Star Delta Load

By using 3 single phase heater to be connected and form a 3 phase heater should be connected in Star point and not delta connection. These connections are the same as the motor connection principle for low voltage and high voltage connection.

thanks for reply ,

is that the reason for heater damage?

if yes then why designers have designed it for delta ( i'm saying about alpha laval separator heater) earlier it used to have in star connection.

The reason for <...heater damage...> is that it is running at a higher temperature than that for which it was designed, which may be due to an excess of heat dissipation than for which it was designed.

The answer to the second question may be had by contacting <...alpha laval...> by telephone and discussing the problem directly, thereby bypassing this forum.

Heaters damages can be the following factors:

a) Heating element material quality.

Good quality of heating element will provide a good lasting operating heater but not for a life long. Maybe 2 to 4 depend how you use those heaters.

b) Quality of the workmanship during making the heaters element.

During manufacture or hand make those heaters should not make any small mistake and every step must be done correctly.

c) Life span of the heaters elements.

Good heaters can last for 2 to 4 years or some can last longer, if it is operated as according to the design capacity. Which means there is enough time for the heaters to "Switch ON" and enough time for the Heaters to "Switch OFF". Heaters are not design for the continuous operating.

There are some heaters that is design operating continuously but the capacity of the heaters are double in size. For example, If your equipment need a 5KW heaters to be operating continuously, you need to size up to 10KW or more so that your heaters are operating at 50% only and still can maintain the heating heat that require by your operating process.

d) Overheating of the heater.

If the design of the heaters are design for certain heating capacity, but those heaters are use to over size the heating capacity, then the heaters will always in operation and has no time to rest, the life of the heaters elements will damage.

e) Unstable Supply of Voltage.

Unstable supply of operating voltage will cause the heaters element to damage, If the operating voltage is lower than the heaters operating voltage, the heaters current will be higher and this the heater element will experience more stress. Any stress in the heaters element will cause the heaters element to expand and contracted during the heaters is cool off. That will cause the heaters element to break off or open circuited.

f) Connection types.

Heaters are just like electrical induction motors. There are some heaters design to be connect in star point and some heaters are design to be connected in delta point. All those connection of the heaters are depend upon the design of the heaters. If the heaters are design to be connected in Delta Point, you cannot connected it in to the Star point configuration. if you did that, the heater still can be use but the heating capacity of the heaters are not enough hot.

If the heaters are design to be in Star Connection configuration and you connected in the Delta configuration the heater will just blown up because the impedance of the heaters, that is design in Star configuration, cannot withstand the applied voltage.

g) Handling and installation of the heaters are also one of the contribution to the heaters failure but the percentage is very minimal and doesn't means it will not happen.

SW is correct.

When using a 3 phase line : (say 415 V) in delta connection each phase will be loaded by this voltage (L-L)

In star the loading will be (L-N) ie 240V ie the singla phase voltage.

And this connection is especially important for these type of loads (resistive)

thanks for reply sw,

is that the reason for heater damage?

if yes then why designers have designed it for delta ( i'm saying about alpha laval separator heater) earlier it used to have in star connection.

& total heater capacity is 50 kw(21 elements 2.38 kw each)

Why and which designers have designed it for delta?

You are saying in post#1 that these are single phase heaters. That case each heater should be connected as if they are independent and the independent connection is between the phase and the neutral (like any of our fan or light at home)

This exactly is the star connection.

You try to put the bulb at home between the phases- then instead of 230V it gets a 415V input.

The current increases (bulb is fused immediately) and tht is what is happening to your heater. Instead of X amp it is forced to take in √3X amp.

The insulation and others will not be in a position to handle it - either electrical or thermal (the thermal W/unit area will increase and the dissipation in terms of heat transfer may not be able to keep up with the heat generation till the temperature significantly rises) and the coils will burn off (fuse).

Who and why the decision to change the Y into Δ was taken?

This is just to educate about the circuit diagram.

My comment was-

You are saying in post#1 that these are single phase heaters. That case each heater should be connected as if they are independent and the independent connection is between the phases and the neutral (like any of our fan or light at home). This exactly is the star connection.

Please refer fig one- here three heaters are connected independently and are they as if in star ?

The OP has connected the heaters as per Fig 2 and there by he is passing extra current through the resistive load, generating heat 3 times the rated and causing the elements to melt.

Hope this refreshes your circuit design (and more than that the interpretation) concept.

At a certain stage of of life the things are visualised in mind and we do not draw circuit for each and every connection.

thanks sir,

i appreciate your response, but we dont have provision for neutral. what will happen without neutral?

send2vaiju,

You will find that the common point connection will become a floating neutral, with the voltages staying near √3*E_L, whether the point is earthed or not. The 'floating' will be slight due to balanced loading.

The 2 changes you will notice most is the reduced voltage resulting in reduced heating, and reduced challenge to the insulation both electrically and due to heat.

The most important features involved with a failure will be the ratings of the heater, voltage, wattage, insulation values, and the physical ability of the heating elements to exchange the heat produced into the ambient surroundings.

The heater must have some way of transferring the heat produced or it will be damaged, even if electrically connected properly. Possibly, the physical placement is more critical than the electrical connectivity.

Regards, CJM

For 3 single heaters or 3 single lamp that is rated for single phase of 220V or 240V and when you wanted to connect it to the 3 phase power supply of 415V, then connection will be in star point. No neutral is needed.

When the 2 heater that is design for single phase of 220V and connected in series, the heater resistance will increase. Therefore, the neutral is not needed in this connection. Power supply from the "RED" Phase will flow to the Heater A and to heater B and back to the "YELLOW" phase. The power supply from the "YELLOW" Phase will flow to the Heater B and to heater C and back to the "BLUE" phase and the cycle goes on with the Blue Phase.

Example: Single Phase Heater Convert to 3 Phase Heater

If you connect the neutral to the star point, the connection will become single phase connection.

Power supply from the "RED" Phase will flow to the Heater A and back to the neutral line and that goes with the Yellow and the Blue Phase. This is the connection for single phase system.

Hi Guys, sorry for the late reply 11 years later.

What would happen if in (Example: Single Phase Heater Convert to 3 Phase Heater) we had to lose one of the elements. What would happen to the load on the two other phases and the voltage on the two remaining 230vac elements.

Dont try to teach me ok..

Just answer if u can otherwise go to...

idiot.....

Please ignore guests with unhelpful criticisms.

DEAR,

1. Definitely, heaters will give you less heat in star connections. So, more time to reach the required setr temperature.

2. Some times, due to bad terminal connections of the heater end wires, elements get damaged, even if it is in star connection. So, pl. check the quality of the end connections of the heater elements, nut bolts should not be oxidised.

If you rewire these heater elements from delta to star, the voltage across them will be 1/sqrt 3 times the former voltage; the current through each also 1/sqrt 3 times previous; and the wattage will be 1/3 of before. For oil, as I recall, a suitable limit on watt density is about 25 watts/sq in. (For water it is about 45; so if this heater was originally rated for water, it would overheat in oil.) Also, is there any possibility that the heater was not fully submerged in oil? That would cause rapid burnout. Finally, if the wattage is reduced to 1/3 of before, will this be sufficient to heat the oil?

Can you give more data on these elements, such as the sheath dimensions? This will help in pinpointing your problem.

If the heaters are rated 3 phase 220 v.,It can be connected in delta for three phase .Because US standerd 3 phase 220v and single phase 110volt.If the heaters are rated single phase 220 volt it can be connected in star only.Othervise the heters will damage.

Follow CJMs advice, no point in repeating what CJ told. Use the floatin neutral concept and it will balance out the currents to required single phase ratings.

HP and Tornado: his heater is a single phase heater (or are 3 of them) so they are rated for the reduced P-N voltages and not P-P.

OP go ahead with the floating neutral (in my circuit diagram forget the black line.

BTW: don't connect this floating point to earth as you may get earth fault trip under some condition without the equipment fault.

Hi send2vaiju,

I would say CJMcGill and SB post are all valid and perfectly correct as these two gentlemen are very knowledgeable in this field, my only additional contribution where it was not mentioned in most comments, if it is submerge heater (heater in lube oil system) I think present of oil or the compartment must always full of oil and the heater is submerged at all time otherwise this could be also possible caused of the problem as I always encountering in my heaters.

Again, most likely and possible is CJMcGill and SB are most useful advised, mine is only contributing factor that must take into account.

In addition vaiju,

Please don't say rude words if you are not happy or satisfied on any comments like wise from the guest as we must also consider positive criticism, we must maintain friendship here as we are just asking for some advise and help from our folks that we think would be helpful. if you think it is not then lets ignore, we are all sharing our knowledge and experience which probably each and everyone can pick up an idea. likewise from CJMcGill and SB where I always harvesting huge.

Kind regards

Roman

If the heater elements are rated for 480V they can be wired delta on a 480 delta/277 Y system. There is nothing about being single phase that forces them to the lower (delta) connection so long as they are rated for the actual applied voltage. Unfortunately, the original poster has not yet said what the individual ratings are for these elements.

Another consideration not yet raised is the possibility of heating the oil to the point of breakdown ("coking"), which relates to the watt density.

It is also sometimes useful to run heating elements at half their rated voltage (1/4 their rated watt density); this can protect against burnout if the element becomes unsubmerged. Calculations should be done for each scenario to which the elements might be exposed.

The floating neutral concept mentioned before will sort of work (if allowed by local code), but only if none of the individual elements burns out. If that happens, the star becomes unbalanced, which increases the voltage across whichever elements were in parallel with the burned-out one, and decreases the voltage across the others. This can cascade into multiple element failures. (In a vector diagram, the "center" of the star shifts off center.)

The typical "three-phase" heater is just some multiple of three single-phase elements, each of which can be operated at whatever its individual voltage rating is. There are several incorrect posts in this thread.

The main industrial systems in the U.S. are 480 delta/277 Y; 208 delta/120 Y, and 240 delta with center tap in one phase. If the center tap D is in phase A-B, then DA = DB = 120V, while DC = 208V (the so-called "hot leg"). These are basically voltage supply ratings. Appliances may be rated at slightly lesser voltages to account for voltage drop (resistance) in the wiring system. E.g., 460V motors on 480V systems, 230V motors on 240V systems, 200V motors on 208V systems, and 110V appliances on 120V systems.

Tornado,

I believe you will find that if one of the elements burns out, the 2 remaining heaters become single-phased, (straight line vector), but since they then voltage divide, they will drop 1/2 of the 415 Line volts each. There should be no adverse effect other than to lose 40% of the heating.

They will drop from 240 volts to 208 volts across each, so will be even less likely to burn out.

You may have just inspired to best solution for the OP (original poster) which would be to retain the Delta configuration, but series two heaters between each leg.

Regards, CJM

Theoritically you are correct about the voltage ratings. But at our place at least I am yet to see (we are on 230V L-N system) a single phase component with 415V ratings. Again theoritically possible, and also may be there.

As far as the another part, in case 3 elements are in star - fusing of one element will shift the neutral yse. But now the neutral (floating) will be the center tapped point (still floating) of the existing two phases.

You can think it as if now 415 V is across two heaters and that will reduce the voltage (and the heating) of these two. the current will be now correspondingly reduced 207.5/220 so no cascading effect here at least in this case.

However the OP has the over all picture now, and he seems to be satisfied. Leave it to him. If he has any queries he will come back.

But still why has he changed the connection from the existing star to delta ? he never answered.

If this were only three heater elements wired in star (Y), CJMcGill would be correct in saying that one burned-out element would result in the other two elements dividing their voltage across two phases. However, the original poster (post 4) said it was 21 elements. There are only two reasonable ways to wire them up: 7 elements in parallel across each pair of line-to-line phases (delta), or 7 elements in parallel from each phase to neutral (star or Y).

If one element out of 7 in one phase of the star fails open, the resistance of the remaining 6 rises to 7/6 of before, and hence the voltage across them rises accordingly, increasing the chance of further burnouts. (The center of the star is shifted toward the two phases with the intact elements). Yes, the voltage across the intact 14 elements does decrease, as pointed out, but the other phase with 6 elements doesn't just go open.

By the way, the shift of the center means that the floating neutral now has voltage to ground, which may create a hazard, and which is why some codes might not allow it.

Will come back with calculations, but the matter is not practically as serious as that.

This is since we have a number of 3 phase electrical furnaces for heating components (used for shrink fitting) and as usual once in a while a coil or two burns out. I have never seen a cascade failure of the rest of the particular phase.

The extra current (10% or so) are well handled by the rest of the coils.

And though it is a floating neutral, still you have to remember it is a equipment floating neutral, with no connection or relation to the external neutral. If that point has been properly electrically insulated for the minor change in voltage, the codes will not have any problem and the problem will be only if the design has graded insulation, which normally most heaters don't have.

Any way we are doing theoretical arguments let us wait for OP to intervene.

Dear Friend,

Please let us know the following:

1. What is the rated voltage of the heater?

2. What is the line to line voltage of your 3-phase system?

Thanks and regards.

Rudy C. Fernando

Dear Sir. You say that this an Alpha Laval piece of kit. Did you check with them or look up the system drawings to confirm if the elements are installed as designed. Normally big companies do things according to regulations to protect themselves against claims etc. if you have discovered an anomaly I am sure that they would like to know about that. You may well find that system has been modified since commissioning. If not insist that they sort it out.

First things to consider are the ratings of your existing elements.

Are the eleements rated properly for the current being passed?

Do you use a thermostat to control your heat circuit?

Are you using the correct size in feed wire to the elements?, which would induce and over current condition, over a period of time. I had a similar problem with a Mart parts washer, after studying the system over with great scrutiny, we discovered that the main feed cables to the starter block were under sized. Thus, they induced a heat build-up and thus caused the over current condition. All the feed lines were directly fed from a common distribution gang block, and with (4) other control circuits being fed from the same block, it was causing premature break down with the other circuits. So, on the single item that drew the most current, we increased the size of the feed lines directly connecting to the starter inputs terminations. This relieved the transfered heat to the gang block, which in turn gave the other circuits more protection to do their spacific jobs in the over all circuite.

We also have our heat elements configured a Delta form. Since you are using (3)phase input, you have no provisions designed for a center tap return on the configuration. Your elements work as very large resistors to heat the oil bath. I know the elements we use, have (6) elements per heat bank, totalling (12) over all.

Each bank is fed from a 60A contactor, each element configuration is rated @ 20KW per set of (3)Delta configured. The elements themselves, are ~ 0.75" O.D., and have a resistance of ~ 5 ohms. Our wirig configuration is calculated to 125% load capacity from the starter contact to the elements, and the feed lines are the same over all.

We use a Honeywell controller to monitor and maintain the bath temps. The PID controls of the Honeywell serve us well for our needs, and the bath takes minimal time to achieve a stable work temp for our process. I do hope this has been a helpful solution to your needs.

Maximo

A heater is basically a resistance that is intended to be flown through by a certain current. This current appears as a consequence of applying a voltage at the two ends of the resistance. It overheats if that current exceeds the one for which the resistance has been designed. In a delta connection the voltage at the 2 connection points is a phase-to-phase voltage, higher by sqrt(3) as compared to the phase-to-neutral voltage in case of a Y/star connection. Consequently the current that flows through the (same) resistance is sqrt(3) times higher and the developed heat is 3 times higher. If the resistor overheats it means that the applied voltage is too high (assuming the 3 resistors are not defective - not short-circuited portions that should lead to a lower resistance and therefore a higher current). So, in case of connecting the single phase resistor between phase and neutral (Y/star) the developed heat in it decreases 3 times, compared to its connection phase-to-phase (delta).

First we don't know how this system is supplied what are the voltages , what is the power he needs in order to heat the lube oil and what is the rated current of the heaters.

It seems to me there was 3 single phase heaters [if “single phase” it means phase_to_neutral] and the individual heaters was connected in star [without neutral ] but the power obtained was too weak so they decided to connect these in delta. After a while the overload damaged the heaters.

Now they have another 3 [identical to the damaged] heaters, I guess, and send2vaiju wants to connect these in star.

Now, if the current was too high for delta how do we know if it will be still too high for star or how we could know if it will be enough to heat the oil?

The act of <...change connections from delta to star...> will have the effect of lowering the heat dissipation, which may cause longer material processing times. So one would check beforehand that an increased heating time would be compatible with the process in question; if not, then given that it fails in delta, the heater is incorrectly specified for the job and requires replacement with one that is compatible.