Cable

Definition: Cables are three-phase circuits, either 1 x 3 conductor or 3 x 1 conductor.

They are modeled by the

π

General Parameters group box

Level (kV) is the rated voltage for this cable, 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 cable into a network, PSAF will calculate its per- unit impedance according to the base voltage of the buses to which it

is connected.

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

Rated Freq. [Hz)

identifies nominal frequency of the selected cable.

Duct Material identifies the type of duct the cable is installed in. For your information only.

Construction 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 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 Limits group box Loading Limits

(A)

Are optional ampacity limits for the cable. CYMFLOW uses them to indicate the overloaded cables in the Abnormal Conditions Report. See the CYMFLOW, CYM-Motor-Start & CYM-AC Contingency, Users’ Guide and Reference Manual.

Ohms / xyz Xxx is the length reference unit in which the impedance is set to. For example, the impedances could be in ohms / kM, in ohms / mile, etc. It is possible to specify a type of unit called “Unit length” which is basically a general purpose length type.

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 cable, expressed in µS / unit length.

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

length unit.

R1’ and R0’ (not used anymore) are alternative values (for operation

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

To calculate R1, X1, B1, R0, X0 and B0 by PSAF, click Compute. According to cable type, choose one of the Cable Impedance Calculation Dialog.

For more information about how to calculate cable parameters and more explanation about this option, refer to section 4.4 Cable Parameters Calculations.

Filter List

command button The Filter 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.

3.5.1 Cables in the Network

When you connect a cable to the network, you must identify which kind of cable it is, how long it is, etc. You may change this information afterward, by editing the cable.

In Graphic mode, you enter the information through a dialog box:

Cable Data group box

Length is a multiple of the length unit chosen in the database. See above section 3.5 Cable.

Override database ampacity values

gives the possibility to modify the default ampacity values specified in the database for that particular cable. This is useful if more than one cable is modeled in one on the one-line diagram and that the combined ampacity is not simply the ampacity of one multiplied by the number of cable represented.

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

3.6 Series Compensation

Definition: Capacitors connected in series on a transmission line in order to reduce

(compensate) the reactance of the line. This enables the line to transmit more power.

PSAF models series capacitors as compensating a percent of the reactance of a

transmission line (See section 3.10 Line). This representation is correct for all PSAF modules.

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.