(In the beginning, in order to design a control panel, we must know some things, such as (knowing the load for which we will design the panel, so it is necessary to know how to read the data panel as shown in the above picture).
This motor has a capacity of 0.25 hp and an average of 0.18 kilowatts. These calculations were explained in a previous lecture. In this case, it is necessary to know the voltage of 220 volts AC or 380 volts AC, in order to choose the contactor and the overload
First, the contactor:
Image result for contactor
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E is an electromagnetic switch and consists of two parts, the lower part is fixed letter
On the middle end, there is a faulty wire coil, which is the coil or the bob between it, and this was explained in a previous lecture (from here).
Three things must be known when buying a contactor
- pregnancy capacity
- voltage difference
- number of touch points
It should be noted that the three main points are the ones that bear the current of the motor, and the greater the value of the contactor current than the load current, the better.
Secondly, the voltage difference for the control circuit is not required to be the same as the voltage value of the source, and if the circuit voltage is 24 volts continuous, it must be The socket for the contactor is 24 volts DC
It is possible that the circuit does not need these points, and another needs a certain number of these auxiliary points (no nc). Third, it is the number of points. There is no contactor with the same value of the current, but it exists in varying degrees such as 9 amps, 16 amps, 25 amps, etc.
So in this example of the motor above
The motor current in the case of 220 volts connection, the current is 1.3 amps, and in the case of 380 volts, the current is 0.75
If the contactor required in this case is 9 amperes, as it is the start of the current in the contactors
Second, the Circuit breaker
It is a circuit breaker switch that we need to protect the circuit from any short current that occurs to the circuit, so the circuit is disconnected. Types of circuit breakers:
- ACB Air Circuit Breaker
- - MCCB: Molded Case Circuit Breaker
- MCB: Miniature Circuit Breaker
There are requirements to choose the type of cutter, according to the following
1- the number of electrodes
2- Operating voltage
3- Normal operating current
4- Cut-off current when a short current occurs
5- Cut-off current when overloading occurs
6- Pregnancy type
7- The capacity of the palace stream
There are three types: Type B, which is the first type:
It has a separation current ranging from 3 to 5 times the load current and is used in lighting circuits.
C type II type:
It has a separation current ranging from 5 to 10 times the load current and is used with fans, adjustments and motors.
D type III type:
It has a separation current ranging from 10 to 20 times the load current and is used with high capacities
The method of calculating the secant value:
Icb=Ir*1.25 for simple loads, according to the law
So in the above example:
The load current is 1.3 amps in the case of 220 volts, if Icb = 1.3 * 1.25 = 1.6 amp
The circuit breaker values are fixed. There is no breaker of 1.6 amps. We choose the nearest circuit breaker of this value, which is 2 amps.
Note, there is an example number of 10000 amps on the cutter
This number indicates the capacity of the shortening current, meaning the maximum current that the circuit breaker can bear without burning
If the short circuit current passing through the switch is greater than the capacity of the short circuit current, the circuit breaker will burn before it is disconnected
Available capacities: 30,000 amps, 60000 amps, and 10000 amps
The price of the circuit increases with the increase in the capacity of the palace current
Third, the overload thermal breaker
It is a tool to protect the device from burning, and if the load pulls a high amp, as the temperature of the coils increases, the motor burns out.
The way it works is a disconnect switch. When the load current increases and the temperature increases, the device has a thin piece of molten metal.
At a certain temperature, it turns the closed contact points into open points, and thus the circuit is separated in order to preserve the motor
How to calculate it in the circle
Io.l=Ir*1.15 (safty )
In the example on the motor, the load current of the motor is 1.3 amps
Iol=1.3*1.15=1.5 amper so
A lecture to explain the automatic loading and the mechanism of its operation (from here)
Fourth, the fuse :
The fuse is used to protect the electrical circuit from danger
Excess current by making an opening in the circuit path, and it is cut off
The current passes and the circuit stops working until a search is made
The reason for the current to exceed its normal value and to fix it, and therefore it is
It keeps the circuit from being damaged, so it is necessary to choose
The appropriate fuse.
It consists of a wire that bears a specific current. If the current flowing through it increases, the wire melts and the current stops.
Ampere Rating
Represents the maximum current that the fuse can transmit, and when the fuse is exposed to a higher amperage for a certain period of time, it turns into an open circuit and the flow of current is interrupted
Voltage Rating
The maximum voltage that the fuse can safely withstand while opening (cutting the circuit path) without an electrical spark, and it is written on the fuse, and its unit is in volts, whether it is AC voltage or DC voltage.
Short circuit rating
It shows the maximum current that the fuse can withstand when the circuit is safely opened so that no damage or electrical spark occurs that leads to the combustion of the fuse body and the place where it is installed.
LBC = Low Breaking Capacity
HRC = High Breaking Capacity
EBC = Enhanced Breaking Capacity
Fast Acting Fuse
It is a type of fuse that opens quickly, when the current increases, as this type of fuse was not designed to withstand a period of time in front of a temporary rise in current
High Speed Fuse
It is a type of fuse that opens as quickly as possible
Slow Acting Fuse
This type of fuse is designed so that
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