STS Heat Trace Reactor

I like the simplicity of the three-phase rectifier. Perfect answer. Simple and maintains phase balance.

Only to those with a willingness to look for them.

Apparently, it does have to be AC, is there a preferable frequency, or is 50 or 60 Hz optional for skin-effect heat-tracing?

You could probably make use of "new" GaN transistor technology to make the power requirements easier to achieve.

Now that I think about it, you should re-consider the choices to be made, and probably go with 3-phase supply, two phases shifted w.r.t. the remaining phase, thus arriving at single phase output.

It works on 1570v 50Hz. But 60Hz is okay too.

what if I disconnected the load balancer. I mean remove the two capacitors and the inductor and connect the load to L1 and L3 directly (see drawing). The current drawn by the heater is about 135A. The question here is, can I take only two phases from the 415/1570v transformer and leave the other phase L2 disconnected? What is the effect on the transformer?

The transformer primary is 415v 600A delta

secondary 1570v 150A delta

I think Solar Eagle already addressed the point of disconnecting the middle phase.

It will work, but I would not expect optimal results, as if you were using a transformer set up specifically designed for the task at hand, i.e. with the load balancer operating.

Okaaaay . . .

It will work with 2 phases giving 1570 V AC. Rated transfo current = 150A, Heater 135 A. But check that the balancing is not to protect generators, which do not like unbalanced loads. It may be that the HV load is negligible compared to generator size anyhow.

I think I would disconnect the middle lead, then try to add some btu's....possibly you could speed the pump up a bit...maybe add an auxiliary portable heater midway down the pipeline....possibly you could raise the voltage a bit...

Your power supply uses a technology more than 70 years old. If it works let it be, but if it gets broken again, it would be better to think of something better. Currently there are power converters way cheaper, smaller, more reliable, and power factor does not depend on the load.

Weather you want the converter to control the amount of energy delivered or you want it to always work at full power is up to you. My company does custom made power converters, but you probably can find something similar in your location.

As pointed out by Rixter, you could enjoy much better control by opting for a 3-phase bridge rectifier with DC output.

So, I disconnected the middle phase L2 and connected the load directly to L1 and L3 and started, it was drawing 145~150A from the transformer, which i thought was too much (transformer rated for 150A). Then I connected the PFC Capacitor (C2 in the drawing) and that reduced the current by about 20A. So it started-up at 135A and as the pipeline temperature increased the current dropped to about 120A when it reached the required temperature (60C). It's been working for two days now.

So my question now is, I looked everywhere on the web but I couldn't find a clear answer on what are the effects of using only two phases at almost rated current of a transformer? Now both L1 and L3 current is ~120A and L2 is zero. The transformer secondary is delta connected so no N. I'm planning on running it that way untill the spare inductor comes, so it's only temporarily, but still I may damage the transformer?

I hope someone can provide me with information about unbalancing a transformer..

Are you then utilizing this as a middle leg grounded delta? I think that is done in quite a few places, including the oil patch. You should make your team aware of possible safety issues if one of the other legs goes open circuit, etc. That is if any safety issues can be identified. I am really not aware of any major problems with grounded middle leg delta configurations.

Are you saying I should connect the middle leg directly to ground? What's the advantage? Is it a must? Remember the secondary voltage is 1570v.

I am most definitely telling you what to do. I know there are places that allow for middle leg grounded delta.

Hi Durguy,

My first thought was that that transfos do not care about unbalanced loading (not unless you are trying to mitigate overload on one phase with underload on another) & that transfo protection relay lore does not require negative phase sequence [unbalance] protection. But my second was to check in J & P Transfo book - un-balanced load chapter does not flag any problem with 3 phase transfos with zero current on one phase in a dozen winding arrangements.

For the avoidance of doubt,

1. please advise the transfo type Yd1? (rating plate diagram if possible, any volts, loss watts on plate?) star-delta or what? Nothing unusual like zig-zag winding?
2. Is it oil or dry?
3. Is the rating site at ? celsius or standard (40 celsius). Is your ambient less than that with current season?
4. Is there an oil temperature or winding temperature indicator so you can spot any changes? Is WTI in a phase you are loading(usually a single phase instrument)?
5. Is it a "shell" type - 50 Hz transfos are usually "core" type.

On a basic level, 120A versus 150 A rating means 64% of full-load resistive loss[I²R, 0.8² = 0.64, and less because winding resistance falls with temperature], that in two windings, third no-loss. That seems a good margin for unquantified losses. What are actual primary voltages and primary rated voltage (i.e. are magnetising losses normal)?

I wonder about harmonic currents, I do not know levels caused by hysteresis and eddy current for pipe heating. I would suggest measuring at transfo secondary, if you can, - fundamental & each harmonic frequency current and then asking transfo maker if it is a problem - to set your mind at rest.

Point by other poster about earthing is relevant - but have you made any change from pre-existing load-side earthing design before reactor failure?

Personally, I can see no benefit for transfo from the reactor, it may help the generator loading.

67model

Hi 67model, thanks for replying.

well,

1. I will post a picture of the name tag of the transformer when I get to the site (Sunday or Monday). But I'm pretty sure it's delta-delta.

2.oil type.

3. normal temperature ranges from 0C in winter to about 45C max in summer. this time of the year it's around 32C max.

4. there's an oil temperature indicator and the transformer has a high temperature alarm and trip. indicator was reading 34C last time I looked (more or less ambient temperature). (I know this may be stupid but the transformer is very cool to the touch). I will check but I'm sure there's no WTI.

5. the transformer is a core type.

The transformer is rated 415V 570A primary. but voltage these days is 400V due to maintenance in the main power station at site. current at primary is 522A.

I will check if we have any means of measuring the harmonics. nothing was changed before reactor failure, although there was a problem with the cabinet air conditioning (the reactor and the two capacitors are placed inside a cabinet outdoors) which wasn't working for a while due to a lack of spare parts (I made a report before the reactor failure about high temperature inside the cabinet causing the insulation on the reactor to become soft).

what would happen if L2 was earthed? is it beneficial to our current setup?

we are not powered by generators except at mains power failure. the site is connected to the main power grid so I think it doesn't matter on a large scale.

In the STS heater project documents, it's written that the heater works on single phase but if it's not available a single phase system that can take the load, or at a different voltage (1570V) the system can be connected to three phase using a load balancer to balance he current draw on the three phases (rated current for heater is 135A and for the three phases with the load balancer is 85A).

ref 3 & 4 You are obviously considerably below normal temperatures. Any wind makes a lot of difference. The temperature you read may not be maximum, could be warming up from lower temperature due to night-time temp. Full load oil temp rise would be about 50'C. Oil filled transfos have big thermal mass.

With 100% rated current load on two phases & D connection, one winding is at normal current & other two at half normal full load [applies to primary & secondary for D-D transfo]. But you are only at 0.8 rated current, so I estimate losses as 1/4 rated normal, expect oil temp about 15 degrees above mean daily temperature. Additionally you are below max ambient & normal volts.

I would expect the philosophy, with dire result of loss of pipe heater, would be unearthed - live with "earth somewhere" while you locate it & bring in repair team. Having an earth could mean instant trip of power on overcurrent due to second earth somewhere on pipe & then heating zero. I guess the design spec would require 1570 V insulation to minimise risk of earth fault [ 3.3 kV cable - normally 1900V to earth?] & assure an earth on one pole would not overstress insulation on the other & cause consequent failure.

Having a balanced load is a normal requirement for power systems, but your load seems negligible compared system capacity & not a problem pending inductor repair.

Can you please take a picture or scan the pages where from j&p transformer book where it explains unbalanced load.

Top of page left out as you have D-D type. Winding currents are amps for 100A load.

so, some old guy at work is convincing the manager that single phase load on a three phase transformer will damage the transformer and the manager is approving a shut down off the system. the old guy reference is a paper he printed form the internet. see pictures.

what do you think?

Thank you for the reply. I have read the book, found it at the university library.

It seems that they insist on shutting down the system, and I'm not concerned about that. I am just kinda mad that they still believe this situation will damage the transformer, I came here for proof because I already knew that, within limits, the system can be operated without a reactor. anyway, it's their decision but I am now continuing to research the subject for my own knowledge.

"Obviously, Zenatrix in your post are in the business of minimising losses by good system design and monitoring of the actual loading situation (and drumming-up business by making unbalanced load seem a serious problem)."

^^ that's exactly what I told them, oh well...

the primary is rated 415V/570A and was reading 522A on two phases. this is is the name tag of the transformer: