PD 7639-1:1994

Committees responsible
National foreword
Section 1. General
1.1 Scope and object
1.2 Normative references
1.3 Application of the factors
1.4 Symbols, subscripts and superscripts
Section 2. Factors used in IEC 909
2.1 Factor c for the equivalent voltage source at the
     short-circuit location
2.2 Impedance correction factors K(KG, KPSU) when
     calculating the short-circuit impedances of
     generators and power-station units
2.3 Factor kappa for the calculation of the peak short-
     circuit current
2.4 Factor mu for the calculation of the symmetrical
     short-circuit breaking current
2.5 Factor lambda (lambda max, lambda min) for the
     calculation of the steady-state short-circuit
     current
2.6 Factor q for the calculation of the short-circuit
     breaking current of asynchronous motors
2.7 Statement of the contribution of asynchronous
     motors or groups of asynchronous motors (equivalent
     motors) to the initial symmetrical short-circuit
     current
Annex
A (informative) Bibliography
Tables
1 Values of kappa calculated with the methods A, B
     and C for the example in figure 15
2 Data of low-voltage and medium-voltage asynchronous
     motors (50 Hz) and calculated values
3 Data for transformers and motor groups for the
     example in figure 28
4 Calculation of the partial short-circuit currents
     I"kM1, I"kM2 and I"kM3; example: figure 28
5 Application of equation (74) respectively equation
     (71) (IEC 909, equation (66)) to determine whether
     the partial short-circuit currents (sum of I"kMi)
     contribute less than 5 % to I"kQ
Figures
1 Model for the calculation of the coherence between
     the voltage drop delta u and the short-circuit
     current deviation delta i"k
2 Calculation of delta i"k according to equation (11)
     for different parameters
3 Partial short-circuit current I"kG of a generator
     directly connected to a network
4 Calculation of I"kG using the superposition method
5 Partial symmetrical short-circuit current I"kPSU at
     the high voltage side of the unit transformer of a
     power-station unit (PSU)
6 Simulation of a power station unit (PSU)
7 Partial short-circuit currents of a power-station
     unit with tap changer
8 Cumulative-frequency-error curves of the partial
     short-circuit currents calculated with simplified
     equations compared to the values calculated from
     the superposition method according to equation (28)
     with KPSU given in equation (29) for 59 power
     station units
9 Cumulative-frequency-error curves
10 Calculation of the factor kappa in the case of a
     single-fed three-phase short circuit (series R-L-
     circuit)
11 Factor kappa and tp (f = 50 Hz) as a function of
     R/X or X/R
12 Equivalent circuit diagram for the calculation of
     kappa in case of two parallel branches (positive-
     sequence system)
13 Factor kappa for the calculation of
     ip = kappa(sqrt2I"k) for the case of two parallel
     branches as shown in figure 12, with ZI = ZII.
     0,005 < or = R1/X1 < or = 1,0 and 0,005 < or =
     RII/XII < or = 10,0
14 Deviations delta kappa a, delta (1,15 kappa b) and
     delta kappa c from the exact value kappa with
     0,005 < or = ZI/ZII < or = 1,0 for the
     configuration of figure 12
15 Example for the calculation of kappa and ip with
     the methods A, B and C
16 Network configuration (single-fed short circuit)
     and relevant data to demonstrate the decay of the
     symmetrical a.c. component of a near-to-generator
     short-circuit
17 Decay of the symmetrical short-circuit current
     (factor mu) based on test station measurements and
     calculations
18 Characteristic saturation curve method to find the
     Potier reactance Xp in accordance with [3]
19 Equivalent circuit with the source voltage Eo(If)
     and the Potier reactance Xp
20 Factor q from measured and calculated values of
     IbM = mu qI"kM' equation (62), at different values
     t min in comparison to q = qIEC
21 Time functions mu, q, mu q and exp-(1t/TAC) for the
     current Ibm = mu qI"kM in this case of a short
     circuit at the terminals of an asynchronous motor
22 Effective time constants TAC for the determination
     of the symmetrical short-circuit breaking current
     IbM and in comparison T mu q = -t min/ln(mu q)IEC.
     (number of motors see table 2)
23 Time function IbM/I"kM in the case of a balanced
     short circuit (Ib3M/I"kM) and a line-to-line short-
     circuit (Ib2M/I"kM) at the terminals of an
     asynchronous motor
24 Contribution of one asynchronous motor or a group
     of asynchronous motors to the initial symmetrical
     short-circuit current I"k = I"kQ + I"kM
25 Example for the estimation of the partial short-
     circuit current I"kM supplied by a single
     asynchronous motor or an equivalent motor
26 Partial short-circuit currents from several groups
     of asynchronous motors fed through several
     transformers
27 Investigation of the left and right side of
     equation (73) to determine the deviation delta
     according to equation (75): ukr = 6 %, ILR/IrM = 5
     for both the transformers and motor groups
28 Example for the contribution of motor groups to the
     short-circuit current - Application of equation
     (70)
29 Partial short-circuit currents of the asynchronous
     motor groups of figure 28 in relation to the
     current I"kQ depending on S"kQ = sqrt(3UnQ.I"kQ)

Shows the origin and the application as far as necessary of the factors used to meet the demands of technical precision and simplicity when calculating short circuit currents. Also gives detailed tables and diagrams.