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Getting to Know: Edward Tsang, our Principal Electrical Engineer and learn more about VSDs

Get ready to be amazed by Ed, one of our founders and principal electrical engineers, a true dynamo in the world of electrical engineering! For two decades, Ed has been electrifying the field with his unparalleled expertise. But what sets him apart? It is the electrifying passion that is sparking within him.

His main areas of expertise include electrical power distribution, mainly LV and HV motors, 33kV distribution system design, battery technologies and systems, VSD integration, transformer procurement and installation, and condition monitoring. He is skilled at constructing and commissioning electrical systems.

Ed isn't just a solver of problems – he's a creator of solutions. He thrives at tackling complex issues under high pressure and is a supercharged arsenal of innovation. When you've got a challenge, Ed is the lightning that ignites the path to success.

His experience in the industry means he knows exactly what it takes to design a reliable VSD system that provides efficient operation. Here he shares some insights on VSDs design, and we’d like to share that with you.

What are two projects that you have been involved in and what were your main responsibilities?

A notable example that comes to mind was at a Tier One Iron Ore Mine. The winch systems on the overland conveyor belts were a very advanced system which demanded very high performance from the machine due to zero speed and large holding torques.

The other notable experience was at the start of my career (in 2006) when the fine's processing plant was upgraded inhouse with all new VSD controlled slurry pumps in Paraburdoo. The VSD controlled slurry pumps were designed with minimum maintenance and best reliability in mind. They are all still working even today.

What are some examples of VSD applications?

Typical examples of VSD application include constant torque loads such as conveyor compressors and winches. Variable torque loads such as pumps are the other most common application.

What are some things to consider when designing a variable speed drive?

Common factors that should be considered before designing a VSD application:

  • The length of the motor cables

  • Type of motor and associated modifications if any - some motors have unsuitable bearings and winding insulation

  • The EMC environment - occasionally there are very sensitive weigh cells that can be impacted or similar sensitive electronic systems

  • The method of cooling - natural air, water cooled or air conditioned room

  • If existing motor cables being used are not shielded

  • The impedance of the power system - if the impedance is too high it could result in serious harmonic issues

  • The stability of the power supply

  • The desired budget

  • Maintenace capabilities of the site staff

  • HV or LV drive

It should be noted that not all DOL (Direct Online) applications can be converted to VSD and in some cases gently starting the load can cause serious damage to the motor. You need to understand the mechanical aspects as well as the electrical aspects. It pays to have an interest in both areas.

How does VSD affect power quality?

In general, VSD degrade the power quality of the supply but these days with ultralow harmonic drives it is possible to minimise issues.

What are some common issues that arise when using VSDs and are there any trouble shooting tips that can be applied when designing a VSD system?

A bogged belt, especially in conveyor belt applications, is easily the most common issue that can arise when using VSDs. Assuming the HSE (health, safety and environmental) aspects are taken care of and it's just a matter of requiring smooth powerful slow force to move the conveyor, the normal approach is to lift the limit on the current and the torque and then start the motor on a low speed. Quite often the motor's peak torque capability is required so don't be surprised if the current limit required is 300% and the torque limit is 200%. It should be noted that current and torque are directly related to each other.

The other common application is speeding up a pump to increase production beyond what it can pump at 50Hz. Here power absorbed is related to its speed by a cubic quantity so to be able to actually achieve the increase in production desired, the power ratings of the motor and drive need careful consideration. Sometimes a short-term overload is all that is needed, and this often is accommodated.

I think the number one cause of issues is over engineering in terms of overcomplicating the design. This can often make it harder to commission and make it more expensive than what is required. This can happen if all options are included in the design without much consideration, but they are not required. An example is adding a brake chopper resistor, sine wave filter encoder when it is not required. In cases like this, my favourite phrase is “less is more” meaning we can do more with less equipment. My priority is always a strong simple system that performs without breaking down for decades.

Want to be like Ed? Please have a look at our careers page for our current opportunities.


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