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Synthetic resin insulated,
indoor current transformer range
for 12, 24, 40 kV highest voltage for equipment
Types 12a,b,c 24a,b,c 40a,b


AM-12 a,b,c


Type marking

The letters and numerals applied in type markings have the following meanings:

A – current transformer
M – synthetic resin insulated
T – equipped with contact blades (optional) (e.g. for EIB „A” or „B” type circuitbreakers)
12, 24, 40 – highest voltage for equipment
a, b, c – dimensional markings, depending on the accuracy class, output and the thermal current.

General description

The current transformers types AM are manufactured for 5–1250 A and 2×5–2×300 A rated current respectively. The current transformers comply with the specifications of MSZ EN 60044-1 and EN 60044-1 standards. It is also possible to produce according to other standards, differing from the afore-mentioned (e.g. knee point voltage planning, rated voltages other than the voltages included in the standards).

These types are manufactured in single, double, triple core synthetic resin insulated, support type design. The material of the primary and secondary windings is copper. The primary terminals are copper blocks located on the upper surface, which make possible a horizontal connection even in case of primary changeover design. The primary and secondary contacts are produced without protective coating. Upon agreement we deliver the current transformers with plated contacts, in finish suitable for use under the requested climatic conditions.
The secondary terminals are on the narrower side of the current transformer, – seen from the “P1” marked primary contact – covered by a sealable plastic cover. The connecting leads pass through openings, situated on the right and left sides of the cover. Independent of the a,b,c, dimensional markings the width of the Current transformers, within the same voltage level, is always the same.
The M8 earthing bolt and the rating plate are on the opposite side to the secondary terminals.
When requested in the order, the primary terminals can be executed also with contact blades (Type AMT-24).
Packing, delivery

The current transformer is delivered in a finish suitable for use under normal climatic conditions, packed in corrugated paper box, but upon agreement also in packing fit for marine or aerial transport.


In case of a long-term storage, it is practical, to keep the current transformer indoor, in a covered, well ventilated room (storage temperature: –5 °C, +40 °C).

Installation, putting into operation, operation

Before installation the Current transformer should be checked in order to discover on the surface, or on the terminals any possible damages occurred during the transportation or the storage. In case of any damages further investigation is necessary.
Generally the current transformer should be mounted in upright position. The fastening to the supporting structure can be accomplished by the help of legs shaped on the bottom of the device. When fixing, it is adviceable to put under the legs a rubber or a rubbercork plate, in order to equalize the accidental unevennesses.
Before connection, any contamination, occurred during the transportation and storage should be removed, the terminals cleaned and smeared with contact vaseline.
The proper connection can be achieved paying attention to the markings on the primary (P1, P2 at primary changeover design C1, P2 and P1, C2) and on the secondary (1S1, 1S2, 2S1, 2S2, 3S1, 3S2) side.
The operation is possible keeping the prescriptions of the relevant security-, labour- and property-protection directives. Any faults and breakdowns emerging in the Customer’s sphere of interest due to breaching, disobeying the afore-mentioned, exempt the manufacturer from the warranty and guarantee liabilities.

The maintenance consists of works to be done according to the general rules for indoor instruments and discontinuing of the accidental irregularities. These are:

– periodical inspection of the contamination and cleaning, depending on the degree of impurity,
– inspection of the surfaces,
– tightening of the bolts of the primary and secondary connections,
– tightening of the fastening bolts.

State verification

The secondary windings of the current transformers in classes 0.2 and 0.5 are manufactured in finish suitable for verification. The verification will be made only on special request, in this case it will be accomplished and documented by an official seal or an affixed verification stamp, by the State Office for Measurement.

Data to be submitted with the order

– type (e.g. AM-12b),
– rated insulation level (e.g. 12/28/75 kV),
– rated primary and secondary currents (e.g. 200/5/5 A or in case of primary changeover function 2×100/5/5 A),
– accuracy class, output and instrument security factor or accuracy limit factor of the secondary windings. (e.g. class 0.5, 15 VA, Fs10 or 15 VA 10P5),
– quantity,
– requested term of delivery.

Other or special requirements:

– climatic zone of use other than normal,
– surface protection (plating) of primary terminals,
– fitted with primary contact blades (e.g. for EIB “A” or “B” type circuit breakers) (e.g. AMT-12b)
– language of the rating plate,
– packing,
– number of pieces and sort of the documentation to be attached.

Warranty period, guarantee

The warranty period is 12 months and otherwise it can also be established upon the mutual agreement of the parties respectively.

All right reserved for subsequent alteration without prior notice.

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