Basler ElectricDECS-200-1C Digital Excitation Control System

Field Current Regulation Operating Mode

DECS-200 provides a manual channel of operation called Field

Current Regulation, or FCR, Mode. In this mode, DECS-200

regulates the field current generated by the internal PWM power

stage. It does not rely on the sensing input to DECS-200 and is,

therefore, a good source of backup excitation control when loss

of sensing is detected. In this mode, control of the generator is

totally dependent upon the operator to maintain nominal generator voltage as the load varies on the generator.

Var/Power Factor Controller Operating Mode

DECS-200 has, as another standard feature, two modes of

operation when the generator is in parallel with the utility power

grid. The DECS-200 has both var and PF modes of operation.

When the generator is in parallel with the utility grid, the DECS200 can regulate the var output of the generator to a specific var

level magnitude or it can vary the var output of the generator to

maintain a specific power factor as the kW load varies on the

generator.

Maximum Excitation Limiters

Overexcitation limiting (OEL) operates in all modes except FCR

mode. OEL senses the field current output of the voltage regulator or static exciter and limits the field current to prevent field

overheating. In FCR mode, the DECS-200 only announces that all

conditions for OEL are fulfilled and does not provide limiting. The

DECS-200 provides two types of overexcitation: Summing Point

and Takeover.

Summing Point Type OEL

Three OEL current levels are defined for on-line operation. They

are high, medium, and low. The generator can operate continuously at the low OEL current level and for programmed times at

the high and medium OEL current levels. Two OEL current levels

are defined for off-line (main breaker open) operation. They are

high and low. The generator can operate continuously at the low

OEL current level and for a programmed time at the high OEL

current level.

FEATURES/FUNCTIONS, continued

Takeover Type OEL

The field current level at which limiting occurs is determined by an

inverse time characteristic. Two current levels and a time dial

setting are defined for the takeover-style OEL limiter. Separate

curves may be selected for on-line and off-line operation. If the

system enters an overexcitation condition, the field current is

limited and made to follow the selected curve. The selection of

on-line or off-line OEL levels/curves is determined by an OEL

option selection.

Minimum Excitation Limiter

The minimum excitation limiter limits the amount of excitation

supplied to the field of the generator from dropping below unsafe

operating levels. This prevents the machine from possibly slipping

poles and from damaging the machine. It limits the amount of

vars being absorbed by the machine, based on user-definable

settings. An internally generated Underexcitation Limiting (UEL)

curve can be utilized based on a var level at 0kW, or a

customizable 5 point UEL curve can be selected to match specific

generator characteristics.

Stator Current Limiter

The stator current limiter (SCL) senses the level of stator current

and limits it to prevent stator overheating. The SCL operates in all

modes except FCR. In FCR mode, the DECS-200 only announces

that a stator overcurrent condition exists; it does not provide

current limiting. Two SCL current levels are provided: high and

low. The generator can operate continuously at the low SCL level

but only for a programmed time at the high SCL level.

Internal Autotracking Between DECS-200 Operating

Modes

DECS-200 is an intelligent device that can provide autotracking

(autofollowing) of the controlling mode by the non-controlling

modes. This allows the operator to initiate a controlled, bumpless

transfer of the DECS-200 operating modes, causing minimum

amounts of line disturbance for the power system. This feature

can be used in conjunction with a set of protective relays to

initiate a transfer to a backup mode of operation, such as FCR

mode, upon the detection of a system failure or fault, i.e., loss of

sensing.

External Autotracking between Dual DECS-200 Units

(Optional)

A DECS-200 can also follow (autotrack) a second DECS-200 unit.

The second DECS-200 is put into a specific operating mode and

follows the excitation level of the first. In the unlikely event of a

failure of the first DECS-200, protective relays can initiate a

transfer of control from the first to the second DECS-200.

Protective Functions

There are several protection functions built into the DECS-200

unit. These functions may be used as backup to the primary

protection relays and can be assigned programmable output

contacts via the PC software. The protection features offer fully

adjustable tripping levels and time delays. The protective features

are as follows:

• Generator Overvoltage • Watchdog Timer

• Generator Undervoltage • Loss of Sensing

• Field Overvoltage • Loss of field

• Field Overcurrent • EDM Exciter Diode Monitor

Sequence of Events Recording (SER)

A sequence of event report (SER) is a very powerful tool when

reconstructing the exact timing of an event or disturbance. The

DECS-200 monitors its contact inputs and outputs for a change of

state, system operation changes, and alarm conditions. If any of