List of the conditional indication and reduction

HV --- high voltage

LV --- low voltage

SC --- short circuit

NL --- no load

P_SC --- loss in short circuit

S_R --- rated power

V_turn --- voltage per turn

V_1ph --- phase voltage of the low primary coils

V_2ph --- phase voltage of the secondary coils

I_1ph --- phase current of low voltage

I_2ph --- phase current of high voltage

W₁ --- low voltage number of turns

W₂ --- high voltage number of turns

B_leg --- inductive in the leg

m --- number per phase

c --- number of rods

d --- diameter of rod

S --- cross section of windings

A --- minimal length of transformer

H --- height of windings of transformer

S_steel ---... active cross sectional steel

L --- approximate height of coil

D’ --- inside diameter of windings

D’’ --- outside diameter of windings

Θ₁ ---… approximate density of heat flow of the low voltage

Θ₂ ---… approximate density of heat flow of the high voltage

Introduction

In a national economy the transformers of a different range with power from several VА up to one million kVA and more are used. The transformers of low power are used in devices of a radio engineering, automatics, signal system, communication and also in household appliances. The power transformers are applied in electrical networks. In the power transformer the electrical energy of one voltage will be transformed to electrical energy of other voltage at the expense of the phenomenon of an electromagnetic induction.

The power transformer is one of the most important elements of electrical networks. On the purpose the power transformers used in electrical networks are divided on step-up and step-down.

The necessity of distribution of the electric power between many consumers with various capacities of loadings results in increase of quantity of transformers in a network in comparison with quantity of generators. Therefore for electrical networks the transformers with large efficiency and small losses of idling and load losses are required. The decrease of losses of idling is achieved at the expense of application of cold-rolled roll electro technical steel with the improved magnetic properties. The decrease of losses of short circuit is achieved at the expense of downturn of density of a current and increase of weight of metal in windings. The device of regulation of voltage is used in the transformers for maintenance of economic work of electrical networks and quality of the electric power at the consumers.

1 The calculation of baSic electrical quantities

Initial data

=160 kVA V_1R = 0.4 kV V_1test =5 kV

V_2R = 6 kV V_2test =25 kV

P_Oc=0.54 kW P_SCc =2.65 kW V_SCc =4.5 %

I_Oc=2.4 %

1.1 The power of one winding on one rod:

S_ph = = 53.333 кVА, S^´ = = 53.333 кVА,

where m = 3 – the phase number;

С = 3 – the rod number in the transformer.

1.2 The phase voltage of low-voltage and high-voltage windings are determined with accordance with scheme of connection of windings:

V_ph1 = = =0.231 kV V_ph2 = = = 3.464 кV.

1.3 The phase currents of low voltage and high voltage windings:

I_ph1 = = 230.94 А;

I_ph2 = = 15.396 А.

1.4 The primary values of active and reactive components of short circuit voltage:

V_SCa = = 1.656 %;

V_SCr = = 4.184 %,

where P_sc – the losses of short-circuit, kW;

– the total power of transformer, kVА.