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DGC Brushless Excitation - Emerson Process Management

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<strong>DGC</strong> <strong>Brushless</strong> <strong>Excitation</strong><br />

System Description<br />

4.3.a Voltage Control<br />

The Control and Protection Software implements the voltage control function of the <strong>DGC</strong>. Many of<br />

the characteristics of the controller are tunable by the user. Tuning constants are entered and<br />

modified using the <strong>DGC</strong> Configuration software. The block diagram below will aid in understanding<br />

the operation of the voltage regulator controller software.<br />

4.3.b Setpoint<br />

The voltage Setpoint is expressed as a fractional percent, ranging from 0.9 to 1.1. The value is<br />

raised or lowered using the Voltage Adjuster control switch. The rate of change is typically set for 1<br />

minute from minimum to maximum.<br />

fld_i_pct<br />

gen_mvars_actual<br />

gen_mw_actual<br />

tgr_value<br />

in_va_up<br />

in_va_down<br />

in_vapre(n)<br />

vhz_actual<br />

tgr_value<br />

line_w_actual<br />

line_vars_actual<br />

Maximum<br />

<strong>Excitation</strong><br />

Limiting<br />

Minimum<br />

<strong>Excitation</strong><br />

Limiting<br />

Voltage<br />

Set Point<br />

Volts Per<br />

Hertz<br />

Limiting<br />

Line<br />

Compensation<br />

mel_out<br />

va_volts_value Σ auto_error<br />

vhl_out<br />

mxl_out<br />

+ -<br />

+<br />

-<br />

-<br />

fb_comp<br />

Π<br />

pss_output<br />

-<br />

tgr_value<br />

Figure 4: Controller Block Diagram<br />

4.3.c Voltage Feedback Signal<br />

The Voltage Feedback Signal is a simple ratio of measured voltage to rated voltage. The Voltage<br />

Feedback Signal is passed through a dead band filter and modified by the compensators. The<br />

damping signal, the limiter outputs, and the power system stabilizer output (if installed) are summed<br />

with the f Voltage Feedback Signal and the setpoint to produce an error output. Each of the<br />

compensators and limiters are discussed in more detail in the following paragraphs.<br />

4.3.d Load Compensation<br />

Load Compensation is normally used when multiple generators of different types are operated in<br />

parallel on a common bus. The compensation is used to balance the reactive droop characteristics<br />

of the various machines to ensure that they share reactive load equally. The effect of the<br />

compensation is to make the apparent terminal voltage rise as the reactive loading of the machine<br />

increases in the over-excited direction. This causes the <strong>DGC</strong> to reduce the terminal voltage,<br />

transferring reactive load to the other machines. This function may also be used to compensate for<br />

a high impedance main transformer.<br />

Power<br />

System<br />

Stabilizer<br />

Proportional<br />

Action<br />

-10<br />

+10<br />

Integral<br />

Action<br />

Transient<br />

Gain Reduction<br />

gen_freq_actual<br />

Load<br />

gen_vars_actual<br />

Compensation<br />

Π gen_v_db Deadband Filter<br />

gen_v_pct<br />

i_output<br />

fld_i_pct<br />

p_output<br />

+<br />

+<br />

Σ<br />

-10<br />

+10<br />

Output<br />

ctlr_out<br />

Limits<br />

regulator_out<br />

© <strong>Emerson</strong> <strong>Process</strong> <strong>Management</strong> Power & Water Solutions. - 18 -<br />

PWS_005075 [3]

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