The switchgear covers an important part of the electrical sector. This article will highlight some important things about switchgear.
Switchgear: Switchgear is not a single object, it refers to the position of the electrical system’s normal activity, including connectors, detectors, and protective devices.
The components of switchgear are-
- Circuit Breaker
- Instrument Transformer
- Conductors etc.
Table of Contents
The components of switchgear
Busbar: Basar is a type of copper or aluminum conductor or sheet or thick rod that collects electrical energy from one or more circuits and distributes that energy through one or more circuits.
Basketball: Basketball is basically a combination of circuit breakers and isolators. There are fireproof walls around the busbar.
Busbar sectionalized: When a fault occurs in any part of the busbar, the operation of the entire busbar system is not stopped and it has the maximum success of the system in the circuit incoming and outgoing circuits of different sections.
The fuse is a short-length current capable of conducting a small and low melting point conductive current, which is capable of carrying a certain amount of current from the electrical circuit connected. The fuse protects the circuit by melting itself when excess current flows beyond a certain amount.
Types of fuses
There are generally two types of fuses:
- Low Voltage Fuse: Semi-enclosed re-warble fuse (500A), HRC fuse (16000A – 30000A)]
- High Voltage Fuse: Cartridge fuse, Liquid type, Metal clad type, Expulsion fuse, Dropout fuse, horn-gap fuse
The circuit breaker is a control and protection device that protects the circuit by disconnecting the faulty circuit from being supplied to the circuit in the abnormal state of the circuit. But after disconnecting it cannot connect the circuit itself. This can be reworked by interfering with a person.
Circuit Breaker Procedures
The circuit breaker has two fixed and one moving contacts. There are CT, relay, and trip coil circuits to handle the moving contact.
Under normal conditions the relay coil is not energized by the current flowing in the line, hence the trip coil is not energized.
Whenever excess current flows in the line due to short circuit or any other fault in the circuit, additional current flows to the CT, resulting in CT. The attached relay coil on which is also energized and engages the link mechanism. This removes the dynamic contact associated with the link mechanism. This is how the circuit breaker protects the circuit by braking.
Types of circuit breakers
According to Voltage-
- Low voltage Circuit breaker (Below 1000V)
- High voltage Circuit breaker (Above 1000V)
According to Extinguishment
- Oil Circuit breaker. ( Bulb oil Circuit breaker, minimum oil Circuit breaker, self-generated Circuit breaker, externally generated Circuit breaker.
- Without oil Circuit breaker. ( water Circuit breaker, air blast Circuit breaker, sulfur hexafluoride Circuit breaker, vacuum Circuit breaker.
A relay is an automated device that responds to a predetermined electrical condition on the electrical circuit and assists in working other devices connected to the circuit for protection.
The relay circuit on the electrical system is located between the breaker and the City. Whenever a fault occurs in the system, the relay is automatically alerted and energizes the circuit breaker’s trip coil. This opens the circuit breaker and protects the system from danger. It is called the silent watchman or the insane watchman who always has to watch out for every flaw in the system.
According to timing specialty-
- Instantaneous type relay.
- Time delay relay.
- Graded time protection type relay.
- Inverse time lag relay.
- Definite time lag relay.
- Inverse definite minimum time relay.
According to the type of use-
- Overvoltage, over current, over-power relay.
- Under voltage, under current, under power relay.
- Over frequency and under frequency relay.
- Overload relay.
- Reverse power relay.
- Sensitive Relay.
- Distance relay
- Instantaneous relay.
- Earthing relay.
The Bukhalage relay is used to detect internal faults in the transformer. It is originally positioned between the main tank of the transformer and the conservator tank.
The circuit to which the protection relay is connected directly to the circuit is called the primary relay.
If the relay is connected to the circuit through CT and PT then the relay is called a secondary relay. A secondary relay is also called a backup relay.
According to the American Standards Association, a relay that does not contain any armature or any rotating material, but produces the desired stimulus without solid motion magnetic or any other material, is called a static relay.
Features of the switchgear system
The essential features of the switchgear system are sensitivity, reliability, high speed, stability, extension benefits and simplicity. It is also important to have the following features of switchgear-
- The defective part must be disassembled no matter what current flows in the fault. But under normal loads, there may be no problem with the system due to the slightly larger load.
- In order to provide continuous supply to the electrical system, only the faulty component must have the ability to identify and disconnect the supply.
- It has to be completed at high speed to provide security, timely enhancement, and various services. The higher the speed, the less prone to damage the error will be.
- It must be trusted, to ensure that it can perform its duties at the right time.
- The Swissgear apparatus must be such that it does not cause any future problems or changes.
- The operation and design of Swissgear and protective devices must be straightforward. So that someone new can easily understand its operation.
Electrical faults or defects of switchgear
Causes and Types of Fault: When two or more conductors come together at normal voltage, the fault is said to have occurred.
Insulator Failure: Electrical fault occurs due to sudden loss of line, lightning charge, voltage drop, un-balance and loss of stability.
Short Circuit Fault Main Two Type –
- Symmetrical Fault: The fault caused by the fault in the electrical system at which an equal fault current flows in each phase is called an asymmetric fault. The circuit breaker rating is determined by the symmetric fault. Symmetric faults are three-phase short-circuit, the three-phase simultaneous short circuit with the earth.
- Asymmetric Fault: The fault caused by an uneven fault current in each phase of an electrical system is called an asymmetric fault. The relay is set through the asymmetric fault. Asymmetric faults are a single line to ground fault, the line to line fault, double line to ground fault, the two-phase short circuit with short circuit and third circuit with a short circuit.
Three methods for determining short circuit current
- Ohmic system
- Per unit system
- Percentage reactant system
Current limiting reactor
The current limiting reactor is essentially an inductive coil, which restricts the short circuit current by providing inductive reactance when needed.
Depending on the composition of the type are Dry-type air cord reactor, iron-core reactor, well-ejected air cord reactor.
Depending on the location, the types are Generator Reactor, Feeder Reactor, Busbar Reactor.
- Stator Winding Fault.
- Stator Inter Turn Fault.
- Rotor fault.
- Field circuits become obsolete.
- Ambulance load.
- Over speed.
Alternator error detection systems are:
- Differential or merge price protection.
- Earth Fault Protection.
- Stator Inter Turn Protection.
The transformer has errors
- Open Circuit Fault.
- Over-heating fault.
- Winding short circuit fault. (Earth Fault, Phase Two Phase Fault, Inter Turn Fault)
The protection systems used to detect transformer defects are:
- Buchalage Relay.
- Earth Fault Relay.
- Over Current Relay.
- Differential or merge price system.
The reasons for the over-voltage are –
Over-voltage on the power system transmission line is mainly for two reasons:
- Internal reasons. (A. Switching Surge, b. Insulation Failure, c. Arking Ground, d. Resonance.
- Non-existent reasons. (A. Direct stroke, b. Indirect stroke.