ABB ACS 502 Series, Installation & Start-Up Manual

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Chapter 2 – Overview of the ACS 502/504
ACS 502 Installation & Start-up Manual 2-7
The output voltage waveform is a pulse-train. The widths of the pulses depend
on the modulation. The purpose of the modulation is to create the fundamental
voltage wave (its amplitude and frequency), e.g., according to the law
V
out
/ f
out
= constant (V/Hz).
The distortion of the output voltage from the sinusoidal fundamental creates
corresponding harmonics in the motor current. However, since the motor is
highly inductive and the modulation frequency is relatively high, the current
waveform is nearly sinusoidal.
Protective features
Should something adverse happen during power-up or normal duty, the drive
incorporates the following features to protect itself:
• Internal overtemperature (warning and trip)
• Overcurrent (two current limits and trip)
• Input line phase loss / unbalance (trip)
• Overvoltage (trip at 130% nominal DC-voltage)
• Undervoltage (trip at 60% nominal DC-voltage)
• Starting at overvoltage (>117% of nominal DC-voltage inhibits start)
• Ground fault (>2.5 amps)
In addition, the drive identifies various internal and external hardware faults
and displays a diagnostic message.
The ACS 504 also has a variety of protective features for the motor, such as:
• Stall (warning and trip)
• Overload (warning and trip)
• Underload (warning and trip)
Power-off sequence
A high voltage remains on the capacitor bank after the line voltage is
disconnected. This voltage is discharged through discharging resistors (R11)
within five minutes. Always use a voltage measurement to determine that the
voltage has dropped before performing any service or making main circuit
connections. Measure between terminals UDC+ and UDC-; also measure
between UDC+ and chassis ground. The meter must be capable of
withstanding 1000 VDC.