• QB9_OP = 1
• QB9_CL = 0
• QC9_OP = 1
• QC9_CL = 0
If, in this case, line voltage supervision is added, then rather than setting QB9 to open
state, specify the state of the voltage supervision:
• QB9_OP = VOLT_OFF
• QB9_CL = VOLT_ON
If there is no voltage supervision, then set the corresponding inputs as follows:
• VOLT_OFF = 1
• VOLT_ON = 0
15.4 Voltage control
15.4.1 Application
When the load in a power network is increased the voltage will decrease and vice
versa. To maintain the network voltage at a constant level, power transformers are
usually equipped with on-load tap-changer. This alters the power transformer ratio in
a number of predefined steps and in that way changes the voltage. Each step usually
represents a change in voltage of approximately 0.5-1.7%.
The voltage control function is intended for control of power transformers with a
motor driven on-load tap-changer. The function is designed to regulate the voltage at
the 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:
Section 15 1MRK 502 071-UEN -
Control
548 Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
Application manual
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