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

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.