Basler Electric DXCB-2 De-Excitation/Crowbar Module

INTRODUCTION

The DXCB-2 De-Excitation/Crowbar Module protects the generator

field and exciter circuits by providing a low impedance path for

currents that would otherwise cause excessively high transient

voltage or damaging arcs. A DXCB-2 module can be operated in

one of two modes: de-excitation (DX) or crowbar (CB).

In DX mode, the DXCB-2 module provides a path for the generator

field current when its field breaker is opening or when the normal

path is not available.

In CB mode, the DXCB-2 module provides a low-resistance path

for large positive voltages across the generator field and exciter

bridge. Generator pole-slip is one source of high voltage.

The enclosure of the DXCB-2 offers electric shock protection from

incidental contact. An identical footprint and functional compatibility

make for simple replacement of a DXCB with a DXCB-2.

DXCB-2 Models

Three versions of the DXCB-2 module are available. Part number

9500900100 is rated for up to 600 Vdc nominal field voltage and

can conduct up to 2.000 Adc for one second.

Part number 9500900101 is rated for up to 1.000 Vdc nominal field

voltage and can conduct up to 5.000 Adc for one second.

Part number 9500900102 has identical ratings to part number

9500900101 but has a higher range of jumper-selectable trip voltage

values.

Reference Table 3 for jumper-selectable trip voltages for each model.

SAFETY

As with all electrical equipment, appropriate safety measures must be

taken when dealing with excitation equipment. High voltage is present

within the excitation cubicles; their magnitudes depend upon the

particular system. Opening the sources (e.g., disconnecting device 41)

does not completely disconnect the high voltages.

As long as the machine is still physically connected to the system, there

is a possibility that a safety hazard exists.

Every precaution must be taken when working at the excitation control

switchgear to ensure that all high voltages are isolated and avoided by

test personnel. In addition to the machine terminal voltage (460 Vac or

greater) at the excitation transformer, there may be other sources of

power entering the cubicles, such as 125/250 Vdc and/or 120/240 Vac

used to feed certain devices. A good rule to follow is to assume that all

connections are live and dangerous until proven otherwise and to avoid

all body contact with any of these voltages.

INSTALLATION

48.6 lb (22.1 kg)

16.25 x 11.22 x 10.52 inches

(412.6 x 285.0 x 267.2 millimeters)

The DXCB-2 is typically preinstalled in the excitation control system. If

replacement is necessary, carefully label and document each of the

connections to the DXCB-2 in order to properly reconnect the new module.

The DXCB 2 must be monitored and adjusted to fit the specific application

at initial startup, whether it is a new unit or a replacement.