Parallel unit detection and the MCC mode
The network connection status information is essential for the MCC operation
mode. The status FALSE needs to be connected to the
CON_STATUS
input to ensure
a proper operation of the MCC calculation if the transformer is disconnected but
OL5ATCC remains in the MCC mode. This way the disconnected transformer is
excluded from the circulating current calculations.
The
CON_STATUS
input is used to identify if a transformer controller can send
the current information to other transformer controllers for circulating current
minimization purposes. As a result, this input has effect only in the MCC or Manual
active operation modes. In these modes, if
CON_STATUS
is TRUE, the information
transmission is started. The circulating current information receiving is allowed only
in the MCC active operation mode when
CON_STATUS
is TRUE. PAR_UNIT_MCC can
be seen in the Monitored data view.
Communication and the MCC mode
The phasor information from the other parallel protection relays is needed for
the circulating current calculation. Therefore, horizontal GOOSE communication is
needed between protection relays when the MCC principle is used.
The transferred current phasor information contains a primary value of the
measured current. The magnitude and angle of the current phasor can be read from
the OLGAPC function input data
TR_I_AMPL
and
TR_I_ANGL
, respectively.
The sent phasor information always represents the difference between the voltage
phasor
U_A and current phasor I_A. The information about the current phasor
can be read from the monitored data TR0_I_AMPL and TR0_I_ANGL. The allowed
active operation modes for sending data are MCC or Manual, both with the input
CON_STATUS
activated. The communication is active when the sent and received
phasor magnitude is not clamped to zero. The communication phasor magnitude
is zero due to a rejected active operation mode or too low signal magnitudes (see
Chapter 9.10.5.1 Voltage and current measurements
). Active
CON_STATUS
indicates
that the corresponding transformer is connected to the network and its current
affects the circulating current of other transformers even when it is in the manual
operating mode.
9.10.5.7
Reverse power flow handling
Power flowing through the transformer can be bi-directional under certain
circumstances. Traditionally, power flows from high voltage (HV) side to medium
voltage (MV) side. In this case the target is to keep the MV side voltage constant
despite of load current and HV side voltage variations. This is achieved by
monitoring the MV side voltage and controlling tap changer position accordingly.
Increasing the HV winding turns will lower the MV side voltage and vice versa.
But when power flow direction changes from the MV side to the HV side, the relay
has to adapt to this situation based on the
Regulation Mode setting.
The direction of power flow in all the parallel connected transformers
should be same at any given point of time.
If the
Regulation Mode is set as “Forward”, normal regulation of MV side voltage
takes place irrespective of the power flow direction, If the setting is kept as “Bi-
dir(meas)” or “Bi-dir(calc)”, when power flow direction reverses, the target is to keep
Control functions
1MRS759142 F
1712
REX640
Technical Manual