Generator Data

Uniquely identifies the equipment item. The program automatically assigns a name, but you can change it, if needed. The name can be up to 16 characters long.

For generators, the program automatically assigns the names GEN-1, GEN-2, GEN-3, and so on.

Generator type. This value is for reference only except for HG and SYN-SP types, which have their momentary reactances determined by X’dv.

• IND - Induction
• SYN-DP - Distributed pole synchronous
• SYN-SP - Salient pole without amortisseur winding
• SYN-SPA - Salient Pole with amortisseur winding
• SYN-COND - Condenser
• HG w/o A - Hydro generator without amortisseur winding (same as SP)

Generator bus type used in modeling the power flow simulation. When you select a particular model, those fields that do not apply become unavailable.

• Swing - A swing bus holds the bus voltage and angle constant. To do this there cannot be limits on the amount of MW or MVAR the swing machine can accept or provide. (See Swing Sources.)
• PV - Constant power, constant voltage generator. This is also known as a regulated generator. This model tries to hold a user-specified bus voltage within generator MVAR limits.
• PQG - Constant power, constant var generator. This is also known as an unregulated generator. This model holds the MVAR generation within given voltage limits.

For a PV generator (regulated), the bus that is to be controlled to the control voltage. If this field is blank in the database, EasyPower fills it in with the name of the bus listed in the To Bus field. (Note that this does not take effect until you accept it by clicking OK to close the database dialog box.)  This field is ignored if the Model is set to Swing.

DC generators have three control modes:

• Swing (Regulated): The voltage is controlled directly on the terminal of the generator. A regulated DC generator has the ability to be the single source that enables a system to enter power flow and solve the system.
• Swing (Un-Regulated): The voltage is held constant internally as a Thevenin source. The terminal of the generator changes with loading. An un-regulated DC generator has the ability to be the single source that enables a system to enter power flow and solve the system.
• Constant Power: The generator is modeled as a constant power generator, similar to a PQ generator in the AC power flow. A constant power DC generator DOES NOT have the ability to be the single source that enables a system to enter power flow and solve the system. To enter power flow focus, at least one other source must be modeled that supplies the system with stiff internal or external source.

This is the scheduled per-unit voltage that the voltage control unit will try to maintain for the generator. This applies only to the Swing (Regulated) model.

Subtransient reactance in percent on generators MVA base. Most synchronous generators have subtransient reactances in the 9-20% range¹. The subtransient reactance is used for ½ cycle, 5 cycle and 30 cycle short circuit calculations in accordance with ANSI Standards.

Reference:
¹ Short Circuit Calculations, General Electric , GET 3550.

Generator neutral ground resistance in ohms. This is the most common method of grounding generator neutrals and is usually given in amperes. The impedance is found from the following equation.

R = Vln / I

If the generator is grounded through a grounding transformer with a secondary resistance, this resistance must be converted to the primary winding. If you know the Amp value for the resistor, you can enter the amp value in the Amp Class field and use the Calculate button to find the resistance.

You can plot short circuit decrement curves “with” and “without” excitation field forcing for comparison purposes.

• Without Field Forcing: Plots TCC for “without field forcing” option.
• With Field Forcing: Plots TCC for “with field forcing” option.
• Maximum Plot Time: The amount of time in seconds that the generator can sustain overcurrents without exceeding safe temperature limits.

Armature time constant in seconds.

A typical generator datasheet will provide the Ta value. However, some manufacturers may not provide Ta in the datasheet. The armature time constant is associated with the rate of change of dc current in the stator when the generator is subjected to a 3-phase fault. Ta for different types of generators is provided in the book “Power System Control and Stability,” by Paul M. Anderson and A. A. Fouad, IEEE Press, 1994.

T_a = (L_d’ + L_q) / 2r

Where Ld’ is the d axis transient inductance and Lq is q axis inductance. A typical value of Ta is 0.15 seconds for fault on the machine terminal.

Prabha Kundur’s book “Power System Stability and Control”, McGraw-Hill, 1994, provides the following equation for Ta:

T_a = (L_d” + L_q”) / 2/ R_a

Typical value for Ta lies between 0.03 and 0.35s.

Forced excitation current at a given load expressed as per unit value of field current at no load, I_fd0.

This section allows you to plot “I^2t” thermal damage curve for the generator.

EasyPower offers two methods for calculating R_H:

• Resistance varying with a power of the harmonic (R-EXP):

R_H = R_Fund * H ^R-EXP

• Resistance varying with a percent eddy current factor (%ECF):

R_H = R_Fund * (1+ECF*H²)/(1+ECF)

EasyPower defaults all skin effect correction to R-EXP and a value of 0.5.