DE164750C - - Google Patents

Description

IMPERIAL

PATENT OFFICE.

As is known, the cores of ordinary AC transformers are made from a large numbers of thin sheets or iron wires are formed, which insulate from one another are to avoid the formation of Foucault's currents, which are in a Express the decrease in the efficiency of the transformer. The use of such cores is expensive, more so than one

ίο cannot use castings.

The invention is based on the knowledge that in a certain type of transformers the core does not necessarily have to consist entirely of many parts, so it is advantageous to use a full core. These are the measuring transformers, i. H. Transformers with a primary winding, those by the current of the line, its intensity, force, phase, energy or other Size is to be measured, flowed through and its secondary winding with the measuring instrument is united.

The invention also regards transformers as belonging to this class, which are also used with these devices, like the automatic inputs and Switches, which are not actually measuring instruments themselves, but are nonetheless in work depending on the specific sizes of the primary current. Both transformers designed for these devices, which work depending on the magnitude of the intensity of the primary current, it is advantageous that the primary intensity is proportional to the secondary intensity and is as independent as possible of the number of periods of the current. Besides, it is at the transformers intended for these apparatuses, whose work is equally influenced by the size as depends on the phase of the primary intensity, necessary the phase to regulate the secondary current to the primary current.

In an ordinary transformer made of carefully rolled iron, if no special devices are provided, the secondary current in the phase im Lagging the primary stream by an angle less than 180 °, and it is so that the one with the Transformer-connected apparatus specifies the necessary phases are exactly opposite, or that the phase exactly to the actual phase of the measuring apparatus is in a certain proportion,

The purpose of the present invention is therefore, in transformers for measuring, control and actuators to use a principle by which one can obtain the said results (Increase in the proportionality of the secondary current to the primary current, decrease the sensitivity in changing the number of periods of the primary current and finally regulation of the phase difference between the primary and secondary currents) by not dividing the core at all or only partially dividing it.

Let us assume a transformer in which 1 and 2 are the primary and secondary windings, which are caused by the currents I ₁

and z ' _{2 are} traversed represent. A third auxiliary circuit 3 may then be assumed, which consists of a simple winding arranged around the core and which is short-circuited; i ₃ is the current that flows through this spiral. It may now with

Ai _{12 is} the coefficient of induction between the

Stream

Af
with

1 and 2,

₁₃ of between streams 1 and 3 and

M ₂₃ which is to be designated between streams 2 and 3.

Let L ₂ be the coefficient of self-induction of circuit 2, which at the same time contains the inductance of the apparatus.

Let L ₃ be the coefficient of self-induction of the circuit 3, which is limited to a single winding.

Z ₁ = J ₁ sin to t,

r ₂ J ₂ -J- M ₁₂ J ₁ w cos wt - \ - M ₂ ,

r ₂ is the total resistance of circuit 2,

r ₃ that of circuit 3.

J ₁ , J ₂ , J ₃ are the largest values of the currents in the three circuits,

Z ₁ , z ₂ , Z _{3 are} the corresponding instantaneous values.

27Γ

or

r _s J ₃ -J- M ₁₃ J ₁ ω cos ω t -J- M ₂ ,

L ₂ r ₃ -J- L ₃ r ₂ d Z ₂

dt di ₂ where - = - is the number of periods of the current.

φ = the phase difference between J ₁ and J ₂ .

The signs of the various currents are related to those of J ₁ .

The general equations that determine the values of the variable once the Circuit 1 is traversed by a current, are the following:

German

German

= ο

dt ' ²

-JZ ι "2 '3

.2 ~ T "

r, r.

L ₂ L ₃ -M _n J dt

-M ₂₃ -M ₁₃ ; .

L ₂ L ₃ -M ₂₃ "

sin ω t- wr ₃ M ₁₂

cos

[- u. ² ; ² + pw ² ; tang φ =

(Q-u?) B —Pwd jQ — w ^ d + Pw b

P represents the coefficient of

tue ₂

and Q

that of Z ₂ ; α and b are those of sin wt and cos w t.

If there were no winding 3, it would be

M ₁₂ ² to ²

Λ 2

AT ₁ -

tang _9l =

The latter two equations show that if winding 3 is absent:

a) φ never == ο, ie the phase angle between J ₁ and J ₂ can never be i8o °. In fact, the limit = O corresponds to the limit r ² = o;

b) that the deviation in the proportionality of the transformer as a result of the change the number of periods of the current is represented by

dk

+ L ₂ co ²

ie by the same percentage change in the number of periods, multiplied by a coefficient which does not _{disappear for the specific values of r 2} and which _{decreases with r 2} towards ο;

c) one takes under the formula Z -j- C μ M ₂ ² the coefficient of self-induction J ₂ , the first part of which relates to the part of the outer secondary circuit of the transformer and the second part of which relates to the inner part, and one takes under the formula B μ U ₁ n ₂ the coefficient M ₁₂ (W ₁ and K ₂ represent the number of turns of circuits 1 and 2, μ the value of the permeability in the core and /, C, B represent the value of the coefficients that are correspondingly dependent on the shape of the outer secondary circuit and the inner primary and secondary circuits in the transformer), the expression searches

to become independent of μ , the more the smaller r ₂ and / are.

In the other case, i.e. if the winding 3 is present, the result is:

a) that the values of tang φ and of φ cannot only vanish for a value of r ₂ different from O and by the equation

(i)

Pw

ίο is determined, but also, if necessary, can change the character;

b) that under these conditions the value of k has the form

k ² =

assumes, where ε is a value dependent on ω that vanishes when equation (i) is satisfied. The presence of the winding 3 means that the minimum sensitivity to changes in the number of periods (which in this case corresponds to the value of w for which the transformer is set up in its phase) is no longer due to the unattainable value limit r ₂ = 0 , but for certain values of r ₂ that correspond to certain values of r ₃ and vice versa;

c) if one assumes, as before,

τ ι ι r 2

L ₂ = Z - \ - C μ n ^
and

L ₃ = ^ Γ μ Tl ₃

(where F is a coefficient depending on the shape of the circuit 3) and

Af ₁₂ = B μ U ₁ n ₂ ,

so if the transformer is set up for one phase,

■ r, B μ w. W,

(I -f C μ Ti ₂ ² J r ₃ -f ffifij ² r ₂

So now this expression is independent

of μ , it is no longer necessary (as before) that r _{2 be} very small, but rather it

suffices that the expression -

B μ Ti ₁ Ti ₂

can be neglected.

It follows that the presence of an auxiliary winding wound around the core of weak resistance (which even from a single short-circuited Coil can exist)

I. makes the transformation ratio k between the primary and secondary currents less dependent on the changes in the permeability of the core due to the variable effect of the intensity of the primary current,

2. makes this ratio less sensitive to changes in the number of periods,

3. the secondary current (which is usually in phase at an angle less than 180 ° back to the primary phase) by exactly 180 ° and, if you want, by one too Angle of over i8o °.

If the Foucault currents operating in the nucleus are allowed to form a Assume sufficient size, one can arrive at the same result as above, since the presence of these currents the has the same effect as a winding that is in a short circuit. One arrives at this result by not doing the division of the core at all or it greatly diminishes, which is also a very remarkable saving in construction and in the material used.

The apparatus which forms the subject of the present invention is thus a Transformer which is constructed without dividing the core or by cutting it divided only as far as necessary, for the purpose of a greater proportionality of the Secondary current to get the primary current, the dependence of the number of periods increases reduce and regulate the phase difference between the primary and secondary currents.

When using a magnetic, relatively weak induction like that is useful for measuring transformers, so there is no risk of excessive heating.

To better understand the invention, the new transformer is in the drawing come to representation.

Fig. Ι is a horizontal section,

Fig. 2 is a vertical section.

These figures show the practical shape of the full core transformer. It However, the invention does not apply to this particular embodiment shown in the drawing limited.

The core is made up of a housing 1 of magnetic material, which is the one shown in the figures Has the shape shown, and formed from a cover 2, which is also made of magnetic Material consists and a cylinder BEZW. carries a prism 3 on which the primary and secondary windings 5 and 6, the ends of which sit on insulated terminals 7 and 8, are wound.

In the figure, the magnetic circuit is closed because the part 1 against the Part 2 is printed and the bottom of the same is supported against the free surface of part 3 is. However, you can also have a certain gap between the part 3 and the Leave part ι what can be useful in certain cases.

If in practice the action of Foucault's currents can be seen too violent Phase shift, it is sufficient in the nucleus or in one part of the same to provide slots, which cause the reduction of the parasite currents, up to the desired phase shift is obtained. 3 and 4 show in section same transformer as before, but with the core with individual slots 9 which are sufficient to reduce the parasite currents to a certain extent.

Claims (1)

Patent claim:
Electrical transformer for measuring instruments and the like., Characterized in that the core is undivided respectively. It is only divided so much that Foucault's currents are still strong enough to increase the proportionality between the primary and secondary currents, to reduce the influence of the number of periods and to regulate the phase between the primary and secondary currents bring about. 1 sheet of drawings.