WG A2 50 Effect of Distributed energy sources and

Report
WG A2 50
Effect of Distributed energy sources
and consequentinduced reverse flow
on transmission and distribution
transformers
First Meeting Zürich
11 September 2013
A2-50 Members
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•
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•
•
•
•
•
BIRENDRA (BOB) SINGH
BOGUSLAW (DR. ) BOCHENSKI
GABOR GURSZKY
HIDEYUKI MIYAHARA
KOJIRO AOKI
MOHAMED ZOUITI
SAEED KAMALINIA
YUKIYASU SHIRASAKA
Utility
3rd Party
Manufacturer
Manufacturer
Utility
Utility
Manufacturer
Manufacturer
A2-50 SCOPE
The scope of this working group is to address the effect of step up
operation on transformers that were not designed for this
purpose.
The effect on flux density, temperature rise, noise and other
performances for both core and shell types designs shall be
addressed.
Possible tap changer control problems will also be taken into
account. Differing transformer locations in final distribution,
primary distribution and principal transmission will be examined,
as well.
The report will address the theoretical consequences for core flux
and voltage regulation, risks and limitations to step up operation
for each technology and the assessments necessary to allow
this mode of network operation.
A2-50 Background
Originally, transmission and distribution networks were designed for
step down operation transmitting energy from the highest voltage to the
final user’s voltages. The introduction of more and more renewable or
distributed small power generation have created power injection in the
lower voltage level which in many cases exceeds the consumption of the
local network. This creates an upstream power flow and change the usual
step down operation of the transformer into a step up mode in order to
evacuate the energy. The design of the transformer and the regulation of
the voltages may not be anymore suitable for a safe and long lasting
operation. Furthermore, most of those distributed energy generator are
base on solid-state inverter, which may produce harmonics on the
network, that may also affect the transformer life.
A2-50 Table of content
Introduction
Report of existing problems
–Example
–Different possible concerns and effects in transformers ( such as harmonics
and winding hot spot, overfluxing and core hot spot) linked to reverse power
flow
–Effect of active and reactive power flow
Transformer construction and a few theory
– How is flux density fixed
• Core type
• Shell type
– Stray flux
• Where does the stray flux go
• Effect of capacitive load
– Voltage drop (and raise)
Forecasted load flow evolution on “smarter grid”
–Some general consideration on load flow and smart grid
A2-50 Table of content
Step up step down operation influence on design
–Typical configuration for distribution network
–double LVs transformers
Effect of flux density and stray flux
– Temperature rise (core, hot spot)
– Noise (due to “overfluxing” due to voltage and current or due to load)
– Other performances
Tap changer design
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Tap changer for both way power flow (asymmetrical pennant cycle ?)
Does it affects the design of the tap changer ?
Differences with conventional tap changer
What about DETC ?
A2-50 Table of content
Voltage regulation
– Tap changer control ( P&C inputs requested)
– System view of the transformer control policy U, I both , where LV ? HV?
For distribution and transmission
– Voltage drop ( effect of high impedance end power factor)
– Reactive power control
– Reactive power circulation
– Tapping range
– Regulated voltage (LV with HV taps ?)
– Tapping winding position (HV/LV)
– DETC ?
Effect of harmonics of current and voltage
– On no load losses
– On load losses
Mitigation and usage restrictions
– Typical example or real cases
A2-50 Table of content
Conclusion : advices
– Risks on existing fleet
– Special requirement for new specification
– Recommendation to standardization update ( 76-1 ?)
Bibliography

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