Two Winding Transformer Data
This dialog box includes the following areas and tabs:
 Database Dialog Box Toolbar
 Connection Information
 Specifications Tab
 Impedance Tab
 TCC Tab
 LTC (Load Tap Changer) Tab
 Harmonics Tab
 Stability Tab
See Common Tabs for information on the Location, Comments, Hyperlinks, or Collected Data tabs.
Figure 1: TwoWinding Transformer Data Dialog Box (ANSI)
Figure 2: Two Winding Transformer Data Dialog Box (IEC)
Connection Information
Specifications Tab
Option  Description 

Standard  Choose either ANSI or IEC. 
Type  Type of cooling medium/insulation in the transformer (oil, liquid, gas, dry, silicone, or vapor). 
Class  Type of cooling used by the transformer. Various combinations of forced air, water and forced oil are available. This field is used to determine the forced cooled rating of the transformer. 
Temp 
Temperature rise rating of the transformer in degrees Celsius. 
Form  Either core or shell type transformers can be selected. If Core is selected, the Z0% value on the Impedance tab is set to 0.85 of Z%. If Shell is selected, Z0% is equal to Z%. 
Winding Information  
Rated kV  Rated kV of a winding. The rated kV can be different than the base kV or the tap kV. EasyPower automatically adjusts the model to account for different taps, turns ratio and bases you choose. 
Tap kV / Tap% 
Tap kV of a winding. You can also specify the tap kV in terms of percentage of the rated value. If the actual tap kV is not known, enter the rated kV. Load tap changer control can be used to determine final tap settings if needed. EasyPower automatically adjusts the model to account for different taps, turns ratio, and bases you select. 
MVA or kVA Rating  Selfcooled rating of the transformer. Use to select the unit in MVA or kVA. 
MVA or kVA O/L  Forcedcooled rating of the transformer. In the absence of this data, use the Calculate button to estimate the forcedcooled rating based on the Type, Class and Temp values you enter. 
Impedance Tab
Figure 3: Impedance tab of TwoWinding Transformer Dialog Box (3phase)
Option  Description 

Z% 
Transformer nameplate impedance in percent. By definition, this is the positive sequence leakage impedance in percent on the selfcooled MVA and nominal voltage rating. The strict definition is the percent of rated voltage impressed on the high voltage winding to produce rated full load current in the short circuited low voltage winding. If the Standard selected on the Specifications tab is set to IEC, the impedance is based on the MVA O/L value instead of the MVA rating. 
@MVA Base @kVA Base 
The base rating at which the Z% and Z0% impedances are applicable. The kVA or MVA text is displayed depending on the rating unit selected in the Specifications tab. When the field is blank, the program uses the standard ratings indicated on the Specifications tab to calculate the transformer per unit impedances:
You can also enter the MVA or kVA base values from the transformer datasheet or nameplate. When you manually enter a value, the entered value is used to calculate the per unit impedances instead of the standard ratings. 
Loss (kW) 
This is the kW losses at full load. Calculate uses this value to obtain the X/R ratio for the positive sequence impedance (Z%). The equation used is:
This field can be left blank. When this field is blank, the X/R ratio is estimated using the ANSI C37 curves. 
X/R Ratio  Transformer reactance to resistance ratio, which is used to determine resistance value. 
Z0% 
Transformer zero sequence leakage impedance in percent. If you don't know this value, enter the positive sequence impedance (Z) for shell transformers (see Form field above). For core transformers, use approximately 85% of Z. If you enter this value as zero (0.0), the positive sequence impedance is used. If Z% is entered, you can use Calculate to compute the Z0% value if it is blank. 
X0/R0 Ratio 
X/R ratio for zero sequence impedance (Z0%). Enter this data from the manufacturer, if available. If this field is left blank, zero sequence R0+jX0 values are calculated based on the positive sequence X/R ratio. 
Calculate 
Fills in a computed value for the X/R ratio. You can override this value by typing in a different number. If Loss(kw) is not entered, the calculated X/R ratio curve is based on the medium ANSI Standard curve [ANSI C37.0101979]. This curve was developed mainly for power transformers and is typically high for low voltage unit substations less than 2500 kVA. If Z% is entered, you can use Calculate to compute the Z0% value if it is blank. 
Grounding Grounding impedances only apply to wye grounded connections. The units are R+jX in ohms. If you only know the ground amperes of the circuit, enter the amp class and use the Calculate button to calculate the grounding impedance. 

R 
Transformer neutral ground resistance in ohms. This is the most common method of grounding the transformer neutral winding. Grounding resistors are usually given in amperes. The impedance is found from the following equation. R = Vln / I If the transformer is grounded through a separate grounding transformer with a secondary resistance, this resistance must be converted to the primary winding. Only wye grounded transformers are modeled with grounds. Mid or corner tapped delta windings are not modeled. 
jX 
Transformer neutral ground reactance in ohms. 
Amp Class 
This is the current in amps through the ground impedance at the rated voltage. You can enter data in this field directly in amps or calculate it based on the voltage and ground impedance R +jX using Calculate. 
IEC 

pT % 
For generator stepup (GSU) transformers, you can specify an impedance correction factor. The range is from 20% to 20%. This appears only if the option is set to Show fields and X/R calculations based on IEC 60909 in Tools > Options > Equipment. 
TCC Tab
Figure 4: TCC Tab for the Transformer Data Dialog Box
LTC (Load Tap Changer) Tab
Figure 5: LTC tab of TwoWinding Transformer Data Dialog Box
Harmonics Tab
Figure 6: Harmonics Tab
Use the Harmonics tab to indicate whether this equipment item is introducing harmonics into your power system.
Resistance Factor
EasyPower offers two methods for calculating R_{H}:
 Resistance varying with a power of the harmonic (REXP):
 Resistance varying with a percent eddy current factor (%ECF):
R_{H} = R_{Fund} * H ^{REXP}
R_{H} = R_{Fund} * (1+ECF*H^{2})/(1+ECF)
EasyPower defaults all skin effect correction to REXP and a value of 0.5.
REXP  %ECF  

Transformer 
0.51.0 
1.03.0 
Utility 
0.00.8 
 
Generator 
0.30.6 
 
Line/Cable 
0.5 
 
Reactor 
0.51.0 
0.83.0 
Motor 
0.20.4 
 
Fundamental Amps
Use to set the fundamental amps. The options are as follows:
 Equipment Rating sets Fundm Amps to the equipment rating of the item described in the Specifications tab.
 User Specified activates the Fundm Amps field, enabling you to specify a value.
To use fundamental current calculated by power flow, select Calculated from Power Flow in the Summation Fundamental Voltage area of the Harmonics Options > Control dialog box.
Stability Tab
Figure 7: Stability Tab
Option  Description 

Enable Transient Inrush Model 
Select the check box to enter stability information. 
Mfr  Provides a list of manufacturers available in the device library. If the desired manufacturer is not listed in the device library, you can add it to the library. 
Type  Equipment types available from the selected manufacturer. If the desired type is not listed, you can add it to the library. 
Model  Equipment models available from the selected equipment type. If the desired model is not listed, you can add it to the library. 
Lib  Populates the table with equipment data from the library. See EasyPower Device Library for more information. 
Other Tabs
See Common Tabs for information on the Location, Comments, Hyperlinks, or Collected Data tabs.
More Information
Database Technical Reference  Common Tabs 
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