The document compares new SINSPoX and existing Dcosj alternative transformer parallel operation methods in the case of lost communication. It finds that the SINSPoX method provides the best results for voltage deviations with acceptable circulation currents. The SINSPoX method uses several inputs like measured values and fixed parameters in its algorithm, along with suppression, whereas existing methods calculate differences in reactive currents based on set and real power factors. Simulation results show the SINSPoX method maintains voltages closer to the set value with lower circulation currents than the other methods tested.

1. 10th Mediterranean Conference on
Power Generation, Transmission,
Distribution and Energy Conversion
6-9 November 2016
Belgrade, Serbia
COMPARISON OF NEW SINSPoX AND EXISTENT Dcosj
ALTERNATIVE TRANSFORMER PARALLEL OPERATION
METHODS IN CASE OF LOSS OF COMMUNICATION
Sinisa Spremic, JP EPS Tehnicki centar Novi Sad,
sinisa.spremic@eps.rs
PAPER 003
&
SESSION
№ 4

2. Introduction
• Mutual communication for data exchange is obligatory for several modern
transformer parallel operation methods in order to obtain proper voltage
regulation: optimal voltage with minimization of circulation currents.
• In case of loss of communication there are nowadays two methods in use
which claim capability to lead transformers in parallel. This methods are two
different Dcosj methods and reverse reactance method but last one only in
case of stable value of power factor.
• Dcosj methods use circulation currents calculated as difference between
transformer actual reactive current and reactive current calculated from
actual apparent current and previously set power factor value or to use power
factor value prior to communication loss or to use self-learning procedure.
• As it can be seen Dcosj method is not proper name and it was probably
chosen because name Dsinj was already taken for DIsinj method.
• New algorithm is attempt to make better parallel operation method in case of
communication loss.
10TH MEDITERRANEAN CONFERENCE ON POWER GENERATION, TRANSMISSION, DISTRIBUTION AND ENERGY CONVERSION
6-9 November 2016, Belgrade, Serbia
Paper 003 &
Session № 4

3. Methodology
• For all methods simulations were made for same High Voltage and Middle
Voltage bus bars as at simplified scheme below (Figure 1.) using different
parallel operation method algorithms. Simulations were made for three
transformers in parallel. Load drop compensation (Z-comp) parameter for all
simulations is 10 % with Z-comp limit 10 %.
• Using substitute connection diagram
at Fig. 2, mathematical method
for parallel operation of n
transformers and calculation
were developed.
10TH MEDITERRANEAN CONFERENCE ON POWER GENERATION, TRANSMISSION, DISTRIBUTION AND ENERGY CONVERSION
6-9 November 2016, Belgrade, Serbia
Paper 003 &
Session № 4
Fig. 1 Simplified scheme of paralleled transformersFig. 2 Substitute connection diagram of paralleled transformers

4. Results – Gossen Dcosj method
Gossen [7] existent Dcosj method have Z-comp with active part of currents with
possibility to limit Yp (Yp is influence of parallel operation) by multiplication with
chosen factor. Factor increasing leads to higher level of voltage deviations and
lower level of circulation currents and vice versa. Simulations could be helpful for
parameters determination for this method. Otherwise only try and error
procedure is possible. Parameter cosjset is 0,94.
10TH MEDITERRANEAN CONFERENCE ON POWER GENERATION, TRANSMISSION, DISTRIBUTION AND ENERGY CONVERSION
6-9 November 2016, Belgrade, Serbia
Paper 003 &
Session № 4
Fig. 3 Voltage deviation of Gossen Dcosj method [7] Fig. 4 Circulation currents of Gossen Dcosj method [7]

5. Results – A-Eberle Dcosj method
• For A-Eberle [3] existent Dcosj method Z-comp is turned off. Voltage is
maintained at Uset±b· DUperm which lead to large voltage deviations at higher
loads. Voltage deviation is percentage difference of actual voltage and desired
voltage if there is Z-comp. Parameter cosjset is 0,94. This method could be
used in cases where Z-comp is not necessary (short feeders) or Z-comp has
low value.
10TH MEDITERRANEAN CONFERENCE ON POWER GENERATION, TRANSMISSION, DISTRIBUTION AND ENERGY CONVERSION
6-9 November 2016, Belgrade, Serbia
Paper 003 &
Session № 4
Fig. 5 Voltage deviation of A-Eberle Dcosj method [3] Fig. 6 Circulation currents of A-Eberle Dcosj method [3]

6. Results – SINSPoX method
• SINSPoX method use Z-comp with active part of currents. SINSPoX method
needs current and voltage analogue inputs and standard transformer data
without any parallel operation parameter. SINSPoX method has not got
parameter cosjset. It is possible to modify algorithm in order to use parameter
cosjset or cosj prior to communication loss with slightly better results for
voltage deviation at values cosjset or cosj prior to communication loss.
10TH MEDITERRANEAN CONFERENCE ON POWER GENERATION, TRANSMISSION, DISTRIBUTION AND ENERGY CONVERSION
6-9 November 2016, Belgrade, Serbia
Paper 003 &
Session № 4
Fig. 7 Voltage deviation of SINSPoX method Fig. 8 Circulation currents of SINSPoX method

7. Results – comparison
10TH MEDITERRANEAN CONFERENCE ON POWER GENERATION, TRANSMISSION, DISTRIBUTION AND ENERGY CONVERSION
6-9 November 2016, Belgrade, Serbia
Paper 003 &
Session № 4
Gossen [7] method A-Eberle [3] method SINSPoX method
Fig. 9 Comparison of considered methods

8. Conclusion
• Basic of algorithms of existent methods is calculation of differences of reactive
currents of real and set power factor cosj. SINSPoX method use different
algorithm which involves several inputs: measured values or values calculated
from measured values and unchangeable parameters. Beside that algorithm
includes suppression.
• According to simulations SINSPoX method gives best results for voltage
deviations with acceptable level of circulation currents for given ranges of load
and power factor.
• It is possible to make even better algorithm than SINSPoX algorithm.
• Certain upgrade of SINSPoX method could be used for transformer parallel
operation without communication among AVRs for different topologies: same
or different remote HV bus bars and same or different (remote) MV bus bars
(paralleled over MV feeders). Also for distribution network MV/LV with
transformers paralleled over common LV feeders. MV/LV transformers should
be equipped with OLTC or other type of on-load voltage regulation. This could
be applicable for smart grids.
Paper 003 &
Session № 4
10TH MEDITERRANEAN CONFERENCE ON POWER GENERATION, TRANSMISSION, DISTRIBUTION AND ENERGY CONVERSION
6-9 November 2016, Belgrade, Serbia

9. Conclusion
Paper 003 &
Session № 4
10TH MEDITERRANEAN CONFERENCE ON POWER GENERATION, TRANSMISSION, DISTRIBUTION AND ENERGY CONVERSION
6-9 November 2016, Belgrade, Serbia
Thank you very much
for your attention!