The main function of a track circuit is to detect the presence or absence of traffic on a given railway section of track. High voltage impulse track circuit (HVITC) designed and manufactured by ALSTOM Transport, is a comprehensive range of jointed track circuit products, which can be adapted to any kind of track configuration.
Basic principles

An HVITC includes:

	A transmitter, which generates impulses with a given shape, amplitude and recurrence frequency injected into the tracks by means of a matching isolating transformer
	A receiver, which detects at the other end of the track section the specific signal and operates the failsafe relay, if the specific signal responds to the correct positive and negative amplitudes.

Applications
HVITC track circuits are adaptable to these applications:
Single rail arrangement for a length between 18 m and 750 m
The length can be extended to 1 000 m, provided one transmitter per track circuit is used
Non-electrified lines
DC electrified lines with: 750 V,
1 500V, 3000 V traction
AC electrified lines with 25 kV, 50Hz or 60Hz
15kV, 162/3 Hz

Installation conditions
Minimum ballast resistance from 0,6 - 2 ohm/km
Drop shunt from 0,15 - 1 ohm
Impulse recurrence frequencies: 3 Hz
Impulse width: 3 milliseconds
Voltage peak value: 100V
Current peak value: 100A
Standard length of track circuit (with ballast resistance equal to 2 x 2 ohm/km).

HVITC consists of the following basic elements:
Power supply

110V-115VAC 50hz or 60Hz

Transmitter
Power 45 VA, 24VDC Voltage limits: +20% - 6%
Peak-to-peak max. ripple: 5%
Transmitter: 50 W for 24 V equipment

Receiver
The receiver NCO RVT 600 consists of two integrating circuits. The first circuit receives energy from the negative part of the impulse; the second circuit receives energy from the positive part of the waveform.
Fail-safe thresholds, and different thresholds eliminate electrical disturbances.

Track relay
NCO CVTH 24.4.0.4
The NCO RVT 600 receiver and NCO CVTH track relay do not require any power. The energy is provided from the track signal.