Littelfuse T3500 Series - Manual

T3500 Frequency Deviation Relay
• Protection of generators from
frequency deviation on the grid
• Visual indication of power, ready,
pick-up and relay tripping
• Accepts high supply voltage
variations: 60 - 110%
• Cost effective and highly reliable
compact design
• 50 hours burn-in before final test
• Operating temperature range:
-20°C to +70°C
• Flame retardant enclosure
• DIN rail or screw mounting
Application
When generators are operating in
parallel with the grid (utility) it is
important to detect that the grid supply
is present. With the grid connected the
system frequency is very stable, but if
there is an interruption of the grid, a
frequency deviation will occur and this
will be detected by the T3500.
Thus the T3500 provides a good
protection to a generator, operating in
parallel with the grid, as the frequency
deviations can damage the generator as
well as the switchgear.
Function
The relay is a D frequency / D time
relay. The working principle of the unit
can be understood as a flywheel. This
means that the unit will adjust itself to
the frequency of the connected grid.
Slow changes in the grid frequency will
not cause the unit to trip, as the
flywheel will only adjust itself to the
new frequency. However a rapid change
in the frequency of 0.5 - 1.5 Hz/sec.,
which is adjustable on the front, will
cause the relay to trip.
When the supply voltage is connected
the output relay is energized and a
delay of 4 sec. is introduced in order to
allow for the measuring circuit to
adjust. The “ready” LED will indicate
and if the input frequency deviates
above the setting in either direction,
the “pick-up” LED will indicate, and
provided the frequency deviation
continues for more than 100 msec., the
output relay will de-energize and this
will be indicated on the “relay” LED.
The 100 msec. delay can be omitted by
bridging terminals 19 and 20 or it can
be reduced to 50 msec. by inserting a
resistor of 620 kΩ between terminals 19
and 20.
The output relay can not be energized
again until the unit has been reset by
disconnecting the supply or by using
the blocking input by connecting
terminals 18 and 19.
As long as the blocking input is present,
the unit will not make any
measurement. This function can be used
to make the unit inactive when the
circuit breaker is open and the
generator thus not operating in parallel
with the grid.
The blocking signal can be a signal from
the circuit breaker auxiliary contact,
present when the breaker is open. The
“ready” LED will be off as long as the
blocking signal is present.
When the blocking signal is cancelled a
delay of 4 sec. is again introduced. After
the delay the “ready” LED will come on
light, indicating that the unit is again
ready to make measurements.
Interconnecting terminals 5 and 6 will
perform a test of the unit by
introducing a phase shift. The phase
shift should cause the relay to trip.
Connection Diagram. Output relay normally energized. Relay shown de-energized.
TRIP
6
NO DELAY
BLOCKING
20
G
19
18
TEST
1
5
3
2
8
10
9
RESET
L 2
3
L
L 1
GRID