ABB REC670 Applications Manual page 414

Section 14
Control
408
secondary side of the power transformer. The control method is based on a step-by-step
principle which means that a control pulse, one at a time, will be issued to the tap
changer mechanism to move it one position up or down. The length of the control
pulse can be set within a wide range to accommodate 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
1MRK 511 401-UUS A
Bay control REC670 2.2 ANSI
Application manual