ABB Relion 670 Series Applications Manual page 366

Section 14
Control
different types of tap changer mechanisms. The pulse is generated whenever the measured
voltage, for a given time, deviates from the set reference value by more than the preset deadband
(degree of insensitivity).
The voltage can be controlled at the point of voltage measurement, as well as at a load point
located out in the network. In the latter case, the load point voltage is calculated based on the
measured load current and the known impedance from the voltage measuring point to the load
point.
The automatic voltage control can be either for a single transformer, or for parallel transformers.
Parallel control of power transformers can be made in three alternative ways:
• With the master-follower method
• With the reverse reactance method
• With the circulating current method
Of these alternatives, the first and the last require communication between the function control
blocks of the different transformers, whereas the middle alternative does not require any
communication.
The voltage control includes many extra features such as possibility to avoid simultaneous
tapping of parallel transformers, hot stand by regulation of a transformer within a parallel group,
with a LV CB open, compensation for a possible capacitor bank on the LV side bay of a
transformer, extensive tap changer monitoring including contact wear and hunting detection,
monitoring of the power flow in the transformer so that for example, the voltage control can be
blocked if the power reverses and so on.
The voltage control function is built up by two function blocks which both are logical nodes in IEC
61850-8-1:
• Automatic voltage control for tap changer, TR1ATCC (90) for single control and TR8ATCC (90)
for parallel control.
• Tap changer control and supervision, 6 binary inputs, TCMYLTC (84) and 32 binary inputs,
TCLYLTC (84)
Automatic voltage control for tap changer, TR1ATCC (90) or TR8ATCC (90) is a function designed
to automatically maintain the voltage at the LV-side side of a power transformer within given
limits around a set target voltage. A raise or lower command is generated whenever the measured
voltage, for a given period of time, deviates from the set target value by more than the preset
deadband value (degree of insensitivity). A time delay (inverse or definite time) is set to avoid
unnecessary operation during shorter voltage deviations from the target value, and in order to
coordinate with other automatic voltage controllers in the system.
TCMYLTC and TCLYLTC (84)are an interface between the Automatic voltage control for tap
changer, TR1ATCC (90) or TR8ATCC (90) and the transformer load tap changer itself. More
specifically this means that it gives command-pulses to a power transformer motor driven load
tap changer and that it receives information from the load tap changer regarding tap position,
progress of given commands, and so on.
TCMYLTC and TCLYLTC (84) also serve the purpose of giving information about tap position to
the transformer differential protection.
Control location local/remote
The tap changer can be operated from the front of the IED or from a remote place alternatively. On
the IED front there is a local remote switch that can be used to select the operator place. For this
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1MRK 511 401-UUS F
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Bay control REC670
Application manual