BECKWITH ELECTRIC M-3520, Instruction Book

Page: 50 / 217

2–17
Application - 2
32 Directional Power
Directional power protection is available in either
the Reverse Overpower, Reverse Underpower,
Forward Overpower or Forward Underpower
configuration presented below. A power import
and export convention that considers DG, Utility
and the M-3520 perspectives is also included. The
directional power function provides two power
elements, each with a direction setting, magnitude
setting and time delay, and configurable as an
underpower or overpower element.
The directional power function provides protection
against large power import or power export by an
DG to a utility. Forward power is defined as power
exported from an DG to a Utility, and reverse power
is defined as power imported by an DG from a
Utility (see Figures 2-1 and 2-2).
Two power elements are provided, each with a
magnitude setting and time delay. The setting range
is from –3.000 PU to 3.000 PU. The choice of the
base PU is typically taken from the MVA rating of
the interconnection transformer, the DG’s
aggregate generating capacity or some other value
agreed upon by the DG and the utility. Normalized
PU power flow measurements are based on the
Nominal Voltage and Nominal Current setting, as
shown in Section 2.3, Configuration.
If the DG is allowed to supply power to the Utility
(export), the forward overpower function can be
used to limit the amount of power flow into the
Utility. The reverse underpower function can be
used to ensure that the DG is importing a minimal
amount of power from the utility, therefore providing
a supplemental means of loss of parallel operation
protection.
Configuration Process
The directional power elements are individually
configured as follows:
1. Input the desired pick up value, positive
(forward) or negative (reverse).
a. Positive pick up value – Places the
pick up point in the forward power
area of the element, creating a
forward power element.
b. Negative pick up value – Places the
pick up point in the reverse power
area of the element, creating a
reverse power element.
2. Select either Overpower or Underpower
application:
Overpower Mode
a. Reverse Overpower – An increase
in reverse power flow that exceeds
the pick up value will cause a trip.
b. Forward Overpower – An increase
in forward power flow that exceeds
the pick up value will cause a trip.
Underpower Mode
a. Reverse Underpower Mode – A
decrease in reverse power flow that
is below the pick up value will cause
a trip.
b. Forward Underpower Mode – A
decrease in forward power flow that
is below the pick up value will cause
a trip.
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CAUTION: Proper CT polarity is important in
defining the direction of power flow. Refer to Figure
2-2 for proper connections.
32 # 1 & #2 Pickup – If the pickup is set positive,
the element is a forward power element. If the
pickup is set negative, the element is a reverse
power element.
32 #1 & #2 Delay – Power relays should be applied
with a time delay to prevent mis-operation
during power swing, heavy load pick up or heavy
load rejection conditions.