3-phase Controlled Soft Starter

Dear all,

We are now developing a 3-phase anti-parallel SCR controlled soft starter for our own use.

We have 3 zero crossing circuits to detect the zero cross of L1, L2 & L3 and 3 SCR firing circuits to trigger the 3 sets of anti-parallel SCRs.

The idea is to fire these 3 sets SCRs at an angle just before zero cross and gradually increase the firing angle and eventually fully turn on all the 3 sets SCRs.

The problem is when we started to fire these SCRs, the motor started to ramp up slowly at CW direction at very low speed, after a short while, the motor started to jerk and then the motor started to ramp up at opposite CCW direction smoothly until it reached full voltage (SCRs fully on).

Does anyone have any idea what is the cause of this problem and how to overcome this problem?

All comments are welcome!

Cheers!

Sensorless Vector Vs Space Vector Drive

Dear all,

Good day!

Can anyone please tell me what are the major differences between 'Sensorless Vector Controlled' & 'Space Vector Controlled' AC drive?

What are the typical applications that need these 2 different technologies?

danke!

Soft Starter With Motors In Parallel Connection

Dear all,

I am now working on a project for a water treatment plant, which the customer would like to use soft starters to control waste water pumps in order to take care of the water hammer problems.

There are about 200 units of 1kW motors used to pump waster water, which are located about 50m away one from the other.

The thing is, due to budget limitation, the customer could not afford to use 1 soft starter for each motor and would like to use, says 1 unit of 15kW soft starter to soft start and stop 15 unit motors. The time between each start is about 2 to 3 hours.

Does any one of you have any experience in this kind of parallel connection application with soft starter?

If this is workable, what is the maximum number of motors to be connect in parallel?

I am afraid if anything happen on 1 motor it will cause the rest of the motors fail as well, would this happen? If this might happen, then the whole world would point the finger at the soft starter before even start to verify the actual cause of failure.

Besides this, is there any other hidden risk, which you guys can foresee?

All comments are welcome!

Danke!

HVAC rating of soft starters?

Dear all,

I believe most of you have ever come accross the term "HVAC Rating" for AC drives, where the drives manufacturers claimed that the same VSD could be applied for one size higher HVAC application (eg. a 22kW constant torque VSD could be used for 30kW HVAC application).

I trust this is mainly due to the typical "square torque" characteristics of HVAC application (on the other hand, perhaps this is one of the marketing strategics of drives manufacturers so that their VSDs are more competitive, AGAIN in terms of pricings!)

Do you think that the same concept is applicable for soft starters, where a 22kW soft starters used for constant torque application could be applied for 30kW HVAC application?

danke!

Using opto-triac to trigger SCRs.

Hi,

I am having a circuit where Fairchild MOC3052 opto-triacs are used to trigger the gate of some SCRs.

Fairchild Semiconductor guarantee that the opto-triac would be fully triggered with 10mA (max) LED forward current but they did not mention what is the typical LED forward current (Toshiba TLP3052 stated 5mA as typical LED forward current).

The problem I am facing now is that due to the limitation of my +5VDC power supply, I am able to provide these opto-triacs a max LED forward current of 5mA only.

I have done some tests on few tens of Fairchild opto-triacs and it seems that the max LED forward current in order to fully turn on the triac is approx 3.8 mA.

My circuit seems to work fine now but I am a bit worry what if after certain time of operation and when the opto-triac gets older, it might require much higher LED forward current to turn on the triac (10mA as stated in the datasheet).

Is anyone out there have any idea what is the typical LED forward current of MOC3052 or some other opto-triacs with much lower LED forward current?

danke!