Wiring Diagram and Control of Direct On Line 3-Phase Motor Starter


Wiring Diagram Direct On Line for 3-Ph Motor Starter, with explanation.
Current surge when motor is operated or commonly called the starting current can reach 4 to 7 times from the normal current of the motor.
Current Starting electric motor = 4 to 7 x In
Given the magnitude of the surge in electricity when an Electro motor is operated (Starting Motor), various systems are used to minimize the surge of the starting current.

Various Motor Starter System
However for Electro motors that have small power in general do not need a starting system that serves to reduce the surge of starting currents, Therefore, one of the starting circuit systems for electro motors with small power, is enough to use the Direct On line circuit.

The Direct On Line (DOL) circuit system is: Electro motor directly gets a voltage supply of 100% of the source voltage (380 Volt).

Motor starter system using the Direct On Line circuit is the simplest, and is commonly used for electro motors that have a power smaller than 5.5 Kw.
Motor 5.5 KW or Smaller = Direct On Line
To get to know more clearly about how the working principle of a starter motor circuit with a DOL system (Direct On Line), follows the wiring DOL circuit diagram (Direct On line), a series of Line diagrams and Control diagrams, along with an explanation.

Wiring Diagram and Control of Direct On Line 3-Phase Motor Starter

wiring-diagram-direct-on-line-motor-starter
Wiring Diagram Direct On Line
Working Principles:
  • When the Push Button "On" is pressed, then the source voltage of the MCB will flow towards the Co1 Magnetic Contactor K1 and cause the Magnetic Contactor to work connecting the main terminal (LINE) and drain the voltage source through the TOR (Thermal Overload Relay) and towards Electro Motor.
  • Because the working principle of the ON Push Button when released will be disconnected again, then the "Locking" series is added.
  • "Lock" functions to drain the voltage source from the MCB through a series of Push Button "OFF", heading directly to the NO (Normally Open) auxiliary terminal on the Magnetic contactor and then the terminal is connected to the Coil.
  • So, when the Push Button "On" is pressed, the voltage from the Push Button "On" will flow to the coil, and the magnetic contactor works, when the magnetic contactor works, the auxiliary terminal NO on the Magnetic contactor will be connected and also drain the voltage source from the Push Button "Off" towards coil.
  • Because the voltage source of the lock has been flowed towards the coil, when the Push button is "ON" removed, the magnetic contactor still works because it still gets a voltage source from the Push Button "Off".
  • Then when the Push Button "Off is pressed, the voltage source that passes through the auxiliary terminal" NO "(Lock) will be disconnected, and the Magnetic contactor will stop operating and disconnect the main circuit.

Conclusion:
  • Push Button "On" pressed-Magnetic Contactor works-Voltage flows to Electromotor-Electromotor operates-Pilot Green Light Lamp (RUN).
  • Push Button "On" is released - Magnetic contactor still works because it gets a voltage from "Locking" - Electro motor continues to operate.
  • Push Button "Off" is pressed - the voltage source to the lock is disconnected - the Magnetic contactor stops - the circuit is disconnected - Electro motor stops operating (STOP).

Components:
1. MCCB (No-Fuse Breaker)
MCCB (Molded Case Circuit Breaker) or commonly called No-Fuse Breaker, serves as the main safety in the circuit, MCCB will work by deciding the power source to the circuit when there is an Over Current or during a Short Circuit.

In addition, the MCCB also functions as a manual circuit breaker by lowering or increasing the lever in the MCCB, size of the MCCB used for the DOL circuit (Direct On Line) is adjusted to the amount of Electro motor power.

How to determine how many amperes MCCB (Breaker) is used in the DOL series, are 125% x In (125 percent of nominal current of motor).

MCCB = 125% x In

Example:
Motor 5.5kw (P = 5,500 Watt), working voltage 380 Volt, Cosphi 0.80, Then the nominal current (In) of the motor is:
  • P = V x I x Cosphi x √3
  • 5,500 watts = 380Volt x I x 0.80 x 1.73
  • I = 5500 watts / 525.92
  • In = 10.45 Amp.
MCCB (Breaker) is : 125/100 x 10.45 = 13 Ampere, Because MCCB 13 Amp is not available in the market, it can use MCCB 15A.

2. Magnetic Contactor
Magnetic Contactor is a component that serves to decide or connect a circuit with the working principle of magnetic induction.

Magnetic Contactor has a coil which serves to convert electric current into a magnetic field, when Coil is given a voltage, it will produce a magnet that will attract a metal element that serves to connect / disconnect the connecting terminal (contact point), "Coil" terminals on Magnetic Contactors are generally given the symbols A1 and A2.

The main terminal on the Magnetic Contactor used in the circuit consists of 3 terminals for connecting R, S, T phase from the voltage source to the Electro motor.

This main terminal is NO (Normally Open), when the magnetic contactor is not given a voltage position the terminal is open or not connected, the main terminal will be connected when the magnetic contactor coil is voltage, (Source voltage in accordance with the magnetic contactor specifications used).

In addition to the main terminal, the magnetic contactor also has additional terminals (Contact points) that are NO (Normally Open), or NC (Normally Close).
  • NO = Normally Open
  • NC = Normally Close
NO = Normally Open, Magnetic contactor is in a normal position or does not get a voltage supply, this terminal is open (not connected), this terminal will be connected (closed) when the coil magnetic contactor is voltage.

NC = Normally Close, Magnetic contactor is in a normal position or does not get a voltage supply, this terminal is closed (connected), this terminal will be disconnected (open) when the coil magnetic contactor is voltage.

3. Thermal Overload Relay
TOR or Thermal Overload Relay, is a component that functions as an electro safety motor when Overload occurs.

Thermal Overload relay works based on the electric current that passes through the Bimetal section inside the Thermal Overload relay, if the amount of electric current passing through the bimetal exceeds the set setting, the bimetal temperature increases so that the bimetal curve.

The bimetal curl will touch the existing lever, and cause the terminal on the Thermal Overload relay to work, the NO terminal will be connected and vice versa the NC terminal will be disconnected.

4. Miniature Circuit Breaker
MCB or Miniature Circuit Breaker in the DOL (Direct On line) starter motorbike circuit, serves as a safety control circuit, If a short circuit occurs in the control circuit, the MCB will disconnect the power source to the control circuit.

So, the MCB is only here to secure the circuit, and the existing components, such as Magnetic Contactor, Pilot Lamp, and circuit cables, (Not to secure Over current of Electro motors).

MCB size commonly used in starter motor DOL circuits, usually not too large, The size of the MCB commonly used is MCB 3 Ampere.

5. Push Button (On & Off)
Push Button On (Start/run) is NO (Normally Open), When the On (Start) button is pressed, then the circuit or contact point that was originally disconnected will be connected, then if the button is released the circuit or the contact point will be disconnected again.

Push Button Off (Stop) is NC (Normally Close)
When the Off (Stop) button is pressed, the circuit or contact point that was originally connected will be disconnected, then if the button is released the circuit or the existing contact point will be reconnected.

Remember:
The working principle of the Push button only works for a moment when pressed, when the pressure is released (Not pressed) the push button will return to its original position.

Pilot Lamp (Green & Red)
Pilot lamp on Direct On Line) Starter motor functions as a sign light (Signal), If the Green light is on indicates that the electro motor is operating (RUN), If the red light lights up indicates that the electro motor stops operating (TRIP) caused by overloading (Over load).


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