Single Phase Or 3 Phase Units; Direction Of Tap-Changer For Voltage Increase; Transformer Impedance; Nominal Voltage Or Winding Load Drop Compensated Target Settings - Siemens 7sg15 microtapp Operation Manual

The tap spacing is calculated regardless of the tap-changer location: -
Vhi*
Vlo*
Vnom*
Tap
* Irrespective of the actual tap changer location

4.4.4 Single phase or 3 phase units

This setting determines load current for the transformer full load rating.

4.4.5 Direction of tap-changer for voltage increase

Some tap-change mechanisms operate to increase voltage by reducing the tap position. This setting allows for
this situation.

4.4.6 Transformer impedance

Transformer impedance is used by all MicroTAPP relays for control of circulating current and, in this application,
for the calculation of winding voltage drop.

4.4.7 Nominal voltage or winding load drop compensated target settings

In some applications where large transient loads are supplied it may be desirable to ignore the transformer
voltage drop and control the voltage at an effective nominal level. This setting allows for this requirement.

4.4.8 Dead-Reckoning Block

Since the MT102 may be controlling the voltage on the opposite side of the Power Transformer from its
measuring point, it is important that the Tap Position reported to the Relay by the TPI is correct. The Relay will
therefore compare the Tap Position received from the TPI with its own "Dead-Reckoned" Tap Position. If a
discrepancy is found the Relay will Alarm "Dead Reckoning Block" and block subsequent tap changes. This will
only be reset once a correct Manual Raise/Lower operation has been carried out.
4.4 MicroTAPP–MicroTAPP communications
At a site each MicroTAPP can connect to other MicroTAPP relays through a screened twisted pair cable. The
MicroTAPP Peer to Peer Communication system (MPPC) is used to transfer data between the relays relating to
the overall operation of the MicroTAPP group at a site. If a MicroTAPP relay is de-energised, communications
between other relays connected to the twisted pair cable is not affected.
4.5

Low Frequency Voltage Reduction

Where voltage reduction is used for load reduction purposes, usually to offset a shortfall in available generation,
the relay can be configured to automatically initiate tap change operations. The power system frequency is
continually monitored, if the frequency falls below a set level the target voltage setting is dropped by 5% to effect
an immediate voltage reduction.
4.6

Transformer Switch out

When one transformer of a group is switched out of service a voltage drop will occur as additional load is 'picked
up' by the remaining transformers, particularly if the transformers are heavily loaded and have a high impedance.
The effect can be eliminated if the individual transformer tap changers are operated to offset the voltage drop
prior to switch-out, e.g. raising the tap position of the transformer that will remain in and lowering the tap position
of the transformer that is to be switched out.
On receipt of a signal (switch out command), MicroTAPP relays (allocated to a group) can be configured to
communicate and operate each tap changer in such a way that minimal change in voltage will occur when the
transformer is switched out. When the optimum tap positions are achieved a completion signal is returned.
©2013 Siemens Protection Devices Limited
= Highest voltage of the variable voltage winding (voltage as nameplate)
= Lowest voltage of the variable voltage winding (voltage as nameplate)
= Nominal voltage of the variable voltage winding (voltage as nameplate)
= Number of taps (not tap intervals)
Tap spacing %
7SG15 MicroTAPP Description of Operation
= (Vhi - Vlo) x 100
Vnom x (Tap-1)
Chapter 1 Page 13 of 38