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Intercircuit bridging protection (TOVI)
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The intercircuit bridging protection, TOVI is intended to detect faults between systems
running at 16 2/3 Hz and 50 Hz (for example connection between a 16 2/3 Hz catenary
line and a 50 Hz system for feeding auxiliary equipment along the railway).
The function will differ depending of frequency setting in the terminal:
1. TOVI with a frequency of 16 2/3 Hz detects whether a 50 Hz-component exists on
the line voltage and blocks the connection of the line-breaker if the 50 Hz compo-
nent exceeds the set operating level of the protection. The function detects whether
an auxiliary power line with a rated frequency of 50 Hz has fallen down on the cat-
enary.
2. TOVI for systems with a set frequency of 50 Hz detects whether a 16 2/3 Hz com-
ponent exists in the voltage on the 50 Hz system. The reason for the occurrence of
a 16 2/3 Hz- component can, for example, be an interruption on the power line
where the line has fallen down on the catenary. In the event of such a fault the cat-
enary must be quickly disconnected to prevent damage to apparatus and transform-
ers in the 50 Hz network.
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The voltage measuring element continuously measures the f1 Hz voltage component
from Ux and compares it with the set operate value U>. A second order bandpass filter
(center frequency f1 Hz) ensures immunity to disturbances and harmonic voltages and
reduces the influence of the fn Hz voltage component with a factor > 10.
Where:
1. f1 = 50 Hz and Ux = U1 if fn = 16 2/3 Hz
2. f1 = 16 2/3 Hz and Ux = U4 if fn = 50 Hz
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