GOST short circuit currents 1 sq. Online calculator for calculating short circuit currents

INTERSTATE STANDARD

SHORT CIRCUIT IN ELECTRICAL INSTALLATIONS

Calculation methods in AC electrical installations with voltage up to 1 kV

Short-circuits in electrical installations.

Calculation methods in a. With. electrical installations with voltage below 1 kV

MKS 29.020 OKP 34 0900

Date of introduction 01/01/95

Preface

1 DEVELOPED by Gosstandart of Russia

INTRODUCED by the Technical Secretariat of the Interstate Council for Standardization, Metrology and Certification

2 ADOPTED by the Interstate Council for Standardization, Metrology and Certification on October 21, 1993.

This standard applies to three-phase electrical installations with voltage up to 1 kV of industrial frequency, connected to the power system or to autonomous sources of electricity, establishes a general methodology for calculating symmetrical and asymmetrical short circuit (SC) currents at an initial and arbitrary point in time, taking into account the parameters of synchronous and asynchronous machines, transformers , reactors, cable and overhead lines, busbars and complex load units.

The standard does not establish a method for calculating currents:

In case of complex asymmetries in electrical installations (for example, simultaneous short circuit and phase conductor breakage), in case of repeated short circuits and in case of short circuit in electrical installations with nonlinear elements;

- during electromechanical transient processes taking into account changes in the rotation speed of electrical machines;

- during short circuit inside electrical machines and transformers.

Clauses 1.5, 1.7, 2.4.2, 2.11, 2.12, 3.6 and appendices are recommended, the remaining clauses are mandatory.

1. GENERAL PROVISIONS

1.1. This standard establishes a general methodology for calculating currents in alternating current electrical installations with voltages up to 1 kV, necessary for selecting and testing electrical equipment under short-circuit conditions, for selecting switching devices, relay protection settings and grounding devices.

1.2. The standard establishes a methodology for calculating the maximum and minimum current values ​​for symmetrical and asymmetrical short circuits, the types of which are determined in accordance with GOST 26522.

1.3. The quantities to be calculated and the permissible error in their calculation depend on the purposes specified in paragraph 1.1.

Simplified methods for calculating short-circuit currents are allowed if their error does not exceed 10

The following are subject to calculations for selecting and checking electrical equipment under short-circuit conditions: 1) the initial value of the periodic component of the short-circuit current; 2) aperiodic component of the short-circuit current; 3) short-circuit shock current;

4) the effective value of the periodic component of the short-circuit current at an arbitrary point in time, up to the estimated time of opening of the damaged circuit.

For other purposes specified in clause 1.1, the maximum and minimum values ​​of the periodic component of the current at the fault location at the initial and arbitrary point in time, up to the estimated time of opening of the damaged circuit, are subject to calculation. For the purpose of selecting grounding devices, the value of the single-phase short-circuit current is subject to calculation.

1.4. When calculating short-circuit currents in electrical installations up to 1 kV, it is necessary to take into account:

1) inductive reactances of all elements of the short-circuited circuit, including power transformers, conductors, current transformers, reactors, current coils of circuit breakers;

2) active resistances of short-circuited circuit elements;

3) active resistances of various contacts and contact connections;

4) values ​​of parameters of synchronous and asynchronous electric motors.

1) resistance of the electric arc at the location of the short circuit;

2) change in the active resistance of the short-circuited circuit conductors due to their heating during a short circuit;

3) the influence of a complex load (electric motors, converters, thermal units, incandescent lamps) on the short-circuit current, if the rated current of the load electric motors exceeds 1.0% of the initial value of the periodic component of the short-circuit current, calculated without taking into account the load.

1.6. When calculating short-circuit currents, the following is allowed:

1) simplify as much as possible and equivalent all external network in relation to the short circuit location

And individually take into account only autonomous sources of electricity and electric motors directly adjacent to the short circuit;

2) do not take into account the magnetizing current of transformers;

3) do not take into account the saturation of magnetic systems of electric machines;

4) take the transformation ratios of transformers equal to the ratio of the average rated voltages of those voltage levels of the networks that connect the transformers. In this case, the following scale of average rated voltages should be used: 37; 24; 20; 15.75; 13.8; 10.5; 6.3; 3.15; 0.69; 0.525; 0.4; 0.23 kV;

5) do not take into account the influence of asynchronous electric motors if their total rated current does not exceed 1.0% of the initial value of the periodic component of the current at the fault location, calculated without taking into account electric motors.

1.7. It is recommended to calculate short-circuit currents in electrical installations with voltages up to 1 kV in named units.

When drawing up equivalent equivalent circuits, the parameters of the elements of the original design circuit should be reduced to the network voltage level at which the short-circuit point is located, and the active and inductive resistances of all elements of the equivalent circuit should be expressed in millioms.

1.8. When calculating short-circuit currents in electrical installations receiving power directly from the power system network, it can be assumed that the step-down transformers are connected to a source of constant voltage amplitude through the equivalent inductive reactance of the system. The value of this resistance (x c) in millioms, reduced to the lowest voltage stage of the network, is calculated by the formula

where U avg.LV is the average rated voltage of the network connected to the low voltage winding of the transformer, V;

U avg.VN - average rated voltage of the network to which the high-voltage winding of the transformer is connected, V;

I k.HV = I along HV - effective value of the periodic component of the current in three-phase

Short circuit at the terminals of the high voltage winding of the transformer, kA;

S k - conditional short circuit power at the terminals of the high voltage winding of the transformer, MV A.

In the absence of the specified data, the equivalent inductive reactance of the system in millioms can be calculated using the formula

where I off.nom is the rated breaking current of the circuit breaker installed on the side

higher voltage step-down transformer circuit.

Note - In cases where the step-down transformer is connected to the power system network through a reactor, overhead or cable line (more than 1 km long), it is necessary to take into account not only the inductive, but also the active resistance of these elements.

1.9. When calculating short-circuit currents in electrical installations with autonomous power sources, it is necessary to take into account the parameter values ​​of all elements of the autonomous electrical system, including autonomous sources (synchronous generators), distribution network and consumers.

2. CALCULATION OF RESISTANCE OF VARIOUS ELEMENTS OF ELECTRICAL INSTALLATION

2.1. Active and inductive resistance of power transformers

2.1.1. The active and inductive resistance of the positive sequence of step-down transformers (r t, x t) in millioms, reduced to the lowest voltage stage of the network, is calculated using the formulas:

where S t.nom - rated power of the transformer, kVA; R t.nom - short circuit losses in the transformer, kW;

U NN.nom - rated voltage of the low voltage winding of the transformer, kV;

and k - short circuit voltage of the transformer, %.

2.1.2. Active and inductive zero-sequence resistances of step-down transformers, the windings of which are connected according to the circuit ∆ /Y 0, when calculating a short circuit in a low voltage network, should be taken equal to active and inductive, respectively

positive sequence resistances. For other connection schemes of transformer windings, active and inductive zero-sequence resistances must be taken in accordance with the manufacturers' instructions.

2.2. Active and inductive reactance of reactors

2.2.1. The active resistance of current-limiting reactors (r 1p = r 2p = r 0p) in millioms is calculated using the formula

where ∆ Р r.nom - active power losses in the reactor phase at rated current, W; I r.nom - rated current of the reactor, A.

2.2.2. The inductive reactance of the reactors (x 1p = x 2p = x 0p) in millioms is taken as specified by the manufacturer or calculated using the formula

where ω is the angular frequency of the network voltage, rad/s;

L is the inductance of the three-phase reactor coil, H; M is the mutual inductance between the phases of the reactor, H.

2.3. Active and inductive resistance of busbars

When determining the active and inductive resistance of the direct and zero sequences of busbars, you should use data from the manufacturer, experiment, or use a calculation method. The recommended method for calculating the resistance of busbars and the parameters of some complete busbars are given in Appendix 1.

2.4. Active and inductive resistance of cables

2.4.1. The values ​​of the positive (reverse) and zero sequence parameters of cables used in electrical installations up to 1 kV are taken as specified by the manufacturer or in Appendix 2.

2.4.2. When determining the minimum value of the short-circuit current, it is recommended to take into account the increase in the active resistance of the cable at the time of disconnection of the circuit due to heating of the cable by the short-circuit current. The value of the active resistance of the cable in millioms, taking into account its heating

short-circuit current (r ϑ) is calculated using the formula

where c ϑ is a coefficient that takes into account the increase in the active resistance of the cable. For approximate calculations, the value of the coefficient c ϑ can be taken equal to 1.5. At

In refined calculations, the coefficient c ϑ should be determined in accordance with Fig. 5-8

Appendix 2 depending on the material and cross-section of the cable cores, short-circuit current and short-circuit duration;

r ϑ 0 - active resistance of the cable at temperature ϑ 0, equal to plus 20 ° C, mOhm.

2.5. Active and inductive resistance of overhead lines and wires

The methodology for calculating the parameters of overhead lines and wires is given in Appendix 3.

2.6. Active resistance of contacts and contact connections

The transition resistance of electrical contacts of any type should be determined based on experimental data or using calculation methods. Data on contact connections are given in Appendix 4. When approximately taking into account contact resistances, the following is accepted: r k = 0.1 mOhm - for contact connections of cables; r k = 0.01 mOhm - for busbars; r k = 1.0 mOhm - for switching devices.

2.7. Active and inductive resistances of current transformers

When calculating short-circuit currents in electrical installations with voltages up to 1 kV, one should take into account both the inductive and active resistance of the primary windings of all multi-turn instrument current transformers that are present in the short-circuit circuit. The values ​​of active and inductive zero-sequence resistances are taken equal to the values

positive sequence resistances. The parameters of some multi-turn current transformers are given in Appendix 5. The active and inductive resistance of single-turn transformers (for currents more than 500 A) can be neglected when calculating short-circuit currents.

2.8. Active and inductive resistance of circuit breaker coils

Calculations of short-circuit currents in electrical installations with voltages up to 1 kV should be carried out taking into account the inductive and active resistances of the maximum current coils (releases) of circuit breakers, taking the values ​​of active and inductive zero-sequence resistances equal to the corresponding positive-sequence resistances. The resistance values ​​of the release coils and contacts of some circuit breakers are given in Appendix 6.

2.9. Parameters of autonomous power sources and synchronous electric motors

When calculating the initial value of the periodic component of the short-circuit current, autonomous sources, as well as synchronous electric motors, should be taken into account as subtransient

resistance along the longitudinal axis of the rotor (x d ′′), and when determining the decay time constant of the aperiodic component of the short-circuit current - inductive resistance for currents

2.10. Parameters of asynchronous electric motors

When calculating the initial value of the periodic component of the short-circuit current from asynchronous electric motors, the latter should be introduced into the equivalent circuit with a subtransient inductive reactance. If it is necessary to carry out refined calculations, the active resistance of the stator should also be taken into account. It is recommended to determine their values ​​as indicated in Appendix 7. For approximate calculations, the following is taken: supertransient

2.11. Design parameters of complex loads

2.11.1. When calculating short-circuit currents from complex loads, their parameters of direct, negative and zero sequences should be taken into account. The recommended resistance values ​​of the direct (Z 1 ) and reverse (Z 2 ) sequences of individual elements of the complex load are given in Table. 1. The values ​​of the impedance modules of the direct (Z 1НГ), reverse (Z 2НГ) and zero (Z 0НГ) sequences of some load nodes, depending on their composition, can be determined as indicated in Appendix 8.

2.11.2. In approximate calculations for nodes containing up to 70% asynchronous motors, it is allowed to accept the values ​​of the complex load impedance modules

2.12. Active arc resistance at the short circuit location

When determining the minimum value of the short-circuit current, one should take into account the influence on the short-circuit current of the active resistance of the electric arc at the fault location.

Approximate values ​​of active arc resistance are given in table. 2.

For other design short-circuit conditions, the values ​​of active arc resistance can be calculated according to Appendix 9.

3. CALCULATION OF THE INITIAL VALUE OF THE PERIODIC COMPONENT OF THREE-PHASE SCHOOL CURRENT

3.1. The method for calculating the initial effective value of the periodic component of the short-circuit current in electrical installations up to 1 kV depends on the method of power supply - from the power system or from an autonomous source.

3.2. When powering an electrical installation from the power system through a step-down transformer, the initial effective value of the periodic component of the three-phase short-circuit current ( I in ) in kiloamperes without taking into account recharge from electric motors is calculated using the formula

closure, B;

r 1 ∑, x 1 ∑ - respectively, the total active and total inductive reactance

direct sequence short-circuit circuit, mOhm. These resistances are equal:

r 1∑ = r t + r r + r TA + r kv + r w + r k + r 1kb + r vl + r d and x 1∑ = x c + x t + x r + x TA + x kv + x w + x 1kb + x vl,

where r t and x t are the active and inductive positive sequence resistance of the step-down transformer, mOhm;

r TA and x TA - active and inductive resistance of the primary windings of current transformers, mOhm;

x c is the equivalent inductive reactance of the system up to the step-down transformer, mOhm, reduced to the lowest voltage stage;

r r - active and inductive reactance of reactors, mOhm;

r kV and x kV - active and inductive resistance of current coils of automatic circuit breakers, mOhm;

r w and x w - active and inductive resistance of busbars, mOhm; r k - total active resistance of various contacts, mOhm;

r 1kb, r vl and x 1kb, x vl - active and inductive resistance of direct sequence of cable and overhead lines, mOhm;

r d - active arc resistance at the short-circuit location, mOhm, taken according to the data in Table 2 or calculated as indicated in Appendix 9, depending on the short-circuit conditions.

3.3. If the power supply of the electrical installation is carried out from the power system through a step-down transformer and there are synchronous and asynchronous electric motors or a complex load near the fault location, then the initial effective value of the periodic component of the short-circuit current, taking into account the recharge from the electric motors or the complex load, should be determined as the sum of the currents from the power system (see paragraph. 3.2) and from electric motors or complex loads.

Initial effective value of the periodic component of short-circuit current from synchronous

electric motor, mOhm; the values ​​of these resistances can be determined as indicated in clause 2.9;

x 1 ∑ and r 1 ∑ - total inductive and total active resistance of the direct line

sequence of the circuit connected between the electric motor and the short-circuit point, mOhm.

For synchronous electric motors that operated with overexcitation before the short circuit, the supertransient EMF (E f "" .SD) in volts is calculated using the formula

where U f 0 is the phase voltage at the motor terminals at the moment preceding the short circuit,

I 0 - stator current at the moment preceding the short circuit, A;

ϕ 0 - phase shift angle of voltage and current at the moment preceding the short circuit, degrees. el.;

x d "" - supertransient resistance along the longitudinal axis of a synchronous electric motor,

For synchronous electric motors operating before the short circuit with underexcitation,

The initial effective value of the periodic component of the short-circuit current from asynchronous electric motors (I in kiloamperes) is calculated by the formula

where x AD "" and r AD are, respectively, subtransient inductive and active resistance

electric motor, mOhm; the values ​​of these resistances can be determined as indicated in clause 2.10;

E f "" .AD - supertransient EMF of an asynchronous electric motor, which can be calculated using the formula

If it is necessary to take into account the complex load, the corresponding initial effective

the value of the periodic component of the short-circuit current should be calculated as indicated in Appendix 10.

3.4. In electrical installations with autonomous sources of electricity, the initial effective value of the periodic component of the short-circuit current without taking into account the recharge from electric motors (I) in kiloamperes is calculated by the formula

where r 1 ∑ and x 1 ∑ are the total active and total inductive, respectively

short-circuit circuit resistance, mOhm. These resistances are equal:

r 1∑ = r TA + r kv + r r + r w + r k + r 1kb + r vl; x 1∑ = x d "" + x TA + x kv + x r + x w + x 1kb + x vl,

where E f "" - equivalent subtransition EMF (phase value), V; the value of this EMF should be calculated in the same way as for synchronous electric motors (see paragraph 3.3).

3.5. If it is necessary to take into account synchronous and asynchronous electric motors or a complex load in an autonomous electrical system, the initial effective value of the periodic component of the short-circuit current should be determined as the sum of currents from autonomous sources (see 3.4) and from electric motors or complex load (see 3.3).

3.6. If it is necessary to take into account the influence of the active resistance of the electric arc on the short-circuit current, it is recommended to use the instructions in Appendix 9 (clause 4).

4. CALCULATION OF THE APERIODIC COMPONENT OF SCHOOL CURRENT

4.1. The largest initial value of the aperiodic component of the short-circuit current ( i a0 ) in the general case is considered equal to the amplitude of the periodic component of the current at the initial moment of the short circuit

where t is time, s;

T a - decay time constant of the aperiodic component of the short-circuit current s, equal to

where x ∑ and r ∑ are the resulting inductive and active resistance of the short-circuit circuit, mOhm; ω s - synchronous angular frequency of the network voltage, rad/s.

When determining x ∑ and r ∑ synchronous generators, synchronous and asynchronous

electric motors must be included in the equivalent circuit in accordance with the requirements of 2.9

The complex load must be introduced into the equivalent circuit in accordance with the requirements of section 2.

4.3. If the short-circuit point divides the design circuit into radial branches independent of each other, then the aperiodic component of the short-circuit current at an arbitrary point in time should be determined as the sum of the aperiodic components of the currents of individual branches according to the formula

i= 1

where K beat = (1 + sin ϕ k e − t beat / T a ) is the shock coefficient, which can be determined by

curves (Figure 1); T a is the decay time constant of the aperiodic component of the short-circuit current (see 4.2);

ϕ k is the phase shift angle of the voltage or emf of the source and the periodic component of the short-circuit current, which is calculated by the formula

ϕ к = arctan x 1 ∑ / r 1 ∑ ;

t beat - time from the beginning of the short circuit to the appearance of the shock current, s, equal to

t = 0.01π / 2 + ϕ k.

beat π

Curves of the dependence of the shock coefficient K beat on the ratios r / x and x / r

x - inductive resistance of the short-circuit circuit, r - active resistance of the short-circuit circuit

Picture 1

5.2. When calculating the short-circuit shock current at the terminals of autonomous sources, as well as synchronous

And for asynchronous electric motors, it can be assumed that:

the shock current occurs 0.01 s after the start of the short circuit;

the amplitude of the periodic component of the short-circuit current at time t = 0.01 s is equal to the amplitude of this component at the initial moment of the short-circuit.

5.3. The shock current from an asynchronous electric motor (i beat.BP) in kiloamperes is calculated taking into account the attenuation of the amplitude of the periodic component of the short-circuit current according to the formula

where T r is the calculated decay time constant of the periodic component of the stator current,

T a is the decay time constant of the aperiodic component of the stator current, s. In this case, T r and T a can be calculated using the formulas

T = x AD"" + x 1kb; p D

ω with r 2

where ω c - synchronous angular frequency, rad/s;

r 1 and r 2 are, respectively, the active resistance of the stator and the active resistance of the rotor, reduced to the stator, which can be calculated as indicated in Appendix 7.

5.4. If the short-circuit point divides the design circuit into radial branches independent of each other, then the short-circuit shock current (i yd) is determined as the sum of the shock currents of the individual branches according to the formula

i= 1

where m is the number of independent branches of the circuit;

T on i - initial effective value of the periodic component of the short-circuit current in the i-th branch, kA;

t beat i - time of appearance of the shock current in the i-th branch, s;

T a i is the decay time constant of the aperiodic component of the short-circuit current in the i-th branch, s.

6. CALCULATION OF THE PERIODIC COMPONENT OF SCHOOL CURRENT FROM AUTONOMOUS SOURCES OF ELECTRIC POWER AT AN ARBITRARY POINT OF TIME

6.1. In complex autonomous systems, the calculation of the periodic component of the short-circuit current from power sources (synchronous generators) at an arbitrary point in time should be performed by solving the corresponding system of differential equations of transient processes using a computer.

Change in the periodic component of the short-circuit current from a synchronous machine

Figure 2

6.2. In approximate calculations, to determine the effective value of the periodic component of the short-circuit current at an arbitrary moment in time from autonomous sources in a radial circuit, the curves shown in Figure 2 are used. The calculated curves characterize the change in this component over time at different distances of the short-circuit point. The values ​​of the periodic component of the short-circuit current at an arbitrary moment in time are related to the initial value of this component, i.e.

the effective value of the periodic component of the current of this machine at the initial moment of the short circuit to its rated current, i.e.

M
.2004. - 192 c., ill.

Based on experimental and computational-analytical studies, the effect on the short-circuit current of an electric arc, an increase in the active resistance of conductors when they are heated, synchronous and asynchronous electric motors, complex loads and generators of autonomous power supply systems with voltages up to 1 kV is shown. The issues of equivalence and mathematical modeling of elements and power supply systems during short circuit are presented.
Methods have been developed for calculating short-circuit currents in electrical installations powered by step-down transformers and autonomous generators for both symmetrical and asymmetrical short-circuits for initial and arbitrary moments of time.
For energy specialists, graduate students and university students of electrical power specialties.

Increase in active resistance of conductors during a short circuit
The influence of various factors on the heating of conductors by short-circuit current
Assessment of temperature changes and active resistance of cables based on field experiments
Development of a mathematical model of the thermal decay of short-circuit current
Study of thermal resistance and non-flammability of cable lines
Arc short circuit modes
Experimental studies of arc short circuits in the auxiliary system of 0.4 kV power plants
Development of a mathematical model of arc fault
Study of the influence of an electric arc on short-circuit current
Study of thermal current decay during arc fault

Equivalence of load nodes
Influence of complex load on short-circuit current
Short circuits in autonomous power supply systems
Mathematical model of an autonomous power supply system
Short circuits in the power supply system of electrical machine units
Short circuits in an autonomous power system
Equivalent parameters and short-circuit current curves of synchronous generators of autonomous power supply systems 230/400 V
Development of methods for calculating short-circuit current
Short circuit design conditions
Development of electric arc accounting methods
Analysis of factors affecting the accuracy of short-circuit current calculation
Comparative analysis of methods for calculating short-circuit currents in AC electrical installations with voltages up to 1 kV
Calculation of short circuit currents in AC electrical installations with voltage up to 1 kV
Assumptions made
Calculation of the initial value of the periodic component of the three-phase short circuit current
Methods for calculating asymmetrical short circuits
Drawing up equivalent circuits
Calculation of the aperiodic component of short circuit current
Calculation of short circuit surge current
Calculation of the periodic component of the short-circuit current for an arbitrary
point in time
Taking synchronous and asynchronous electric motors into account when calculating
short circuit currents
Taking into account complex load when calculating currents
short circuit
Accounting for electric arc resistance
Taking into account changes in the active resistance of conductors
in case of short circuit
Examples of short circuit current calculations
Application
Bibliography

Download file

• 10.32 MB
• added 03/31/2010

Basic information about transient processes in electrical systems. Design conditions of short circuit. Equivalent circuits and their transformations. Examples of short-circuit current calculations. Symmetrical short circuits in electrical networks connected to powerful sinusoidal voltage sources. Steady-state three-phase short circuit. Initial...

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• added 02/13/2010

MPEI, 2005 , 160 pp., ill.
For electric power specialists, graduate students and students of electrical power specialties of higher educational institutions.
Methods for calculating and experimentally determining short-circuit currents in DC electrical installations are presented. The purpose of electrical installations, consumers...

Nebrat I.L. Calculations of short circuit currents in 0.4 kV networks

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• added 06/29/2009

Nebrat I. L. Calculations of short circuit currents in 0.4 kV networks: Tutorial. Publication of the St. Petersburg Energy Institute for Advanced Studies executives and specialists. Ministry of Energy of the Russian Federation. 2001.
Methods and examples of calculating short-circuit currents in networks with voltages up to 1 kV are considered. The necessary...

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• added 02/04/2012

Tutorial. Publication of the St. Petersburg Energy Institute for Advanced Training of Managers and Specialists. Ministry of Energy of the Russian Federation, 2001.
Methods and examples of calculating short-circuit currents in networks with voltages up to 1 kV are considered. The necessary reference data is provided.
This manual is the third part...

• doc,ppt
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• added 10/13/2009

Issues considered -
Introduction
Short circuits in three-phase circuits
Three-phase short circuit in the simplest electrical
Short circuit in the synchronous generator circuit
Basics of calculating short circuit currents
Methods for calculating short circuit currents
UNIVERSITY - NIZHNY NOVGOROD HIGHER MILITARY ENGINEERING...

It can't be done without calculations. One of them is the calculation of short circuit currents. In the article we will consider an example of calculation in 0.4 kV networks. You can download a file with an example calculation in Word towards the end of the article, and you can also perform the calculation yourself without leaving the site (there is an online calculator at the end of the article).

Initial data: The main switchboard of the building is powered from transformer substation with two transformers of 630 kVA.
Where:
E C – network EMF;
R t, X t, Z t – active, reactive and impedance of the transformer;
R к, X к, Z к – active, reactive and impedance of the cable;
Z c – resistance of the phase-zero loop for the cable;
Z w – busbar connection resistance;
K1 – short circuit point on the main switchboard buses.

Transformer parameters:
Rated power of the transformer S n = 630 kVA,
Transformer short circuit voltage U k% = 5.5%,
Transformer short circuit losses P k = 7.6 kW.

Supply line parameters:
Type, number (N k) and cross-section (S) of cables AVVGng 2x (4×185),
Line length L = 208 m

X t = 13.628 mOhm

Power system resistance:
X c = 1.00 mOhm

Total reactance of the section:
X Σ =X c +X t +X k =20.448 mOhm

Total active resistance of the section:
R Σ =R t +R k =23.864 mOhm

Total total resistance:

R Σ =31.426 mOhm

i У =10.39 kA (Icu)

In order not to count manually each time on a calculator and transfer the numbers into Microsoft Word, I implemented these calculations directly in Word. Now you just need to answer the questions he asks. This is what it looks like:

The entire calculation took less than a minute.

To download an example of calculating TKZ in Word, click on the button:

Online calculator for calculating short circuit currents

For those who need to quickly calculate short-circuit currents, I made a calculator directly on the site. Now you can calculate short-circuit currents online. Click switches, move sliders, select values ​​from the list - everything will be automatically recalculated instantly.

The resistivity of copper and aluminum in the online calculator is taken in accordance with the recommendations of GOST R 50571.5.52-2011, Part 5-52 (1.25 resistivity at 20°C):

• resistivity of copper - 0.0225 Ohm mm/m
• The resistivity of aluminum is 0.036 Ohm mm/m.

If the capabilities of the calculator are not enough for you (you need several sections of cables of different sections, you have different transformers, or simply the calculation must be done in Word), then feel free to click the button and order.

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