ABB VD4 Installation And Service Instructions Manual page 4

V D 4 D I G I TA L A D D E N D U M - TO VD4 INSTALLATION AND SERVICE INSTRUCTIONS
4
—
3. Description
General
VD4 Digital circuit breaker with embedded sensors
and a new relay, for instance type REF 615, has been
designed to provide a powerful electrical plant
protection system.
VD4 Digital circuit-breaker uses current sensors or
combined current and voltage sensors
(combisensors) able to measure the current and
voltage applied to each pole.
The VD4 Digital circuit-breaker is available in
withdrawable version for UniGear ZS1 switchgear,
PowerCube units, and OneFit. It can be used in fixed
version for the design and supply of roll-in-retrofit
solutions to MV circuit breaker installed base, in
particular when original circuit breaker had current
or voltage instrument transformers or direct acting
relay mounted on withdrawable truck.
VD4 Digital is mechanically interchangeable with the
VD4 series circuit-breaker.
Combined current-voltage sensors.
Combined current-voltage sensors
The current is measured by a Rogowski coil: a
uniform winding on a closed circular support with a
constant crosssection and without a ferromagnetic
core. The voltage induced in the winding is directly
proportional to the variation in the let-through
current.
The current sensors are characterized by the
absence of saturation and hysteresis phenomena
and by their accurate measurement for fault
currents up to the maximum adjustable setting
value of the protection thresholds.
The voltage is measured by a capacitive divider: a
cylindrical metal electrode moulded in the sensor
and facing the circuitbreaker bushing. The output
signal is a voltage directly proportional to the
primary voltage.
The voltage sensors are characterized by the
absence of ferroresonance phenomena.