Marc James Foxall.
New High Current (1000A) Ferrite Rogowski HFCT PD Sensor.
Development of a New High Current (1000A) Ferrite Rogowski HFCT PD Sensor
"High Frequency Current Transformers (HFCT) are a commonly used
sensor for on-line partial discharge (PD) detection in medium voltage (MV)
and high voltage (HV) systems. Requirements for them to be used on high
current (1000A) machinery induces problems, due to the magnetic core
of the HFCT becoming saturated. Insertion of insulation gaps between the
split ferrite cores increases the saturation point of the HFCT, however due
to the trade-off with the transfer impedance, this reduces its sensitivity.
After working for Manchester based company High Voltage Partial
Discharge (HVPD) Ltd on a 12 week summer placement after my second
year of University, I enquired about research projects and was supplied with
this unique project.
My report uses frequency response and high current saturation results to
identify a proposed insulation gap size between the split ferrite core, which
makes the sensor as sensitive as possible and maintains a high saturation
point. The present, low current, HVPD 140/100 HFCT was used as a basis
for the new high current model. A proposed insulation gap size between the
split ferrite core, with 10 turns on the secondary was resulted. Independent
verification of the use of 10 secondary turns around the HFCT also took
place. Use of this insulation size promotes a saturation current of 690A
and maintains an almost constant transfer impedance of 2Ω, within
its working frequency of 300kHz to 10.5MHz.
As an impact of the research carried out in my report, the saturation point
of the present low current design has been increased from approximately
140A to around 690A with the new high current design.
In the future, further testing could be conducted into using more than two
gaps in the ferrite core and also on the effects of varying the temperature of
the sensor, on the transfer impedance at numerous currents (0A to 1000A).
I am currently putting together a professional publication on my project
to be published by and demonstrated at the International Wire and Cable
Symposium (IWCS) with the help of my project supervisor Dr Alistair Duffy."
