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Summation Current Transformers

Summation C.T.′s are designed to summarize several synchronous A.C. currents of equal phase relation with any angle of phase difference, i.e. summarize the secondary currents of a number of main C.T.’s. The secondary circuits of the main C.T.’s are to be connected to the corresponding marked primary terminals of the summation C.T., i.e. each main C.T. feeds with its secondary current a specific portion of the primary winding of the summation C.T. The number of turns of the particular sections of the primary winding must fit in with ratios of the main C.T’s. If all main C.T.’s have identical ratios, it is irrelevant for their secondary circuits to which section of the primary winding of the summation C.T. they are connected.

Technical data:

: 0,2…3 : max. 20 VA : 720 V. : 50-60 Hz. : (2…6) x 5 A (or 1 A on request). : 5 A (or 1 A on request). : FS 5 : -20 … +45°C. : 4 kV eff, 50 Hz, 1 min. : IP 00

Typical Summation CT


In case of absence of current in one of the main C.T.’s, the corresponding circuit must not be short-circuited, neither at the summation C.T. nor at the main C.T. If one circuit of a summation C.T. is unused because the corresponding main C.T. is to be connected at a later stage, the relevant section of the summation C.T. has to be used on open circuit. Errors of main C.T.’s and summation C.T.’s could accumulate. The rated secondary current of the main C.T. and the rated primary current of the corresponding circuit of the summation C.T. must be equal.

In order to facilitate the user in making the right selection of components of a measurement set-up with summation current transformers, the following examples have been listed.

The total current and the total power of three branches shall be measured by one ammeter one current transducer and one power transducer.

Relation of main C.T.′s are:

600/5 A 300/5 A 200/5 A Σ= 1100/5 A

The burden to be supplied by the three main C.T.′s can be calculated as follows:

0,5 VA 0,5 VA 0,5 VA 2,0 VA 4,0 VA Σ= 7,5 VA

The individual transformer must provide its VS share from its 7,5 VA corresponding to its ratio to the overall transmission

1 Main C.T.
600/5 A
600 x 7,5 VA = 4,1 VA+ incl. possible losses
2 Main C.T.
300/5 A
300 x 7,5 VA = 4,1 VA+ incl. possible losses
3 Main C.T.
200/5 A
200 x 7,5 VA = 4,1 VA+ incl. possible losses

The C.T. could also be used for any other main C.T.s if they have corresponding ratios, e.g. 60/5, 30/5, 20/5 A. The ratio of the nominal primary current of a main transformer to the sum of the nominal primary currents of all the main transformers may not exceed the ratio 1:8

Order specification format:

0,5 5+5+5/5 A. 600/5A, 300/5A and 200/5A 5 A. 15 VA