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MAIN CIRCUIT Service Manual M4 - M10

29.12.1999 Page 67

8.2.7 Spare Parts

Rectifier module or diode thyristor module.

Contactor, if used

Power terminals, if needed.

Detailed information for the spare parts is available from spare parts lists in

section “SPARE PART LIST”.

8.3 DC bus and precharging circuit

8.3.1 Description

Precharging circuit provides smooth charging for DC capacitors at powering

up a drive by mains. The precharging resistor(s) limits surge current passing

one phase (L3) of charging contactor. Type of the precharging resistors is

thick foil resistor, which is functioning as a fuse in case of excessive current

while precharging procedure. In normal operation, the fuse type precharging

resistors will not open.

The DC capacitor bank filters and stores electrical energy to maintain smooth

and stable DC-energy for a PWM-inverter. Stable voltage in DC bus is

required for proper high performance operation with topology of voltage

source inverter.

Negative feature of the DC capacitors is internal leakage current, through

insulation layer, which variates some amount from individual capacitor to

another. This feature causes variation in voltages divided cross the serial

connected capacitors. To avoid voltage to be concentrated cross the capacitor

with less internal leakage, external balancing resistors are needed. Therefore

balancing resistors / discharging resistors are playing important role by

balancing voltage cross the capacitors connected in serial.

When input energy from front end is disconnected, energy from DC capacitors

has to be discharged down to safe level within reasonable time. The

discharging resistors are now operating such as discharging resistors.

Irpre

Rdis

Rpre

Prpre

Udc-bus

Figure 8.7 Charging circuit by charging contactor

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