Types of Relay

 

Types of Relay

The many types of Relay is available in the market but we use some types of relay in our work, so we will discuss about some important types.

1-Normal Relay

The normal relay is mostly useful relay it most used in Stabilizer, Auto change over switch, UPS, and etc.

This types of relay has 5v, 9v, 12v, 24v, also 110 and 220v coil, means its coil can operates by both currents such AC and DC, but typically used of 12v DC coil's relay, because it’s easy to use in every circuit.

The normal Relay available in different current rating, because it used by its ampacity, means if we needs to control high current equipment, then we required high ampacity relay, and if we require to control low current equipment then we can use of low ampacity's relay.

The normal relay's current rating is minimum 10 Ampere, and maximum 100-150 Ampere current.

In terms of pins we have 4 Types of relay

1- SPST
2- SPDT
3- DPST
4- DPDT

     1-    SPST Single pole single throw

The SPST relay works as a normal switch button, it can only "ON" or "OFF" to any equipment, when its coil will energized then it act as close circuit, and when its coil de energized then it remain in open circuit condition.

It has only Four pins, which is 2 pins of coil, and other two pins is common and output.

This type relay mostly used in, single switching equipment, Cars, Remote control appliances and etc.

Because in Cars we needs to only 'ON" or "OFF" to any equipment, such as for Self start, Headlights, Horn, and etc.

2-    SPDT Single pole double throw

The SPDT relay works as two way switch button, means it can operates two equipment by one common wire, it has five pins, which is two pins for coil, and other three pins, "1" used for Common, and "2" pin is Normal close, and "3" pin is normal open.

When its coil de energized then it remain in normal condition, and its common pin or connector connected with normal close pin, and when its coil energized then its same common pin will connected to normal close pin, thus when its coil energized so its pins will changed.

The “SPDT” relay mostly used in Stabilizer, and voltage changer equipment or where we need only one wire changing.

3-    DPST Double pole single throw

The DPST relay works as a switch button, but it can control two equipment by two common wires, it has six pins, which is two pins for coil, and other four pins, 3 & 4 is used for Common, and 5 and 6 is Normal open.

When its coil de energized then it remain in open circuit condition, and its common pin or connector not connected to each other, and when its coil energized then its both common pins will connected to its other two connectors, then it act like close circuit, thus this type of relay can operates two wires together.

The DPST relay used where we required two equipment switch "ON" or "OFF" together by one signal.

4-    DPDT Double Pole Double Throw

This type of Relay is very similar to DPST relay, because it can change two wires by one signal, but it has one difference that it is Double throw, means its work as a two way switch, it can operates two equipment by two different voltage source,
It has eight pins which is two pins used for coil, and other six pins used for input and output, its 2 pins is Common pins, and two pins normal close and other two pins is normal open.

The DPDT type relay use in automatic change over switch, because in automatic changeover we needs to control both wires such as Neutral and phase, for this we used this types of Relay in auto change over switch.

Different types of relay

We have many types of relay are used but here discussed about major different relay.

1- Reed Relay

This type of relay has only two metallic contact which is sealed in tube shape glass, so when any magnetic will come to around it, then its contact will close together by magnetic filed and contact act by closed circuit.

So wire wounded there top of glass body which will energized by electrical current and create magnetic field, so contact will close together  by this magnetic field.

2- Electromagnetic Relay

This type of relay is most used, basically you will see this of Relay in many circuits, such as stabilizer, ups, inverter, automatic switches, and also this type of Relay used in cars.

This relay has a permanent coil, which when energized by electrical current then coil will attract to metallic contact, so when contact will attach this coil, contact will change own first place and will connect to other contact, thus line will change by electrical signal, because coil has energized by current.

3- Solid state relay

The Solid state relay also known by SSR, this types of relay is different than other relays, when the other type of relays has a coil and movable parts which works by magnetic.

But the SSR relay has not any movable part, basically it has a LED and Photo resistor inside, so we will give signal to LED then LED will glow and out light, so photo resistor will take its Light, and flow a current to Load.

Such as other relays primary side has coil, but SSR relay has LED, and other relays secondary side has metallic contact, but SSR relay has Photo transistor in secondary side.

4- Buchholz relay

Buchholz relay is used for protective purpose for oil transformers, this relay is used in transformers above 500kva.

It used in center of conservator and main oil tank, basically it not has any electrical or electronics part, the Buchholz relay works by mechanical setup.

When transformer in running condition it will generate some heat, but when load will increase from its rating power then its heat will be increase and also Oil will go to above from its original level. so you known that when oil get heat it produce some steam, so this steam will pass through Buchholz relay, because Buchholz relay is connected in center of conservator and oil tank.

The Buchholz relay basically has two mercury switches, one switch used for Alarm activation in normal faulty condition, and other mercury switch used for circuit breaker which will do off the transformer in heavy faulty condition.

So when transformer near about full load such as 80% to 90% then it will generate some steam which will put pressure only at Alarm switch, for this in normal faulty condition only alarm will active.

And when transformer get any fault or more load from its rating then oil will get more heat and also steam will out with high pressure, so its high pressure will active to circuit breaker switch, thus transformer will save from burnt.