  The high voltage system supplies the bias voltage to the 88 silicon sensors
which comprise the LHCb Vertex Locator (VELO). This note describes the results
of the tests which have been performed on the hardware of the high voltage
system of the VELO. Each individual test detailed in this note corresponds to a
specific requirement of the system. These requirements arise primarily from
ensuring the safety of the silicon sensors and the quality of the data taken
from the VELO modules. The tests performed are in four categories: normal
operation of the high voltage system; verification of its stability under
operation; discussion of its behaviour in failure modes; and details of
operation at low voltage. Noteworthy issues, identified through the tests,
include the behaviour of the high voltage modules at voltages below 9V, the
current limit that can be applied during ramping of the voltage, and the speed
with which the voltage is cut during failures of the system. The results of
these tests provide high confidence that the high voltage system can be safely
used and demonstrate that low noise is produced by the power supplies.
