Three-phase circuits - reading & definitions

📚Read the text below and do the task below.

Basic Information about

Three-phase Circuits

Almost all power systems are based on three-phase circuits. In the energy

sector, three-phase generators, transformers, and transmission lines are

commonly used.

A polyphase system

is a set of electrical circuits in which

sinusoidal source voltages of the same frequency operate, shifted in phase

relative to each other and usually generated in a single power source called a

If the phases of a polyphase system are not galvanically connected, the

system is called

The voltages generated in a polyphase system form a symmetrical system

when all phases have equal effective (or maximum) values and are shifted

relative to each other by the same angle.

     This system is called a positive-sequence symmetrical system

because, assuming a counter clockwise direction of rotation, the phase sequence

is

 Symmetrical System:

• The effective value and angular frequency of the

  source voltage in each phase are the same.

• The load impedance in each phase is the same.

• There is a phase shift of ± (2π/m) (120º) between

  the phases.

An asymmetrical system

occurs when any of these conditions are not

met.

Types of Three-phase Systems

Three-phase systems are most commonly connected in a star (Y) or

delta

(Δ) configuration

The following notations are used:

• I_A, …

  – Line

  currents

• I_AB, …

  –

  Phase currents

• U_A, … E_A

  –

  Phase voltages

• U_AB, …

  –

  Line-to-line voltages

• I_N

  – Current in the neutral

  or zero conductor

based on the lecture: 'Three-phase Circuits' by dr hab. inż. Andrzej Waindok, prof. PO

adapted by mgr Hanna Kośmider- Matwiejczuk

Match the key terms with their

correct definitions: