# Delta-Delta 3 phase transformer HNC help

• craig clarke
In summary, a Delta-delta, 3 phase transformer steps down the system line voltage of 132kV to a local power distribution level of 11kV. The total connected load is 21 MW at 0.86 pf lagging. The apparent power taken by the load is 32MW. The current in the HV lines is 139.9A and the current in the LV lines is 1679.5A. The current in the primary winding is 80.25A and the current in the secondary winding is 969A. The load carried by each phase winding of the transformer can be calculated using the formula kilovolt-amps = √3 × amps × volts / 1000,
craig clarke
<< Thread moved from the technical engineering forums to HH >>

I'm currently studying for a HNC in electrical engineering and am currently stuck on a question on one of my assignments. The question is:

A Delta-delta, 3 phase transformer steps down the system line voltage of 132kV to a local power distribution level of 11kV. The total connected load is 21 MW at 0.86 pf lagging. Calculate:

a) The apparent power taken by the load
b) The current in the HV lines
c) The current in the LV lines
d) The currents in the primary and secondary windings of the transformer
e) The load carried by each phase winding of the transformer

a) Apparent power = 21MW/cos(0.86 = 32MW

b) Current in HV line = 32MW/√3x132kV = 139.9A
c) Current in the LV line = 32MW/√3x11kV = 1679.5A
d) Current in primary winding = Primary current/√3 = 80.25A
Current in secondary winding = Secondary current/ √3 = 969A

Could someone please check these answers for me and I'm not sure how to calculate the load carried by each phase winding but am I correct in thinking that each winding have the same answer?

Last edited by a moderator:
Delta-Delta 3 phase transformer HNC help

Hi craig clarke. http://img96.imageshack.us/img96/5725/red5e5etimes5e5e45e5e25.gif

If you'd like some answers checked then you need to include your working. That's the requirement when seeking homework help at Physics Forms. Otherwise, helpers would have to work the problem themselves in its entirety.

Where the load is balanced, phase currents and voltages are all identical.

Last edited by a moderator:
craig clarke
I have included my calculations and answers of a,b,c and d I'm stuck on quest e. I'm not sure on what formula to use. I want to know what formula to use for calculating the load carried by each phase winding and if I've answered the other questions correctly.

Thanks

In (e) the intended answer might be its kVA.

Last edited:
craig clarke said:
a) Apparent power = 21MW/cos(0.86 = 32MW
Isn't 0.86 already cos(Φ)? Why take the cos of a cos?

PF=cos(φ

where φ is the phase angle between the voltage and current, the power factor is 0.86 lagging, so φ=0.86

The PF is the cosine of the phase angle which is 0.86?

NascentOxygen said:
In (e) the intended answer might be kVA.

Will the equation for this calculation be

Has it is a delta transformer and will be balanced?

kilovolt-amps = 3 × amps × volts / 1000

craig clarke said:
PF=cos(φ

where φ is the phase angle between the voltage and current, the power factor is 0.86 lagging, so φ=0.86

The PF is the cosine of the phase angle which is 0.86?
The power factor is indeed the cosine of the phase angle. Here it's given to you as PF = 0.86. So 0.86 = cos(φ).
That would make φ = cos-1(0.86). Or if you prefer, φ = arccos(0.86).

craig clarke
winding voltage x winding current /1000, I think, for kVA

craig clarke

## 1. What is a Delta-Delta 3 phase transformer?

A Delta-Delta 3 phase transformer is a type of electrical transformer that has three sets of windings, each connected in a delta configuration. This type of transformer is commonly used in power distribution systems to step down high voltage to low voltage for use in buildings and homes.

## 2. How does a Delta-Delta 3 phase transformer work?

A Delta-Delta 3 phase transformer works by using electromagnetic induction to transfer electrical energy from the primary winding to the secondary winding. The three sets of windings are connected in a delta configuration, which allows for the transformation of three-phase AC power.

## 3. What is the purpose of a Delta-Delta 3 phase transformer?

The purpose of a Delta-Delta 3 phase transformer is to step down high voltage power to a lower voltage that is suitable for use in buildings and homes. It also helps to balance the three-phase power supply and improve the overall efficiency of the power distribution system.

## 4. What are the advantages of using a Delta-Delta 3 phase transformer?

The main advantage of using a Delta-Delta 3 phase transformer is its ability to handle high power loads and provide a balanced three-phase output. It also has a simple and robust design, making it easy to maintain and repair.

## 5. How can I troubleshoot issues with a Delta-Delta 3 phase transformer?

If you are experiencing problems with a Delta-Delta 3 phase transformer, it is recommended to check the connections and make sure they are secure. You can also use a multimeter to measure the voltage and check for any abnormalities. If the issue persists, it is best to consult a professional electrician or contact the manufacturer for assistance.

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