Ampcontrol Pty Ltd
– ABN 28 000 915 542
HPB USER MANUAL
HPBB012 Version 9
– March/2020
Uncontrolled Copy - Refer to Ampcontrol Website for Latest Version
Page 14 of 61
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CAUTION!
When installing the CCMB
– 22kV, measure the resistance between the
transformer primary star point and earth before applying power. Ensure
that it is less that 10Ω.
4.3.4 Overload & Earth Leakage Toroids
Current transformers (CT) are not ideal devices and if correct procedures are not followed during
installation, nuisance tripping can result.
If using, for example, a single-phase earth leakage system where active and neutral pass through a
toroid then at all times currents in the two wires are equal and opposite so that the net current through
the toroid is zero. An ideal current transformer would have all the flux from each wire contained in the
core and so would accurately add the opposing fluxes to get a net result to zero. A real current
transformer has “leakage fluxes”. That is, a very small proportion of the total flux from each cable is not
contained in the core, but in the space outside it and as a result it may link some turns but not others,
depending on the positioning of the cables. The effect of this is that a small output may be obtained
from the CT when none would arise if the device was ideal.
The size of the error will vary from CT to CT of the same type because of slight differences in the core
and the symmetry of the winding.
Problems caused in this way become worse as CT sizes increase, as currents increase and a
decrease in the symmetry of the cables.
Nuisance tripping tends to occur when the total current rises, such as when a large motor is started.
To help avoid such problems, select to smallest internal diameter CT, which will allow the cables to fit
through.
4.3.5 Toroid Installation Guide Lines
a. Keep cables as close to the centre of the toroid as possible. Do not tie them to one side of the
toroid. Remember aim at symmetry.
b. Do not bring the cables back past the toroid within on diameter of the CT, trying to cram cables into
a small space reduces symmetry and may lead to problems, which are difficult to solve.
c. Avoid placing the CT near any device, which produces magnetic fields, whether it is a transformer
or other cables. Try to maintain several CT diameters clearance.
d. Many small cables tend to be worse than for example, three large ones. Try to position the CT in
the circuit with this in mind.
4.3.6 Wiring Installation
The connections to the HPB Relay consist of a mix of low and high voltage supplied and relay contact
circuits. To reduce induction from high voltages, care needs to be taken in the layout of the wiring and
the installation.
When using a 110V HPB a power supply filter, e.g. Schaffner FN612-1106 (1A, 250VAC chassis
mounted filter) or similar, should be installed adjacent to the HPB Relay. The earth should be
connected to Pin 7 on the relay as directly as possible.
4.3.7 Low Voltage Signals
Care must be taken to ensure these circuits cannot come into contact with higher voltages (e.g. via
insulation breakdown, or broken wires etc.). It is recommended that these circuits be run in a separate
loom from the “high” voltage circuits. To ensure that interference is kept to a minimum, the following
cabling is required.
