a substation. They are oil
filled to provide cooling and to prevent arcing when the switch is activated.

12. A type of insulator with a bell or pot-like shape used to connect underground electrical cables to overhead
lines. It serves to separate the bunched-up conductors from one another in the cable to the much wider
separation in the overhead line. It also seals the cable end from the weather. Potheads are mounted on a
distribution pole and the assembly is called a riser pole.

22. Capacitor Voltage Transformers (CVT), are used for voltage metering and protection in high voltage
network systems. They transform the high voltage into low voltage adequate to be processed in
measuring and protection instruments secondary equipment, such as relays and recorders).
A Voltage Transformer (VT) isolates the measuring instruments from the high voltage of the
monitored circuit. VTs are commonly used for metering and protection in the electrical power
industry.
Main applications of CVTs in HV Networks
 Voltage Measuring: They accurately transform transmission voltages down to useable levels for revenue
metering, protection and control purposes
 Insulation: They guarantee the insulation between HV network and LV circuits ensuring safety condition to
controlroom operators
 HF Transmissions: They can be used for Power Line Carrier (PLC) coupling
 Transient Recovery Voltage: When installed in close proximity to HV/EHV Circuit Breakers, CVT’s own
High Capacitance enhance C/B short line fault / TRV performance
Mechanical Features
 Available with standard/heavy/very heavy creepage distance
 All external components are made by aluminum
 Inox steel bellows
 High earthquake strength capability
 Suitable for ambient temperature -60 / +70 °C (extended range upon request)
 Available for Line Traps mounting on the top
Electrical Features
 Best capacitance/accuracy stabilities in all service conditions
 Design solutions allow to reach High Rated Capacitance in reduced CVTs dimensions
 Passive ferroresonance suppression circuit provides superior damping while not degrading transient response
 Best accuracy as transient performance – suitable for ultra-rapid line protection devices
Type TCVT (for International Market)
Types TECF, TECP, TEVF, TEMF, TEVP, TERP, TEMP, TETP, TEICF, TEIRF, TEIMF, TEHCF,
TEHCP, TEHMF & TEHMP
(for North American Market only)
 Available from 46 kV up to 1200 kV
 Designed in accordance with main international standards
 Optimized insulation system design utilizing state-of-the-art processing techniques with
 either mineral oil or synthetic insulating fluids
 Composite or Porcelain insulator
 Oil expansion by way of hermetically sealed stainless steel bellows assures the integrity
 of the insulation system over time
 Bellows puncture pin provides for release of internal pressure in the event
of severe service conditions leading to internal discharges
 High range of Customization according specific customer requirements