Protection History

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

Relay Testing in 1940s

In the middle of the last century testing was kept simple. A controllable voltage source, current source, voltage- and current measurements and a clock have been sufficient. For testing current relays and primary tripping devices test sets have been in use. They could be connected to the 220 V battery in the substation. A current transformer was built in to deliver high currents at low voltages on the secondary side.

To control the current slide resistances have been used or additional tapped resistors. Another possibility has been ring transformers as current transformers. The outer windings have been blank and so a connection via carbon crush was possible. Secondary relays for 5 A or 1 A could be tested when an additional resistance was connected.

Since -depending from the setting- currents between 5 A and 10 A have been possible, the power consumption could reach 1…2 kW at 200 V.  So, the series resistor must have been powerful. Also, voltage relays could be tested with slide resistances (Figure 1). In that case the resistance will be used as voltage divider, relays and measurement device could be connected in parallel.

The weight was 2 kg. If voltage relays for 220 V must be tested, the resistance must be specified for 380 V.

To measure, portable devices have been used (Figure 2). Moving iron instruments for the voltage and currents, for the power electrodynamic measuring elements without iron have been used. To guarantee operation also in case of other magnetic fields, static galvanometers have been common. So, measurements also close to generators and transformers were possible.

For the pointers toe bearing was used. The peaks made of steel have been polished.  The mounting was made of diamond. Everything had to be handled quite carefully, because it was very sensitive.

Doing so, the accuracy reached was ±0.1 %. The instruments must be operated horizontally. To make reading the values easy the scales contained mirrors and the pointers have been quite thin (Figure 2). To make interpretation of results easy, the scales came with different labels or scales. Also, the measurement values have been arranged considering scaling factors and resistances.

Figure 3 shows the suitcase ready to be used for testing. It contains voltage, current and power-measurement-devices.  Additionally, the resistances can be seen. This suitcase was produced in 1940 by S&H. Stable design with bail and attachable legs made the usage as desk possible. (See Table 1).

A case was used for the transport of 10-Ohm-resistance (class 0.2) with 6 auxiliary resistances and one series resistance. The weight was 4.5 kg, (Figure 4).

Portable winding type transformers have been used to measure high currents. They offered a wide range of opportunities and came with small weight. The clips on the primary side have been used to switch between the different currents up to 150 A. For higher currents the cable had to be moved several times through the transformer’s opening (Figure 5). (See Table 2).

The portable test set REK came as a suitcase by AEG in 1933 (Figure 6).

It was developed for secondary testing of voltage and current relays. Also 1-phase-testing of distance relays was possible- if the phase shift between current and voltage was not needed. The current was taken directly from the low voltage grid. The control was again by resistance. The current measurement was possible for AC and DC between 0…10 A or 0…20 A. The testing voltage could be used on voltage dividers. Additionally, the device was equipped with seconds counter, even automated measurment was already possible. (See Table 3).

A portable high current resistances have been also used to generate high currents at low voltage. The variant ERJ, S&H, (Figure 7) came with wheels, handle and cover. The raw control was possible with step switches, the fine tuning with resistance and knob.

The range was between 0.025 A and maximum 500 A at 6 V. Short term overload was possible by 20%. (See Table 4).

To allow continuous control at low consumption special ring core transformers have been used ( Figure 8, Figure 9), (See Table 5).

A three-phase portable ring core transformer 3RRf10 by S&H is shown in Figure 10.

The secondary voltage U2 can be taken between the ends of secondary winding V and U via special coal rolls and the raw control arm a. To this voltage an additional voltage is added- controlled by fine control b.

The figure on page 70 shows the portable device ER3 with additional ERZ3 as produced by S&H in 1941. This device made very fine control without any interruption possible.

Small voltages between 0 and 20 V at high currents made testing overcurrent relays, fuses and releases possible. It was used in laboratories as well as on-site. As the others, it consisted of ring core transformers for secondary voltages between 0...20 V at max. 100 A.

Additionally, devices delivered at 4V or 2V between 500 A and 1000 A. A time measurement device could be connected. (See Table 6).

H&B produced the Multavi II in 1943 (Figure 12a and 12b). This was a universal measurement device.

Utilizing the knob under the window, the scale could be set to zero with a screwdriver.

For connection, the screw nuts could be used, banana plugs could be put in. So, voltage and current could be measured at the same time and several measurements have been realized quite fast. Switching from current to voltage brought a short circuit between “+” and “A”.

Doing so, the Multavi could stay connected the entire time. (Figure 11).

There was no need for special handling of Multavi. In case of frequent use, it was recommended to open the back once per year and to grease the contacts with Vaseline.

The dimensions have been 180x90x60 mm3 the weight  was 1.10 kg.               

To record transient events, S&H released in 1942 a portable oscilloscope. (Figures 13 and 14).

The dimensions were 310 x 130 x 130 mm3 with a weight of 6 kg. 

The Metropolitan-Vickers Electrical Co. Ltd., MV, Manchester (UK) presented their Portable Relay-Testing Set “TESTLAY” for primary and secondary injection for current up to 1000 A and for secondary injection for current up to 30A in 1949.

M. Kaufmann was with this company and worked as a part-time lecturer in protection systems at the college of technology on Manchester. His “Protective Gear Book” was first published in 1945 and several times reprinted until the 1960s. He explained secondary injection testing for the diverse types of relays.

For overcurrent and earth-fault relays he recommended a small power transformer suitably rated to give up to about 30 amperes through the impedance represented by the standard overcurrent or earth-fault relays, control of the current being effected by means of variable resistance in series with the secondary (low-voltage) winding (Figures 16 and 17).

For higher currents MV called the device “TESTLAY” (Figure 15). This was also available as small device (Figure18). Time interval meters measured the time and could be connected to the test set directly (Figure 19).

Split plugs made the connection easy (Figure 21.)  For distance protection and general purpose testing a device such as the one in Figure 20 was used.

Figure 22 shows the connection diagram to this test set.

Relays used in pilot-wire differential systems can be tested by secondary injection in one form or another.

It is preferable to extend the scope of the tests whenever possible to include the pilot wires or, in other words, to include stability tests by secondary injection. The feeder under test does not need to be deenergized and can even remain on load.  See Tables 7, 8 and 9.

Type HCB pilot wire relays have been common at this time. Figure 23 shows the scheme proposed to determine the characteristic curve for external faults.

Also, percentage differential relays, negative sequence filters and other new ideas have been taken into account.     

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