LB7-110 · LB7-110W2
Oil-immersed current transformer with capacitor-graded oil-paper insulation for current measurement, energy metering and relay protection in 110 kV, 50 or 60 Hz networks. Two transformation ratios are selected by reconnecting links outside the expansion tank.
The LB7-110 is a high-voltage current transformer for current and energy metering and for relay protection in 110 kV, 50 Hz or 60 Hz AC lines.
The full designation of this type of transformer is LB7-110W2 P/P/P/0.5a-b/c. The designation consists of three parts.
The first part is the basic type; the letters and figures mean:
| L | current transformer |
| B | with protection class windings |
| 7 | design serial number |
| 110 | rated voltage, kV |
| W2 | for areas with pollution degree II |
The second part is the class combination: the transformer has four secondary windings — one metering winding of accuracy class 0.5 and three protection windings of class "P".
The third part is the transformation ratio 2*a/c: the same product has two transformation ratios, obtained by changing over the connecting plates outside the expansion tank at the top of the product. With series connection the transformation ratio is a/c, with parallel connection — 2*a/c. Here 2*a is the primary current value and c is the secondary current value; for specific versions see Table 1.
The transformer is of oil-immersed design; it consists of an oil tank, active part, porcelain housing, expansion tank, metal bellows, etc. The active part is immersed in transformer oil and consists of the primary and secondary windings. The primary winding is U-shaped. In products rated 2*400 A and below, the primary winding conductor is paper-insulated flat copper wire; in products from 2*500 to 2*1000 A — two semicircular aluminium tubes. The main insulation is of the capacitor type, oil-paper: high-voltage cable paper is wound onto the primary winding conductor with several capacitor screens between the layers; the inner screen is connected to high potential, the outer screen is earthed (the outer screen is also called the end screen or earthing screen). The primary winding conductor is divided into two sections with four terminals, which are brought out into the expansion tank; the transformation ratio is changed by changing over the connecting plates outside the tank. The secondary windings are fixed on a support at the bottom of the primary winding.
All secondary winding terminals and the terminal of the outer screen of the primary winding are brought out into the terminal box on the oil tank. The polarity of the transformer is subtractive: when the primary current flows from P1 to P2, the secondary current leaves S1 and returns through the external circuit to S2 or S3. At the bottom of the terminal box there are terminal clamps through which the external circuits are connected. The terminal box and the bottom of the oil tank have earthing bolts — for earthing the secondary windings and the entire product. The oil tank is welded from steel sheet; the base frame has four holes for lifting the product.
The transformer is fully sealed. A metal bellows is installed at the top, which compensates for changes in transformer oil volume due to temperature and isolates the oil from the outside air — this prevents moisture ingress into the product and oil ageing, extends the service life, improves reliability and significantly reduces maintenance. The bellows has an inspection window with an oil level mark for monitoring the oil level in the product.
| Parameter | Value |
|---|---|
| Rated operating voltage | 110/√3 kV |
| Highest operating voltage | 126/√3 kV |
| Rated frequency | 50 Hz |
| Polarity | subtractive |
| Rated primary current, A | 2*50; 2*75; 2*100; 2*150; 2*200; 2*300; 2*400; 2*500; 2*600; 2*750; 2*1000 |
| Rated secondary current | 1 or 5 A |
| Secondary winding combinations | P/P/0.5; P/P/0.2; P/P/0.5/0.2; P/P/P/0.5; P/P/P/0.2; P/P/0.5/0.2; P/P/P/P/0.5; P/P/P/P/0.2; P/P/P/P/0.5/0.2; P/P/P/P/P/0.5; P/P/P/P/P/0.2; P/P/P/P/0.5/0.2 |
| Note: in products of versions from 600–1200 to 1000–2000 A, the secondary windings have intermediate taps; for the corresponding transformation ratios, accuracy classes and rated output — see Table 1. | |