Line

Series capacitors are usually provided with a protection system which bypasses (short-circuits) the capacitor when a certain amount of current flows through it.

Note:

CYMFAULT takes the series compensation into account, but not the protection system. If the calculated short-circuit current flowing through the transmission line with the series capacitor is higher than the threshold for the capacitor’s protection system, then you should reset the series

compensation to 0% temporarily and run the fault calculation again. This

situation will arise for faults at buses which are “electrically close” to the line with the capacitor.

CYMSTAB takes both the capacitor and its protection into account. Series compensation modeling is now considered in CYMHARMO as well.

3.7 Generator, Synchronous

Definition: In PSAF−FLOW, three types of synchronous generators are permitted:

Swing, Voltage-controlled and Fixed. More than one generator and more

than one type of generator may be connected to a bus. (See the note about

Generators in parallel, in the CYMFLOW, CYM-Motor-Start & CYM-AC

Contingency, Users’ Guide and Reference Manual.

Default scheduled active gen. [MW]

is the scheduled active power produced by the generator.

Note: The Active Gen value entered in the database is only a

default. PSAF will assume it whenever you connect a

generator of this type into a network, but you may then define the true Active Gen for each individual generator (See section 3.7.1 Generators in the Network).

Max. MVAR

And

Min. MVAR

define the limits of the generator's reactive capability. Aside from being constraints on a load flow solution, they are used by PSAF to apportion reactive generation among generators connected at the same bus. See Generators in parallel, in the CYMFLOW, CYM- Motor-Start & CYM-AC Contingency, Users’ Guide and Reference Manual.

Q = f(Pgen) is a way to define the max and min VAR limits but, as a function of the active power output.

Impedances are expressed on the machine’s MVA rating, except for the default grounding impedances Rg and Xg, which are expressed in Ohms. (See section 3.7.1 Generators in the Network).

Note: If you will perform IEC type fault calculations enter the

saturated direct-axis reactance Xdsat instead of X of Steady-

state Z in above dialog box. (see Short-Circuit IEC Version in the Short-Circuit (ANSI & IEC), ARC Flash & CYMBREAK, User’s Guide and Reference Manual.

3.7.1 Generators in the Network

When you connect a generator to the network, you must identify which database entry to use, what type it will be, etc. You may make changes afterward, by editing the generator.

Generator Type defines the generator’s behavior in CYMFLOW and CYMFAULT-IEC.

• A Voltage Controlled generator produces the active power (Pgen) specified here and varies its reactive power to maintain the Operating Voltage at the Voltage Control Bus.

• A Fixed generator produces the active and reactive power (Pgen and Qgen) specified here. It does not control the voltage at any

bus.

• A Swing generator produces (or absorbs) excess power not accounted for by other generators. It always controls the voltage

at the bus where it is connected.

Note: There must be at least one Swing generator in every

network (or isolated sub-network) if that network is to be solved by CYMFLOW.

See:

• Chapter on CYMFLOW in the CYMFLOW, CYM-Motor-Start & CYM-AC Contingency, Users’ Guide and Reference Manual. • And Chapter on CYMFAULT-IEC in the Short-Circuit (ANSI &

IEC), ARC Flash & CYMBREAK, User’s Guide and Reference Manual.

Voltage Control

Bus is a bus whose voltage is controlled by this generator.

Hint: Specify the desired Operating Voltage in the Bus Dialog. Initial (voltage)

Angle (optional) Default initial angle is “ 0 ” degree. This Angle is the initial _{angle for all bus in an analysis but it is fixed for Swing generators.}

Note: If two or more swing generators exist in a network, the swing

angles affect load-flow analysis. Even a swing angle would be the reason for analysis failure.

Grounding Z _{defines the Rg and Xg of this particular generator. These values will}

be used only if the winding connection is Yg (star-grounded) in the database (See 3.7 Generator, Synchronous, above).

Model as power

system unit refers to fault analysis based on IEC 60909-0 Standard.

When this option is selected, that means that the generator will be considered as a power system unit as far as there is one step-up transformer connected to its terminal bus and also the option “Apply impedance correction factors to…” Power station units (PSU) located in the “IEC Conformable Parametrs” tab of the “Short Circuit IEC Study Dialog” is checked.

3.8 Generator, Induction (IG)

Definition: An Induction generator is an induction machine that is driven by a prime

mover, which receives its excitation from the grid. Therefore, Induction Generator generates active power to the system and draws reactive power from it.

Voltage is the Generator rated voltage in kilovolts.

Rating [kW] is the active power generation and may be entered as MVA,

Horsepower[HP] or kW. Enter one value and the other two will be calculated, using the power factor and efficiency. (You should enter the power factor and efficiency before the rating.)

Subtransient Impedance

is given in per-unit on the IG’s own base power. (See section 3.12 Motor, Induction). You may estimate it from the NEMA code letter and other (American) nameplate data, if you click on the Estimate button.

Motor Group (ANSI)

group box

Choose and enter Induction Generator group [ANSI] or let PSAF estimate it according to other IG parameters.

Note: The Active Gen entered in the database is only a default

value. PSAF will assume it, whenever you connect a generator of this type into a network, you may then define the

true “Active Gen” for each individual generator (See section

3.7.1 Generators in the Network).

Eq. Circuit tab

To enter parameters of the equivalent circuit, choose the “Eq. Circuit” tab. Select the Rotor type and enter its parameters. If the parameters are not available, you can estimate them by PSAF.

To estimate the Induction generation parameters of equivalent circuit (in the above dialog), select Rotor Type and estimation method based on known values. Click Estimate .

3.8.1 Induction Generator in network

To connect an induction generator to a network, you must identify which database entry to use (Database ID), desired active generation [MW] and negative reactive power [MVAR].

3.9 HVDC Line

Definition: HVDC (High Voltage Direct Current) Line controls the active power flow between two buses. The reactive power absorbed at both ends depend on the voltages available there.

The converter bridges are taken to be in series, fed by one transformer each.

CYMFLOW approximates the commutating reactance of the rectifier and the inverter as

Xc = (# bridges) × (reactance of transformer). The reactance presented by the rest of the AC network is neglected. (The network is assumed to have a high short circuit level.) The commutating reactance, DC current and firing angle determine the overlap angle.

3.9.1 How HVDC Lines operate in CYMFLOWHow

The converter transformer taps are adjusted to maintain roughly the desired AC voltage at the rectifier and inverter buses.

Normally, the inverter controls the DC voltage by adjusting its firing (delay) angle to maintain the minimum extinction angle in the presence of overlap

[α

inv

= π – µ – γ

min

]

. This maintains the highest possible power factor at the inverter. The rectifier controls the DC current

[I

DC

= (V

DCrec

– V

DCinv

)/R]

by maintaining its DC voltage slightly above the inverter DC voltage. The active power delivered at the inverter is

P

DC

= V

DCinv

⋅ I

DC.

If the AC voltage is depressed at the rectifier side, so that the rectifier cannot produce enough DC voltage, even with its firing angle reduced to 0, then the rectifier takes over voltage control and current control passes to the inverter. The rectifier is set to produce the most voltage that it can

(α

rec

= α

min

= 0)

and the inverter lowers its voltage to maintain 85% of the normal IDC. This means that

P

DC

< 85%

of the desired value.

3.9.2 HVDC Lines in the Network

When you connect a DC Line to the network, you must identify which database entry to use, desired MW flow, etc. In Graphic mode, you enter the information through a dialog:

Note: Both terminals of a DC Line must be connected to buses that are connected to and controlled by Voltage Regulating Transformers (TCUL). No other equipment is to be connected to these buses, including capacitors.

Note: Both the rectifier and inverter transformers must be connected to networks that contain voltage sources (generators).

Connect the DC line to AC network by one typical transformer (TcuL Xmer) on each side of the DC line. PSAF consider one such transformer per bridge, in series.

Example (4 bridges): Put one 220-100kv, 250/333 MVA transformer to obtain 400 kV at the

rectifier and 1000/1333 MVA capacity

27

.

1

_

_

×

≅

bridges

of

Number

Voltage

DC

Desired

inverter

or

rectifire

at

Voltage

AC

The dotted lines show that the transformers are controlling the AC voltages at the rectifier and Inverter buses.

The capacitors are optional, they illustrate where capacitors (closest to rectifier and inverter) can be connected (not on the secondary of the transformers).

Note that the DC voltage output at the rectifier is higher than the AC voltage input. Neglecting the voltage drop due to commutation overlap, we estimate:

3.9.2.1 Some practical advice:

It is recommended that before connecting a DC line, you represent it by

constant-power Loads at the rectifier and inverter buses, and run a load flow (see section

4.2 Special Harmonic Line Models supported by HLINPAR). Doing this will help you make consistent choices for transformer data and the firing and extinction angles when you replace the loads with the DC line.

The load at the inverter:

Pinv = − [Desired DC Power (MW)]

Qinv ≈ Pinv ⋅ tan (γmin + µ/2)

where overlap

µ

≤ 30° usually. The load at the rectifier:

Prec = [Desired DC Power (MW)] + R⋅(IDC)2

Qrec ≈ Prec ⋅ tan (α + µ/2)

3.10 Line

Definition: For the purposes of CYMFLOW and FAULT, Lines represent three-phase

transmission lines transposed such that the impedance is equal in all phases. They are modeled by the

π

-circuit, with one-half the shunt susceptance lumped at each end. This model is suitable for lines up to 200 km (125 miles) long. Longer lines can be modeled by connecting several lines in series. Other models are for use in CYMHARMO.

General parameters group box

Level (kV) is the rated voltage for this line, for your information only if you are entering Ohmic impedances. If you are entering impedances in per-

unit, however, then PSAF will multiply them by [kV Level]2 / Base

MVA to convert them to Ohmic values.

Once you connect a line into a network, PSAF will calculate its per-unit impedance according to the base voltage of the buses to which it is

Note: If you enter impedances in per-unit instead of in Ohms, you must make the voltage level [kV] equal to the base voltage of the buses, which the line will be connected.

Type

and

Size

are descriptions used for your own information only. If you use the impedance estimation function, these variables will reflect the data of your conductor.

Rated Freq. [Hz]

identifies nominal frequency of the selected cable.

Type refers to the conductor construction type. For your information only.

Temperature

[°C] refers to the conductor resistance rated temperature. This information, along with the Alpha factor is used when resistance are derated for the purpose of a simulation.

RT2 = RT1 * ( 1 + (T2 – T1)*Alpha ) For more details, see the following manuals :

• Load Flow: CYMFLOW, CYM-Motor-Start & CYM-AC Contingency, Users’ Guide and Reference Manual.

• Short-Circuit: Short-Circuit (ANSI & IEC), ARC Flash & CYMBREAK, User’s Guide and Reference Manual.

Alpha factor that accounts for the resistivity increase with temperature. This value is known if the material type is cooper or aluminum but must be provided for the other type of material. The default is 0.004. This parameter is only needed if you intend to derate the resistance based on the temperature in an analysis simulation.

Standard allows you to specify is this is a North American or European type of cable. For you information only.

Material Refers to the conductor material. For your information only.

Loading limit [A] group box

Loading Limits (A) are optional ampacity limits for the line.

CYMFLOW uses them to indicate overloaded lines in the reports. (Abnormal Conditions Report in the CYMFLOW, CYM-Motor-Start & CYM-AC Contingency, Users’ Guide and Reference Manual.).

Sequence parameters group boxes

Impedances R1, X1, R0, X0 are to be expressed in Ω / unit length (e.g., Ω /km., Ω /mile). Susceptances B1 and B0 are the total (not one-half) shunt susceptances of the line, expressed in µS / unit length.

Hint: PSAF converts the impedance values if you select a different

length unit.

R1’ and R0’ are alternative values (for operation at a different

temperature). You may choose which resistance values to use when you select the parameters for power flow or short-circuit calculations.

Example: Suppose you enter the values of R1 and R0 at 25°C, to represent the night-time or cold-weather situation. You might want to enter R1’ and R0’ at 50°C, to represent the day-time or hot-weather situation. Since the resistivities of both copper and aluminum conductors increase with temperature at about 4% /10°C rise, you could compute

R1’ = R1 x (1 + 0.004dT), where dT is the rise in

temperature in °C. In this example, dT = 25 °C , and R1’ = 1.1⋅R1.

Filter List

command button

The Filer list option is used to keep in the database id list only the elements that correspond to certain specification. You may choose one or more item to filter the cables on. For example, you may only want to keep the 60 Hz 3 core cables between 5 and 15 kV in your main list. Select the filtering and click ok to enable the filter. When the list is filtered, the Is Filtered radio button turns green. To stop filtering the main list, click on that button.

3.10.1 Lines in the Network

When you connect a line to the network, you must identify which kind of line it is, how long it is, etc. You may change this information afterward, by editing the line. In Graphic mode, you enter the information through a dialog:

Length is a multiple of the length unit chosen in the database (See section 3.10 Line, above). This unit (example: km, mile) is displayed for convenience. The impedance of the line is proportional to its length.

Degree of series

compensation

refers to the presence of a series capacitor. (See 3.6 Series Compensation.) The reactance of the capacitor partially cancels out the reactance of the line, allowing greater power transit and less voltage drop across the line. The capacitor itself is not retained as a separate component:

Note: You may define mutual coupling between lines. See section 3.26 Mutual Coupling between Lines or Cables in the Network.

In document PSAF (Page 86-101)