Protection History

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

Relay Testing - Test Sets and Testing Technology in the 1950s

The development of test sets since the 1920s was covered within the last issue of the magazine. After World War II the developments by the vendors were restarting.
When the cold war began, the established vendors were not available anymore in the communist countries, so own developments began. Some of these developments were done at distribution and transmission system operators at this time.

ZERA (DE) produced the mobile relay test device R1 in 1950 (Figure 1). This allowed testing of primary tripping devices with nominal values of up to 2000 A (doubled). To test measurement transformers, high current meters and secondary relays it was necessary to deliver the current continuously and to control it. In a high power current regulator, current transformer and measurement transformer could be united (Figure 2). The housing was made of metal and quite stable. Handle and rolls allowed the transport of the unit - the weight was 175 kg (Table 1).

 In France Compagnie des Computers, CdC, produced a special testing generator, especially used for phase shifting. The BJY1 (Figures 3 and 4) was 250 mm wide.
Schlumberger/CdC in 1952 came with the test equipment DLF110 (Figure 7). Combined with transformer TA 110 (Figure 5) it could be used especially for testing distance relays. The dimensions of DLF110 were 580 and 250 mm.

Also, BBC produced testing devices. It was a compact device released in 1950 and relaunched in 1958. It was portable and designed especially for high-speed distance-relays. The distance relays recognized 2 and 3 phase faults. The fault location can be defined between a wide range and finely tuned. The test set comes with 2 plugs to connect the time measuring device. This makes the measurement of the time grading possible. The power consumption is rather low. This makes the utilization of the voltage transformers possible. Figure 6 shows the device made in 1950, the 1958 device is shown in Figure 8.

The testing apparatus BB was used for routine testing of distance relays L1, L2, L4 and L6. An application for secondary voltage and current relays was possible with restrictions. (Figures 8/9).
There have been 2 variants- one with 110 V AC and one with 220 V AC nominal voltage.
The variant with 110 V could test distance relays with nominal voltage 100 or 110 V.
The variant with 220 V was use for 200 and 220 VAC respectively (Figure 14).
Table 2 shows characteristics of Relay Test Set B/ BB, BBC.

Developments started also in the Soviet Union. Utilizing existing equipment as rheostats, measurement devices, auto transformers, phase regulators and switches the testing engineers used their knowledge in building own devices.

A test set produced in the Soviet Union in 1954 can be seen in Figure 10. This device was called - 2. (Figure 11, and Figure13).
SIEMENS started production of test set SRP4 in 1954. With the new naming scheme introduced later the device was called 7VP44. An additional suitcase called SRP3a (later 7VP45, see title page, could be used for testing overcurrent devices (independent, dependent, with and without direction), differential and comparison protection as well as distance protection. The case of the testing set SRP4 was made of deep-drawn sheet. The removable cover had a carrying handle. The control and setting elements and an ammeter are on the front plate at the top, while the mains supply plug is fitted in the rear of the case.

A circuit diagram showing the internal wiring of the unit, as well as various connection diagrams for frequent methods of measurement are attached to the inside of the cover to enable the tester to make the required connections (Figure 12).
The auxiliary suitcase SRP3a can be used only together with SRP4. Its main application was testing the characteristics of distance protection. The nominal current was 1 A. To test 5 A devices an additional device AGT t0,5 (later 4AM53 60-3CS) was necessary. The control of the SRP3a was done via SRP4.

The supplementary unit is a portable test set of the same size as the SRP4. It contains transformer with 2 primary windings (110 V) and two electrically isolated secondary windings. The voltage selector switch connects the primary windings in series or parallel for 220 V or 110 V voltage, respectively (Figure 15).
To use it for 5 or 1 A was an order option. With an auxiliary transformer it could be used for both nominal currents (Figure16).
The technical data are collected in table 3.
Test sockets are provided near the protection devices to enable these units to be tested safely while the system is live. The test socket has two contacts which open two tripping circuits before the test. Unscrewing terminals before starting the test is thus obviated.

The test plug has four contacts. Two for transmitting the test current to a CT input, the other two for transmitting the tripping impulse from the relay to the testing set to measure the operating time. At the same time, the plug opens the tripping line from the circuit breaker, thus preventing the latter from opening inadvertently. The test current is injected through a circuit parallel to the current transformer, so that the latter is bypassed (Figure 18).
The combination of SRP4 with SRP3a became the standard solution.
It was presented at Hanover Fair in 1959 (Figure 17).

Portable test sets have been used mainly in substations with limited number of devices as impedance and overcurrent protection. The relay is associated to a test plug where the current is connected to the test set. Those devices were single phase at the time.
For more units such as protection of huge generators testing devices were built in the protection field. This made it possible to generate 3 phase currents.

Requirements for a Modern Test Set
 At the time there have been numerous discussions on the requirements for testing. The goal was to have the relays in operation. The testing time should be reduced dramatically. The testing time was defined as this time, when the connection relay - tripping coils is open. Protection relays at this time have been already faster than 0.1 s and the operating time of the test set should be faster- less than 10 ms. Additionally, it was required that the test set must operate properly in case of any issue at the device under test. False trips must be avoided.

Routine testing was estimated as essential and became mandatory at this time. Built-in test sets have been recommended "to reduce the testing time including wiring from one day to several minutes" Figure 20 shows protection panel with built in test device.
The area available on the panel could be used for protection relays, since just a switch, a button and an emergency button had to be added. The lamp was used for indications.

The transmission system operator of Eastern Germany (220/110-kV-grid) "Verbundnetz Mitte" in Berlin built a single-phase test set RPE157 (Figure 19). In the current and voltage path resistances only are built in, so the phase shift is almost 0°. The changeover switch allows to choose between
± 2, 4 or 6 %. (Table 4).
ZERA produced their first secondary test set in 1958 - BS2508 (Figure 21).
The technical data is collected in table 5.

Later in the 1950s ZERA came with a bunch of portable or moveable relay testing devices: R1, R2, Ra2, Ra5, Ra6, Rs7 and RA7,5 (Figure 22).  Table 6 collects the technical data of the Ra5.
ZERA produced in 1958 the phase transformers FW63 (Figure 23) and one year later- FW203 (Figure 24). To make transport possible, they have been divided into several parts- this made combination for dedicated applications possible.
For instance:

  • Phase shifter
  • Transformer
  • Current control
  • Voltage control.

Technical data are collected in table 7.
The year numbers are taken from vendor’s statements, schematics and papers.

They might differ but deliver a good hint on activities in the 1950s. Further developments will be the content of future articles.     

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