Buss Bar Forces, Distribution Chassis, Short Circuit Testing

Hi all.

Apologies if I'm posting this in the wrong area of the forum, but......

I'm currently involved in the development of a 400VAC 50Hz 3phase +N 1600A MCCB chassis. This chassis is double ended, as such, amongst many design requirements, we need to succesfully pass a 63kA thru current short circuit test.

Whilst I'm reasonable confidant I understand the level of force produced between the bars (horizontal, with the chassis lying down), actual tests seem to indicate a vertical force which is upsetting the applecart.....bending the bars upwards and breaking our bussbar support system.

This vertical force may be the result of the bars twisting out of the intermediate supports we have developed......or it may be the result of interaction between the bussbars and the mild steel chassis pan located approximately 1 phase spacing distance below.

So far I have found no reference to such an interaction, though I can imagine it does exist. What I don't know is how to estimate the effect or if it can be simply ignored.

Any comments or suggestions will be most welcome.

Cheers!

BigMax

Want To Get Started In Pic Micros?

Hi,

Intested in getting started in the wonderfull world of PIC micros?

Get hold of a copy of "An introduction to PIC Microcontrollers", published by 'Babani Electronic Books', written by R.A.Penfold.

I have no reason to recommend this particular book other than the fact the I own a copy and have found it an excellent place to get started. I'm sure there would be others also.

Best to advise that I have no association with MicroChip either. I also have no reason to recommend PIC micros over other types other than a personal interest in a RISC based 'Non Von Neumann Architecture', and I'm impressed by a cheap micro family that can run at around 10 million instruction per second (20Mhz, 1 instruction per cycle, jumps take 2 cycles);c;

Also, check out the MicroChip web site for lots of good info and FREE development tools!

Cheers and happy coding!

BigMax:D

3 Term Control Routine?

Hello,

This is probably a big ask, and I don't want to scare newbies off this topic for life, but does anyone know where I may be able to find a (Pseudo) 3 term loop control routine suitable for the PIC 16Cxx series uControllers?

I have so far (over 2 years!) developed a simple proportional routine for the process I'm working on, but this process is subject to 'bump' disturbances and my simple routine totally lacks dynamic response and stability.

Simple would be good, source code would be great, although even some basic ideas would be appreciated.

Thanks in advance and Cheers!

BigMax;f;

Testing IGBTs?

Hi,

Over the past few years, with reference to 'larger' (ie >30kW) VSDs, I've noted a migration from 'dumb' IGBT modules to 'smart' types and back again!.

By dumb, I mean basically 3 connections, Gate, Emitter, Collector with no inbuilt Overcurrent or SOAR protection.

By 'smart', I mean with comprehensive inbuilt protection, with two power connections and a multipin 'interface' to the rest of the VSD (or other product).

I see each having inherent advantages and disadvantages. The smart types rely on protection designed by the people who probably know best, the IGBT manufacturer themselves, the dumb types rely on external protection circuitry. The smart types cost many $, the dumb types are relatively cheap. Catastrophic failure of the smart types usually leaves the external driver circuitry undamaged, catatrophic failure of the dumb type can cause cascading damage to external circuitry.

Which all brings me to my point / question.

When faced with IGBT failure on a large and complex drive, consideration needs to be made regarding replacement of all IGBT modules (up to 12 or more!) or risk having to spend time dissassembling and reassembling when static tests didn't reveal all the failed modules. Blindly changing all modules when not all have failed can be expensive.

Testing of smart modules external to the VSD has not proved practical (for me anyway), but testing of dumb types is a practical proposition. Now that the dumb types are making a return, here's what I suggest (assuming 'enhancement mode' IGBTs, are there other types?).

Connect a 100W lamp in series with the IGBT collector and +ve of a 200VDC power supply. Connect the IGBT Emitter to -ve of the same power supply. Short the IGBT Gate to the Emitter. Apply power, no current should flow, the lamp should be dim. Remove power. Connect another 0-30VDC power supply +ve to gate, -ve to emitter. Set this power supply to 0V. Apply 200VDC power, slowly increase the other power supply Voltage from 0V upwards, a good IGBT should go from 'off' to fully 'on' over a few Volts once a particular Voltage range is reached (anywhere from 6-20V depending on the type, compare to a known good example to be sure).

Without being too dramatic, I'm sure other forum members know what they're doing (:D), but 200VDC can be LETHAL and the IGBT gate can be subject to static discharge damage if care is not taken.

ANYWAY, what do other members think? What IGBT test methods do you use?

Cheers!

BigMax.

15kW Belt Driven 'Barrel Fan' Wanted

Hello all,

My workplace is interested in obtaining a 15kW belt driven fan (or similar, relatively high inertia is required), with or without motor.

Air flow rates and static pressure are unimportant, 15kW power absorbtion at full speed is the main objective, with the inlet and outlet open to atmosphere (a throttle would be 'nice'...)

Basic serviceabilty is preferred, physical appearance is not relevant.

Ohh, and availabilty somewhere in Australia would be helpfull.

Anyone have such a specimen taking up space, that they would like to off-load to a good home (for the right price of course!)? Or any ideas as to who may sell such an item second hand?

For those interested, we require this to test small motor starters of various kinds and VSDs.

Please U2U any offers.

Ta.

BigMax