Difference between HF Transformer and Normal Transformer in electrostatic precipitator 1

[SA07]

Hi
Can someone explain in detail what is the difference in the operation of an HF transformer compared to a normal transformer in an electrostatic precipitator (ESP) so that the HF transformer which is the latest technology will enable the ESP to capture more ash coal particles and is more efficient? Thks

 

[Skogsgurra]

The electro-static precipitator works very close to flash-over voltage. The closer, the better separation and the cleaner the gases that leave the precipitator.

Gas composition, temperature, pressure and humidity changes in short time and when flash-overs occur, you need to reduce voltage (typically in the 50-80 kV range very quickly because A, efficiency is zero during a flash-over and B, flash-overs remove solids from the electrodes.

HV rectifiers therefore needs to be fast. The rotating (disc) rectifiers were very slow and could take seconds to adjust voltage. Motorized Variacs were a bit faster and the more modern ones (50/60 Hz with thyristors/SCR:s) are faster but still in the 10 ms region.

I do not have any personal experience with HF high voltage rectifiers, but the time to reduce voltage (and avoid long flash-overs) will be less than 0.1 ms - probably shorter. That alone makes the precipitator more efficient.

Then, there is the better efficiency that a Ferrite has vs electro-plate. That may also be important. But the superior separation is the dominating factor.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[thebard3]

My precipitator days ended 25 years ago. At that time our best available technology for voltage control was to use a saturable core reactor, (SCR) which is basically a variable inductor using a 0-90VDC control signal to vary inductance, inline with single phase 480VAC supply to a transformer/rectifier to supply HVDC. We attempted for a short time to use silicon controlled rectifier (also SCR) but experienced reliability problems. We did not employ any type of electro-mechanical devices as Skogsgurra describes above. The semiconductor type was much faster and able to quench the arc (flashover) faster but we never identified this as a significant issue with performance. This is all 60 hZ and DC stuff. As far as I understand precipitator theory, it will not work using AC power on the plates/grids so I assume the high frequency component is only used to power the transformer, which still converts output power to DC voltage. If that is the case, I would assume any efficiency gains would be modest, as the precipitator design itself would be the predominant component.

Brad Waybright

It's all okay as long as it's okay.

 

[Compositepro]

I believe that most of the ESP's that I have seen use voltage multipliers to create the high voltage at low current. Voltage multipliers cannot supply much current and are safer where arcing may occur.

https://en.wikipedia.org/wiki/Voltage_multiplier

Voltage multipliers work much better at higher frequencies - smaller components can be used.

 

[itsmoked]

I expect the entire high-freq aspect is simply smaller-cheaper. A high frequency voltage transformer can be order-of-magnitude smaller.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

A high frequency voltage transformer can be order-of-magnitude smaller.

Size and weight.
That's why 400 Hz was a standard aircraft voltage. I haven't seen any aircraft equipment for decades. Is 400 Hz still in common use in aircraft?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[itsmoked]

Yes, Bill.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[SA07]

Does someone has HF Transformer of the make NWL USA (Nothelfer Winding Laboratories)or Kraftelecktronik AB Converter installed on your Electrostatic precipitator? We are planning to install one on our ESP. We want to know if it is working satisfactorily.

 

[electricuwe]

There is a business in Vaxjö, Sweden, initially independent, then belonging to Alstom Power, but sold to General Electric recently. They are supplying such systems already for decades and they have published a lot. On the benefits in application as well as on the resonant inverter topology used.

The main benefit of this HF-transformer approach is better efficieny and lower weight (important as These Units are to pe placed on the Roof of the filter buidling).

 

[Skogsgurra]

Would that be former company Transductor AB? Pioneers in toroid cores and winding.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[RRaghunath]

The DC would be smoother when rectified from HF AC. That is the reason HF transformers are used in ESPs.
We used to call them Rectifier Transformers. The rectifiers and voltage boosters used to be integral to the transformer.
Depending on the type of ash (like the one that fuses together to form large masses causing shorting of Anode and cathode plates in the ESP, the duty of these rectifier transformers or ESP transformers could be onerous.

Rompicherla Raghunath

 

[thebard3]

The DC would be smoother when rectified from HF AC.

That actually makes sense, as there are no filtering capacitors on the rectifiers.

Brad Waybright

It's all okay as long as it's okay.

 

[waross]

It is many years since I have worked on a large ESP, I forget most of the details but I do remember that we had rappers generations before they became popular on the music scene. grin

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[electricuwe]

If you want to dig more into details look for publications on electrostatic percipiators from Per Randstad.