calculation of star delta circuit

 How to choose contactor and overload:

First, choose the contactor for delta curtain circuits:

 main contactor=

I full load ÷ 1.732

or i full load ×0.58

This is if the delta contactor current is connected from the main contactor input, then the full load current is divided by the two and not completely passed

But if the current of the delta contactor is connected from the output of the main contactor, then the main contactor passes the entire current through it first, and then it is distributed with the delta contactor in this case.

 Main contactor = i full load x 100% i.e. full load current.

Delta contactor:

I full load÷1.732

or i full load ×0.58

I mean, the main and delta currents are equal, and of course we should divide

The full load is divided by 2 instead of root 3, but we divide by 1.732 as a safety factor.

 Contact star:

I full load ÷3

i full loaf ×0.33

That is, 1/3 of the full load current

In the case of direct connections

The contactor will be = 100 × full load of the full load current.

Secondly, calculate the overload in the delta curtain circles:

First, if the overload is placed directly after the fuse, it is placed on a stream

I over load=i delta current

If the overload is placed after the main contactor, it is placed on a current

I over load =i curtain current

or (i over load=( i full load x 0.58 .)

NB :

The curtain current if the overload is placed after the main contactor = half of the total of the curtain and main contactor current together

In the case of the overload in direct connections direct

Calculates 100% x full load overload at full load current

Example :

Triple load working Star Delta 15 hp working with an efficiency of 90% Its power factor is 0.85

At a voltage of 220/380, calculate the load current, contactor, main circuit breaker and overload.

First, calculate the current:

I = 15×746/380×1.73×0.8×0.9=

23.6 A 24 A

cutter account:

Since the star-delta circuit will reduce the starting current, we do not need a large safety factor:

I breaker =1.25 ×i full load

I breaker=1.25 x 24=30A

We choose a breaker equal to or higher than this value, let it be 32 amps

Main and Delta contactor

=i full load ×0.58

I contactor=24×0.58=13.92 A

Star Connector

 =i full load ×0.33

I contactor= 24×0.33=7.92A

Calculation of the overload if it is placed before the main contactor:

I over load=i full load ×100%

I over load = 24 A

Calculation of the overload if placed after the main contactor:

I over load = i full load x 0.58

I overload = 24 × 0.58 = 13.92A

So we set the overload at 125% of the current

(13.92 x %.125) = 17.4

We choose an overload, a range that includes this current from (12 to 18).

In a star connection:

Line voltage = 1.732 x face voltage (phase)

380 = (1.732 x 220)

By measuring the potential difference between L1 and L2, we will find 380 volts, but the potential difference between LI and N is 220 volts

VL = 1.73× v Phase

line current = face current

The current in the feed line is the same as the current in the face

IL = iphase

Delta connection:

Line voltage = face voltage (phase)

By measuring the potential difference between L1 and L2, we will find 380 volts, which is the same voltage on the face

VL=vphase

Line current = 1.73×face current

IL = 1.73×iphase