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The blocks of terminals situated on the rear of the case are identified with the letters A, B, C and D, and
optionally E and F, as shown in figure 9. In addition, each terminal is identified with a number.
The communications connectors are situated on left-hand side of the front and on the right-hand side of the
rear of the case. The front port is labeled as PORT 1 and the rear ports as PORT 2 and PORT3. The IRIG-B
connection is made using a block of two additional terminals.
5.2. OPERATING THEORY
The SMOR unit measures voltage and current signals, carries out complex calculations using internal data,
stores relevant events, activates trip relays and generates information which can be used to determine the
status of the power system to which it is connected. The functionality of the SMOR can be divided into the
following sections :
- Magnetic module
- CPU board
- Power supply
- Keyboard and display
The magnetic module carries out two essential functions : galvanic insulation and scaling analog input
signals. In the case of voltage transformers it scales the input voltage so that internally the unit works with
voltages which are greatly below the input voltages. In the case of current transformers the input current for
the primary winding is converted into a scaled voltage in the secondary winding of the transformer. Each
voltage and current transformer must be linear in the whole measurement range of the relay. The voltages
supplied by the input transformers are applied directly to the CPU signal processing board.
The SMOR uses two 16-bit microprocessors operating at a clock frequency of 20 MHz. One of these
microprocessors is used to carry out relay communications and the other to carry out the calculations which
are necessary for the protection functions. The microprocessor chosen is designed to carry out input and
output calculations and operations at very high speed. The use of two microprocessors is especially
recommendable so as to make the protection and communication functions totally independent of each other
inside the unit itself, and thereby increase the reliability of the system.
The analogue-digital converter converts the voltage inputs into their digital equivalent with a resolution of 10
bits.
The unit's code is stored in non-volatile EPROM memory while the settings and events are stored in non-
volatile EEPROM memory. The data related to the oscillography is stored in RAM memory which is
maintained using a capacitor, thus avoiding the loss of information when the unit is disconnected.
A high resolution real time clock is used to time-tag the events and ensure an appropriate post-fault analysis
can be done, with a resolution of one millisecond. This clock can be synchronized externally using an IRIG-B
type input.
The input and output functions are divided between the two microprocessors. The serial ports, the keyboard
and the display are controlled by the communications microprocessor. External communications are
processed by a serial communications controller circuit which contains a universal asynchronous transceiver
(DUART). The digital inputs and outputs are processed by the protection microprocessor.
The SMOR contains 6 independent circuits to process digital inputs. These circuits check the presence or
absence of input voltage and are designed to insulate them electrically from the microprocessor, thus
increasing the reliability of the system.
GEK-105593C
44
5.2.1. MAGNETIC MODULE
5.2.2. CPU BOARD
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