Instructional Literature
Page
94
Effective: May 2008
Instructions for the FP-6000 Protective Relay
For more information visit: www.eaton.com
IB02602004E
Calc:
Calculated reset, which is defined by ANSI C37.112. This setting
represents the electromechanical induction disk model and best
integrates in a system utilizing E/M relays.
T
reset
= (t
r
x D) / [(I/I
pu
)
2
– 1]
where t
r
is a curve constant and D is the time multiplier.
See Section 8 for more information.
Figure 19 provides a graphical representation of the three reset
characteristics. The rms current value is the bottom square wave
and assumes that the current level is either above or below the
pickup setting for a period of time. The three curves above the
current are the time values for the accumulator based on the
three reset characteristic settings. The Instantaneous reset
appears as a saw tooth and will not reach a trip time for this
example. The T Delay setting holds the time fixed at last value for
the specified reset time delay. This model will eventually
accumulate enough time and trip provided the current is not
below the pickup setting for a time greater than the reset time.
The calculated reset option emulates the electromechanical disc
action and will slowly reset over time to complete reset. This
model will also trip in time.
Figure 19. Graphical Representation of the TOC Reset T Setting.
Time t
1
, as shown, is less than the TOC Reset T time delay setting.
If t
1
was greater than the TOC Reset T time delay setting, then the
51/w Time Delay Reset curve above would reset to zero.
The direction setting enables the user to select the direction(s) of
current flow for which operation is permitted, forward, reverse or
both.
51P and 51P-2; pickup range (0.02 to 4.00 per unit)
These are the 51 device Phase Inverse Time Overcurrent pickup
and time multiplier settings. A proper coordination study should
be completed to determine the overcurrent pickup and time delay
settings prior to commissioning the FP-6000 relay. The pickup
setting (range: 0.1 to 4.0 per unit in 0.01 steps) is the overcurrent
value in per unit at which the FP-6000 starts to time out to trip. To
reference this setting to the Primary System Current simply
multiply this setting by the CT primary connected rating. For
example, if the CT is an 800/5 multi ratio CT connected at 600/5,
then a setting of 0.7 will represent a primary current pickup of 420
A (0.7 times 600). In terms of the relay current used for bench
testing, use the nominal current rating of the FP-6000 model,
which is either 5 A or 1 A. So for a 5 A version a setting of 0.7 will
require 3.5 A (0.7 times 5) relay current to operate.
To determine the pickup setting from the coordination study,
simply divide the primary current value that you want the relay to
trip at by the primary CT rating. For example, if you want the
relay to operate at 570 A; set it to 0.95 per unit (570 A divided by
600 A).
The time multiplier setting (range: 0.05 to 10.0) sets the time
portion of the TOC curve. Refer to Section 13 to view the Inverse
Time Overcurrent Curves. The ANSI and IEC curves and
multipliers are per their respective standards and definitions. The
current scale along the x-axis is in terms of multiples of pickup
(I/I
pu
).
For the thermal curves, the current scale along the x-axis is in
terms of I
nom
(or CT). The time multiplier is defined as the relay
trip time at a current value equal to 3 times (I
nom
) for phase and
1 times (I
nom
) for ground. The relay trip times are dependent on
the curve type selected. See Section 8 for curve equations and
application of the protective curves and time multipliers.
The Vrestraint, available on the 51P-2 TOC setting, restrains
operation which reduces pickup levels. This allows the user to
lower the pickup value of each phase time overcurrent in
relationship with the corresponding phase input voltage. The
Vrestraint on the 51P-1 TOC setting is reserved for future use.
When the minimum fault phase current is close to the load
current, it may make the phase time overcurrent protection
coordination difficult. In this case an undervoltage function may
be used to alleviate this situation. When the voltage is low, the
phase time overcurrent pickup threshold may be set low
accordingly, so that the phase time overcurrent protection may
achieve adequate sensitivity and better coordination. The
FP-6000 uses a simple linear model to determine the effective
pickup by characterizing the relationship between the voltage and
the phase time overcurrent pickup threshold.
Vmin = 0.25*Vmax;
P%min = 25%;
P% = 25%, if V <= Vmin;
P% = 1/Vmax*(V - Vmin) + 25%, if Vmin < V < Vmax;
P% = 100%, if V >= Vmax;
Where Vmax is less or equal to the phase to neutral
voltage for the wye connection or the phase to phase
voltage for the delta connection.
