Protection History - Generations of Protection

Author: Walter Schossig, Germany

Passive and Active Semiconductors, Transmitters and Transistors

Passive and Active Semiconductors, Transmitters and Transistors

Since moving parts of electromechanical relays have been an uncertainty in protection devices, the tube (see last number of PACWorld) was the choice as a solid state control element. Unfortunately the lifetime of filament was limited- semiconductors (active and passive) should be the solution. Experiments with vacuum tubes have been dismissed in 1955, separate from some exceptions. Semiconductors promised a maximum of reliability. Developing the so called “static relays” produced mature solutions, complementing electromechanical relays. The transistor was invented by the US physicist William Bradford Shockley in 1948, who later received the Nobel prize award with Bardeen and Brattain. This was a revolution for the entire world as well as for the protection devices. It took 10 years before papers described their application for protection and another 10 years for the first series production of relays with transistors inside.

Electronic Timing Elements
Timing elements in electromechanical relays have been mechanical escapements with electromagnets, motors, cogwheels and springs. Staining as well as abrasion has been quite normal. Gumming occurred, synchromotor’s time subject to variations depending from grid’s frequency. Static relays used the behavior of a capacitance while loading, as well as logic operations utilizing monostable multivibrators and counters (Figure 2.) Connecting a voltage loads the capacitance CL (depending from the variable resistance RL) according to an exponential function until the trigger starts. Since the voltage UC does not have linear, behavior, the timing differs, even when the battery voltage UB stabilizes. The Bootstrap-(or Miller-) scheme linearizes the voltage (Figure 3.) To realize a delay, binary elements (Figure 4) has been used in the scheme. The main part is the multistable multivibrator S, used during the instable state the delay has reached. Connecting the voltage resets the count-up counter CT> (Figure 5). The pulses of the clock generator G are counted. The time delay can be set by varying the connection of the AND-gates to the counter. Such “counter schemes” started a new era to realize time grading.

When the transistor and its amplifying behavior was invented, they have been used as a switch. Good blocking capabilities and the small residual voltage in conducting state allowed doing so. Amplifiers with tubes have been known already but with transistors not even the small residual voltage was an advantage, also neither heating nor waiting for warm up was necessary. The element was more reliable, more compact and robust. Compared with magnetic amplifiers transistors do operate without mechanical inertia. But also some disadvantages have been observed: the residual current as well as the amplifying does depend from the temperature. Changing from germanium to silicon solved most of the issues (Figures 6 and 7.) Additionally, operational amplifiers have been used.

Auxiliary relays with transistors
The term “transistor relay” describes the application of single relays with transistors as well as transistor schemes taking over functionalities of relays. Transistors at auxiliary relays should improve relay’s behavior - for instance by decreasing driving power. A single transistor OC 604 (Telefunken) reduced the driving power of a common auxiliary relay RH100 (AEG) from 2W to 20 mW (Figure 8.) The relay’s auxiliary coil A is equipped with a diode D in parallel to protect the transistor from the dangerous turn-off voltage. AEG combined the small elements with their small housing in a housing called “RHG”.

Multistage Schemes
Trigger and impulse schemes offered new advantages. Figure 10 shows a “snap relay” with such a stage. From the two pre-stage transistors only T2 carries current as long as the input voltage is zero. T1 is blocked. If the voltage between 2 and 3 decreases, T1 takes over the current if the value of U1 is reached. T2 is blocked now. This operates the power transistor T3, and the relay A. Decreasing the input voltage U2 operates the flip-flop and T3 is blocked again. This scheme operates even in case of slightly changing voltages. Since U1/U2 > 1 the holding action is fine. With a driving power of less than 0.1 this is less than a telegraph relay. P changes the startup value between 1 and 6 V.

Transistor Time Relays
Also with transistors simple time relays can be realized with a delayed trigger (Figure 12). Connecting the voltage, the current Ic is carried by T1 , T2 is blocked. If Ic is smaller than the threshold, T2 takes over the current immediately and operates the relay. Such relays have been developed at first to substitute quicksilver control timer in recloser relays (AEG.)
At the end of the 1950s the first miniature elements and printed circuits with transistors became popular (Figure 11). Figures 9 and 13 show an example from the Soviet Union.

Electronic Measurement Elements
In an input circuit the measurement values are prepared utilizing measurement transformers, rectifiers, networks of resistances. The resulting voltage is connected to the flip flop. Figure 16 shows the main part of an overcurrent relay.

The electronic voltage measurement relay RUy (Figure 1) made by AEG in 1975 consists of a transistor-amplifier controlling an auxiliary relay H with high current contacts. The input of the amplifier is within the bridge circuit (resistances R1, R3 and R6 and the Zener diode D1 (Figure 17). The internal resistance is dimensioned in such manner (15Ω/V) that transistors Tr1 is positive against the base, Tr1 stays open. Tr2 is closed because of the voltage drop over R5. In case of voltage increase the potential between emitter and base of Tr1 changes in such manner, that Tr1 closes and Tr2 opens immediately- the output relay operates. In Zener diodes the value of breakdown voltage is defined exactly, which allows the usage as reference element in controller circuits.

Electronic Protection Relays
When the transistor relays became a part of recloser relays at AEG (RKU30, 1959) they started their protection career. The most important was immediate reaction and a long lifetime was expected. The very fast operation was used in earth fault relays as well –the electronic RERy was an example. The scheme (Figure 19) allowed short operating time and decreases the power consumption to 0.002 VA at nominal current. The “wrapped-around” measurement transformer could be small (W). It took a long time to implement full-electronic protection relays in Germany. The engineers in the US have been faster- the first distance relay made of transistors was presented in the 1950s.

W.C.Feaster, Edison Company and E.E.Scheneman, Westinghouse Company presented in 1956 an “Application of Transistors in Power-Line Carrier Relaying” (Figure 25).The tests started in July 1952 with Raytheon type transistors CK22, later in June 1952 the improved Westinghouse transistors WX-3347 and WX-4813 have been used. Figure 25 shows the front view of transmitter-receiver assembly and Figure 24 the receiver.

The use of transistors for phase comparison in distance protection was proposed by C. Adamson and L.M. Wedepohl (British Subject of The College of Technology in Manchester) in 1956 (Patent. GB 840711)-Figure 20. Dr. L.M.Wedepohl (the guru in PACWorld.Summer 2008) developed with GEC a transistor distance relay and transistor phase comparison power line carrier relays in 1962 - 1964.

The East German EAW developed a control system with transistors in 1962 - named Translog system (title picture & Figure 23). All electronic elements such as diodes, transistors, capacitances and resistances are on a printed card. The elements are within epoxy resin that makes them resistant against shocks. Encapsulated with a cap made of aluminum protects against dust. The supply voltage was ± 12 V.

All elements are equipped with pins to allow interchangeability. The Translog-System realizes OR- and AND-gates, flip flops as well as mulivibrators, RC-elements and amplifiers. Using these elements a directional earth fault relay (TRER) was presented in 1966 (Figure 23) and was widely used in compensated 110-kV-grids as transient earth fault protection.

Another typical application of transistors was in a control technique. Georg Neugebauer, he was with East German TSO Verbundnetz Berlin, developed an automated voltage controller with transistors in 1967. The device SR166 was produced by BRA Saalfeld (Figure 14). Figure 18 shows the measurement element. The Zener voltage is the reference voltage. In addition to the described elements, others have been used as well. BBC used thyristors in their overcurrent relay with instantaneous values measurement IHX103 (Figure 15, Figure 26) for the usage in 16⅔-Hz-railway grids. The reaction time was 0.6 ms.

The usage of a so called “Metrosil” (what is a non-linear resistor) M in an Out-of-step relay type FOS made by GEC is shown in Figures 22 and 31. The goal was a small drop-off/pick-up differential. The coil is fed through a bridge rectifier from a differential circuit in which the vector of the line voltage across two phases of the system is compared with that of the current drawn from the supply in the third phase. An auxiliary current transformer rated for either 1A or 5A is fitted with tap selection and is mounted with relay element and other components in one case. A Metrosil non-linear resistor, connected across the output terminals of the auxiliary CT serves to extend the operation zone of the relay and also to protect the rectifier from overvoltage which might otherwise arise from system faults.

Transductors offered new possibilities- the galvanic separation between control circuit and outputs. A sensitive “transductor- percent-relay” CF11 (Figure 27) was used in the Sokor line differential protection.
The advantage of these devices compared with electromechanical relays was shown in the field of thermal protection. A thermal replica of motor and generator windings was much easier to realize with the new devices. Figure 33 shows the implementation of inverse time overcurrent protection of AEG in the device RSZ2ay1. An application of transistors for inrush detection in the SIEMENS differential protection 7UT1 (1972) shows Figure 30.

Hall effect relays consider that certain semiconductors develop a transverse voltage in case of a surrounding magnetic field. This allows analog multiplication of tow values. The Hall elements have been very expensive, so the only applications known from the literature are in the Soviet Union and the US.

The same happened with the use of the Gauss-effect. Here semiconductors have been used, which changed their resistance in a magnetic field. Diodes, Zener-Diodes, Avalanche-Diodes, quadruple diodes, tunnel diodes, Unijunction-transistors as well as field effect -Transistors allowed in several combinations to realize static protection.

Development of electronic distance protection
The first electronic distance protection with transistors was realized by by Reyrolle & Co in Hebburn (UK) in 1956. 1961 VILLENKI (later VEIKI) from Hungary (Figure 28) and BBC followed. BBC presented a solution in 1962, also other companies as Maschinenfabrik Oerlikon (MFO) or Siemens developed distance protection.

The term “2-value-relays” was created because two electrical values have been connected to the inputs (currents, voltages or a combination of them). Transforming them with interposing transformers (Figure 32) the result is connected to a diodes-bridge (DC value with waves).
Control networks consisting of resistances, potentiometers, diodes etc. have been connected to a harmonics filter because the measurement part operates with DC values only.

By comparing the magnitudes of two measurement values the ratio Z = U/I could be calculated. To do this, the average values over at least half of a period have been compared. The measurement was realized with AD-converters. If the value of the voltage exceeds a certain value, the output voltage changes. The base circuits were Schmitt triggers (Figure 34.)

An electronic minimal impedance relay EUI was developed by MFO in 1965 (Figure 29). Its application was line and backup protection for generators.

When a new design of apparatus is to be produced in order to fill a recognized need, specifications are prepared to take the account of what is feasible in the present state of the art as well as what is thought desirable from a user’s standpoint. The designer adapts the known mechanisms and components and circuits, often inventing new ones where necessary, and correlates them to produce a device or a system to fulfill the specifications, then he tests the first completed product in the factory to check conformance with their specifications. A companion paper describes the means adopted and the results obtained in this work with reference to a new form of phase comparison relaying intended to provide greater sensitivity and less maintenance as its principal advantages over the superseded equipment.

This is how Horowitz,S.H.; McConnel,A.J. and Seeley,H.T. reported in AIEE about the application and test of transistorized phase-comparison relaying type SLD, CEYB and CEY, (GE) in an 138-kV-grid in 1960.
On the occasion of Swiss’ national exhibition in 1964 BBC presented a set of products applicable in 750 kV systems. One device was an electronic distance protection with operating times between 8 and 13 ms.

Further developments up to the fully static protection will be covered in the next issue of the magazine.

Let?s start with organization in protection testing