Suparule Systems Ltd Page 8 of 24 CFZ DCF2038 v1.09
During the monitoring period the device is powered from a split-core current
transformer power supply that draws power from one of the phases being
monitored. The primary indication is a Mechanical Flag, which is normally
black, and flips to a red colour when a fault is detected.
When the external power source (current flowing in the phase where the Power
CT is attached) is first applied or when it returns after the fault is cleared, the
unit will first require up to 40 minutes (where the phase current is minimum
50A) to charge the on-board backup power supply before it can function
properly. This backup power supply is used to retain power to the unit on fault
detection for a typical period of 10 hours for the purpose of driving the
mechanical flag indicator and Aux. Relay, if fitted.
The standard unit is factory programmed to trip at a nominal earth fault current
of 50A (other trip values can be supplied on request). Units with -S in the
model number have user-selectable trip levels, from 3 or 4 factory-set levels.
The EFI will reset automatically from a fault state on detecting the presence of
the external power supply for more than 10 seconds continuous. It can also be
reset manually, prior to the external supply being restored. (See section 3.6).
The unit is designed to operate in the harsh environment of medium voltage
networks (1 - 38kV).
2.2 CT Sensor
The Sensorform CT sensor comprises of a flexible iron-core belt with a
magnetic field pickup coil attached. The belt is fitted around the three-phase
cable system being monitored and works on the principle of core-balance
current sensing. Under normal operating conditions the magnetic flux produced
by the three phase currents sums to zero resulting in the pickup coil on the
iron-core generating no voltage output. When an earth fault occurs the flux will
be non-zero resulting in a voltage proportional to the magnitude of the earth
fault being generated by the pickup coil. The CT sensor has no exposed iron
parts and is completely encapsulated in corrosion proof material. The CT is
supplied with a 3-meter length of cable as standard.
