Star–delta configurations

1. Star–delta configurations

Level 3 Diploma in Electrical Installations (Buildings and Structures)
PowerPoint
presentation
Unit 302: Principles of electrical science
Star–delta configurations
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2.

Level 3 Diploma in Electrical Installations (Buildings and Structures)
Three-phase supplies
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3.

Level 3 Diploma in Electrical Installations (Buildings and Structures)
Star connection
VL
=
√3 x VP
IL
=
IP
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4.

Level 3 Diploma in Electrical Installations (Buildings and Structures)
EXAMPLE 1 – A three-phase, four-wire Star connected transformer
has a line voltage of 520 volts and supplies a line current of 25 amps.
Calculate:
a) the phase voltage of the transformer
b) the phase current in each winding.
a) In star
VL = 3 ´VP
VP =
=
VL
3
520
3
= 300 volts
b) In star
IL = IP
= 25 amperes
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5.

Level 3 Diploma in Electrical Installations (Buildings and Structures)
Delta connection
VL = VP
IL = 3 ´ IP
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6.

Level 3 Diploma in Electrical Installations (Buildings and Structures)
EXAMPLE 2 – A three-phase balanced Delta connected resistive load is
supplied from a transformer at a line voltage of 400 volts and draws a line
current of 13.86 amps. Calculate:
a) the phase voltage
b) the phase current
c) the resistance of the load.
a) In delta
VP = VL
= 400 volts
b) In delta
IL = 3 ´ IP
IP =
=
IL
3
13.86
3
= 8 amperes
© 2018 City and Guilds of London Institute. All rights reserved.
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7.

Level 3 Diploma in Electrical Installations (Buildings and Structures)
EXAMPLE 2 – A three-phase balanced Delta connected resistive load is
supplied from a transformer at a line voltage of 400 volts and draws a line
current of 13.86 amps. Calculate:
a) the phase voltage
b) the phase current
c) the resistance of the load.
c)
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8.

Level 3 Diploma in Electrical Installations (Buildings and Structures)
Balancing loads
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9.

Level 3 Diploma in Electrical Installations (Buildings and Structures)
EXAMPLE 3 – A three-phase unbalanced star connected system has
the following loads connected to each phase:
• Brown phase – 10 amperes
• Black phase – 20 amperes
• Grey phase – 15 amperes
Using the graphical method
(phasors) determine
the neutral current.
Br phase: 10A
Resultant: 8.7A
Bl phase: 20A
Gr phase:
15A
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10.

Level 3 Diploma in Electrical Installations (Buildings and Structures)
In = ((Ia 2 + Ib 2 + Ic 2 ) - (Ia ´ Ib) - (Ib ´ Ic) - (Ia ´ Ic))
Where: In = neutral current
Where: Ia = current in brown phase
Where: Ib = current in black phase
Where: Ic = current in grey phase
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11.

Level 3 Diploma in Electrical Installations (Buildings and Structures)
EXAMPLE 4 – Using the figures in Example 3, calculate the neutral
current.
In = ((Ia 2 + Ib 2 + Ic 2 ) - (Ia ´ Ib) - (Ib ´ Ic) - (Ia ´ Ic))
= ((10 2 + 20 2 + 15 2 ) - (10 ´ 20) - (20 ´ 15) - (10 ´ 15))
= (725 - 200 - 300 - 150)
= 75
= 8.66 amperes
© 2018 City and Guilds of London Institute. All rights reserved.
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12.

Level 3 Diploma in Electrical Installations (Buildings and Structures)
Any questions?
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