Siemens MJ-5 Installation And Operation Manual page 51

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component of current is greater than 1% of the full scale
current.
Reverse power flow is indicated when the real power is
negative and the real component of current is greater than
1% of the full scale current. To avoid excessive switching
between Forward and Reverse Operation (defined below),
the microprocessor delays five seconds after the occurrence
of a current flow reversal before switching from forward to
reverse, and vice-versa.
As an example, assume current is flowing in the forward
direction. When load current magnitude drops through zero
and increases to a magnitude that exceeds 1% rated current
in the reverse direction, the microprocessor delays five
seconds and then considers reverse power flow to be in
effect. Reverse power flow remains in effect until current
direction becomes forward once again and its magnitude
exceeds 1% of rated current in the positive direction for
five seconds. At that time, the microprocessor considers
forward power flow conditions to have resumed.
Power flow direction is indicated on many of the metering
screens. "F" indicates forward power flow; "R" indicates
reverse power flow. "F" is shown when: kW > 0 and |Ireal|
> 1% (of full scale) for 5 seconds minimum. "R" is shown
when: kW < 0 and | Ireal | > 1% (of full scale) for 5 seconds
minimum. If the real current magnitude is below the 1%
threshold, the last known power flow direction remains in
effect. If the real current magnitude is below the 1%
threshold after power up or unit reset, the MJ-5 defaults to
forward power flow operation.
It is possible for Reverse Power Flow conditions to occur in
regulators with no source-side voltage input (e.g., no
"Source-Side PT" for Siemens Inverted Regulators). In this
case, the MJ-5 uses the calculated source-side voltage for
performing reverse power flow regulation. See sections 5.1
and 5.2 for details on source-side voltage calculation.
When determining power flow direction, the system takes
into account the current-to-voltage phase relationship
associated with the system as specified in the
<CONFIGURE> menu (System, Utility Polarity, and I
[current] Shift parameters).
6.5.2 Forward/Reverse Operation
The MJ-5 Control Panel accommodates power flow
reversals by alternating between "Forward" and "Reverse"
modes. Because the microprocessor monitors (or derives)
the voltage on both sides of the regulator, it can reverse
modes by simply reversing its definition of "source" and
"load."
•
In Forward Operation mode, the microprocessor senses
the "L" Bushing (or derives the "L" Bushing voltage
from the "S" Bushing voltage and the knowledge of the
tap position) to determine load voltage and controls the
tap changer on the basis of the Forward set points
(Voltage, Bandwidth, Time Delay, Line Drop
Compensation). During Forward Operations, "forward"
Meter data is displayed.
Siemens Industry, Inc.
MJ-5 Control Panel Automatic Mode
•
In Reverse Operation mode, the microprocessor senses
the "S" Bushing (or derives the "S" Bushing voltage
from the "L" Bushing voltage and the knowledge of the
tap position) to determine load voltage and controls the
tap changer on the basis of the Reverse stipends
(Voltage, Bandwidth, Time Delay, Line Drop
Compensation).
During Reverse Operations, "reverse" Meter data is
displayed. The following parameters determine whether the
tap change motor is energized to raise the tap position or to
lower it:
1. Power flow direction,
2. Forward/reverse operation,
3. Out-of-band status,
4. Power flow mode (see below for details).
Tables 6.3 and 6.4 on the next page summarize the tap
change direction for each Power Flow mode
6.5.3 Current Bias and Bias Percent
This option is only in effect when the power flow mode is
Bi-Directional. For this special operation, the Bias percent
must be greater than the I Threshold%. Typically I
Threshold % should be set to 0%.
The operation of this feature is described below,
categorized into direction and magnitude of current flow.
Current is greater than the Bias percent (no change in prior
functionality):
•
Forward Power Flow: tap changes will occur based on
the Load bushing voltage.
•
Reverse Power Flow: tap changes will occur based on
the Source bushing voltage.
Current is less than the Bias Percent (new functionality):
•
None: no tap changes will occur.
•
Fwd: tap changes will occur based on Load bushing
voltage.
•
Rev: tap changes will occur based on Source bushing
voltage.
•
NeutT: tap changer will run to Neutral Tap.
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