Current transformer CTB size 4
bushing current transformer, encapsulated in epoxy resin • highest permissible system up to 36 kV • rated primary currents up to 10 kA • option: airtight bushing
Current transformers of CTB type are designed for indoor use at medium voltages. Epoxy resin casting (containing wounded cores inside) is the main electrical insulation. Excellent parameters of electrical insulation (including low level of partial discharges) are guaranteed.
The typical areas of application are switchgear cubicles and busducts of power generators. With regard to the possibility of sealing of the primary current conductor, CTB current transformers can be used as end‑bushings of the busducts with overpressure.
The epoxy resin castings are manufacured without primary current conductors: the current conductor of busduct or switchgear is the primary winding of a current transformer. Inside diameter of the casting is 330 mm.
CTB current transformers size 4 have up to 5 cores for measuring and/or protection. CTB current transformers can be mounted in any position.
Technical data:
| highest permissible system voltage | 7.2/12/17.5/24/36 kV |
| power frequency withstand voltage, 1 min | 20/28/38/50/70 kV |
| impulse withstand voltage 1.2/50 µs | 60/75/95/125/170 kV |
| rated frequency | 50 or 60 Hz |
| rated primary current IPn | up to 10 000 A |
| rated short–time thermal current Ith1s | 200 kA/1s (r.m.s. value) |
| rated dynamic current Idyn | 500 kA (peak value) |
| number of cores | up to 5 |
| rated secondary currents ISn | 1 A or 5 A or fractional |
| rated outputs Sn | 5 – 90 VA |
| accuracy classes | 0.2, 0.2S, 0.5, 0.5S, 5P, 10P, PX, PR |
| instrument security factor (FS) | 5, 10, 15 |
| accuracy limit factor | 10, 20, 50 |
| ambient temperature | –25oC ÷ 80oC |
| weight | ca 110 kg |
| according to standards | PN-EN 61869-1:2009; PN-EN 61869-2:2012 |