Protection History

Author: Walter Schossig, Germany

Digital Relays Continued

The Development From 8 to 32 bit Microprocessors in Digital Relays

In the last issues we covered the first digital relays and their predecessors.

For digital relays in the 1980s 8-bit-microprocessors have been used. For the setup a serial interface on the front of the relay was used with setup-terminals in the first years and later with laptops (Figure1). Keypad terminals have also been used to change single parameters (Figure 4).

To setup distance protection 7SA500 SIEMENS introduced the software DIGSI in 1987.

One of the first digital protection series was ELIN's DRS (Digital Relay System). Built in modular design in 19" racks the protection functions could be combined for generator protection (with block transformer, motor and line protection). The connection to PC was also realized with an RS232 interface on the front. Measurement transformers have been connected to the rear. The optional communication interface according to DIN 19244 could be connected to the SCADA system. Even remote setup was already possible (Figure 3, Figure 6).

Introduction of Local Control

The local control consisting of display and keys allowed to observe the device and setup the protection parameters. All values could be read out and the settings could be changed. To access the fault records (transient values) and real time assessment was not possible at the beginning.

The requirements for safe and reliable operation of protection devices have been defined in a cooperation of specialists from vendors and users in the utilities.        

Protection and Control Come Together

The first discussions about digital control systems took place at the German VDEW in 1982 and the input of the users was considered. The working group "Integrated control in substations" was founded in 1984. The recommendation of this group was published in 1988 ("Integrated control in substations"), the VDEW recommendation "Digital control in substations" came out in 1994. The goal was the standardization of the interfaces of protection and control to achieve compatibility between different vendors. The already mentioned DIN 19244 standardized the protocol for the first time. It was the predecessor of IEC 60870 and later the IEC 61850. The history of control will be covered later.

ASEA's first overcurrent relay with microprocessor came out 1984 - the RACID (Figure 5). In the same year BBC released first comparison protection for transmission lines, while SIEMENS presented the 7SJ50 (Figure2).

To use multiple processors with a common bus for exchange of information was an advantage for complex protection tasks. An AEG's distance protection SD36 (used in medium voltage grids since 1985) had data acquisition, calculation and operation distributed on 8-bit-µPs. An example for busbar protection is shown in Figure 11. An example of a circuit board for numerical relay (AEG) is shown in Figure 9.

An example with 16-bit-µP is BBC's MCX913 (motor protection) and MODURES 216 (digital generator protection). Equipped with Intel's 80186 (10 MHz) they have been released in 1987.

At the end of the 1980s BBC/ABB produced numerical generator protection REG100, 110, 216, and 316 (Modures series). REG216 had 36 analog inputs and it realized (59N) (64) (87G) (87T) (50/51) (49) (64R) (59) (27) (81) (32) (46) (59) (59R) and (51/27) protection. (Figure 10, Figure 19).

Jörg Strobl (ELIN) developed the frequency relay MF with a µP (Figure 8) in 1987.

1987 was also the year when Elmore, W. A. and Kramer, C. A. (Westinghouse) presented an 8-but-µP "complete motor protection by microprocessor relay" MPR (Figure 13). Figure 7 shows the block diagram.

SIEMENS' first digital busbar protection for 100 kV was put into operation in 1988. In the substation Eichtersheim (Badenwerk) distance protection 7SA501 was delivered for the first time as well as a protection data concentrator (Figure 22).

Toshiba presented in 1986 the second generation numerical relay (D2).  Since then, numerical relays have been developed to satisfy all types of application. In 1989 the world's first microprocessor-based substation automation system was applied to a 275 kV substation. In 1993 the third generation numerical relay (D3) came out.

SIEMENS 7SJ52 (overcurrent) is shown in Figure 14- analyzed by my grandson Jonathan.

SEL's first microprocessor based feeder overcurrent and voltage relay- SEL-151, was released in 1990. It came with multi-shot reclosing, multiple settings groups, fault location, and user programmable logic. One year later SEL-251 (Figure 16) followed- the first distribution protection relay with current, voltage, ground protection elements, multi-shot reclosing, multiple settings groups, fault location, transformer high side blown fuse detection, and user programmable logic.

SEL's first line distance relay with multiple settings groups, password protection, oscillographic event reports, multiple MHO and quadrilateral zones, and user programmable logic, communications assisted tripping logic, and single pole tripping could be presented in 1992 - SEL-321 (Figure 17).

ABB produced the microprocessor based distance relay system MDAR (REL300) in 1988, REL350 (first microprocessor based segregated phase comparison relay) followed in 1991.

Since 1989 full digital protection relays with 16-bit-µP have been available.

Utilizing the 16-bit-processors the calculation power for single processor solutions realizing overcurrent and differential protection was available. For more complex tasks (distance, busbar) multiprocessor solutions have been used.

The new series of protection devices with improved measurement algorithms and communication interfaces could be integrated in centralized operation schemes.

Figure 15 shows a multiprocessor distance protection solution presented by AEG in 1990. Measurement and calculation as well as operation have been segregated. The slave equipped with own 16-bit-µP, analog-digital converter and input and output ports was responsible for signal processing. The master, with another 16-bit-µP was responsible for protection calculations and operation. The data exchange was possible with a powerful bus system.

For setup purposes a PC software was available (FPC).

Numerical differential protection 7UT512 (SIEMENS) was already available in 1989, as well as the three-winding variant 7UT513. 7SS50 was the new busbar protection.

Busbar protection for the first time in digital could be realized by ABB in Mannheim in 1989. The numerical fault recorder REOR100 was available in this year as well.

Reyrolle's product line DUOBIAS was also presented in 1989 (Figure 12). Transient earth fault protection was possible with AEG's PD551 - realized in 1990 (Figure 18, Figure 20).

An example for generator protection was SIEMENS 7UM51 in 1990 (Figure 24).

Basler's relays have been ground directional overcurrent Relay BE1-67N and multiplex reclosing relay BE1-79M (1992).  One year later time overcurrent relay BE1-50/51 and synch-check reclosing relay BE1-25/79TR (Figure 26) were presented.

The BE1-25/79TR relay integrated all the components of a reclosing system into one compact microprocessor package. It was designed for use on transmission systems, utility interties and distribution systems with cogeneration.

Westinghouse's digital frequency relay MDF-1 and MDF-2 have been produced in 1991. Also numerical transmission line distance relay MDST (REL301) was introduced.

When ABB was formed, 316LZ became REL316 and the transformer protection RET316 was also available. The first substation with digital protection in the eastern part of the reunited Germany was UW Bleicherode (110-/20-kV, ENAG) with ABB protection in 1991 (Figure 25).

AEG extended the product range in 1993 with distance protection (PD571), overcurrent (PM421 and PM431) and auto recloser (PK341). In 1994 new versions PS441 (overcurrent) and PD571 (digital protection for high voltage) could be presented (Figure 28, Figure 29).

GEC ALSTHOM in Stafford developed a distance relay with microprocessor and free programmable matrix in 1980- the Micromho. 5 year later a new and improved version was available- the Quadromho, especially designed for medium voltage application. Two phase comparators and a wide range of functions allowed wide usage with advanced reliability and performance. Optimho- with µPs used for impedance measurement replaced the previously used phase comparison. In 1995 the distance protection LFZR was presented. The first digital generator protection LGPG was available already in 1994 (Figure 30).

Distance protection EPAC 3000, presented by GEC ALSTHOM in 1995, operated with classical algorithms and additional fast algorithms to evaluate the values before and during disturbance (Figure 31).

Chinese SIFANG produced digital line protection CSL200A and CSL160A since 1994, transformer protection CST200A and distribution automation system CSC2000, SIFANG have been available as well (FIGURE 27).

Hungarian Protecta presented a numerical event recorder applied in a dedicated equipment for busbar protection in 1994 (FIGURE 23).

In 1994 also Reyrolle's ARGUS product line was available.

Also in Poland digital protection was produced in 1997- Computers and Control presented distance protection ZCS4 with 16-bit-µP. Application was high voltage.

The pictures on page 70 shows the different sizes of the devices- electromechanical, static and as an example SIEMENS series from the early 1990s.

Later in the 90s 32-bit-µP became available. The new possibilities will be described in the next issue.     

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