AC Motor Starter

 DOL Starter

Star-Delta Starter

AC Motor

SQIM
WRIM

DC Motor Starter

Starters are used to protect DC motors from damage that can be caused by very high current and torque during startup. They do this by providing external resistance to the motor, which is connected in series to the motor’s armature winding and restricts the current to an acceptable level. Then the removal of this resistance is done in steps as the motor accelerates.

It is very important and desirable to provide the starter with protective devices to enable the starter arm to return to the OFF position for the following conditions.

1. when the supply fails, thus preventing the armature from being directly across the mains when this voltage is restored. For this purpose, we use a no-volt release coil.
2. when the motor becomes overloaded or develops a fault causing the motor to take an excessive current. For this purpose, we use an overload-release coil.

Types of Starter

1. Two-point starter
2. Three-point starter
3. Four-point starter

• Three-point starter:

1. In a three-point starter, the no-volt release coil is connected in series with the
2. Shunt field circuit so that it carries the shunt field current.
3. While exercising speed control through the field regulator, the field current may be weakened to such an extent that the no-volt release coil may not be able to keep the starter arm in the ON position.
4. This may disconnect the motor from the supply when it is not desired. This drawback is overcome in the four-point starter.

• Four-point starter:

1.  In a four-point starter, the no-volt release coil is connected directly across the supply line through a protective resistance R.
2. Now the no-volt release coil circuit is independent of the shunt field circuit. Therefore, proper speed control can be exercised without affecting the operation of the no-volt release coil
3. Note that the only difference between a three-point starter and a four-point starter is the method in which a no-volt release coil is connected. However, the working of the two starters is the same.
4. It may be noted that the three-point starter also provides protection against an open-field Circuit. This protection is not provided by the four-point starter.

 

 

• Two-point starter:

1. This starter is only for D.C. series motors. The basic construction of a two-point starter is similar to that of a three-point starter except for the fact that it has only two terminals namely line (L) and field (F).
2. The F terminal is one end of the series combination of field and the armature winding. The action of the starter is similar to that of a three-phase starter.
3. The main problem in the case of d.c. the series motor is its speeding action when the load is less.
4. This can be prevented using two-point starters. The no-volt coil is connected in series with the motor so both currents are equal.
5. In a no-load situation load current drawn by the motor decreases causing the no-volt coil losses its required magnetism and release the handle to the OFF position.

Reference:
[1] https://www.scribd.com/doc/38037500/d-c-Motor-Starter
[2] https://www.javatpoint.com/starting-of-dc-motors

DC Motor

A DC motor, or direct current motor, is an electrical motor that uses AC current to transform electrical energy into mechanical energy. There are two types of DC motors based on the construction such as 

1. Self-excited DC Motor 
2. Separately excited  DC Motor
3. Permanent Magnet DC Motor

Similarly, self-excited motors are classified into three types namely 

1. DC series motor
2. DC shunt motor 
3. DC compound motor

DC series motor: The Series motor has a field coil connected in series to the armature winding. For this reason, a relatively higher current flows through the field coils, and it is designed accordingly as mentioned below.

1. The field coils of the DC series motor are wound with relatively fewer turns as the current through the field is its armature current and hence for required MMF less numbers of turns are required.
2. The wire is heavier, as the diameter is considerably increased to provide minimum electrical resistance to the flow of full armature current.
3. Despite the above-mentioned differences, about having fewer coil turns the running of this DC motor remains unaffected, as the current through the field is reasonably high to produce a field strong enough to generate the required amount of torque.

DC shunt motor: A DC shunt motor (also known as a shunt wound DC motor) is a type of self-excited DC motor where the field windings are shunted to or are connected in parallel to the armature winding of the motor. Since they are connected in parallel, the armature and field windings are exposed to the same supply voltage.

DC compound motor: A compound wound DC motor (also known as a DC compound motor) is a type of self-excited motor, and is made up of both series field coils and shunt field coils connected to the armature winding.

• Both the field coils provide for the required amount of magnetic flux, that links with the armature coil and brings about the torque necessary to facilitate rotation at the desired speed.
• Like a shunt wound DC motor is bestowed with an extremely efficient speed regulation characteristic, whereas the DC series motor has high starting torque.
• The compound wound DC motor can further be subdivided into 2 major types based on its field winding connection concerning the armature winding, and they are:
• Long Shunt Compound Wound DC Motor
• Short Shunt Compound Wound DC Motor

DC Generator

DC Fuse and DC MCB

A fuse is an electrical safety device that operates to provide overcurrent protection of an electrical circuit. Its essential component is a metal wire or strip that melts when too much current flows through it, thereby stopping or interrupting the current. It is a sacrificial device; once a fuse has operated it is an open circuit, and must be replaced or rewired, depending on its type.

DC Miniature Circuit Breaker (DC MCB) is particularly designed for DC over-current and short-circuit protection in an electrical circuit. DC MCB and the AC MCB have the same functions. Only application scenarios are different. DC MCB is mainly used for direct current (DC) systems applications, line Solar Photovoltaic (PV) and Solar Battery Energy Storage Systems (BESS). The voltage state of DC MCB is generally DC 12V-1500V.

Reference:
[1] https://en.wikipedia.org/wiki/Fuse_(electrical)

Array and Array Junction Box

We commonly use 72 Cell panels or 144 Half-Cut Cell Panels. A 72-cell panel produces 46-50 Volts while not under load. At maximum power point, it drops around 37-42 Volts. A standard On-grid Inverter requires a much higher voltage than this. Sometimes off-grid inverters also require multiple modules in series. 
A solar photovoltaic array is formed by a series/parallel combination of SPV modules to attain the desired voltage and current level. Usually in an Array modules are kept in series to obtain a certain voltage. Arrays are kept in parallel to increase the current.
Before connecting to the inverter sometimes protection is required (if it is not built in the inverter). Like DC Fuse, DC MCB, DC SPD and Current Measurement Unit. These are installed in an Array Junction Box or String Combiner Box. 

Reference:
[1] https://creativestudio1973.blogspot.com/2021/06/introduction-to-solar-panel.html
[2] https://creativestudio1973.blogspot.com/2021/06/on-grid-systems.html
[3] https://creativestudio1973.blogspot.com/2021/09/surge-protection-device.html
[4] https://creativestudio1973.blogspot.com/2023/11/dc-fuse-and-dc-mcb.html