BENSHAW RSi-030-SG-4B, Service Manual

Page: 85 / 116

Pub # 890046-10-00
Dec. 2015
Section 4, Page
3
of
32
4.1 Over Voltage Fault
Fault Display:
Over Voltage
Auto Resettable:
Yes
Background
- What is the DC Bus Voltage?
The line voltage (input) to the drive gets rectified with a 3 phase full bridge rectifier. This DC
voltage is filtered with the capacitor bank within the drive. The DC voltage (referred to as the
DC Bus Voltage or DC Link Voltage) on the capacitor bank is the peak value of the AC input
voltage and can be calculated by multiplying the line voltage by
√ 2. The drive uses the DC Bus
voltage to create the PWM output voltage. The drive monitors the DC Bus to detect low voltage
and over voltage conditions. The DC Bus voltage can be viewed at parameter DRV-11. It can
also be measured across terminals P and N at the drive power terminals.
Description:
What is an Over Voltage Fault?
The DC Bus voltage of the drive has reached ~123% of the normal DC Bus voltage.
Note: The
trip level is not adjustable as it is a hardware protection fault.
Summary
Causes:
Over Hauling Load conditions. Any time during running or stopping, when the load
causes the motor to rotate faster than the drive commanded speed, the motor will produce torque
in the opposite direction (negative torque or brake torque) resulting in energy fed back into the
drive from the motor. The result of this regenerative power is an increase in the DC Bus voltage.
Drives can handle some regenerated energy (~15% of their HP/kW rating), but certain loads or
operating conditions will increase the DC Bus voltage to the trip level resulting in an over
voltage trip.
The most common cause of an over voltage trip is trying to decelerate the motor/load too quickly.
Increasing the deceleration time is the most common solution. However, if this does not solve
the tripping, dynamic braking (resistor and module) may be required. Typical applications are
high inertia type loads (centrifuges, large fans/blowers, large conveyors, loads that use a
flywheel). When decelerating or changing to slower speeds an over voltage fault could occur.
Other applications where over voltage faults are likely involve changing load conditions from
heavy load to light load (lumber mill saws or simply belts slipping).
System Voltage
(Vac)
Normal DC Bus
(VDC)
Trip Level
(VDC)
460/480 650/680 800
230/240 325/340 400
575 813 1000