Basler Electric DECS-250E, Digital Excitation Control System

Introduction

The FGD-2 Field Ground Detector Module is a transducer that continuously

monitors the resistance of the field circuit of a synchronous machine with

respect to ground. It applies a fixed voltage with respect to ground which

causes a small leakage current to flow. The FGD-2 provides a low voltage

output signal proportional to the leakage current.

The voltage output is measured by a compatible product and used for field

ground protection.

Two versions of the FGD-2 are available. A low-voltage version, rated for

800 Vdc maximum generator field voltage, is provided for brush or brushless

exciter systems. A high-voltage version, rated for 1.750 Vdc generator field

voltage, is provided for static exciter systems.

The metal enclosure of the FGD-2 offers electric shock protection from

incidental contact. A compatible footprint and identical functionality make

for simple replacement of a Field Ground Detector (FGD) with the FGD-2.

Installation

The FGD-2 is typically preinstalled in an excitation control system. If replacement

is necessary, carefully label and document each of the connections to the FGD-2

in order to properly reconnect the new module. FGD-2 connectors and indicators

are illustrated in Figure 1. Locator letters in Figure 1 correspond to the lettered

descriptions in Table 1. When a replacement FGD-2 is installed in a DECS-2100

or ECS2100 system, the system calibration values may need to be updated.

Retrofitting an FGD

Although the FGD-2 is smaller in size than the FGD, it may still be mounted in

place of an FGD using only four of the six existing mounting holes.

Either the upper four or the lower four mounting holes may be used.

The DGC-2020HD provides integrated engine-genset control, protection,

and metering in a single package. Microprocessor-based technology

allows for exact measurement, setpoint adjustment, and timing functions.

Front panel controls and indicators enable quick and simple DGC-2020HD

operation. A backlit liquid crystal display (LCD) can be viewed under a wide

range of ambient light and temperature conditions.

Basler Electric communication software (BESTCOMSPlus®) allows units to

be easily customized for each application. Because of the low sensing burden

in the DGC-2020HD, dedicated potential transformers (PTs) are not required.

These expansion modules eliminate the need for expensive external devices

by providing additional contact and analog inputs and outputs to certain

Basler Electric products.

Current Boost Module

The Current Boost Module rectifies the ac current received from the CTs

and provides dc current boost to the generator exciter field.

During normal generator operation, power from the generator output

provides sufficient exciter field power and the CBS 212A remains dormant.

During normal operation, the CTs are effectively shorted by the internal

SCRs of the CBS 212A. Normal generator operation is indicated by the

Operating Point Indication LED being lit.

If the generator output voltage decreases below the operating-point setting,

the CBS 212A detects the voltage drop, turns off the Operating Point Indication

LED, and removes the SCR “short-circuit” from the CTs.

The CBS 212A then provides full current boost to the generator exciter until

the voltage returns to a level just above the operating point setting.

The Controls and Indicators and Installation chapters provide information

about setting the Operating Point Adjustment.

An adjustable voltage limiting circuit prevents the Current Boost Module

output from exceeding the specified percentage of the nominal output

voltage (60. 120. or 220 Vdc). The Output Limit Select Jumpers are used

to select the nominal output voltage (60. 120. or 220 Vdc) and the Output

Limit Adjustment is used to set the desired percentage of the nominal output

voltage. The Output Limit Adjustment is adjustable over a range of 50 to

100 percent of the jumper-selected nominal output voltage.

The CBS 212A Current Boost System assists Basler SSR-series voltage

regulators during generator overload conditions and supplies the exciter

field during generator short-circuits. When used with three wire or 4-wire

generators, the CBS 212A supports sustained single-phase and multiple

-phase, line-to-line faults.