RELAY DESCRIPTION
2. HARDWARE MODULES
The relay is based on a modular hardware design where each module performs a separate function within the relay operation. This section describes the functional operation of the various hardware modules.
2.1 Processor board
The relay is based around a TMS320VC33-150MHz (peak speed) floating point, 32-bit digital signal processor (DSP) operating at a clock frequency of 75MHz. This processor performs all of the calculations for the relay, including the protection functions, control of the data communication and user interfaces including the operation of the LCD, keypad and LEDs.
The processor board is located directly behind the relay’s front panel which allows the LCD and LEDs to be mounted on the processor board along with the front panel communication ports. These comprise the 9-pin D-connector for RS232 serial communications (e.g. using MiCOM S1 and Courier communications) and the 25-pin D-connector relay test port for parallel communication. All serial communication is handled using a two-channel 85C30 serial communications controller (SCC).
The memory provided on the main processor board is split into two categories, volatile and non-volatile: the volatile memory is fast access (zero wait state) SRAM which is used for the storage and execution of the processor software, and data storage as required during the processor’s calculations. The non-volatile memory is sub-divided into 3 groups: 2MB of flash memory for non-volatile storage of software code and text together with default settings, 256kB of battery backed-up SRAM for the storage of disturbance, event, fault and maintenance record data and 32kB of E2PROM memory for the storage of configuration data, including the present setting values.
2.2 Co-processor board
A second processor board is used in the relay for the processing of the distance protection algorithms. The processor used on the second board is the same as that used on the main processor board. The second processor board has provision for fast access (zero wait state) SRAM for use with both program and data memory storage. This memory can be accessed by the main processor board via the parallel bus, and this route is used at power-on to download the software for the second processor from the flash memory on the main processor board. Further communication between the two processor boards is achieved via interrupts and the shared SRAM. The serial bus carrying the sample data is also connected to the co-processor board, using the processor’s built-in serial port, as on the main processor board.
From software version B1.0, coprocessor board works at 150MHz.
2.3 Internal communication buses
The relay has two internal buses for the communication of data between different modules.
The main bus is a parallel link which is part of a 64-way ribbon cable. The ribbon cable carries the data and address bus signals in addition to control signals and all power supply lines. Operation of the bus is driven by the main processor board which operates as a master while all other modules within the relay are slaves.
The second bus is a serial link which is used exclusively for communicating the digital sample values from the input module to the main processor board. The DSP processor has a built-in serial port which is used to read the sample data from the serial bus. The serial bus is also carried on the 64-way ribbon cable.
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2.4 Input module
The input module provides the interface between the relay processor board and the analogue and digital signals coming into the relay. The input module consist of two PCBs;
the main input board and a transformer board. The P441, P442 and P444 relays provide three voltage inputs and four current inputs. They also provide an additional voltage input for the check sync function.
2.4.1 Transformer board
The transformer board holds up to four voltage transformers (VTs) and up to five current transformers (CTs). The current inputs will accept either 1A or 5A nominal current (menu and wiring options) and the nominal voltage input is 110V.
The transformers are used both to step-down the currents and voltages to levels appropriate to the relay’s electronic circuitry and to provide effective isolation between the relay and the power system. The connection arrangements of both the current and voltage transformer secondaries provide differential input signals to the main input board to reduce noise.
2.4.2 Input board
The main input board is shown as a block diagram in figure 2. It provides the circuitry for the digital input signals and the analogue-to-digital conversion for the analogue signals. Hence it takes the differential analogue signals from the CTs and VTs on the transformer board(s), converts these to digital samples and transmits the samples to the processor board via the serial data bus. On the input board the analogue signals are passed through an anti-alias filter before being multiplexed into a single analogue-to-digital converter chip. The A – D converter provides 16-bit resolution and a serial data stream output. The digital input signals are opto isolated on this board to prevent excessive voltages on these inputs causing damage to the relay's internal circuitry.
2.4.3 Universal opto isolated logic inputs
The P441, P442 and P444 relays are fitted with universal opto isolated logic inputs that can be programmed for the nominal battery voltage of the circuit of which they are a part. i.e.
thereby allowing different voltages for different circuits e.g. signalling, tripping. They nominally provide a Logic 1 or On value for Voltages ≥80% of the set voltage and a Logic 0 or Off value for the voltages ≤60% of the set voltage. This lower value eliminates fleeting pickups that may occur during a battery earth fault, when stray capacitance may present up to 50% of battery voltage across an input.
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CT CT
Buffer 16-bitADC
Sample control SerialInterface
16:1 Multiplexer Up to 5 current inputs
Serial sampledata bus
Parallel bus
Parallel bus
Trigger from processor board Anti-alias filtersUpto5Upto5Upto5 Diffntosingle
Diffntosingle LowpassfilterLowpassfilter VT VT
3/4 voltage inputs
Transformer board Input board
44 Diffntosingle
Diffntosingle LowpassfilterLowpassfilter
Calibration E²PROM Opticalisolator 8 digital inputs
Noisefilter Opticalisolator
P3027ENa
4
Buffer Noisefilter
FIGURE 2 - MAIN INPUT BOARD
The other function of the input board is to read the state of the signals present on the digital inputs and present this to the parallel data bus for processing. The input board holds 8 optical isolators for the connection of up to eight digital input signals. The opto-isolators are used with the digital signals for the same reason as the transformers with the analogue signals; to isolate the relay’s electronics from the power system environment. A 48V ‘field voltage’ supply is provided at the back of the relay for use in driving the digital opto-inputs.
The input board provides some hardware filtering of the digital signals to remove unwanted noise before buffering the signals for reading on the parallel data bus. Depending on the relay model, more than 8 digital input signals can be accepted by the relay. This is achieved by the use of an additional opto-board which contains the same provision for 8 isolated digital inputs as the main input board, but does not contain any of the circuits for analogue signals which are provided on the main input board.
Each input also has selectable filtering which can be utilised (available since version C2.0).
Duals optos are available since C2.0 (hysteresis value selectable between 2 ranges).
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The P440 series relays are fitted with universal opto isolated logic inputs that can be programmed for the nominal battery voltage of the circuit of which they are a part i.e. thereby allowing different voltages for different circuits e.g. signalling, tripping. From software version C2.x they can also be programmed as Standard 60% - 80% or 50% - 70% to satisfy different operating constraints.
Threshold levels are as follows:
Standard 60% - 80% 50% - 70%
Nominal battery voltage
(Vdc) No Operation (logic 0) Vdc
Operation (logic 1) Vdc
No Operation (logic 0) Vdc
Operation (logic 1) Vdc
24 / 27 <16.2 >19.2 <12.0 >16.8
30 / 34 <20.4 >24.0 <15.0 >21.0
48 / 54 <32.4 >38.4 <24.0 >33.6
110 / 125 <75.0 >88.0 <55.0 >77.0 220 / 250 <150.0 >176.0 <110 >154
This lower value eliminates fleeting pickups that may occur during a battery earth fault, when stray capacitance may present up to 50% of battery voltage across an input.
Each input also has selectable filtering which can be utilised. This allows use of a pre-set filter of ½ cycle which renders the input immune to induced noise on the wiring: although this method is secure it can be slow, particularly for intertripping. This can be improved by switching off the ½ cycle filter in which case one of the following methods to reduce ac noise should be considered. The first method is to use double pole switching on the input, the second is to use screened twisted cable on the input circuit.
2.5 Power supply module (including output relays)
The power supply module contains two PCBs, one for the power supply unit itself and the other for the output relays. The power supply board also contains the input and output hardware for the rear communication port which provides an RS485 communication interface.
2.5.1 Power supply board (including RS485 communication interface)
One of three different configurations of the power supply board can be fitted to the relay.
This will be specified at the time of order and depends on the nature of the supply voltage that will be connected to the relay. The three options are shown in table 1 below.
Nominal dc range Nominal ac range 24 – 48 V dc only
48 – 110 V 30 – 100 V rms 110 – 250 V 100 – 240 V rms TABLE 1 - POWER SUPPLY OPTIONS
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The output from all versions of the power supply module are used to provide isolated power supply rails to all of the other modules within the relay. Three voltage levels are used within the relay, 5.1V for all of the digital circuits, •16V for the analogue electronics, e.g. on the input board, and 22V for driving the output relay coils. All power supply voltages including the 0V earth line are distributed around the relay via the 64-way ribbon cable. One further voltage level is provided by the power supply board which is the field voltage of 48V. This is brought out to terminals on the back of the relay so that it can be used to drive the optically isolated digital inputs.
The two other functions provided by the power supply board are the RS485 communications interface and the watchdog contacts for the relay. The RS485 interface is used with the relay’s rear communication port to provide communication using one of either Courier, Modbus or IEC60870-5-103 protocols. The RS485 hardware supports half-duplex communication and provides optical isolation of the serial data being transmitted and received.
All internal communication of data from the power supply board is conducted via the output relay board which is connected to the parallel bus.
The watchdog facility provides two output relay contacts, one normally open and one normally closed which are driven by the processor board. These are provided to give an indication that the relay is in a healthy state.
2.5.2 Output relay board
The output relay board holds seven relays, three with normally open contacts and four with changeover contacts. The relays are driven from the 22V power supply line. The relays’ state is written to or read from using the parallel data bus. Depending on the relay model seven additional output contacts may be provided, through the use of up to three extra relay boards.
Since version D1.X: ‘High break’ output relay boards consisting of four normally open output contacts are available as an option.
2.6 IRIG-B board (P442 and P444 only)
The IRIG-B board is an order option which can be fitted to provide an accurate timing reference for the relay. This can be used wherever an IRIG-B signal is available. The IRIG-B signal is connected to the board via a BNC connector on the back of the relay. The timing information is used to synchronise the relay’s internal real-time clock to an accuracy of 1ms.
The internal clock is then used for the time tagging of the event, fault maintenance and disturbance records.
The IRIG-B board can also be specified with a fibre optic transmitter/receiver which can be used for the rear communication port instead of the RS485 electrical connection (IEC60870 only).
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2.7 2nd rear communications board
For relays with Courier, Modbus, IEC60870-5-103 or DNP3 protocol on the first rear communications port there is the hardware option of a second rear communications port,which will run the Courier language. This can be used over one of three physical links:
twisted pair K-Bus (non polarity sensitive), twisted pair EIA(RS)485 (connection polarity sensitive) or EIA(RS)232.
The second rear comms board and IRIG-B board are mutually exclusive since they use the same hardware slot. For this reason two versions of second rear comms board are available;
one with an IRIG-B input and one without. The physical layout of the second rear comms board is shown in Figure 3.
P2083ENa
Language:
Courier always
Physical links:
EIA 232 or
EIA 485 (polarity sensitive) or
K-Bus (non polarity sensitive) SK5
SK4
Physical links are s/w selectable Optional IRIG-B
Courier Port (EIA232/EIA485)
Not used (EIA232)
FIGURE 3 - REAR COMMS. PORT 2.8 Ethernet board
The ethernet board, presently only available for UCA2 communication variant relays, supports network connections of the following type:
− 10BASE-T
− 10BASE-FL
− 100BASE-TX
− 100BASE-FX
For all copper based network connections an RJ45 style connector is supported. 10Mbit/s fibre network connections use an ST style connector while 100Mbit/s connections use the SC style fibre connection. An extra processor, a Motorola PPC, and memory block is fitted to the ethernet card that is responsible for running all the network related functions such as TCP/IP/OSI as supplied by VxWorks and the UCA2/MMS server as supplied by Sisco inc.
The extra memory block also holds the UCA2 data model supported by the relay.
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2.9 Mechanical layout
The case materials of the relay are constructed from pre-finished steel which has a conductive covering of aluminium and zinc. This provides good earthing at all joints giving a low impedance path to earth which is essential for performance in the presence of external noise. The boards and modules use a multi-point earthing strategy to improve the immunity to external noise and minimise the effect of circuit noise. Ground planes are used on boards to reduce impedance paths and spring clips are used to ground the module metalwork.
Heavy duty terminal blocks are used at the rear of the relay for the current and voltage signal connections. Medium duty terminal blocks are used for the digital logic input signals, the output relay contacts, the power supply and the rear communication port. A BNC connector is used for the optional IRIG-B signal. 9-pin and 25-pin female D-connectors are used at the front of the relay for data communication.
Inside the relay the PCBs plug into the connector blocks at the rear, and can be removed from the front of the relay only. The connector blocks to the relay’s CT inputs are provided with internal shorting links inside the relay which will automatically short the current transformer circuits before they are broken when the board is removed.
The front panel consists of a membrane keypad with tactile dome keys, an LCD and 12 LEDs mounted on an aluminium backing plate.
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