Inverter merupakan rangkaian elektronik yang merubah dari AC ke DC lalu merubah dari DC ke variable AC dan output variable AC inilah yang dipergunakan untuk mensuplai motor.

Contoh sederhananya adalah dengan lampu pijar, ketika kita beri tegangan 220 V maka lampu akan berpijar dengan terang/normal dan jika diberi tegangan dibawah 220 V maka pijar lampu akan redup. Begitu pun sebaliknya jika diberi tegangan melebihi 220 V/rating lampu maka lampu akan sangat terang bahkan putus.

Konsep inilah yang digunakan pada inverter, dimana kita mengharapkan tegangan yang bervariable sesuai dengan kebutuhan kita. Ingat, perubahan bukan pada tegangannya tetapi pada frekuensi tegangan. Biasanya digunakan pada synchronous motor dimana kecepatan putaran dari motor berhubungan dengan frekuensi tegangan input.

Gambaran system inverter itu sendiri

Input->converter AC/DC->high voltage DC bus->inverter DC/AC->output

Converter, merupakan komponen penyearah dari AC menjadi DC

High-voltage DC bus, menghasilkan tegangan tinggi di sisi tegangan DC sehingga tegangan DC siap dirubah kembali menjadi AC.

Inverter DC/AC, menggunakan IGBT (power transistor) untuk merubah DC menjadi AC kembali dengan frekuensi yang berbeda-beda dengan melakukan pencacahan terhadap tegangan.

Mengapa menggunakan inverter

Sesuai dengan pengertian inverter tersebut maka kita akan memanfaatkan frekuensi tegangan yang bervariasi untuk mendapatkan putaran yang kita inginkan.

Secara teori :

Putaran RPM= frekuensi x 60 / jmlh pole (kutub)

Ketika kita menghubungkan motor AC secara langsung ke sumber tanpa melalui inverter maka akan menghasilkan putaran sesuai dengan ratingnya, sedangkan kebutuhannya tidak selalu seperti name plate, bahkan kurang ataupun lebih dan ini tidak bisa dilakukan hanya menghubungkan langsung dengan sumber.

Selain itu kebutuhan untuk melakukan koordinasi kecepatan antara mesin satu dengan yang lain dengan inverter hal tersebut dapat dilakukan.

Kerugian penggunaan metode lama

Sesuai dengan perjalanan waktu, untuk mendapatkan putaran yang variable penggunaan system mekanik dan hydraulic pun dilakukan seperti penggunaan belt dan gear.

Perbandingan gear dapat menghasilkan kecepatan yang berbeda-beda begitupun dengan penggunaan belt.

Metode mekanik dan hydraulic menimbulkan side effect/kerugian antara lain:

1. i.      losses dalam system mekanis itu sendiri (gear, belt)
2. ii.      suara yang bising/keras saat start dan stop.
3. iii.      banyak oli karena system mekanik membutuhkan pelumasan.
4. iv.      Torsi yang dihasilkan rendah pada saat kecepatan rendah.
5. v.      Kecepatan variable dapat dihasilkan tetapi acceleration dan deceleration tidak dapat dikontrol.
6. i.      Energy saving – HVAC
7. ii.      Koordinasi kecepatan pada prosess – textile dan printing
8. iii.      Sensitive load – elevator, food processing, pharmaceutical.

1. Penggunaannya di industry

Penggunaan inverter pada industry cukup banyak seperti textile, printing, elevator, food processing, pharmaceutical dan HVAC.

Untuk penggunaan terhadap hemat energy terjadi pada HVAC system, ketika tanpa penggunaan inverter motor akan running full load sedangkan kebutuhannya hanya 50% atau 75% sesuai dengan pengaturan damper.

Inverter dapat digunakan untuk mengatur kecepatan motor pada HVAC system sehingga tidak diperlukannya lagi system damper karena pengaturan suhu dapat diatur dengan kecepatan motor.

Penurunan konsumsi listrik dapat dihemat sekitar 5%-25% tergantung dengan system dan design dan aplikasinya sudah banyak diterapkan oleh industri.

Dengan adanya inverter kita dapat mengatur kecepatan yang di inginkan dan mengkoordinasikan satu motor dengan yang lainnya. Hal ini banyak dilakukan dalam industry printing dan textile. Dari kecepatan dapat dikonversikan menjadi tegangan maupun hal lainnya sesuai dengan kebutuhan design.

Penggunaan pada beban yang membutuhkan torsi tinggi saat kecepatan rendah dapat juga diterapkan menggunakan inverter. Contohnya pada elevator dimana ketika awal membutuhkan torsi yang cukup sedangkan kecepatannya masih cukup rendah dan hal ini dimungkinkan dengan inverter, begitupun sebaliknya ketika terjadi pengereman dapat diatur waktunya sehingga penurunan kecepatannya tidak drastis.

It is often desirable or essential to isolate one circuit electrically from another, while still allowing the first circuit to control the second.  For example, if you wanted to control a high-voltage circuit from your computer, you would probably not want to connect it directly to a low-voltage port on the back of your computer in case something went wrong and the mains electricity ended up destroying the expensive parts inside your computer.

One simple method of providing electrical isolation between two circuits is to place a relay between them.  A relay consists of a coil which may be energized by the low-voltage circuit and one or more sets of switch contacts which may be connected to the high-voltage circuit.

How Relays Work

The metal arm is at its rest position and so there is contact between the Normally Closed (N.C.) switch contact and the ‘common’ switch contact.

If a current is passed through the coil, the resulting magnetic field attracts the metal arm and there is now contact between the Normally Open (N.O.) switch contact and the common switch contact.

Advantages of Relays

The complete electrical isolation improves safety by ensuring that high voltages and currents cannot appear where they should not be.

Relays come in all shapes and sizes for different applications and they have various switch contact configurations.  Double Pole Double Throw (DPDT) relays are common and even 4-pole types are available.  You can therefore control several circuits with one relay or use one relay to control the direction of a motor.

It is easy to tell when a relay is operating – you can hear a click as the relay switches on and off and you can sometimes see the contacts moving.

Disadvantages of Relays

Being mechanical though, relays do have some disadvantages over other methods of electrical isolation:

Their parts can wear out as the switch contacts become dirty – high voltages and currents cause sparks between the contacts.

They cannot be switched on and off at high speeds because they have a slow response and the switch contacts will rapidly wear out due to the sparking.

Their coils need a fairly high current to energise, which means some micro-electronic circuits can’t drive them directly without additional circuitry.

The back-emf created when the relay coil switches off can damage the components that are driving the coil.  To avoid this, a diode can be placed across the relay coil, as will be seen in any Electronics in Meccano circuits that use relays with sensitive components.

Choosing a Relay

When choosing a relay to use in a circuit, you need to bear in mind properties of both the coil and the switch contacts.  Firstly, you will need to find a relay that has the required number of switch poles for your application.  You then need to make sure that the switch contacts can cope with the voltage and current you intend to use – for example, if you were using the relay to switch a 60W mains lamp on and off, the switch contacts would need to be rated for at least 250mA at 240V AC (or whatever the mains voltage is in your country).

Also of importance is the material that the switch contacts are made of – gold is good for low-voltages, whereas tungsten is suitable for switching high voltages and currents.

Finally, you need to choose a relay that has a coil that can be energised by your low-voltage control circuit.  Relay coils are generally rated by their voltage and resistance, so you can work out their current consumption using Ohm’s Law.  You will need to make sure that the circuit powering the coil can supply enough current, otherwise the relay will not operate properly.

The Latching Relay Circuit

If a relay is connected, it will become ‘latched’ on when the coil is energised by pressing the Trigger button.  The only way to turn the relay off will then be to cut the power supply by pressing the Reset button (which must be a push-to-break type).

The technical name for this type of behaviour is ‘bistable’, since the circuit has two stable states for its output – on and off.  Bistable circuits can also be constructed using many other components, including the 555 timer IC and transistors.

What’s the point of this circuit?  The Normally Open switch contact of the relay could also be connected to a device such as a motor.  The device will then run indefinitely until some event (maybe triggered by the device) momentarily presses the Reset button, thereby turning off the coil ready for the Trigger button to be pressed again.

This system could be used in a model which needs a ‘Push to Operate’ button.  A motor and gearing system in the model can be used to press the Reset button to cut the power to the relay coil after the model has been running for a certain amount of time, or until a certain event has occurred.  Of course, you would have to be sure that there was enough momentum in the mechanism that the button is released ready for the next cycle.

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Having problem with compressor made me very hassle, because compressor is one of important machine. Why I could say that, compressor produce compressed air that used in pneumatic machine. Our mastering machine is using pneumatic system for moving some part, rotating table and sucking the glass.

My problem are unstable pressure, no backup system and compressor always have problem. Unstable pressure it mean Mastering machine needed min 7 bar for normal operation and I don’t know how many consumption for air because name plate in compressor is 29 CFM (cubic feet per minute) its around 13 litter per second.

Actually we have 2 compressors for running normal and backup but our machine not new anymore that’s why pressure can’t reach. If I only running one machine can’t support and reach 7 bar even name plate of compressor can reach 10 bar maximum.

I try to explore deeper, the main problem is I don’t know the air consumption of machine, our compressor are too old, and some leak in pipe installation.

So for backup we need another supply for backup if something happen with both compressors. We try to bypass the neighbor factory compressor, because their compressor have two and big capacity. After calculation of installation we finally can done this one.

I try to calculate air consumption for the machine; we have two compressors with 13 litters per second if we assume both compressors running so total air consumption below 16 liters per second. And with bypass compressor we have 56 litters per second, its mean we have fourth time from each compressor and twice time from machine needed.

After this method I can solve problem, so if our compressors down we still have backup.

For note, 1 CFM is 28.3 litters/minute