Master/Follower Control; Load Drop Compensation; Mt102 Advanced Features; Description Of Operation - Siemens 7sg15 microtapp Operation Manual

IT1
When conventional negative reactance control is used the transformer current, IT1, is used to produce a voltage –
VXT1, which should have no effect on the relay for load current. When the load current power factor is less than
unity, as shown, an error voltage is introduced into the circuitry which causes the relay to measure an incorrect
higher voltage that results in a tendency to reduce the power system voltage below the required level.
MicroTAPP is set to operate at the true power factor. This gives reliable accuracy when set to the average system
power factor and overcome the problems associated with other schemes.

4.2.3 Master/Follower control

The MicroTAPP can be configured for use with a Master/Follower tap change control scheme; however this
arrangement is complex and imposes severe limitations on network operation. It is not recommended.
4.3

Load Drop Compensation

The MicroTAPP includes a 'Load Drop Compensation' facility which is be used to offset the effect of load related
voltage drops. Unlike normal controls that respond to transformer load only, the MicroTAPP uses a
communication system for the transfer of load information to other relays, thus allowing each relay to determine
the summed site load (I load) as shown in Figure 4. Regardless of the number of transformers in service at any
time the LDC effect will be accurate, unlike those systems where the transformer load and thus the LDC effect
changes as the number of transformers in a group changes.
A single control determines the LDC setting and is based on the load at the chosen power factor (a Z setting). It is
widely recognised that this arrangement gives the best overall predictable accuracy for load related voltage
boosting. Maximum LDC will be applied when the measured load is equal to the System Group Capacity setting.
4.4

MT102 Advanced Features

4.4.1 Description of Operation

MicroTAPP voltage control relay (VCR) can be provided with functionality that will allow effective control to be
exercised on either side of the transformer using a single fixed voltage transformer and includes load related
voltage regulation.
Figure 8 shows a normal arrangement for a voltage regulation system that employs a MicroTAPP relay taking a
voltage and current measurement input from the network side of the power transformer. Any adjustments to the
target voltage level are initiated by the VCR to drive a tap-changing mechanism that may be connected to either
the 'primary' or 'secondary' windings of the power transformer.
©2013 Siemens Protection Devices Limited
7SG15 MicroTAPP Description of Operation
Voltage
Figure 7
Measurement
Error
-VXT1
Chapter 1 Page 11 of 38