Protection History

Authors: Walter Schossig, Germany, and Thomas Schossig, OMICRON electronics GmbH, Austria

Testing Relays in the 1930s

To make mounting onsite easy and because of standardization and unification of assets, sheets have been produced. One example is this produced by A.-G. Brown, Boveri & Cie in 1930 (Figure 1).

All apparatus of a line feeder are fixed there. The connection cables are mounted and connected to the plugs. Only the connections to measurement transformers and tripping the circuit breaker must be realized on site.

To test such relays BBC developed an own testing apparatus shown in Figure 2.

After opening the black plate in the middle, the test set can be connected (see title picture). The schematic in the cap delivers a guideline. The information there is as follows:

1 = Plugs in operation

2 = short circuit for current transformers

3 = disconnecting the relay sheet from power

4 = connecting the test set.

Table 1 shows the technical details and Figure 3 the opened device.  Figure 4 shows the operation panel.

To adapt the voltage to the local one (110, 220 or 380 V) the switch 3 is used. The infeed source can be connected directly as well, normally the connection to voltage transformer of line is used. So, connecting the test set means just preparing the test plugs and connecting the multiple plug. During the test switch 2 is used. Pressing main switch 1 the different faults can be chosen. Eleven different positions are possible.

Position 0 = test set is without voltage

Position 1 = normal operation.

The relays receive 110 V and 5 A and stay silent. Position 1 checks the test sets as well as the auxiliary power. Pressing switch number 1 combined with switch 6 makes it possible to test the different phases. Position 2 causes a three-phase short circuit. The relay indicates the same time for all phases, the Ohm meter can be tested.  All claps (most common there was one relay per phase) all falling at the same time- so everything works properly.

Position 3 to 5 cause a 2-phase short circuit in cyclic order. The relays will again show the same time, additionally signal lamp 7 indicates proper functionality of tripping circuit. For isolated star points positions 6 to 8 are used. Double earth faults in cyclic order can be checked as described already. If the neutral is grounded, single phase short circuits with earth could be tested. The apparatus is calibrated in that manner, that positions 2 to 5 with 99% tap of calibration transformer 2 seconds are indicated by the relay. The tap is defined by length of line and will differ for every feeder. If the tap is kept, the resulting value can be drawn into a diagram.  In positions 6 to 11 the operating time of the relays is approximately half of the time in the other positions. The scheme is visualized in 5. The choke coil 4 work as line impedances. For maintenance purposes the apparatus can be taken out of the wooden housing. For transport two bags made of leather are mounted on the housing. For convenience, a carrier was available.

At the same time (in 1930) S&H produced a portable relay testing set. (see Figure 5, Figure 6, Figure 8, Figure 10, Figure 11). The combination of raw and fine tuning allowed seamless definition of voltages and currents. (Table 2).

Also, AEG produced portable, as well as non-portable devices in 1931. For simple tests, portable devices (“suitcases”) have been produced (Figure 7). Such devices contain rheostats for controlling voltage (0-230 V) and current (2-15 A); measurement equipment and clock. The suitcases could be adapted for different applications.

Figure 9 shows the portable relay test set RP1, produced by S & H in 1931. The auxiliary device RPZ1 allowed tripping currents up to 2000 A (Table 3).

For testing timed overcurrent, voltage and impedance protection S&H produced in 1932 the portable test set SRP1. They called it “test box” (Prüfkasten).  A plug connection made testing in operation possible (Figure 14 and table 4).  To test the directional elements and the phase shift between voltage and currents a star delta combination was used (see Figure 12).

Dr. Paul Meyer A.-G. and S&H produced phase transformers in 1930 (Figure 15 and table 5). They allowed phase shift of 180 degrees into both directions. It consists of stator with 3-phase-winding and a rotor, also with 3 phases. The stator could be moved via handle, for the fine tuning a handle valve was available. A scale displayed the resulting value. To adjust zero there was a moveable pointer. The phase transformers have on the secondary as well the primary 6 connection plugs. So, they can be changed from star connection to delta.

Also, SIEMENS came with a small portable test set for currents up tp 40 A (1936, Figure 16 and table 6)

The main part is a controllable transformer with ring core within portable housing. The primary and the secondary winding are separated, the secondary is on the primary. To allow fine tuning there is a sliding area where the current contacts are connected to. The primary winding is designed for 110 and 220 V. The secondary is made for 20 V and carries permanent current of up to 40 A (= 800 VA). For a short time 100 A are allowed. To achieve higher currents, additional transformers have been used. Those transformers connected in series made the voltage from 20 to 8 V and allowed current of 100 A. Connected in parallel the voltage changed from 20 to 4V and delivered 200 A. Bigger designs allowed even 200, 400 or 800 A. With another additional transformer, up to 2000 A have been possible. To measure the time, a special clock measuring the seconds was use (Figure 17).

To measure the time the 50 Hz period was used. A small synchro motor counts. 2 scales visualized the tenth seconds and seconds. The accuracy was very good, because the error of the motor was just 0.02 seconds. The current consumption was just 0.04 A.

In AIEE an electronic timing meter (Figure 18) was proposed in 1936. It was designed for testing high speed relays. It measured down to millisecond, and hence was very much better than existing synchronous timers and easier to use than an oscillograph. Since there have been several miscellaneous electronic applications to relays, mostly about the war effort; but in general, during the 10 years before, there have been a few cases where it was felt that an electronic relay would do a better job than an electromagnetic relay.

BBC presented a new testing device for main current relays HB4 and HK4 in 1938 (Figure 19).

In the same year, S&H presented the RP2 with RPZ2 (Figure 20 and table 7).

The application of resistances to measure big AC currents is neither handsome, nor economic. That’s why in most of the cases inductive controllers are used. They are autotransformers with taps. The resistance is small, so there will be no heat and the control can be done with almost no losses. Figure 21 and table 8 show the test set REW2 (1939) with built in measurement transformer.`     

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