Circuit Analysis of 3 Phase System – Balanced Condition

The 3 Phase system is divided mainly into two types. One is Balanced three phase system and another one is unbalanced three phase system.

Contents:

Analysis of Balanced 3 Phase Circuit

It is always better to solve the balanced three phase circuits on per phase basis. When the three phase supply voltage is given without reference to the line or phase value, then it is the line voltage which is taken into consideration.

The following steps are given below to solve the balanced three phase circuits.

Step 1 – First of all draw the circuit diagram.

Step 2 – Determine XLP = XL/phase = 2πfL.

Step 3 – Determine XCP = XC/phase = 1/2πfC.

Step 4 – Determine XP = X/ phase = XL – XC

Step 5 – Determine ZP = Z/phase = √R2P + X2P

Step 6 – Determine cosϕ = RP/ZP; the power factor is lagging when XLP > XCP and it is leading when XCP > XLP.

Step 7 – Determine V phase.

For star connection VP = VL/√3 and for delta connection VP = VL

Step 8 – Determine IP = VP/ZP.

Step 9 – Now, determine the line current IL.

For star connection IL = IP and for delta connection IL = √3 IP

Step 10 – Determine the Active, Reactive and Apparent power.

Analysis of Unbalanced 3 Phase Circuit

The analysis of the 3 Phase unbalanced system is slightly difficult, and the load is connected either as Star or Delta. The topic is discussed in detail in the article named as Star to Delta and Delta to Star Conversion.

Interconnection of 3 Phase System

In a three-phase AC generator, there are three windings. Each winding has two terminals (start and finish). If a separate load is connected across each phase winding as shown in the figure below, then each phase supplies as independent load through a pair of wires. Thus, six wires will be required to connect the load to a generator. This will make the whole system complicated and costly.

circuit-analysis-of-3-phase-system-fig1

Therefore, in order to reduce the number of line conductors, the three phase windings of an AC generator are interconnected.The interconnection of the windings of a three phase system can be done in following two ways

Star or Wye (Y) connection  Also See: Star Connection in 3 Phase System

Mesh or Delta (Δ) connection. Also See: Delta Connection in 3 Phase System

Connection of 3 Phase Loads in 3 Phase System

As the three phase supply is connected in star and delta connections. Similarly, the three-phase loads are also connected either as Star connection or as Delta Connection. The three phase load connected in the star is shown in the figure below.

circuit-analysisi-of-3-phase-system-fig2The delta connection of three phase loads is shown in the figure below.

circuit-analysis-of-3-phase-system-fig3The three phase loads may be balanced or unbalanced as discussed above. If the three loads Z1, Z2 and Z3 have same magnitude and phase angle, then the 3 phase load is said to be a balanced load. Under such connections, all the phase or line currents and all the phase or line voltages are equal in magnitude.

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