Rated Current (A)
Breaking Capacity (kA)
Relay Range (A)
Rated Residual Current (mA)
No. of Cores
Total Slots (MW)
Horse Power (HP)
No. of Poles
No. of Way
No. of Phases
Energy Consumption (kW)
LOW VOLTAGE SWITCHGEARS
An electrical switchgear is a centralised combination of fuses, circuit breakers and switches. When these devices are lined in series, this arrangement is called a switchgear line-up or an assembly.
A low voltage switchgear is a three phase power distribution device that ensures safe and effective power supply at voltages as high as 1000 V and currents at 6000 A. It is found on the secondary windings of a power supply transformer. This arrangement of the switchgear and the transformer is called a Substation.
- It protects the electrical equipment by interruption of short circuits and overload faults
- It isolates circuits from the power supply, hence handing the control to you.
- It allows more than one source to feed the load, thus enhancing system availability.
MAIN PARTS OF A LOW VOLTAGE SWITCHGEAR
Typically, a low voltage switchgear system consists of three segregated parts:
It is an arrangement of four vertically aligned power circuit breakers boxed in a compartmentalized manner.
- BUS COMPARTMENT:
A set of bus compartments is fixed right behind the breaker compartment, each individualized in solid insulated barriers
- CABLE COMPARTMENT:
Cable Compartment is fixed at the rear of the switchgear with optional compartmentalizing through unvented or vented barriers.
RATINGS A LOW VOLTAGE SWITCHGEAR CAN CARRY
upto 635 Volts
upto 2.2 kV
50 Hz and 60 Hz
upto 10,000 A
Short circuit withstand current
upto 200 kA
Short time withstand current
upto 100 kA and 30 cycles
DIFFERENT TYPES OF LOW VOLTAGE SWITCHGEAR
There are several types of Low voltage switchgear available in the market:
MCCB’s come in a wide range of ratings specific for low current, low energy power circuits. They come with self contained over current trip devices. They depend upon the thermal magnetic trip elements for their tripping characteristic. They are predominantly used for short circuit protection. MCCB’s with magnetic trips are used in motor circuit protection. Other then this, there are non-automatic circuit breakers as well that provide no overload or short circuit protection, thus are used for manual switching and provide isolation alone.
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INSULATED CASE CIRCUIT BREAKER
Insulated case circuit breakers are very similar to MCCB’s in their construction, instead they use glass reinforced insulated material for greater dielectric capacity. Various features of an insulated case circuit breaker includes- quick break protection, push to open button, spring-charged mechanism with low torque handles. They are apt continuous current ratings as high as 4,000 A and an interrupting capacity of 200,000 A. They are costly, bigger in size and slightly difficult to maintain. These drawbacks can be overcomed by providing extra parts of the circuit breaker that duplicate the objectives of the costly parts. They are used for light industry or commercial building, etc.
POWER CIRCUIT BREAKERS:
These are heavy duty power circuit breakers that use spring operated, energy storing elements for varied electric operations. They work on the draw-out mechanism wherein numerous individual circuit breakers are put to de-energized state for maintenance needs and testing. Their range of continuous frame ratings is between 400 A to 4,000 A, which can still be extended to 5000 A to 6000 A as per needs. Short circuit interruption capacity of a power circuit breaker ranges from 50,000 A to 85,000 A.
FUSED POWER CIRCUIT BREAKER:
Typically, these fused power circuit breakers are nothing but an arrangement of bigger unit substation transformers and bigger kVA loads with current limiting fuses. This arrangement provides the short circuit interrupting rating of the switchgear. They are compatible with all frame sizes. The fuse assemblies are directly connected to the circuit breaker making it impossible to take out or install fuses unless the breaker is out of service. They also make use of the blown fuse detection mechanism to ensure the tripping of the breaker right after the fuse is cleared. Overcurrent trip elements in the breaker handle the overcurrent protection for overloads, implying that the fuse does not clear unless the highest short circuits take place.
SELECTION AND APPLICATION OF LOW VOLTAGE DEVICES
There are certain criteria that must be accorded to while selecting in a Low voltage device (switchgears in this case):
The main purpose of installing a circuit breaker is to provide adequate protection.
For the protection equipment to perform optimally, an ambient temperature of 40 °C, and if, by any chance, it exceeds, the manufacturer is to be consulted.
In case of Fuse power switchgear, the voltage of the system should be compatible with the fuse voltage rating.
Major brands that deal in Low Voltage Switchgears are:
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