Medium-voltage instrument transformers
Current instrument bushing transformer
CTT 25
Current instrument transformers CTT 25 are designed for measurement and protection of high voltage distributing equipment for indoor design for the highest voltage of system of 25 kV.
The value of secondary current is 5 A or 1 A with the possibility of combination. The accuracy classes for the circuits of measurement are 0.2, 0.5, 0.2S, 0.5S, 1, 3, for the circuits of protection are 5P, 10P and PX. The transformers fulfill the required accuracy class at intervals from 25 % to 100 % of rated load.
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Description
Current instrument transformers CTT 25 are designed for measurement and protection of high voltage distributing equipment for indoor design for the highest voltage of system of 25 kV.
The value of secondary current is 5 A or 1 A with the possibility of combination. The accuracy classes for the circuits of measurement are 0.2, 0.5, 0.2S, 0.5S, 1, 3, for the circuits of protection are 5P, 10P and PX. The transformers fulfill the required accuracy class at intervals from 25 % to 100 % of rated load.
The terminal working current is 120 % IN, in case of the agreement of the producer and the customer it is possible to deliver also the other values, for example 200% IN.
Transformers CTT 25 are constructed as bushing transformers. They can be supplied with the accessory equipment (the primary conductor and fixation enclosures) and so they can serve as the passaging design (see dimensional sketch). The primary winding (drawing die) must be connected to the inner shielding by the means of Cu wire strand and by the means of the screw M4 (see dimensional sketch).
The secondary winding is wound on the magnetic core made of directed plates, eventually made of the alloy of nickel, iron and copper (“permalloy”). The maximum number of cores can be from 1 to 3 according to the request of customer and
according to the required parameters. The construction of transformers allows the switching of ranges of the primary current on the secondary side.
All active parts of transformer are compound-insulated with epoxy-mixture. This material performs both the electrical insulating and the mechanical functions.
The mounting position of transformers is arbitrary. Transformers are fixed by the means of four screws M12 in the holes in the basic plate. We recommend use terminal ends corresponding to the used cross-section of the conductor for attaching to the secondary outlets.
The secondary terminal plate is equipped with cover with sealing screw. Inside, there is the set with jumpers and small screws for the possibility of earth connection and short circuiting of the wiring. (See “The Instructions for the mounting and operation”).
Transformers CTT 25 fulfilled all the tests according to the IEC 61869-1, IEC 61869-2.
For the customer’s request we provide official calibration.
It is possible to consult other technical parameters with the producer.
Parameters
- Highest voltage for equipment: 24/25 kV
- Power frequency test voltage: 50 kV
- Lightning impulse test voltage: 125 kV
- Nominal primary voltage: 100 – 2500 A
- Nominal secondary voltage: 5 A or 1 A
- Rated short-time thermal current, Ith: max 80 kA/1s (31,5 kA/3s)
- Rated dynamic current, ldyn: max 200 kA
- Rated continuous thermal current, Icth: 120 % In
- Accuracy class – measurement: 0.2S, 0.2, 0.5S, 0.5, 1, 3
- Overcurrent factor – measurement: FS 5, FS 10
- Accuracy class – protection: 5P, 10P, PX
- Overcurrent factor – protection: 5, 10, 15, 20, 25, 30
- Nominal power: 5 – 60 VA
- Nominal frequency: 50 Hz
- Weight: 17 kg
- Thermal insulation class: E
- Operating temperature: corresponds to temperature class -5/40 according to IEC 61869-1
- Standard: IEC 61869-1, IEC 61869-2
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