L. T. ROBINSON & J. E. O-RAIGHBAD.
APPLICATION FILED JAN. 3, 1918.
L1 2mm; Patented Feb. 23, 1915.
Inventors Witnesses: Lewis T Robinson James RCrigheaz'l,
j by If m w w 1 M His DTLtorney.
t uman LEWIS '1. ROBINSON AND JAMES R. CRAIGHEAD, OF SCHENECTADY, NEW YORK, ASSIGNORS TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.
TRANSFORMER Specification of Letters Patent.
- rateuteareb. as, 1915.
Application filed January 3, 1913. Serial No. 739,981.
rent transformers for power measurement,
the object being to provide a transformer in which the phase angle between the primary current and the current delivered by the transformer is controlled in a mannermost favorable for the purpose of accurate power measurement. Our invention, however, is not limited -in its application tocurrent transformers but is generally applicable to all transformers where a reduction in the phase angle or its elimination is desirable,
but since the current or series transformer is one of the most common pieces of apparatus to winch our lnventlon s applicable,
and in connection with which it may be readily understood, we shall describe our invention as applied to such a transformer.
The current transformer which is ordinarily used for power measurement consists of a core of iron on which is wound a coil of insulated wire to be connected in series with the supply circuit, and another coil of insulated wire to which the instrument or instruments are-to be connected. Due to various causes, the current delivered to the instruments is not in exact phase opposition to the current in the primary of the trans former, and thereby error is introduced, the secondary current not accurately representing the primary current. We propose to minimize this error.
In accordance with our invention we provide the transformer with a third or auxiliary circuit having its constants so chosen with reference to the constants of the instrument circuit that at any predetermined load the instrument current may be made to be substantially in phase opposition to the primary current.
In the preferred form of our inventionnumber of turns in this apparatus the total secondary current in effect consists of the summation of the current 1n the instrument circuit (or main secondary circuit) and the current in the auxillary circuit. Thus the product of the current 1n the mainsecondary winding by the winding (ampere turns) combined, with due regard to phase relation, with the product of the current in the auxiliary winding by its number of turns (ampere turns), constitutes the total secondary ampere turns and is substantially equal to the product of the primary current by its number of turns (primary ampere turns). By providing the auxiliary circuit w thsuitable constants the current in that winding may be made to be in phase with the induced voltage or may be made to lag behind or to lead the induced voltage by any desired angle. Thus the main secondary current, usually somewhat lagging with respect to the induced voltage, may be made to lag or lead the total secondary current as may be necessary, and thus may he brought Into phase opposition to the primary current. The loading of the auxiliary circuit should preferably be such that the current in the'auxiliary circuit is as nearly as possible 1n quadrature with that in the instrument circuit, since then the change of phase angle with a given change of primary cur rent is a minimum. If the normal phase angle is positive, that is, if the secondary current is leading with respect to the normal primary current, capacity or resistance, or a combination of the two is suitable, while in the case of the secondary current lagging with respect to the primary current, inductance in the auxiliary circuit is preferable. Resistance and inductance combined is not ordinarily desirable since for the correction desired these two act in a measure to oppose each other.
The amount and kind of load required on the extra winding is not a simple function of the exciting current of the transformer but depends also on the amount and kind of load on the primary and main secondary circuits. The phase angle of a current transformer usually varies with the value of the current flowing in its primary and with the nature of the secondary load, and therefore it will not usually be possible to make any single at zero for the entire range of primary curof at rent'and for different instrument loads. It is possible, however, to make such an adjustment with a particular instrument load that the phase angle becomes zero at any desired value of primary current. Thus, if this value is the average or normal value of the primary current, the average value of the phase angle is zero and "the maximum value is greatly decreased. By making separate adjustments for each secondary load and each primary current value, the phase angle may be brought practically to zero for every condition. By so designing the aux-' iliary circuit that the current therein is approximately in quadrature to the instru-.
ment current a minimum change in phase angle occurs with a change in load current without change of adjustment.
Our invention may be further explained by means of the accompanying drawings.
Figure 1 is a vector diagram of a series transformer; Fig. 2 is a vector diagram of a series transformer provided with a third or auxiliary circuit arranged in accordance with our invention; Fig. 3 illustrates the preferred embodiment of our invention, in which the third circuit comprises a separate secondary winding.
' The vector diagram of an ordinary series transformer may be constructed as illus trated in Fig. 1. I is the current in the secondary circuit represented in phase and value (the latter in ampere turns). F is the phase of the flux in the transformer core. E 'is the electromotive force induced in the secondary circuit (value disregarded). The load on the secondary circuit has been assumed to be an inductive one, since this is the usual condition 'met with in practice. :An exciting current L, is required to produce the flux in'the core. The total rimary current required is the summation o the ex citing current I and the secondary current reversed A; adding these vectorally we find the primary current (in ampere turns) to be I in phase and value, It is apparent from these considerations that there is under all conditions a certaina'ngle between the secondary current reversed A and the primary current 1 unless the secondary cur-' rent is in-phase with the exciting current 1..., since there must always be an exciting current of appreciable value. The secondary current in exact phase opposition to the exciting current-is an unusual condition. The angle between the two currents is called the .phase angle of the transformer and for the conditions already given is represented by the angle X. This is never zero for any finite value of currents. By our invention we propose to reduce the maximum value of the phase angle, and to make this phase angle zero at some particular load and value primary current. As has already been set forth, we prefer to do this by providing a third or auxiliary circuit having the proper constants.
In Fig. 2 we have shown a vector diagram of a transformer constructed in accordance wlth our invention, whereln the third auxillary circuit includes both resistance and capacity. The flux is represented by F as in the preceding diagram; the main secondary current 1 which is the instrument current and which is lagging with respect to its electromotive force E since this is the most common condition, and the exciting current 1 are both again represented in ampere turns. I represents in ampere turns the current in the auxiliary secondary circuit, approximately in quadrature to the instrument current by preference, this current being determined in phase and value by the amount of resistance and capacity in the auxiliary circuit and the number of turns on the common core. Combiningl and L, the resultant or 'total secondary current is found to be 1,. I reversed as shown by A and combined with the exciting current I shows the current I in the primary. It will Although now the phase angle maychange with an increase or decrease of primary current, the constants of the auxiliary circuit remaining the same, it must chan e from ,zero in each case, and'b causing t e auxiliary current to be in qua rature to the instrument current a minimum change is experienced. We have provided therefore a transformer with a smaller maximum phase angleand one in which the phase angle can be made zero for any desired value of primary current and in which the change of phase angle is a minimum with a given change in value of primary current.
Fig. 3 illustrates diagrammatically a series transformer constructed in accordance with our invention wherein the auxiliary secondarycircuit U'contains both resistance R and capacity C, the resistance member R, however, only being used where resistance in addition to that offered b the windings and connections is require The main secondary S is located on the single core V and supplies an instrument winding as, flolil' example, a winding of a wattmeter W.
e the line, as will be. understood. The values of the resistance R and capacity C are referably adjusted so that the current in t eir circuit is substantially in quadrature with the current in the instrument circuit and of such value that the instrument rimary P is connected in series withcurrent is approximately in phase with the primary current at the normal or average value of the primary current with the given instrument load W.
What we claim as new, and desire to secure by Letters Patent of the United States, 1s:-
' 1. A transformer including a primary winding, a secondary winding and a closed'auxiliary winding, the constants of the auxiliary winding circuit being such that with a load of definite constants on the secondary winding the currents in the secondary winding and auxiliary winding are approximately in quadrature.
2. transformer including a primary winding, a secondary winding and a closed auxiliary winding, the constants of the auxiliary winding circuit being such that with a load of definite constants on the secondary winding the currents in the secondary winding and auxiliary winding are approximately in quadrature, and that with a certain value of current in the primary Winding, that. current and the main secondary current are in phase opposition.
3. The combination with a transformer comprisinga primary Winding, a secondary winding and an auxiliary winding, of an instrument connected to the secondary windmg, a resistance member and a capacity member connected to the auxiliary winding,
the constants of the auxiliary winding circuit being such that currents induced in the secondary circuit and auxiliary circuit are approximately in quadrature.
- 4. The combination With a transformer comprising a primary winding, a secondary winding and an auxiliary winding, of an instrument connected to the secondary winding, and a capacity member connected to the auxiliary winding, the constants of the auxiliary winding circuit being such that currents induced in the secondary circuit and auxiliary circuit are approximately in quadrature.
5. The method of reducing the phase angle,
in a transformer which consists in adding to the effect of the instrument-current on the primary circuit another secondary current effect in quadrature to the instrument current efi'ect.
1 6. The method of reducing the phase angle in a transformer which consists in adding to the effect of the instrument current on the primary circuit another secondary current winding circuit being such that with a load of definite constants connected to the secondary winding and at a predetermined value of current in the primary winding, the
current in the main secondary winding is in phase opposition to the current in the pr1- I mary winding.
In witness whereof, we have hereunto set our hands this 31st day of December, 1912.
LEWIS T. ROBINSON. JAMES R. RAIGHEAD. \Vitnesses:
MARGARET E. WOOLLEY, ESTHER H. MYERS.