1. ENERGY EFFICIENCY
IMPROVEMENT BY DECREASING
UNBALANCED LOAD IN
ELECTRICAL NETWORKS
Siniša Spremić, dipl.el.inž. - EPS-P.D. "Elektrovojvodina"
Dušan Obradović, dipl.el.inž. - EPS-P.D. "Elektrovojvodina”

2. CAUSES OF ASYMMETRY OCCURENCE
- Basic cause of asymmetry occurence is consumer.
- Single-phase consumers have the biggest influence on asymmetry, but
also three-phase consumers could have big influence on asymmetry due
to mode of using different devices.
- Each other influences of consumers (devices) could effect on asymmetry
increase but also decrease towards main supply point. It is possible that
there is a low level of asymmetry on transformer secondary side, but
asymmetry on some feeders could be significant. Also some sections of
one feeder could have significant asymmetry and other sections low level
of asymmetry.
- Load and asymmetry changes in time.
- Asymmetry could be amplitude and phase.
- Asymmetry transfers from low voltage to medium voltage level in lower
quantity because of connection type of transformers (e.g. Dy and Yz).
Asymmetry yields to additional losses because of unbalanced phase loads
and also because of appearance of current through neutral wire in four
wire systems. Four wire system is considered in particular in this article.

3. CALCULATION MODEL, RESULTS AND
ANALYSIS
Short description of calculation model
Inputs for calculations are:
- feeder resistance and reactance (cross-section and length),
- nod power factor,
- nod load current and
- phase voltages at start of feeder.
Using nod currents instead impedances enables to make simple calculation model.
Zv 1
Zn 1
Zn z
Zv z
I k section 1 I k section z
I n section zI n section 1
U k nod z-i I k nod 1
I k nod z

4. CALCULATION MODEL, RESULTS AND
ANALYSIS
Calculation results for different asymmetry types

5. CALCULATION MODEL, RESULTS AND
ANALYSIS
Calculation results for different asymmetry types
Examples for voltage, nod power factor and phase shifts changes.
Daily diagrams of load and power factor of one distribution transformer

6. CALCULATION MODEL, RESULTS AND
ANALYSIS
Calculation results for different asymmetry types
Neutral wire currents for different types of asymmetry.
Power losses increasing due to asymmetry
Calculation results
analysis
According to measured level of
asymmetry on secondary sides
of distribution transformers and
at start of feeders it can be
assumed that on low voltage
feeders losses increasing
mostly go up to around 10 %
due to different combined
common types of amplitude
and power factor asymmetry
comparing to symmetrical load
with same apparent power.
Some types of asymmetry has
bigger influence on losses
increasing. Beside power
losses increasing negative
influences on low voltage
network are voltage asymmetry
and shifts among phases.

7. HOW TO RECOGNIZE, DETERMINE AND
MITIGATE LEVEL OF ASYMMETRY?
The easiest way to recognize asymmetry at low voltage level network and installations is to
measure voltage. Voltage is easy accessible in every connector and also at cable and
installation cabinets.
Far more better way to recognize and determine level of asymmetry is measuring phase
currents and current through neutral wire. Basic and the easiest mode of current measurement
is using current clamps.
The best way to recognize and determine asymmetry is to have recording devices which will
record currents and voltages and calculate all other needed data. Advantage is complete time
characteristics.
Desirable points to measure voltages and/or currents are supply point and end point, but also
points in between.
After consideration of all available data, load balancing among phases by moving consumers
or devices from phase to phase should be done. In distribution low voltage network there is
possibility to rotate phases of three-phase consumers at the point of connection and the same
in sectioning or connecting cable cabinets of distribution network or installations. Rotation of
phases should be done with care in order to obtain same direction of rotation electromagnetic
field for electrical machines or correct phases position for other devices.
It is necessary to consider possible positive and negative mutual influences of emerging
dispersed energy resources and asymmetry at low voltage networks, in particular for four wire
low voltage networks.

8. CONCLUSION
• Energy efficiency could be improved by decreasing
asymmetry in electrical networks and installations.
• Amplitude and phase load asymmetry have
influence on power losses increasing, voltage
asymmetry and phase shifting.
• Simple measures in detecting and determining
asymmetry and measures for mitigation asymmetry
could help to decrease amplitude and power factor
asymmetry and thus decrease negative effects of
asymmetry.