Electro-Mechanical star delta starter

Star Delta starter is the most widely used application especially for Air-compressor and HVAC system.This starter used for 6 or 12 wire for motor terminal depend on electric motor that chosen for the application.

Basically this starter used 3 unit contactor,1 unit timer delay,1 unit overload relay and start/stop button to control the star delta motor.Around the world,it have many types of control circuit design for star delta.

It have different design and technique  for the control circuit but the main objective is same,to reduce starting inrush current.

For safety condition for the star delta control circuit,it include with interlock for star and delta sequence to avoid serious damage for electric motor.That mean during star sequence,contactor for delta cannot energize or vise versa. read more

How calculate ampere for electric motor?

Generally for electric motor size,it rated by horsepower (hp) or kilowatts (kW) unit.We can recognize the electric motor size when refer to their kilowatts or horsepower.So from power (kW/hp), how we can know the full load ampere for electric motor?

This time i want share about how to calculated the full load ampere (FLA) of electric motor from their power rated.It not difficult if we know the right formula to get the answer.From this calculation we only can estimate the value of full load ampere.

We cannot get the actual full load ampere because it depend on efficiency of motor.If electric motors have a higher efficiency rating,it will draw fewer amps, for example a 10 HP motor with a 60% efficiency rating will draw about 65 amps at 230 VAC compared to about 45 amps for a motor with a 80% rating. read more

NEC calculation for overload sizing

Sizing for overload is important to avoid serious damage for electrical application such as motor starter,machinery or others electrical equipment.

According to NEC,the general requirement for overload sizing be set around 115% or 125% from full load ampere.We should setting the overload relay within this parameter to avoid electric motor from serious damage.

For calculation of overload sizing,it depend on the motor full load ampere current rating,the service factor and temperature for motor.I already explain in my last post about several factor effected for overload relay sizing. read more

Safety interlocking devices

For the electrical power distribution,we used a switch gears to control our distribution power supply to user.One of important things when design the system,we must include with safety interlocking device.

Motor control design also need to attach with interlocking system to ensure the operation is safe for user and can prevent for serious damage of equipment.

Before we design the control circuit or operation sequence,the important aspect that we should consider is about interlocking and must have a deep study to make sure it function properly.

Types of interlocking method

Normally in industry,interlocking devices have a two (2) types of method such as electrical and mechanical control.Their main purposes for interlocking system are  : read more

Transformer winding connection

When we want to install the transformer for our project or any application and auto transformer stater,firstly we must know the transformer winding connection.If not it will cause the damage or serious injury when it install with wrong connection.

So how we can identify the transformer winding connection?Here i want share some tips how to identify the winding connection.This basic information can effected to our voltage supply and if not done i  proper way,it can cause serious damage to our application or equipment.

Commonly manufacture already setting their code or identification method using a letters and numbers.Below is a standard identification code for transformer winding connection for USA,UK and EUROPE :- read more

Three phase transformer winding

In the market now,commonly it have three methods of three phase transformer winding such as a star, delta and zig-zag. Each method can be applied to either or both of the primary and secondary winding of transformer.

This connection must suitable with our output voltage for application and equipment.We should decide which connection is suitable and not effected when power supply energizes.

This 3 types of winding is used for different application and we need to identify a suitable condition to apply this types of transformer winding.This time i want shared some information about transformer winding. read more

Star delta starter

This is a starting method that reduces the starting current and starting torque. Star delta starter design normally consists of three contactors, an overload relay and a timer for setting the time in the star-position (starting position).

For the star delta starter, a motor must be in delta connected during a normal run and the main purpose is to be able to use star delta starter.

Star delta starter received the starting current is about 30 % of the starting current during direct on line start and the starting torque is reduced to about 25 % of the torque available at a D.O.L start.

Star delta starter only works when the application is light loaded during the start. If the motor is too heavily loaded, there will not be enough torque to accelerate the motor up to speed before switching over to the delta position. read more