RFL 9300 RFL Electronics Inc.
October 29, 2001 2 - 10 (973) 334-3100
While the RFL 93B SV is initializing, the microcontroller’s internal timers of are programmed to generate a 2-kHz
clock (1980 Hz for a 3-terminal application). The phase controllers use this clock to synchronize their program
execution to the RFL 93B SV. In 3-terminal applications the supervisor phase locks the system clock to the line
frequency on the basis of error signals received from the phase controllers.
Once the RFL 93B SV has initialized, it establishes an interface with all the controllers at the local RFL 9300.
The RFL 93B SV interfaces to the display controller through an RS-485 serial link. It interfaces to all other con-
trollers through an 8-bit bi-directional data bus and a 10-bit control bus located on the system backplane.
First, the RFL 93B SV establishes the RS-485 interface with the display controller. Once this interface is estab-
lished the display controller will supply the transmit address of the communications channel. Two separate ad-
dresses are required if the relay is configured for 3-terminal operation.
The RFL 93B SV initiates contact with the RFL 93B CC by sending it the transmit address of the communica-
tions channel. This triggers a set initialization routine between the two controllers. During this routine, the RFL
93B SV receives verification that the RFL 93B CC has established communications with the correct remote sta-
tion, that both stations have the same configuration, and are measuring the same channel delay value.
Each phase controller will trigger an initialization sequence with the RFL 93B SV by passing its software ID
number. The supervisor will not complete the sequence until a valid channel delay value is available from the
communications controller.
All communications between the RFL 93B SV, RFL 93B CC, and all four RFL 93B PC phase controllers is
through a non-volatile static RAM "mailbox" on the RFL 93B SV. The RFL 93B SV controls all access to the
mailbox; the other controllers are granted access to the mailbox through a hardware-generated sequential se-
ries of interrupt signals. Each phase controller is allowed a maximum of 50 µs to read three bytes from and to
write three bytes to its mailbox locations. The RFL 93B SV has access to the memory for about 30 µs and then
grants access to the Communications Controller for the remainder of the 0.5-ms interval. The RFL 93B CC and
RFL 93B PC controllers will only have access to the mailbox when the interrupt signal received from the RFL
93B SV is low. Once this signal goes high, hardware control will isolate the controller from the mailbox. Since
the RFL 93B PC modules and the RFL 93B CC use a different language, messages originating at one must be
formatted by the supervisor before they can be passed to the other.
The RFL 93B SV supplies the received DTT trip signal to the Oscillography Board through a dedicated hard-
ware line. It also monitors the local RFL 9300 's DTT input port. The DTT input trip signals it detects are passed
to the Communications Controller for transmission to the remote RFL 9300. The DTT signal is described in de-
tail later in this section.
Breaker open/closed status is determined by the RFL 93B SV on the basis of a zero-true-current signal (ZTC)
received for each phase controller. A phase controller will send this signal to the supervisor if it has not detected
a CT current >1/8A peak for 40ms. A phase controller will not rescind its’ ZTC signal until a CT current >1/4A
peak is detected. If the RFL 9300 is configured for three-pole trip operation and is receiving a ZTC signal from
all four phase controllers it will issue an open breaker signal to all of them. If any one of the phase controllers
rescinds its ZTC signal the RFL 93B SV will signal all phase controllers that the breaker is closed. When the
RFL 9300 is configured for single-pole operation the open breaker condition is determined on a phase-by-phase
basis. Any phase controller sending a ZTC signal to the RFL 93B SV will wait to declare its breaker to be open
until the RFL 93B SV returns the open breaker signal.
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