transformer merged slides

When is it required to set up transformers in Parallel

• When the Load exceeds the rating of one transformer

if the primary windings are connected to supply busbars and the secondary windings are connected to load busbars. Are they connected in series or parallel

• Parallel

Does the reliability of the load increase or decrease when the using transformers in Parallel vs a Single Larger Unit

• The reliability to the load is increased with parallel operation

Is cost associated with maintaining

spares more or less when two

transformers are connected in parallel

• The Cost is less

What are the 4 requirements when using transformers in Parallel

• Must have Identical Polarity

• Must have Identical Voltage

• Must have Identical Frequency

• Must have Identical Impedance

Who sets the standards for the way Terminals are marked on a transformer?

• ANSI= American National Standards Institute

According to the ANSI, how should the High side of the transformer be labeled?

• H1 & H2

How should the Low voltage sides be labels?

X1 & X2

how is the polarity of a transformer determined?

• the dots

How can we determine if a transformer is additive or subtractive

• Additive = If the voltage on the primary and secondary side are added together

• Subtractive= If the voltage

What is important in when constructing a three phase transformer

• The polarity

What is transformer Impedance

• The % of nominal voltage needed to produce full load current under short circuit conditions

‘What are the 4 types of Losses in a Transformer?

• Iron or Core Losses

• Copper or Ohmic Losses

• Stray Losses

• Dielectric Losses

What are the 2 types of losses with an Iron Or Core

• Hysteresis

• Eddy Current Losses

What are the 3 mains reasons for Hysteresis Losses?

• Losses due to the magnetization and demagnetization of the core

• Energy is lost in each cycle as the magnetization is reversed

• Reduced by manufacturer using low reluctance core materials

What are Eddy Currents

• What the Magnetic flux influences the core

• Eddy currents flow in a circular manner and provide no productive power

How can eddy currents be reduced

• use a laminated core instead of a solid core

What are the benefits of a laminated core

• Reduces Eddy currents

• Reduces heat within the core

What are Copper Losses

• Transformer Copper Losses due to electrical resistance in the windings (primary and secondary)

Can both Copper and Aluminum wire have losses?

• Yes, Losses are caused by the resistance in the wire

When load is connected, the current in the windings cause power loss known as what?

• I2R losses (2=squared)

What cause larger I2R losses (2=squared)

• Larger wire

How can Copper losses be reduced

• Use larger Wire (less resistance= less heat)

• Better Cooling

What causes Stray Losses?

• Stray losses are due to the leakage field in the transformer

What are 2 types of Stray Currents

• Eddy currents in the walls of the transformer

• Eddy Currents in the Winding Conductors

When does Dielectric loss happen

• Loss occurs due to failing insulation value of the transformer

Losses due to Leakage Flux are?

• Flux that does not cross the conductor cannot produce a voltage

How doe leakage flux impact a transformer efficiency?

• Leakage flux reduces transformer efficiency

How can Leakage Flux be reduced

• Placing the primary and

  secondary windings on the

  same leg of the core.

When hooking up multiple secondary winding in Series, how must the ends be hooked up?

• Ends must be hooked up in different polarity

When hooking up windings in parallel we must hook up ends with

• The same polarity

What information can be found on a transformer name plate?

• VA and KVA ratings

• Primary and Secondary Voltage rating

• Impedance Rating

• Clearance and Ventilation requirements

• Type of insulation liquid used (if liquid filled)

• class temperature rating of the winding insulation.