Power losses in network elements.

Calculation of power losses in power lines.

Calculation of power losses in power transmission lines with a uniformly distributed load.

Calculation of power losses in transformers.

The given and calculated loads of consumers.

Calculation of electricity losses.

Measures to reduce power losses.

Power losses in network elements

For a quantitative characteristic of the operation of the elements of the electrical network, its operating modes are considered. Work mode- this is a steady electrical state, which is characterized by the values ​​of currents, voltages, active, reactive and apparent powers.

The main purpose of calculating modes is to determine these parameters, both to check the admissibility of modes, and to ensure the efficiency of the operation of network elements.

Determining the values ​​of currents in the elements of the network and voltages in its nodes begins with building a picture of the distribution of the total power over the element, i.e. with the definition of capacities at the beginning and end of each element. This pattern is called flow distribution.

When calculating the power at the beginning and at the end of an electrical network element, the power losses in the element resistances and the influence of its conductivities are taken into account.

Calculation of power losses in power lines

Active power losses in the PTL section (see Fig. 7.1) are due to the active resistance of wires and cables, as well as the imperfection of their insulation. The power lost in the active resistances of a three-phase power transmission line and spent on its heating is determined by the formula:

Where
full, active and reactive currents in power transmission lines;

P, Q, S- active, reactive and apparent power at the beginning or end of the power transmission line;

U

R- active resistance of one phase of the power transmission line.

Losses of active power in the conductance of the power transmission line are due to the imperfection of the insulation. In air transmission lines - the appearance of a corona and, to a very small extent, current leakage through insulators. In cable transmission lines - the appearance of conduction current and its absorption. Losses are calculated according to the formula:

,

Where U- linear voltage at the beginning or end of the power transmission line;

G– active conductivity of the LEP.

When designing overhead power transmission lines, the power losses to the corona tend to be reduced to zero by choosing such a wire diameter when the possibility of a corona is practically absent.

Reactive power losses in the PTL section are due to inductive resistances of wires and cables. The reactive power lost in a three-phase transmission line is calculated similarly to the power lost in active resistances:

The charging power of the power transmission line generated by capacitive conduction is calculated by the formula:

,

Where U- linear voltage at the beginning or end of the power transmission line;

B- reactive conductivity of the LEP.

Charging power reduces the reactive load of the network and thereby reduces power losses in it.

Calculation of power losses in a lep with a uniformly distributed load

In the lines of local networks (
) consumers of the same power can be located at the same distance from each other (for example, light sources). Such transmission lines are called lines with a uniformly distributed load (see Fig. 7.2).

In a uniformly loaded three-phase alternating current line with a length L with total current load I current density per unit length will be I/L. With linear active resistance r 0 active power losses will be:

If the load were concentrated at the end, then the power loss would be defined as:

.

Comparing the given expressions, we see that the power losses in the line with a uniformly distributed load are 3 times less.