Wiring Diagrams; Application Of Tap Change Control - Siemens 7sg15 microtapp Operation Manual

If use of LDC is considered as LOAD Drop Compensation it can be employed in a practical way to increase the
network utilisation. Using the data from Table 1 as an example, a modified basic level setting of -4% and an LDC
setting of 8% is applied to the AVC. The effect on the voltage levels at the extremes of substation loading is seen
by reference to Table 2.
% Voltage Difference (from
nominal)
33/11kV Transformer
(Basic 96%)
33/11kV Transformer
(LDC 8%)
MV System
LV System
Total
No load/Full load variation
The maximum variation across the network is now reduced from 15% to 7% through the change to the BASIC and
LDC controls, resulting in an improved overall supply to the connected customers or, if the original deviation was
acceptable, allowing the feeder lengths to be extended and the maximum variation indicated in Table 1 still
achieved.
Theoretically the use of LDC will improve the situation to the ideal point where the absolute voltage variation is the
same at both the source and remote ends of all feeders.
While abnormal network running and disparate feeder load profiles may cause the use of LDC to be reduced from
the ideal, advantage can still be gained by the use of restricted settings, including those networks where voltage
drops occur only on the LV system.

3 Wiring Diagrams

The MicroTAPP has been designed as a complete system. The external wiring requirement necessary for
connection to other equipment is minimal. Examples of typical arrangements for control of a tap changing
transformer are attached at the end of this section.

4 Application of TAP change control

Reference to the Description of Operation section of this document explains that the use of the MPPC
communication between MicroTAPP relays for summation of load current purposes. The minimisation of
circulating current is carried out by each relay using that transformer's own current. When transformers are
grouped consideration must be given to the Load Drop Compensation (LDC) requirements and effects of different
running arrangements.
MicroTAPP is easily applied to double bus-bar substations allowing flexibility in the system running arrangements.
The transformers do not have to be identical and can be supplied from different sources.
There are three main methods of application for MicroTAPP, as described in the description of operation section
of this manual, each with particular advantages, giving the customer a wide choice depending on the particular
application.
For maximum operational advantage the TAPP system is recommended.
©2011 Siemens Protection Devices Limited
7SG15 MicroTAPP Application Guide
At Source
No Full
Load Load Load
-4 -4
0 +8
0 0
0 -1
-4 +3
7
Table 2
Remote End
No Full
Load
-4 -4
0 +8
0 -8
0 -7
-4 -11
7
Chapter 5 Page 4 of 21