Protection Against Over-Speed; Electrical Supply Failure - Edwards nEXT730D Instruction Manual

7.8.3 Protection against over-speed

Control software within the motor controller regulates the pump rotational speed and
prevents the pump operating above its normal full rotational speed.
In the unlikely event of a failure of this control software, the motor controller has a built-
in safety circuit that checks whether the pump is running at over-speed. If an over-speed
condition is detected, the motor controller automatically shuts down power to the
pump motor and slows it down to rest. The motor controller will signal a fail condition if
over‑speed has been detected.
If the pump appears to be running at over-speed, switch it off and consult Edwards or
the supplier.

7.8.4 Electrical supply failure

If the electrical supply to the nEXT pump fails when the pump is rotating, the pump
motor is used as a generator.
WARNING:
If the power supply fails when the pump is running, the rotor could continue to spin
for approximately 30 minutes. The control circuit may not give any indication that the
rotor is still running.
CAUTION:
If the parallel start control signal on the logic interface connector is set to start, the
pump may automatically restart when the electrical supply is restored after an
electrical supply failure. Ensure that people cannot be injured by the rotating blades
of the pump.
The regenerated power is used to maintain the output signals on the logic interface
(such as the normal signal and serial communications), to power the indicator LEDs on
the motor controller and to maintain power at the motor controller auxiliary outputs (to
control the vent valve and/or fan, if fitted). The regenerated power is also available at
the power supply interface connector, but only when electronic braking is enabled (refer
to Electronic braking
through short power interruptions. The minimum voltage of this supply will be 48 V d.c.
- 15 % (40.8 V) provided that the external load is not excessive and it can be sustained at
that minimum voltage when operating from supply voltages above 48 V d.c. -20% and
below 48 V d.c. +5%.
As the pump rotational speed decreases, the motor's ability to generate power also
decreases until it is no longer able to maintain power to the logic interface or LEDs. This
will occur at speeds below 50% full rotational speed. In this case, there will be no
indication of pump rotational speed yet the rotor may still be turning.
When the power is reinstated after a power failure, the behaviour of the pump will
depend on the control mode at the time of failure (parallel or serial) and the length of
time the pump was without power.
instated after an electrical supply failure
B8J200880_D
300812671_002_C3
B8J200880_D - Operation
on page 17). This could be used to power other instruments
Table: Behaviour of a pump when the power is re-
shows a number of scenarios.
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