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Current sensing is provided by three current transformers
located in the recloser and interfaced to the Form 5 control
via the control cable. This cable also supplies Trip, Close,
and Recloser status, and connects to the Recloser Inter-
face (RIF) module to provide isolation for reliable opera-
tion. Voltages for metering are also connected to the RIF
module via the connector terminal block, TB-1 (Figure 3).
A functional block diagram of the Form 5 control is shown
in Figure 3. Line current flowing through the recloser is
converted by the CPU module to a digital signal suitable
for metering and fault current calculations. Data sampling
occurs at a rate 32 times per cycle. The CPU contains a
data acquisition section that uses the acquired samples to
compute the fundamental currents and voltage for use in
overcurrent, under/over voltage and under/over frequency
protection, as well as currents and voltages for metering
functions. The current for overcurrent protection is calcu-
lated on a sub-cycle basis; it includes only the fundamen-
tal and DC component. For metering, the fundamental and
harmonic current and voltages are determined.
When the phase or ground current exceeds its pro-
grammed minimum-trip value and associated time-cur-
rent curve (TCC) timing, the control initiates the
programmed sequence of recloser tripping and reclosing
operations via the CPU and RIF modules. If the fault is
temporary, the control ceases to command recloser oper-
ations after a successful reclose, and the control resets to
the start of its operating sequence after a preset time
delay. If the fault is permanent, the control performs its
complete programmed sequence of reclose commands
and locks out with the recloser open. Once locked out, the
control must be closed via the operator panel or SCADA
communications. This resets the control to the start of the
operating sequence.
The following chain of events occurs for an operating
sequence of two trips to lockout:
1. The overcurrent signal is integrated with time on the
selected curve for the first trip operation (TCC1) to
produce the signal which energizes the trip circuit.
2. Energizing the trip circuit connects the battery and
capacitor to the trip solenoid to open the recloser.
3. Upon opening, the control starts timing on the first
reclosing interval-delay time.
4. Upon expiration of this reclosing interval-delay, a clos-
ing signal is issued from the control, closing the
recloser and selecting the time-current characteristics
for the second trip operation (TCC2).
5. If current remains above the minimum-trip level, the
tripping and reclosing sequence is repeated.
6. The control begins the reset-delay timer if the over-
current is cleared before the operating sequence
reaches lockout indicated by a closed recloser and
current below minimum trip.
7. When the reset-delay times out, the control is reset to
the home state and is ready for another programmed
operating sequence. If current rises above minimum
trip prior to the reset-delay timing out, the timer is
halted and the control resumes the operating
sequence while the accumulated reset-delay timing is
restarted.
S280-79-10
5
!
SAFETY
FOR LIFE
Figure 3.
Form 5 control operational flow diagram.
FORM 5 CONTROL DESCRIPTION
BATTERY
TRIP SOLENOID
CLOSE SOLENOID
A Ø CT
B Ø CT
C Ø CT
OPEN / CLOSE
SWITCHES
CT COMMON
RECLOSER
RIF
OPTICAL
ISOLATION
OPTICAL
ISOLATION
OPTICAL
ISOLATION
OPTICAL
ISOLATION
MATCHING
TRANSFORMERS
AND SIGNAL
CONDITIONING
TB1 TERMINAL BLOCK
CUSTOMER P.T. INPUTS
POWER SUPPLY
CPU
RS232
Or
FIBER-OPTIC
PORT
RS232
Or
FIBER-OPTIC
PCB
OPTIONS
OPERATOR'S
PANEL
KEYBOARD
LED's
LCD
RS232 PORT
DIF#1
(OPTIONAL)
DIF#2
(OPTIONAL)
USER
CONNECTIONS
6 unlatched outputs
6 latched outputs
12 inputs
12
12
USER
CONNECTIONS
6 unlatched outputs
6 latched outputs
12 inputs
12
12